巴基斯坦北部区块抗高温高密度柴油基钻井液体系

巴基斯坦北部区块地质条件复杂，地层重复反转，油气埋藏深，井底高温高压，二开井段存在长段页岩层，易吸水膨胀、垮塌，三开井段存在盐膏层易缩径、卡钻，同时盐水侵入污染高钻井液密度易造成钻井液流变性恶化，难以控制，导致该区域钻井作业异常艰难，使其成为巴基斯坦乃至世界上钻井最复杂的地区之一。针对上述难题，同时满足当地油公司的技术要求，以0#柴油为连续相，氯化钙水溶液为分散相，通过处理剂和加量优选形成了一套柴油基钻井液体系。室内评价结果表明，该钻井液抗温达180℃，最高密度达2.20 g/cm3，老化前后破乳电压大于1200 V；有良好的沉降稳定性；在高温高压下仍能保持较好的流变性，对重晶石的悬浮稳定性好，具有良好的携带岩屑能力；且具有抗15%盐水、10%页岩和石膏污染的能力，满足巴基斯坦北部区块钻井作业的应用需求。 

A High Temperature High Density Diesel Oil Base Drilling Fluid Used in North Block in North Pakistan

In the North Block in Pakistan, the geological condition of the formations is very complex, and the formations penetrated have repeated inversion. The petroleum resource is buried deep in high temperature high pressure formations. Wells drilled in this block penetrated long section of shales in the second interval and salt/gypsum sections in the third interval. The shales swell and slough when in contact with water, and tight spots and pipe sticking were encountered in the salt/gypsum sections. Contamination of salt water from the formation to the drilling fluid spoiled the mud and made the mud properties difficult to control. These problems have made the drilling operations in this block extremely difficult, and the North Block is thus famous for being one of the most complex drilling areas in Pakistan or even worldwide. To deal with these problems, a diesel oil drilling fluid was formulated with 0# diesel oil (the continuous phase), CaCl₂ water solution (dispersed phase) and other additives selected. This drilling fluid has satisfied the requirements of the local operator company. Laboratory evaluation showed that the properties of the drilling were stable at temperatures up to 180℃. The drilling fluid can be weighted to a density of 2.20 g/cm3. The emulsion stability of the drilling fluid before and after aging was 1200 V. The drilling fluid had good suspending capacity and cuttings carrying capacity. The rheology of the drilling fluid remained stable at high temperature and high pressure. The drilling fluid has the ability to resist contamination from 15% salt water, 10% shale cuttings and gypsum. All these characteristics of the drilling fluid have satisfied the requirements of the drilling operations in the North Block in Pakistan.