Showing papers on "Effective porosity published in 2019"

Application of well log analysis to estimate the petrophysical parameters and evaluate the reservoir quality of the Lower Goru Formation, Lower Indus Basin, Pakistan

Abstract: The present study deals with the petrophysical evaluation using well log data of Lower Goru Formation from five selected wells namely Nara-1, Kadanwari-3, Kadanwari-4, Gajwaro-1 and Mehrab-1 in the Lower Indus Basin. Various cross plots indicate that the formation of interest is mainly composed of sandstone, shale and carbonates. In addition, clay content is also analysed using potassium versus thorium and PEF versus Th/K ratio plots. Interactive Petrophysics (IP-2013) software is used to assess the petrophysical parameters. The volume of shale has been estimated between 6.1% and 14.07% from the studied wells. Similarly, the total porosity is observed between 14.6% and 18.02% while the effective porosity ranges 12.5–16.5%. The water saturation is quite low and exhibits between 14.05% and 31.58%. Moreover, the hydrocarbon saturation ranges 68.42–85.95% in the studied wells. 23 pay zones of variable thickness and significant hydrocarbons presence have been identified within the studied wells, thus proving the Lower Goru Formation as a promising reservoir. The study also indicates Nara-1 Well as the most prolific in terms of high hydrocarbon saturation and low water saturation. The study method can be used within the vicinity of Lower Indus Basin and similar basin elsewhere in the globe to quantify petrophysical properties of oil and gas wells and comprehend the reservoir potential.

Comparative Porosity and Pore Structure Assessment in Shales: Measurement Techniques, Influencing Factors and Implications for Reservoir Characterization

Abstract: Porosity and pore size distribution (PSD) are essential petrophysical parameters controlling permeability and storage capacity in shale gas reservoirs. Various techniques to assess pore structure have been introduced; nevertheless, discrepancies and inconsistencies exist between each of them. This study compares the porosity and PSD in two different shale formations, i.e., the clay-rich Permian Carynginia Formation in the Perth Basin, Western Australia, and the clay-poor Monterey Formation in San Joaquin Basin, USA. Porosity and PSD have been interpreted based on nuclear magnetic resonance (NMR), low-pressure N2 gas adsorption (LP-N2-GA), mercury intrusion capillary pressure (MICP) and helium expansion porosimetry. The results highlight NMR with the advantage of detecting the full-scaled size of pores that are not accessible by MICP, and the ineffective/closed pores occupied by clay bound water (CBW) that are not approachable by other penetration techniques (e.g., helium expansion, low-pressure gas adsorption and MICP). The NMR porosity is largely discrepant with the helium porosity and the MICP porosity in clay-rich Carynginia shales, but a high consistency is displayed in clay-poor Monterey shales, implying the impact of clay contents on the distinction of shale pore structure interpretations between different measurements. Further, the CBW, which is calculated by subtracting the measured effective porosity from total porosity, presents a good linear correlation with the clay content (R2 = 0.76), implying that our correlated equation is adaptable to estimate the CBW in shale formations with the dominant clay type of illite.

Prediction of contaminant transport in fractured carbonate aquifer types: a case study of the Permian Magnesian Limestone Group (NE England, UK)

Abstract: Viruses and bacteria which are characterized by finite lives in the subsurface are rapidly transported via fractures and cavities in fractured and karst aquifers. Here, we demonstrate how the coupling of a robust outcrop characterization and hydrogeophysical borehole testing is essential for prediction of contaminant velocities and hence wellhead protection areas. To show this, we use the dolostones of the Permian Magnesian Limestone aquifer in NE England, where we incorporated such information in a groundwater flow and particle tracking model. Within this aquifer, flow in relatively narrow (mechanical aperture of ~ 10−1–1 mm) fractures is coupled with that in pipe cavities (~ 0.20-m diameter) following normal faults. Karstic cavities and narrow fractures are hydraulically very different. Thus, the solutional features are represented within the model by a pipe network (which accounts for turbulence) embedded within an equivalent porous medium representing Darcian flowing fractures. Incorporation of fault conduits in a groundwater model shows that they strongly influence particle tracking results. Despite this, away from faulted areas, the effective flow porosity of the equivalent porous medium remains a crucial parameter. Here, we recommend as most appropriate a relatively low value of effective porosity (of 2.8 × 10−4) based on borehole hydrogeophysical testing. This contrasts with earlier studies using particle tracking analyses on analogous carbonate aquifers, which used much higher values of effective porosity, typically ~ 102 times higher than our value, resulting in highly non-conservative estimates of aquifer vulnerability. Low values of effective flow porosities yield modelled flow velocities ranging from ~ 100 up to ~ 500 m/day in un-faulted areas. However, the high fracturing density and presence of karstic cavities yield modelled flow velocities up to ~ 9000 m/day in fault zones. The combination of such flow velocities along particle traces results in 400-day particle traces up to 8-km length, implying the need for large well protection areas and high aquifer vulnerability to slowly degrading contaminants.

Structural characteristics and hydraulic conductivity of an eluvial-colluvial gravelly soil

Abstract: Gravelly soil is a typical heterogeneous porous medium with a multiscale structure and hydraulic conductivity that is challenging to quantify. The aim of this study is to examine the structure of an eluvial-colluvial gravelly soil at different scales and link the structural characteristics to the hydraulic conductivity. To this end, large gravelly soil samples and small fines-sand mixture samples were prepared and then characterized by X-ray computed tomography (CT) and optical microscopy, respectively. Through image analyses, the pore structural characteristics at the gravel scale (≥ 1.0 mm) and sand scale (0.01–1.0 mm) were identified. Constant-head tests were performed on the large gravelly soil samples to measure the saturated coefficients of permeability (k). The results show a relatively small gravel-scale porosity and a large sand-scale porosity in compacted gravelly soils. The dominant sizes of gravel-scale pores and sand-scale pores are several millimeters and approximately 0.06 mm, respectively. An evaluation of ten existing permeability equations indicates that most of the previous empirical equations proposed for sand and gravel are not applicable to well-graded gravelly soils. For this reason, the existing permeability equations were improved. In addition, novel empirical equations for estimating the k value of gravelly soils were proposed based on the structural parameters of pores, as well as the concepts of the effective porosity and the effective grain size.

A Modified Approach for Volumetric Evaluation of Shaly Sand Formations from Conventional Well Logs: A Case Study from the Talhar Shale, Pakistan

Abstract: In potential shale-gas basins, due to limited data availability, volumetric evaluation of shaly sand formations is a challenging task for researchers, as well as for exploration and production companies, with the use of conventional well logs. This paper is intended to provide a better understanding of volumetric evaluation in unconventional shaly sand formations. Petrophysical parameters derived from conventional well logs play a significant role in the volumetric estimation of shale. The assessment was performed using numerical equations, well log indexes, and cross-plot analysis. Deep and shallow resistivity logs overlap with each other; this phenomenon indicates that the Talhar Shale in Pakistan can be considered to be an unconventional formation. The average values of shale volume, total porosity, effective porosity, and matrix volume are 29, 16, 12, and 59%, respectively. The Talhar Shale is dominantly characterized by intergranular porosity. It has been observed that at low shale volumes (10–20%), porosities (total and effective), and resistivity measurements (deep, shallow, and microlaterolog), well log signatures have close contents with the shale volume. In contrast, for the remainder of the shale volume, there is significant separation of log signatures. Well log indexes indicate significant responses in 10–20% shale volume zones.

A Multiscale Fractal Transport Model with Multilayer Sorption and Effective Porosity Effects

Abstract: In order to study gas transport properties of fractured shale gas reservoirs for the accurate estimation of shale gas production, a new multiscale fractal transport model with an effective porosity model was proposed based on the fractal theory and the multilayer fractal Frenkel–Halsey–Hill (FHH) adsorption. In shale matrix, both fractal microstructures of pores (such as pore size distribution, flow path tortuosity, and pore surface roughness) and multiscale flow mechanisms (including slip flow and Knudsen diffusion) were coupled. In fracture network, fractal fracture length distribution, stress compaction, and gas pressure were introduced to formulate a new fracture permeability model. These permeability and effective porosity models were then incorporated into the governing equations of gas flow and the deformation equation of reservoirs to form a numerical model. This numerical model was solved within COMSOL Multiphysics for shale gas recovery. Both transport models in shalematrix and fracture network were validated by experimental data or compared with other models. Finally, sensitivity analysiswas conducted to identify key parameters to gas recovery enhancement. Itwas found that themultilayer gas adsorption and fractal microstructures have great impacts on gas production in shale reservoirs. The cumulative gas production can be increased by 26% after 8000 days when themultilayer adsorbed gas is considered. Larger surface fractal dimension and larger tortuosity fractal dimension represent more roughness pore surface, higher flow resistance, and lower cumulative gas production. Bigger pore diameter fractal dimension means more pores, higher permeability, and higher cumulative gas production. Our model with fractal FHH adsorption was in better agreements with field data from Marcellus and Barnett shale reservoirs than other models.

Evolution Model of Seepage Characteristics in the Process of Water Inrush in Faults

Abstract: Although the mechanism and influence of fault water inrush have been widely studied, there are still few studies on the migration of filling particles and the evolution process of seepage characteristics within faults. In this work, the coupling effects of water flow, particle migration, and permeability evolution are considered synthetically, and the evolution model of seepage characteristics with multifield coupling is established. This model was used to investigate the evolution process of water inrush within faults and the effects of water pressure, initial effective porosity, and initial permeability on water flow rate. The results show that the evolution of seepage characteristics can be divided into three phases: (i) low velocity seepage, (ii) drastic changes with substantial particle migration, and (iii) steady-state water flow. The multifield coupling causes the effective porosity, permeability, flow velocity, and particle concentration to accelerate each other during the dramatic phase. Moreover, the increases in initial water pressure, initial porosity, and initial permeability have different degrees of promotion on the water flow rate. Finally, the simulation results are approximately the same as the data of water inrush in the mining area, which verifies the correctness of the evolution model established in this work. This work provides new approaches to the evolution process and prevention of water inrush in faults.

Revisiting the methods for gas permeability measurement in tight porous medium

Abstract: Permeability is a key parameter to describe fluid transport properties of porous medium; however, the permeability measurement is extremely difficult for tight porous medium, e.g. fine-grained rock or dense soil. In this paper, three methods for gas permeability measurement, i.e. steady state method, pulse decay method (PDM) and pressure oscillation method (POM), are first reviewed and then their advantages and drawbacks are discussed. Both analytical and numerical solutions of gas permeability are presented for the tight porous medium. The results show that the analytical method is relatively simple but only valid under certain conditions, whilst the numerical method is more robust and generic, which can take into account several factors such as porosity, saturation, gas leakage, and unconventional boundary conditions. The influence of the effective porosity on the permeability determination is further analyzed using the proposed numerical method. In this study, new pressure data interpretation procedures for PDM and POM are proposed, and the obtained results can serve as a guidance to define a proper method for permeability measurement of the tight porous medium.

Petrophysical analysis of well logs for reservoir evaluation: a case study of “Kadanwari” gas field, middle Indus basin, Pakistan

Abstract: Our study focuses on the interpretation of wire-line logs to evaluate the hydrocarbons potential of sandstone reservoir in the Kadanwari gas field, Sindh, Pakistan. We have considered wire-line logs of four drilled wells (K-01, K-03, K-10, and K-11) in the research area and interpreted 13 reservoir zones. Analytical reservoir analysis includes the shale content (Vsh), effective porosity (Oeff), hydrocarbon and water saturation (Shc and Sw), and net pay thickness variations. Hydrocarbon-bearing zone characterized by high resistivity values, porosity high, permeability high, saturation of water low, and less Vsh suggest clean sand. The petrophysical analysis revealed the hydrocarbon potential of lower Goru sandstone packages at different levels (2886–3797 m). The petrophysical parameters of sub-reservoirs were carefully analyzed which are ranked as good quality sand reservoirs with average effective porosities ranging from 0.11–0.44%, average water saturation ranging from 0.18–0.45%, hydrocarbon saturation averaging between 0.59–0.86%, and permeability ranging from 10.539 to 477.76 m Darcy. Water saturation for heterogeneous shaly sand reservoirs was successfully tested by Indonesian model which suggests that Sw in each well is fewer than 60% therefore over all the region bearing good quality of hydrocarbon potential of the targeted formation and selected zones. The vertical and horizontal variations of reservoir parameters are studied through constructing the litho-saturation cross-plots and isoparametric maps of the petrophysical parameters, respectively. The isoparametric maps help to visualize the geographical distribution of reservoir configuration in the subsurface. The petrophysical estimates of this study appraise the national conventional fuel treasure of lower Goru formation in Kadanwari gas fields and suggest new prospects to drill more wells on the central portion of the southwestern part of the study area. The neighboring area to the south of Kadanwari-01 is economically viable for hydrocarbon exploration. The northeastern side of the study area is avoided due to the high concentration of water and excessive shale content.

Quantification of macropores of Malan loess and the hydraulic significance on slope stability by X-ray computed tomography

Abstract: The accurate identification and quantitative characterization of loess structural properties at the pore scale are important in the study of macroscopic permeability. To characterise the macropore structure of Malan loess systematically, a non-destructive detecting method, that is, X-ray computed tomography (CT), was adopted for scanning five undisturbed specimens. A series of processing steps, including image filtering by a novel compositing image filter, image segmentation with the effective combination of threshold and top hat method, and three-dimensional (3D) reconstruction and visualisation by marching cube algorithm and volume-rendering technique were finished in AVIZO® software to acquire the 3D pore network model and to extract the two-dimensional (2D) and 3D structural parameters, such as porosity, equal diameter, aspect ratio, shape factor (SF), node density, number of terminal and branching nodes, coordinate number, dip angle, dip direction angle and tortuosity. Results show that (1) Malan loess is a kind of porous geological material with strong verticality and spatial anisotropy reflected by the 2D parameters including porosity, equal diameters and aspect ratio as well as the 3D dip angle and 3D-visualised loess macropores; (2) Malan loess has higher permeability in the vertical direction than that in the horizontal direction so that prone to induce excessive infiltration and preferential flow, thereby threatening the loess slope stability; (3) SF is an effective parameter for pore classification in both 2D and 3D scales; (4) the macropores with a large diameter have a larger volume fraction, better connectivity (effective porosity) and greater contribution to water permeability; (5) the larger the coordinate number, the greater the hydraulic conductivity, nevertheless other than the aggregates for the water repellency caused by organic matter. In conclusion, the combination of CT and AVIZO® is excellent for quantifying the key macropore structural parameters (e.g., shape factor and tortuosity) and their hydraulic significance on slope stability.

Geohydrodynamic Parameters and Their Implications on the Coastal Conservation: A Case Study of Abak Local Government Area (LGA), Akwa Ibom State, Southern Nigeria

Abstract: A total of 14 vertical electrical soundings using Schlumberger electrode configuration and the complementary laboratory analysis of aquifer samples were carried out in the Abak Local Government Area of Akwa Ibom State, the coastal region of Nigeria. The study focused on the estimation of geohydrodynamic parameters of the frequently exploited aquifers and the implication of hydrodynamic parameters on the lithostratigraphy and the anticipated exposure of the assessed geologic formation at the shorelines. These parameters were porosity (ϕ), tortuosity (τ), formation factor (F), aquifer water formation resistivity (Rw) and coefficient of permeability/hydraulic conductivity (K). Computation of the effective porosities from the aquifer cuttings was carried out using wet weight–dry weight technique and petrophysical techniques. The F values were computed using the aquifer formation bulk resistivity measured from field 1-D resistivity data analysis, whose interpretation was constrained by nearby borehole information. The formation pore water resistivities were estimated from the laboratory using electrical resistivity metre. The Win RESIST software program was used in interpreting the field data electronically. The results of interpretation gave the primary parameters of saturated and unsaturated units of the coastal regions used in this work. The area generally shows seemingly high porosity with high coefficient of permeability. The primary and secondary parameters have been contoured to model their distributions. Besides, some functional relations have been realized through regression analyses. The contour distribution of the geohydrodynamic parameters indicates the vulnerability of the water repositories to contaminations as well as the vulnerability of the shoreline to waterborne erosion. The seemingly high effective porosity in the compliant laboratory and calculated values indicate that the coastal region is neither lithified nor compacted/consolidated. This signals the possibility of the formation to be easily eroded, weathered or flooded where these units are exposed to water current. With these revelations, the shorelines could be properly managed and conserved by geotechnically reinforcing with hard and water-resistant concrete that can protect the vulnerable and erosion-prone porous sediments.

Characterization of the coal pore system by resistivity and NMR methods

Abstract: The development of the coal pore system is extremely significant for gas disaster prevention in coal mines and coalbed methane exploitation. To accurately, quantifiable, and non-destructively chara...

Investigation of reservoir characteristics, depositional setting and T–R sequences of the Lockhart Limestone of Meyal Oil Field, Pakistan: a petrophysical approach

Abstract: The present study is focused on formation evaluation of the Lockhart Limestone in two wells (Meyal-05P and Meyal-10P) located in Northern Deformed Potwar Zone of the Potwar sub-basin, Pakistan. The geological formations ranging from Triassic to Pliocene have been drilled in these wells. The formation evaluation of the Lockhart Limestone mainly involves reservoir potential evaluation, interpretation of depositional environment and transgressive–regressive sequences using petrophysical logs. In either wells, the reservoir characterization is steered by various petrophysical parameters including calculation of volume of shale, porosity, permeability and hydrocarbon saturation. The thickness of the Lockhart Limestone is 50 m and 77 m in the Meyal-05P and Meyal-10P wells, respectively. In Meyal-05P and Meyal-10P wells, the average petrophysical parameters values and ranges are given as follows: volume of shale 48% and 20%; density porosity 1–5.6% and 1–31.7%; neutron porosity 1–23% and 1–42.9%; sonic porosity 1–29% and 1–39%; effective porosity 5% and 1–21%; and hydrocarbon saturation 92.21–99.8% and 97–99.6%. The petrophysical parameters indicate that the Lockhart Limestone of Meyal-10P well is quantitatively better reservoir than that of the Meyal-05P. In Lockhart Limestone of either wells, the permeability is < 0.1 mD. The bulk volume water deciphered the presence of vuggy and intercrystalline porosity in the Lockhart Limestone. Similarly, the lithological interpretation using logs shows mainly limestone with minor shales. Different electrofacies are interpreted from the log trends of gamma ray log such as aggrading, prograding and retrograding depositional sequences deposited in tidal channel fill, shallow water, shore line and offshore buildup and regressive-to-transgressive shore face depositional setting.