Abstract

The existing geophysical, geological and petrophysical data of CA-CD area and adjoining fields of Tapti-Daman block of Mumbai offshore Basin, India, have been evaluated for delineation and mapping of pay sands. The pays were found, mainly, in Mahuva Formation of Lower Oligocene age by two exploratory wells in 1986. The reservoir sandstones were deposited by fluvial /Estuarine channels which incised older shale/limestone sequences. Delineation of these sands by conventional interpretation methods is difficult because of thin and discontinuous occurrences, high degree of vertical and lateral variability in net sand thickness, weak impedance contrasts at sandstone interfaces, high impedance of overlying limestones and limited bandwidth of seismic data. We applied strategic scheme of interpretation by integrating geodata, experiences and tools. Tying of seismics with well data and fixing of the stratigraphic and structural framework by tracking the sequence boundaries (unconformities) was the first step. Integrating well and petrophysical data, realistic field geometry and parameters, we simulated synthetic seismic responses by numerical modeling. In the zone of interest log facies were found, mainly, of four types and assuming interdependence between log and seismic facies, the zone of interest was analyzed in four types of seismic facies classes. Synthetic responses and seismic facies maps helped in analyzing seismic attributes and their relationships with subsurface features favourable for hydrocarbon accumulation. Fault pattern, geometry and edges of channels and their fills were inferred by volume rendering, vertical and horizontal slice displays of different volume attributes and spectral decomposition frequency slices. Channels, within Upper Mahuva Formation, were found vertically stacked. Validation with well data showed the occurrence of reservoir sandstones within mapped channels and thus authenticating the models and interpretation