An analytical model of hydraulic dilation area for Karamay oil sand reservoir under water injection in SAGD wells

摘要

Based on the mechanical mechanisms of shear and tensile parting dilations, water injection into oil sand reservoirs prior to steam circulation can effectively establish inter-well hydraulic communication and create an expected initial steam chamber. To quantitatively evaluate the effectiveness of water injection, this paper defined some novel concepts including the effective permeability to injection water, hydraulic dilation area (HDA) as well as radius (HDR) incorporating longitudinal and lateral hydraulic dilation radii (HDRa and HDRb) for a more intuitive description of the hydraulic dilation behavior. An analytical model of hydraulic dilation area under water injection was established considering the interference effects of mudstone cap and base rocks, effective permeability to injection water, SAGD well geometry and operation parameters. The figures of analytical results are exhibited for evaluating the hydraulic dilation response under given geometry and flow properties and for finding an achievable path for improving the HDR and HDA through artificial operations for an operator. Major conclusions through an application on the wellpair A-2 in area A of Karamay Fengcheng oil field can be drawn that the HDR and HDA can be improved by increasing the injection pressure or decreasing the fluid viscosity and injection rate of unit well length. A higher effective permeability to injection water induced by a larger volumetric expansion is beneficial to the HDR and HDA. A larger wellbore radius, a closer distance between P well and base rock, and a closer well distance designed in the drilling process are advantageous to the HDR and HDA. The HDA and HDR are essentially controlled by the volumetric dilation resulting from pressure transfer capability and pressure interference by mudstones and SAGD wells. These findings provide an analytical approach for evaluating the efficiency of water injection, and offer some suggestions to improve the HDA by artificial operations for engineers.