| This paper integrated the characteristics of coalbed methane generation,its production mechanism and previous research results,then formed a comprehensive evaluation method of the coal reservoir geological conditions,namely,in place resource abundance evaluation,fluid mobility evaluation,and theoretical recoverable resource abundance evaluation.Based on the characteristics of multiple/thin coal seams in the study area,a geological condition evaluation method for multi-coal reservoirs was developed.The study shows that the thickness of single coal seams in Enhong and Laochang blocks is low and the gas content is low to medium,so that the main coal seam monolayer and accumulated resource abundances in place are all relatively low,compared to multiple coal seams(thickness greater than 0.5m Coal bed)high cumulative resource abundance.The analysis of fluid mobility shows that compared with Laochang block,the adsorption time in Enhong block is shorter,permeability is higher.The relationship between adsorption time and coal structure is not obvious,and permeability of a single coal layer is affected by the coal structure,while the difference in permeability between blocks is caused by the difference in ground stress intensity.The average theoretical recovery of the coal seam in the Enhong block is 69% by Monte Carlo simulation.The accumulated theoretical recoverable resource abundance is very high,however,it is unsatisfactory if only the main coal seams are drainaged.Moreover,in well control area of 300m×350m,EUR of multi-coal seams of EH-C6 wells is four times that of the combined coal of the main coal seams.The productivity prediction results show that the single well of the Enhong block only has a low production capacity with drainaging the main coal seams,but has a higher prodution after draining all coal seams with a thickness greater than 0.5 m.Permeability is another factor that affects single well productivity. |
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