Abstract:

The use of the gas-injection underbalanced drilling(UBD) in horizontal wells or high-angle deviated wells is one of the significant aspects to broaden the UBD application. Currently, gas-injection measures include mainly the drill-string gas injection and annular gas injection. When the drill-string gas-injection measure is used, the conventional downhole dynadrill and mud-pulse measurement-while-drilling(MWD) tools usually can not work normally, while existing annular gas-injection measures, such as parasitic casing and dial casing, are not applied widely due to higher cost and many technical problems. Therefore, combined with the theory and practice of underbalanced drilling and horizontal wells, the present paper proposed a new annular gas-injection measure with attached casing, and its key techniques, including the design of advanced gas-injection casing head, the proper size design of casing and bit series, and the depth calculation of the annular gas-injection point, were theoretically analyzed and verified. This gas-injection measure solved some special problems in drill-string gas injection, constituting a set of feasible annular gas-injection underbalanced drilling techniques for horizontal wells.

Key words: underbalanced drilling(UBD), horizontal well, gas-injection measure, casing, advanced casing head

摘要：

充气欠平衡钻井技术应用于水平井或大斜度井，将是拓展欠平衡钻井应用领域的重要方向之一。目前注气方式主要是钻柱注气和环空注气。采用钻柱注气方式，常规井下动力钻具和泥浆脉冲随钻测量工具无法正常工作，而现有的环空注气方式（如寄生套管、双层套管)，由于成本高，技术问题多，应用不够广泛。由此，结合欠平衡钻井和水平井的理论和实践，提出了附加套管环空注气方式，并针对其关键技术进行理论分析和论证。该注气技术克服了钻柱注气的特殊问题，形成一套实用的环空注气欠平衡钻水平井技术。

关键词: 欠平衡钻井, 水平井, 注气方式, 套管, 新型套管头