estimation of kerogen porosity in source rocks as a function of thermal transformation example from the mowry shale in the powder river basin of wyoming evaluations of porosity relevant to hydrocarbon storage capacity in kerogen rich mudrocks i e source rocks have thus far been plagued with ambiguity in large part because conventional core and petrophysical techniques were not designed for this rock type the growing recognition of an intraparticle organic nanopore system that is related to thermal maturity is beginning to clarify this ambiguity this mode of porosity likely evolved with the thermal transformation of labile kerogen and probably neither depends nor interacts except perhaps chemically with previously assumed matrix or mineral porosity that is dominated by bound water and that may be largely irrelevant to hydrocarbon storage capacity in these rocks to address this newly recognized and important nonmatrix kerogen pore system that is arguably the dominant hydrocarbon storage and mobility network in these rocks we introduce a relatively simple kinetic model that describes porosity development within kerogen as a function of thermal maturation kerogen porosity development is estimated within the upper albian mowry shale in the powder river basin of wyoming to illustrate the approach relevant storage capacity is considered to have evolved with thermal decomposition of organic matter during catagenesis where we estimate that kerogen porosity does not typically exceed 3 of bulk rock volume modeled oil in place estimates are comparable to residual oil estimates from pyrolysis data s1 at lower maturities but exceed pyrolytic s1 yields at higher maturities we hypothesize therefore that a subsurface kinetic porosity model might represent a means to account for s1 losses at surface conditions and to circumvent difficulties surrounding estimations of expulsion efficiencies that are inherent to more traditional mass balance calculations

spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related mudrock pores matrix related pore networks in mudrocks are composed of nanometer to micrometer size pores in shale gas systems these pores along with natural fractures form the flow path permeability network that allows flow of gas from the mudrock to induced fractures during production a pore classification consisting of three major matrix related pore types is presented that can be used to quantify matrix related pores and relate them to pore networks two pore types are associated with the mineral matrix the third pore type is associated with organic matter om fracture pores are not controlled by individual matrix particles and are not part of this classification pores associated with mineral particles can be subdivided into interparticle interp pores that are found between particles and crystals and intraparticle intrap pores that are located within particles organic matter pores are intrap pores located within om interparticle mineral pores have a higher probability of being part of an effective pore network than intrap mineral pores because they are more likely to be interconnected although they are intrap om pores are also likely to be part of an interconnected network because of the interconnectivity of om particles in unlithifed near surface muds pores consist of interp and intrap pores and as the muds are buried they compact and lithify during the compaction process a large number of interp and intrap pores are destroyed especially in ductile grain rich muds compaction can decrease the pore volume up to 88 by several kilometers of burial at the onset of hydrocarbon thermal maturation om pores are created in kerogen at depth dissolution of chemically unstable particles can create additional moldic intrap pores

specific surface area and pore size distribution in clays and shales one of the biggest challenges in estimating the elastic transport and storage properties of shales has been a lack of understanding of their complete pore structure the shale matrix is predominantly composed of micropores pores less than 2 nm diameter and mesopores pores with 2 50 nm diameter these small pores in the shale matrix are mainly associated with clay minerals and organic matter and comprehending the controls of these clays and organic matter on the pore size distribution is critical to understand the shale pore network historically mercury intrusion techniques are used for pore size analysis of conventional reservoirs however for unconventional shale reservoirs very high pressures 414 mpa 60 000 psi would be required for mercury to access the full pore structure which has potential pitfalls current instrumental limitations do not allow reliable measurement of significant portions of the total pore volume in shales nitrogen gas adsorption techniques can be used to characterize materials dominated by micro and mesopores 2 50 nm a limitation of this technique is that it fails to measure large pores diameter 200 nm we use a nitrogen gas adsorption technique to study the micro and mesopores in shales and clays and compare the results from conventional mercury porosimetry techniques our results on pure clay minerals and natural shales show that i they have a multiscale pore structure at different dimensions ii fine mesopores with a characteristic 3 nm pore size obtained with n2 gas adsorption are associated with an illite smectite group of clays but not with kaolinite iii compaction results in a decrease of pore volume and a reduction of pore size in the inter aggregate macropores of the illitesmectite clays while the fine intra tachoid mesopores are shielded from compaction iv for natural shales mineralogy controls the pore size distributions for shales and the presence of micropores and fine mesopores in natural shales can be correlated with the dominance of the illite smectite type of clays in the rock our assessment of incompressible 3 nm sized pores associated with illite smectite clays provides an important building block for their mineral modulus

organic matter rich shales of china abstract organic matter rich shales are the main target rocks for unconventional oil and gas exploration and development across the world in china shale gas geological resources are estimated as approximately 110 1012 m3 with recoverable gas reserves of ca 20 1012 m3 recoverable shale oil reserves are estimated as ca 5 109 t a total 35 important organic matter rich shale units have been recognized from mesoproterozoic to cenozoic strata across the entire china these shales are categorized according to their origin under marine marine nonmarine transitional and lacustrine conditions shales of marine origin with ca 9 1012 m3 recoverable resources dominate china s potential in terms of total volume of organic carbon currently the most favorable marine shales for oil and gas exploration are found in the sichuan basin within the lower cambrian qiongzhusi formation and in the wufeng longmaxi formations of uppermost ordovician through lower silurian a fortuitous combination of of sea level variations of paleo productivity of tectonic activity causing development and migration of partially closed deep basin depocenters and of sediment accumulation rates controlled the extensive deposition and distribution of organic matter rich shales in these wufeng and longmaxi formations organic matter rich shales in marine nonmarine transitional facies associated with coal measures occur in north china within the carboniferous and permian and in south china within the permian these carboniferous permian organic matter rich shales are important source rocks for the gas fields in the ordos and sichuan basins abundant organic rich shales are also widely distributed within coal bearing clastics and coal measure shales of fluvial lacustrine and swamp facies in upper triassic to middle jurassic successions of many basins lacustrine organic rich shales were deposited during the permian through neogene in various freshwater to saline lake settings lacustrine organic matter rich shales are the main oil source rocks in the songliao bohai bay ordos and junggar basins lacustrine algae contributed to the rain of organic matter and the preservation of organic matter and distribution of organic rich shale was controlled by lake currents water depth and oxygen poor conditions with enhanced preservation when buried by turbidity currents algal blooms were partly induced by trace nutrients from volcanic ash falls in all of these lacustrine basins seawater intrusion into the freshwater lake of the songliao basin promoted some episodes of black shales saline lacustrine basins such as middle permian junggar basin contain organic rich dolomite mudstone that mainly formed during hot climate conditions when the lakes had high salinity and stratified water columns that deprived the bottom waters of oxygen thereby preserving massive amounts of organic matter laminated calcite rich mudstone in the saline lacustrine settings formed in more brackish waters under stable warm conditions and weak biological activity the modeling of the factors controlling the distribution of organic matter rich shales within china s basins is important for the exploration and development of unconventional oil and gas resources

characteristics of silty laminae in zhangjiatan shale of southeastern ordos basin china implications for shale gas formation shale oil and gas have been discovered in the lacustrine organic rich zhangjiatan shale of the upper triassic yanchang formation ordos basin china core observations indicate abundant silty laminae in the producing shales this study documents the stratigraphic distribution of silty laminae and their relationship with interlaminated clay laminae the type structure and characteristics of pores and mineral composition of silty laminae were observed and analyzed through thin section and scanning electron microscopy x ray diffraction low pressure formula 1 and formula 2 adsorption mercury porosimetry and helium pycnometry results from silty laminae are compared with those of clayey laminae the frequency and thickness of silty laminae vary over a wide range the thickness ranges from 0 2 to 4 mm and is 1 5 mm on average the frequency ranges from 4 to 32 laminae m and is 23 laminae m on average the thickness percentage of silty laminae in the measured segments ranges from 6 to 17 silty laminae consist of quartz feldspar mixed layer montmorillonite and chlorite in comparison to clayey laminae non clay detrital grains are larger quartz and feldspar are more common and clay minerals are less abundant pores in silty laminae are primary interparticle dissolutional intercrystalline and microfracture types mesopores 2 50 nm in diameter and macropores 50 nm 1 m are common whereas micropores formula 3 are rare the distribution of pore diameters is multimodal however microscopic pores with a diameter commonly smaller than 100 nm are common in clayey laminae thus pore volume and surface area of micropores in silty laminae are less than those in the adjacent clayey laminae and vice versa for meso and macropores the porosity of shales increases with the proportion of silty laminae in the shales the silty laminae provide the storage space and flow conduit for oil and gas and they play a significant role in the migration accumulation occurrence and amount of gas in the shales 1 embed mml math 1 gif 2 embed mml math 2 gif 3 embed mml math 3 gif

generation of gas and oil from coal and other terrestrial organic matter abstract late carboniferous permian sedimentary rocks contain the world s largest coal reserves which have generated and released gas but little if any oil in comparison organic matter deposited in lacustrine fluvial deltaic or brackish water sediments has sourced large quantities of waxy oils in countries such as china australia the u s a argentina venezuela and indonesia plus gas and condensate in deltas worldwide why is more oil coming from land derived organic matter disseminated in sediments than from the carboniferous permian coal beds which also are land deposits the answer appears to be in the hydrogen content and the ease of migration when organic matter and coals have high hydrogen contents relative to carbon they can form oil when the hydrogen is low mainly gas is formed most of the world s coal is low in hydrogen whereas much of the terrestrial organic matter disseminated in sediments is higher in hydrogen so it forms more oil also both gas and oil are adsorbed on coal more strongly than on the disseminated kerogen of sedimentary rocks this makes migration of oil out of the coal more difficult compared to migration from conventional shale source rocks

post oil solid bitumen network in the woodford shale usa a potential primary migration pathway abstract an important if not predominant component of porosity in many gas shales has been identified in organic matter an organic network in shales has been described in the literature as organic matter generalized term kerogen primary or bitumen secondary recognition of the type and origin of an organic network in shales has relevance in establishing the origin and timing of porosity and fracture development the pervasive nature of the organic network adopting the shape of pores in type ii kerogen rich woodford shale suggests it is the residue of primary oil migration we use the term post oil solid bitumen to distinguish this bitumen occurrence from pre oil solid bitumen defined as a precursor of oil three forms of this post oil solid bitumen network are recognized in reflected white light at 500 magnification and confirmed in backscattered scanning electron microscope images at 2500 magnification namely speckled 1 2 m wispy 2 5 m and connected 5 m the post oil solid bitumen network demonstrates the prior occurrence of oil generation and migration within this hydrocarbon source rock provides porosity for hydrocarbon storage sites and forms hydrocarbon migration pathways

the importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs abstract the effect of shale composition and fabric upon pore structure and ch 4 sorption is investigated for potential shale gas reservoirs in the western canadian sedimentary basin wcsb devonian mississippian d m and jurassic shales have complex heterogeneous pore volume distributions as identified by low pressure co 2 and n 2 sorption and high pressure hg porosimetry thermally mature d m shales 1 6 2 5 vro have dubinin radushkevich d r co 2 micropore volumes ranging between 0 3 and 1 2 cc 100 g and n 2 bet surface areas of 5 31 m 2 g jurassic shales which are invariably of lower thermal maturity ranging from 0 9 to 1 3 vro than d m shales have smaller d r co 2 micropore volumes and n 2 bet surface areas typically in the range of 0 23 0 63 cc 100 g co 2 and 1 9 m 2 g n 2 high pressure ch 4 isotherms on dried and moisture equilibrated shales show a general increase of gas sorption with total organic carbon toc content methane sorption in d m shales increases with increasing toc and micropore volume indicating that microporosity associated with the organic fraction is a primary control upon ch 4 sorption sorption capacities for jurassic shales however can be in part unrelated to micropore volume the large sorbed gas capacities of organic rich jurassic shales independent of surface area imply a portion of ch 4 is stored by solution in matrix bituminite solute ch 4 is not an important contributor to gas storage in d m shales structural transformation of d m organic matter has occurred during thermal diagenesis creating and or opening up microporosity onto which gas can sorb as such d m shales sorb more ch 4 per weight percent wt toc than jurassic shales inorganic material influences modal pore size total porosity and sorption characteristics of shales clay minerals are capable of sorbing gas to their internal structure the amount of which is dependent on clay type illite and montmorillonite have co 2 micropore volumes of 0 78 and 0 79 cc 100 g n 2 bet surface areas of 25 and 30 m 2 g and sorb 2 9 and 2 1 cc g of ch 4 respectively dry basis a reflection of microporosity between irregular surfaces of clay platelets and possibly related to the size of the clay crystals themselves mercury porosimetry analyses show that total porosities are larger in clay rich shales compared to silica rich shales due to open porosity associated with the aluminosilicate fraction clay rich sediments low si al ratios have unimodal pore size distributions

volcanic structures and oral traditions of volcanism of western samoa sw pacific and their implications for hazard education abstract the samoan islands have experienced 2 million years of volcanism culminating in historic eruptions at both the east and western ends of the chain including a major lava producing episode on the island of savai i from ad 1905 1911 upolu in western samoa has several areas mapped as early holocene in age 5 ka but here we present new evidence for fresh volcanic landforms and deposits supported by a radiocarbon date of 1915 65 yrs b p giving a maximum age to a phreatomagmatic tuff cone offshore of cape tapaga east upolu in addition we report on a parallel investigation of the oral traditions of communities surrounding fresh volcanic landforms that may reflect distant volcanic memories passed down over generations to accommodate samoan cultural structures oral traditional knowledge was sought through semi structured interviews with small groups 3 4 or individuals samoan facilitators focused on high ranking and traditionally respected particularly elderly individuals for explanations of the origins of local features including their genesis use and any related geo hazards areas targeted were those where young eruptions

composition and pore characteristics of black shales from the ediacaran lantian formation in the yangtze block south china the ediacaran period was critical in the evolution of the biosphere and ocean in the history of the earth shales rich in organic matter om are well developed for this period in the yangtze block china and have recently been related to shale gas exploration in south china to date detailed characterisation of the ediacaran shales is not available the present work sets out a detailed investigation of the composition and pore characteristics of samples from a shallow drill core in the ediacaran lantian formation in the lower yangtze area and the effects of shale composition on the pore growth are discussed the 90 m thick lantian black shales are highly over mature equivalent vitrinite reflectance evro value approximately 4 0 with a total organic carbon toc content up to 12 they are dominated by quartz 33 72 generally with low clay or feldspar content bulk porosities of the shales range from 1 0 to 7 9 and are positively correlated with toc content high magnification scanning electron microscopy sem images support the crucial importance of om content on pore development generally pore volume shows excellent positive correlation with toc content for micropores good correlation for mesopores and relatively poor correlation for macropores two samples with mostly high toc content showed very low macropore volume and medium mesopore volume these results suggest a close relationship between om with relatively small pores and enhanced compaction effect on large pores in highly om enriched shales

pore types and pore network evolution in upper devonian lower mississippian woodford and mississippian barnett mudstones insights from laboratory thermal maturation and organic petrology abstract pore evolution models from immature organic matter om rich barnett 0 42 r o and woodford 0 49 r o mudstones were compared with models previously developed from low maturity om lean boquillas eagle ford equivalent mudstones to investigate whether 1 different mineralogy siliceous vs calcareous exerts different catalytic and sorption effects and influences om pore origin and evolution and 2 different types of macerals show different om pore evolution history laboratory gold tube pyrolysis scanning electron microscopy sem and thin section petrography organic petrography and geochemical characterization were used to investigate the role of bulk mineralogy maceral type and thermal maturation on om pore evolution results suggest that mineralogy has little impact on om pore development and evolution macerals identified using both sem platy om particulate om organic mineral admixtures tasmanites and organic petrology vitrinite inertinite amorphous organic matter aom bituminite telalginite leiosphaeridia tasmanites do affect the origin and evolution of om pores owing to differences in chemical compositions generation kinetics and activation energy distributions between tasmanites matrix bituminite and other types of macerals leiosphaeridia and tasmanites in woodford mudstone samples exhibit a delay in onset and a shorter period of petroleum generation and pore development compared to the matrix bituminite in the barnett and woodford mudstone samples pre oil solid bitumen was observed to have migrated into initial primary mineral pore networks at the bitumen generation stage in both barnett and woodford samples at higher levels of thermal maturation the volume of primary mineral pores decreases and the pore volume composed of modified mineral pores and om pores becomes greater pore evolution and pore type heterogeneity in these mudstones is a function of the initial mineral pore network types of kerogen and macerals and generation kinetics of individual macerals upon thermal maturation

assessing thermal maturity of palaeozoic rocks from reflectance of chitinozoa as constrained by geochemical indicators an example from southern ontario canada the reflectance of chitinozoa chr0 was investigated as an alternative technique of determining the level of thermal maturity of organic rich palaeozoic rocks in southern ontario these sedimentary strata which include the ordovician collingwood member and the blue mountain formation as well as the devonian marcellus formation lack vitrinite precluding the application of a standard vitrinite reflectance vr0 technique chr0 shows a proportional increase at marginal to moderate maturities being on average 20 to 25 higher than expected vitrinite reflectance the reflectance data fall into a very narrow range showing a high degree of consistency for each lithostratigraphic unit the average chr0 are as follows collingwood mbr 0 63 georgian bay area and 0 88 toronto area blue mountain fm 0 92 marcellus fm 0 68 correlation with more conventional optical and geochemical maturity parameters obtained from the same set of samples fluorescence of tasmanites leiosphaeridia and gloeocapsomorpha alginite rock eval tmax extract data distribution of terpanes and steranes in extracts indicates that within the area of study the beginning of the catagenetic stage corresponds to chr0 0 65 equivalent vr 0 50 whereas the threshold of significant oil generation is reached at chr0 0 9 equivalent vr 0 70 therefore the blue mountain formation is thermally mature with respect to hydrocarbon generation throughout the whole area of study the collingwood shales are mature only in the toronto area while those occurring in the georgian bay area as well as the marcellus shales have yet to enter the main stage of hydrocarbon generation this integrated approach of assessing thermal maturity shows that chr0 when constrained with other maturity parameters is a very reliable indicator of thermal maturity in lower to middle palaeozoic sedimentary rocks

organic matter hosted pore system marcellus formation devonian pennsylvania the marcellus formation of pennsylvania represents an outstanding example of an organic matter om hosted pore system most pores detectable by field emission scanning electron microscopy fe sem are associated with om instead of mineral matrix in the two wells studied here total organic carbon toc content is a stronger control on om hosted porosity than is thermal maturity the two study wells span a maturity from late wet gas vitrinite reflectance ro 1 0 to dry gas ro 2 1 samples with a toc less than 5 5 wt display a positive correlation between toc and porosity but samples with a toc greater than 5 5 wt display little or no increase in porosity with a further increasing toc in a subset of samples 14 across a range of toc 2 3 13 6 wt the pore volume detectable by fe sem is a small fraction of total porosity ranging from 2 to 32 of the helium porosity importantly the fe sem visible porosity in om decreases significantly with increasing toc diminishing from 30 of om volume to less than 1 of om volume across the range of toc the morphology and size of om hosted pores also vary systematically with toc the interpretation of this anticorrelation between om content and sem visible pores remains uncertain samples with the lowest om porosity higher toc may represent gas expulsion pore collapse that was more complete as a consequence of greater om connectivity and framework compaction whereas samples with higher om porosity lower toc correspond to rigid mineral frameworks that inhibited compactional expulsion of methane filled bubbles alternatively higher toc samples may contain om low initial hydrogen index relatively unreactive that is less prone to development of fe sem detectable pores in this interpretation om type controlled by sequence stratigraphic position is a factor in determining pore size distribution

oil retention and porosity evolution in organic rich shales petroleum is retained in shales either in a sorbed state or in a free form within pores and fractures in shales with oil resource potential organic matter properties i e richness quality and thermal maturity control oil retention in general in gas shales organic pores govern gas occurrence although some pores may originate via secondary cracking reactions it is still largely unclear as to how these pores originate here we present case histories mainly for two classic shales the mississippian barnett shale texas and the toarcian posidonia shale lower saxony germany in both cases shale intervals enriched in free oil or bitumen are not necessarily associated with the layers richest in organic matter but are instead associated with porous biogenic matrices however for the vast bulk of the shale hydrocarbon retention and porosity evolution are strongly related to changes in kerogen density brought about by swelling and shrinkage as a function of thermal maturation secondary organic pores can form only after the maximum kerogen retention swelling ability is exceeded at tmax the temperature at maximum rate of petroleum generation by rock eval pyrolysis around 445 c 833 f approximately 0 8 vitrinite reflectance shrinkage of kerogen itself leads to the formation of organic nanopores and associated porosity increase in the gas window

pore types and pore size distributions across thermal maturity eagle ford formation southern texas pore types pore size and pore abundance vary systematically across thermal maturity in the eagle ford formation maverick basin southern texas scanning electron imaging of 20 samples from four wells is used to assess the complex response of pores to chemical and mechanical processes entailing both destruction of primary porosity and generation of secondary pores primary mineral associated pores are destroyed by compaction cementation and infill of secondary organic matter whereas secondary pores are generated within organic matter om destruction of primary pores during early burial to 0 5 occurs by compaction of ductile detrital om and clays and to a lesser degree as a result of cementation and infill of secondary om larger pores are associated with coccolith debris the dominant om is spatially isolated detrital om stringers porosity is volumetrically dominated average 6 2 by relatively large mostly interparticle mineral associated pores median size 51 6 nm 0 000002 in detection limit near 3 4 nm 0 00000012 0 00000015 in at low maturity porosity and pore size correlate directly with calcite abundance and inversely with om volumes at higher maturity further destruction of primary pores occurs through cementation secondary om infill and greater compaction mineral associated pores are present at high maturity 1 2 1 3 but are smaller median size 30 2 nm 0 0000011 in and less abundant average of 2 5 than at low maturity a large portion of om within high maturity samples is diagenetic in origin and has pervaded into primary pore space coating cement crystals and filling intraparticle pores substantial mineral associated porosity is locally present in samples where incursion of primary pore space by secondary om has not occurred abundant secondary porosity is generated as om matures into the wet gas window porosity in most high maturity samples is volumetrically dominated average of 1 3 by smaller om hosted pores median size 13 2 nm 0 00000051 in

experimental investigation of changes in methane adsorption of bitumen free woodford shale with thermal maturation induced by hydrous pyrolysis this study quantifies the effects of organic matter om thermal maturity on methane ch4 sorption on the basis of five samples that were artificially matured through hydrous pyrolysis achieved by heating samples of immature woodford shale under five different time temperature conditions ch4 sorption isotherms at 35 degrees c 50 degrees c and 65 degrees c and pressures up to 14 mpa on dry solvent extracted samples of the artificially matured woodford shale were measured the results showed that ch4 sorption capacity normalized to toc varied with thermal maturity following1 the trend maximum oil 367 degrees c oil cracking 400 degrees c maximum bitumen early oil 333 degrees c early bitumen 300 degrees c immature stage 130 degrees c the langmuir constants for the samples at maximum oil and oil cracking stages are larger than the values for the bitumen forming stages the total pore volume determined by n 2 physisorption at 77 k increases with increased maturation mesopores 2 50 nm in width were created during the thermal conversion of organic matter and a dramatic increase in porosity appeared when maximum bitumen and maximum oil generation stages were reached a linear relationship between thermal maturity and brunauer emmett teller bet surface area suggests that the observed increase in ch4 sorption capacity may be the result of mesopores produced during om conversion no obvious difference is observed in pore size distribution and pore volume for samples with pores 2 0 nm with the increase of thermal maturity based on co2 physisorption at 273 k the isosteric heat of adsorption and the standard entropy for artificially matured samples ranged from 17 9 kj mol 1 to 21 9 kj mol 1 and from 85 4 j mol 1 k 1 to 101 8 j mol 1 k 1 respectively these values are similar to the values of immature woodford kerogen concentrate previously observed but are larger than naturally matured organic rich shales high temperature hydrous pyrolysis might have induced lewis acid sites on both organic and mineral surfaces resulting to some extent in chemical interactions between the adsorption site and the methane c h bonds the formation of abundant mesopores 2 50 nm within organic matter during organic matter thermal maturation makes a great contribution to the increase in both bet surface area and pore volume and a significant increase in 2 6 nm pores occurs at maximum oil generation and oil cracking to gas ultimately controlling the methane adsorption capacity therefore consideration of pore size effects and thermal maturity is very important for gas in place gip prediction in organic rich shales c 2014 elsevier ltd all rights reserved

thermal cracking of kerogen in open and closed systems determination of kinetic parameters and stoichiometric coefficients for oil and gas generation abstract the purpose of the study is to compare artificial maturation of kerogens representative of the main types of organic matter kerogen types i ii ii s and iii in open and anhydrous closed pyrolysis systems the generated compounds are fractionated according to their thermal stability into six chemical classes c 1 c 2 c 5 c 6 c 14 c 15 saturates c 15 aromatics and nsos which include resins and asphaltenes in both systems primary cracking of kerogen can be described by two main reactions oil generation together with early gas generation followed by late gas production mass balances obtained in the two pyrolysis systems are reasonably similar although some secondary cracking of the nsos and underestimation of methane potential due to incomplete pyrolysis may occur in the open system kinetic parameters of thermal cracking are derived from experiments in the open system using an optimization procedure which determines a unique frequency factor and a weight distribution of chemical classes for a discrete series of activation energies the resultant frequency factors are checked with those obtained for specific molecular tracers such as n c 12 and n c 24 alkanes generated from kerogens in open and closed systems under isothermal conditions the results show that using a unique frequency factor as determined by optimization is correct for type i ii and ii s kerogens this factor is more questionable however when the distribution of activation energies is very broad such as for type iii coals based on this study a strategy for determination of kinetic parameters on any new source rock sample is proposed

thermal history model for the south central graben north sea derived using both tectonics and maturation abstract the thermal history modelling of basins is essential for petroleum systems analysis the methodology involves the derivation of the heat flow history by calibration using a kinetic model to match the predicted and observed vitrinite reflectance values in wells although this method is almost universally used by basin modellers a simple check using two independent methods with tectonic subsidence history being the second method shows that the thermal histories derived from the subsidence history do not match those predicted by the vitrinite reflectance method for any point in a basin there can only be one thermal history and the derivation of two different thermal histories indicates that there is a problem that has been ignored by geochemists and basin modellers the thermal history must predict the tectonic subsidence history and this heat flow history must also account for the maturation data e g vitrinite reflectance sediments subside under the action of forces and energy e g heat is a function of force during subsidence the downward force exceeds the upward force and the heat flow supplied to the basin must be reduced as the upward force is reduced while force and heat flow must be increased during uplift applying this relationship to the central graben north sea a heat flow history is derived that accounts for the rifting and subsequent subsidence tectonic history of two wells the british 23 26 2z and the danish lulu 1 the vitrinite reflectance predicted by this thermal history and the easy ro kinetic vitrinite reflectance model are higher than the measured values in both wells both wells are overpressured and the problem with the vitrinite reflectance calibration method is that the kinetic parameters used do not correctly account for the retardation produced by pressure le chatelier s principle without the pressure retardation effect incorporated into the kinetic parameters the modeller has to use lower temperatures to simulate retardation using the presro vitrinite reflectance model which incorporates pressure retardation as required by thermodynamics the thermal history derived from the rifting subsidence history can also be used to model the vitrinite reflectance data in the british 23 26 2z and danish lulu 1 wells this method of deriving an unknown e g thermal history using two independent models is widely used in physical sciences as an essential check on any prediction and this scientific rigor has to be followed by geoscientists modelling the thermal history of basins

combined sem and reflected light petrography of organic matter in the new albany shale devonian mississippian in the illinois basin a perspective on organic pore development with thermal maturation abstract organic matter hosted pores are an important aspect of pore systems in unconventional gas shale reservoirs along with thermal maturity organic maceral type critically controls the development of secondary organic matter hosted pores three new albany shale samples devonian mississippian kerogen type ii sequence having thermal maturities ranging from a vitrinite reflectance ro of 0 55 to 1 42 were analyzed using a reflected light microscope and a field emission scanning electron microscope organic pores were examined in specific organic macerals and solid bitumen at different thermal maturities vitrinite and inertinite derived from terrestrial woody materials occur as discrete particles in this black shale within the resolution limits of the scanning electron microscope these two macerals do not appear to display enhanced secondary pores associated with increases in thermal maturity cellular pores 0 2 10 m in inertinite were observed throughout the entire maturity range and were typically filled with authigenic quartz or solid bitumen because of thermal degradation amorphous organic matter was not observed at maturities greater than ro 0 80 alginite derived from tasmanites cysts matures later than amorphous organic matter and is still present at ro 0 80 however it is in the process of transforming to pre oil bitumen and shows weak orange yellow fluorescence compared to strong greenish yellow fluorescence in lower maturity samples at a maturity of ro 1 42 alginite could no longer be observed as a distinct phase because of its complete transformation to hydrocarbons and bitumen alginite began to develop secondary pores when it was in the process of transforming to pre oil bitumen which indicates that some liquid and gaseous hydrocarbons left the alginite during this part of the maturation process solid bitumen developed along the original amorphous organic matter networks and now occupies interparticle space between quartz dolomite k feldspar clay and mica grains as well as the cellular pores in inertinite particles solid bitumen becomes smaller and more porous with thermal maturation and thus becomes increasingly unidentifiable with the optical microscope solid bitumen hosted pores 20 1000 nm are the main organic pore type documented in the studied samples and they are more common in shales within the gas window than those in the oil window secondary nanopores in the solid bitumen network play a significant role in hydrocarbon storage and migration

seismotectonics of the el asnam earthquake the mechanism of the el asnam earthquake of 10 october 1980 ms 7 2 the strongest recorded in northwestern africa is compatible with a convergence between the african and european plates the thrust is also consistent with field observations and with long period data from the global network aftershocks cluster around the fault trace with a maximum depth of 12 km maximum vertical displacement is 6 m and there is some left lateral motion the fault trace of the 1954 earthquake at beni rached was also reactivated

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

do all fractions of organic matter contribute equally in shale porosity a case study from upper ordovician utica shale southern quebec canada abstract in many unconventional hydrocarbon systems organic matter om substantially contributes to total porosity of the rock that led to a positive correlation between total organic carbon toc and porosity while organic porosity is an important reservoir property of unconventional hydrocarbon systems toc of these rocks consists of different macerals or petrographic fractions these toc fractions can be geochemically divided and quantified by the revised extended slow heating esh rock eval analysis this study discusses the contribution of different fractions of om on porosity variation in the mature to overmature utica shale in southern quebec using esh rock eval analysis helium pycnometery scanning electron microscopy sem and x ray diffraction xrd mineralogy selected samples from three wells at depths of 400 700 and 2000 m covering a range of thermal maturity from late peak oil window vroeqv 1 to dry gas zone vroeqv 2 1 were analyzed in this study the predominant om constituents are solid bitumen chitinozoans and minor graptolites with mean toc of 1 1 0 4 wt the mean porosity for oil and gas window samples decreases with depth from 3 9 0 9 to 2 6 0 5 respectively the sem images reveal that organic porosity is limited to pores developed in solid bitumen while regardless of thermal maturity chitinozoans have a non porous structure throughout the oil to dry gas window this observation suggests that the impact of thermal maturity on porosity is different for different om fractions i e macerals leading to different contribution of om fractions to total porosity the latter conclusion is further supported by the improved correlation observed between the solid bitumen fraction and porosity compared to toc porosity correlation for oil window samples our entire data set suggests that om i e bitumen fraction especially in the dry gas window is not the major controlling factor on the total porosity in the utica shale whereas intergranular porosity has the dominant control on total porosity this observation suggests that the hydrocarbon storage potential may largely reside in inorganic pores rather than organic pores in the analyzed intervals of the utica shale the decrease in total porosity observed from shallower samples i e oil window to deeper samples i e dry gas window also suggests that intergranular porosity is the dominant porosity component which decreases with burial

evolution of porosity and pore geometry in the permian whitehill formation of south africa a fe sem image analysis study abstract since the advent of technologically efficient exploitation of economic hydrocarbon reservoirs in shales increasingly more research has been devoted to identifying and characterizing pore systems within shales however only a handful of these studies focused on the development of porosity in thermally mature unconventional reservoirs in this study the evolution of porosity and pore geometry in the permian whitehill formation is addressed with the aid of ultrathin sections 2 3 cm 10 20 m thick and field emission scanning electron microscopy fe sem on samples with mean random vitrinite reflectance values ranging from 1 03 to 4 07 ro we document a strong positive covariation of porosity and total organic carbon content toc in all localities however for samples with vitrinite reflectance values greater than 2 88 ro porosity per unit toc decreased by over 25 relative to samples with lower thermal maturities the positive covariation of thermal maturity and total porosity recorded here is unsurprising and have been documented previously in many gas shales however the dramatic decrease in porosity restricted to samples from localities that experienced advanced maturation ro 2 88 is viewed as an evidence that porosity decrease is directly related to late thermal decarboxylation of organic matter this is supported by the presence of pores and micro fractures infilled by fibrous grains including carbonates clays silicates and phosphates and residual fluid inclusions these grains were likely generated from re precipitation of framework grains previously dissolved by organic acids carboxylic phenolic that were generated during thermochemical decarboxylation of the om our findings do not only fill important gaps in the understanding of organic pore development including processes that create preserve and destroy porosity the porosities described here are also key to gas transfer from shale matrix to induced fractures during fracture stimulation programs

welcoming a monster to the world myths oral tradition and modern societal response to volcanic disasters abstract volcanic eruptions can overwhelm all senses of observers in their violence spectacle and sheer incredibility when an eruption is catastrophic or unexpected neither individuals nor communities can easily assimilate the event into their world view psychological studies of disaster aftermaths have shown that trauma can shake the very foundations of a person s faith and trigger a search supernatural religious or scientific for answers for this reason the ability to rapidly comprehend a traumatic event by accepting the catastrophe as part the observer s world represents an important component of community resilience to natural hazards a relationship with the event may be constructed by adapting existing cosmological ancestral or scientific frameworks as well as through creative and artistic expression in non literate societies communal perceptions of an event may be transformed into stories that offer myth like explanations as these stories make their way into oral traditions they often undergo major changes to allow transmission through generations and in some cases to serve political or religious purposes disaster responses in literate societies are no different except that they are more easily recorded and therefore are less prone to change over time here we explore ways in which the language imagery and metaphor used to describe volcanic events may link disparate societies both present and past in their search for understanding of volcanic catastrophes responses to modern eruptions 1980 mount st helens usa and 1995 present soufriere hills montserrat provide a baseline for examining the progression to older historic events that have already developed oral traditions 1886 tarawera new zealand and finally to oral traditions many hundreds of years old in both the pacific northwest us and new zealand nz we see that repeated volcanism over many generations produces rich webs of cosmology and history surrounding volcanoes nz maori have incorporated volcanoes into the lineage of tribes and individuals thus good and bad outcomes from volcanism are part of long term cycles of reciprocity and equilibrium that link modern maori to their ancestors in both regions cosmologies and mythologies not only document the attempts of past cultures to recover from the impacts of volcanic disasters but also provide a means by which following generations can understand contextualize and therefore recover from future volcanic catastrophes we further suggest that such local traditions can provide a valuable community education tool as well as an important means of aiding the psychosocial recovery of individuals and communities after volcanic disasters

an experimental study of organic inorganic interactions during vitrinite maturation abstract vitrinite reflectance is a parameter widely used to determine the extent of thermal maturation in sedimentary basins laboratory heating experiments were conducted to examine the role of aqueous fluid and sediment composition temperature and time on the development of vitrinite reflectance at elevated temperatures and pressures samples of organic lean middle valley sediment containing dispersed vitrinite and wyodak coal composed almost entirely of vitrinite were heated in the presence of compositionally variable aqueous fluids at 225 to 375 c and 350 bars inorganic fluid composition was monitored as a function of time and vitrinite reflectance was measured at the termination of each experiment the rate of vitrinite maturation was influenced by inorganic fluid and vitrinite composition in addition to time and temperature during the experiments in particular the rate at which vitrinite reflectance increased for a given temperature correlated positively with in situ h activity this observation suggests that acid catalyzed ionic reaction mechanisms and or catalytically active transition metals and sulfur species play an important role in organic transformations responsible for increased vitrinite reflectance the activity of other inorganic ionic species such as mg ca na k and so 4 and the redox state of the fluid did not influence the rate of vitrinite maturation during these experiments results of this study demonstrate that the geochemical environment surrounding vitrinite influences the rate of maturation the presence of water may facilitate reaction pathways that are not readily available in dry systems vitrinite maturation profiles that deviate from what are considered to be normal trends may reflect subsurface variations in the composition of pore fluids or the presence or absence of an aqueous phase in contact with vitrinite particles accordingly kinetic models that consider organic reactions responsible for increased vitrinite reflectance in terms of time and temperature alone may not accurately account for geochemical processes occurring in natural systems

the eruptive history and volcanic hazards of savo solomon islands savo island is the 6 km diameter emergent summit of an andesitic dacitic stratovolcano rising from the iron bottom sound 35 km nw of honiara solomon islands savo has erupted at least three times within recorded history and the 3 000 inhabitants maintain extensive oral traditions of past events through description and interpretation of the volcaniclastic sequences on the island in conjunction with historical accounts and oral traditions we reconstruct the eruptive processes on savo block and ash flow baf deposits are volumetrically dominant on the island within three main depositional environments near vent sequences thick medial channel sequences and distal fan sequences the deposits comprise universally non vesicular and highly porphyritic 40 70 phenocrysts high silica andesite and dacite clasts these appear to have been derived from collapsing lava domes during an 1560 1570 a d eruption however eyewitness descriptions and crater morphology suggest that similar deposits formed from dome explosions or collapses of eruption columns during later eruptions 1830 1840 a d the high sodium magmas ca 5 7 wt na2o apparently crystallised and strongly degassed prior to eruption shallow explosions were possibly caused by entrapment of magmatic gases beneath a dome or conduit plug of highly crystalline near solid magma repeated sealing of the vent may have been due to inward collapse of the highly altered rocks of the surrounding hydrothermal system these rocks probably were saturated due to contemporaneous high intensity rainfall events bafs were hot enough to char vegetation and attain aligned clast trm thermal remnant magnetism up to 3 km from the vent many being accompanied by ash cloud surges changes with distance in the baf deposits appear mostly dependent on flow confinement and are limited to an overall decrease in thickness and maximum clast size and an increased definition of weak planar fabrics in distal fan sequences there is strong evidence for syn and post eruptive redeposition of primary deposits since the savo population is concentrated on coastal volcaniclastic fans we consider the greatest volcanic risk to life is from bafs associated ash cloud surges and lahars hence the main channels and fans are designated as the highest of three relative hazard zones on a simple map prepared to aid local education and planning initiatives on savo

results of a microearthquake study one year before the el asnam earthquake of october 10 1980 abstract in november 1979 five portable instruments were installed in the el asnam area during a ten day recording period nine events of magnitude 0 5 to 1 9 were located in the focal region of the 1980 earthquake all but one of the events occurred in the north western block defined by the main fault a composite fault plane solution agrees with the mechanism of the main shock no abnormal behaviour of the v p v s ratio was observed

bib sem characterization of pore space morphology and distribution in postmature to overmature samples from the haynesville and bossier shales abstract four haynesville shale and four bossier shale samples were investigated using a combination of scanning electron microscopy sem and broad ion beam bib polishing this approach enables the microstructure and porosity to be studied down to the mesopore size r in the haynesville shale to 1 79 2 26 vr r in the bossier shale this variety within the samples enabled us to study controls on the porosity distribution in these shales visible pores exist as intraparticle pores mainly in carbonate grains and pyrite framboids and as interparticle pores mainly in the clay rich matrix pores in organic matter show a characteristic porosity with respect to the type of organic matter which mainly consists of mixtures of amorphous organic matter and minerals organic laminae and discrete macerals a clear positive trend of organic matter porosity with maturity was found pore sizes are power law distributed in the range of 4 4 m to at least 36 nm in equivalent diameter the differences in power law exponents suggest that a more grain supported coarse grained matrix may prevent pores from mechanical compaction porosities measured in the bib cross sections were significantly lower in comparison to porosities obtained by mercury intrusion porosimetry mip this difference is mainly attributed to the different resolution achieved with bib sem and mip and type of pore network extrapolation of pore size distributions psds enables the bib sem porosity to be estimated down to the resolution of the mip and thus to upscale microstructural observation at the confined space of the bib sem method to bulk porosity measurement these inferred porosities are in good agreement with the mip determined porosities which underpins the assumption that pores segmented in bib sem mosaics are representative of the mip methodology

geochemical controls on shale microstructure the uptick in hydrocarbon production from shale in the united states has generated interest in metrics of unconventional reservoir quality like permeability we use conventional gas sorption to characterize shale microstructure which provides insight on the features that govern mass transport the gas sorption data are analyzed to determine the surface area a s m2 g and pore volume v p cm3 g of 30 samples from basins across north america with this information we quantify the effect of composition and thermal maturity on shale microstructure in particular we find that the specific surface area of the organic component evolves from 50 m2 g total organic carbon toc in immature shale to 500 m2 g toc for regions that produce dry gas the increase in a s is accompanied by an increase in v p and concomitant decline in average pore size e g r h 4 v p a s we contend that the latter is due to the development of nanometer sized pores in kerogen as it is converted to mobile hydrocarbon which is ultimately expelled this hypothesis is supported by similar measurements on companion samples after bitumen extraction or combustion which underscore the intimate spatial association of petroleum and kerogen coupled with information on accessibility to the porosity garnered by varying the particle size these results establish a clear link between organic matter thermal maturity and reservoir quality in unconventional shale systems

geochemical effects of primary migration of petroleum in kimmeridge source rocks from brae field area north sea i gross composition of c15 soluble organic matter and molecular composition of c15 saturated hydrocarbons in mature oil prone source rocks of the upper jurassic kimmeridge clay in the brae field area north sea the yield and the gross composition of solvent extractabte pctroleum likc compounds as well as the molecular proportions of c15 saturated hydrocarbons are primarily controlled by the effects of hydrocarbon expulsion during primary migration within sample series extending from shale centres towards adjacent reservoir sandstones regular and pronounced yield decreases have been documented as well as marked compositional changes for c15 soluble organic matter and its compound class fractions saturated hydrocarbons aromatic hydrocarbons nso compounds and for normal and isoprenoid alkanes relative migration losses indicating relative expulsion efficiencies were determined for the c15 alkanes throughout the outer five meters of thick shales relative expulsion efficiencies increase regularly and drastically for all compounds considered e g exceeding 90 for the c15 n alkanes in the outermost shale samples samples from thin 5 50 cm shale layers interbedded between reservoir sandstones reveal similarly high expulsion efficiencies for n alkanes the degree of depletion remains uniform throughout the molecular range c15 to c30i e no compositional fractionation occurred during primary migration which is interpreted to reflect expulsion of oil as a single phase fluid a simple conceptual model is proposed to explain the mechanisms and relationships of generation and expulsion processes in time and space a geochemically relevant conclusion is that the c15 soluble organic matter recovered by solvent extraction of mature source rocks represents only a portion of the total non volatile petroleum like material originally generated

the nature of porosity in organic rich mudstones of the upper jurassic kimmeridge clay formation north sea offshore united kingdom abstract analyses of organic rich mudstones from wells that penetrated the upper jurassic kimmeridge clay formation offshore united kingdom were performed to evaluate the nature of both organic and inorganic rock constituents and their relation to porosity in this world class source rock the formation is at varying levels of thermal maturity ranging from immature in the shallowest core samples to mature in the deepest core samples the intent of this study was to evaluate porosity as a function of both organic macerals and thermal maturity at least four distinct types of organic macerals were observed in petrographic and sem analyses and they all were present across the study area the macerals include in decreasing abundance 1 bituminite admixed with clays 2 elongate lamellar masses alginite or bituminite with small quartz feldspar and clay entrained within it 3 terrestrial vitrinite fusinite semifusinite grains and 4 tasmanites microfossils although pores in all maceral types were observed on ion milled surfaces of all samples the pores largely nanopores with some micropores vary as a function of maceral type importantly pores in the macerals do not vary systematically as a function of thermal maturity insofar as organic pores are of similar size and shape in both the immature and mature kimmeridge rocks if any organic pores developed during the generation of hydrocarbons they were apparently not preserved possibly because of the highly ductile nature of much of the rock constituents of kimmeridge mudstones clays and organic material inorganic pores largely micropores with some nanopores have been observed in all kimmeridge mudstones these pores particularly interparticle i e between clay platelets and intraparticle i e in framboidal pyrite in partially dissolved detrital k feldspar and in both detrital and authigenic dolomite are noteworthy because they compose much of the observable porosity in the shales in both immature and mature samples the absence of a systematic increase in organic porosity as a function of either maceral type or thermal maturity indicates that such porosity was probably unrelated to hydrocarbon generation instead much of the porosity within mudstones of the kimmeridge appears to be largely intraparticle and interparticle adjacent to inorganic constituents so the petroleum storage potential in these organic rich mudstones largely resides in inorganic pores

seismotectonics of the lower cheliff basin structural background of the el asnam algeria earthquake the 1980 el asnam earthquake should be understood within its tectonic environment a seismotectonic map of the lower cheliff basin scale 1 500 000 has been synthesized from known geologic tectonic and seismological work on the region and from satellite photos the data set was integrated by a computer in order to handle different scales and projections several important tectonic features divide the region into 5 domains active faults and recent folds are consistent with a nnw sse direction of compression the cheliff basin is limited to the south by the relizane fault the basin is also crossed by three broken folds the eastern one being the one associated with the el asnam fault historical and instrumental seisinicity seems to be located at both ends of relizane fault it is suggested that the sites corresponding to folds and reverse faulting crossing the basin are relevant to seismic risk a simple tectonic model is proposed

impacts of volcanism on pre european inhabitants of taveuni fiji taveuni is a fijian ocean island volcano that sporadically erupted throughout the holocene the 437 km2 island is an active monogenetic volcanic field with a constantly shifting locus of activity along a single apparent rift axis although the eruptions were not large vei 2 unexpected shifts in taveuni volcanism had the potential to affect habitation sites since known human settlement of the fiji group ca 950 750 bc there have been at least 58 eruptions on taveuni up to 25 of these eruptions potentially affected pre european inhabitants of the island and at least four former occupation sites are known to have been affected by volcanic products despite apparent earliest settlement of taveuni post dating other nearby islands by up to 600 years volcanism probably did not hinder or stall settlement of taveuni compared with neighbouring islands however a period of voluminous eruptions between 300 and 500 ad covered much of south taveuni with lava and or thick tephra apparently causing abandonment of at least this portion of taveuni until approximately 1100 ad most eruptions were not of catastrophic proportions and due to their localised effects re settlement was rapid in marginal unaffected areas localised stories and a relict place name survive to describe former eruption locations and effects since approximately 120 320 ad knowledge of the impacts on taveuni s past inhabitants forms the basis of volcanic disaster mitigation strategies to minimise future effects on the current 14 500 residents

distinct evolution trends of nanometer scale pores displayed by the pyrolysis of organic matter rich lacustrine shales implications for the pore development mechanisms abstract organic matter om compositions greatly affect hydrocarbon generation and expulsion processes which are critical for the organic porosity development in shale lacustrine shale samples of low thermal maturity were pyrolyzed using two pyrolysis systems closed and semi closed systems pore development was measured by low pressure gas adsorption and field emission scanning electron microscopy fe sem and bulk porosity was modeled utilizing organic geochemical data the gas adsorption analysis indicated that shale samples of different om compositions differed in pore volume evolution with thermal maturity mainly related to the different amounts of hydrocarbon generated and expelled residual bitumen significantly reduced the pore volume of om rich oil generative shale samples and restricted the micro meso and macro pore volumes to different extents calculations and experiments both showed that om rich and oil generative shale experienced a greater increase in pore volume after the oil peak in addition it was observed that variations in the main pore types were associated both with shale compositions and with exerted overburden pressure increase in overburden pressure were found to greatly facilitate the development of nanometer size spongy and complex om pores in shales containing type kerogens possibly as a result of the expulsion of gaseous hydrocarbons by contrast the shale with abundant type kerogen tended mainly to develop relatively large pores following oil expulsion regardless of overburden pressure the modeled organic porosity of pyrolyzed samples of type iii om was similar to the porosity of geological shale but the porosity of om rich oil generative shale samples with high expulsion efficiency at the oil generation stage was two to three times the measured porosity of the geological shale in some cases the higher modeled shale porosity might be related to the higher expulsion efficiency for geological shales of expulsion efficiency comparable to the pyrolyzed samples geological processes e g compaction and cementation may have greatly reduced the om associated pore volume

organic matter pores and oil generation in the tuscaloosa marine shale the upper cretaceous tuscaloosa marine shale tms is an oil play across central louisiana and southwest mississippi the lower tms is characterized by relatively high log resistivity 5 ohm m compared to the upper part and this elevated resistivity zone erz has become the primary target zone this study is to investigate the cause of variation in log resistivity based on the data of petrography mineralogy and organic matter property and porosity the results suggest that log resistivity is not controlled by mineralogy or porosity rather it is associated with oil generation during organic matter maturation total organic carbon toc content rock eval free hydrocarbon yield s1 and hydrogen index hi in the studied core increase with depth porosity within organic matter om measured by field emission scanning electron microscopy fe sem is also higher within the erz the correlated variations among toc content s1 values om porosity and log resistivity suggest that the higher log resistivity resulted from in situ oil generation and that the om pores were generated during oil generation thermal maturity varies little in the core whereas the downward increasing hi indicates an increasing abundance of oil prone type ii kerogen higher om porosity appears to be related to the greater proportion of type ii kerogen in the erz the data set demonstrates that higher contents of toc and oil prone kerogen are the combined factors for higher oil generation therefore higher log resistivity in the erz the study provides a quantitative relationship between om porosity and oil generation

geochemical evolution of organic rich shales with increasing maturity a stxm and tem study of the posidonia shale lower toarcian northern germany hydrocarbon generation and retention processes occurring within gas shales as a response to increases in thermal maturation are still poorly constrained while efforts have been directed at unravelling the resource potential composition and textures of these economically important unconventional systems their spatial variability in chemistry and structure is still poorly documented at the sub micrometer scale here we have characterized samples of the lower toarcian posidonia shale samples from northern germany at varying stages of thermal maturation using a combination of compositional organic geochemistry and spectromicroscopy techniques including synchrotron based scanning transmission x ray microscopy stxm we document geochemical and mineralogical heterogeneities down to the nanometer scale within the investigated samples as a function of their level of thermal maturity in particular authigenic albite crystals containing nanometric halite inclusions have been documented within the investigated mature and overmature samples the presence of such tracers of palaeobrine carbonate interactions supports a maturation scenario for the lower toarcian posidonia shale intimately related to ascending brine fluids rather than a maturation scenario solely resulting from high heat flows in addition various types of asphaltene and nso rich bitumen have been detected within the same samples very likely genetically derived from thermally degraded organic precursors furthermore the formation of nanoporous pyrobitumen has been inferred for samples of gas window maturity likely resulting from the formation of gaseous hydrocarbons by providing in situ insights into the fate of bitumen and pyrobitumen as a response to the thermal evolution of the macromolecular structure of kerogen the results reported here constitute an important step towards better constraining hydrocarbon generation processes during natural shale gas maturation

effects of oil expulsion and pressure on nanopore development in highly mature shale evidence from a pyrolysis study of the eocene maoming oil shale south china abstract the influence of oil expulsion efficiency on nanopore development in highly mature shale was investigated by using anhydrous pyrolysis 425 600 c on solvent extracted and non extracted shales at a pressure of 50 mpa additional pyrolysis studies were conducted using non extracted shales at pressures of 25 and 80 mpa to further characterize the impact of pressure on pore evolution at high maturity the pore structures of the original shale and relevant artificially matured samples after pyrolysis were characterized by using low pressure nitrogen and carbon dioxide adsorption techniques and gas yields during pyrolysis were measured the results show that oil expulsion efficiency can strongly influence gas generation and nanopore development in highly mature shales as bitumen remained in shales with low oil expulsion efficiency significantly promotes gaseous hydrocarbon generation and nanopore diameter 10 nm remains flat at high maturation in addition high pressure can promote the development of micropores and fine mesopores in highly mature shales

pore and pore network evolution of upper cretaceous boquillas eagle ford equivalent mudrocks results from gold tube pyrolysis experiments low maturity boquillas formation eagle ford formation equivalent organic lean calcareous mudrock samples collected from outcrop were heated in gold tubes under confining pressure to investigate the evolution of organic matter om pores and mineral pores the majority of om in the boquillas samples was migrated petroleum bitumen based on evidence from geochemical analyses solvent extraction and scanning electron microscopy sem petrography the sem images showed several diagenetic events including framboidal pyrite precipitation and euhedral calcite quartz kaolinite and chlorite cementation that were all interpreted to have occurred prior to petroleum expulsion and pore scale to bed scale petroleum bitumen migration two major pore types were present prior to heating primary mineral pores and modified mineral pores with migrated relic om from heating experiments pores were found to be associated with stages of om maturation during the bitumen generation stage modified mineral pores were dominant and primary interparticle and intraparticle pores were present during the oil generation stage modified mineral pores with isopachous om rim were observed to be the most abundant pore type during the gas generation stage both modified mineral pores and nanometer sized spongy om pores were predominant we interpreted the occurrence of modified mineral pores to be the result of 1 oil and gas filled or partially filled voids that developed during petroleum migration and water expulsion 2 voids after removing of oil gas and water during sample preparation and 3 trapping of water molecules the formation of these nanopores was interpreted to be related to gas generation and structural rearrangement of om

porosity of devonian and mississippian new albany shale across a maturation gradient insights from organic petrology gas adsorption and mercury intrusion the evolution of porosity in shales with increasing maturity was examined in a suite of five new albany shale samples spanning a maturity range from immature vitrinite reflectance ro 0 35 to postmature ro 1 41 devonian to lower mississippian new albany shale samples from the illinois basin used in this study contain marine type ii kerogen having total organic carbon contents from 1 2 to 13 0 wt organic petrology co2 and n2 low pressure adsorption and mercury intrusion capillary pressure techniques were used to quantify pore volumes pore sizes and pore size distributions increasing maturity of the new albany shale is paralleled by many changes in the characteristics of porosity the total porosity of 9 1 vol in immature new albany shale decreases to 1 5 vol in the late mature sample whereas total pore volumes decrease from 0 0365 to 0 0059 cm3 g in the same sequence reversing the trend at even higher maturity the postmature new albany shale exhibits higher porosity and larger total pore volumes compared to the late mature sample with increasing maturity changes in total porosity and total pore volumes are accompanied by changes in pore size distributions and relative proportions of micropores mesopores and macropores porosity related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition but maturity exerts the dominant control upon these characteristics we conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences

microscopic and sedimentologic evidence for the generation and migration of hydrocarbons in toarcian source rocks of different maturities abstract this study is part of a comprehensive research program on the generation and migration of petroleum from the organic rich posidonia shale lower toarcian jurassic of the hils syncline northern germany four cores of the complete posidonia shale with varying amounts of underlying pliensbachian and overlying aalenian mudstones provided the sample base depending upon their distance from a presumed subjacent heat source the vlotho massif the cores display progressive levels of increasing thermal maturation with r 0 values 0 48 0 68 0 88 and 1 45 which span the limits of the oil generation window primary stratigraphic lithologic and petrographic attributes of the four sections are all very similar each includes a lower marlstone member about 5 m thick overlain by 11 31 m of calcareous clay shale clay minerals calcite pyrite kerogen and quartz are the principal constituents thus there is no evidence that depositional conditions of the posidonia shale varied significantly over the sampled area the omnipresence of framboidal pyrite clearly formed from the activity of sulphate reducing bacteria at or near the depositional interface is strong evidence that uniform reducing anoxic conditions were persistent at all localities this conclusion supports the assumption that initially each section was identical in overall properties and that significant differences observed in geochemistry organic macerals and other properties are directly related to the variable levels of thermal maturation kerogen from the least mature section r o 0 48 is type ii and composed of alginite a alginite b liptodetrinite bituminite and some terrestrial sporinite vitrinite and inertinite macerals with increasing maturation the alginite macerals exhibit a progressive change in morphology and fluorescence properties alginite of the least mature section displays a strong green fluorescence at 0 68 r o alginite macerals exhibit yellow orange fluorescence and are structurally well preserved although geochemical data indicate generation and loss of large amounts of oil at 0 88 r o hydrocarbon generation is almost complete and few primary alginites remain they have been transformed into secondary liptinites designated as metaalginite which have similar fluorescence colours at the highest maturation level 1 45 r o metaalginites are only weakly fluorescent with a shift toward red colours calcite and or bitumen filled bedding plane micro and macrofractures occur exclusively in the organic rich posidonia shale at maturity levels of 0 68 r o and above such features are totally absent in the immature posidonia section and in the adjacent organic poor mudstones this observation indicates that the fractures developed in direct response to overpressuring i e pore pressure exceeding lithologic load related to oil and gas generation in the source rock the fractures undoubtedly provided important expulsion conduits for generated products

a revised method for organic porosity estimation in shale reservoirs using rock eval data example from duvernay formation in the western canada sedimentary basin studies suggest that nanometer scale pores exist in organic matter as a result of thermal decomposition of kerogen depending on the host rock lithology organic pores could be the primary storage for hydrocarbon accumulation in unconventional petroleum plays although various methods are publicly available estimation of organic porosity remains a challenge because the procedures involve certain simplification or some implicit assumptions on the calculation of initial total organic carbon toc in this study we propose a revised method to address some of these issues a model of estimating hydrocarbon expulsion efficiency is developed and incorporated into the calculation of initial toc thus producing an estimate of organic porosity with an improved mass balance the method has been tested and compared with estimates using other methods based on a rock eval data set in the literature an application of the method to a large data set from the upper devonian duvernay formation petroleum system in the western canada sedimentary basin reveals that the modification has a significant effect on the estimated organic porosity this study also indicates that organic porosity in the duvernay formation ranges greatly from none in immature intervals to 6 in highly mature and organic rich shale intervals scanning electron microscope images of immature and mature organic rich shale samples of the duvernay formation show a progressive increase in organic porosity with increasing thermal maturity supporting the proposed model calculation the presence of a large volume of organic porosity in mature shale intervals suggests a significant amount of hydrocarbon may be stored in the organic nanopores in the duvernay formation

pore characteristics of lacustrine shale within the oil window in the upper triassic yanchang formation southeastern ordos basin china abstract organic matter om rich shale in the yanchang formation is recognized as a promising hybrid shale oil shale gas system in lacustrine strata in china being mainly in the oil window both the type and distribution of the pores in the shale have been affected by several factors including petroleum expulsion and retention mineral and organic composition and compaction to obtain a better understanding of the factors controlling om pore development 10 core samples were selected with various om content from the chang 7 and chang 9 members of the yanchang formation for pore characterization the investigation combined microscopic observation both of thin sections and ion milled surfaces of samples with low pressure carbon dioxide and nitrogen adsorption and bulk porosity measurements with the main emphasis being on om associated pores the selected samples generally have relatively low total porosity with the pores being poorly connected most pore types found in marine shales were present the size of porous om is usually small mostly measuring several hundreds of nanometers to a few micrometers which suggest a general compaction effect on pore development the pore development is related to different petroleum expulsion processes shale with very porous om was a very important feature the om coexisting with fluorescent lipitinites was present in a cross linked nanofiber structure possibly related to altered extracellular polymeric substances eps by compaction and maturation various om types that varied in both size and shape did not contain any visible pores e g woody relics migrated solid bitumen and om laminae in close association with clay minerals unusually low meso and macropore volume in the sample with the highest total organic carbon toc content was confirmed by the predominance of om laminae without visible pores however abundant micropores were indicated by co 2 adsorption analysis meso and macropores in this sample had probably not developed due to a significant compaction effect due to the small numbers of studied samples these om pore characteristics need to be viewed with caution

evolution of porosity and pore types in organic rich calcareous lower toarcian posidonia shale low and high resolution petrographic studies have been combined with mineralogical toc rockeval and porosity data to investigate controls on the evolution of porosity in stratigraphically equivalent immature oil window and gas window samples from the lower toarcian posidonia shale formation a series of 26 samples from three boreholes wickensen harderode and haddessen in the hils syncline was investigated the main primary components of the shales are microfossiferous calcite 30 50 clay minerals 20 30 and type ii organic matter toc 7 15 hi 630 720 mg gc in immature samples characteristic sub centimetric light and dark lamination reflects rapid changes in the relative supply of these components total porosities decrease from 10 to 14 at ro 0 5 to 3 5 at ro 0 9 and then increase to 9 12 at ro 1 45 these maturity related porosity changes can be explained by a the primary composition of the shales b carbonate diagenesis c compaction and d the maturation micro migration local trapping and gasification of heterogeneous organic phases calcite undergoes dissolution and reprecipitation reactions throughout the maturation sequence pores quantifiable in sem ca 50 nm account for 14 25 of total porosity at ro 0 5 sem visible macropores1 are associated mainly with biogenic calcite at this maturity clays and organic matter are not visibly porous but nevertheless hold most of the shale porosity porosity loss into the oil window reflects a compaction b carbonate cementation and c perhaps the swelling of kerogen by retained oil in addition porosity is occluded by a range of bituminous phases especially in microfossil macropores and microfractures in the gas window mineral hosted porosity is still the primary form of macroporosity most commonly observed at the organic inorganic interface increasing porosity into the gas window also coincides with the formation of isolated spongy and complex meso and macropores within organic particles related to thermal cracking and gas generation this intraorganic porosity is highly heterogeneous point counted macroporosity of individual organic particles ranges from 0 to 40 with 65 of organic particles containing no macropores we suggest that this reflects the physicochemical heterogeneity of the organic phases plus the variable mechanical protection afforded by the mineral matrix to allow macroporosity to be retained the development of organic macroporosity cannot alone account for the porosity increase observed from oil to gas window major contributions also come from the increased volume of organic micro and meso porosity and perhaps by kerogen shrinkage

a preliminary study on the characterization and controlling factors of porosity and pore structure of the permian shales in lower yangtze region eastern china abstract permian organic rich shales occur throughout the lower yangtze region in eastern china and are potentially a future target for shale gas exploration due to the lack of data the gas potential of these permian shales is difficult to evaluate in this study a total of 22 permian shale samples were collected from two wells and their geochemical and rock property porosity characteristics were investigated the results show that the samples have a total organic carbon toc content of 0 6 17 4 wt derived from mainly gas prone kerogen with a vitrinite reflectance ro value ranging from 2 3 to 2 7 total porosity of the samples ranges between 1 and 5 5 the micropore and mesopore surface areas range between 5 41 35 69 m2 g and 3 59 11 23 m2 g respectively micropore and mesopore volumes range between 0 22 1 44 cm3 100 g and 0 67 1 76 cm3 100 g respectively total porosity and pore structure data of these samples show a correlation with toc for samples with toc 12 wt negative correlation relationships were observed toc content strongly impacts gas storage capacity of the permian shales in the lower yangtze region and the preliminary results of the present study have important implications for the shale gas play evaluation in this area

influence of maceral composition on geochemical characteristics of immature shale kerogen insight from density fraction analysis abstract variations in the relative proportions of individual macerals in shales can significantly influence the geochemical characteristics of bulk organic matter density fractions of kerogen from the thermally immature new albany shale devonian and mississippian with contrasting maceral compositions exhibit strong geochemical differences the parental shale is characterized by a vitrinite reflectance ro of 0 45 a total organic carbon content of 13 wt and a sulfur content of 6 2 wt organic matter is dominated by amorphinite and alginite with vitrinite and inertinite accounting only for 1 by volume alginite dominated density fractions density ca 1 0 1 15 g cm3 contain significantly more aliphatic hydrogen a stronger carboxyl carbonyl contribution and reduced fourier transform infrared spectroscopy absorbance in the 1000 to 1100 cm 1 region assigned to ether bonds c o c as compared to the amorphinite dominated density fraction density ca 1 2 1 6 g cm3 aromaticity generally increases from alginite dominated to amorphinite dominated fractions density fractions dominated by amorphinite are more deuterium depleted dn values of nonexchangeable hydrogen up to 105 than alginite rich density fraction dn values reach 90 in contrast changes in relative proportions of alginite and amorphinite in the new albany shale do not significantly affect the amount of isotopically exchangeable hydrogen in total hydrogen i e hydrogen exchangeability alginite is relatively 13c enriched whereas density fractions having a high content of amorphinite are relatively 13c depleted our results suggest that even small bulk geochemical and isotopic differences can gain relevance after deconvolution from maceral related variability the masking influence of maceral abundance patterns must be considered when interpreting bulk geochemical data as paleoenvironmental proxies the findings of this study on shale and type ii kerogen are relevant for all types of kerogens in sediments and rocks

the impact of composition on pore throat size and permeability in high maturity shales middle and upper devonian horn river group northeastern british columbia canada abstract shale reservoirs of the middle and upper devonian horn river group provide an opportunity to study the influence of rock composition on permeability and pore throat size distribution in high maturity formations sedimentological geochemical and petrophysical analyses reveal relationships between rock composition pore throat size and matrix permeability in our sample set measured matrix permeability ranges between 1 69 and 42 81 nanodarcies and increases with increasing porosity total organic carbon toc content positively correlates to permeability and exerts a stronger control on permeability than inorganic composition a positive correlation between silica content and permeability and abundant interparticle pores between quartz crystals suggests that quartz may be another factor enhancing the permeability pore throat size distributions are strongly related to toc content in organic rich samples the dominant pore throat size is less than 10 nm whereas in organic lean samples pore throat size distribution is dominantly greater than 20 nm sem images suggest that in organic rich samples organic matter pores are the dominant pore type whereas in quartz rich samples the dominant type is interparticle pores between quartz grains in clay rich and carbonate rich samples the dominant pore type is intraparticle pores which are fewer and smaller in size high permeability shales are associated with specific depositional facies massive and pyritic mudstones rich in toc and quartz have comparatively high permeability laminated mudstone bioturbated mudstone and carbonate facies which are relatively enriched in clay or carbonate have fairly low permeability

a preliminary study on the pore characterization of lower silurian black shales in the chuandong thrust fold belt southwestern china using low pressure n2 adsorption and fe sem methods although lower silurian black shales within and around the sichuan basin have received renewed attention during the past few years because of their potential prospectivity for shale gas studies associated with shale gas reservoir evaluation are still rare in this study eight black shale core samples were collected from a well drilled recently in the chuandong thrust fold belt southwestern china and their geochemistry and pore structures were investigated using low pressure n2 adsorption analysis and field emission scanning electron microscopy fe sem observations the results show that the black shales have total organic carbon toc values ranging from 1 01 to 3 98 and their equivalent vitrinite reflectance values are in the range of 2 84 3 05 both mineral matrix and organic matter pores are well developed with pore sizes ranging from several to several hundred nanometers the total porosity for the eight samples ranges from 2 60 to 4 74 and the percentages of organic matter pores are estimated to be in the range of 31 62 the total surface area ranges from 5 06 m2 g to 19 32 m2 g and the micropore 2 nm surface area estimated by the t plot method ranges from 3 13 m2 g to 9 27 m2 g the toc values have positive relationships with the total porosity total surface area and the micropore 2 nm volume and surface area indicating toc may be an effective parameter for shale gas reservoir evaluation in the studied area

aspects of armageddon an exploration of the role of volcanic eruptions in human history and civilization volcanic eruptions are frequently invoked as the mechanism responsible for changes observed in the archaeological and environmental record this paper argues that the evidence for this assumption is slight and that while there are examples of this they are rare several case studies are discussed which illustrate the complex nature of the relationship between human cultures and volcanic eruptions and it is suggested that volcanic activity frequently acts as a stimulus rather than a brake to cultural development

simple kinetic models of petroleum formation part iii modelling an open system abstract the movement of petroleum from organic rich source beds to potential carrier beds is the net result of two processes expulsion the release of generated petroleum from kerogen within the source bed and primary migration flow of a petroleum phase through the inorganic void networks of the source bed and all other intervening fine grained rocks expulsion is by far the more important process within the source bed orgas a simple zero dimensional model of the source rock as an open system explicitly models expulsion concurrent with oil and gas generation and oi lgas cracking as a storage threshold problem oil and gas are retained adsorbed absorbed within kerogen until their concentrations exceed the respective sorptive capacity of the residual organic carbon 0 1 and 0 02 g g ck 1 the initial hydrogen index hl 0 controls the important balance between potential sorbate petroleum and sorbant residual carbon using simple geochemical measurements the initial organic carbon is divided into initial oil inert kerogen and oil and gas generative reactive kerogen components reactive kerogens are assigned to one of five global kinetic organofacies with pre determined kinetic parameter sets governing separately rates of oil and gas generation kinetic parameters governing the rates of oil cracking within the source rock are predicted from hl 0 the two most important determinants of source rock behaviour are organofacies and hl 0 at a reference constant heating rate of 2 c ma 1 the projected oil expulsion threshold for typical organofacies members increases in the order a de 100 110 120 135 c f typically expels no oil an order of magnitude increase decrease in heating rate increases decreases these thresholds by ca 15 c typical cumulative gas mass fractions in their ultimate expulsion products are a f 0 25 0 3 0 25 0 65 and 1 0 g g 1 a value of 200 mg hc g c 1 is an approximate minimum hl 0 prerequisite for oil expulsion irrespective of absolute petroleum potential p 0 as a family coals vary dramatically in their expulsion behaviour as their hl 0 ranges both above and velow this value primary migration is efficient for expulsive source rocks movement within the source bed is limited only at low p 0 a source rocks total genetic potential p 0 thickness becomes important during migration outside the source bed it potentially restricts the primary migration distance and the excess of petroleum available for secondary migration and entrapment we evaluate primary migration approximately using a small migration loss factor no more than about 10 saturation of porosity or 1 mg g 1 coupled with an understanding of fluid potential gradients which determine migration direction within the stratigraphic architecture ultimately kerogen degradation and oil to gas cracking in the source rock are the rate limiting processes in petroleum accumulation

relationships between porosity organic matter and mineral matter in mature organic rich marine mudstones of the belle fourche and second white specks formations in alberta canada abstract this study presents approaches for evaluating hybrid source rock reservoirs within tight rock petroleum systems the emerging hybrid source rock reservoir shale play in the upper cretaceous second white specks and belle fourche formations in central alberta canada is used as an example to evaluate organic and inorganic compositions and their relationships to pore characteristics nineteen samples from a 77 5 m long core were analyzed using organic petrography organic geochemistry several methods of pore characterization and x ray powder diffraction xrd the lower part of the studied section includes quartz and clay rich mudrocks of the belle fourche formation with low carbonate content whereas the upper portion contains calcareous mudrocks of the second white specks formation strata are mineralogically composed of quartz plus albite 18 56 wt carbonates calcite dolomite ankerite 1 65 wt clays illite kaolinite chlorite 15 46 wt and pyrite 2 12 wt petrographic examinations document that organic matter represents marine type ii kerogen partly biodegraded with limited terrestrial input vitrinite reflectance r o 0 74 0 87 t max values 438 446 c and biomarkers indicate mid maturity within the oil window the relatively poor remaining hydrocarbon potential expressed as an s2 value between 2 1 and 6 5 mg hc g rock may result from an estimated 60 83 of the original kerogen having been converted to hydrocarbons with the bulk having migrated to adjacent sandstone reservoirs however the present day remaining total organic carbon toc pd content remains relatively high 1 7 3 6 wt compared with the estimated original toc o of 2 4 5 0 wt the calculated transformation ratio of 60 83 suggests that the remaining 17 40 wt of kerogen is able to generate more hydrocarbons the studied section is a tight reservoir with an average swanson permeability of 3 37 10 5 md measured on two samples and total porosity between 1 7 and 5 0 vol 3 vol on average the upper part of the sandy belle fourche formation with slightly elevated porosity values 3 5 5 vol likely represents the interval with the best reservoir properties in the studied core interval total pore volume ranges between 0 0065 and 0 0200 cm 3 g measured by a combination of helium pycnometry and mercury immersion mesopores 2 50 nm are the most abundant pores and occupy 34 67 of total porosity or a volume of 0 0030 0 0081 cm 3 g in comparison micropores 3 g and macropores 50 nm reach up to 57 with the exception of some samples failing to indicate the presence of this pore fraction volume 0 0000 0 0107 cm 3 g macroporosity is mostly responsible for variations in total porosity as suggested by macroporosity s strongest correlation with total porosity within the section the relatively narrow ranges of toc and minerals contents among measured samples limit our ability to further deconvolute factors that influence changes in total porosity and pore size distribution

pore characterization of organic rich lower cambrian shales in qiannan depression of guizhou province southwestern china abstract nine organic rich shale samples of lower cambrian black shales were collected from a recently drilled well in the qiannan depression guizhou province where they are widely distributed with shallower burial depth than in sichuan basin and their geochemistry and pore characterization were investigated the results show that the lower cambrian shales in qiannan depression are organic rich with toc content ranging from 2 81 to 12 9 thermally overmature with equivalent vitrinite reflectance values in the range of 2 92 3 25 and clay contents are high and range from 32 4 to 53 2 the samples have a total helium porosity ranging from 2 46 to 4 13 and total surface area in the range of 9 08 37 19 m2 g the estimated porosity in organic matters defined as the ratio of organic pores to the volume of total organic matters based on the plot of toc vs helium porosity is about 10 for the lower cambrian shales in qiannan depression and is far lower than that of the lower silurian shales 36 in and around sichan basin this indicates that either the organic pores in the lower cambrian shale samples have been more severely compacted than or they did not develop organic pores as abundantly as the lower silurian shales our studies also reveal that the micropore volumes determined by dubinin radushkevich dr equation is usually overestimated and this overestimation is closely related to the non micropore surface area of shales i e the surface area of meso and macro pores however the modified bet equation can remove this overestimation and be conveniently used to evaluate the micropore volumes surface area and the non micropore surface areas of micropore rich shales

variation of organic matter density with thermal maturity an estimate or measurement of organic matter density is required for converting between the weight percent of total organic carbon toc and the volume percent of organic matter for wireline log calibration it is therefore important to recognize when significant changes in organic matter density occur a method is presented for calculating organic matter density from measurements of crushed rock dry grain density and soxhlet extracted toc i have investigated the thermal evolution of organic matter by tracking changes in the intrinsic density of organic matter as a function of thermal maturity organic matter density shows two step increases that correspond to the generation of liquid hydrocarbons in the oil window up to 1 2 vitrinite reflectance ro and the conversion of organic matter to graphitelike carbon more correctly turbostratic carbon at high thermal maturity 4 ro profound structural changes of organic matter may in part determine the maturity limits of source rock tight liquids and shale gas plays particularly at high thermal maturity where gas is hosted within the organic matter hosted pore system

evolution of petrophysical properties of oil shales during high temperature compaction tests implications for petroleum expulsion abstract the transport properties of permian to miocene oil shales torbanite posidonia messel himmetoglu and condor were studied using petrophysical and geochemical techniques the aims of this study were to assess permeability of oil shales evaluate the evolution of porosity specific surface area and intergranular permeability during high temperature compaction tests and to verify the suitability of intergranular permeability for petroleum expulsion measured permeability coefficients for two samples were 0 72 10 21 m for the eocene messel shale and 2 63 10 21 m for the lower jurassic posidonia shale from s germany respectively bet specific surface areas of the original samples ranged from 0 7 to 10 6 m g and decreased after compaction to values from 0 3 to 3 7 m g initial porosity values ranged from 7 6 to 20 1 for pre deformation and from 9 99 to 20 7 for post deformation samples porosity increased during the high temperature compaction experiments due to petroleum generation and expulsion permeability coefficients estimated using the kozeny carman equation varied from 6 97 10 24 m to 5 22 10 21 m for pre deformation and from 0 2 10 21 m to 4 8 10 21 m for post deformation samples reflecting the evolution of their porosity and bet specific surface areas measured and calculated permeability were similar for the messel shale whereas calculated permeability was two orders of magnitude lower for the posidonia shale from s germany petroleum expulsion efficiencies under the experimental conditions ranged from 38 6 for the torbanite to 96 2 for the posidonia shale from s germany they showed strong positive correlation with the petroleum generation index r 0 91 and poor correlations with porosity r 0 46 average pore throat diameters r 0 22 and compaction r 0 02 estimated minimum pore system saturations for petroleum expulsion during the experiments were 12 for the torbanite and 30 for the posidonia shale from n germany pore system saturation determines whether expulsion occurs mainly through matrix or fracture permeability for samples with saturation levels above 20 fracture permeability dominated during the experiments evidence based on the measured permeability coefficients expulsion flow rates consideration of capillary displacement during generation related pore invasion and the existence of transport porosity suggests that fracture permeability is the principal avenue of petroleum expulsion from source rocks this conclusion is supported by microscopic observations

experimental investigation of pore development of the chang 7 member shale in the ordos basin under semi closed high pressure pyrolysis abstract semi closed heat simulation experiments were conducted on cylindrical samples and a series of residue samples of chang7 shale heated to different temperature were acquired to characterize the evolution and controlling factors of shale reservoir structure low pressure adsorption experiments with carbon dioxide and nitrogen as the adsorbents were conducted to characterize the evolution of shale nanopores mercury intrusion capillary pressure micp and he hg porosities of the raw and residue shale columns were measured to study the evolution of porosities with increasing maturity also the morphology of nanopores and microfractures of argon ion polished shales was examined using scanning electron microscopy decreasing trends of micro and meso pores with increasing temperature were mainly caused by masking or occupation of pores by generated oil and bitumens during the oil generation stage then the specific surface areas ssas and volumes of micro and meso pores increase dramatically with increasing temperature as further nanopores were formed through secondary cracking of the generated oil and bitumens destruction of nanopores occurred at the over maturation stage and caused decreasing trends of ssas and volumes of micro pore meso pore and macro pore from 450 c 489 c and 500 c respectively shale porosity showed a generally positive correlation with temperature suggesting that macro pores and micro fractures were the predominant reservoirs that was also observed with focused ion beam scanning electron microscopy the insights into the evolution of shale nanopores presented in this study are generally in accordance with previous research in north america and china on the properties of these structures in shales at different maturation level

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores

reconstructing eruptions from historical accounts makaturing c 1765 philippines abstract for some volcanoes the only evidence for past eruption is provided by historical accounts when interpreted carefully these have the potential to be a rich source of information and yet they have so far been under utilised in reconstructing eruption histories the navigator thomas forrest describes a large eruption at makaturing volcano southern philippines in approximately 1765 that he considers the catalyst for the local iranun population transitioning from an agrarian society to long distance piracy and slave raiding within the historical literature the eruption is attributed to large scale physical impacts around the volcano and disruptions to trading routes and livelihoods that ultimately changed the course of southeast asia s history however no such eruption or impacts are recognised in the scientific literature or in eruption databases and fieldwork to the region remains difficult here we reinterpret the account of forrest from a multi disciplinary perspective with a historian and physical volcanologists working together to incorporate the greatly needed local context into identifying credible volcanic processes and impacts associated with the reported activity we used a novel approach to eruption reconstruction by cross referencing deposits and impacts inferred from the historical record with stochastic tephra dispersal modelling that considered multiple eruption sources and characteristics we found that forrest s account was best characterised by an eruption of vei 4 between may and october with plume heights in the range of 12 to 16 km while at least one eruption of this size was required to reproduce the impacts described in the historical record it may have formed part of a longer sequence of multiple repeated eruptions in this way such an eruption could have acted as a tipping point for a local population already on the verge of socio political and economic collapse disproportionately affecting regions on a much larger scale than the reported deposits suggest there remains a disconnect between the eruption characteristics recorded in historical accounts and those reproduced by numerical modelling for which we propose alternative interpretations of the historical record unfortunately given the minimal details available about the eruption this discordance is unlikely to be resolved even when geological studies are possible however a valuable benefit of the probabilistic modelling approach presented here is that it highlights the likely direction of tephra dispersal and deposition during a future eruption of makaturing supporting rapid tephra hazard assessment in the event of future unrest

quantitative evaluation of toc organic porosity and gas retention distribution in a gas shale play using petroleum system modeling application to the mississippian barnett shale abstract shale reservoirs have not benefited from advanced modeling tools to the extent of conventional resources thus an approach is proposed to integrate key parameters such as total organic carbon toc content methane adsorption and organic porosity in a basin simulator original toc has an impact on both gas generated volume and gas retention within source rocks the conversion of organic matter into hydrocarbons also creates additional intraparticle kerogen porosity in which oil and gas can be stored in this work a method is proposed to calculate the evolution of toc organic porosity and gas retention capacity free versus adsorbed through time in shale gas by means of petroleum system modeling gas adsorption potential on organic material is calculated using a langmuir model which accounts for pressure temperature and remaining solid toc organic porosity is calculated as the result of the change of the organic matter from solid immature kerogen to less dense fluid hydrocarbons during thermal maturation the method is tested on a 3d basin model of the mississippian barnett shale in texas usa the computed organic porosity varies from 0 in immature zones to a maximum of 4 of rock volume in organic rich and mature zones computed retained methane in the lower barnett shale ranges between 20 and 60 scf t from 1 to nearly 3 kg m3 and is mainly concentrated in mature areas of the basin simulated results are consistent with available barnett shale data possible effects of assumptions made in the approach and perspectives are discussed

calculation of petroleum masses generated and expelled from source rocks abstract an algebraic scheme for calculating the masses of petroleum formed in mature source rocks has been constructed the scheme exploits routine geochemical measurements and a basic understanding of the behaviour of sedimentary organic matter at elevated temperatures under both laboratory and subsurface conditions application of these techniques to data from a wide range of source rock types has led to the following general conclusions 1 1 major oil and gas generation from kerogen occurs between 120 and 150 c in the subsurface gas generation continues to temperatures 160 c 2 2 oil prone source rocks with average initial potential 5 kgt 1 of rock and average organic carbon contents 1 5 expel 60 90 of the total oil generated 3 3 oil expulsion from leaner source rocks is less efficient most of the oil generated remains in the source rock it is subsequently converted to lighter components at higher temperatures and expelled in the vapour state 4 4 the major loss of organic carbon from rich oil prone source rocks during generation and expulsion means that the petroleum potential and organic carbon content of mature source rocks are much less than their initial immature values hence the algebraic scheme must be used to calculate the initial values before expelled petroleum masses can be determined