Practice and understanding of vertical well fracturing for deep CBM reservoirs in Sulige gasfield,Ordos Basin
Currently,deep(˃3000 m)coalbed methane(CBM)exploration and development are in the initial stages.Issues in under-standing the physical properties of deep coal and matching reservoir stimulation processes have constrained the large-scale exploration and development of deep CBM.Considering the characteristics of CBM reservoirs,including deep burial,high pressure,high tempera-ture,high free gas,large filtration loss,and post-frac single hydraulic fracture,a set of large-scale and-discharge fracturing process suitable for such CBM reservoirs was preliminarily established by extracting the advantages of previous stimulation treatments,opti-mizing fracturing parameters,upgrading fracturing fluid performance,supporting tertiary fractures,and energizing low-pressure reser-voirs to break reservoirs,connect cleats,control filtration loss,support efficiently,and improve stimulated volume.Field application in a pilot test area,Well A block,shows that,(i)the stimulation with high-viscosity fracturing fluid as ahead fluid to create the main fractures,low-viscosity fracturing fluid to create the fracture network,supporting tertiary fractures,and liquid nitrogen for energy re-plenishment helps realize the post-frac backflow rate up to 86.2%;(ii)an effective long support fracture network is created by various means including large discharge,extreme sand adding,short perforation section with few clusters,and multiple particle size combi-nation of proppants for connecting main fractures,branch fractures and cleat microfissures;and(iii)the created hydraulic fractures extend well,showing a bidirectional distribution,with the length of about 380 m;the fractures are basically consistent with the trend of the maximum principal stress;and the stimulated area is approximately 7.2×104 m2.The research results are referential for the field application of deep CBM reservoir fracturing.
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维普
