Development and distribution of carbonate ramp reservoir in the Persian Gulf Basin

On the basis of regional study, combined with drilling, logging, and seismic profiling, the development and distribution of the Upper Cretaceous carbonate ramp reservoir in the Persian Gulf Basin were studied, and the depositional pattern, favorable reservoir development facies, and distribution control factors were clarified. The Upper Cretaceous carbonate ramp sediments could be divided into inner ramp, middle ramp, and outer ramp; and the inner ramp could be sub-divided into the sedimentary microfacies of Sabha, tidal flat, lagoon, tidal shoal, shoal, and intershoal. The shoal facies and tidal shoal facies are favorable for reservoir development. The identification and prediction of shoal bodies are very important for oil and gas exploration in the area. The shoal lithofacies are mainly bioclastic limestone and the tidal shoal lithofacies are mainly bioclastic dolomite. In seismic profiles, the shoal body is lenticular in shape, and the seismic reflections have a certain clinoform structure and generally have weak amplitudes. The logging pattern of the shoal body is characterized by “three high and two low”, namely, high acoustic time difference, high neutron, and high porosity or permeability; and low gamma and low density. In the Persian Gulf Basin, the palaeogeomorphic high formed by extrusion in the Late Cretaceous controlled the distribution characteristics and development degree of reservoir. This study provided a good reference for the exploration onto carbonate oil and gas to clarify the development and distribution of the reservoir in shoal and tidal shoal facies.