致密油开发水平井段页岩坍塌周期的确定  

Modeling of time-dependent wellbore instability of shale in horizontal wells for tight oils

作　　者：程远方 黄浩勇 韩忠英 贾江鸿 李梦来 吴学升 

机构地区：[1]中国石油大学石油工程学院,山东青岛266580 [2]中石化胜利石油工程有限公司钻井工艺研究院,山东东营257017 [3]长庆油田油气工艺研究院,陕西西安710018

出　　处：《中国石油大学学报（自然科学版）》2016年第1期62-68,共7页Journal of China University of Petroleum(Edition of Natural Science)

基　　金：教育部长江学者和创新团队发展计划(RT1086)

摘　　要：鄂尔多斯盆地致密油资源丰富,具有很大的开发潜力,但长庆油田A井区在页岩油长水平段钻进时井壁失稳问题突出。现有的水平井防塌技术重点关注钻井液体系优化问题,无法给出页岩的坍塌周期。本井区页岩的主导坍塌机制是钻井液滤液沿天然微裂缝渗入地层,引起黏土矿物水化,导致岩石强度降低。考虑化学势变化和流体流动与骨架变形的耦合作用以及岩石吸水扩散过程和强度弱化规律,建立致密页岩井壁坍塌周期分析模型。结果表明:活度较低、膜效率较高的钻井液可以有效抑制地层孔隙压力增长;封堵性强的钻井液可以降低地层水含量的增长,减缓地层岩石强度的弱化;A井区使用密度为1.3 g/cm3的细分散聚合物钻井液体系和复合盐钻井液体系钻进水平段时井眼坍塌周期分别为4.5和9 d,而使用油基钻井液体系时相同密度下浸泡10 d井眼扩大率仅为4%,油基钻井液体系效果最好,坍塌周期大于10 d。In the development of tight oil and gas in Ordos Basin,the wellbore instability issue is of great significance,especially in the drilling of long horizontal sections in A-block of Changqing Oilfield. The current anti-sloughing technique applied to horizontal drilling is mainly focused on optimizing the drilling fluid system,while an accurate prediction of time-dependent wellbore instability is still not available. Infiltration of drilling fluids into shale matrix through micro fractures can cause hydration of clay minerals and weaken the strength of the rock,which is considered to be the dominant mechanism for wellbore collapsing in the region. In this study,a time-dependent wellbore instability model of tight shale layers was established considering the effects of chemical potentials,fluid flow,water diffusion,deformation and strength weakening of the rock. The results show that drilling fluids with low activity and high membrane efficiency can effectively control the increase of pore pressure,and drilling fluids with good plugging performance can reduce the content of formation water and slow down the weakening of rock strength. During horizontal well drilling in A-block,the well bore collapsing is delayed up to 4. 5 and 9days,respectively,when a finely dispersed polymer drilling fluid and a compound salt drilling fluid with density of 1. 3 g /cm3 are used. The wellbore enlargement ratio after 10 days soaking is only 4% when an oil-based drilling fluid is applied,and the delay time for wellbore collapse can be over 10 days. Oil-based drilling fluid is the best for controlling the wellbore collapse in the region.

关 键 词：致密油 坍塌周期 钻井液优选 强度弱化 

分 类 号：TE254.3[石油与天然气工程—油气井工程]