Study on Diagenesis of Deeply-buried Strata in Anpeng Oilfield of Biyang Sag and Its Application to Prediction of Diagenetic Traps
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摘要: 深层系一般指沉积盆地中埋藏深度在2 500～2 700 m以下的地层,其储集物性普遍很差,但在一定条件下,深部溶蚀作用可产生优质储层,形成成岩圈闭.然而这种成岩圈闭的预测一直是一个难题.安棚油田位于河南泌阳凹陷东南部,勘探成果表明,在该油田深层系下第三系核桃园组核三段下部(简称(核三下)席状的扇三角洲砂体中存在成岩圈闭.本次通过定量的成岩作用研究和成岩阶段划分,对成岩圈闭的形成机理和分布进行了探讨.研究表明,该区核三下的砂体经历了压实、胶结、溶蚀等多种成岩作用,不同的成岩作用发生于不同的埋藏深度.2 700～3 100 m之间以胶结强烈为特征,属于胶结带.3 100～3 900 m之间以次生溶蚀孔隙发育为特征,尤其是3 200～3 600 m之间, 属于深部溶蚀带.本区核三下砂体自南而北埋藏深度逐渐变浅,其上倾方向处于胶结带的部分由于强烈胶结而变成致密层,可封堵油气,而下倾方向处于溶蚀带的部分由于次生溶蚀孔隙发育而成为良好储层,从而形成成岩圈闭.根据不同埋藏深度、不同成岩阶段孔隙发育和保存的特征,可预测成岩圈闭分布。Abstract: Deeply-buried strata refer to strata buried beneath the depth of 2 500～ 2 700 m. Their porosity and permeability are commonly very low. But under certain conditions, dissolution in depth can create good reservoirs and form diagenetic traps. However, prediction of diagenetic trapshas long been a difficult problem, which is dealt with in this paper. Anpeng Oilfield is located in the southeast part of the Biyang Sag, Henan Province. Explo-ration shows that diagenetic traps exist in the sheet-like sandbodies deposited in a fan-delta of lower Member Ⅲ of Lower Tertiary Hetaoyuan Formation.In this paper, based on quantitative study on diagenesis and diagenetic stage, origin and distribution of diagenetic traps were discussed. The study shows that sandbodies of the studied interval experienced various diagenesis such as compaction, cementation, dissolution, etc. Different diagenesis oc-curs in different depth. Based on this and other data, the diagenetic stage is divided into early diagenetic stage and late diagenetic stage. Early diagenetic stage is further divided into early diagenetic stage A and early diagenetic stage B. Late diagenetic stage is further divided into late diagenetic stage A, late diagenetic stage B, and late dia-genetic stage C, and late diagenetic stage A is further divided into substages A1, A2 and A3. In the study area,deeply buried strata( lower Member III of the Hetaoyuan Formation)are mainly in late diagenetic substage A3 and late diagenetic stage B. Substage A3 ranges in depth from 2 700 to 3 100 m, and characterized by strong cementa-tion. Late diagenetic stage B ranges in depth from 3 100 to 3 900 m, and characterized by development of sec-ondary dissolution pores, especially between 3 200～ 3 600 m. In the study area, sandbodies dip down from north to south. When sandbodies extend from late diagenetic substage A3 to late diagenetic stage B, the part in substage A3 becomes compact due to strong cementation and can seal oil and gas, while the part in stage B may become good reservoirs due to secondary dissolution. In this way, diagenetic traps are formed. Thus according to burial depth,characteristics of development and preservation of pores in different diagenetic stages, diagenetic traps can be pre-dicted.
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Key words:
- Biyang Sag /
- diagenetic trap /
- diagenesis /
- diagenetic stage /
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