塔里木盆地玉科区块超深井膏盐层段套管损坏机理与防治措施

Damage mechanism of casings used in ultra-deep well salt layers of Yuke Block in the Tarim Basin and prevention measures

塔里木盆地塔北隆起轮南低凸起哈得逊鼻状隆起东翼的玉科区块超深井在钻井过程中出现了严重的膏盐层段套管损坏问题,导致卡钻频发甚至被迫回填侧钻,极大地影响了该区块新井的顺利钻进和后续油气开发进程,造成了较大的损失。为此,在分析该地区几口套管损坏井现状的基础上,利用GMI和WELLCAT等软件对造成套管损坏的地质因素和工程因素进行了分析,初步地揭示了该地区膏盐层段套管损坏的机理,认为膏盐层蠕变引发的非均匀载荷因素和膏盐层段套管不居中、水泥浆顶替效率差等固井质量因素是导致套管损坏的主要原因。进而提出了在盐层厚度大于40 m的地区一系列预防套管损坏措施:(1)井身结构优化调整为四开井身结构;(2)调整钻井液性能,推荐使用饱和盐水钻井液或油基钻井液,并将盐层段钻井液密度上限提高至1.70 g/cm^3;(3)提高固井质量,形成规则井眼,增大套管与地层的环空间隙,适当增加泵排量,提高顶替效率。

The Yuke Block is located at the eastern flank of Hadexun nose-like uplift in the Lunnan low salient, North Tarim uplift, Tarim Basin. The ultra-deep wells in the block suffered serious casing damage in salt layers in the process of well drilling, leading to frequent pipe sticking and even back-filling sidetracking. Consequently, the drilling of new wells and subsequent oil and gas devel- opment in this block were seriously hindered, and great loss was caused. In this paper, the actual situations of several casing failure wells were analyzed, and then the geological and engineering factors that were related to casing damage were investigated by using the GMI and WELLCAT software. The mechanism of casing damage in salt layers was preliminarily revealed. It is indicated that casing damage is mainly caused by the non-uniform load induced by the creep of salt-gypsum layers and the poor cementing quality （e.g. uncentralized casing in salt-gypsum layers and low displacement efficiency of cement slurry）. Finally, a series of measures were proposed to prevent casing damage in the areas with a salt thickness greater than 40 m. First, optimize the casing program into a four-section casing one. Second, adjust the performance of drilling fluid. It is recommended to adopt saturated brine drilling fluid or oil-based drilling fluid and increase the upper density limit of the drilling fluid used in salt layers to 1.70 g/cm3. And third, im- prove cementing quality, build up regular wellbore, increase the casing-formation annulus and increase the pumping rate appropri- ately to improve the displacement efficiency.