Geological Theory And Technology For Coalbed Methane Development With Thin And Medium Coal Seam Zones In Guizhou

Coalbed methane (CBM) development technology has particularity under condition ofcoalbed groups, and the developing characteristic of coalbed groups lies in definite geologicsurrounding, that influenced the choice of CBM technology. Taking coalfields of Liupanshui andZhina in western Guizhou as the study objects, the paper was mainly depended on geologicalstatistics analysis, the development geological characteristic and reservoir characteristic of CBMwere studied based on characteristics of geological setting, coal reservoir parameters andexploration testing, the developmental geology model was built, the adaptability of geology andengineering processes was also clarified. Furthermore, CBM Resource type and technology wereclassed and explained again based on geology and technology principle. Eventually, this papershowed a selected choice for technology mode, and a localized system of developmenttechnologies. The following major innovations were achieved.1) Based on analysis of coal geology and tested data of CBM well, developmental geologycharacteristic and its controlling mechanism were discussed, and developmental geology modelwas established. The geostress field was analyzed, and the type of reservoir permeability wasredrawn. Different types of coalbed groups were distinguished from coal seam thickness, coalseam space, coal seam number and their combination. There were some specific and typicalcharacteristics for developmental geological environment, such as several thin coal seams,coexisting normal pressure and abnormal pressure, medium-high geostress, especially lowpermeability of reservoir, and so on. The developmental geology model was comprised ofcoalbed group development, anisotropy of reservoir parameters, macro structure of coal,drainage effect and fluid migration, and this model gave a continuous description of multi-scalefrom plane distribution anisotropy of reservoir, and hierarchical of internal/interlayer. This modecould be used for cognition of coal reservoir at different levels step by step.2) Geological selectivity for some key technologies was also discussed under condition ofcoalbed group, three geological features were revealed for their restriction to developmenttechnology. The features were multiple coal seams, reformation of coal structure, and weakabundant water for formation. Based on geological condition and technique principle, newdevelopment type of CBM resource and technology mode of CBM development were proposed.Geological selection of development technology was built, and it included three alternative keymodes. The CBM resource included28types, and could be summarized four kinds of resource.They were CBM resource type of medium-low and difficult renovation, medium-low and easy renovation, medium-low and more difficult renovation as well as unusual lower-low and difficult.The technology mode of CBM development was divided into five types. In fact, two modes wereused frequently, and they were the mode of release of pressure due to fracturing and waterdischarge and mode of release of pressure due to relieved stress and increasing permeability.3) Geological selection of development technology was built, including development modeselection, well selection and relieved CBM technology selection. Every mode could be appliedwith technology selection or combined.The Liupanshui coalfield had inherent disadvantages of applying some technologies of themode of water discharge by fracturing, but the technology of relieved CBM drainage by surfacewell or underground extraction technology were adapted. The mode of well selection supportedthis conclusion. However, the two selection modes had a similar conclusion to Zhina coalfieldby using the mode of water discharge by fracturing. However, the technology must be differentbecause of different CBM resource and well selection.4) The technology system of CBM development was localized. Based on inspiration ofdevelopment engineering and geological selection of development technology, this paperachieved a good matching of different improving technologies and geological setting. Firstly, theadaptability of vertical well and horizontal well was intensified by well construction, accuracy oftarget-entering and commingled production. Secondly, multi-lateral horizontal well and buttedwell were interrelated, and a new well type was obtained. The well adapted a variety of CBMresource type consisting of â… 1, â…¡1, â…¢1and B, C, E, F, G, and provided technology type forCBM resource type of medium-low permeability and hard renovation. At last, considering themining safety and well stability, a series of ways were proposed. According to the coal and gassimultaneous extraction, geological mechanism of instability for surface well, identificationmethod of risk position and preventive measures, the relieved drainage technology was localized.Finally, geological theory and technology of CBM development for zones comprising thin andmedium-thickness coal seams was obtained, covering geological model building, limitedgeological condition screening, CBM resource type distinguishing, technology mode selectingand key technology process applying.