Abstract: It is difficult to accurately predict breakdown pressure of high stress reservoir or reservoirs with complex in-situ stress conditions, which leads to problems such as difficulties in reservoir fracturing, risk of liquid pumping and difficulties in sand pumping. Perforation hole is an important channel connecting wellbore and formation. Studying the initiation pressure and orientation of perforation hole is helpful to the understanding of the breakdown behavior of high stress reservoir or reservoir with complex in-situ stress conditions, and provides a basis for subsequent optimization of sand fracturing process. In this paper, based on the theory of elastic mechanics, the stress field model around the casing perforation well and the perforation hole are established. Based on this model, the initiation pressure and orientation of perforation hole are determined. Compared with the field data of a high stress reservoir, the reliability of the model is proved. Hole initiation pressure and orientation in vertical well under different in-situ stress conditions of high stress reservoir are also analyzed. The results show that for in-situ stress state in both strike-slip fault and reverse fault, when perforating along the direction of the maximum horizontal principal stress, the hole always fracture horizontally, forming a horizontal fracture near the hole, and the initiation pressure is the lowest, and the pattern of near-wellbore fracture on strike-slip fault is more tortuous; when perforating along the direction of the minimum horizontal principal stress, the smaller the horizontal ground stress difference is, the easier the hole is to fracture horizontally, forming a horizontal fracture near the hole, and the initiation pressure is higher, and the pattern of near-wellbore fracture on strike-slip fault is more tortuous; the larger the horizontal stress difference is, the easier the hole is to fracture longitudinally, which tends to form vertical fracture near the hole, and the initiation pressure is lower, and the pattern of near-wellbore fracture on reverse fault is more tortuous. The results of this study are conducive to the efficient development of high stress reservoirs or reservoirs with complex in-situ stress conditions.

Key words: perforation hole initiation, high stress reservoir, initiation pressure, initiation direction