An integrated analysis of mineralogical and microstructural characteristics and petrophysical properties of carbonate rocks in the lower Indus Basin, Pakistan

Abstract

Carbonate rocks are believed to be proven hydrocarbon reservoirs and are found in various basins of Pakistan including Lower Indus Basin. The carbonate rock intervals of the Jakkher Group from Paleocene to Oligocene age are distributed in south-western part of Lower Indus Basin of Pakistan. However, there are limited published petrophysical data sets on these carbonate rocks and are essential for field development and risk reduction. To fill this knowledge gap, this study is mainly established to collect the comprehensive high quality data sets on petrophysical properties of carbonate rocks along with their mineralogy and microstructure. Additionally, the study assesses the impact of diagenesis on quality of the unconventional tight carbonate resources. Experimental techniques include Scanning Electronic Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and X-ray diffraction (XRD), photomicrography, Helium porosity and steady state gas permeability. Results revealed that the porosity was in range of 2.12 to 8.5% with an average value of 4.5% and the permeability was ranging from 0.013 to 5.8mD. Thin section study, SEM-EDS, and XRD analyses revealed that the samples mostly contain carbon (C), calcium (Ca), and magnesium (Mg) as dominant elemental components.The main carbonate components observed were calcite, dolomite, micrite, Ferron mud, bioclasts and intermixes of clay minerals and cementing materials. The analysis shows that: 1) the permeability and porosity cross plot, the permeability and slippage factor values cross plots appears to be scattered, which showed weaker correlation that was the reflection of carbonate rock heterogeneity. 2) The permeability and clay mineralogy cross plots have resulted in poor correlation in these carbonate samples. 3) Several diagenetic processes had influenced the quality of carbonates of Jakkher Group, such as pore dissolution, calcification, cementation, and compaction. 4) Reservoir quality was mainly affected by inter-mixing of clay, cementation, presence of micrite muds, grain compactions, and overburden stresses that all lead these carbonate reservoirs to ultra-tight reservoirs and are considered to be of very poor quality. 5) SEM and thin section observations shows incidence of micro-fractures and pore dissolution tended to improve reservoir quality.

Unveiling the Diagenetic and Mineralogical Impact on the Carbonate Formation of the Indus Basin, Pakistan: Implications for Reservoir Characterization and Quality Assessment

“…Stress sensitivity was also conducted to assess the impact of stress on the carbonate rock permeability and pore throat structure under various stress conditions. The net stress is described by Equation ( 6) [28]:…”

“…The variations in the slippage parameters and permeability may be attributed to the heterogeneity in the carbonate rocks and nonuniform pore sizes in the samples under study. Consequently, it is evident that the permeability results could not be reliably calculated using the available empirical correlations, as the carbonate rocks exhibited significant heterogeneity and a variety of pore geometries [28]. The slippage effect in a conventional reservoir core is negligible due to the larger pore radius, and the gas slip factor becomes close to zero.…”

“…In carbonate formations, the impact of pore sensitivity becomes even more pronounced when compared to clastic sand stones. This heightened sensitivity is due to their complex lithofacies and diagenetic processes, which tend to affect the reservoir quality and recovery efficiency [28,29]. Stress sensitivity is often overlooked during reservoir characterization, leading to severe complexities in interpretation, estimation, modeling, and development.…”

Quantitative characterization of the carbonate rock microstructure considering topological features: a case study from the Gaoshiti–Moxi block of the Sichuan Basin

“…The microstructure characterization of subsurface systems is crucial for determining the permeable regions, petrophysical properties, and associated reservoir quality (Tahmasebi, 2017;Dong et al, 2023). These microstructural petrophysical properties of the rocks control the macroscopic properties and flow behavior (Daigle et al, 2017;Fagbemi et al, 2018;Tahmasebi and Kamrava, 2018), which include the topological and geometrical characteristics (Dong et al, 2017;Abro et al, 2019). In this context, carbonate rocks offer a relatively complex microstructure, which is attributed to a range of factors, including but not limited to multimodal pore radius distribution (e.g., micro-porosity and vugs) and mineral heterogeneity (e.g., the classic case of the Arab-D reservoir, where dolomitization leads to massive heterogeneous lithologies) (Arif et al, 2020;Chandra et al, 2021;Li et al, 2022).…”

Wettability Alteration of Limestone Carbonate Cores Using Methylene Blue and Alumina-Based Nanofluid: Implications for EOR

“…Fossil fuels are a significant contributor to the world energy demand [1][2][3][4][5]. It is reported that carbonate reservoir rock formations exhibit a high volume of about 60% of all the global reserves.…”