Showing papers on "Permeability (earth sciences) published in 1986"

Quantitative prediction of permeability in porous rock

Abstract: We show that percolation concepts lead to the definition of a characteristic length for the permeability in random porous media. Application of the model to sandstone and carbonate rocks yields quantitative agreement between theory and experiment with no adjustable parameters.

Relative Permeability Of Petroleum Reservoirs

Abstract: This book enables petroleum reservoir engineers to predict the flow of fluids within a hydrocarbon deposit. Laboratory techniques are described for both steady-state and unsteady state measurements, and the calculation of relative permeability from field data is illustrated. A discussion of techniques for determing wettability is included, along with theoretical and empirical methods for the calculation of relative permeability, and prediction techniques. Contents include: Measurement of Rock Relative Permeability; Two-Phase Relative Permeability; Factors Affecting Two-Phase Relative Permeability; Three-Phase Relative Permeability; and Index.

An Equivalent Continuum Model for Coupled Stress and Fluid Flow Analysis in Jointed Rock Masses

Abstract: To provide a set of governing equations for solving the coupled stress and fluid flow, a rock mass, which commonly contains a large number of geological discontinuities, is treated as an anisotropic, elastic porous medium with the corresponding elastic compliance and permeability tensors, hydro-mechanical equivalents to the discontinuous mass. The hydromechanical equivalents, with the special emphasis on the permeability tensor, are formulated on the assumption that any crack can be replaced by a set of parallel planar plates connected by two springs. Two-dimensional numerical analyses on seepage flow networks support the validity of the permeability tensor. Some field evidence is analyzed to examine the applicability of the present model for the practical purpose of rock hydraulics.

Dynamic gas slippage: a unique dual-mechanism approach to the flow of gas in tight formations.

Abstract: A mathematical formulation, applicable to both numerical simulation and transient well analysis that describes the flow of gas in very tight porous media and includes a dual-mechanism transport of gas is developed. Gas is assumed to be traveling under the influence of a concentration field and a pressure field. Transport through the concentration field is a Knudsen flow process and is modeled with Fick's law of diffusion. Transport through the pressure field is a laminar process and is modeled with Darcy's law (inertial/turbulent effects are ignored). The combination of these two flow mechanisms rigorously yields a composition-, pressure-, and saturation-dependent slippage factor. The pressure dependence arises from treating the gas as a real gas. The derived dynamic slippage is most applicable in reservoirs with permeabilities less than or equal to0.01 md. The results indicate that in reservoirs of this type, differences between recoveries after 10 years of production with the dynamic-slip and constant-slip approaches were as great as 10%, depending on the initial gas saturation. If an economic production rate is considered, differences as great as 30% can be expected.

Relations Between Permeability and Electrical Resistivity in Granular Aquifers

Abstract: Increased demand for quantitative answers to ground-water problems, particularly associated with the use of numerical models, has increased the need to accurately determine the distribution of hydraulic parameters. Researchers have attempted to find correlations between electrical resistivity and the permeability of fresh-water aquifers since 1951. Several recent studies report either direct or inverse relations between apparent formation factor and aquifer permeability. The basis for these relations is a direct or inverse relation between porosity and permeability and, as matrix conduction effects are not taken into account, constant fluid conductivity is either implicitly or explicitly assumed. Laboratory experiments conducted on granular materials suggest that matrix conduction (surface conduction) effects are either as important as, or dominant over, porosity-permeability relations. Our experiments on granular materials show only weak relations between true formation factor and permeability. Relations between apparent formation factor and permeability are good only for constant fluid conductivity. Most importantly, the strongest relationship found was that between permeability and matrix conductivity. These data suggest either that (1) relations between permeability and apparent formation factor must be applied in very restricted geologic environments and only where fluid conductivity remains relatively constant, or (2) more fundamental relations between matrix conductivity and aquifer permeability should be applied.

Prediction of gas barrier properties of high polymers

Abstract: This paper studies the correlation of polymer structure and morphology and gas permeability A scale of numerical values based on polymer cohesive energy density and fractional free volume has been devised to predict permeability and also to estimate diffusion and solubility properties

Petroleum Engineering: Principles and Practice

Abstract: 1 Introduction.- 1.1 Petroleum Engineering: A creative technology.- 2 Reservoirs.- 2.1 Conditions for occurrence.- 2.2 Reservoir pressures.- 2.3 Fluid pressures in a hydrocarbon zone.- 2.4 Reservoir temperatures.- 2.5 Nature of reservoir fluids.- 2.6 Reservoir data - sources.- 3 Oilwell Drilling.- 3.1 Operations.- 3.2 Costs.- 3.3 Well completions and oilwell casing.- 3.4 Completion.- 3.5 Drilling fluid control.- 3.6 Rheology of well fluids (drilling muds and cements).- 3.7 Formation breakdown pressures and leak off tests.- 3.8 Data acquisition during drilling.- 3.9 Mud fluids for core recovery.- 3.10 Drilling optimization.- 3.11 Turbine versus conventional rotary.- 3.12 Special problems in drilling.- 3.13 Completion for production.- 4 Properties of Reservoir Fluids.- 4.1 Volumetric and phase behaviour of hydrocarbon systems.- 4.2 Applications to field systems.- 4.3 Compressibility.- 4.4 Measurement and prediction of reservoir fluid properties.- 4.5 Formation volume factors, B.- 4.6 Gas-oil ratios.- 4.7 Direct measurements - PVT analysis.- 4.8 Generalized correlations for liquid systems.- 5 Characteristics of Reservoir Rocks.- 5.1 Data sources and application.- 5.2 Coring decisions.- 5.3 Conventional and oriented coring.- 5.4 Coring mud systems.- 5.5 Core preservation.- 5.6 Well site controls.- 5.7 Core for special core analysis.- 5.8 Core-derived data.- 5.9 Geological studies.- 5.10 Routine core analysis.- 5.11 Porosity.- 5.12 Permeability.- 5.13 Relationships between porosity and permeability.- 6 Fluid Saturation: influence of wettability and capillary pressure.- 6.1 Equilibrium conditions.- 6.2 Laboratory measurements and relationship with reservoir systems.- 6.3 Pore size distribution.- 6.4 Capillary pressure hysteresis.- 6.5 Saturation distributions in reservoir intervals.- 6.6 Correlation of capillary pressure data from a given rock type.- 7 Relative permeability and multiphase flow in porous media.- 7.1 Definitions.- 7.2 Fractional flow.- 7.3 Effects of permeability variation.- 7.4 Wettability effects.- 7.5 Laboratory determination of relative permeability data.- 7.6 Residual saturations.- 7.7 In situ wettability control.- 7.8 Relative permeability from correlations.- 7.9 Validation of relative permeability data for use in displacement calculations.- 7.10 Pseudo-relative permeability in dynamic systems.- 7.11 Static pseudo-relative permeability functions.- 8 Representation of volumetric estimates and recoverable reserves.- 8.1 In-place volume.- 8.2 Areal extent of reservoirs.- 8.3 Thickness maps.- 8.4 Lithofacies representation.- 8.5 Isoporosity maps.- 8.6 Isocapacity maps.- 8.7 Hydrocarbon pore volume maps.- 8.8 Probabilistic estimation.- 8.9 Recovery factors and reserves.- 8.10 Distribution of equity in petroleum reservoirs.- 9 Radial Flow Analysis of Well Performance.- 9.1 Radial flow in a simple system.- 9.2 Development of the line source solution.- 9.3 Radial equations in practical units.- 9.4 Application of analytical solutions in well test methods.- 9.5 Pressure build-up analysis.- 9.6 Skin effect.- 9.7 Pressure drawdown and reservoir limit testing.- 9.8 Gas well testing.- 9.9 Well test procedures.- 9.10 Well testing and pressure analysis.- 10 Reservoir Performance Analysis.- 10.1 Recovery from gas reservoirs.- 10.2 Primary recovery in oil reservoirs.- 10.3 Gravity segregation and recovery efficiencies.- 10.4 Material balance for reservoirs with water encroachment or water injection.- 10.5 Accuracy of the gross material balance equation.- 11 Secondary Recovery and Pressure Maintenance.- 11.1 Displacement principles.- 11.2 Factors influencing secondary recovery and pressure maintenance schemes.- 11.3 Quality of injection fluids and disposal of brines.- 12 Improved Hydrocarbon Recovery.- 12.1 Targets.- 12.2 The influence of recovery mechanism on residual oil.- 12.3 Permeability improvement.- 12.4 Miscible displacement mechanisms.- 12.5 Miscible flood applications.- 12.6 Chemical flood processes.- 12.7 Heavy oil recovery.- 12.8 Thermal energy.- 12.9 Gas condensate reservoirs.- 12.10 Volatile oil reservoirs.- 13 Factors Influencing Production Operations.- 13.1 The production system.- 13.2 Reservoir behaviour in production engineering.- 13.3 Wellbore flow.- 13.4 Field process facilities.- 13.5 Natural gas processing.- 13.6 Crude oil processing.- 13.7 Heavy oil processing.- 13.8 Produced water treatment.- 13.9 Injection water treatment.- 13.10 Crude oil metering.- 14 Concepts in Reservoir Modelling and Application to Development Planning.- 14.1 Models.- 14.2 Equations of multiphase flow.- 14.3 Simulator classifications.- 14.4 Simulator application.- 14.5 Reservoir description in modelling.- 14.6 Application of reservoir models in field development.- Appendix 1 SPE Nomenclature and Units.- Units.- SPE Symbols Standard.- Symbols alphabetized by physical quantity.- Subscripts alphabetized by physical quantity.- Appendix 2 Solutions to Examples in Text.

Fracture permeability and groundwater flow in clayey till near Saskatoon, Saskatchewan

Abstract: Field and laboratory studies of a clayey unweathered glacial till have shown that its bulk permeability exceeds its matrix permeability by two orders of magnitude. Such findings are common for weathered till but are rare for unweathered till, and have important implications for groundwater recharge and contaminant transport. The till in question is 6 m thick and appears to be unweathered and unfractured. It is overlain by 12 m of weathered and highly fractured till. Results of consolidation tests on the unweathered till indicate a mean vertical hydraulic conductivity of 3.5 × 10−11 m∙s−1 and a mean specific storage of 1.3 × 10−4 m−1. Results of slug tests yield a horizontal hydraulic conductivity of about 5 × 10−9 m∙s−1. Drawdowns in the till in response to pumping from the aquifer below indicate a vertical hydraulic diffusivity of 4.5 × 10−5m2∙s−1. The slug test results combined with specific storage results from consolidation tests indicate a similar value for horizontal hydraulic diffusivity of 4 × 10−...

Permeation of Compacted Clay with Organic Chemicals

Abstract: Hydraulic conductivities were measured on three compacted clays that were permeated with water, methanol, and heptane in rigid-wall and flexible-wall permeameters. The type of permeameter had little effect when the soils were permeated with water. However, rigid-wall permeameters generally yielded much higher hydraulic conductivities than flexible-wall cells when the soils were permeated with organic compounds. Differences in effective stress and confinement along the sidewall of the test specimen are thought to be responsible for the different patterns noted. Permeation of water-saturated clay with heptane caused the hydraulic conductivity to drop to practically zero because of surface tension effects at the water-heptane interface. There appeared to be a threshold hydraulic gradient below which the hydraulic conductivity to heptane was zero. The results of this study show order-of-magnitude differences in hydraulic conductivity depending on testing apparatus and procedures.

The Effect of Stress-Dependent Permeability on Gas Production and Well Testing

Abstract: The effect of stress-dependent permeability on gas production and well testing in tight gas sands was studied by use of a modified pseudopressure that included stress dependence. This work assumes that information on cores is applicable to reservoir behavior. Because microcracks are the primary path for flow through tight-gas sand cores, average stress-dependent permeabilities were found as an average over all crack orientations in a nonuniform stress field, with a horizontal stress only 0.6 times the vertical one. Initial in-situ permeabilities are found to be two to five times the values obtained from uniformly restressed cores. Stress dependence decreases initial gas production by at most 30%, with the loss increasing over reservoir depletion. Buildup tests yield reliable results for the properties at average reservoir pressure. Drawdown tests are more sensitive to stress effects and are much less reliable.

Method for evaluation of formation invasion and formation permeability

Abstract: A method is presented for evaluation of formation invasion and formation permeability by conducting a series of formation resistivity loggings in the operation of a measurement while drilling (MWD) logging system.

Flow in Porous Media III: Deformable Media

Abstract: Stokes flow in a deformable medium is considered in terms of an isotropic, linearly elastic solid matrix. The analysis is restricted to steady forms of the momentum equations and small deformation of the solid phase. Darcy's law can be used to determine the motion of the fluid phase; however, the determination of the Darcy's law permeability tensor represents part of the closure problem in which the position of the fluid-solid interface must be determined.

Method and apparatus for determining hydraulic properties of formations surrounding a borehole

Abstract: A method and apparatus are disclosed for determining hydraulic properties of formations surrounding a borehole. In one embodiment, trial values of hydraulic properties such as vertical and horizontal permeability are selected and used to obtain computed formation pressure responses that are compared to measured pressure responses taken at a source and two observation probe positions. Trial values can then be modified to bring the computed pressure responses closer to the measured ones. An improved technique is also disclosed for obtaining the computed pressure responses.

Porosity Reduction in Sandstone by Quartz Overgrowth

Abstract: A mathematical model for predicting porosity histories due to quartz overgrowth in quartz-rich sandstone reservoirs has been developed. The model neglects secondary dissolution porosity and other diagenetic processes such as compaction and precipitation of carbonate and clay minerals. Nevertheless, the model is straightforward and easy to use to calculate porosity. The calculated porosity corresponds to measured porosity of simple quartz-cemented sandstones in 27 wells in North and South America. The model is based on fluid flow through initially porous, unlithified sands in which the fluid phase is saturated with Si(OH)4 and is always in equilibrium with quartz. As the continuously circulating fluid migrates updip toward the basin edge, it cools, and quartz precipitates into the pore spaces causing a loss of porosity. Basinal fluid velocities may be calculated assuming (1) thermal convection and (2) hydrostatic pressure due to recharge at the edge of the basin. Porosity diagrams relating porosity to geothermal gradient, burial rate, and depth of burial are compared to thermal maturation models of source rocks, fluid flow history, and grain-size distribution. The rate of porosity reduction depends on the following variables in decreasing order of significance: buria rate, age, initial porosity, basin size (dip angle), fluid dynamics, initial permeability, and geothermal gradient.

Temperature-dependent relative permeability and its effect on oil displacement by thermal methods

Abstract: An analytical theory is presented that permits the formulation of a mathematical model to describe the variation of relative permeability with temperature in a water/oil system The theory develops analytical equations for temperature-dependent relative permeability in terms of water saturation, irreducible water saturation, and differential change in irreducible water saturation with temperature These equations predict and agree reasonably well with experimental results reported by other researchers The implications of temperature-dependent relative-permeability data on reservoir performance of a thermal process are also presented These data together with the application of the Buckley-Leverett frontal-advance theory and the fractional-flow equation are used to predict oil recovery

Influence of a Critical Gradient on the Consolidation of Clays

Abstract: Several studies in the laboratory have shown the existence of a permeability law which is different from Darcy's law and which defines the flow of the pore water in certain natural clays. Consolidation tests in the laboratory, including the measurement of permeability at different stages of loading, that were carried out on Saint Herblain clay at the E.N.S.M. Soil Mechanics Laboratory prove the existence of major critical gradients (12 < i 0 < 20). According to this observation, a consolidation model worked out with a non-Darcian permeability law has been produced by means of a finite-difference computer program. On the one hand, this model is compared with Terzaghi's consolidation model and, on the other hand, the law that has been established is tested next to the laboratory tests.

Permeability Testing in the Triaxial Cell

Abstract: It has been suggested that a triaxial shear test chamber can be used to measure the permeability of low permeability soils. To verify this, the influence of a number of test parameters on the measured coefficient of permeability was investigated. Results indicate such permeability tests should be performed on samples having a minimum diameter of 71.1 mm (2.8 in.) and a length to diameter ratio of 0.5 to 1.0. It was found that a permeant consisting of 1 g of magnesium sulfate heptahydrate (epsom salt) dissolved in 1 L of deaired, distilled water is adequate for general permeability testing. The triaxial, falling head permeability test should be conducted at a gradient that results in an applied effective stress at the outflow end of the sample less than the preconsolidation stress of the material. It was found that with very careful trimming, the influence of the smear zones created at the ends of the samples during the trimming process can be minimized.

Electrical conductivity of brine-saturated fractured rock

Abstract: A theoretical analysis shows that electrical conductivity along fractures in a saturated porous rock is a function of many factors: fluid and rock conductivities, initial fracture aperture and contact area, fracture surface geometry (asperity height distribution and tip curvature), elastic moduli of the rock, and confining pressure or normal stress acting across the fracture. The conductivity in the fracture plane decreases approximately in proportion to log pressure, but the conductivity is influenced by the increased contact area, and hence flow‐path tortuosity, along the fracture surface at elevated pressures. Electrical conductivity in fractures is more affected by flow‐path tortuosity than is permeability. The dependence on pressure was tested using laboratory measurements of conductivity through split cores containing ground, saw‐cut surfaces in a variety of rocks under confining pressures to 200 MPa. The conductivity decreased approximately in proportion to log pressure (there was little effect of ...

Low permeability rocks: Laboratory measurements and three‐dimensional microstructural analysis

Abstract: Traditional techniques for measuring permeability and traditional models relating permeability to porosity are inadequate for low-permeability (< or =10/sup -18/ m/sup 2/) geologic materials. Special techniques have been developed for measuring fluid flow through such rock samples and for quantifying their three-dimensional pore microstructure. Permeability is measured by a modified transient pulse technique, pore structure is quantified using a computerized microgeometric modeling system, and portable three-dimensional display is produced by an optical imaging system. Results of applying this processing to a low-porosity ''tight gas sandstone'' from the Cotton Valley Formation agree with the well-documented diagenetic history of these samples. We find that the porosity distribution is very inhomogeneous and skewed. The pore system is slightly anisotropic, which is consistent with the differences in permeability measured in two orthogonal directions. We indicate how such data could be used to develop more geologically and geometrically realistic models relating porosity and permeability in low-permeability gas formations.

Applied open-hole log analysis

Abstract: The Petroleum Reservoir. The Basics of Resistivity. Spontaneous Potential. Resistivity Logs. Sonic Logs. Analyzing the Log. Nuclear Logs. Resistivity-Porosity Crossplots. Porosity Crossplots. Mineral Crossplots. Permeability. New Technology. Shaly Sand Analysis. Appendixes.

Determination of gas-condensate relative permeability on whole cores under reservoir conditions

Abstract: Rock samples from a Middle East carbonate retrograde condensate gas field were studied to determine their relative permeability to gas and condensate curves. The authors emphasized the determination of condensate minimum flowing saturation-or critical condensate saturation-and the reduction of permeability to gas in the presence of immobile condensate saturation. A ternary pseudoreservoir fluid of methane/pentane/nonane made it possible to work in simulated reservoir conditions with a greater flexibility for experimental procedures. The initial water saturation equaling that in the reservoir was restored. The results of the gas-condensate indicate that the critical condensate saturations are high (the average value is 36% PV) and that the reduction of permeability to gas is higher than for a standard gas/oil system. Also presented are the details of the experimental procedures, the fluid characteristics, the results, and a discussion.