RESERVOIR CHARACTERIZATION OF THIN BEDDED SANDS OF RANIKOT FORMATION VIA SOPHISTICATED GEOSTATISTICAL INVERSION OF MEHAR AREA, LOWER INDUS BASIN, PAKISTAN

Abstract

Reservoir characterization is crucial in the exploration and exploitation of hydrocarbon reserves. Effective assessment of reservoir characteristics is achievable using well log data. However, the well log data is restricted to a single dimension. This calls for the application of seismic data along with well log data for spatial characterization of reservoirs. Developing proper relation between the seismic and well log data therefore holds the key for precise delineation of reservoir properties. The study deals with characterization of reservoir of interest in Mehar gas field, Lower Indus Basin Pakistan, using Deterministic and Geostatistical inversion techniques along with petrophysical analysis. The area was analyzed while keeping in mind that the Ranikot Formation acts as a potential reservoir in this vicinity. 3D seismic data interpretation was carried out including horizons demarcation based on synthetic seismogram and observation ofregional structure analysis. Petrophysical analysis was performed using well log data of three wells namely; Mehar-l, Mehar-2 and Mehar-3 to identify the hydrocarbon-bearing zones. Thin layers of gas sands of Ranikot Formation have been evaluated via sophisticated seismic inversion techniques namely, Deterministic and Geostatistical inversion. The Deterministic teclmique namely Sparse Spike inversion has been applied which provides lateral continuity but lacks the vertical resolution required for del ineation of thin bedded sands. For that purpose, Geostatistical model based on Gaussian Simulation has been generated. Furthermore, spatial porosity distribution has been carried out using regression line equation from cross plot developed between effective porosity and impedance log. The seismic interpretation gives a clear subsurface image by showing an anticlinal structure having a fault in a NE-SW trending direction. Geologically, the presence of thrust fault in the study area confirms the compressional tectonic regime. The Petrophysical analysis depicts the presence of thin layered sands in the Lower Ranikot Formation. Sparse Spike inversion confirmed presence of laterally continuous low impedance sand layer within the Lower Ranikot Formation indicating potential hydrocarbon reservoir. Gaussian Simulation inversion further characterized the reservoir by confirming the presence of low impedance thin beds within the Lower Ranikot Formation. Spatial porosity distribution estimated for the zone of interest in Lower Ranikot Formation depicts high effective porosities particularly in the region surrounding the wells.