Characteristics and controls of the reservoir sandstones from the Dongying Formation on the western slope of the Bozhong depression

With the aid of the cores, thin sections and SEM examination, the present paper gives a detailed study of the reservoir sandstones from the Dongying Formation on the western slope of the Bozhong depression. The reservoir sandstones in the Dongying Formation consist mainly of arkose and lithic arkose, with subordinately feldspathic litharenite. The porosity types comprise intergranular and intragranular solution openings and microfissures, suggesting the mesopores and low-to medium-permeability reservoir sandstones. The controlling factors include the deposition influencing the development of the reservoir sandstones and diagenesis exercising a major control on the internal structures of the reservoir sandstones. The deep-seated overpressure may be favourable for the preservation of the secondary porosity. However, the overloaded formation pressure may bring about the velocity sensitivity and decrease the oil productivity of the low-permeability reservoir sandstones.