高压低渗透气井欠平衡固井技术——以宝龙1井为例

Underbalanced cementing technology for high-pressure and low-permeability gas wells:Case story of the well Baolong-1

宝龙1井是四川盆地川中龙女寺构造上的一口典型的压力窗口窄、漏喷共存的预探井。宝龙1井下177.8mm尾管至井深2250.05m发生井漏失返,下至井深4569.70m井漏未返,反灌钻井液4.6m3见返,循环井漏,采用桥浆堵漏仍然井漏,不能建立循环。为此,提出采用正反注水泥法来固井施工的技术思路。正注水泥施工结束后出现溢流不能起钻,决定在喇叭口处直接反注水泥然后起钻,反注水泥完仍然出现高压低渗透溢流,被迫循环排除水泥浆。在管内注入密度为2.42g/cm3的加重钻井液,在环空有限溢流的前提下把钻具起至设计位置,进行反注水泥施工作业,固井成功,电测固井质量合格率为84.33%、优质率为76.79%。该技术为高压低渗透气井欠平衡固井提供了新的途径。

The well Baolong-1 is a wildcat well typical of narrow pressure window and kick-loss scenario at Longnushi Structure in Central Sichuan Basin.When the 177.8 mm diameter base liner ran to 2250.05 m measured depth,lost circulation occurred.When it ran to 4569.70 m measured depth,there was no fluid return at all.So 4.6 m3 of drilling fluid was injected through the annulus and the fluid return was finally observed.Then circulation was continued and the bridging slurry was used to attempt to plug the well,but the lost circulation could not be completely controlled and the circulation could not be recovered.In such a case,the cementing operation by injecting cement slurry through both casing and annulus was then planned.However,at the end of slurry injection through casing,kick occurred,which prevented tripping out.And when the slurry was injected into the annulus afterwards at the bell nipple before tripping out,the high-pressure low-permeability kick occurred again.At that moment circulation to remove cement slurry had to be performed.A weighted 2.42 g/cm3 drilling fluid was injected downhole,and the drilling string was pulled up to the designed point on condition that the kick out of the annulus was limited.And then cement slurry was injected into the annulus to conduct cementing job.The log showed the cementing quality,with a pass rate of 84.33% and a good quality rate of 76.79%.These cementing procedures will provide a new way for underbalanced cementing in high-pressure and low-permeability gas wells.