涠洲W油田多压力系统储层定向井钻井液优化技术

涠洲W油田储层段存在多压力系统,导致常规PLUS/KCl钻井液因流变稳定性较差而老化后增黏变稠、封堵材料单一使钻井压差超过26 MPa时发生井漏、暂堵剂粒径分布不合适使储层保护效果欠佳等问题。在常规PLUS/KCL钻井液配方基础上,通过优化处理剂加量提高体系流变稳定性,优选封堵剂及复配组合提高封堵能力,同时优化暂堵剂粒径分布提高储层保护效果,形成了一套适用于多压力系统储层定向钻进的PLUS/KCl钻井液体系。室内性能评价结果表明:优化后的PLUS/KCl钻井液具有良好封堵承压能力,120℃/35 MPa条件下12 h,在天然岩心上的侵入深度仅4.1 cm,可有效减小井漏风险;截断污染端后岩心的渗透率恢复率大于90%,储层保护效果好;钻井液性能稳定,岩屑滚动回收率高达90%以上。现场应用结果表明:采用优化后的PLUS/KCl钻井液作业,未发生井漏、井壁失稳等复杂情况,各井产量均超配产,有效解决了高压差下定向井安全钻井和储层伤害难题,具有较好的推广应用价值。

Optimization technology of drilling fluid for directional wells in multi-pressure system reservoirs in Weizhou Woilfield

Due to the existence of multi-pressure system in the reservoir section of Weizhou W oilfield,there are many problems in drilling fluid,such as conventional PLUS/KCl drilling fluid thickening after aging due to insufficient rheological stability,single plugging material leading to lost circulation when the drilling pressure difference exceeds 26 MPa,improper size distribution of temporary plugging agent leading to poor reservoir protection effect,etc.On the basis of conventional PLUS/KCl drilling fluid formula,a set of PLUS/KCl drilling fluid system suitable for directional drilling in multi-pressure system reservoir is formed by optimizing the dosage of treating chemicals to improve the rheological stability of the system,optimizing the plugging agent and compound combination to improve the plugging ability,and optimizing the size distribution of temporary plugging agent to improve the reservoir protection effect.The results of indoor performance evaluation show that:the optimized PLUS/KCl drilling fluid has good sealing and pressure bearing capacities for its invasion depth into natural core is only 4.1 cm at 120℃/35 MPa for 12 h,proving that it can effectively reduce lost circulation risk;the permeability recovery rate of core after cutting off the polluted end is more than 90%,showing a good reservoir protection effect;the drilling fluid has stable rheological properties and the rolling recovery rate of cuttings is more than 90%.The results of field application show that:when the optimized PLUS/KCl drilling fluid is adopted,no complicated situation such as lost circulation or wellbore instability occurs,and the production of each well exceeds the production proration,which effectively solves the problems of safe drilling and reservoir damage of directional wells under high pressure difference,and has better application and promotion value.