The impact of diagenesis on the reservoir quality of the early Cretaceous Lower Goru sandstones in the Lower Indus Basin, Pakistan

Qamar Uz Zaman Dar,Ghulam Shabeer,Renhai Pu,Rana Imran Ali,Mubashir Mehmood,Christopher Baiyegunhi,Umar Ashraf,Zulqarnain Sajid

doi:10.1007/s13202-021-01415-8

Abstract

AbstractThe sandstone units of the Early Cretaceous Lower Goru Formation are significant reservoir for gas, oil, and condensates in the Lower Indus Basin of Pakistan. Even though these sandstones are significant reservoir rocks for hydrocarbon exploration, the diagenetic controls on the reservoir properties of the sandstones are poorly documented. For effective exploration, production, and appraisal of a promising reservoir, the diagenesis and reservoir properties must be comprehensively analyzed first. For this study, core samples from depths of more than 3100 m from the KD-01 well within the central division of the basin have been studied. These sandstones were analyzed using petrographic, X-ray diffraction, and scanning electron microscopic analyses to unravel diagenetic impacts on reservoir properties of the sandstone. Medium to coarse-grained and well-sorted sandstone have been identified during petrographic study. The sandstone are categorized as arkose and lithic arkose. Principal diagenetic events which have resulted in changing the primary characters of the sandstones are compaction, cementation, dissolution, and mineral replacement. The observed diagenetic processes can be grouped into early, burial, and late diagenesis. Chlorite is the dominant diagenetic constituent that occurs as rims, coatings, and replacing grains. The early phase of coating of authigenic chlorite has preserved the primary porosity. The recrystallization of chlorite into chamosite has massively reduced the original pore space because of its bridging structure. The current study reveals that diagenetic processes have altered the original rock properties and reservoir characteristics of the Lower Goru sandstone. These preliminary outcomes of this study have great potential to improve the understanding of diagenetic process and their impact on reservoir properties of the Lower Goru sandstone in the Lower Indus Basin and adjoining areas.

Highlights

The effect of diagenesis and depositional environment on reservoir properties is significant in petroleum exploration (Morad et al 2010) because it will advocate the economic appraisals Ashraf et al 2016
Reservoir characteristics of the sandstone such as geometry, mineralogical composition, pore characteristics, porosity, permeability, textural framework, and maturity are evaluated by depositional settings of the sandstones, whereas the diagenesis may affect the reservoir porosity by post-depositional processes (Bjørlykke 2014; Cantarero et al 2020; Mangi et al 2020)
Lower Goru Formation of the Early Cretaceous consists of some sand units which are showing good characters of a reservoir, upper portion of the formation is comprised of siltstone, sandstone along with shale, in the basal portion some intercalated limestone and shale are present within the sandstone (Kadri 1995)

Summary

Introduction

The effect of diagenesis and depositional environment on reservoir properties is significant in petroleum exploration (Morad et al 2010) because it will advocate the economic appraisals Ashraf et al 2016. Baig et al (2016) investigated the Basal and Massive sand of the Lower Goru Formation and assess the diagenetic control on the reservoir properties of the sandstone they concluded that existence of abundant chlorite coats and low quartz cement are the main diagenetic reasons for the occurrence of high porosity in the massive and basal sands. A gap still exists between the reservoir characteristics and associated impacts on reservoir quality of the other sand units of the Lower Goru Formation because of the diagenesis of the Early Cretaceous Lower Goru sandstone reservoir in the area. Lower Goru Formation of the Early Cretaceous consists of some sand units which are showing good characters of a reservoir, upper portion of the formation is comprised of siltstone, sandstone along with shale, in the basal portion some intercalated limestone and shale are present within the sandstone (Kadri 1995). The stratigraphic section of exploration well KD-01 is shown in (Fig. 3)

Material and methods

Findings

Conclusions