Seismic Sequence Stratigraphic, Pock Physical and Petrophysical Analysis for Reservoir Characterization in Sawan Area of Middle Indus Basin, Sindh, Pakistan

Abstract

This research represents the subsurface structural and stratigraphic evaluation of the Upper Jurassic to Lower Cretaceous Sembar and Goru formations in study area of the Middle indus platform. This evaluation is based on the eight 2D seismic line data integrated with three wells (A, B & C) Thorough regional geological and petroleum geological aspects of the study area are reviewed. Acquisition and processing parameters of the seismic data are discussed. Six horizons (Top Sui Main Limestone (SML), Top Upper Goru (TUG), Top Lower Goru (TLG), C-Sand Interval, B-Sand Interval and Chiltan Formations) are picked and their TWT maps are prepared. Depth conversion is done by T-D chart data. Amplitude and Isochrone are also prepared for selected horizons. Strike-slip fault pattern with horst and graben features are interpreted. Some of the blocks may be interpreted as tilted fault blocks. Structurally the study area lies within a depression while the adjoining areas in the east and west are uplifted. On the suitable selected seismic sections, the Sembar and Goru (B & C-sand) strata are picked for every event to reveal the seismic geometries (onlap, downlap etc.). This picking is used to develop a seismic sequence stratigraphic model. Three higher-order sequences (alternative TST and FIST packages) and one complete third-order sequence (LST, TST and HST packages) are identified within Sembar, whereas the Goru-A sand has one complete sequence comprising of LSW (Lowstand Wedge), TST (Transgressional System Tract) and FIST (Highstand System Tract). The aim of the study is to map the productive sands of the Lower Goru Formation of the study area. Rock physics parameters (bulk modulus, Poisson's ratio) are analyzed after a detailed sequence stratigraphic study. Sequence stratigraphy helps to comprehend the depositional model of sand and shale. Conformity has been established between seismic stratigraphy and the pattern achieved from rock physics investigations, which further helped in the identification of gas saturation zones for the reservoir. Rheological studies have been done to map the shear strain occurring in the area. This involves the contouring of shear strain values throughout the area under consideration. Contour maps give a picture of shear strain over the Lower Goru Formation. The identified and the productive zones are described by sands, high reflection strengths, rock physical anomalous areas and low shear strain.