Reducing uncertainty with fault seal analysis: A case study of Jherruck Block, Lower Indus Basin, Pakistan

Authors: MUDASSAR NAWAZ, MUHAMMAD RUSTAM KHAN, UMAIR BIN NISAR, MUHAMMAD RIZWAN MUGHAL

Abstract: Faults can be either conduits or baffles for hydrocarbon flow. Assessing the sealing potential of faults plays a vital role in reducing the risks associated with hydrocarbon exploration. The study area is located in Jherruck Block, Lower Indus Basin, Pakistan. Several intervals within the Lower Goru Formation in Lower Indus Basin are proven hydrocarbon reservoirs. The main aim of the study is to predict the cause of failure of 3 wells (Jherruck B-1, Jamali-1, and Jamali Deep-1), and to propose a new well location based on juxtaposition analysis and shale gouge ratio (SGR). The Upper Sands (sandstone) of the Lower Goru Formation (A-Sand, B-Sand, C-Sand, and D-Sand) have reservoir potential in the region including the Jherruck Block. These reservoir sands have been interpreted in seismic sections to generate time and depth surface maps. Using depth surface maps, Allan diagrams have been constructed for juxtaposition and shale gouge ratio analysis. The integration between juxtaposition and shale gouge ratio analysis suggested that the main reason for the failure of these wells was sandstone to sandstone juxtapositions leading to updip hydrocarbon leakage to the adjacent fault block. In addition to this, the shale gouge ratio indicated low shale gouge distribution in the fault zones. Allan diagram and shale gouge ratio analyses helped us to propose a new well location further northwest of Jherruck B-1 well where sands are juxtaposed against impermeable shale lithology of the Goru Formation and SGR ratio is above 80%.

Keywords: Horst and graben, Lower Goru Formation, well failure, fault seal analysis, juxtaposition diagram, shale gouge ratio

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