The Gas Flow In Triple Pore Structure Of Coalbed Methane Reservoir With Complex Wells

Coalbed methane is one of the clean and efficient fossil energy which has risen in nearly twenty years.It's abundant in the world as an important unconventional natural gas resource.Coal rocks have double pore networks of fissures and matrix pores.The process of coalbed methane flowing involves desorption,diffusion and fracture seepage of the matrix pores of the gas.Due to the influence of the sedimentary environment,the seepage properties of coal and rock have strong heterogeneity in the plane.In addition,the good type of CBM wells is complicated with the wide application of hydraulic fracturing technology,horizontal well and multi-branch horizontal well drilling technology in CBM mining.All these factors make the process of coalbed methane seepage much more complicated than the conventional gas reservoir.Therefore,it is of great significance to study the seepage theory of complex structural wells in coalbed methane reservoirs.Based on the experiment of the microstructure characteristics of coal and rock and the experiment of desorption-diffusion-seepage mechanism,this paper sets up mathematical models of double-hole and single-seepage flow in complex structure wells,such as CBM vertical wells,partially perforated vertical wells,fracturing vertical wells,horizontal wells,multi-branch horizontal wells,segmented fracturing horizontal wells,fractured horizontal wells and so on,to obtain corresponding well type mathematical model of bottom hole pressure response function and production decline.The mathematical model of seepage flow in the above well types with complex outer boundary,impermeable zone,and non-homogeneous zone is established with the method of boundary element,the effects of different boundary types,shapes,impermeable block sizes,shapes,heterogeneous region sizes,and shapes on bottom hole pressure response characteristics and production decline law are analyzed,and a software for single well dynamic evaluation of coalbed methane reservoir is developed,guiding the scene of the dynamic control reserves of single good evaluation,evaluation of single good productivity and work productivity prediction.(1)The experimental process and evaluation method of coal and rock seepage considering desorption-diffusion effect are presented,The mathematical model of coalbed methane reservoir seepage for vertical wells,partial perforating wells,fracturing wells,horizontal wells,multi-branch horizontal wells,segmented fracturing horizontal wells,fracturing horizontal wells with fracture network and other types is improved,and the bottom hole pressure response characteristics and production decline law of different good types are analyzed.Langmuir parameters,diffusion coefficient and storage ratio affect the time of radial flow stage and the rate of production decline.(2)The basic boundary element solutions of vertical wells,partially perforated wells,fractured wells and horizontal wells in coalbed methane reservoirs are solved.And the effects of different external boundaries,different shapes of internal impermeable blocks and different shapes of composite zones on pressure response and production decline are analyzed.the outer boundary of different shapes can be approximately replaced by a circular boundary on the premise of equal area The derivative curve of pressure is slightly upwarped when there is an inner impermeable block.the pressure response characteristics and the law of production decline are influenced by fluidity ratio,area,shape and position of the composite region.(3)Software for dynamic analysis of coalbed methane reservoir production can be used to evaluate single well dynamic control reserve,original production capacity,current production capacity and predict production,and so on.It solves the main problem that spot management faces.In summary,this paper establishes a set of seepage theory of complex structure wells in planar heterogeneous coalbed methane reservoirs,which solves the problems of pressure response and production decline law of coalbed methane reservoirs.The results have certain theoretical guiding significance for guiding field production management and efficient development of coalbed methane reservoirs.