关键词: 钻井液, 堵漏, 裂缝, 应力强度因子, 诱导应力, 裂缝重启压力

Abstract:

According to basic theories of the linear elastic lithomechanics and rock fracture mechanics,the present paper dealt with the plugging mechanism of drilling liquid by preventing induced fractures from extension and enhancing wellbore pressure through the increase of fracture reopening pressure.A fracture mechanics model was developed by means of analyzing the pressure distribution in factures after plugging,requirements for preventing induced fractures from extension by plugging were presented,and mechanic behaviors of the induced fracture reopening pressure enhanced by sealing were dealt with based on a mathematical model for the induced stress field of fractures in neighboring rocks of wellbore.Theoretical studies demonstrated that the best way of plugging induced fractures was to apply the lost circulation materials (LCM) at a certain distance near fracture mouth,the hydrodynamic pressure at the pointed end of fractures must be lower than the minimum horizontal major stress and the lower the pressure,the better the sealing effect. The increase of the fracture reopening pressure depended on the induced hoop stress,the lost circulation materials (LCM) must prop fracture walls to maintain the induced hoop stress.As the plugging mechanism of drilling fluid by enhancing wellbore pressure contained both sealing and propping fractures,the LCM should have a sealing property and certain mechanical strength.

Key words: drilling fluid, plugging, fracture, stress intensity factor, induced stress, fracture reopening pressure