A prediction of breakdown pressure from damaged deviated well

Abstract

It has been proved that formation damage is an important reason of abnormal high breakdown pressure (BP), but few quantitative prediction model considering formation damage has been established. In this paper, formation is considered as homogeneous linear elastic small deformation material, an arbitrary deviated well is taken as the research object, in-situ stress and the wellbore injection pressure in the surroundings of borehole wall are calculated on the base of elastic mechanics. Additional fracturing fluid infiltration pressure is calculated based on the empirical relationship of permeability and porosity combined with Darcy’s law of fracturing fluid in poro-elastic media. Based on the stress superposition principle as well as the tensile stress failure criterion, the breakdown pressure prediction model of deviated open hole well with damage is established for the first time, and influence of formation damage on breakdown pressure is quantitatively simulated. For a given in-situ stress regime, the results display breakdown pressure of both damaged well and undamaged well increases with the increase of deviation angle and azimuth angle, the former is always higher than the latter. Moreover, the BP and additional BP Increment is not large when deviation or azimuth angle is less than 30°. On the other hand, additional BP increment rapidly rises more when damaged permeability ratio is less than 0.135 and it can even reach 10MPa in this example.