钻井液完井液屏蔽环重复形成的实验模拟

深探井及多目的层油气探井在进行中途测试、完井测试和起下钻作业中，不可避免地造成钻井完井液滤饼遭受多次形成与破坏，此时滤饼的性能发生了较大的变化并对测试结果产生重要的影响。选取四川盆地川东北区长兴组和飞仙关组碳酸盐岩储层不同渗透率级别的岩样及改性钻井完井液，利用高温高压动态损害评价仪进行了钻井完井液屏蔽环重复形成与返排的实验模拟。结果表明，多次形成于基块和裂缝岩样中的钻井完井液屏蔽环的暂堵率和强度都得到了提高。重复作业时滤饼不断地向裂缝深部推进并因应力敏感损害而难返排，致使裂缝岩样渗透率恢复率降低明显，相反基块岩样一般仍可得到满意的渗透率恢复率。适当增大返排压差可以提高岩样渗透率的恢复率。

Experimental simulation on shield ring formation repeatedly by drilling fluid & completion fluid

In the operation of drill-stem test, well completing test and trip in deep exploration well and multi-target stratum oil-gas exploration well, the mud cake formed by drilling fluid and completion fluid must be destroyed and formed repeatedly. The results tested are seriously influenced due to the mud cake character changing. By means of HTHP dynamic damage evaluation instrument, some simulating experiments of mud cake formed repeatedly were performed with various permeable core sample from Dongbei Changxing, Feixian guan formation carbonate reservoirs and modified drilling fluid. Results tested showed that the temporary plugging efficiency and strength of shielding ring formed repeatedly in bedrock and fractured core were improved. In many operations, the cake was squeezed into deep fracture and the rock occurred stress sensitivity damage, as a result the permeability recovery of fractured core is reduced obviously because the cake can not return easily, while the permeability recovery of bedrock is better. Moreover, the permeability recovery of core sample can be improved by increasing backflow pressure differential.