nmr measurements in carbonate rocks problems and an approach to a solution carbonate rocks are well known for their complex petrophysical behavior where in contrast to siliciclastic rocks different parameters including porosity and permeability usually are not directly related this behavior is the result of thorough reorganization of porosity during diagenesis and it turns prediction of reservoir quality of carbonate rocks into a challenge the study presented here deals with the problem of utilizing nmr techniques in prediction of petrophysical properties in carbonates we employ a visual porosity classification as a priori knowledge for better interpreting nmr data for prediction purposes this allows for choice of suitable t2 cutoff values to differentiate movable from bound fluids adapted for the specific carbonate rock thus resulting in better interpretation of nmr data the approach of using a genetic pore type classification for adapting the conventional method for t2 cutoff determination which originally was developed for siliciclastic rocks is promising similarly for permeability determination on the basis of nmr measurements the classification of carbonate rocks based on porosity types also shows potential the approach implemented here has the promise to provide a basis of standardized interpretation of nmr data from carbonate rocks

critical porosity and elastic properties of microporous mixed carbonate siliciclastic rocks by integrating elastic property measurements and quantitative mineralogic and petrographic analyses of 45 mixed carbonate siliciclastic samples from two wells drilled in late cretaceous rock of the south provence basin southeast france we can 1 identify and quantify the parameters controlling elastic properties 2 demonstrate that micrite can be considered as a porous medium with a low critical porosity averaging 18 and 3 relate diagenetic transformations pore structure modifications and elastic property changes microporous carbonates with compact anhedral and euhedral microrhombic micrites display a steeper decrease in compressional and shear velocities with increasing porosity than do carbonate rocks with moldic intergranular or intercrystalline macroporosity the low value of critical porosity estimated in micrites 18 as well as the steep slopes of velocity porosity relationships at low porosity is believed to result from a pore network geometry characterized by very flat thin pores bounded by planar faces of micrite crystals cementation of microrhombic micrite steeply increases elastic moduli whereas dissolution processes significantly increase porosity with low variations of elastic moduli thus critical porosity concepts can help describe and model elastic properties of micritic microporous carbonate

controls on sonic velocity in carbonates compressional and shear wave velocities v p and v s of 210 minicores of carbonates from different areas and ages were measured under variable confining and pore fluid pressures the lithologies of the samples range from unconsolidated carbonate mud to completely lithified limestones the velocity measurements enable us to relate velocity variations in carbonates to factors such as mineralogy porosity pore types and density and to quantify the velocity effects of compaction and other diagenetic alterations

revisiting the wyllie time average equation in the case of near spherical pores we suggest a generalized form of the wyllie equation to better describe acoustic velocity variation with porosity in rocks with a mixture of intercrystalline and near spherical pores introducing a pore shape factor in the wyllie equation allows different weights to be applied to the solid phase p wave velocity to account for rock frame stiffness this is demonstrated in carbonate and igneous rocks having variable amounts of spherical porosity ranging from 0 to 80 of the bulk porosity the generalized equation describes a velocity porosity envelope instead of the simple line given by the wyllie equation the lower limit of the velocity envelope is for rocks that have only interparticle or intercrystalline porosity wyllie equation behavior and the upper limit is when all pores are spherical or near spherical this upper limit corresponds to the hashin shtrikman upper bound for porosities up to 30 the realization portrays wyllie s velocity porosity relationship as one particular case in which all por

theoretical seismic wave radiation from a fluid filled borehole this paper concerns far field radiation of compressional p and shear s waves into the surrounding medium from a fluid filled borehole in an infinite medium and tube waves propagating along a borehole using a low frequency approximation two kinds of sources are considered 1 a volume displacement point source acting on the axis of a borehole and 2 a uniform radial stress source acting on the wall of a borehole when the tube wave velocity is close to the shear wave velocity the effect of the borehole fluid on the p wave radiation pattern and on the s wave radiation pattern is substantial

pore space evolution and elastic properties of platform carbonates urgonian limestone barremian aptian se france abstract a dataset of 214 ultrasonic velocity and porosity measurements on barremian aptian carbonates from provence se france provides well constrained velocity porosity transforms and allows the quantification of the impact of pore type and diagenetic history on these velocities a numerical approach epar equivalent pore aspect ratio was used to link diagenetic transformations pore network evolution and elastic properties three categories of samples characterized by their dominant pore type were discriminated from the velocity and porosity database by means of the epar values derived from bulk k epar and shear epar moduli 1 purely microporous limestones low k and epar 0 3 three velocity porosity trajectories related to three diagenetic paths were defined and quantified from the urgonian database 1 epar preserving micro scale cementation of micrite 2 non epar preserving dissolution with moldic pore development and 3 epar preserving sparry calcite cementation of molds equivalent pore aspect ratio can therefore be regarded as a robust tool to decipher diagenetic trends in velocity porosity transforms and may help predicting pore architecture from subsurface data

borehole seismic source radiation pattern in transversely isotropic media we extend previous discussions on crosswell tomography in anisotropic formations by deriving the radiation patterns of three typical downhole seismic sources impulsive air gun or dynamite wall clamped vertical vibrators and cylindrical bender inside a fluid filled borehole embedded in a transversely isotropic ti formation the method of steepest descents in conjuncture with the low frequency and far field assumptions is applied to the exact displacement integrals of these sources to obtain their radiation patterns asymptotically in spite of complications caused by quasi p and quasi sv wave coupling and wavefront triplication in homogeneous ti media the final results can still be expressed in slowness components determined by a ray direction which is desired when source radiation effects are to be accounted for by ray based tomography techniques tests with the radiation patterns show that while the effect of anisotropy on p waves is moderate its effect on the s wave pattern is significant eve

effects of microporosity on sonic velocity in carbonate rocks the elastic moduli of a rock are affected by three main factors pore fluid rock framework and pore space in carbonate rocks the latter two factors are a function of the depositional environment and the diagenetic history cementation recrystallization and dissolution processes can change the mineralogy and texture of the original framework and thereby alter the original grain to grain contacts and or occlude pore space dissolution processes can enlarge interparticle pore space or dissolve grains entirely thereby increasing porosity these diagenetic alterations and associated changes in the rock frame and pore structure result in a wide velocity range at a given porosity

radiation from seismic sources in cased and cemented boreholes far field stationary phase approximations are often used to study the radiation of p and s waves from seismic sources located in boreholes usually with an assumption of low frequency and in application to uncased boreholes these two assumptions allow explicit analytical results for the radiation patterns to be derived as boundary condition equations can be solved analytically in fairly simple forms applying the same methodology to cased and cemented boreholes however is much more difficult because of the increased number of simultaneous boundary condition equations i circumvent this difficulty by solving the boundary condition equations numerically using propagator matrices as is generally done in the calculation of synthetic full waveform acoustic logs in this way the assumption of low frequency is also avoided and a generalized stationary phase solution for sources in general concentrically layered borehole models is easily obtained computation of the radiation patterns for cased and uncased boreholes in various formations shows that the amplitude reduction because of the introduction of casing is a function of both source type and of formation velocities axial stress sources are less affected by the casing than either radial stress or volume injection sources and as formation velocity decreases the effect of the casing becomes more significant as the impedance contrast between steel and the formation becomes larger the new generalized stationary phase solution also shows that as frequency approaches 1000 hz the results obtained by low frequency approximations for stress sources can be inaccurate and that the energy radiated from the source becomes more highly directed in the horizontal directions the radiation pattern begins to change relatively rapidly as a function of frequency so that the resulting observations from broad band sources will show changes in waveforms that mimic the effects of attenuation these changes occur because the length of the source becomes important as wavelength decreases demonstrating the need to consider the influence of frequency as well as casing and cement on source radiation

acoustic properties of ancient shallow marine carbonates effects of depositional environments and diagenetic processes middle jurassic paris basin france abstract examination of petrophysical properties acoustic velocity porosity permeability and density and petrographical characteristics texture facies composition and diagenesis of more than 250 core plugs from the middle jurassic carbonates of the eastern paris basin provides insights into the parameters controlling acoustic velocities in relatively low porosity carbonate rocks 20 the pore type observations reveal distinct acoustic velocities in samples with intergranular macropores and samples with micropores in subhedral micrite such that velocities in microporous mudstone wackestone lagoonal deposits are greater than in macroporous grainstone shoal samples at a given porosity range 15 20 the standard wyllie and raymer transforms fit very well with the linear regression between acoustic velocity and porosity from mudstone or lagoonal facies marls and fine grained deposits interpreted as lagoonal facies include statistically significant correlation r 0 9 between velocity and porosity however the data suggest that the wide scatter in velocity porosity relationship from grainstones are not the result of different sorting grain size pore type dolomite content or clay content instead early cementation greatly influences acoustic properties during diagenesis and are interpreted to account for the high variability of velocities over a given porosity range specifically at a given porosity acoustic velocities in compacted grainstone that did not undergo early cementation are higher than in early cemented grainstone petrographic observations suggest that early cementation limits mechanical compaction creating a heterogeneous medium from the earliest stages of diagenesis non touching grains preservation of intergranular macropores that are partially to totally filled by later blocky calcite cement the abundant interfaces between micritized ooids early cement fringes and blocky calcites in grainstones may induce significant wave attenuation as a result the standard time average equations fail to predict the effect of diagenetic features such as early cementation on sonic velocity conversely an absence of early cementation favors mechanical compaction grain to grain contact and suturing the result is a homogeneous micritized grain supported network that may facilitate wave propagation through demonstration of the key role of early cementation in the explanation of variability in acoustic properties the results of this study illustrate the complicated factors influencing velocity transforms in carbonates wyllie and raymer i e classical tools for predicting reservoir properties these insights on the interpretation of vp and the refinement of velocity porosity transforms in grainstone units may be broadly applicable to enhancing seismic based exploration in carbonate successions

modeling elastic properties in carbonate rocks carbonate limestone and dolomite reservoirs account for approximately 50 of oil and gas production worldwide however seismic responses in carbonate rocks are poorly understood in addition dhi ranking and avo classification systems developed for clastic rocks are unlikely to be applicable to carbonate rocks an accurate and physically sound carbonate rock physics model is needed to address these technical issues

the importance of a small wall deformation in the three dimensional acoustic logging results summary a variety of seismic techniques use fluid filled boreholes to host detectors and seismic sources the complexity of the wavefield generated depends on the position of the receivers and the source frequency excited type of formation and type of source in the present paper the boundary element method is used to study the wavefield elicited by monopole or dipole sources within a fluid filled cylindrical cavity drilled through an unbounded elastic formation this model is used to assess the effects of the existence of a small localized wall deformation on the response such a deformation may occur through the mechanical action of the drill string rock failure adjacent to a drilled borehole plastic deformation and washing out of the borehole in soft or poorly consolidated rocks in addition the effect of a source receiver tool placed in an off centre and or tilted position inside the fluid filled borehole on the propagation of both axisymmetric and non axisymmetric wave modes are studied

effects of differential cementation on the sonic velocities of upper cretaceous skeletal grainstones southeastern netherlands abstract p wave velocities measured in cretaceous skeletal grainstones from limburg southeastern netherlands are significantly higher in moderately cemented samples than in poorly cemented samples from similar depositional facies petrography suggests that this relationship is due to differences in the extent of development of intergranular cementation as influenced by original grain mineralogy rather than a significant difference in primary porosity the time average velocity equation for a calcite matrix fails to predict the cementation effect on sonic velocity at high porosities linear and nonlinear time average regressions show strong correlation between velocity and porosity whether the underlying trend is linear or nonlinear is a fundamental question that cannot be determined with this data set comparison between carbonate grainstones and siliciclastic sandstones reveals that 1 the grainstones have gradients in velocity porosity space similar to those in siliciclastic arenites but have velocities that are up to 0 3 km s higher than those in clean arenites and up to 0 8 km s higher than in argillaceous arenites and 2 grainstones develop a rigid framework that transports elastic waves at significantly higher porosities than arenites 40 50 compared to 30 40 higher sonic velocity presumably results from the higher matrix velocity of calcite versus quartz and the higher elastic moduli created by the effective cement bridges connecting grains

structural evolution timing and tectonic style of the sole pit inversion abstract the nw se oriented sole pit high located in the western half of the southern north sea basin is the result of three different structural processes initiated during the late palaeozoic basin subsidence probably related to late hercynian pull apart movements led to continuous sedimentation from the permian to the middle jurassic mid jurassic doming of its eastern flank followed by erosion transtensional movements and differential subsidence until the early cretaceous reflect the mid and late kimmerian crustal distension and fragmentation of the north sea rift basinwide inversion occurred between the turonian and the campanian and was repeated in the oligocene resulting in a total uplift of some 1500 m the present structural style is represented by a complex network of transpressional and transtensional faults at permian rotliegend levels which are thought to represent the upward termination of a series of wrench induced flower structures with a right lateral sense of displacement these faults are detached by zechstein and triassic salt from more orderly transtensional faults systems at shallower levels in areas where salt is absent late kimmerian normal faults became reactivated in a reverse sense during inversion however the relationship of these shallow mappable tectonic components to the deeper pre permian structure of the sole pit high and to the underlying crustal configuration remains speculative

sandbox model studies of inversion tectonics abstract scaled plane strain sandbox models have been used to simulate basement controlled structural inversion in a sedimentary overburden two basement configurations were tested in the first one reversal of movement along vertical and normal faults that controlled a graben relief induced only a partial recovery of displacement along the pre existing overburden faults the inversion produced new reverse faults in the footwall of the pre existing overburden faults the reactivated normal faults and the new reverse faults defined wedge shaped fault blocks at the edges of the inverted structure in the second configuration the relationship between inversion and tilted fault blocks was tested when a tilting basement block does not move parallel to its bounding fault a compression is induced in the overburden which generates an inverted structure bounded by new reverse faults both experiments show that structural inversion not only reactivates pre existing faults but also generates new faults in the overburden faults related to inversion are the result of horizontal compression either associated with rotation of one of the fault blocks or with vertical uplift of basement blocks

factors controlling elastic properties in carbonate sediments and rocks carbonate sediments are prone to rapid and pervasive diagenetic alterations that change the mineralogy and pore structure within carbonate rocks in particular cementation and dissolution processes continuously modify the pore structure to create or destroy porosity in extreme cases these modifications can completely change the mineralogy from aragonite calcite to dolomite or reverse the pore distribution whereby original grains are dissolved to produce pores as the original pore space is filled with cement to form the rock figure 1 all these modifications alter the elastic properties of the rock and therefore the sonic velocity the result is a dynamic relationship among diagenesis porosity pore type and sonic velocity the result is a wide range of sonic velocity in carbonates in which compressional wave velocity vp ranges from 1700 to 6600 m s and shear wave velocity vs from 600 to 3500 m s

integrated characterization of carbonate ramp reservoirs using permian san andres formation outcrop analogs the san andres formation permian guadalupian of the permian basin is representative of carbonate ramp reservoirs in that it has highly stratified character complex facies and permeability structure and generally low recovery efficiencies of 30 of original oil in place the approach used here to describe carbonate ramp reservoirs such as the san andres formation produces detailed reservoir models based on integration of sequence stratigraphic analysis petrophysical quantification through definition of rock fabric flow units and fluid flow simulation synthesis of these subdisciplines clarifies which aspects of the geologic petrophysical model are most significant in predicting reservoir performance and ultimately in understanding the location of remaining oil satur tion the san andres formation crops out along the algerita escarpment a long oblique dip continuous shelf to basin exposure in the central guadalupe mountains these outcrops provide a unique opportunity to study lateral relationships in geologic and petrophysical structure analogous to those occurring between wells in subsurface reservoirs on the basis of sequence stratigraphic analysis three scales of cyclicity are recognized depositional sequences high frequency sequences and cycles examination of the cycles in two detailed window areas provides a practical scale for petrophysical quantification and fluid flow simulation an understanding of cycle position within the high frequency sequence framework also provides predictive information petrophysical analysis revealed six rock fabric groups dominated by intergranular separate vug or dense intercrystalline pore types comparison of these rock fabric groups with facies descriptions produced a rock fabric flow unit model that honors the geologic structure of the cycle and sequence framework permeability data were averaged within rock fabric flow units using a geometric mean approach based on fine scale fluid flow modeling of deterministic and stochastically generated permeability fields two dimensional black oil fluid flow models illustrate that 1 major differences in sweep efficiency and fluid flow performance are predicted when linear interwell interpolations are compared with actual interwell scale geologic structure as determined by outcrop geologic and petrophysical mapping 2 an understanding of static geologic petrophysical conditions provides only a partial understanding of reservoir performance defined by the interaction of these static properties and dynamic properties of fluid flow interaction within the flow unit architecture and 3 because of the orderly distribution of high and low permeability facies within cycle stacks of high frequency sequences this larger scale of geologic description can give a reasonable first order approximation of fluid flow patterns and early breakthrough end page 181

matrix microcrystalline structure and acoustic properties of oomoldic dolograinstone previous studies have shown that carbonate rock with rounded moldic macropores has a higher compressional velocity at a given porosity than rock with interparticle or intercrystalline porosity and high aspect ratio macropores our study of permian dolograinstone challenge this comonlny accepted results petrophysical and acoustic velocities were measured on 55 mini core plugs collected along an approximately 1 kilometer km long horizontal transect within a single grainstone unit having lateral changes from grainstone with dominantly interparticle porosity to grainstone with mostly moldic porosity the studied dolograinstone samples have a large scattering of acoustic velocity up to 1 500 meters per second m s at equal porosity one some oomoldic grainstone samples have either higher velocity or significantly lower velocity than that of the intercrystalline grainstone samples petrographic analysis under plain light and uv light combined with mercury injection capillary pressure micp data and scann

acoustic properties of carbonates effects of rock texture and implications for fluid substitution more than 250 plugs from outcrops and three nearby boreholes in an undisturbed reef of miocene tortonian age were quantitatively analyzed for texture mineralogy and acoustic properties we measured the p and s waves of carbonate rocks under dry humidified and brine saturated conditions at 10 mpa effective pressure with an ultrasonic pulse transmission technique 1 mhz the data set was compared with an extensive database of petrophysical measurements of a variety of rock types encountered in carbonate sedimentary sequences two major textural groups were distinguished on the basis of trends in plots of compressional wave velocity versus poisson s ratio a specific ratio of p wave over s wave velocity in granular rocks the framework of depositional grains is the main medium for acoustic wave propagation in crystalline rocks this medium is provided by a framework of interlocking crystals formed during diagenesis rock textures are connected to primary depositionalparameters and a diagenetic ov

structural evolution of inverted basins in the dutch offshore abstract the structural evolution of the dutch central north sea graben and the fault bounded broad fourteens basin is discussed graben formation started during the early triassic and culminated in strong differential subsidence during the late jurassic early cretaceous narrow fault bounded grabens and troughs and broad intervening highs were formed as a result of crustal distension and associated transtensional deformations the thickness of the late jurassic to early cretaceous fill of these basins may have exceeded 3000 m concurrent with the filling of these basins the bordering highs became deeply truncated during the late cretaceous and early tertiary compressive stresses resulted in inversion of these basins whereby movements along their bounding normal faults were reversed giving rise locally to overthrusting as for instance in the broad fourteens and west netherlands basins the timing of these compressional deformations has been palaeontologically dated and coincides with major orogenic events in the alps

the development and seismic expression of synsedimentary features within the chalk of southern england seismic reflection data acquired onshore to the north of bournemouth southern england image clearly a series of prominent concave up troughs or depressions and concave down mounded structures within the white chalk subgroup the chalk lithostratigraphy in the area of study is established from borehole geophysical log correlations these correlations then provide calibration of the seismic reflection data indicating that the structures are concentrated at levels between the lewes nodular chalk formation and tarrant chalk member and towards the base of the portsdown chalk formation onlap downlap and truncation of reflectors are observed with the most dramatic features forming a stacked series directly overlying faulting of jurassic strata similar stratal geometries have been described from comparable levels in the chalk of the north sea and in outcrop in britain and france to many they represent channels formed by submarine erosion and redeposition of the chalk during relative sea level falls linked to tectonics we also interpret a number of apparently incisive structures and slumped infill sequences described here as being of primary syndepositional origin the slumping and the close association of these features with underlying faults and proximity to nearby major crustal faults may be indicative of submarine erosion of the chalk caused by sea level changes linked to syndepositional fault movements however evidence of toplap downlap pairs is also suggestive of more aggradational mounding or laterally migrating surfaces or facies belts the presence of any such structures implies rapid lateral variations in the chalk that would have implications not only for aquifer management and future storage schemes but also during the processing of seismic reflection data and general studies and correlations of the chalk across southern britain

radiation patterns of a shear wave vibrator in near surface shale two shallow surface to borehole field tests were conducted to investigate the radiation patterns of a shear wave vibrator in near surface shale in the in line direction for which baseplate motion is transverse to the source geophone raypath the vibrator produces a broadband high amplitude signal of the sh type and virtually no signal of the sv or p types the amplitude of the sh radiation is approximately constant as a function of polar angle but it falls off as the cosine of the azimuthal angle measured with respect to the in line direction in the broadside direction the vibrator produces a strong uncontaminated signal of the sv type the radiation pattern of the sv signature is lobate in the polar plane and peaks at an incident angle of 30 to 35 degrees in the horizontal plane the sv radiation varies as the sine of the azimuthal angle measured with respect to the in line direction the field tests were conducted on a permian shale in oklahoma and an eocene shale in east texas comparison between sh and sv wave surfaces indicates that both shales behave approximately like transversely isotropic solids with a vertical axis of symmetry theoretical wave surfaces are fit to the observed data by using elastic moduli determined from the field measurements and by making the assumption that the near surface shale at each field site is a single homogeneous inherently transversely isotropic material the analyses indicate that horizontal sh group velocity is about 30 percent greater than horizontal sv group velocity in the permian shale and about 25 percent greater in the eocene shale

quantification of pore structure and its effect on sonic velocity and permeability in carbonates carbonate rocks commonly contain a variety of pore types that can vary in size over several orders of magnitude traditional pore type classifications describe these pore structures but are inadequate for correlations to the rock s physical properties we introduce a digital image analysis dia method that produces quantitative pore space parameters which can be linked to physical properties in carbonates in particular sonic velocity and permeability the dia parameters derived from thin sections capture two dimensional pore size domsize roundness aspect ratio ar and pore network complexity poa comparing these dia parameters to porosity permeability and p wave velocity shows that in addition to porosity the combined effect of microporosity the pore network complexity and pore size of the macropores is most influential for the acoustic behavior combining these parameters with porosity improves the coefficient of determination r2 velocity estimates from 0 542 to 0 840 the analysis shows that samples with large simple pores and a small amount of microporosity display higher acoustic velocity at a given porosity than samples with small complicated pores estimates of permeability from porosity alone are very ineffective r2 0 143 but can be improved when pore geometry information poa r2 0 415 and domsize r2 0 383 are incorporated furthermore results from the correlation of dia parameters to acoustic data reveal that 1 intergrain and or intercrystalline and separate vug porosity cannot always be separated using sonic logs 2 p wave velocity is not solely controlled by the percentage of spherical porosity and 3 quantitative pore geometry characteristics can be estimated from acoustic data and used to improve permeability estimates

fundamentals of seismic rock physics during the past 50 years or so tremendous progress has been made in studying physical properties of rocks and minerals in relation to seismic exploration and earthquake seismology during this period many theories have been developed and many experiments have been carried out some of these theories and experimental results have played important roles in advancing earth sciences and exploration technologies this tutorial paper attempts to summarize some of these results

the velocity deviation log a tool to predict pore type and permeability trends in carbonate drill holes from sonic and porosity or density logs the velocity deviation log which is calculated by combining the sonic log with the neutron porosity or density log provides a tool to obtain downhole information on the predominant pore type in carbonates the log can be used to trace the downhole distribution of diagenetic processes and to estimate trends in permeability laboratory measurements on over 300 discrete carbonate samples reveal that sonic velocity is a function not only of total porosity but also of the predominant pore type in general there is an inverse porosity velocity correlation but significant deviations occur from this relationship for certain pore types frame forming pore types such as moldic or intrafossil porosity result in significantly higher velocity values at equal total porosities than do pore types that are not embedded in a rigid rock frame such as interparticle porosity or microporosity the results of the laboratory measurements can be applied to expand interpretations of standard wireline log data as shown in this study on two drill holes through neogene carbonates from the great bahama bank the velocity deviation log is calculated by first converting porosity log data to a synthetic velocity log using a time average equation the difference between the real sonic log and the synthetic sonic log can then be plotted as a velocity deviation log because deviations are the result of the variability of velocity at a certain porosity the deviation log reflects the different rock physical signatures of the different pore types positive velocity deviations mark zones where velocity is higher than expected from the porosity values such as zones where frame forming pore types dominate zero deviations show intervals where the rock lacks a rigid frame such as in carbonates with high interparticle porosity or microporosity negative deviations mark zones in which sonic log velocities are unusually low caused for instance by a cavernous bore hole wall fracturing or possibly by a high content of free gas by tracing the velocity deviations continuously downhole one can identify diagenetic zones that are characterized by these different pore types in addition this method can be used to observe permeability trends because pore types influence the permeability of the rock