The Study Of Main Influence Factors On Productivity Of Coalbed Methane Well And The Development Performance

In this paper, geological, engineering and discharge and mining factors for the main influence factors on productivity of CBM (coalbed methane) well are discussed on the basis of geologic features and production characteristics in Baode area of eastern edge of the Ordos Basin.Quantitative analysis for main controlling factors of CBM well productivity is used gray relational analysis method. The dynamic characteristics of coal reservoirs during CBM drainage are revealed from three aspects: the change of reservoir pressure, the characteristics of well interference and dynamic reserve evaluation. On this basis, the methods and adjustment measures of CBM well productivity are proposed from development favorable area division,well pattern deployment and optimization, drainage and mining optimization. The main research achievements are concluded as follows.(1 ) The main controlling factors and the mechanism of CBM well productivity are revealed by geologic conditions, engineering technology and discharge and mining factors.Quantitative analysis for main controlling factors of CBM well productivity used gray relational analysis method. The influencing geological factors of the productivity of CBM well are coal seam thickness, fluid potential of groundwater, gas content, permeability and critical reservoir ratio. The influencing engineering factors of the productivity of CBM well are well space,fracturing fluid and sand amount. The influencing discharge and mining factors of the productivity of CBM well are descending speed of bottom hole pressure and working fluid level and casing pressure. The gray relational analysis method is used to quantitative analysis for main controlling factors of CBM productivity. And the influencing factors of CBM well productivity in Baode block is in the order of critical reservoir ratio, fluid potential of groundwater,equivalent coal seam thickness, equivalent gas content, equivalent sand amount, equivalent fracturing fluid, equivalent permeability, well space.(2 ) This paper expounds the dynamic characteristics of coal reservoirs during CBM drainage by analysis of typical examples and construction model of pressure drop. The characteristics and the regularity of coal reservoir pressure change are revealed during the discharge and mining process. The pressure expression of single-phase liquid stable seepage is obtained at any point in a single and multiple well discharge and mining. The change of reservoir pressure in the single well discharge and mining is simulated. The influencing factors of pressure drop funnel are put forward. According to the two kinds of observation methods of well interference, which are mainly used in actual production wells, the characteristics of well interference and the influence of well interference on the CBM well productivity are systematically analyzed in the study area. And the application way of well interference is put forward. The dynamic reserves are calculated in the study area and re-estimated the static reserves. The reserves producing degree and recovery percent are analyzed.(3) The methods and adjustment measures of CBM well productivity are proposed from development favorable area division, well pattern deployment and optimization, drainage and mining optimization. In the aspect of development favorable area division, the evaluation index system of CBM development favorable area is constructed. The study area is divided into 4 development blocks. It included that development condition best area, development condition better area, development condition good area and development condition worse area. In the aspect of well pattern deployment and optimization, well pattern design and optimal deployment of CBM can be divided into three stages: well pattern pre-development design stage, well site optimization stage and later well pattern adjustment stage. And the adjustment of the CBM well recovery method is the put forward. In the aspect of drainage and mining optimization, the drainage and mining of CBM well is divided into six stages, those are drainage, anterior gas production stage, initial gas production stage, rising gas production stage, stable gas production stage and gas production decreased stage, and the requirements and measures are proposed according to these different stages. The differences in the control methods of typical drainage well in different geological conditions are analyzed.