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Microfacies, diagenesis and hydrocarbon potential of Eocene carbonate strata in Pakistan
Carbonates and Evaporites ( IF 1.4 ) Pub Date : 2020-06-10 , DOI: 10.1007/s13146-020-00601-9
Umer Khitab , Muhammad Umar , Muhammad Jamil

The role of microfacies and diagenesis was focused to assess the hydrocarbon potential of Eocene carbonate strata exposed in Sulaiman–Hazara mountain ranges. Thin- to thick-bedded Eocene limestone exhibits wackestone, packstone, mudstone, and grainstone texture and comprises larger benthic forams such as Nummulite , Assilina , Lockhartia , Discocyclina , Orbitolites and Operculina . The accumulation of the strata occurred in lagoon, inner to deeper shelf. The microfacies and textural variations revealed stable shallow shelf conditions in early Eocene. The marine sedimentation ceased in Hazara and Salt ranges, but Kohat and Sulaiman regions remained under water during middle Eocene. The deposition of Habib Rahi Formation in deeper shelf attests to local scale normal faulting due to the northward movement of the Indian Plate. The Eocene reservoir zones were sourced by Patala and Ghazij Formations and capped by thick cover of fluvial shale, establishing favourable conditions for stratigraphic traps. Thick limestone packages of foraminiferal wackestone/packstone and dolomitized/dolomitic wackestone microfacies are regarded as estimable targets for hydrocarbons exploration in the region. Several diagenetic processes were observed in the studied limestone which includes: micritization, dolomitization, neomorphism, cementation, mechanical and chemical compaction, fracturing and dissolution which were caused in marine, meteoric and burial diagenetic environments. Compaction was the main factor for the destruction of primary porosity along with cementation effect. The porosity in the limestone was significantly enhanced by late stage dissolution, fractures enclosed by calcite cement and dolomitization.

中文翻译:

巴基斯坦始新世碳酸盐岩地层微相、成岩作用及油气潜力

微相和成岩作用的重点是评估苏莱曼-哈扎拉山脉出露的始新世碳酸盐岩地层的油气潜力。薄层至厚层始新世石灰岩具有碎屑岩、泥灰岩、泥岩和颗粒岩结构,包括较大的底栖有孔虫,如 Nummulite、Assilina、Lockhartia、Discocyclina、Orbitolites 和 Operculina。地层的堆积发生在泻湖,从内到更深的陆架。微相和结构变化揭示了早始新世稳定的浅层陆架条件。Hazara 和 Salt 山脉的海洋沉积停止,但 Kohat 和 Sulaiman 地区在始新世中期仍处于水下。由于印度板块向北移动,Habib Rahi 组在更深的陆架中的沉积证明了局部规模的正断层。始新世储集层来源于 Patala 和 Ghazij 组,被厚厚的河流页岩覆盖,为地层圈闭创造了有利条件。由有孔虫类泥灰岩/泥灰岩和白云石化/白云质泥灰岩微相组成的厚石灰岩包被认为是该地区油气勘探的可估计目标。在所研究的石灰岩中观察到几种成岩过程,包括:在海洋、大气和埋藏成岩环境中引起的微晶化、白云石化、新形作用、胶结作用、机械和化学压实、压裂和溶解。压实作用和胶结作用是破坏原生孔隙的主要因素。后期溶蚀作用显着提高了石灰岩的孔隙度,
更新日期:2020-06-10
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