Showing papers in "Spe Formation Evaluation in 1990"
TL;DR: In this article, the authors present a formulation for a fractal fracture network embedded into a Euclidean matrix, which is described by an appropriate modification of the diffusivity equation.
Abstract: The authors present a formulation for a fractal fracture network embedded into a Euclidean matrix. Single-phase flow in the fractal object is described by an appropriate modification of the diffusivity equation. The system's pressure-transient response is then analyzed in the absence of matrix participation and when both the fracture network and the matrix participate. The results obtained extend previous pressure-transient and well-testing methods to reservoirs of arbitrary (fractal) dimensions and provide a unified description for both single- and dual-porosity systems. Results may be used to identify and model naturally fractured reservoirs with multiple scales and fractal properties.
293Â citations
TL;DR: In this article, flow tests were performed by continuously circulating CO{sub 2}-saturated brines through Cardium formation cores and all the cores initially showed a large drop in permeability, after which permeability rose steadily but did not regain its initial value.
Abstract: When CO{sub 2} is injected into petroleum reservoirs it forms carbonic acid in the brine phase and interacts with reservoir rock. Flow tests were performed by continuously circulating CO{sub 2}-saturated brines through Cardium formation cores. All the cores initially showed a large drop in permeability. after which permeability rose steadily but did not regain its initial value. Microscopic examination of the cores indicates that fines had been released and had migrated toward pore throats, reducing permeability, In addition, mineral alterations occurred, including the dissolution of calcite and siderite, which may account for the gradual rise in permeabilities noted in the experiments.
108Â citations
TL;DR: In this article, a fractal model is used to model the spatial correlation structure of reservoir-property variations and their spatial correlations, which can be used to address the two major issues in characterizing reservoirs for performance modeling.
Abstract: The displacement efficiency of fluids injected into heterogeneous formations depends on the nature of reservoir-property variations and their spatial correlations. Conditional simulation is a geostatical technique for creating property distributions, with any desired resolution, that have a prescribed spatial correlation structure and that match measured data at their sampling locations. Conditional simulations of reservoir heterogeneities can be used to address the two major issues in characterizing reservoirs for performance modeling: scaling of flow process and properties and dealing with the uncertainty resulting from missing information in reservoir description. The correlation structure emphasized here is a fractal model.
99Â citations
TL;DR: In this paper, a study of the average process of the diffusion equation for the pressure response of a well situated in an infinite reservoir where permeability is an arbitrary function of position was solved for the case of small variations from a mean value.
Abstract: Permeability estimates from the pressure derivative or the slope of the semilog plot usually are considered to be averages of some large ill-defined reservoir volume. This paper presents results of a study of the averaging process, including identification of the region of the reservoir that influences permeability estimates, and a specification of the relative contribution of the permeability of various regions to the estimate of average permeability. The diffusion equation for the pressure response of a well situated in an infinite reservoir where permeability is an arbitrary function of position was solved for the case of small variations from a mean value. Permeability estimates from the slope of the plot of pressure vs. the logarithm of drawdown time are shown to be weighted averages of the permeabilities within an inner and outer radius of investigation.
99Â citations
TL;DR: In this paper, four flow periods may occur during the transient behavior of a horizontal well and drawdown and buildup equations describing the flow behavior of each of the four flow period are given.
Abstract: Four flow periods may occur during the transient behavior of a horizontal well. Drawdown and buildup equations describing the flow behavior of each of the four flow periods are given. Methods for analyzing data obtained from testing the well to determine permeability anisotropy in its drainage volume and the skin factor are presented. Calculation procedures are illustrated by examples.
78Â citations
TL;DR: Stress-dependent permeability was measured in a high-porosity/high-permeability sandstone with mechanical and fluid-flow parameters similar to those found in typical North Sea reservoirs, particularly the little-investigated effect of triaxial stress configurations as mentioned in this paper.
Abstract: Stress-dependent permeability was measured in a high-porosity/high-permeability sandstone with mechanical and fluid-flow parameters similar to those found in typical North Sea reservoirs, particularly the little-investigated effect of triaxial stress configurations. Hydrostatic loading from atmospheric conditions to stress levels comparable to those found in situ causes a slight permeability reduction. When the applied stress is nonhydrostatic, the permeability decrease is more pronounced. In particular, as failure is approached in triaxial loading or unloading, the permeability may be significantly reduced (in some cases to {lt}10% of its initial value). This paper discusses the consequences of these results for interpretation of standard permeability measurements. An example quantifies the formation damage (skin) induced by the near-wellbore stress field.
78Â citations
TL;DR: In this article, changes in the pore geometry and petrology as conventional sandstones become tight are examined within a single east Texas sandstone formation, where diagenetic alteration changes a wide variety of fluvial, deltaic, and marine sands into similar low-permeability rocks with nearly identical pore structures.
Abstract: Petrographic and petrophysical analyses have revealed that tight sandstone possesses distinct petrological properties that differentiate it from conventional sands. Diagenetic alteration changes a wide variety of fluvial, deltaic, and marine sands into similar low-permeability rocks with nearly identical pore structures. In this paper, changes in the pore geometry and petrology as conventional sandstones become tight are examined within a single east Texas sandstone formation.
56Â citations
TL;DR: In this article, generalized procedures to interpret pressure injection and falloff data following cold-water injection into a hot-oil reservoir are presented. Butler et al. showed that saturation and temperature gradients have significant effects on the pressure data for both the injection and the falloff periods.
Abstract: This paper presents generalized procedures to interpret pressure injection and falloff data following cold-water injection into a hot-oil reservoir. The relative permeability characteristics of the porous medium are accounted for, as is the temperature dependence of the fluid mobilities. It is shown that the saturation and temperature gradients have significant effects on the pressure data for both the injection and falloff periods. The matching of field data to type curves generated from analytical solutions provides estimates of the temperature-dependent mobilities of the flooded and uninvaded regions. The solutions also may be used to provide estimates of the size of the invaded region, the distance to the temperature discontinuity, heat capacities, and wellbore-storage and skin effects.
53Â citations
TL;DR: In this paper, the authors measured in-situ stresses directly and used these values to calibrate acoustic log measurements to develop stress profiles across the Devonian shales across the Appalachian basin.
Abstract: The in-situ stress contrast between a reservoir rock and the surrounding formations is important to the design and analysis of hydraulic fracture treatments. The stress contrast between layers controls the fracture's vertical (height) growth, which in turn affects the fracture length and width. As part of the Gas Research Inst.'s (GRI'S) Comprehensive Study Well (CSW) program in the Devonian shales of the Appalachian basin, the authors measured in-situ stresses directly and used these values to calibrate acoustic log measurements to develop stress profiles across the Devonian shales. This paper discusses the measurement and interpretation of in-situ stresses, the use of acoustic logs to determine mechanical properties and a more complete stress profile, and the practical use of the stress profile in fracture-treatment design and analysis.
52Â citations
49Â citations
TL;DR: In this paper, a study of the rate/time and pressure/cumulative production depletion performance of a two-layered gas reservoir producing without cross-flow was performed and the results demonstrated the effects of change in reservoir layer volumes, permeability, and skin on the depletion performance.
Abstract: presentation of a study of the rate/time and pressure/cumulative-production depletion performance of a two-layered gas reservoir producing without crossflow. The field data demonstrate that Arps depletion-decline exponents between 0.5 and 1 can be obtained with a no-crossflow, layered reservoir description. Rate-vs.-time and pressure-vs.-cumulative-production predictions were developed from both 2D numerical and simplified tank model of a two-layered, no crossflow system. These results demonstrate the effects of change in reservoir layer volumes, permeability, and skin on the depletion performance.
TL;DR: In this article, an analytical method was proposed to calculate effective block permeabilities as a full tensor based on the geometry, block size, full local tensorial permeabilities, and the geology within the block.
Abstract: The authors propose an analytical method to calculate effective block permeabilities as a full tensor based on the geometry, block size, full local tensorial permeabilities, and the geology within the block. The method was validated with a finite-element numerical simulator and was applied to a simulation of flow through an outcrop of the eolian Page sandstone. Results show that the relative positions of the main geologic features and the ratio between the grain-flow and wind-ripple permeabilities are more important than bounding surfaces and dispersion in determining flow behavior.
TL;DR: The Compensated Dual Resistivity (CDR) tool as discussed by the authors provides two resistivity measurements with several novel features that are verified with theoritical modeling, test-tank experiments, and log examples.
Abstract: Presentation of the Compensated Dual Resistivity (CDR) tool, electromagnetic propagation tool for measurement while drilling. The CDR provides two resistivity measurements with several novel features that are verified with theoritical modeling, test-tank experiments, and log examples.
TL;DR: In this paper, a formulation of pressure transients in terms of the intrinsic, or core, properties of the two media that compose the fractured reservoir, establishes the influence of these properties, and reciprocally, their corroboration from - the pressure-time relationship observed in well tests and interference tests.
Abstract: A formulation of pressure transients in terms of the intrinsic, or core, properties of the two media that compose the fractured reservoir, establishes the influence of these properties, and reciprocally, their corroboration from - the pressure-time relationship observed in well tests and interference tests. The following reservoir characteristics are analyzed: the area of fractures transverse to flow; the dimensions, shape and properties of rectangular parallelepiped matrix-rock blocks; and a permeability reduction in the blocks surface. A restatement of the so-called pseudo-steady state inter-media flow gives to parameters alfa and lambda in the theory of a previous study the physical meaning they lacked, and allows a direct determination of the blocks minimum dimension.
TL;DR: In this article, a single-phase 1D mathematical model is used to study unsteady-state micropore sorption in composite micropores/fracture coalbed-methane-transport problem.
Abstract: A single-phase 1D mathematical model, is used to study unsteady-state micropore sorption in the composite micropore/fracture coalbed-methane-transport problem. The mathematical model is solved numerically by writing the transport equations in finite-difference form and linearizing the residual form of the difference equations with the generalized Newton-Raphson procedure. The numerical model is used to compare methane production rates predicted by unsteady- and quasisteady-state sorption formulations. Results indicate that the two models give different rates during early degasification periods. The high rates predicted by the unsteady-state model, however, generally approached lower quasisteady-state rates within the first few months of simulation. The numerical model is also used to examine the time-dependent response of concentration gradients in the micropores to changes in fracture pressure, to compare diffusion rates predicted by spherical and cylindrical micropore elements, and to construct dimensionless type-curve solutions to the coalbed-methane flow problem.
TL;DR: In this article, a critical study of 3D stochastic simulation of a fluvial reservoir and of the transfer of the geological model to a reservoir simulation grid is presented, which is conditioned by sand-body thickness and position in wellbores.
Abstract: This paper presents a critical study of 3D stochastic simulation of a fluvial reservoir and of the transfer of the geological model to a reservoir simulation grid. The stochastic model is conditioned by sand-body thickness and position in wellbores. Geological input parameters-sand-body orientation and width/thickness ratios-are often difficult to determine, and are invariably subject to interpretation. Net/gross ratio (NGR) and sand-body thickness are more easily estimated. Sand-body connectedness varies, depending on the modeling procedure; however, a sedimentary process-related model gives intermediate values for connectedness between the values for a regular packing model and the stochastic model. The geological model is transferred to a reservoir simulation grid by use of transmissibility multipliers and an NGR value for each block. The transfer of data smooths out much of the detailed geological information, and the calculated recovery factors are insensitive to the continuity measured in the geological model. Hence, the authors propose improvements to the interface between geological and reservoir simulation models.
TL;DR: In this paper, an integrated outcrop and subsurface study of permeability variations in the San Andres formation demonstrates the extreme heterogeneity present in this economically important carbonate horizon.
Abstract: An integrated outcrop and subsurface study of permeability variations in the San Andres formation demonstrates the extreme heterogeneity present in this economically important carbonate horizon. Permeability measurements were made with a field permeameter and were compared to subsurface core data. Geostatistical techniques were used to predict variability and scales of spatial correlation. Measured permeability showed substantial variability within units arranged in three correlation scales. Outcrop permeability data exhibited no marked permeability anisotropy in predicted spatial correlation length. Several scales of spatial variability have been observed in an outcrop section, with subsurface results in agreement.
TL;DR: In this paper, a multistep pseudofunction-generation process is described to incorporate several scales of heterogeneities into one set of final pseudofunctions to be used in large gridblocks for field simulations.
Abstract: This paper describes a multistep pseudofunction-generation process designed to incorporate several scales of heterogeneities into one set of final pseudofunctions to be used in large gridblocks for field simulations. A detailed description of the multistep scale-up process is provided. The calculation procedure and the results of an extensive numerical scaling-up experiment from Kyte and Berry pseudofunctions are described. Three geological descriptions involving random permeability variations are used. The effect of three scales (sizes) of heterogeneities on a standard oil/water relative permeability curve is determined from a three-step pseudofunction-generation process. Ranges of mobility ratios, viscosity/gravity ratios, and viscosity/capillary ratios are used in the displacements to provide a guide to the effect of various types and scales of hetrogeneities on fluid flow in several regimes.
TL;DR: In this paper, a method based on the difference between the chemical compositions of formation and drilling fluids for analyzing drilling mud to forecast fluid-producing zones was proposed, which was successfully applied in three boreholes in crystalline rocks in France.
Abstract: This paper describes a method based on the difference between the chemical compositions of formation and drilling fluids for analyzing drilling mud to forecast fluid-producing zones. The method was successfully applied in three boreholes in crystalline rocks in France. Subsequent geophysical logs and hydraulic tests confirmed the occurrence of flowing fractures.
TL;DR: In this article, an interpretation method based on nonlinear regression is proposed for well tests from infinite-reserve constrained-entry well with pressure support from a gas cap, bottomwater drive, or combination of both.
Abstract: Analytical solutions are presented for the pressure response of a slanted limited-entry well in an infinite reservoir subject to pressure support from a gas cap, bottomwater drive, or a combination of both. The well's inclination angle ranges from 0 to 90{degrees}, covering vertical and horizontal wells as limiting cases. An interpretation method based on nonlinear regression provides a useful analysis procedure for well tests from such reservoirs. The pressure support from the gas cap or bottomwater often masks the late-time reservoir features, making conventional semilog analysis difficult. Field tests are interpreted to illustrate the applicability and limitations of the regression method.
TL;DR: In this article, a generalized rate-convolution method is presented to obtain the reservoir pressure and a new formula is also presented to determine the vertical permeability for partially penetrated wells, and two well-test field examples, interpreted with these methods, suggest that the downhole flow rate is crucial for system identification and parameter estimation and that the wellbore volume below the pressure gauge and flowmeter must be taken into account.
Abstract: Presentation of the application of convolution and deconvolution interpretation methods. Two well-test field examples, interpretated with these methods, suggest that the downhole flow rate is crucial for system identification and parameter estimation and that the wellbore volume below the pressure gauge and flowmeter must be taken into account. A new generalized rate-convolution method is presented to obtain the reservoir pressure. A new formula is also presented to determine the vertical permeability for partially penetrated wells.
TL;DR: In this article, the influence function of a well/reservoir system from the deconvolution of wellbore flow rate and pressure is determined using a variety of different deconvolutions.
Abstract: Determination of the influence function of a well/reservoir system from the deconvolution of wellbore flow rate and pressure is presented Deconvolution is fundamental and is particularly applicable to system identification A variety of different deconvolution algorithms are presented The simplest algorithm is a direct method that works well for data without measurement noise but that fails in the presence of even small amounts of noise The authors show, however, that a modified algorithm that imposes constraints on the solution set works well, even with significant measurement errors
TL;DR: In this paper, a geostatistical approach is used to characterize reservoir transmissibility with the aim of assigning simulator parameters in 2D models, where the authors define block transmissibilities as spatial geometric averages.
Abstract: A geostatistical approach is used to characterize reservoir transmissibility with the aim of assigning simulator parameters in 2D models. Transmissibility is represented as a spatial random function where heterogeneity is described by the probability distribution and the variogram of sample values. The key element of the geostatistical model is the definition of block transmissibilities as spatial geometric averages. Published analytical results have shown that the effective transmissibility of infinite, statistically isotropic flow fields is equal to the ensemble geometric mean. Numerical results presented show that a spatial geometric average is an excellent approximation of effective transmissibility in such finite fields as simulator gridblocks. The geostatistical model for transmissibility is used to show that the mean and variance of block-averaged values depend on the averaging area. As the averaging area is increased, mean block transmissibility decreases toward the ensemble geometric mean while the block variance decreases to zero. The geostatistical model is also used to investigate the kriging of block transmissibilities from well data. The current method of correcting bias in kriged values is found to cause artifacts of gridblock size in flow simulation results. The simpler, uncorrected kriging estimator is shown to preserve overall flow-field transmissibility, regardless of gridblock size.
TL;DR: In this paper, les caracteristiques de profondeur d'invasion sont analytiques et les carottes de the penetration of particules, du debit and the concentration des particules.
Abstract: Etude en laboratoire de l'endommagement de la formation due a l'invasion de particules lors d'injection d'eau.L'influence du mode de preparation des carottes sur l'invasion des particules est determinee ainsi que celle de la penetration des particules,du debit et de la concentration des particules sur l'endommagement de la formation.Les caracteristiques de profondeur d'invasion sont analysees.
TL;DR: In this article, an analytical solution for pseudopressure function that represents the reservoir and wellbore responses resulting from production at a constant oil rate in a solution-gas-drive reservoir is presented.
Abstract: This work presents an analytical solution for the pseudopressure function that represents the reservoir and wellbore responses resulting from production at a constant oil rate in a solution-gas-drive reservoir. The solution can also be reduced to obtain the analytical solution for the corresponding single-phase-flow problem. The general analytical solution suggests a new definition for the dimensionless flow rate. The analytical solutionis used to construct new type curves for analysis of interference tests conducted under multiphase-flow conditions. It is shown that if one ignores multiphase-flow effects and analyze interference data with the line-source-solution type curve, then the estimates of the permeability and porosity-compressibility product obtained may be in error by 20 to 40%.
TL;DR: In this paper, the authors used nuclear tracers to label the fluid phases and detect radiation with a movable detector in long-core flood experiments to obtain information on 1D fluid saturation distributions.
Abstract: Fluid saturation development in long-core flood experiments is investigated. Information on 1D fluid saturation distributions is obtained by labeling the fluid phases with nuclear tracers and detecting radiation with a movable detector. Various flood experiments were done on 2.5-ft (76-cm)-long sandstone cores. In miscible displacements where radioactive brine is displacing inactive brine, dispersion and ion adsorption are evaluated. Imaging saturation profiles during drainages and waterfloods gives information on saturation front velocity and time development of local saturation variations. Experimental results are compared with numerical results from a 1D front-tracking black-oil simulator that incorporated inhomogeneities and capillary effects. Surfactant floods were investigated to test the applicability for EOR studies.
TL;DR: In this paper, the economic benefit of gel-based fracturing treatments, the optimal well spacing for higher- and lower-permeability settings, and how to establish proper values for permeability and achievable hydraulic-fracture dimensions for optimal well-spacing were investigated.
Abstract: Conventionally, proper well spacing and stimulation govern the economic attractiveness of producing natural gas from coalbeds. To provide an analytical foundation for this empirical evidence, reservoir simulation and economic analyses were conducted to gain insights into the optimum well spacing and hydraulic-fracturing treatments in typical good and poor geologic settings of the Oak Grove field in Alabama. The authors report their study of the economic benefit of gel-based fracturing treatments, the optimal well spacing for higher- and lower-permeability settings, and how to establish proper values for permeability and achievable hydraulic-fracture dimensions for optimal well spacing.
TL;DR: In this article, the dual-resistivity MWD tool uses a section of a drill collar as electrodes and provides two independent resistivity measurements: a principal well-focused lateral measurement of the current flowing radially from a defined segment of the drill collar and a secondary axial or bit measurement of a defined portion of the lower bottomhole assembly (BHA).
Abstract: This article reports on the dual-resistivity MWD tool, which uses section of the drill collar as electrodes and provides two independent resistivity measurements: a principal well-focused lateral measurement of the current flowing radially from a defined segment of the drill collar and a secondary axial or bit measurement of the current flowing from a defined portion of the lower bottomhole assembly (BHA). In oil-based muds, a single (bit) measurement is made of the current flowing to the formation through the drill bit.
TL;DR: In this paper, a conceptual electrical model of a steamflood porous reservoir, based on a qualitative description of the fluid zones of an ideal heavy-oil steam flood, is presented.
Abstract: An essential part of the development of electrical geodiagnostic techniques for mapping thermal recovery processes is understanding the relationship of formation resistivity to the thermal recovery process As a result of laboratory measurements of a ID steamflood, a preliminary understanding of some of the mechanisms of the electrical resistivity change has been gained The theory of electrical resistivity of a steamflood is reviewed and used to evaluate the resistivity changes expected A conceptual electrical model of a steamflood porous reservoir, based on a qualitative description of the fluid zones of an ideal heavy-oil steamflood, is presented The model assumes that salinity, temperature, and saturation are the important factors controlling resistivity changes and that Archie's law applies The authors found that the characteristics of each individual reservoir must be considered before the in-situ resistivity changes are predicted and that in-situ resistivity can either increase as a result of steamflooding