Analysis on the causes of the open-hole section collapse of oil production wells in Halahatang Oil field

The oil wells in Halahatang Oilfeld are mainly in the pattern of open hole completion. Due to the borehole instability in the process of production, wellbore collapse of different degrees happen in some open-hole sections, leading to production reduction and even shut in of the oil wells. And as a result, the normal production of the oil wells is seriously impacted. In this paper, the return cuttings and the caliper log of collapsed wells were analyzed comprehensively. It is fgured out that the wellbore collapse mainly occurs in the Lianglitage Formation and Yijianfang Formation. Then, the in-situ stress feld and the collapse horizon, completion mode, reservoir type and production performance of collapsed wells were analyzed from the viewpoint of wellbore collapse mechanisms. It is indicated that the wellbore collapse is mainly caused by the joint effect of internal and external factors of oil wells. The internal factors include reservoir property, reservoir scale and regional in-situ stress, and the external factors include completion mode and reservoir stimulation measure. It is revealed that the matching relation between the well track and the natural fracture has some effect on wellbore stability(the internal factor), and in-situ stress imbalance, low rock strength, formation pressure release, acid fracturing and perforation are the external factors as well as the main causes of wellbore collapse in Halahatang Oilfeld.