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尼日尔Agadem区块,地质条件复杂,井壁失稳严重,易造成起下钻阻卡、沉砂卡钻、下套管下不到底等井下复杂情况。其中,Kaola-1D井井塌情况尤为严重,二开扩大井眼占该开次的90%,频繁引发井下复杂情况,严重影响井身及固井质量。本文通过分析该井的测井数据,通过岩石力学相关理论计算出三压力剖面,再结合井径数据、地层岩性、钻井液性能及该井井塌特点,分析了失稳原因,认为主要原因为:一、部分井段钻井液密度低于地层坍塌压力,造成应力垮塌;二、部分井段裂隙发育好,地层呈破碎性,钻井液体系封堵性不足,造成钻井液进入地层,引发岩石强度降低,坍塌压力升高,造成井壁失稳;三、水力参数设计偏低,造成岩屑在井筒堆积,在钻进过程中,产生较大的压力波动,从而诱发井塌。
The Agadem block in Niger has complicated geological conditions and serious instability of the borehole wall, which can easily lead to complicated downhole drilling, stuck grit and stuck under the casing. Among them, the Kaola-1D well is particularly severe. The second well borehole expansion accounts for 90% of the opening volume, frequently causing complicated underground conditions and seriously affecting wellbore quality and cementing quality. In this paper, the well logging data are analyzed and the three pressure profiles are calculated through the related theories of rock mechanics. Based on the data of borehole diameter, formation lithology, drilling fluid properties and the characteristics of well collapse, the causes of instability are analyzed, and the main reasons As follows: First, part of the well section of the drilling fluid density is lower than the formation collapse pressure, resulting in stress collapse; Second, part of the well fractured well, the formation was crushing, drilling fluid system sealing insufficient, resulting in drilling fluid into the formation, Lower strength and collapse pressure, resulting in instability of the shaft wall; Third, the design of hydraulic parameters is low, resulting in the accumulation of cuttings in the wellbore, resulting in large pressure fluctuations in the drilling process, thus inducing well collapse.