| The dispersion of coalbed methane resources in multiple coal seams in the west Guizhou determines the particularity of its exploration and development.Basic geological research and adaptive development technology exploration are still the main research targets currently.The multiple seams in the western Guizhou were taken as the research object to reveal the static and dynamic variation of coalbed methane(CBM)storage and seepage space,and their effects on CBM adsorption-desorption-seepage flow were also discussed.The coal texture identification method in thin seams was established by using the well logging information.The mechanism of in-situ stress related superimposed CBM system was revealed.Finally,the combination optimization method for CBM co-production was proposed by considering the changes in liquid level,reservoir pressure,and CBM desorption dynamics.Also,the influence of different engineering mode and drainage method on the productivity of co-production wells were analyzed.The static and dynamic variation of coalbed methane(CBM)storage and seepage space were revealed.The main controlling factors affecting the CBM adsorptiondesorption characteristics were summarized,and the identification chart of gas desorption process and desorption efficiency was established.The higher rank coals are dominated by the micropores with the weakest stress sensitivity of coal space.It is favorable for coalbed methane adsorption and has the innate advantage in achieving high desorption efficiency.The cataclastic coal has the highest permeability,followed by the primary coal,while the fragmented coal with the strongest adsorption capacity is not conducive to fracturing and stimulation.Vertically,coal seams with high ash yield will reduce methane adsorption capacity;Under the condition of in-situ temperature and pressure,methane adsorption capacity is mainly controlled by the "positive effect" of reservoir pressure.With the physical properties of different coal texture and well logging information,a precise identification method of coal texture in these thin seams was constructed.Firstly,considering the “boundary effect” of well logging data,the wavelet frequency division weighted reconstruction technology was used to improve the vertical resolution of the logging curves.Then,the gamma,density,acoustic wave,and deep lateral resistivity log data were selected to establish the coal texture log identification plate and classification function by the FISHER linear discriminant method.The in-situ stress variation with increasing depth and its influencing factors were determined,and the concept of the “stress related superimposed CBM system” were proposed.The horizontal stress gradient changes with depth is non-uniform and is overprinted by the effect of syncline,and the stress gradient is remarkably high nearing the axis.Vertically,the in-situ state can be divided into stress extrusion,stress release,stress transition,and high stress regimes,respectively.The stress extrusion regime(500-750 m)is favorable for a relatively high permeability reservoir and a unified gasbearing system.For seams at 200-750 m and >750 m in depth,penetration is restricted by reduced permeability,resulting in discontinuous gas-bearing systems with irregular gas content distributions and unpredictable reservoir pressure gradient.By analyzing the gas and water production data from the typical co-production wells in the Zhijin block,the combination optimization method and drainage advice were proposed.Under the premise of balanced liquid supply between layers,ensuring that the production layers still have a certain burial degree while achieving high desorption efficiency can maximize the gas recovery rate.The “large fluid volume and high sand volume” fracturing transformation method is an important guarantee for high production.The rapid drainage,stable pressure,high or stable casing pressure production are unsuitable for CBM co-production management. |
PDF Full Text Request