Study On Mechanism Of Formation Of Water Inflow Area In Marked Bed Casing Damage Zone

Problem of casing damage always exists in the process of oilfield development and has a great impact on normal production of oil field. In recent years, casing damage in marked bed becomes more and more serious, which has become one of the main layers of casing damage,and seriously restricts development of oil field. In accordance with problem of casing damage in marked bed, field measured data shows that there is a phenomenon of water inflow in marked bed casing damage zone, which indicates that there is a direct relationship between the water inflow and the casing damage. Therefore, it is necessary to carry out the research on formation of water inflow area.To formation of water inflow area problem in 307 team block of Beisandong area, this paper hope to reveal mechanical mechanism of water inflow area formation in marked bed by carrying out the rock mechanics experimental research and finite element numerical simulation, and to provide reference for effective prevention and control measures of water inflow area formation in marked bed.Firstly, this paper carried out the rock mechanics experiment of mudstone and shale of marked bed. Uniaxial compressive strength, triaxial compressive strength, tension strength,shear strength and other mechanics parameters of the mudstone and the shale along with parallel and vertical with cleats were obtained through the rock mechanical experiments.Experimental results show that the shale and mudstone mechanics parameters have obvious difference to the different coring direction, existing the obvious anisotropic characteristics.Tension strength, cohesive force and shear strength in parallel to cleat direction is smaller,and then so it is easier to broken along with the bedding direction, forming a horizontal seam.Secondly, from point of view of mechanics, the precondition and the mechanical mechanism of formation of water inflow area in marked bed are analyzed. The precondition of formation of water inflow area is the existence of the influent channel, analyzing and explaining three possible influent channels. According to the mechanical properties of marked bed rock, the calculation model of the transverse isotropy wall rock stress of is established, and the calculation model of the critical rupture pressure is derived, and analyze that water inflow area have been along with the direction of in the process of formation of water inflow area due to tensile failure π/2 and 3π/2 of well perigon and extending direction of water inflow area changes.Then, according to the structure and mechanical properties of the rock, the transverseisotropic porous media geological model is established. Based on the calculated water inflow area maximization principle, the principle of water inflow area by numerical simulation calculation is obtained. Distribution of water inflow area in marked bed from 2010 to 2012 are obtained applied to finite element numerical simulation, and the results show that formation pressure of marked bed casing damage zone increase, so as to the vary of water inflow area in marked bed, and the changes of press and water inflow area exist consistency.Finally, applying to established geological model, analyze the change of water inflow area in marked bed along with changes of fault, injection pressure, porosity, cohesive force and tensile strength. The results show that due to the barrier effect of the fault, under the same condition of formation pressure, water inflow area in marked bed of the zone with fault is larger; as the injection pressure increasing, water inflow area in marked bed increases rapidly;as increase of rock porosity, water inflow area in marked bed firstly increases and tends to be stable; as increase of rock cohesion increases, water inflow area in marked bed firstly decreases and tends to be unchanged; as increase of rock tensile strength, water inflow area in marked bed firstly decreases.