干旱区生态环境知识资源中心

Identification of the types of the depositional environments that have control or influence on the distribution of petrophysical parameters is required to assess the potential utility of these parameters in the reservoir analysis. The primary depositional facies plays an important role in the reservoir quality and assessment of the petrophysical characteristics of hydrocarbon bearing zones in exploration and development operations. Petrophysical characteristics, depositional environment, and hydrocarbon prospectivity of the Middle Jurassic Upper Safa reservoirs in the Obaiyed Field (Western Desert, Egypt) are described using data from wireline logs (gamma ray, density, neutron, sonic, and resistivity) from 14 wells. Petrophysical characteristics of Upper Safa reservoirs (unit A and unit B) change significantly with variations of depositional facies and lithology. These units are interpreted to be composed of fluvial channel sands (unit A) and tidal channel sands (unit B) based on a gamma ray curve signatures. Litho-saturation analysis, petrophysical parameters, and net pay thickness maps of the Upper Safa reservoirs show variations along the study area. The main factor controlling differences in petrophysical properties and thickness for these reservoirs is the type of sandstone facies. Shales cause a major reduction in the porosity and gas saturation of the reservoir sandstones especially in the unit B reservoir which has dispersed and laminated shale and low resistivity net pay zone. The best reservoir characteristics belong to the unit A, which has high effective porosity (PHIE), low shale content (V (sh)), and high gas saturation (S (g)). Maps of reservoir parameters based on precise understanding of its depositional environment indicate the location of possible sites for future gas development activities in the Obaiyed Field.