Quantitative assessment of the petroleum generation potential of early Cretaceous source rock in the northern part of Mari-Kandhkot High, north Sindh and southern Punjab, Pakistan
Abstract
ABSTRACT
A source rock study and thorough petroleum system modelling have been performed as part of an exploration evaluation programme in one of the blocks in the northern part of the Mari-Kandhkot High (northern Sindh and southern Punjab) to determine the potential of Early Cretaceous sources and evaluate petroleum generated volumes in cubic feet gas per sq. km. The primary source rock in this region are the shales of the Early Cretaceous Sembar Formation (BerriasianValanginian, 145-132 Ma), while the Lower Goru Formation (Albian-Aptian, 125-113 Ma) shales can be considered the second most efficient source due to their high organic content.
Our study database involved 10 wells in the study area, where detailed source rock analyses were carried out on 106 samples in the Maluk -1, POGC Sabzal X-1, and Sara -1 wells, and the Total Organic Carbon (TOC) on seven additional wells was calculated through the Δlog R method. Study has determined, the mixed Type-II and Type-III kerogen, the TOC in the Sembar Formation ranges from 0.06% to 2.15%, with an average of 1.0%, and vitrinite reflectance (Ro) ranges from 0.7% to 1.95%. As a secondary source rock in the region, the Lower Goru Formation primarily contains Type-III organic matter, with TOC averaging 0.9% and Ro ranging from 0.80% to 1.45%. Depending on the quantity and quality of organic matter, oil generation depth ranges from 2200 to 2700 metres at temperatures between 100⁰ and 125⁰ C, whereas the minimum depth at which gas generation begins is 3000 metres at a temperature of approximately 125⁰C.
According to the results of the petroleum system modelling, the first hydrocarbon generation reached maturity at 53 Ma and peaked at 25 Ma, with a potential to generate 60–80 bcf/sq km of gas.
In our paper, we discussed the results of the organic geochemical analysis of the Lower Goru and Sembar formations from the Early Cretaceous, and we presented maps of the thickness of the organically rich layers, the distribution of thermally mature areas, and the intensity of hydrocarbon expulsion. These maps may offer future operators interested in exploring the area substantial data by supporting them understand the geological history of a source rock.
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