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基于機器學習的煤層氣產能標定智能算法及影響因素分析

Forecasting and influencing factor analysis of coalbed methane productivity utilizing intelligent algorithms

  • 摘要: 煤層氣是我國常規天然氣現實可靠的戰略補充資源之一,智能化標定煤層氣產能對于天然氣工業的發展具有重要意義. 對山西沁水盆地某煤層氣區塊的煤層氣井進行了實際地質、生產數據的收集及數據預處理,提出了基于生產井史的煤層氣單井產能計算公式. 利用預處理后的生產數據及儲層數據,建立了基于深度神經網絡、支持向量回歸機、隨機森林的煤層氣產能標定智能算法,對煤層氣單井產能進行了預測,比較了三種機器學習模型的預測結果,分析了不同排采天數的生產數據作為輸入參數對模型精度的影響. 基于預測效果最好的機器學習模型,進行了動態參數(排采前期的日產氣、日產水和井底流壓)和靜態參數(煤層埋深、孔隙度、滲透率、煤層厚度和含氣量)對煤層氣產能標定模型的重要性程度分析. 結果表明:三種機器學習模型標定煤層氣單井產能的平均決定系數為0.828,其中深度神經網絡模型決定系數最高,達0.923;增加生產數據前期排采天數,決定系數增長趨勢明顯,之后增長趨勢減緩并最終趨于平穩;動態參數和靜態參數對產能的影響都較強,這兩類參數對于產能預測模型的貢獻度分別為48%和52%.

     

    Abstract: Coalbed methane (CBM) is one of the realistic and reliable strategic supplementary resources of conventional natural gas in China, and intelligent calibration of CBM production capacity is of great importance for developing the natural gas industry. Actual geological and production data were collected and preprocessed for CBM wells in a CBM block in the Qinshui Basin, Shanxi Province. For CBM wells that have been exploited for a long time, a calculation formula based on production well history was proposed for single well productivity based on formation pressure in static data, daily gas production, and bottom-hole flow pressure in production data. The accuracy of the calculation formula was determined using the maximum daily gas production curve of CBM wells. Using the preprocessed production and reservoir data, an intelligent algorithm was developed for CBM productivity calibration based on deep neural network (DNN), support vector regression machine, and random forest for predicting the productivity of a single CBM well. A comparison of the prediction results of three machine learning models was performed, and the effect of production data for different discharge days as input parameters on model accuracy was examined. Based on the machine learning model with the best prediction effect, the importance of dynamic parameters (daily gas production, daily water production, and bottom-hole flow pressure in the early stage of drainage and production) and static parameters (coal seam depth, porosity, permeability, coal seam thickness, and gas content) to CBM was explored. The findings revealed that the fluctuation coefficient for 100 CBM wells is approximately zero, and the fluctuation range is small, indicating high calculation accuracy. The average coefficient of determination of CBM well productivity calibrated using the three machine learning models is 0.828, and the coefficient of determination of the DNN model is the highest, attaining 0.923, with mean absolute error and root mean square error values of 194.44 and 214.66 m3·d?1, respectively. With increasing days of production data collection in the early stage, the coefficient of determination clearly increases, and then the growth trend slows down and finally becomes stable. Daily gas production, daily water production, production pressure difference, gas content, and permeability are important factors affecting coalbed methane productivity in the early stage of drainage and production. Productivity is highly sensitive to dynamic and static parameters in the early stage of drainage and production,and these two types of parameters contribute 48% and 52%, respectively, to the capacity prediction model.

     

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