侧钻井钻完井一体化工程可行性探讨

Feasibility of drilling-completion integration engineering in sidetracked holes

某低孔低渗-特低渗气藏深层进行了2轮次的勘探,虽发现了高产井,但后期展开勘探未能规模突破;钻遇的深部硬脆性泥岩和火成岩地层井壁稳定性差,出现坍塌、掉块、漏失等复杂井下事故;储层试油、压裂改造效果不理想,发现和解放油气藏是面临的难题。提出在老井眼上进行开窗侧钻,尽可能保护储层高效开发的钻完井兼顾储层改造一体化工程设计思路。利用测井资料预测了储层出砂可能性及出砂临界压差,结合完井风险评估和储层改造要求,确定了侧钻井采用复合完井方式较好;进行了侧钻井地层三压力剖面预测,地层坍塌压力大于孔隙压力,实施欠平衡钻井易造成井壁坍塌;提出目的层进行储层专打的思路,论证了液相精细控压钻井优于气体欠平衡钻井,并配套了储层保护的液相钻井液体系。储层改造建议下部地层采用裸眼笼统压裂,压裂后产能预测达到了增产改造目的。

After two rounds’ exploration in a certain deep low porosity,low permeability-extra low permeability gas reservoir,high-yield wells are achieved,but no large-scale breakthrough is realized during the late exploration.In the encountered deep layers of friable hard mudstone and volcanic rock,the wellbore stability is poor and complex downhole accidents happen,e.g.collapse,drop and leakage.The well test and fracturing stimulation results are not satisfactory and it is difficult to discover and liberate oil and gas reservoirs.It was proposed to carry out window sidetracking in old wells and ensure the design idea of integration engineering of well drilling and completion while paying attention to reservoir stimulation for reservoir protection and efficient development as much as possible.Then,the sand production possibility of the reservoir and the critical sand production pressure difference were predicted based on the logging data,and combined with the well completion risk evaluation and the reservoir stimulation requirements,it is determined that the composite well completion mode is better suitable for sidetracked holes.Tri-pressure profile prediction was conducted on the strata where sidetracked holes were located.It is revealed that the formation collapse pressure is higher than the pore pressure,so underbalanced drilling tends to result in wellbore collapse.Finally,the idea of only being used for reservoir in the target layers was put forward,it was demonstrated that the liquid-phase accurate managed pressure drilling is superior to the underbalanced air drilling,and the liquid-phase drilling fluid system with the property of reservoir protection was prepared.As for reservoir stimulation,it was recommended to carry out open-hole commingled fracturing in the lower reservoirs.The postfrac productivity prediction reaches the target of stimulation.