Research On Combined Mining Technology Of Coalbed Methane And Tight Gas Based On Gas Lift

In China,Ordos Basin has abundant coal-measure gas reserves such as coalbed methane,tight gas and shale gas,but some gas wells have the problem of low efficiency of single mining resources,while the coal-measure strata in the study block are characterized by vertical overlapping distribution,and have the geological conditions of the same well co-mining.Aiming at the reservoir-stacking relationship between the upper tight sandstone layer and the lower coal seam,this thesis proposes the design of the combined mining string based on gas lift,According to the principle of gas-carrying liquid,using the upper high-pressure tight sandstone gas to carry the coal seam well fluid to drain and depressurize the coal seam,and realize the co-exploitation of the two reservoirs,it has a positive driving significance for improving China’s unconventional gas production.First of all,according to the characteristics of co-mining reservoir and the exploitation mode of coalbed methane and tight gas,starting from the actual formation conditions,the main problems of the two-layer combined mining are analyzed,and optimized selection of gas-lift combined production method;Due to the low production fluid of the coal seam and the limited gas volume of the tight layer,it is necessary to redesign the gas-lifting combined pipe string structure,the combination of gas lift and velocity tube technology is combined with the variable diameter tubing short section,and the process of gas lift combined mining is designed according to the principle of step-by-step unloading.Secondly,the simulation experiment of gas-carrying liquid relationship was designed,and the dynamic formula of gas lifted liquid was revised.The core of the gas lift co-mining process is the principle of gas-carrying,as for the relationship between gas and liquid carrying capacity,numerous calculation methods are derived based on a large number of experimental data.and the applicability is low.Therefore,the thesis built a gas-carrying liquid experimental platform,and designed a gas-carrying liquid simulation experiment system composed of gas-liquid supply system,flow pressure regulation system and data acquisition system,by the compressed gas enters the oil pipe and mixes with the liquid,the thesis analyzed the relationship between the gas volume and the liquid carrying capacity,and combined more than 90 sets of experimental data to correct the gas lift dynamic formula,so that the calculation result is more accurate.Thirdly,applicability analysis of combined reservoirs in research blocks based on gas lifting co-mining technology,the gas production of tight sandstone bed should meet the gas demand of carrying the liquid production of lower coal seam,and it is also necessary to satisfy that the bottom-hole pressure of coal seam after gas lift is lower than the desorption pressure of coal seam gas at the same time,so that coal seam gas can be discharged by tubing,and gave the range of the lowest pressure drop of the coal seam.this thesis analyzed the relationship between gas volume and pressure of tight sandstone gas required for different fluid production and reservoir depth conditions in coal reservoirs,The selection basis of key parameters such as wellhead oil pressure,casing pressure,gas lift depth,annular air volume,and tubing diameter are obtained.;according to analytic hierarchy process(AHP)to make a significant analysis of the influencing factors of gas-lift combined production,then,determined the priority of adjusting a certain factor as the production system changes with cost,safety,environmental protection,and easy control.Finally,the design and calculation of key equipment for gas lift combined mining column.and the parameters of installation depth should be designed according to the maximum lifting depth,so,it is necessary to analyze the distribution curve of downhole pressure and temperature,this thesis uses Hagden-Brown to calculate the gas-liquid two-phase flow pressure and the average deviation coefficient to calculate the annular air column pressure.In order to minimize the bottom hole pressure of the coal seam after gas lift,redesigning the gas injection point to reduce fluid pressure in the tubing from coal reservoir to wellhead,and give an example calculation process according to the geological data.