Effective porosity

About: Effective porosity is a research topic. Over the lifetime, 1199 publications have been published within this topic receiving 26511 citations.

A coupled hydromechanical system defined through rock mass classification schemes

Abstract: Changes in the hydraulic conductivity field, resulting from the redistribution of stresses in fractured rock masses, are difficult to characterize due to complex nature of the coupled hydromechanical processes. A methodology is developed to predict the distributed hydraulic conductivity field based on the original undisturbed parameters of hydraulic conductivity, Rock Mass Rating (RMR), Rock Quality Designation (RQD), and additionally the induced strains. The most obvious advantage of the methodology is that these required parameters are minimal and are readily available in practice. The incorporation of RMR and RQD, both of which have been applied to design in rock engineering for decades, enables the stress-dependent hydraulic conductivity field to be represented for a whole spectrum of rock masses. Knowledge of the RQD, together with the original hydraulic conductivity, is applied to determine the effective porosity for the fractured media. When RQD approaches zero, the rock mass is highly fractured, and fracture permeability will be relatively high. When RQD approaches 100, the degree of fracturing is minimal, and secondary porosity and secondary permeability will be low. These values bound the possible ranges in hydraulic behaviour of the secondary porosity within the system. RMR may also be applied to determine the scale effect of elastic modulus. As RMR approaches 100, the ‘softening’ effect of fractures is a minimum and results in the smallest strain-induced change in the hydraulic conductivity because the induced strain is uniformly distributed between fractures and matrix. When RMR approaches zero, the laboratory modulus must be reduced significantly in order to represent the rock mass. This results in the largest possible change in the hydraulic conductivity because the induced strain is applied entirely to the fracture system. These values of RMR bound the possible ranges in mechanical behaviour of the system. The mechanical system is coupled with the hydraulic system by two empirical parameters, RQD and RMR. The methodology has been applied to a circular underground excavation and to qualitatively explain the in situ experimental results of the macropermeability test in the drift at Stripa. Copyright © 1999 John Wiley & Sons, Ltd.

Improved log analysis in shaly-sandstones-based on Sw and hydrocarbon pore volume routine measurements of preserved cores cut in oil-based mud

Abstract: Routine measurements of properly preserved cores cut in oil-based mud (OBM) give accurate porosity (Φ) and water saturation (S w ) values in hydrocarbon reservoirs. Above mobile water zones the Hydrocarbon Pore Volume (HPV) of these OBM cores is usually accurate in both clean and shaly sand reservoirs. HPV evaluations from the 'core' and the 'total' and 'effective' porosity systems must all be the same: HPV = Φ core (1 - S wcore ) = Φ t (1 - S wt ) = Φ e (1 - S we ), where the subscripts denote the specific system being addressed. In shaly reservoirs, core porosity (Φ core ) and total porosity (Φ t ) may be larger than effective porosity (Φ e ), with the extra porosity being generated from the drying of the clay minerals, especially smectites. The water volumes measured by Dean-Stark extraction of OBM core plugs includes this clay-bound water, so OBM Φ core and S wcore used together as a pair give an accurate evaluation of HPV. Example core and log data from a shaly-sand formation are evaluated using several well-known log analysis models. As tested, the Dual-Water, Cyberlook and Indonesia models all provide quite similar S w results and agree fairly well with the OBM S wcore corrected to reservoir conditions Because the standard Cyberlook and Indonesia S w results are close to S wt , they are paired with total porosity for HPV calculations. They have previously been thought to give S we , not S wt, and have been paired with 'effective' porosity giving pessimistic HPV results. The Archie total porosity model also gives useful, but pessimistic, results. The Archie effective porosity model gives very pessimistic S w and HPV results in shaly sands. The most accurate evaluation method, the OBM core analysis, can be used to calibrate current resistivity-S w models for shaly sands. This process leads to improved estimates of oil- and gas-in-place and, potentially, to improved shaly-sand models for application in worldwide log analysis.

Petrophysical Properties and Well Log Interpretations of Tertiary Reservoir in Khabaz Oil Field / Northern Iraq

Abstract: The aim of this study is interpretation well logs to determine Petrophysical properties of tertiary reservoir in Khabaz oil field using IP software (V.3.5). The study consisted of seven wells which distributed in Khabaz oilfield. Tertiary reservoir composed from mainly several reservoir units. These units are : Jeribe, Unit (A), Unit (A'), Unit (B), Unit (BE), Unit (E),the Unit (B) considers best reservoir unit because it has good Petrophysical properties (low water saturation and high porous media ) with high existence of hydrocarbon in this unit. Several well logging tools such as Neutron, Density, and Sonic log were used to identify total porosity, secondary porosity, and effective porosity in tertiary reservoir. For Lithological identification for tertiary reservoir units using (NPHI-RHOB) cross plot composed of dolomitic-limestone and mineralogical identification using (M/N) cross plot consist of calcite and dolomite. Shale content was estimated less than (8%) for all wells in Khabaz field. CPI results were applied for all wells in Khabaz field which be clarified movable oil concentration in specific units are: Unit (B), Unit (A') , small interval of Jeribe formation , and upper part of Unit (EB).

Application of sequential indicator simulation, sequential Gaussian simulation and flow zone indicator in reservoir-E modelling; Hatch Field Niger Delta Basin, Nigeria

Abstract: The study was carried out with the aim of predicting uncertainty using Sequential Indicator Simulation (SISIM) for lithofacies modelling, sequential Gaussian simulation (SGSIM) for reservoir property modelling and inferring the depositional environment using Flow Zone Indicator (FZI). Five well logs, core analysis data and 3D seismic data were used for the study. Reservoir sand named “Reservoir-E” was correlated across the five wells in the field, and its surface was mapped on the seismic sections from the 3D cube. Petrophysical evaluations revealed average, net to gross, porosity, permeability, the volume of shale, water saturation, hydrocarbon saturation (SH), Reservoir Quality Index (RQI) and FZI as 0.70, 0.29, 2342 mD, 0.158, 0.50, 0.50, 2.44 and 5.62 μm, respectively. Structural interpretations on seismic sections revealed five major faults which trend NE-SW, NW-SE and W-E. A 3D grid with dimension 204 × 120 × 5 = 122,400 was constructed to accommodate our model. Validation of lithofacies models shows a correlation coefficient of 89.43–92.98% for well data and model. The property model shows variability in effective porosity and permeability 0.24 to 0.38 and 560 to 5600 mD. The low amount of SH in well HT-2 and HT-3ST1 is attributed to the presence of baffles with low reservoir quality index with 1.81 and 1.67 for RQI and 5.05 and 5.27 for FZI as compared to well HT-1, HT-4ST1 and HT-5 with RQI of 3.61, 2.71 and 2.41 and FZI of 6.25, 5.85 and 5.66. The environment of deposition is interpreted to be mouth bar-upper shoreface. High porosity and permeability values are linked with high FZI and RQI which are targets for exploitation.

Correlation of unsaturated soil and dielectric property for monitoring of subsurface characteristics: development of unsaturated dielectric mixing models and its application

Abstract: The behavior due to rainfall infiltrating the ground plays a role in landslides, groundwater recharge and various other ground responses. Most of these geotechnical behaviors have a correlation between soil pore space and soil volumetric water content in the unsaturated and saturated soil porous media. Therefore, the soil porosity associated with soil pores and the distribution of volumetric water content are significantly important hydrological characteristics. In the case of shallow slope failure such as landslide, the infiltration activity due to the connectivity of soil pore spaces in a porous media is induced. Slope failure may be attributed to the effect of a wetting front with the slope due to liquid infiltration, which changes the volumetric water content, soil matric suction and shear strength of the slope. This study was performed with an unsaturated injection test using a frequency domain reflectometry (FDR) dielectric device which measures the dielectric constant of unsaturated soil and the study then proposed the unsaturated dielectric mixing models to calculate soil porosity and effective porosity of unsaturated soils. From the experimental results the ratio of effective porosity to porosity of soils are measured in a range of 70–85%. These experimental results show a decrease of about 5–10% for unsaturated soil compared to the ratio of effective porosity to porosity of saturated soil. The infiltration passages of tracer material are restricted within the pore connectivity in the unsaturated soil which is caused by dead-pores in the soil. Using the FDR device and the unsaturated dielectric mixing models, we can consider the acquisition of physical properties to detect the infiltration activity, the response of the dielectric constant along with the injected tracer and hydrological parameters for the unsaturated soil porous media.