Abstract:

Serious well collapse in the 2h well horizontal section of a CFD oilfield took place during drilling in carbonaceous mudstone before landing. In order to satisfy the requirements of drilling the rest wells, the analysis of drilling collapse and the research on anticollapse countermeasures were carried out. By investigating the correlation between drilling fluid performance and wellbore collapse,bedding structure and clay minerals, the low drilling mud density, and the poor performance of plugging and anti?swelling were determined to the main factors leading to the well collapse. From the point of view of mechanical countermeasures, the relationship curve between well deviation and collapse pressure were established based on the strength anisotropy model, for the future selection of mud density. In view of chemical countermeasures, 1% inhibitor along with 5% calcium carbonate and 1% nano?materials as plugging agents were added in the drilling fluid. The results show that the cuttings roller recovery using optimized drilling fluid could reach to 91.39%, the dynamic HTHP filtrate loss performance be decreased by 22.41%. The point load strength of the optimized drilling fluid is only 13.60%, which is superior to the original one of 32.45%.The research results can provide reference for solving the problem of lack of physical data and urgent need of anti?sloughing measures.

Key words: Carbonaceous mudstone, Drilling fluid, Collapse, Inhibition, Plugging

摘要：

CFD某油田2h井水平段着陆前钻遇碳质泥岩层发生坍塌，影响钻井时效，为满足该油田后续钻井需求，针对性开展坍塌原因分析和对策研究。综合分析钻井液性能与井壁坍塌的关联性、坍塌掉块的层理结构和黏土矿物组分，确定钻井液密度低、封堵性能和抑制性能不足是碳质泥岩层坍塌的主要因素。从力学对策方面，基于强度各向异性模型建立了井斜与坍塌压力的关系曲线，为钻井液密度的选择提供指导。从化学对策方面，通过抑制剂和封堵剂的优选，加入体积分数分别为1%聚胺抑制剂+5%细目碳酸钙+1%纳米封堵材料后的钻井液岩屑回收率达91.39%，高温高压失水降低22.41%，坍塌掉块的点荷载强度降低率从优化前的32.45%降至13.6%。研究结果为解决实物资料少及现场亟需钻井防塌措施提供参考。

关键词: 碳质泥岩, 钻井液, 坍塌, 抑制, 封堵