摘要：Unconventional shale gas is rapidly increasing as an available source of natural gas in the worldwild. Horizontal well drilling and multistage fracturing are two principle techniques of shale gas resources production. Benefiting most from these two techniques, the United States, Canada, and China have become only three countries to produce shale gas in commercial quantities. The key technical issues emerged in the horizontal drilling and fracturing involve the rock fragmentation issues, wellbore trajectory optimization and control, wellbore stability, cementing and its quality control for long horizontal lateral, and hydraulic fracturing design. Although some progress associated with those technical issues have been achieved in China, there are still many geologic and engineering challenges: (1) the low rate of penetration and fast bit wearing for both PDC and Cone bits are still the primary issues, which makes hard achieve the "one-trip" drilling; (2) wellbore collapse and lost circulation are serious with a certain collapsing period due to natural fractures system; (3) complex multi-fractures propagation behaviors still need to be understood and the fundamentals of fracturing design should be established after undstanding multi-fractures propagation behaviors. In this paper, three fundamental issues are proposed including the rock fragmentaion and high-efficiency drilling techniques, the long lateral wellbore collapsing and its control techniques, and the complex multi-fractures propagation behaviors. The most important thing is to understand multi-physical coupling of work fluid (drilling mud, completion fluid, and fracturing fluid) and shale. The future investigation would emphasize on three parts. (1) The effects of spontanuous imbibition, thin-film lubrication on micro-cracks faces, and brittleness on shale rock fragmentation: Drilling fluid suddenly flows into pores and micro-cracks due to the spontanuous imbibition. Then a thin-film lubrication layer occurs on the micro-cracks surfaces that reduces the interface friction of the cracks. Thus, the spontanuous imbibition is positive to accelerate the rock fragmentation. (2) The effects of rock-fluid interaction, hydro-mechanical-chemical coupling on wellbore collapsing behaviors: The reasons of shale collapse are different from those of the clay. The natural cracks and weak planes may be the primary contributors for shale collapse. Drilling fluid penetrates into natural cracks and weak planes under the differential pressure, capillary forces, and concentration difference. The fluid lubricates the crack surfaces and make them easier shear slip. Further, the rock-fluid interaction makes the clay minerals swell that reduces the cohesive strength of rock. Consequently, the hydro-mechanical-chemical coupling is strong enough to be considered. (3) The flow pressure assignment and multi-fractures competitive propagation within fracture network: Multi-fractures competitively propagate because of the diversity of the fracture opening pressure and fluid assignment. Fracturing fluid is self-assigned into branch fractures and fluid pressure is time and space dependent, making the net pressure of branch fractures diverse. Meanwhile, fracture opening pressures present the localized character due to the complex naturally fracture system and rock anisotropy. Thus, three fundamental issues should be studied involving the fluid assignment properties, the influence factors of fracture opening pressure, and the competitive propagation mechanisms. This paper reviews the research progress of the key fundamental issues, and analyzes their possible mechanisms from veiws of shale rock charcterization, hopefully to provide insights on current research status and future emphases.
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ISSN号：0023-074X

卷、期、页：v 61,n 26,p2883-2890

发表日期：2016-09-15

期刊分区（SCI为中科院分区）：无

收录情况：EI（工程索引）

发表期刊名称：Kexue Tongbao/Chinese Science Bulletin

第一作者：李根生,盛茂,田守嶒,葛洪魁,黄中伟,宋先知

论文类型：期刊论文

论文概要：李根生,盛茂,田守嶒,葛洪魁,黄中伟,宋先知，Key issues and investigation of horizontal well drilling and multistage fracturing in shale gas reservoir，Kexue Tongbao/Chinese Science Bulletin，2016，v 61,n 26,p2883-2890

论文题目：Key issues and investigation of horizontal well drilling and multistage fracturing in shale gas reservoir