深层脆性页岩水平井裸眼完井井壁稳定性研究

常规页岩气储层改造工艺为套管射孔与多级压裂改造相结合，施工成本高、周期长，若实施水平井段裸眼完井可一定程度降低成本、缩短周期，但水平裸眼井段井壁稳定是实施裸眼完井的前提条件。通过对威荣地区龙马溪组页岩水理化及力学性能进行实验研究，结合建立的裸眼完井理论模型评价威荣地区页岩水平段裸眼完井井壁稳定性。结果表明，龙马溪组页岩为脆性层理页岩，岩体较为致密，力学强度高，力学各向异性明显；现场油基、水基钻井液对岩石膨胀性能及力学性能的改变不明显，现场所用钻井液与该地层配伍程度高；井眼轨迹、层理缝走向、力学各向异性等可对裸眼井段稳定性产生影响，致使不同方向井筒内应力差异明显，沿最小水平主应力方向钻水平井井壁稳定性最好，完井工况下井壁坍塌压力当量密度在1.26 g/cm³，完井投产初期井壁存在轻微崩落掉块，但崩落范围小于30 °，判断认为威荣区块龙马溪组页岩地层可考虑采用水平井裸眼完井方式。

Borehole Completion Stability of Deep Brittle Shale Horizontal Wells

The conventional shale gas reservoir reconstruction process combines casing perforation with multi-stage fracturing reconstruction, with high construction cost and long cycle. With the horizontal well open hole completion, the cost can be reduced and the cycle can be shortened, but the horizontal open hole The stability of the section wall is a prerequisite for the implementation of open hole completion. In this paper, the physicochemical properties and mechanical properties of the Longmaxi Formation shale are studied, and the established open hole completion model is used to evaluate the stability of the open hole wall in the horizontal section of the shale in the Weiyuan-Rongxian area. The results show that the Longmaxi Formation shale is a brittle layered shale with dense rock mass, high mechanical strength and obvious mechanical anisotropy. The oil-based and water-based drilling fluids cause no obvious change to rock swelling performance and mechanical properties. The drilling fluid used in the field has a high compatibility with the formation; the well trajectory, the bedding direction, the mechanical anisotropy, etc. can affect the stability of the open hole section, resulting in a significant difference in the internal stress of the wellbore in different directions; drilling horizontal wells along the direction of minimum horizontal principal stress has the best wall stability. Under the completion condition, the equivalent density of borehole wall collapse pressure is 1.26 g/cm³. In the initial stage of completion, the well wall has a slight collapse, but the collapse range is less than 30°. The horizontal wells can be considered for open hole completion in the Longmaxi Formation shale formation.