Experimental Investigation on Compressibility of Karamay Oil Sands Under Water Injection

摘要

Steam assisted gravity drainage (SAGD) adopts a stimulation process through water injection to a pair of horizontal wells. Two deformation mechanisms named shear dilation and tensile parting occur in this process. Triaxial shear and hydrostatic pressure tests were conducted on specimens sampled from field-collected oil sand cores, so as to investigate the compressibility of shear dilation and tensile parting dilation of oil sand under the real water injection pressure as well as in-situ stress and temperature states in the field. It is revealed that the compressibility of the specimens under shear increases with increasing mean effective stress until strain-softening takes place, but displays an opposite trend thereafter. Moreover, such a compressibility increases with decreasing effective confining stress and temperature, or an increase in uniaxial strain. The tensile dilation tests, on the other hand, disclosed that the associated compressibility changes inversely proportional to the mean effective stress or temperature. Interestingly, an increased temperature of the injected fluid suppresses rather than promoting the compressibility of an oil sand reservoir. A wellpair in the Fengcheng oilfield of Karamay was examined to predict its ultimate injected water volume, producing a result very close to that recorded in the field.