Reservoir characteristics and controlling factors of Paleogene carbonate-rich shale in Dongying Sag, Bohai Bay Basin

Abstract

In this paper, the mineralogical composition, sedimentary structure, laminar type, pore size distribution, pore volume, specific surface area, number of laminae and morphological characteristics of dissolution pores of the lacustrine shale from the upper sub-member of the fourth member of the Paleogene Shahejie Formation of the wells NY1 and FYP1 in the Dongying Sag of Bohai Bay Basin were finely characterized by a combination of core observation, thin section observation, nitrogen adsorption and X-ray diffraction. On this basis, the main lithofacies types and laminar characteristics, the pore size, pore volume and specific surface area of different lithofacies, and the pore and laminar characteristics of carbonate-rich shale in this area were summarized. The results show that there are four lithofacies types in the Dongying Sag: organic-rich laminated argillaceous limestone, organic-rich laminated sandy limestone, organic-bearing laminated sandy limestone and organic-bearing massive limestone. The microscopic features of the laminae are mainly flat, lenticular, interbedded and undulating. The measured nitrogen adsorption data show that the carbonate-rich shale in the Dongying Sag has a larger pore volume and specific surface area. At the same time, the development of dissolution pores and laminae allows the carbonate-rich shale to have higher storage capacity and horizontal permeability. Therefore, the carbonate-rich shale is a high quality reservoir in the Dongying Sag.

Keywords

• shale
• carbonate-rich shale
• lithofacies characteristics
• laminar characteristics
• reservoir characte-ristics
• main controlling factors
• dongying sag
• bohai bay basin