3D SEISMIC INTERPRETATION AND RESERVOIR CHARACTERIZATION USING AVO MODELLING OF GAMBAT AREA, SOUTHERN INDUS BASIN, PAKISTAN

Abstract

The basic objective of research is to get preliminary understanding of the subsurface structural trend and reservoir characterization of study area. Reservoir characterization is a process of describing various reservoir properties using all the available data to provide reliable reservoir models for accurate reservoir performance prediction. Gambat block lies in lower Indus basin which is an extensional regime resulting extensive horst and graben geometry that may be considered as hydrocarbon bearing zone. The producing reservoirs in this area of Lower Goru Formation are shallow marine sandstones. This research aimed to find and locate such prospects in the sand of Lower Goru Formation in Gambat area. Four reflectors namely Lower Goru, A interval, B interval and C interval were marked on seismic sections on the basis of depth and velocity of these depth and time contour maps of selective horizons were prepared to see the depth variation of these reflectors in the study area. Petrophysical analysis was done to evaluate the properties of reservoir (effective porosity, hydrocarbon saturation and net pay) for prospect zone in Tajjal wells. Gassmann Fluid Substitution analysis provides information about impact of depleting reservoir on seismic properties. Low impedance sand is difficult to image, AVO modeling carried out in this research to tackle this problem. Horst and graben structures were marked on seismic data along with probably stratigraphic traps which contains gas bearing sand as confirmed by petrophysical analysis and AVO modeling. These studies nominate Tajjal structure as a probable prospect for future exploration.