The micro-scale hydraulic fracturing is a technique which is used to shorten the preheating period by means of controlling water injection to horizontal wells to create homogenously distributed microcracks in the zone between the two wells. Numerous simulation studies have been previously conducted to understand the growth of the steam chamber, however, the model to simulate mini-frac before preheating is left undone. Especially, counterpart research on land facies ultra-heavy oil sand of Xinjiang oilfield is few.
The provides micro-scale hydraulic fracturing model, in this study, is based on experimental analysis in terms of geomechanics theory and mini-frac tests result from field experiment in Xinjiang oilfield. First, laboratory triaxial tests were designed to determinate the mechanical behavior of the oil sand and the mudstone caprock. Drucker-Prager model was used to investigate the two dilation mechanisms, namely, shear dilation and tensile parting, during the simulation of micro-fracturing propagation. Finally, a micro-fracturing model coupled fluid-solid is implemented by with the finite element program ABAQUS, to describe the early SAGD start-up demonstrated on the SAGD well pair in Xinjiang oilfield.
The first-hand target of ABAQUS simulation in this study is to evaluate the performance of micro-fracturing process, particularly, to determine the degree of connectivity of injection and production wells. Thereby to predetermine the bottom hole pressure (BHP) and volume of injection in order to provide a specific guidance for work program carried out in oilfield. As the matter of convenience, this study, according to the simulation results, have discussed how to define the extent of the connected parameters to determine the connectivity of the well pairs. Furthermore, sensitivity analyses have been done to realize the different parameters on proficiency of micro-scale hydraulic fracturing in the field.
Our works are significantly important for the future development and promote the mini-frac tests to enhance the in-situ thermal recovery in Xinjiang oil field. In addition, the model and method can be implemented for any type of heavy oil field which requires early SAGD start-up to increase the oil recovery.