松辽盆地陆相致密油井壁失稳机理及钻井液对策

大庆油田松辽盆地北部为陆相致密油资源，在勘探开发中存在井壁失稳难题，制约着致密油的高效开发。因此，采用扫描电镜和X-衍射分析对地层岩心的微观结构和黏土矿物成分进行分析，并对其水化特性进行研究，从而分析了大庆油田致密泥岩油地层井壁失稳机理。通过研究钻井液抑制性、封堵能力、理化参数和泥饼质量对井壁稳定性的影响，最终研发了一套氯化钾低聚胺基钻井液体系。室内实验表明，该钻井液体系的抗温达120 ℃，极压润滑性系数小于0.12，滚动回收率大于96%，能抗10%膨润土侵，在大庆油田致密油区块现场应用20口井，井壁稳定效果良好，水平段平均井径扩大率小于6%，固井优质率大于90%，起下钻、下套管作业顺利。研究成果表明，氯化钾低聚胺基钻井液体系能够有效提高松辽盆地陆相致密油地层井壁稳定性，为提高大庆油田致密油开发效率、降低井下复杂事故提供了技术支撑。 

Mechanisms of Borehole Wall Instability of Terrestrial Tight Oil Wells in Songliao Basin and Drilling Fluid Countermeasures

Borehole wall instability has long been a problem in the development of the terrestrial tight oil in the Songliao Basin (Daqing Oilfield). To understand the mechanisms of the borehole wall instability, SEM and X-ray diffraction were used to analyze the microstructure of the core samples and the mineral composition of clays taken from the wells drilled in the basin. Laboratory studies were conducted on several aspects that are related to the stability of borehole walls, such as the hydration capacity of the core and clay samples, the impact of the mud cake quality, the physical-chemical parameters, the plugging capacity and inhibitive capacity of the drilling fluids used on the stability of the borehole walls etc. Based on these studies, a KCl oligomer polyamine drilling fluid was developed. Study on this drilling fluid showed that it functions normally at temperatures as high as 120 ℃, the extreme pressure friction coefficient of the drilling fluid is 0.12, percent recovery of shale cuttings in roller oven test with this drilling fluid is greater than 96%, and it is resistant to contamination by invasion of 10% bentonite. This drilling fluid has been used on 20 tight oil wells in Daqing, no borehole wall instability was encountered. The average percent hole enlargement of these wells was less than 6%, and 90% of the wells were cemented with excellent job quality. Tripping of drill string during drilling and casing running were all conducted smoothly. Field application has proved that this KCl oligomer polyamine drilling fluid is able to improve the borehole wall stability of the tight oil wells drilled in the Songliao Basin, and its use has provided technical support to the efficient development of the tight oil in Daqing Oilfield and to the mitigation of downhole troubles.