关键词: 碳酸盐岩, 隔夹层, Mishrif组, 层序, 沉积作用, 成岩作用

Abstract: Strong vertical heterogeneity of thick carbonate reservoirs that led to disproportionate production. To clarify the mechanism and distribution of reservoirs and interlayers, taking based on a case study in the Cretaceous Mishrif Formation of A oilfield in the Middle East, the effects of sedimentation and diagenesis on reservoir physical properties were studied under the control of sequence stratigraphy frameworks. The results showed that there were 6 quaternary sequences in the Mishrif Formation, and the sea level controlled the evolution of the sedimentary environment, and had an important impact on the early diagenetic process. On the basis of water energy and sedimentation diagenesis characteristics, it could be divided into 5 combinations (1) High-energy environment+constructive diagenesis. The non-selective dissolution of the shoal greatly improved the reservoir physical properties of the rock forming high-quality reservoirs. (2) High-energy environment+destructive diagenesis. Different degrees of cementation occurred on the shoal, reducing the physical properties of the rocks and forming poor reservoirs or physical interlayers. Which were highly hidden and difficult to be identified, increasing the reservoir heterogeneity. (3) Lowenergy environment+constructive diagenesis. Selective dissolution and dolomitization occurred in lagoons, open shallow seas, and the back shoal, effectively improving rock physical properties, and mainly forming poor reservoirs. (4) Low-energy environment +destructive diagenesis. Under humid climate conditions, rocks in lagoon were compacted and cemented, and carbonaceous mudstone deposited at the top of the sequence, forming an exposed cemented-carbonization zone. Under the alternating conditions of arid and humid climates, rocks in lagoon were subjected to multiple stages of weathering and leaching, forming dense cemented breccia. This configuration usually developed in low system tract, forming stable interlayers. (5) Low-energy environment+weak diagenesis. The original physical properties of the rocks were poor with high lime mud, and the subsequent diagenesis had not significantly improved the physical properties, and lithological interlayers were usually formed. Under the control of multi-stage sequences, the Mishrif Formation had continuously been changing the combination of sedimentation and diagenesis. The physical interlayers, mainly distributed in high-quality reservoirs, were thin, and small in scale and unstable. The lithological interlayers were associated with poor reservoirs. Lithological interlayers developed in different environments had different continuity. The tight cement zones were stable and the formation was divided into different development layer series of development.

Key words: carbonate rock, interlayers, the Mishrif Formation, sequence, sedimentation, diagenesis