Research Of Fracturing Through Ultrashort Radius Radial Well In Coalbed And Optimization Of The Fracturing Process

Ultrashort radius radial drilling technology can make the drilling bit turning at a very small curvature radius in the casing,so it can reduce the complexity and amount of costs when drilling a horizontal wellbores.Its drilling bit breaks rock into holes by hydraulic jet flow,so this technology is very suitable for applying in coalbed which is soft very much.Therefore,in recent years,ultrashort radius radial drilling technology has been gradually used in coalbed gas reservoirs in Shanxi and other places.In order to obtain a better development effect,a preliminary test of staged fracturing in the radial borehole was conducted on site,but because of the high hydraulic frictional resistance,it was difficult to form effective cracks.Under this circumstance,the research field of this paper is pinpointed to the direct-hole fracturing in radius well-hole which is different with the predecessors' researches,and after that the fracturing operation methods and process is optimized.Based on the fluid-structure interaction of porous media and the stress concentration at the radial wellbore,some three-dimensional elastic finite element models,which has the similar physical properties of the real coalbed,has been established in order to study the characteristics of the fractures separated though ultrashort radius radial wells(URRW).In this way,the influence of diameter,length,number,azimuth,and geostress difference of URRW on the starting-crack pressure,position and direction of the fractures is revealed.It is found that the radial wellbore has a strong controlling effect on the initial direction of the crack.Based on the XFEM method,this paper studies the fracture extension process and fracture morphology.The effect of radial borehole length,azimuth angle,fracturing fluid displacement,and geostress difference on crack extension is clarified.It is found that width of the fractures is not regular along with its length due to shear action produced by geostress difference.The fracturing process through radial wells in coalbed is optimized.Reasonable radial wellbore parameters and arrangement methods are given.The propping agent type,fracturing fluid type and its formulation are optimized.The technological parameters of the fracturing process in the coal seam are optimized.