长庆气田碳质泥岩防塌钻井液技术

Drilling Fluid Technology for Preventing Collapse of Carbargilite Formation in Changqing Gas Field

针对长庆气田碳质泥岩段井壁失稳造成井下复杂频发、侧钻率高的问题,开展了岩样的微观结构、阳离子交换容量、矿物组成及理化性能分析,测试了钻井液对岩石力学特性及坍塌压力的影响,确定了碳质泥岩坍塌机理及防塌钻井液技术研发思路。通过实验优选出封堵剂、抑制剂等钻井液处理剂,综合采用纳米乳液、软硬结合的封堵技术,形成了强封堵强抑制高性能钻井液体系配方。该体系的HTHP滤失量≤6 m L,API滤失量≤2 m L,石盒子砂岩封堵率≥85%,人造岩心线性膨胀降低率≥60%。在长庆气田现场试验18口井,钻遇碳质泥岩后侧钻率降低至16.7%,平均钻井周期缩短30 d,达到预期效果,该钻井液技术满足长庆气田碳质泥岩井段安全钻进的需要。

Wellbore collapse in the carbargilite section in Changqing gas feld has resulted in frequent occurrence of downhole troubles and sidetracking. To resolve these problems, rock samples taken from the carbargilite formation were studied for the microstructure, cation exchange capacity, mineral composition and physiochemical property. The effect of drilling fuid on the mechanical characteristics and collapse pressure of the rock samples was tested, and the mechanisms in which the carbargilite formation collapses and ideas on which the drilling fuid technology for preventing carbargilite formation collapse was studied were determined. A high performance drilling fuid having strong plugging capacity and high inhibitive capacity was formulated through laboratory experiment. Plugging agents of different hardness and shale inhibitors selected, and nano-emulsion were used to render the drilling fuid properties required. The HTHP flter loss and API flter loss are ≤ 6 mL and ≤ 2 mL, respectively. Rate of sandstone （Shihezi formation） plugged by the drilling fuid is ≥ 85%. Rate of linear swelling of artifcial rock cores is reduced by at least 60%. Field application of the drilling fuid on 18 wells in Changqing gas feld showed that the percentage of sidetracking when drilling the carbargilite formation was reduced to 16.7%. Average drilling time was reduced by 30 d. The use of this drilling fuid has achieved the desired effect, and satisfed the needs of safely drilling the carbargilite formation in Changqing gas feld.