Analysis on wellbore stability of open hole in fractrued formation

Carbonate rocks in westward oilfield are characterized by deep bury, high temperature, rich in fracture-cave and well collapse, blocking and burying of testing tool always appear in the open-hole completion well formation in the process of production. The reasons of well collapse have analyzed in this article based on in-situ data, at the same time, since the high temperature and high pressure of formation, comprehensive prediction model about borehole stability has been set up, considering with temperature field, flow field, fracture occurrence and hydration. Collapse mechanism of openhole completion deep well in high temperature hydration carbonate stratum also been analyzed. The research results indicated that the minimum bottom hole pressure of maintain wellbore stability acquired from this model is 2-3 MPa higher than that from other conventional models, which promote prediction accuracy; rock strength increases at first and then decreases with the fracture dip from 0° to 90°; The most secure formation is that the formation dip keeps in line with direction of minimum horizontal stress and the fracture dip is lower than 20°, besides, the second is the condition that formation dip consistent with maximum horizontal stress direction and fracture dip is greater than 60°. The minimum of bottom hole pressure maintaining wellbore stability increase with the decrease of inner friction coefficient and cohesive of weak surface after hydration, and increase with stress difference increasing.