Showing papers on "Effective porosity published in 1988"

A water absorption test for concrete

Abstract: Synopsis The durability of concrete near an exposed surface is largely determined by the rate at which harmful agents can penetrate into the concrete. This paper presents a simple analysis of the penetration of' water into unsaturated concrete and describes a method by which the material constant that determines the rate of penetration, the sportively, can be measured, together with the effective porosity. The sorptivity is found to depend on the permeability and porosity of the concrete and the strength of capillary forces. The experimental results conform well to the predictions of the analysis and significant variations in sorptivity have been observed for concrete containing cement replacement materials and subject to different curing regimes.

Fundamentals of gas reservoir engineering

Abstract: 1. Introduction. Natural gas. Gas reservoir engineering. Objective and organization. Units and symbols. 2. Reservoir properties. Introduction. Rock types. Porosity. Viscous flow resistance. Inertial flow resistance. Rock compressibility. Capillary pressure. Relative permeability. 3. Gas properties. Introduction. Composition. Phase behaviour. Real-gas law. Z-factor. Compressibility. Condensate/gas ratio. Formation-volume factor. Viscosity. 4. Phase behaviour. Introduction. K-value method. Equation-of-state method. Laboratory experiments. Multistage separation. 5. Recoverable reserves. Introduction. Bulk volume. Pore volume. Hydrocarbon pore volume. Gas and condensate initially-in-place. Recoverable reserves. Uncertainty. 6. Material balance. Introduction. Wet-gas reservoirs. Gas-condensate reservoirs. Non-volumetric depletion. Aquifer influx. 7. Single-phase gas flow. Introduction. Steady-state Darcy flow. Steady-state radial flow. Non-Darcy flow. Transient flow. Linear flow - constant terminal rate. Linear flow - constant terminal pressure. Radial flow - Constant terminal rate. Non-radial flow. 8. Gaswell testing. Introduction. Backpressure equations. Flow-after-flow tests. Isochronal and modified isochronal tests. Transient well-pressure equations. Drawdown tests. Buildup tests. Multiple-rate transient tests. Example of multiple-rate transient test analysis. 9. Wellbore flow mechanics. Introduction. Single-phase flow equations. Pressure distribution in shut-in wells. Rate-dependent pressure losses. Pressure distribution in producing wells. Multi-phase flow. Minimum unloading rate. 10. Water coning. Introduction. Dupuit critical production rate. Schols critical production rate. Cone breakthrough. Water/gas ratio. 11. Natural depletion. Introduction. Development chronology. Reservoir performance. Well-inflow performance. Tubing-flow performance. Well deliverability. Depletion simulator. 12. Gas injection. Introduction. Injection-well performance. Microscopic mixing. Viscous fingering. Gravity overlay. Stratification. Well Pattern. Pattern-flood model. Appendices. Units and conversion factors. Physical and mathematical constants. Physical properties natural-gas components. Author index. Subject index.

Evolution of pore space in the Poza Rica trend (Mid‐Cretaceous), Mexico

Abstract: The Poza Rica trend of the Tampico embayment, Mexico, will ultimately produce more than 2.3 × 109 barrels of oil from Mid-Cretaceous (Albian-Cenomanian) basin-margin deposits. Bioclastic grainstone, packstone, and wackestone are interbedded with polymictic lime breccia and dolomitized debris; all were deposited by sediment gravity flow. Indigenous sediment was pelagic lime mud. Typical reservoir porosities are about 10%; permeabilities average 2 md and rarely exceed 100 md. Porosity is largely the result of selective dissolution of rudist fragments, which were originally aragonite. Detailed petrographic study, with emphasis on the diagenetic products, allows quantitative assessment of porosity at various diagenetic stages from original sediment to reservoir rock. A relatively simple diagenetic history is reflected by about 90% of the samples studied: primary porosity was reduced through lithification of matrix mud and initial cementation by clear, equant to bladed, non-ferroan calcite. Later dissolution produced extensive skelmoldic and minor vuggy porosity. Subsequently, non-ferroan calcite cement reduced porosity before the emplacement of hydrocarbons. Reconstructed sediment porosities are comparable to, but lower than, modern counterparts. The initial phase of cementation and presumed lithification of mud greatly reduced porosity in all lithologies, but appreciably more porosity persisted in grainstone and packstone than in wackestone or mudstone. Dissolution produced a porosity resurrection, which exceeded that of the initial sediment in some grainstones. Calcite cementation and local multiphase quartz cementation and dolomitization reduced porosity to present average values of 8–12% in grain-supported rocks and 3% in mud-supported rocks. The greater persistence of primary porosity and, therefore, permeability in grain-supported rocks probably accounts for their greater secondary porosity development and ultimate reservoir quality. Geometrically averaged permeabilities range from only 0.17 md in wackestone to 3.85 md in dolomite, but differ significantly with rock type and grain size. Permeability increases with porosity in all lithologies; the rate of increase is greater at higher porosities and with coarser grain sizes. The agent for both early cementation and development of secondary porosity appears to have been meteoric water. Subaerial exposure appears to be ruled out, however, by a basin-margin depositional environment and continued burial beneath Upper Cretaceous pelagic sediments. Early exposure to meteoric water can be explained by a hydrologic head developed during penecontemporaenous exposure that produced cavernous porosity in the adjacent Golden Lane trend. Descending meteoric water likely emerged as submarine springs along the Tamabra trend. Deposition of pelagic limestone during the Turonian blanketed part of the Golden Lane escarpment to enhance development of a large freshwater lens; gaps in the blanket localized springs and influenced flow patterns within the Poza Rica field. Analogous freshwater circulation exists today in northern Florida.

A simple model for describing variation of permeability with porosity for unconsolidated sands

Abstract: There is some experimental evidence that the relationship between permeability and porosity is not always linear sime-logarithmic. Different theoretical models that relate the permeability, porosity and particle size are reviewed and discussed. The Kozeny-Carman relationship is extended to model the flow of fluid between soil particles and flow of fluid around soil particles. It is demonstrated why for low porosities the relation between permeability and porosity is linear semi-logarithmic but at high porosities it becomes non-linear. Experimental data for heavy oil bearing sands has been characterized using this non-linear (quadratic) model.

Analysis of Geophysical Well Logs Obtained in the State 2–14 Borehole, Salton Sea Geothermal Area, California

Abstract: A complete suite of conventional geophysical well logs was obtained in the upper part of a 3220-m- deep borehole drilled into geothermally altered alluvial sediments on the southeastern edge of the Salton Sea. In situ temperatures greater than 300°C and an inability to cool parts of the borehole by circulation limited the suite of logs run below 2000 m in depth to deep induction, spontaneous potential, un-calibrated neutron, natural gamma, and temperature. Bottom-hole temperature trends given by repeat temperature logs were extrapolated to undisturbed temperatures approaching 355°C at a depth of 3220 m. Geophysical logs obtained in the State 2–14 borehole indicate that neutron porosity, gamma-gamma, and deep-induction logs provide useful information on lithologic trends with depth. The natural gamma log contains almost continuous, high-frequency fluctuations that obscure lithologic trends and that may be related to recent radioisotope redistribution and departure from radiometric equilibrium. Acoustic transit time logs give unrealistically low in situ compressional velocities ranging from 1.8 to 3.0 km/s, whereas acoustic waveform logs indicate that sediment compressional velocities range from less than 3.0 km/s shallower than 1000 m in depth to almost 5.0 km/s at depths greater than 2000 m. Analyses indicate that most log values lie between two lithologic end points: an electrically conductive claystone with moderate neutron porosity, but no effective porosity, and an electrically nonconductive, fully cemented siltstone that has small but finite porosity. A limited number of clean sandstones depart from this trend; geophysical logs from these sandstones indicate an effective porosity ranging from 5 to 14%, and saturation with brines having equivalent NaCl concentrations greater than 100,000 mg/L. Depth- averaged trends in neutron porosity and deep-induction logs, along with trends in acoustic velocity determined from acoustic waveform logs, demonstrate that major changes in the properties of alluvial sediments occur within the depth range from 1200 to 1800 m. Although caliper logs were not obtained deeper than 2000 m, resistivity values less than 10 ohm m at those depths probably correspond to borehole enlargements in production zones rather than local increases in effective porosity. The transition in sediment properties indicated by the geophysical logs in the depth interval from 1200 to 2000 m apparently represents a detailed vertical profile of the transition from relatively unaltered clay minerals in alluvial sediments to electrically nonconductive alteration products such as epidote and feldspar.

Reservoir characterization, porosity, and recovery efficiency of deeply-buried paleozoic carbonates: Examples from Oklahoma, Texas and New Mexico

Abstract: Capillary-pressure data from the Early Ordovician Ellenburger Dolomite (west Texas and New Mexico) and the Late Ordovician-Early Devonian Hunton Group carbonates (Oklahoma) are used to calculate or infer petrophysical characteristics, such as median pore-throat size, pore-throat size distribution, effective porosity, and recovery efficiency (RE). For both data sets, porosity and RE are inversely related. A positive relationship between RE and porosity has been reported by other workers, but the relative importance of these opposed trends is unknown. The ability to accurately predict which relationship will hold in a given reservoir unit would be of great value for predicting reservoir performance.

Laboratory‐Determined Transport Properties of Core From the Salton Sea Scientific Drilling Project

Abstract: Two cores from the Salton Sea Scientific Drilling Project have been studied in the laboratory to determine electrical resistivity, ultrasonic velocity, and brine permeability at pressures and temperatures close to estimated borehole conditions. Both samples were siltstones; the first sample was from 1158-m depth, and the other was from 919-m depth. A synthetic brine with 13.6 weight percent NaCl, 7.5 weight percent CaCl2, and 3.2 weight percent KCl was used as a pore fluid. The dry bulk density of the first sample was 2.44 Mg m−3 with an effective porosity of 8.7%. The second sample had a dry bulk density of 2.06 Mg m−3 with an effective porosity of 22.2%. At the midplane of the first sample, electrical impedance tomography was used to map the spatial variation of resistivity during the experiment. Also, at the midplane of both samples, ultrasonic tomography was used to map the spatial variation of P wave velocity. In addition, resistivity was measured with six pairs of electrodes along the sample axis. Both samples showed a strong anisotropy in resistivity and ultrasonic velocity measured perpendicular and parallel to the sample axis. The brine permeability of the first sample decreased from 5 μD to about 1.6 μD during the experiment. The second sample permeability had the same trend, but the permeability values were about 3 orders of magnitude larger. The second sample was subjected to temperatures and pressures exceeding those experienced in situ. Permeability, resistivity, and ultrasonic velocity of this sample showed a discontinuous change just beyond these in situ conditions. This discontinuity implies a structural change in the rock under conditions which would be found below its origin depth in the borehole. A model is proposed to explain the observed velocity anisotropy and variations in velocity, electrical resistivity anisotropy, and permeability with effective depth. When in situ stress is released, microcracking may occur along grain boundaries preferentially oriented parallel to bedding. This microcracking controls velocity and resistivity anisotropy at room conditions. When pressure and temperature are restored, competing effects of compaction and thermal softening of the minerals cause a reversal in the anisotropy. At temperatures and pressures above those at in situ conditions, thermal fracturing or geochemical alteration along grain boundaries causes a discontinuous change in sample physical properties.

Scale effect on rock fissuration porosity

Abstract: Scale effect on rock fissuration porosity is analyzed by means of structural conceptual schematic diagram designed for a reservoir of cubical blocks separated by clefts with constant openings. Two cases are considered: (1) either the blocks are compact (simple porosity due to clefts), or (2) the blocks are affected by fissuration porosity (in which case the system has double fissural porosity). This hexahedral schematization is consistent with what is often noted in tectonic fissuration. Porosities are calculated for increasing volumes whether they be spherical or cubic, and these porosities are expressed in relation to the average effective porosity of the aggregate. If we refer to the different sizes of the interfissural distances normally observed, we note that the representative porosities can probably be reached only for volumes in excess of 106 m3, even in the best circumstances. (This is the Representative Elementary Volume).

Determination of effective porosity of soil materials

Abstract: Hazardous waste disposal landfills require liners constructed of compacted soil material to help prevent the migration of hazardous wastes. The performance of a compacted soil liner is partly a function of the porosity. Porosity is important because the transport of materials through the liner will occur via the pore space. The main purpose of this project is to study the pore spaces of compacted soil materials and to estimate the effective porosity, which is the portion of the pore space where the most rapid transport of leachate occurs. The pore space of three soil materials, till, loess, and paleosol, is studied by using mercury intrusion porosimetry, water desorption, and image analysis. These analyses provide cumulative porosity curves from which the pore size distribution of a soil sample may be estimated. Theory is developed to estimate the effective porosity of a compacted soil material based upon a model of its pore size distribution and pore continuity. The effective porosities of the compacted till, loess, and paleosol materials are estimated to be 0.04, 0.08, and 0.09, respectively. These values are 10 to 20% of the total porosities. Comparisons between measured and predicted Cl travel times through compacted soil samples are made in order to verify the estimated effective porosities. The estimated effective porosities are reasonable because predicted Clfirst breakthrough times are similar to the measured first breakthrough times in compacted till, loess, and paleosol materials. For the three soil materials used in this study., predicted first breakthrough times are 5 to 10 times earlier when effective porosity is used in the Darcy-equation-based calculations as compared to Darcy-equation-based calculations that u~ilize total porosity. This report was submitted in fulfillment of cooperative agreement CR-811093-01-0 by Iowa State University under the sponsorship of the U.S. Environmental Protection Agency. This report covers a period from 10/1/83 to 4/30/86, and work was completed as of 12/31/85.

Device for measuring effective porosity

Abstract: A device for measuring the effective porosity of a sample comprising, a device for defining a cavity defining an opening, a device for sealing the sample around the cavity opening, a device for measuring the internal pressure of the cavity, a device for passing gas into the cavity, a device for measuring the flow rate of the passed gas, and a device for adjusting the flow rate of the passing device until a predetermined value of the internal pressure is obtained in the cavity.

Determination of effective porosity of soil materials. Final report

Abstract: The performance of a compacted soil liner is partly a function of the porosity, where the transport of materials through the liner occurs via the pore space. The project studies the pore spaces of compacted soil materials to estimate the effective porosity, which is the portion of the pore space where the most rapid transport of leachate occurs. Pore space of three soil materials, till, loess, and paleosol, was studied. These analyses provided cumulative porosity curves from which the pore size distribution of soil samples were estimated. Theory was developed to estimate the effective porosity of a compacted soil material based upon a model of its pore-size distribution and pore continuity. Comparisons between measured and predicted chloride travel times through compacted soil samples were made in order to verify the estimated effective porosities. The estimated effective porosities are reasonable because predicted chloride first breakthrough times are similar to the measured first-breakthrough times in the soils studied. For these three soils, predicted first-breakthrough times are 5 to 10 times earlier when effective porosity is used.

The tensorial nature of effective porosity and large-scale dispersion coefficients: Application to the Creston study area, Eastern Washington

Abstract: To describe flow in a complex system of fractures requires an understanding of the effects of direction or orientation on several hydrologic characteristics, such as hydraulic conductivity, porosity, and dispersion coefficient. The theory for hydraulic conductivity is well understood; this report deals with the effects of fracture orientation on porosity and dispersion coefficient. The tensorial nature of effective porosity was examined and was found to be a second-rank tensor in fractured rock units. Porosity varies at a fixed point, depending on its orientation. A method to calculate a dispersion coefficient from field tracer tests is described. The components of the dispersion coefficient can be calculated from the concentration profiles observed in downgradient observation wells. The method provides a procedure for studying the dispersion effect in large-scale field testing. The application of this method was successfully demonstrated in a tracer test performed in the research wellfield at the Creston study area, Lincoln County, Washington.

Sandstone porosity as function of thermal maturity - an approach to porosity comparisons and prediction

Abstract: The porosity of sandstones typically decreases during burial, and porosity-reducing processes of burial diagenesis operate at all depths so long as porosity exists. Plots of porosity against depth describe sandstones at a point in time, but do not incorporate the idea that the section is in disequilibrium. In many cases, sandstone porosity can be more advantageously described as a function of thermal maturation (time-temperature exposure) than of depth. Specifically, empirical data indicate that general trends of sandstone porosity in the subsurface can be well represented by a power function of thermal maturity: /phi/ = A(M)/sup B/, where /phi/ is porosity, M is a measure of time-temperature history such as vitrinite reflectance or Lopatin's index of thermal maturity, and A and B are constants for a given sandstone population but which vary between data sets. Plots of porosity vs. thermal maturity take into account the overprint of time and temperature effects upon burial diagenesis and thus aid in direct comparisons of sandstones from diverse tectonic settings; differences in porosity trends on such plots are primarily related to petrologic properties. Logarithmic plots of porosity vs. a measure of thermal maturity also establish norms by which secondary porosity development and unusual porosity (andmore » petrology) within a sandstone sequence can be recognized, and they offer a systematic rationale for the prediction of porosity ahead of drilling and at times in the geologic past.« less

Diagenesis and porosity development in Oriskany sandstone of West Virginia

Abstract: Petrographic investigation of 12 Oriskany cores from West Virginia and surrounding states shows a complex relationship between diagenesis and porosity development. Deposited as a fossiliferous marine sandstone, the Oriskany is cemented by calcium carbonate and/or quartz, depending on the predominant clastic material (fossils or quartz). Porosity ranges from less than 2% to approximately 8%, and pore types vary across the state. Primary-intergranular and fracture are the major porosity types observed in all cores. Primary porosity is best developed in central and western areas where cementation is incomplete. Petroleumlike materials (paraffin in nature) commonly occur as pore linings or inclusions in secondary quartz. To the east, fracture porosity dominated in tightly cemented sandstones, but vertical and horizontal fractures are observed in all cores. Many fractures, however, have been healed with quartz and calcite. Minor amounts of carbonate leaching supplements primary porosity. In Marion County, partial replacement of carbonate fossils by fringing microcrystalline quartz, along with recrystallization and subsequent leaching of the carbonate, has produced distinctive secondary pores. Porosity increases dramatically in western areas of the state. In addition to primary and secondary porosity, microcrystalline porosity within chert and phosphatic zones is present. Other minor and relatively insignificant porosity types in themore » Oriskany from all regions include intraskeletal, intragranular quartz and feldspar, and intercrystalline dolomite. Although overall porosity is low, intergranular porosity and fracture porosity are best developed in quartz-rich zones.« less