Study On The Stimulation Mechanism And Technology Of Coalbed Methane Reservoir By Surface Modification

The coalbed methane mainly exists in the micropores of coal matrix blocks in absorbing state,and its output complies with the process of "desorption-diffusionseepage".Only the increasing of desorption of coalbed methane,improvement of diffusion flux of coalbed methane and the perfection of permeability of coalbed methane reservoir can essentially ensure the high and stable production of coalbed methane well;therefore,the stimulation technology of coalbed methane reservoir by surface modification is put forward.This thesis takes coalbed methane geology,coal chemistry,coalbed methane bioengineering,surface physics and chemistry,seepage mechanics,etc.as its guidelines,and various coals with different coal ranks and different coal structures as its study objects,to re-recognize the occurrence and the migration and production mechanism of coalbed methane and to systematically study the effect of strong oxidant,microorganism and surfactant on stimulation mechanism of coalbed methane reservoir,through the combined method of laboratory experiment,theoretical analysis and engineering application.The conclusions are as follows:(1)This thesis verifies the existence of overpressure environment of coalbed methane reservoir micropore,reveals the formation mechanism of overpressure environment of coal reservoir micropore,establishes the calculation method of quantity of coalbed methane resource on the basis of existence of micropore overpressure,and finds out the impact of micropore overpressure on estimation of quantity of coalbed methane resource.(2)It re-recognizes the occurrence and migration & production mechanism of coalbed methane.It points out that at the saturated water single phase flow stage,the desorbed gas migrates in dissolved state;and at the unsaturated single phase flow stage,the bubbles gradually generate in micropores and will be discharged after the drainage of water in micropores;and then at the gas-water two-phase flow stage,no water exists in the micropores.The migration of coalbed methane complies with the two-stage and two-class diffusion(Knudsen diffusion and Fick diffusion),and the migration in cleat/ fracture conforms to the two-stage and two-class seepage(low velocity nonlinear seepage and linear seepage).In addition,it finds out that at the gas-water two-phase flow stage,the improper discharge and mining control will cause the slug flow,leading to serious velocity sensitivity harm to reservoir;and it preliminarily discusses the formation conditions and mechanism of slug flow.(3)In terms of the coalbed methane reservoir,the strong oxidant has the desorption and permeability improvement effect.After the modification of coal by strong oxidant,the condensation of aromatic ring of coal molecule and the methane affinity are reduced,beneficial to the desorption of coalbed methane;and the pore volume and the porosity of coal are increased and the connectivity of pore is enhanced,beneficial to the seepage of coalbed methane.(4)For coalbed methane reservoir,the microorganism has desorption and permeability improvement effect and the resource increasing significance.The coal generates certain quantity of methane through the degradation after the microbial metabolism,which is a supplement to the coalbed methane resource.After degradation,the molecular structure of coal is changed and the methane affinity is correspondingly reduced,thus realizing the desorption increasing.The total pore volume and the volume of large pore of coal are increased and the connectivity of pore are enhanced,thus perfecting the permeability of coalbed methane reservoir and realizing the permeability increasing.(5)Regarding to the coalbed methane reservoir,the surfactant fracturing fluid(1.5%KCl+0.05%AN)has the stimulation effect.On one hand,the surfactant fracturing fluid perfects the wettability of coal powder,increases the cohesion between pulverized coal particles to make the pulverized coal sediment and accumulate quickly,thus preventing the velocity sensitivity and restraining the harm to coalbed methane reservoir during the discharge and mining process.On the other hand,the surfactant fracturing fluid reduces the capillary pressure of fluid in coal pore to make the fracturing fluid easily access into the coalbed methane reservoir,thus significantly reduce the water blocking damage.Meanwhile,this paper finds out that the surfactant fracturing fluid can restrain the formation of slug flow,thus realizing the stimulation.(6)This thesis puts forward 4 active water and modifying agent compatibility schemes.The surfactant fracturing fluid is the optimum fracturing fluid for the transformation of coalbed methane reservoir.The application of such fracturing fluid in Permo-carboniferous system coal measure gas reformation of Wulihou Well Field of Lu'an Group is a complete success and realizes the long-term(from March 2014 to today)stable single well gas production(1,000m3/d),with high bottom hole pressure at present.