Online Journal for E&P Geoscientists

Hakimi, Mohammed H.^*1; Shalaby, Mohamed R.¹; Abdullah, Wan H.¹
(1) Geology, University of Malaya, Kuala Lumpur, Malaysia.

Biyadh Formation, the late Early Cretaceous in age, is a clastic rock containing substantial amounts of proven oil and located in the western central Masila Basin. The lithofacies of this formation reflects braided river channels, shoreface and shallow-marine settings. The Biyad Formation is divided into the Lower and Upper Members, the latter containing the most prolific hydrocarbon reservoirs in the East Shabowah oilfields. The Upper Biyad clastic also can be subdivided into three units (S1, S2 and S3 pay zones) based on lithofacies, mineralogy and depositional environments. This study was to evaluate the reservoir characteristics of the Biyadh Sandstone units. The dataset includes core data, electrical logs, thin sections and scanning electron microscopy analysis. Biyadh intervals with good reservoir quality occur throughout the oilfields, with net pay thickness of up to 130 m, and net sand ratios ranging from 40% to 80%. Porosity varies from 2% to 27%, and permeability from 0.01 to 3,000 millidarcies. The main petrographic facies consist of quartzarenite and quartzwackes. Both contain sub-facies that differ in secondary components, cement and matrix types. The sub-facies reflect different depositional environments and diagenetic histories that control the quality of the reservoirs. The S2 and S3 Units are the main reservoir producing in the East Shabowah oilfields. The S3 sandstone is excellent quality reservoir, with no inhibiting authigenic clays or diagenetic problems, largely because of their quartz-rich composition and high porosity and permeability followed by S2 Unit; while the S1 Sandstone reservoir quality mostly destroyed by the pore occluding cements due to diagenetic processes, finer grain size and high clay content. Therefore, the Upper Biyad reservoir units have good reservoir quality and reveal promising reservoir characteristics which should be taken into consideration during future development of the East Shabowah oilfields especially S3 and S2 units.