Effective porosity

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

Petrophysical Evaluation for a Geothermal Project in Tønder

Abstract: The paper focuses on the petrophysical evaluation of wells for the development of a geothermal district heating plant in Tonder,Denmark. The evaluation was carried out by analysis and interpretation of available data. The data used included completion reports, well logs, conventional core and side wall core data. The results from interpretation of the data include total porosity, permeability, clay volume and effective porosity for three wells. An unusual finding was the inverse relationship between porosity and permeability in the targeted layer of the reservoir. This inverse relationship, maybe attributed to the precipitation of salt and the presence of caverns or fractures.

The Validation of the Granular Reservoir Petrophysical Model

Abstract: Petrophysical modeling makes possible estimation of effective reservoir properties (effective porosity and permeability) with standard log suite data. Petrophysical invariant (current effective porosity, divided by the maximum effective porosity for the particular reservoir) is considered as the main log interpretative and petrophysical parameter analysis in case of complex polymineral reservoirs, which reflects the wide range of factors that characterizes the sedimentation conditions, occurrence and secondary lithogeochemical transformations of reservoir rocks. Characteristic parameters of the model allow studying petrophysical principles and relations directly on the results of the laboratory core analysis. There are two points for petrophysical model validation. First point is a clear inverse relation between the shale volume and total porosity of the particular reservoir and their sum is equal to the porosity of the matrix. Second point is the close inverse correlation between the sand content and aleurite fractions content. The main area of the developed model practical application is 3D digital geological and hydrodynamic simulation.

Application of hybrid uncertainty-clustering approach in pre-processing well-logs

Abstract: In the subsurface geology, characterization of geological beds by well-logs is an uncertain task. The thesis mainly concerns studying vertical resolution of well-logs (question 1). In the second stage, fuzzy arithmetic is applied to experimental petrophysical relations to project the uncertainty range of the inputs to the outputs, here irreducible water saturation and permeability (question 2). Regarding the first question, the logging mechanism is modelled by fuzzy membership functions. Vertical resolution of membership function (VRmf) is larger than spacing and sampling rate. Due to volumetric mechanism of logging, volumetric Nyquist frequency is proposed. Developing a geometric simulator for generating synthetic-logs of a single thin-bed enabled us analysing sensitivity of the well-logs to the presence of a thin-bed. Regression-based relations between ideal-logs (simulator inputs) and synthetic-logs (simulator outputs) are used as deconvolution relations for removing shoulder-bed effect of thin-beds from GR, RHOB and NPHI well-logs. NPHI deconvolution relation is applied to a real case where the core porosity of a thin-bed is 8.4%. The NPHI well-log is 3.8%, and the deconvolved NPHI is 11.7%. Since it is not reasonable that the core porosity (effective porosity) be higher than the NPHI (total porosity), the deconvolved NPHI is more accurate than the NPHI well-log. It reveals that the shoulder-bed effect is reduced in this case. The thickness of the same thin-bed was also estimated to be 13±7.5 cm, which is compatible with the thickness of the thin-bed in the core box (<25 cm). Usually, in situ thickness is less than the thickness of the core boxes, since at the earth surface, there is no overburden pressure, also the cores are weathered. Dempster-Shafer Theory (DST) was used to create well-log uncertainty range. While the VRmf of the well-logs is more than 60 cm, the VRmf of the belief and plausibility functions (boundaries of the uncertainty range) would be about 15 cm. So, the VRmf is improved, while the certainty of the well-log value is lost. In comparison with geometric method, DST-based algorithm resulted in a smaller uncertainty range of GR, RHOB and NPHI logs by 100%, 71% and 66%, respectively. In the next step, cluster analysis is applied to NPHI, RHOB and DT for the purpose of providing cluster-based uncertainty range. Then, NPHI is calibrated by core porosity value in each cluster, showing low √MSE compared to the five conventional porosity estimation models (at least 33% of improvement in √MSE). Then, fuzzy arithmetic is applied to calculate fuzzy numbers of irreducible water saturation and permeability. Fuzzy number of irreducible water saturation provides better (less overestimation) results than the crisp estimation. It is found that when the cluster interval of porosity is not compatible with the core porosity, the permeability fuzzy numbers are not valid, e.g. in well#4. Finally, in the possibilistic approach (the fuzzy theory), by calibrating α-cut, the right uncertainty interval could be achieved, concerning the scale of the study.

Predicting Attainable Goals and Depletion Timeframes for DNAPL Source Zones

Abstract: PREDICTING ATTAINABLE GOALS AND DEPLETION TIMEFRAMES FOR DNAPL SOURCE ZONES Grant R. Carey University of Guelph, 2015 Advisor: Professor Edward A. McBean The primary goal of this research was to develop and validate new statistical and process-based, screening-level modeling tools for estimating attainable goals and depletion timeframes for DNAPL source zones under a wide range of soil texture and other conditions. A process-based screening model (NAPL Depletion Model, or NDM) was developed to simulate the relative influence of surface discharge and through-discharge for one or more DNAPL sub-zones in an overall source zone. Empirical assessment of depletion rates at field sites are compared to model simulated results for pool-dominated source zones to provide insights on the influence of site complexity. Statistical analysis of empirical data for a similar site dataset defined the mean confidence interval for technology-specific, attainable mass discharge reduction. The lower end of this confidence interval is demonstrated to be applicable to complex sites. Empirical regression equations are derived for estimating the tortuosity coefficient based on either hydraulic conductivity or effective porosity, and for estimating total porosity and effective porosity based on hydraulic conductivity. An empirical regression equation is also developed for estimating transverse vertical dispersivity based on hydraulic conductivity, demonstrating that this relationship is inverse to what has been concluded in previous studies. An alternative model for simulating the decline in through-discharge for layers of residual DNAPL is presented, and is demonstrated to be more applicable to a broad range of conditions relative to previously developed regression equations. NDM was used to simulate complex multicomponent DNAPL dissolution trends based on a previously published study (Emplaced Source experiment in Borden, Ontario). Model results demonstrate the influence of re-equilibration and transient effective solubility in a multicomponent DNAPL source zone, on the overall through-discharge decline rate that was observed during the physical experiment. An empirical regression equation is developed for estimating the through-discharge decline rate for residual DNAPL layers over a broad range of conditions. This regression equation allows estimation of the decline rate a priori i.e. without fitting to site-specific data.