吴起油田长7页岩油层钻井液优化研究

Optimization of drilling fluid for Chang7 shale reservoir in Wuqi Oilfield

吴起油田长7页岩油层在钻井过程中易发生大规模井壁掉块,这是影响吴起区块长7页岩油水平井钻井提效和综合录井效果的主要原因。为解决页岩失稳问题,利用岩心观察、扫描电镜和X射线衍射分析等实验设备,分析了长7页岩的微观特征和理化特性。研究表明:通过扫描电镜观察,长7页岩微裂缝发育,黏土矿物比例较高,高岭石相对占比为37.56%,遇水易泥化破碎;伊利石和伊/蒙混层接近50%,岩层膨胀压力大,井壁不稳定,在钻井过程中需要注重油层保护;针对吴起地区长7页岩提出了强封堵强抑制的聚合物钻井液的技术对策。钻井液配方为4%膨润土+适量烧碱+适量纯碱+0.3%(HVCMC)+2%(NH4HPAN)+2%(WNP2)+5%PTGE+1%超细碳酸钙+3%纳米碳酸钙+荞麦皮+重晶石。评价表明,该体系老化后黏度和切力小,塑性黏度为16 mPa·s,动塑比为0.44;滤失量和润滑性满足现场要求,API失水3.8 mL,摩擦系数为0.614;岩屑回收率高,达到98.3%,渗透恢复率高,配液污染前后性能稳定。该研究成果对吴起区块水平井的实施具有一定的参考价值。

Large scale borehole wall falling is easy to occur during the drilling of Chang7 shale oil reservoir in Wuqi Oilfield,which is the main reason affecting the drilling efficiency improvement and comprehensive logging effect of Chang7 Shale oil horizontal wells in Wuqi Block.To solve the problem of shale instability,experimental equipment such as core observation,scanning electron microscopy,and X-ray diffraction analysis were used to analyze the microscopic and physicochemical characteristics of the Chang7 shale.The research shows that the scanning electron microscope observation of Chang7 shaleshows that micro cracks and a high proportion of clay mineral,the relative proportion of Kaolinite is 37.56%,which is easy to be muddy and broken when encountering water;The illite and illite/smectite formation are close to 50%,the rock stratum expansion pressure is high,and the borehole wall is unstable,so pay attention to reservoir protection during drilling;The technical countermeasures of strong plugging and strong inhibition polymer drilling fluid for Chang7 shale in Wuqi area are proposed.The drilling fluid formula is 4%bentonite+appropriate caustic soda+appropriate soda+0.3%(HVCMC)+2%(NH4HPAN)+2%(WNP2)+5%PTGE+1%ultra-fine calcium carbonate+3% nano calcium carbonate+buckwheat bran+Baryte;The evaluation shows that after aging,the viscosity and shear force of the system are low,and the plastic viscosity is 16 mPa·s with a dynamic plastic ratio of 0.44;The filtration loss and lubricity meet the on-site requirements,with an API water loss of 3.8 mL and a friction coefficient of 0.614;The recovery rate of rock cuttings is high,reaching 98.3%,and the permeability recovery rate is high.The performance is stable before and after liquid contamination.This research result has certain reference value for the implementation of horizontal wells in the Wuqi Block.