Smectite illitization of the Talhar shale, Lower Goru Formation, Southern Indus Basin, Pakistan

Subsurface samples of the Talhar shale, Lower Goru Formation, are analyzed for smectite (montmorillonite) and illite in the Nur-dep#1 (ND‒1), well 2, Southern Lower Indus Basin, Pakistan. The ND‒1, well 2 is an unsuccessful well drilled by the OGDCL, Pakistan, for the shale gas exploration. Illitization and elemental content constrained using XRD qualitative and XRF quantitative analyses, respectively. The illite content increases from 15 to 55% with increasing depth. The fine-grained shale comprises chlorite, kaolinite, halloysite, allophane, muscovite, microcline, illite and montmorillonite. Chlorite was observed at 3450–3452 m, whereas kaolinite is present at depth range of 3450–3482 m. The mix layer expandability decreases from 40 to 20% at depth ranges from 3450 to 3552 m, respectively. The interstratification is random to ordered. Potassium and silicon contents with respect to aluminum and calcium are increasing with depth. Data obtained in this research indicate that the shale gas is immature and the oil is an early–medium stage of maturation.

Predicting the gas resource potential in reservoir C-sand interval of Lower Goru Formation, Middle Indus Basin, Pakistan

The integrated study of seismic attributes and inversion analysis can provide a better understanding for predicting the hydrocarbon-bearing zones even in extreme heterogeneous reservoirs. This study aims to delineate and characterize the gas saturated zone within the reservoir (Cretaceous C-sand) interval of Sawan gas field, Middle Indus Basin, Pakistan. The hydrocarbon bearing zone is well identified through the seismic attribute analysis along a sand channel. The sparse-spike inversion analysis has efficiently captured the variations in reservoir parameter (P-impedance) for gas prospect. Inversion results indicated that the relatively lower P-impedance values are encountered along the predicted sand channel. To further characterize the reservoir, geostatistical techniques comprising multiattribute regression and probabilistic neural network (PNN) analysis are applied to predict the effective porosity of reservoir. Comparatively, the PNN analysis predicted the targeted property more efficiently and applied its estimations on entire seismic volume. Furthermore, the geostatistical estimations of PNN analysis significantly predicted the gas-bearing zones and confirmed the sand channel as a major contributor of gas accumulation in the area. These estimates are in appropriate agreement with each other, and the workflow adopted here can be applied to various South Asian regions and in other parts of the world for improved characterization of gas reservoirs.

Effects of Diagenesis on the Reservoir Quality in the Upper Sands of Lower Goru Formation, Badin Block, Lower Indus Basin, Pakistan

The core samples of B member of upper sand reservoir rocks of the lower Goru Formation from three wellsof the Badin block were studied using thin section, XRD, and SEM techniques to investigate the diagenetic trends andtheir effect on reservoir quality. Microscopic study indicates that the B sand unit is mature with quartz as thepredominant mineral constituent with variable amount of feldspar and lithic minerals. The QFL plot indicates that mostof the samples are plotted in the field of quartz arenite, sub-litharenite and sub-arkose respectively. A few samplesbelong to the category of litharenite and feldspathic litharenite. The feldspars were partially to completely altered tokaolinite and other clay minerals. Coarse-crystalline or micro-crystalline calcite is the predominant cementing material.Bulk rock XRD analysis also confirms that the main mineral constituents of there samples are quartz and calcite invariable proportions. The undulose extinction and fracturing of quartz grains indicate that the area remained understress. Moreover, such fracturing is post-depositional and therefore is the product of late diagenesis. Scanning ElectronMicroscopic (SEM) images at 50 micrometer (μm) size show irregular type of fracturing within the quartz grains. Thislate stage fracturing of quartz has also generated various types of channels which may serve as secondary porosity. Thequartz overgrowth was observed in some samples due to late stage diagenesis. The micro-crystalline cement in the formof calcite is mostly present within the pores in fractured quartz. The results indicate that the diagenesis played asignificant role in improving the reservoir characteristics of B sand by increasing the porosity due to quartz fracturing,feldspar dissolution, alteration and quartz corrosion. Hence, better understanding of reservoir heterogeneities inporosity through diagenetic studies can be helpful in evaluating potential reservoir horizons for hydrocarbonaccumulation on spatial and temporal scales.

WELL LOGS ANALYSIS TO ESTIMATE THE PARAMETERS OF SAWAN-2 AND SAWAN-3 GAS FIELD

The lower Indus basin is leading hydrocarbon carriage sedimentary basin in Pakistan. Evaluation of two sorts out wells namely Sawan-2 and Sawan-3 has been assumed in this work for estimation and dispensation of petro physical framework using well log data. The systematic formation assessment by using petro physical studies and neutron density cross plots reveal that lithofacies mainly composed of sandstone. The hydrocarbon capability of the formation zone have been mark through several isometric maps such as water saturation, picket plots, cross plots, log analysis Phie vs depth and composite log analysis. The estimated petro physical properties shows that reservoir have volume of shale 6.1% and 14.0%, total porosity is observed between 14.6% and 18.2%, effective porosity ranges 12.5-16.5%, water saturation exhibits between 14.05% and 31.58%, hydrocarbon saturation ranges 68.42% -86.9%, The lithology of lower goru formation is dominated by very fine to fine and silty sandstone. The study method can be use within the vicinity of central Indus basin and similar basin elsewhere in the globe to quantify petro physical properties of oil and gas wells and comprehend the reservoir potential.

Evaluation of Gas Potential in Early Cretaceous Shale Lower Indus Basin, Pakistan

The shale gas potential of the early Cretaceous Talhar shale member of the lower Goru Formation in lower Indus basin of Sanghar district, Sindh province, has been evaluated using 2D seismic and well logs data. Graphical and empirical techniques were applied to calculate various geochemical parameters for the evaluation of shale plays. Total Organic Carbon (TOC) is calculated by Passey's (∆LogR) Overlay technique and its values are about 2.44 wt.%. Vitrinite Reflectance (Ro) is estimated by graphical and empirical relation and the value lies between 0.95-1.0 which implies that the Talhar shale member is in peak oil and initial gas generation phase. Log-derived Maturity Index (LMI) is calculated by NPHI, RHOB or density log and uranium logs. The average value is about 0.55 which reflects that the formation is probably in the initial maturation phase. Kerogen Volume (Vk) is estimated by empirical relation using RHOB log as input and it is about 13 wt. % which reflects that the formation has enough potential of oil/gas expulsion. The results are compared and validated with a study of the adjacent field of the same basin. This study reveals that Talhar member of lower Goru Formation could be the future probable potential unconventional reservoir for exploration in lower Indus basin of Pakistan.

Evaluation of Gas Potential in Early Cretaceous Shale Lower Indus Basin, Pakistan

The shale gas potential of the early Cretaceous Talhar shale member of the lower Goru Formation in lower Indus basin of Sanghar district, Sindh province, has been evaluated using 2D seismic and well logs data. Graphical and empirical techniques were applied to calculate various geochemical parameters for the evaluation of shale plays. Total Organic Carbon (TOC) is calculated by Passey's (∆LogR) Overlay technique and its values are about 2.44 wt.%. Vitrinite Reflectance (Ro) is estimated by graphical and empirical relation and the value lies between 0.95-1.0 which implies that the Talhar shale member is in peak oil and initial gas generation phase. Log-derived Maturity Index (LMI) is calculated by NPHI, RHOB or density log and uranium logs. The average value is about 0.55 which reflects that the formation is probably in the initial maturation phase. Kerogen Volume (Vk) is estimated by empirical relation using RHOB log as input and it is about 13 wt. % which reflects that the formation has enough potential of oil/gas expulsion. The results are compared and validated with a study of the adjacent field of the same basin. This study reveals that Talhar member of lower Goru Formation could be the future probable potential unconventional reservoir for exploration in lower Indus basin of Pakistan.

Evaluation of Gas Potential in Early Cretaceous Shale Lower Indus Basin, Pakistan

The shale gas potential of the early Cretaceous Talhar shale member of the lower Goru Formation in lower Indus basin of Sanghar district, Sindh province, has been evaluated using 2D seismic and well logs data. Graphical and empirical techniques were applied to calculate various geochemical parameters for the evaluation of shale plays. Total Organic Carbon (TOC) is calculated by Passey's (∆LogR) Overlay technique and its values are about 2.44 wt.%. Vitrinite Reflectance (Ro) is estimated by graphical and empirical relation and the value lies between 0.95-1.0 which implies that the Talhar shale member is in peak oil and initial gas generation phase. Log-derived Maturity Index (LMI) is calculated by NPHI, RHOB or density log and uranium logs. The average value is about 0.55 which reflects that the formation is probably in the initial maturation phase. Kerogen Volume (Vk) is estimated by empirical relation using RHOB log as input and it is about 13 wt. % which reflects that the formation has enough potential of oil/gas expulsion. The results are compared and validated with a study of the adjacent field of the same basin. This study reveals that Talhar member of lower Goru Formation could be the future probable potential unconventional reservoir for exploration in lower Indus basin of Pakistan.