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- Title
Formation, evaluation technology and preservation lower limit of ultra-deep ancient fracture-cavity carbonate reservoirs below 7 000 m.
- Authors
Guang-you ZHU; Chong-hao SUN; Bin ZHAO; Ting-ting LI; Zhi-yong CHEN; Hai-jun YANG; Lian-hua GAO; Jin-hua HUANG
- Abstract
With the development of oil and gas exploration to deep layers, ultra-deep layers below 7 000 m have become the focus of exploration. The formation, preservation and prediction of ultra-deep ancient carbonate reservoirs are key problems. Based on the analysis of the drilling data below 7 000 m of Ordovician in Tarim Basin, China, this paper characterizes the development characteristics and formation and evolution process of ultradeep carbonate reservoirs. The formation of ultra-deep carbonate reservoirs is controlled by high-energy depositional bodies, penecontemporaneous exposed karstification and the reconstruct of faults. Through seismic attribute extraction, beads were found and a method of drilling along the fault zone along the karst layer was proposed. The success rate of drilling was increased to 95%. The quantitative sculpture and characterization technology of fracture-cavity has been established, and hydrocarbon accumulation regularity and well point optimization method for fracture-cavity reservoirs have been formed. Mechanical models of vugs in fault and fracture-cavity carbonate reservoirs are established, and numerical simulation and theoretical analysis are carried out. The results show that the distance from fault plane increases, and the fracture development ability decreases. Over 8 500 m is the dominant distribution area of carbonate reservoir, 8 500-9 200 m is the effective distribution area, 9 200-9 500 m is the general distribution area, below 11 000 m, large vugs are gradually disappearing. Parabolic pressure arches are formed at the top of the paleocave in the ultra-deep carbonate reservoir in the platform basin area to prevent the cave from collapsing completely. Take the parabolic cave with the height-span ratio of 1 and arrow height 8 m as an example, its fully closed depth is over 50 000 m. Therefore, the lower limit of exploration depth for carbonate cave reservoirs far exceeds the current drillable depth.
- Subjects
CHINA; CARBONATE reservoirs; SHALE gas reservoirs; NATURAL gas prospecting; FAULT zones; PETROLEUM prospecting; MECHANICAL models
- Publication
Natural Gas Geoscience, 2020, Vol 31, Issue 5, p587
- ISSN
1672-1926
- Publication type
Article
- DOI
10.11764/j.issn.1672-1926.2020.04.013