Quantitative evaluation of the influence of siderite cements on middle-shallow reservoirs: A case study of the southern oil area in the Enping Sag, Pearl River Mouth Basin

Abstract

In order to clarify the cause of formation of siderite cement, and study the influence of siderite cement on reservoir and its geological model, and explore the influence of siderite-bearing reservoir on oilfield development and production, the study of the cause of formation of siderite cement and its influence on physical properties was carried out. Based on conventional core analysis, thin section analysis and X-ray analysis, statistics on the types and characteristics of cements in middle-shallow reservoirs in the Enping oil area, Pearl River Mouth Basin, reveal that siderite cement is abundant. The redox state and sedimentary environment of the paleo-ocean were used to study the genetic mechanism of siderite and quantitatively study the influence of siderite on middle-shallow reservoir quality. The results show that siderite in the reservoir is the product of the combination of CO2 produced by the degradation of organic matter and Fe2+ enriched in pore water during diagenesis. It formed in the early diagenetic stage when the primary pores of sandstone developed, which has a positive significance for the preservation of the overall pores of the reservoir. However, the local cementation of siderite (mostly developed in thin argillaceous belts) is destructive to the reservoir because it occupies a large proportion of the primary pore space. The "permeability control" effect of siderite cement makes the vertical permeability of the muddy strip much lower than that in other directions, thus greatly increasing the shielding effect of the muddy thin layer on the bottom water, which is conducive to reservoir development. Due to the blocking of argillaceous belts, the reservoir geological pattern will change from bottom water reservoir to edge water reservoir and edge water reservoir to multilayer edge water reservoir, which can be exploited by corresponding development measures. The development of siderite leads to differences in the energy supply in the top, middle and edge of the reservoir, which can guide water injection and improve the well pattern strategy. The research results were applied in Oilfield B, where the horizontal strip interlayer of fulling siderite cements resulted in insufficient energy supply in the high position. By injecting hot water to increase energy, oil field production is doubled, and reservoir recovery is greatly improved.

Keywords

• pearl river mouth basin
• enping oil area
• middle-shallow reservoir
• siderite
• cement
• permeability
• argillaceous thin layer