Study On Mechanical Deformation And Seepage Characteristics Of Oil Sands

Traditional thermal development for oil sands,due to the high viscosity of crude oil,is faced with the problems of long cycle pre-heating period,high steam energy consumption and low recovery.Micro-fracturing,an efficient way,is employed to create micro-fractures around the wellbore,which can shorten the production cycle and improve the development.Water injection pressure control and connectivity improvement between injection-and production horizontal well,however,is an urgent engineering problem to be solved.Mechanism of dilation by water injection,the key to solving the problem,need more deep-insight in theory and technology.In this paper,focus on the deformation and seepage characteristics of oil sands during water injection,the following study has been systematically carried out:(1).Experimental investigation on mechanical properties of oil sandsConsidering the problem of the unsolid structure and perturbable of natural oil sands,new methods including coring and artificial manufacture have been put forward.The dilation pattern and seepage behavior of oil sands are recognized through laboratory test analysis.Low strength and high plasticity are proved to be the main controlling factor affecting the interaction between the oil sands matrix and pore fluid.(2).Investigation on mesoscopic seepage and deformation mechanism of oil sandsBased on the physical experiment of CT core scanning,the meso-structure of oil sands has been investigated using digital core technology.The multiple contact relationships between matrix and bitumen are precisely characterization using a new method of triple media segmentation.The pore-scale seepage simulation under multiple factors has been studied based on the three-dimensional pore network model,and the absolute and effective seepage pattern of oil sands is obtained.By comparing the pore connectivity and pore throat characteristics before and after injection,the interaction between matrix and pore fluid was quantitatively characterized,and the dilation mechanism of oil sands has been revealed.(3).Oil sands deformation during water injection by visual physical simulationThe deformation of oil sands during water injection has been studied using visual physical experiment.The total displacement and strain field of matrix deformation was obtained by the digital image correlation analysis method and the multi-core iterative calculation at multiple initial points.The variety process of the oil sands from disconnection to connection was observed,and a method of identifying shear dilation and tensile dilation was proposed.Meanwhile,the pattern of tensile dilation that happened following by shear dilation at the far injection field has been found,and seepage pattern under different injection condition was also obtained.(4).Dilation evaluation of water injection by numerical simulationAccording to the field water injection condition,a three-dimensional finite model coupling dilation-seepage has been built considering the mechanism of the hyperosmotic zone around the wellbore.The effectiveness of micro-fracturing has been evaluated using two new concepts including hydraulic connectivity coefficient and hydraulic sweep range,and the influence of reservoir property on dilation has been analyzed.The new concepts provide a basis judgment for injection pressure and the hydraulic connection and get good feedback.