三压力剖面计算在彭州气田复杂情况预防中的应用

Application of Three-pressure Profile Calculation to Prevention from Complexities in Pengzhou Gasfield

为找出彭州气田复杂情况发生的原因,通过优选伊顿法计算地层孔隙压力、根据库仑—摩尔强度准则计算地层坍塌压力、基于最大拉应力理论计算地层破裂压力等方法,建立地区三压力剖面。在此基础上,通过对三压力剖面、岩性、掉块形态、井径曲线等资料分析得出:井涌是钻遇高压气层时钻井液密度过小,在压井过程中使用过高钻井液密度压破上部疏松地层;井壁掉块是因地层微裂缝发育,高密度钻井液易滤失沿微裂缝渗透进入地层,增大坍塌压力导致井壁失稳;四开卡钻是因马鞍塘组一段发育的页岩掉块卡入取心钻头和井壁。针对复杂情况发生原因,根据三压力剖面特征,通过采取优化井身结构以及改善钻井液防塌性能和封堵性确定合理钻井液密度等预防措施,使气田钻井复杂情况减少59.5%,钻井周期缩短29.8%。

To find out reasons causing drilling complexities in Pengzhou gasfield,in this study,we established a three-profile pressure profile for the gasfield by calculating the pore pressure through Eaton method,the collapse pressure by Coulomb-Moore Strength Criterion,and fracture pressure by the maximum pulling stress individually.Through this profile,and some data on the lithology,falling debris shape,and caliper curve,we made clear the reasons.Results show that(1)well kick occurs while drilling highpressure formations with small-density drilling fluid or when highdensity drilling fluid is used in a killing to drilling across the upper loose layers;(2)falling debris is caused by microfracture development,high-density drilling fluid easily generates leak-off and subsequently enters into formations along microfactures,consequently leading to the increase of collapse pressure and wellbore instability;and(3)fourth-interval sticking is just due to shale falling-off adhere to cored bit or sidewall.So,many countermeasures are made,including to optimize the casing program,to improve the anti-collapse and sealing properties of drilling fluid,and to determine a reasonable density.After that,the complexities decreased 59.5%,drilling cycle reduced 29.8%,and drilling speed increased evidently and drilling cost saved.