关键词: 欠平衡钻井, 近平衡钻井, 完井, 钻井液, 储层保护, 负压值, 井底压力, 松辽盆地北部

Abstract: The main reservoir for deep-layer natural gas exploration in the northern part of Songliao Basin is mainly volcanic rock of Yingcheng Formation, which is the reservoir medium with seams and pores containing tuff. Conventional drilling operation causes serious pollution of the reservoir. The high pressure differential at the well bottom and irregular borehole diameter affect discovery and appraisal of the gas layers through well-log and logging. Those issues directly impair natural gas discovery and confirmation. To solve the issues existing in the conventional drilling operation, seven items of research work have been completed in the recent years, such as study of wellbore structural optimization, application of low-density drilling fluid suitable for formation fluid properties and reservoir pressure coefficients, negative pressure value controlling technology at under-balance well bottom, development of the automatic parameters acquisition and analysis system for under-balance drilling, measurement tools for under-balance MWD for well bottom pressure and temperature, acquisition of formation pressure and determination of killing fluid density. A series of process technology has been developed for near-balance and under-balance drilling and completion. The near-balance drilling technology is used in drilling three wells including the deep Xushen-1 in the northern part of Songliao Basin while under-balance drilling technology is used in drilling the other eight wells in the area, such as Weishen-5. The high-yield commercial gas flow is obtained from those wells with the gas formations effectively protected. Those desirable exploration results have played a key role in discovery of the 1000×108m3 reserves of the deeplayer natural gas in Xujiaweizi region in the northern part of Songliao Basin