bluuebunny/crossref_metadata_2025 huggingface dataset:
Eolian Sandstone Reservoirs: Bedding Facies and Production Geology Modeling
Authors: Nurmi R. D.
Published: December 2007

The purpose of this discussion is to define the characteristics of eolian sandstones that are important for geometrical and. geological modeling. Although eolian sandstones are thick, widespread blankets of sandstone that are relatively free of shale, eolian sandstone reservoirs are far from being homogeneous and isotropic. Experience has shown that a sedimentological understanding of eolian facies is important for realistic reservoir analysis. Sedimentological knowledge can guide the study of reservoir geometry and/or performance characteristics of sandstone reservoirs of eolian origin.

The continuous measurement and evaluation of eolian bedding characteristics are critical to the evaluation of eolian reservoirs. By analyzing the bedding characteristics using continuously oriented cores and/or dipmeters, the internal and external characteristics of eolian reservoir units can be modeled. In simple cases where the reservoir unit is comprised of a single, thick crossbed set, the geometrical modeling of the depositional characteristics can be directly related to reservoir geometry. Geological modeling can also be done in complex cases where the reservoir units are comprised of vertical and lateral sequences of crossbed sets. Each of these crossbed sets is commonly underlain by an impermeable interdune deposit which results in a complex multi-layered reservoir; multi-layered because each of these crossbed sets may perform as an individual reservoir. Eventually each may even develop a separate gas cap. These crossbed reservoir units generally are elongated in the depositional transport direction; whereas, the pronounced directional permeability is perpendicular to this direction. Although the number of tests are limited, it appears that average crossbed thickness is related to areal extent of these reservoir units. In summary, the knowledge of bedding is a valuable tool for the analysis and modeling of eolian sandstone reservoirs.
Seismic Visibility of Stratigraphic Objectives
Authors: Neidell N. S. , Beard J. H.
Published: December 2007

In the recent past it was well recognized that certain stratigraphic exploration objectives could be most subtle in seismic terms. The classic work by Bubb and Hatlelid1 illustrates this view in discussions concerning certain reefal developments and the requirements for their detection. Hence, some appreciation of limitation in the seismic perspective was an important element in the interpretive view.

Most recent works explored in some depth the question of seismic resolution potential. One of the earliest of such studies by Widdess2 considered detection of thin beds, and an in-depth method described by Neidell3 demonstrates not only detection of thin beds at substantial depth, but also their detailed mapping. Later published works document thin bed mapping at significant depths using more or less conventional seismic data.

The fact that reliable contouring of 5 ft. (9.5m) units at 12,000 ft. (3,658m) depths can be accomplished leads to an unwarranted confidence about the ultimate detection capability of usual seismic approaches. It is easy to demonstrate that where stratigraphie developments entail some subtlety in their geometry, the conventional seismic display can fail totally in presenting them. Carbonate banks of the order or 300 ft. (91m) thick having good velocity contrasts can be missed at depths of 12,000 ft. (3,658m) and 600 ft. (182m) thick channels again having good reflectivity contrast can be lost entirely at depths of 15,000 ft. (4,573m).

Even when the seismic display is refined far beyond the usual state-of-the-art, the limitations persist. They are in good measure a consequence of both the narrow dynamic range of a black and white presentation and inadequate handling of seismic velocities. We argue here for refined use of seismic data and color or other innovative displays. A short catalogue of noteworthly failures of the conventional procedure supports our case. Two conclusions follow: Effective stratigraphie exploration cannot be conducted without improved processing practices and enhanced displays which overcome the limitations cited here.Presently available seismic views very likely have caused us as an industry to miss a substantial number of stratigraphie targets and even in mature areas.

Substantial avenues for technological progress and economic success appear to be ahead in view of these findings.
The Prediction of Interpretation of Downhole Mud Temperature While Drilling
Authors: Thompson M. , Burgess T. M.
Published: December 2007

The prediction of downhole mud temperature throughout all the operations of drilling has long been a clear objective, tackled by several previous authors. A method is given here for performing this prediction in an accurate yet rapid manner which differs from all previous methods used and is suitable for extension to the interpretation of measurements downhole.

The problem lies in the coupling of the heat conduction in the formation, which can involve a lengthy solution process, with the heat convection in the mud, the numerical solution of which can suffer from non-physical instabilities in response to some of the fast changing conditions of rig operation. A justifiable approximation to the formation conduction reduces it to analytical form and a space transformation yields a stable solution procedure for the convection problem. Details are given of the equations used, the approximation involved and the space transformation which result in a computer model which is simple and fast in execution. Despite the speed, the model is comprehensive in terms of the drilling, circulating and static operations modelled and the complete specification of evolving well geometry and constraints.

The prediction method is validated by checking against recent field data of temperature measured downhole during drilling.

The speed of the model makes it feasible to consider its use for realtime interpretation of measurements downhole and a promising application would be the continuous determination of geothermal gradient. Thus the model described includes both predictive and interpretative aspects.
A Simulator for Gas Kicks in Oil-Based Drilling Muds
Authors: Ekrann S. , Rommetveit R.
Published: December 2007

Mathematical techniques used in a newly developed simulator for gas kicks in oil based drilling fluids are presented.

The simulator works in one spatial dimension. By deleting the material derivative term in the momentum equation, a quasi-stationary approximation is obtained, which does not contain (hyperbolic) pressure propagation effects.

The equations are solved using a finite difference predictor-corrector shooting technique. Simple front tracking is employed for mud fronts and gas front.

The simulator is very modular in its structure. For several effects, a number of alternative formulations are programmed. Effects included in the simulator are frictional pressure losses (one- and two-phase), pressure loss in bit and choke, rise velocity of free gas, dissolution of gas in mud (including non-equilibrium effects), pressure and temperature dependent densities.

The simulator is equipped with interactive graphics, allowing the process to be observed and controlled (BOP, choke, pump rate, mud type pumped).
The Effect of Dissolved Gas on Reservoir Brine Viscosity
Authors: Ostermann R. D. , Bloori A. , Dehghani K.
Published: December 2007

Correlations are available in the literature for the prediction of reservoir brine viscosity as a function of temperature, pressure, and salinity. Despite the fact that natural gas is soluble in brines, little useful data has been published regarding the effect of dissolved gas on viscosity. In the current work, the effect of dissolved methane on the viscosity of pure water has been measured at 100, 150, and 250°F, over a saturation pressure range of 0-7500 psi. The viscosity was found to increase by up to 6% with gas saturation at moderate pressures. A correlation of this data is presented, along with a recommendation for the extension of the correlation to brine/natural gas systems. In addition, a simple modification to the standard electrical contact rolling ball viscoslmeter to allow its use with electrolyte solutions is described.
Mathematical Model of the Polycrystalline Diamond Bit Drilling Process and Its Practical Application
Authors: Ziaja M. B.
Published: December 2007

Assuming that rock failure during cutting with a polycrystalline diamond compact (PDC) cutter is in progress to the theory of the pulverside zone, a mathe-matical model of PDC bit drilling process has been developed. Using this theory, expressions for bit torque and bit weight are obtained in terms of bit penetration rate. The model takes into account the reduction in penetration rate during drilling resulting from bit wear. Some tests in the field conditions have shown that theoretical results agree reasonably well with available experimental data. A graphical method for estimating so-called indexes of rock properties also has been established.
Implications of Thermal Wear Phenomena for PDC Bit Design and Operation
Authors: Glowka D. A.
Published: December 2007

Previous work has suggested that thermal phenomena can greatly accelerate the wear of polycrystalline diamond compact (PDC) drag cutters under certain conditions. In this paper, the implications of that finding for PDC bit design and operation are examined. An abrasive wear model for cutters is developed and applied to rotary drilling applications to demonstrate the significance of thermally-accelerated wear on bit life. Under conditions where thermal effects are not important, it is concluded that in order to maximize bit life, greater bit weights and lower rotary speeds are preferable over shallow cuts and high speeds. It is found that even under normal abrasive wear conditions, a PDC cutter develops a significant wearflat before one-half its useful life is expended, suggesting that PDC bits should be designed to operate effectively in the worn condition. A cutter placement criterion is presented for designing bits for equal cutter wear. Through analysis of new experimental data, a technique is developed for approximating cutter penetrating forces in the presence of cutter interactions on a bit face and for estimating relative cutter wear. A hypothetical bit designed for equal rock removal volume per cutter is examined to determine the relationship between the equal volume and equal wear criteria for cutter placement. The complex role of thermal wear phenomena in this relationship is also examined for the hypothetical bit in three different rock types.
Case Study of a Low-Permeability Volatile Oil Field Using Individual-Well Advanced Decline Curve Analysis
Authors: Fetkovich M. J. , Vienot M. E. , Johnson R. D. , Bowman B. A.
Published: December 2007

This paper presents a detailed case history study of a low permeability volatile oil field located in Campbell County, Wyoming. The field was analyzed on an individual well basis using advanced decline curve analysis for 40 individual well completions. Well permeabilities, skins and original oil in place are calculated for each well from rate-time analysis using constant wellbore pressure type curve analysis techniques.

Original oil in place values calculated from rate-time analysis for individual wells are used with recoverable reserve projections from the decline analysis to obtain fractional recoveries for each well. Gas-oil ratios versus fractional recovery curves are also made for each well using historical cumulative production and the calculated oil in place values. Ultimate fractional recovery numbers and GOR vs fractional recovery curves, plotted for each well, are shown to suggest different rock types and reservoir fluids. Multi-well decline curve analysis shows the validity of the variables s (skin), k, 00IP, ultimate fractional recovery and G0R vs fractional recovery evaluated from each well's type curve evaluation. These variables must all give consistent and reasonable numbers when compared with each other. A single well analysis can easily give results that are not recognized as being invalid unless compared with other wells in the field.

The study also illustrates flowing and pumping well backpressure changes in a well's decline, the method of handling such changes, and their effect on ultimate recoverable reserves predictions. Conventional decline curve analysis can not handle backpressure changes because of its constraint that what controls the decline in the past will also continue in the future.
Unified Relationship To Predict Future IPR Curves for Solution Gas-Drive Reservoirs
Authors: Kelkar B. G. , Cox R.
Published: December 2007

Several methods have been proposed in the literature to predict future IPR curves for solution gas drive reservoirs. Apparently all of these methods require different types of data to predict these future curves. This paper presents a unifying relationship which can be applied to any of the referenced methods. The theoretical justification for the underlying uniformity is based on the assumption that the relation(kro/ µo Bo) varies linearly with the average reservoir pressure. The new technique requires two sets of data points (each at different average reservoir pressures) to predict future IPR curves.
A Simple Gravity Override Model of Steamdrive
Authors: Miller M. A. , Leung W. K.
Published: December 2007

A steamflood predictive model for horizontal reservoirs based on severe steam override is presented. Unlike previous models, the current model is based on Vogel's1 observation that oil production is not driven by the growth of the steam zone, but rather vice-versa. Oil production rate In the current model is determined by conductive heating of oil below the steam zone. An "effective" steam condensate zone size is used to match the model to field data. The model was tested with twenty-three field cases and against thermal simulator results reported in the literature. Acceptable results were obtained with eleven field cases and with simulator results.
Induced Fracture Orientation Determination in the Kuparuk Reservoir
Authors: Griffin K. W.
Published: December 2007

The orientation of hydraulic fractures is often a significant factor in the generation of an optimum fieldwide development plan. The ability to predict or determine fracture orientation allows evaluation of the impact of fracturing on drainage patterns and on waterflood performance, and planning of further development drilling. In the Kuparuk A Sand--a medium porosity, heavily mineralized, shaly sandstone--hydraulic fractures are required to achieve the necessary injection and production rates to sustain waterflood and peripheral development.

A program was developed to test the applicability of a variety of fracture orientation determination techniques, and also to provide information on the orientation of Kuparuk hydraulic fractures. Seven fracture orientation determination and prediction techniques were compared in a single wellbore: Calculation of wellbore ellipticity from four-arm dipmeter calipers; on-site measurement of core strain relaxation; laboratory measurement of differential strain on oriented core samples (DSA); laboratory measurement of sonic velocities through oriented core samples; analysis of triaxial borehole seismic data; evaluation of expandable packer impressions and evaluation of borehole acoustic televiewer results. Results from this, and other, single-wellbore tests were then compared with fieldwide DSA data, sonic velocity data, wellbore ellipticity data, and fault and structure mapping.

All of the techniques examined provided indications of fracture orientation. The downhole triaxial seismometer surveys proved to be both definitive and economical as a method of determining fracture orientation. The methods which require rock property measurements to infer stress orientation (on-site strain relaxation, differential strain, and sonic velocity), require careful orientation of the core samples, a homogeneous sand with low shale content, and multiple samplings to ensure a correct interpretation of the results. Wellbore ellipticity measurements provide fair to good approximations of stress field orientation. The quality of the data increases with an increasing degree of borehole spalling or eccentricity. The openhole techniques, while very useful for verification and diagnostic purposes, are too expensive for general use as fracture orientation determination tools.
Compressibility Factors for High-Molecular-Weight Reservoir Gases
Authors: Sutton R. P.
Published: December 2007

This paper examines the effect of high concentrations of the heptanes-plus fraction in natural gases on the calculation of gas compressibility (Z) factors. Laboratory measured gas compositions and Z factors are used to evaluate the accuracy of the Standing-Katz chart. It was determined that the chart itself provides satisfactory accuracy; however, Kay's molar average combination rules or comparable gravity relationships for calculating pseudo-critical pressure and temperature result in unsatisfactory Z factors for high molecular weight reservoir gases. The contributions of this paper are two-fold. First, new pseudo-critical property – gas gravity relationships are developed, and second, alternate methods for calculating pseudo-critical properties from composition are established. By utilizing either of these methods to calculate pseudo-critical pressure and temperature, the overall accuracy of Z factors from the Standing-Katz chart is increased almost three-fold.
A Simple Statistical Method for Calculating the Effective Vertical Permeability of a Reservoir Containing Discontinuous Shales
Authors: Begg S. H. , Chang D. M. , Haldorsen H. H.
Published: December 2007

This paper describes a quick, simple, easy to use method of calculating the effective vertical permeability of a reservoir region containing discontinuous shales. The method, which is derived in both two and three dimensions, can be applied to a layered medium in which the sand permeability anisotropies (in three mutually perpendicular directions) and the shale frequencies and dimensions can vary from layer to layer. The method is validated for specific cases by using numerical simulation and an analogue model of a real outcrop. The latter consists of conducting paper with slits cut in it to represent impermeable shales. Although strictly the method is only applicable to impermeable shales we show that it would appear to be generally valid when the real shale permeability is more than about two orders of magnitude lower than the effective permeability derived by assuming impermeable shales.
Using Sidewall Sample Thin Sections To Evaluate the Completion Potential of Low-Resistivity Pleistocene Sands, Offshore Louisiana
Authors: Morphy P. H. , Thomson A.
Published: December 2007

The most common reason that low-resistivity completions in South Marsh Island 130 fail to pay out is a lack of reservoir permeability. The non-commercial low-resistivity zones have a clay matrix which has only microporosity, probably due to the reworking of the sediment by burrowing organisms (bioturbation). In contrast, the commercial low-resistivity zones have visible porosity with almost no clay. This distinction can be determined by evaluating sidewall samples with the pétrographie and scanning electron microscopes. The method is applicable whether or not the low-resnstivity pay is geopressured.
Measurement of Remaining Oil Saturation in Northern Michigan Using Nuclear Magnetism Log Data and Pressure Core
Authors: Setser G. , Williams M. R.
Published: December 2007

Remaining oil saturation measurements were made in a pinnacle reef field of Northern Michigan. Pressure core was taken in the Al Carbonate and Niagaran formations. A Nuclear Magnetism Inject-Log procedure was used as an independent measure of remaining oil saturation. Using procedures outlined in this paper, the core-measured and log-derived remaining oil saturations agree, well within their error limits.
Wireline Coring Device Aids Evaluations of Complex Geologic Areas
Authors: Hashmy K. H. , Robinson K. A. , Rojas J. M. , Skopec R. A.
Published: December 2007

A new wireline coring device which uses a diamond core bit to drill sidewall plugs is described. Sidewall cores thus obtained are not subject to mechanical damage, and even hard, indurated rocks are easily cored. A wellsite core analysis system has also been introduced which provides mineralogical information in addition to porosity and permeability, etc. Accurate reservoir characterization is possible by using core data and geological information with well log data in a computer program based on an error optimization technique. Results of log analysis are presented where core information has been extensively used.
Experimental and Simulation Studies of CO2 Flood Performance at High Water Saturation
Authors: Inoue S. , Yazawa N. , Arihara N.
Published: December 2007

The objective of this study is to evaluate the effects of a high water saturation in the vicinity of the CO2 miscible displacement front on the oil displacement efficiencies of CO2 slug and water-alternating-gas (WAG) injection processes. The results of CO2-flood core displacement tests under high water saturations and compositional simulation studies are presented.

Core displacement tests were conducted with a water-wet Berea sandstone core to evaluate differences among continuous CO2 injection in the secondary recovery mode and CO2 slug and WAG injection in the tertiary mode. The results of core-flood tests were strongly characterized by fingering of CO2 into oil and waterblocking of oil from contact with invading CO2. The slug injection process appeared to be superior to the WAG injection process.

One-dimensional simulation studies were carried out to reproduce the experimental results with an equation-of-state (EOS) based compositional model. EOS parameters were first tuned by matching laboratory phase behavior data and slim tube results. The use of Koval K-factor and Todd's waterblocking function, to express the fingering and waterblocking phenomena respectively, successfully duplicated the results of the core displacement tests.

Finally, based on experimental data matching, two-dimensional, cross sectional simulation studies were conducted to predict oil displacement performance in a waterflooded, vertically heterogeneous reservoir. Although the WAG process mitigates the undesirable effect of crossflow, oil recovery of the WAG process remains lower than that of the CO2 slug process in the strongly water-wet reservoir.
Visual Investigation of Multiphase Flow and Phase Interactions Within Porous Media
Authors: Peden J. M. , Husain M. I.
Published: December 2007

The dynamics of multiphase flow in porous media are extremely complex when compounded with the thermodynamic behaviour of multicomponent reservoir fluids and the potential phase interactions. Continual changes in the phase compositions will result in variations in the physical properties and flow characteristics of the phases.

A further complication is that these fluid flow mechanisms, occuring at the microscopic level, have to be extrapolated to the macroscale for application to field studies.

To grasp the essential phenomena involved in such flow situations, an experimental system has been developed that enables displacements to be carried out at simulated reservoir pressures and temperatures of up to 41. 4 MPa (6000 psi) and 150°C. This system incorporates a specially designed high pressure visual micromodel cell in parallel with, optionally, either a slim tube or a long core holder. Such an approach aims at complementing the viusal information obtained at the micro level with quantitative data from the larger scale flow studies.

Visual models have been constructed of realistic scale, geometry and topology which operate at high pressures and temperatures. This paper reviews the characteristics of previously used models and describes the developments in the microprocessing technique and the approach to the application of micromodels which were developed in the present study.

The paper also reports on the application of a range of homogeneous and heterogeneous models to investigate the potential deposition of heavy hydrocarbon fractions within the pore space of reservoirs subjected to gas injection processes. The heterogeneous models were produced from real rock micrographs. The interaction between CO2, N2, hydrocarbon gases and a specific North Sea crudes have been studied. Observations obtained from video recordings, along with measurements made during these experiments, are presented.

In conclusion, the processes associated with the observed phase interactions and the role of micromodel experiments to such studies are discussed.
Pressure Transient Behavior of the Composite Reservoir
Authors: Brown L. P.
Published: December 2007

The composite reservoir, representing a variety of important reservoir configurations, has been studied using a semi-analytical method to determine the characteristics of its pressure transient response. This study extends the work of a previous semi-analytical study1 whose primary concentration was on the pressure transient response in the "altered zone", the zone nearest the wellbore. Important conclusions regarding the nature and duration of the transition period between the altered and unaltered zones are given. This study also presents information which corrects conclusions given in a previous study2 done with a numerical simulator. Specifically, this study shows that the slope of the semilog straight line representing the unaltered zone is independent of the storage ratio.

The study presents equations for calculating mobility in the altered and unaltered zones, for calculating the radius of the altered zone using traditional graphical analysis of well test data and for calculating the skin factor.
Formation Damage Index Number: A Model for the Evaluation of Fluid Sensitivity in Shaly Sandstones
Authors: Basan P. B.
Published: December 2007

Formation Damage Index (FDI) is a number determined by petrographic techniques to classify the potential for formation damage in shaly sandstones. The numbers, which indicate increasing tendency toward damage, represent a formation condition model that is based on ten (10) generic reservoir lithologies. They are: 1) sandstones with less than 5% clay and where clay is part of the matrix; 2) sandstones where more than 10% clay is from structural or laminated shale; 3) sandstones with less than 10% clay and where clay is authlgenic pore-fill; 4) sandstones with varying amounts of clay and where organic content is high; 5) sandstones with varying amounts of clay (10-15±%) and where clay is dispersed matrix but not the primary cement; 6) sandstones with less than 10% clay and where clay is authigenic grain attachments; 7) sandstones with more than 10% clay and clay is homogenized by bioturbation; 8) sandstones with less than 10% or more clay and where clay is authlgenic grain coating; 9) sandstones with 10% or more clay and where clay is the primary binder; and 10) sandstones with less than 10% clay that are semi-or unconsolidated.

Rock-related damage, as opposed to other types of wellbore damage, is best understood where the potential triggering mechanism can be identified. Although there are a few minor mechanisms that contribute to damage, the important ones are: 1) dispersion/migration; 2) particle migration; 3) mineral precipitation; 4) lattice expansion; and or unconsolidation. Each number in the FDI model has an increasing potential to one or more of these mechanisms. Overall, the most fluid sensitive rocks are those that have a small .pa amount of clay (less than 10%) that occurs in a form that produces a high surface area to pore volume. Where clay is responsible for formation integrity, there is a high potential for formation unconsolidation.
Flash X-Ray Analysis of the Interaction of Perforators With Different Target Materials
Authors: Aseltine C. L.
Published: December 2007

Recent investigations have shown that target size and boundaries have a significant effect on the overall penetrating ability of perforators. This paper presents results of X-ray studies that were conducted in an effort to understand the physical mechanisms that caused the observed changes in penetration depth. These preliminary studies are necessary in order to develop a model for downhole penetration.

This paper deals with the interactions that occur within large- and small-diameter targets, with different target boundaries, and with different target materials such as concrete, Berea, and limestone. The difference in performance for perforators shot into cores with kerosene rather than air in the pores is correlated with disturbances within the jet passing through the previously penetrated portions of the core. The X-rays show the origin of the interactions within the core and the resulting effect on the remaining portion of the jet.
A Study of How Heavy-Weight Drillpipe Affects Jarring Operations
Authors: Lerma M. K.
Published: December 2007

In order to optimize jar placement in a drilling string, the force transmitted to the stuck point when the jars are tripped must be determined. Skeem's1 average force method determines this and can be used to evaluate the effect of using heavy weight drill pipe above the jars instead of drill collars. This paper applies Skeem's method to compare two cases for jar effectiveness: (See Figure 1) Drill Collars (DC) are used above the jarsHeavy Weight Drill Pipe (HWDP) is used above the jars
Flame-Jet Induced Thermal Spallation as a Method of Rapid Drilling and Cavity Formation
Authors: Rauenzahn R. M. , Tester J. W.
Published: December 2007

The recent, favorable results of field testing of spallation drilling have directed new research into the rock mechanics and jet dynamics associated with rock spallation under high heat fluxes. Wei-bull's statistical theory of rock failure has been applied to define the mechanics of spallation of brittle materials. A reasonable spallation temperature of 500°C at the rock surface can be computed using typical physical property values for granite, neglecting any temperature dependence of the Weibull parameters because of additional microcracking upon heating. A numerical simulation of the jet dynamics and rock cutting has been formulated to model the spallation drilling process. Conservation equations for the heat, mass, and momentum of the gas jet with appropriate models of turbulent transport phenomena are used to estimate rock spallation rate and steady-state hole geometries as a function of heat flux and position of the drill. The predicted trends in drilling performance with changes in flow input are reasonable in comparison with field data but require future verification. Experiments with well-characterized granites are proposed to test both the Weibull fracturing theory and the dynamic simulation results. Specific tests involve the use of high-speed videotaping to measure spallation times under defined heat flux conditions with laser and gas-jet heating. Quarry-face drilling will also be attempted with a scaled-down jet penetrator. Results of all experiments will be presented at the conference.
Further Development and Application of Simulated Distillation for Enhanced Oil Recovery
Authors: MacAllister D. J. , DeRuiter R. A.
Published: December 2007

Simulated distillation by gas chromatography is useful for determining compositional changes in crude oils undergoing enhanced oil recovery. Area counts generated by simulated distillation are shown to correspond to weight rather than volume fractions by comparing simulated distillation results to true boiling point results for three oils. Recent applications of simulated distillation are discussed including light end enrichment of crude oil in a CO2 pilot, determination of visicracking in thermal laboratory studies, and contamination of heavy oils. The use of an internal standard to calculate the noneluted, heavy fraction of the oil has proven useful and reasonably accurate for a wide variety of applications.
The Use of Microorganisms To Increase the Recovery of Oil From Cores
Authors: Raiders R. A. , Freeman D. C. , Jenneman G. E. , Knapp R. M. , McInerney M. J. , Menzie D. E.
Published: December 2007

A method for oil recovery enhancement by stimulating the growth of indigenous microbial populations in sandstones by nutrient injection was investigated. Incremental oil recovery from the cores ranged from 10–38% of the original oil in place. Volumetric and microscopic sweep efficiency was improved by the microbial selective plugging process. Biogenic gas production accompanied the oil produced from the cores. The combination of stratification correction, gas production, and pressure increase assisted in recovery of previously trapped oil.
Murchison: A Review of Reservoir Performance During the First Five Years
Authors: Massie I. , Beardall T. J. , Hemmens P. D. , Fox M. J.
Published: December 2007

The first five years of the Murchison Field Reservoir Development have been a success. The field has produced 50% of its recoverable reserves and despite the sands having marked permeability contrasts, the water cut is just 26%, considerably lower than similar water floods nearby. Results of three delineation wells in 1976 led to a development plan of initally perforating wells in the lowest productivity sands. At the start of development drilling the need for an extensive data acquisition programme was recognised and planned with full management and partner support.
Powell Pressure Maintenance Unit Enhanced Recovery Project That Is Providing Liquid Sales in a Limited Gas Market Environment
Authors: Heath L. B. , Bross R. E. , Givens W. A. , Morrow R. J.
Published: December 2007

A retrograde condensate Frontier reservoir in Wyoming's Powder River Basin is proving amenable to pressure maintenance through injection of dry hydrocarbon gas. The Powell Pressure Maintenance Unit, operated by Woods Petroleum Corporation, is successfully producing substantial condensate and natural gas liquids without the threat of curtailment due to gas market limitations, while providing approximately a three-fold increase in recoverable liquid hydrocarbon reserves through pressure maintenance. Difficulties encountered in unitizing this field during its development were overcome by establishing equitable expansion provisions in the unit agreements. This was made possible by the cooperation of the owners with the state and federal regulatory bodies. Centralized facilities were designed and constructed prior to unitization to maximize liquid recoveries and reduce operating costs.
Evaluation of Naturally Fractured Gas Reservoirs Through Pressure Transient Testing
Authors: Samaniego-V. F. , Cinco-Ley H. , Montiel-H. D.
Published: December 2007

Field cases are presented of naturally fractured gas reservoirs where the main storage capacity is in the fractures, since the matrix permeability is negligible for practical purposes. Wells in these reservoirs initially exhibit high productivity. These fields are located in the north of Mexico. Upon completion of the exploratory wells a set of multiple rate tests were carried out in open hole conditions. All information available indicates that the reservoirs are located in strati graphic traps in uniformly fractured packstone formations of Cretaceous age. Peculiar to these cases is the fact that pseudosteady-state flow conditions are reached in a very short time (about 2 to 4 hours). Both formation flow conductivity kh and pore volume were estimated for each case. Results indicate that fracture pore volume were exceedingly small for the reservoirs to be developed. Estimation of pore volume from pseudosteady-state pressure data shows a good agreement with those obtained from material balance calculation as applied to reservoir performance.
Gulf Coast Geopressured Gas Reservoirs: Drive Mechanism and Performance Prediction
Authors: Bernard W. J.
Published: December 2007

A new, simple method is presented for estimating reserves and predicting the performance of abnormally-pressured (geopressured) natural gas reservoirs. The method is applicable for reservoirs undergoing either depletion drive or very limited water drive. Reasons for the differences in performance between normally-pressured and abnormally-pressured gas reservoirs are discussed.
Reserve Determination Using Pseudosteady-State Techniques in a High-Pressure Sour Gas Field: A Case History
Authors: Lewis R. C.
Published: December 2007

The application of pseudo-steady-state techniques to assist in reserve determination is presented for three high pressure sour gas reservoirs. The techniques discussed in this paper utilize stabilized flowing wellhead pressures, gas production rates, and pressure adjusted gas well performance coefficients to calculate a representative average pressure for the reservoir. Original gas-in-place and recoverable reserves are determined using the calculated average pressures and gas material balance equation.

As of publication date, various bottom-hole pressure measurements, cumulative gas recovery, and current gas well deliverabilities have supported reserve estimates based on the procedure. These techniques have been successfully applied to other reservoirs in the south Texas area to enhance gas reserve estimates in the absence of shut-in, bottom-hole pressure data.
The Effects of Permeability Variations on Flow in Porous Media
Authors: Giordano R. M. , Salter S. J. , Mohanty K. K.
Published: December 2007

By using a compositional simulator together with experiments, we analyze the physical processes that control the initiation and propagation of fingered fronts in porous media which contain permeability variations. Miscible displacements at both favorable and unfavorable mobility ratios are studied and the effects of the standard deviation and spatial variability of the permeability on these displacements are discussed. A developed-miscible process is also studied and the interplay of capillary pressure with permeability variations is presented.

To represent the spatial and frequency distribution of the permeability in the simulator, we have taken 1600 (40 × 40) surface permeability measurements on each of two 2 ft by 2 ft slabs of Berea rock and entered these numbers directly into the simulator. Displacement experiments at various mobility ratios were then conducted in this rock and the results compared to the simulations.

Although only laboratory-scale systems are studied, the concepts and insights which we present can help interpret larger-scale systems. The results can be used not only to judge the degree of detail needed to simulate permeability variations for a given process, but also to gauge the robustness of a process to permeability variations.
Steam Diversion by Surfactants
Authors: Gall J. W.
Published: December 2007

A large problem associated with steamflooding is the overriding or bypassing of the oil by the highly mobile steam. Surfactants have often been injected along with the steam in attempts to create a foam that would inhibit the flow of steam in these depleted zones or channels. Laboratory studies have shown that the magnitude of resistance to the flow of steam through a porous medium containing foam was directly related to the permeability. Because of these higher resistance factors in higher permeability zones, the relative amount of fluid flowing through zones of differing initial permeability can actually be reversed. Results with several surfactants will be discussed.

Experimental techniques developed to permit determination of the amount of steam diverted from one zone to another enabled the examination of variables related to foam diversion processes such as surfactant type, surfactant concentration, slug size and most importantly, permeability. A description of these experimental techniques and the data analysis will be discussed.
Some Experiences With a Critical Reservoir Fluid
Authors: Huang W. W.
Published: December 2007

Fluid properties and composition in a naturally occurring near critical reservoir show significant variations between samples. Highly undersaturated volatile oil and rich condensate gas coexist in the same reservoir without a gas-oil contact. Producing gas-oil ratios (GOR) at undersaturated reservoir conditions have been observed to vary up to more than two fold among wells. An equation of state (EOS) reservoir simulator was used to predict performance of nitrogen injection into this reservoir where fluid variation is the rule, not the exception. Phase behavior of the fluid samples predicted by the EOS is sensitive to their plus fraction characterizations. Estimated characterization parameters such as Watson's factor and Whitson's1 molar distribution parameter a differ among the reservoir samples. Values of these characterization parameters decline generally with producing GOR of the sampled well, indicating richer fluids tend to be more paraffinic and higher in heavier components. Variations in heptanes plus (C7+) properties correlate better with producing GOR than with depth. Saturation pressure does not exhibit clear correlations with GOR or depth. It is difficult to explain by the gravity-thermodynamic equilibrium theory of Schulte2 and Hirschberg3. To account for observed GOR variation in the field, reservoir fluids are thought to vary areally rather than vertically in the oil/gas column.

An EOS tuned for one sample usually gives unsatisfactory predictions of phase behavior of other samples. Describing these property variations and the effect of injected nitrogen with an EOS becomes a challenging task. This study uses calculated Watson characterization factor in regression to improve the match of extensive PVT cell data and to treat changing fluid characterization. This procedure was found to improve the PVT match significantly when the common regression practices yield unsatisfactory results and extended analyses of the plus fraction are unavailable.

This paper addresses compositional grading occurred in the near-critical reservoir and a method to account for it in an EOS reservoir model. Interfacial tension effects associated with the critical fluid are also discussed briefly.
Imaging of Wetting and Nonwetting Phase Distributions: Application to Centrifuge Capillary Pressure Measurements
Authors: Wunderlich R. W.
Published: December 2007

An epoxy casting technique has been developed which permits the imaging of wetting and nonwetting phase distributions in porous media. First, a rock sample is saturated with a colored epoxy. Air is forced in at a particular pressure, and after equilibrium has been reached, the epoxy is solidified. The sample is then evacuated and saturated with a different colored epoxy, which is also solidified. Finally, thin sections of the sample are prepared to image the phase distributions.

This method has been applied to study contrasting models for centrifuge capillary pressure measurements. These measurements are usually interpreted in terms of the work of G. L. Hassler and E. Brunner.1 One of their assumptions was that a region of 100% wetting phase saturation always is present at the face of the sample furthest from the axis of rotation. The epoxy casting technique has been used to demonstrate that this assumption fails beyond a critical capillary pressure.

The technique is also being used to identify petrographic controls on the distribution of the wetting and nonwetting phases. For example, the influence of clays on the distribution of the wetting phase between intergranular and intragranular porosity can readily be distinguished.

Areas in which this and similar techniques could prove valuable include studying the pore-level structure of the residual nonwetting phase, and the electrical conductivity of porous media as a function of saturation. Techniques are currently being developed to aid in such studies.
Research on Simultaneous Production Logging Instruments in Multiphase Flow Loop
Authors: Davarzani J. , Sloan M. L. , Roesner R. E.
Published: December 2007

The capability to accurately record log data in multiphase flow was greatly enhanced with the introduction of well logging instruments designed for simultaneous data acquisition. Presented is an overall evaluation of the simultaneous production logging instruments and dynamic flow test results. Investigations of water holdup and water cut and the effects on the response of the downhole logging instruments are presented. Also, the multiphase slip velocities at various fluid compositions, flow rates, and deviation angles are presented in relation to the simultaneous flowmeter measurement data. Derived are recommended logging procedures that will improve log quality in multiphase flow.
Fracture Conductivity Damage Due to Crosslinked Gel Residue and Closure Stress on Propped 20/40 Mesh Sand
Authors: Kim C. M. , Losacano J. A.
Published: December 2007

The commonly used cross-linked fracturing fluids, called gels, were broken in a 20/40 mesh sandpack. The san dpa ck simulated a 2.0 lbm/ft2 propped fracture and was used to test the effects of gel residue and closure stress on fracture con ductivity.

The gel residues that were evaluated in this test were derived from the gels made with hydroxypropyl guar (HPG), guar, and carboxymethyl hydroxyethyl cellulose (CWEC) polymers. The relative gel residue volumes for these polymers were determined. Reduction in sand permeability due to these residue volumes was compared between polymers at given closure stress levels. A linear-flow proppant conductivity test cell was used to measure the permeability of the sand under closure stresses up to 10000 psi. For the HPG polymer, both cross-linked and linear fluids were evaluated.

Among the three polymers evaluated, the CMHEC gel cross-linked with trivalent aluminum caused the least reduction in sand permeability. The borate cross-linked guar gel resulted in the greatest reduction. However, the difference in permeability reduction caused by the borate cross-linked guar and titanate cross-linked HPG gels was small. Test results for the HPG polymer indicated that the reduction in permeability both due to the cross-linked and linear fluids was nearly the same. Sand permeability was continuously reduced with increasing closure stress. However, the permeability reduction above 4500 psi closure stress was inconsistent. An increase of polymer concentration further reduced sand permeability, but the amount of reduction was not directly proportional to the increase of polymer concentration.