Study On Productivity Prediction And Stimulation Techniques Of Coalbed Methane Well

CBM is an unconventional natural gas resources, and the CBM exploiting is rapid development with countries around the world increasing importance of environmental protection and energy demand. Coalfield structure in China is complex, varied shapes and generally has the characteristic of "three low", making unique patterns of the exploitation of CBM in China. The law of production and the research of determining the capacity of CBM is not perfect in the domestic currently, for this subject, the law of the Qinshui Basin coal bed methane gas production and production forecast have been studied in this paper, hoping that it will provide advice on the development of China’s CBM site.The capacity of the coal bed methane wells is impacted by a number of factors, such as the coal reservoir characteristics, the characteristics of CBM reservoirs, the process of coal bed methane migration output and exploitation parameters of the well itself, et. In order to accurately forecast the production of CBM wells, it must make a correct judgment on the above factors in the study block.CBM in coal seams is divided into the adsorptive state, free state and dissolved state, and about90%is based on the adsorption states. When the reservoir was opened, the reservoir pressure is decreased with the conduct of mining. In the surface of coal matrix, the dynamic equilibrium of CBM adsorption and desorption was broken when the pressure decreases to the critical desorption pressure, a large number of CBM desorb from the surface of coal matrix, it make a high concentration of CBM in the coal matrix hole. As a result of concentration difference, CBM migrate into the coal cleat system by diffusion. In the progress of drainage gas, CBM and formation water seep to the bottom in the coal cleat system, and then it is picked out of the ground.The law of CBM migration in the coal matrix hole is in line with the Fick’s law, and the law of CBM seepage in coal cleat system can be used Darcy’s law to describe. According to Fick’s law and Darcy’s law, this article build differential equations for CBM output motion, with the use of mathematical methods, such as non-dimensional transform, Laplace transform and numerical inversion, it propose calculation model for the production of coalbed methane wells. And then combined with the Qinshui Basin reservoir parameters, through numerical solution, it makes prediction of the capacity of coalbed methane wells using the computational model. Through theoretical calculations compared with actual gas production, we can know that the mathematical model is suitable for the predict of CBM wells production. And the result show that steady state and unsteady state show the same trend, but the unsteady-state calculation result is closer to the actual value. Using yield prediction curves of unsteady flowing at different bottom hole pressures, it can paint the IPR curves of CBM wells, it can be used for prediction of the CBM wells.If the coal reservoir pore fracture system developes well and reservoir permeability is large, CBM desorption diffusion and seepage to the bottom of the well can be more successfully when the bottomhole pressure is reduced to below the critical desorption pressure, thereby to achieve more ideal mining efficiency. But China’s coal reservoir and coalbed methane exploitation have the status quo of low permeability, difficult to desorption, lack of driving force and tectonic coal development, which caused the expected effectiveness difficult to achieve simply by controlling flowing pressure of bottom hole. The face of the status quo of the coal reservoir and coalbed methane exploitation, in the actual mining process it must take effective artificial stimulation to speed up CBM desorption, improve reservoir energy, increase reservoir permeability, and to promote CBM output of the ground at higher speed, and thus it can get better value for money. There are serval stimulation techniques for coalbed methane well currently at home and abroad, such as:gas injection stimulation techniques, fracture stimulation technology, vibration technology, Electromagnetic heating stimulation technique, enzyme technology, Surfactant stimulation technique, acid stimulation technology et.