Journal of Earth Science & Climatic Change
Open Access

Abstract

Aiming at the phenomenon of the waterflooding breakthrough in the Khasib reservoir of AHDEB oilfield in Iraq, this paper studies the Khasib reservoir evolution and genesis of the abnormal high permeability zone. Results indicate that the karst reservoir of Khasib forming is controlled by the depositional karst and multiple phase deep buried karst. The reservoir evolution can be divided into three stages: Syndiagenetic stage, shallow-medium burial of organic acid dissolution stage, and rapid settlement of deep burial period of hydrocarbon filling stage. The depositional karst is featured as the fabric selective dissolution of vertical infiltration, which forms the two high porosity zones. During the buried diagenesis stage, the reservoir is through the buried karst that inherited karstification in non-fabric selective dissolution way based on the post-depositional pore, and featured as the strikeâ�?�?slip fault as the fluid migration path, the acidizing fluid from organic substance degradation as the dissolution media, the post-depositional high porosity zone as the dissolution carrier. After the depositional karst and least two stages deep buried karst, formed the two â�?�?abnormal high perm zonesâ�? that are intraclast grainstone zone of Kh2-1-2 and the algal debris packstone zone of Kh2-3-2. The intraclast grainstone zone is fluid flow passage to cause the early water breakthough in water-flooding. In summary, high connectivity origin intraclast intergranular pore, the pore integrity was conserved during the depositional karst period, long-term shallow buried diagenetic environment, favorable potential area for fluid migration, good coupling relationship of the hydrocarbon fluid filling and fast formation burying period, which make the Kh2-1-2 zone forming the abnormal permeability zone.

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