易失稳火成岩气井欠平衡钻井技术关键

APPLICATION OF UNDERBALANCED DRILLING TECHNOLOGY IN IGNEOUS ROCK FORMATION GAS WELL

冀东南堡5号构造深部沙河街组储层物性差,孔隙度和渗透率较低,以往常规过平衡钻井过程中多发生漏失,严重伤害了储层。为了有效地发现和评价5号构造深层天然气含气情况,冀东油田开展了南堡5号构造沙河街储层欠平衡钻井技术的研究与应用。由于沙河街储层的坍塌压力比孔隙压力高,不满足欠平衡钻井的压力窗口。通过对南堡5号构造深层沙河街砂泥岩及火成岩地层井壁稳定性分析,研究发现当欠压值合理的情况下,井径扩大率达20%后的坍塌压力小于地层孔隙压力,可以满足欠平衡钻井及探井井身质量的要求,通过6口井的成功应用,证实该理论是可行的,同时也表明在井壁稳定性差的南堡5号构造沙河街地层可实施液相欠平衡钻井技术。

The deep reservoir physical property of Shahejie Formation in 5th structure of Jidong Nanpu Oilfield is poor and the porosity and permeability is relatively low.Drilling fluid circulation loss happened usually in the past conventional overbalance drilling process which polluted the reservoir seriously.In order to explore the gas reserves in 5th structure of Nanpu,Jidong Oilfield carried out the research and application of underbalanced drilling technique.For the caving pressure is higher than pore pressure in Shahejie Formation,it can't meet the pressure window of underbalanced drilling.Through analyzing the borehole stability in mud-sand stone and igneous rock layer of Nanpu 5th structure,the results showed that when underbalanced pressure differential was rational and hole diameter expanding rate reached 20%,the caving pressure was lower than pore pressure which met the requirement of underbalanced drilling technique and wellbore quality.The underbalanced drilling technique was successfully used in 6 wells,application results showed that this theory was feasible.