Productivity controls in CBM directional wells,Zhijin block
Most coalbed methane(CBM)directional wells in Zhijin block are confronted with challenges,such as signifi-cant difference in the productivity,short time in the stable production,and unclear productivity controls.So,23 directional wells deployed at large and small well groups in the study area were taken as examples to analyze the effect of both geolog-ical conditions and operational parameters on the productivity.Moreover,the influential degree of different geological condi-tions and technological measures on the productivity was pointed out for these wells.Results show that(i)the controls mainly include desorption pressure,coal seam thickness,working-fluid volume,lead volume and displacement;(ii)geologi-cally,the average development horizons in large well groups are about 4 times those in small ones.And No.16,17 and 21 coal seams are better than others in terms of sedimentary environment,preservation conditions and reservoir structure;and(iii)the working-fluid volume,lead volume and displacement have a great impact on fracturing stimulation.Practical data indicates that,at a certain displacement,the stimulation effect is better when the working-fluid volume is about 5 times of the lead volume.Two conclusions are made.In addition to great in quantity,the coal seams in Zhijin block feature small in thickness,layer spacing and heterogeneity difference in vertical.Thus,a better effect may been achieved from multilayer commingled production by directional wells,and the overall effect in the lower to middle coal groups is better than that in the middle to upper groups.What's more,various stimulation scale and methods have a great impact on the productivity.For the Zhijin coal seams which are provided with high coalification and less brittle than the other seams or shale reser-voirs,to raise the proportion of lead volume is helpful to induce fractures better,thus to scale up the stimulated reservoir volume.
万方数据
维普
