| Predicting productivity of CBM wells can provide the basis for adjusting the later development plan and searching for productivity replacement area.The production phase of CBM can be divided into five stages by analyzing the production data.According to the characteristic of CBM wells,the producing pattern can be divided into six kinds.Analyzing decline regular of CBM wells by using the Arps decline analysis method,it can be known that the majority CBM wells of Fanzhuang block is Exponential decline and harmonic decline.The decline rate of the initial production was different.The annual decline rate was 5.7% ~ 40.5%.The various geological factors and engineering factors which affect the productivity of CBM wells are studied by means of statistical method.Hydrogeological conditions are not active and far from fault is conducive to gas content and the CBM wells is the high yield Wells.The original coal bed permeability is higher,the productive is higher.The permeability is controlled by the minimum principal stress.The stress is higher and the permeability is lower.Storage in the higher position,the wells production is higher.the Reasonable speed is 1.5~2 min-1;Wells with steady decline fracturing operation curve have high production.Using R/S analysis method combined with GM(1,1)model,WengShi model,multiple stepwise regression method to predict the different types of wells in study area respectively,the applicable conditions and errors of various models are obtained.The WengShi model is suitable for long gas-producing wells and the average error is 14.9% ~ 23.4%,the overall forecast error is 6.88% ~ 7.92%.The multivariate stepwise regression method is suitable for the overall productivity prediction in the well areas,it's not suitable for low productivity wells,the forecast error of the productivity of the high and middle wells is lower than 20%.R/S analysis method combined with GM(1,1)model is suitable for the wells which produce smoothly. |
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