Investigation of reservoir characteristics, depositional setting and T–R sequences of the Lockhart Limestone of Meyal Oil Field, Pakistan: a petrophysical approach

摘要

The present study is focused on formation evaluation of the Lockhart Limestone in two wells (Meyal-05P and Meyal-10P)located in Northern Deformed Potwar Zone of the Potwar sub-basin, Pakistan. The geological formations ranging fromTriassic to Pliocene have been drilled in these wells. The formation evaluation of the Lockhart Limestone mainly involvesreservoir potential evaluation, interpretation of depositional environment and transgressive–regressive sequences usingpetrophysical logs. In either wells, the reservoir characterization is steered by various petrophysical parameters includingcalculation of volume of shale, porosity, permeability and hydrocarbon saturation. The thickness of the Lockhart Limestoneis 50 m and 77 m in the Meyal-05P and Meyal-10P wells, respectively. In Meyal-05P and Meyal-10P wells, the averagepetrophysical parameters values and ranges are given as follows: volume of shale 48% and 20%; density porosity 1–5.6%and 1–31.7%; neutron porosity 1–23% and 1–42.9%; sonic porosity 1–29% and 1–39%; efective porosity < 1–> 5% and1–21%; and hydrocarbon saturation 92.21–99.8% and 97–99.6%. The petrophysical parameters indicate that the LockhartLimestone of Meyal-10P well is quantitatively better reservoir than that of the Meyal-05P. In Lockhart Limestone of eitherwells, the permeability is < 0.1 mD. The bulk volume water deciphered the presence of vuggy and intercrystalline porosityin the Lockhart Limestone. Similarly, the lithological interpretation using logs shows mainly limestone with minor shales.Diferent electrofacies are interpreted from the log trends of gamma ray log such as aggrading, prograding and retrogradingdepositional sequences deposited in tidal channel fll, shallow water, shore line and ofshore buildup and regressive-totransgressive shore face depositional setting.