Kawanishi Repeated Fracturing Wells Stress Field Studies

As the fracturing wells of oil and gas exploration, the first fracturing crack will gradually lose their support effect and stimulation function gradually reduced. Therefore, it is necessary to carry out refracturing to maximum increase the oil and gas production. Sichuan Western areas have low permeability reservoir. Because of the compacted sandstone reservoir and the poor seepage condition, there are currently wells lost a great part of stimulation function. Therefore needs to be further studied field stress of refracturing.The article based on the geological data from Sichuan Western areas and used the ABAQUS software to study the change rule of stress field around the wellbore and crack. The study is from two aspects. On the one hand, the influence factors of stress steering range are analysised from the modeling without considering the fluidsolid coupled. On the other hand, pore elastic medium modle was established according to the basic theory of fluid-solid coupling. This modle is full of single-phase saturated fluid. It considering about the coupling of seepage and rock solid deformation to educes the equation between pore pressure changes and deform amount. And it also educe the equation between the rock permility changes and deform amount. According to the several basic formula, the USDFLD subroutines was written by Fortran language for the second development of geotechnical module which in the ABAQUS software. Through the simulation.The change rule of pore pressure and permeability was got around hole and cracks.The following main achievements and understandings were made:(1) Through the simulation analysis of the stress distribution around borehole that due to the existence of the stress field near the borehole happened obvious steering, stress direction along the borehole tangent roughly. In the primitive maximum principal stress direction, stress to obvious steering. But in the primitive minimum principal stress direction, stress almost did not happen steering. (2) Around the crack, there are obvious induce stress field and the induced stress in crack tip obviously concentrated. (3) The sizes of stress steering range are associated with producing pressure drop, in-situ stress drop, penetration ratio and crack width. But the influence degree of each factor is different. (4) Fluid-solid coupling analysis concluded that, with production, the change rule of pore pressure and permeability around hole and cracks. And through the relationship between stess steering range and time, the best time of refracturing could be choose.Through the research in this paper, the field stress steering range in Sichuan Western areas could be defined. And whether it has the possibility of realizing redirection fracturing could be determined. The fluid-soid coupling modle can reflecting the distribution of stress field and choose appropriate refracturing time. The research result can guide a lot of refracturing engineering and improve process feasibility and economic feasibility. And it has the extremely vital significance for stimulation of Sichuan Western areas tight gas reservoir.