塔河南岸跃满区块三叠系防塌钻井液研究与应用

针对塔河南岸跃满区块三叠系井段井壁垮塌严重的问题，对井壁失稳机理及防塌钻井液体系研究。三叠系地层岩性为泥岩和砂泥岩，黏土矿物含量为28.6%，黏土矿物中伊蒙混层含量45%，岩石吸水后抗压强度下降，现场钻井液密度低于井壁坍塌压力当量密度，这些是井壁坍塌的主要内因。现场钻井液滤失量大、泥饼厚而韧性差，岩屑滚动回收率和线性防膨率低，封堵性差，固相颗粒粒径分布不合理，这些是井壁坍塌的主要外因。通过优选降滤失剂、复合防塌抑制剂，引入防塌封堵剂FTDA等研究出防塌钻井液体系。该体系API滤失量和高温高压滤失量低，泥饼薄而且韧性好；岩屑滚动回收率比现用体系提高15.7%，对砂盘的封堵性提高50%以上。现场应用时钻井液流变性稳定，滤失量低，无卡钻、无掉块现象，平均井径扩大率为10.35%，比该区块平均井径扩大率下降50.24%。该体系的应用为跃满区块三叠系井壁稳定提供一种新的技术思路。 

Research and Application of Triassic Anti-collapse Drilling Fluid in Yueman Block on The South Bank of Tahe River

Studies on the mechanisms of borehole wall collapse and the drilling fluid capable of controlling the borehole wall collapse were performed to solve the problem of bad borehole wall collapse happening in drilling the Triassic System in the Yueman block, south bank of Tarim river. The Triassic System is mainly composed of mudstones and sandy mudstones containing 28.6% clay minerals in which 45% is the mixed layer of illite and montmorillonite. When in contact with water the formation rocks absorb the water, and the compressive strength of the rocks decreases. On the other hand, the density of the drilling fluid used is less than the equivalent density calculated from the collapse pressure of the formations. These are the the immanent causes resulting in borehole wall collapse. In field operation, the drilling fluid used had high filtration rate, leaving a thick mud cake with poor toughness. Laboratory test with the drilling fluid showed that the percent recovery of shale cuttings is low, while the linear expansion rate is high. Other shortages of the drilling fluid include poor plugging capacity and bad particle size distribution. A new drilling fluid was formulated based on these findings using optimized filter loss reducers, compound inhibitive additives such as FTDA. This drilling fluid has low API and HTHP filtration rates, and the mud cake is thin and tough. The percent recovery of shale cuttings with this drilling fluid was increased by 15.7% compared with the old mud. Plugging test on sand-bed showed that the plugging capacity of the new drilling fluid was increased by at least 50%, indicating that the drilling fluid has reasonable particle size distribution. In field application, the new drilling fluid had stable rheology and low filtration rate, no pipe sticking and borehole sloughing were encountered. The average rate of hole enlargement was 10.35%, which is 50.24% lower than the average rate of hole enlargement of the wells drilled in the same block. The application of the new drilling fluid has provided a new technical clue for stabilizing the borehole wall of the wells penetrating the Triassic System in the Yueman block.