SEISMIC CHARACTERIZATION OF GAS-HYDRATES IN MAKRAN OFFSHORE AREA, PAKISTAN

Abstract

2D seismic data of the offshore area of Pakistan including Makran and Indus was studied and interpreted to see the clear picture of gas hydrate present in the area and to estimate the volume of gas hydrate. The presence of the gas hydrate indicates that large volumes of methane are being generated at ~500m in these regions. The coastal line of Pakistan is approximately 900km long including Makran coast which is about 700km. The stratigraphic chart of the area suggests that the Parkini and Panjgur are the reservoirs with folds and fault system acts as a trapping and fluid flow pathway from the source rock. Off Makran seven multi-channel reflection seismic (MCS) profiles with a total length of >900 km were acquired during RV SONNE cruise SO122 in 1997. No gas hydrates are evidenced in Indus Offshore from the literature review. BGR studied the offshore part of the Makran accretionary wedge in details during Sonne Cruises S0122 and 130 and searched for submarine gas seeps, vents of fluids, gas hydrates, sampled “cold seep" sites at the sea floor and in the water column and also investigated the structure and origin of the accretionary wedge. Monsoonal upwelling controls the high biological productivity in the surface water controlled in the area of Makran continental margin. This is one of the causes for the formation of an oxygen minimum zone resulting in a high accumulation rate of predominantly marine organic matter in the marine sediments of the study area. 2D seismic data helped to identify and observe the characteristics of the gas hydrate related bottom simulated reflector (BSR) and fluid flow features. BSR identified in the north eastern part of the study. BSR identified on few seismic lines and showed behavior of cross-cutting the sedimentary strata and mimicking the seafloor with reversed polarity to that of seafloor. BSR marked the base of gas hydrate stability zone (BGHSZ. The extent of BSR marked with depth ranging 600 to 4000ms TWT. Volume of gas hydrate calculated is 0.7% of the total study area and the total volume of free gas estimated in this study is 1241250 m3.