Study On The Reservoir And Resource Evaluation Technique Of CBM In The Stabilization Region After Mining

Energy is one of the three pillars of development in today’s society, and the crisisof “energy shortage” has become more and more serious with the rapid developmentof China’s economy. As a high-energy clean energy, the technologies about CBM ofexploring, developing and utilizing have been paid more and more attentions by everycountry in the world, which means CBM is becoming a research hotspot in the field ofenergy.The technology draining CBM with surface borehole from stabilition regionafter mining has developped up since the late1990s,because it can make full use of coalmining pressure relief effect and avoid the strenuous activity period of undergroundrock strata, realizing ground pumping well lifetime maximization, the technology hascaused the major mines’ attention and interest, which means the glorious development prospect in China. Because of the high ground well construction cost, it is necessary toselect the CBM development area and analyze economic benefit before production,which requires early resource evaluation of CBM in the target area. However, there isno a relatively complete assessment method for CBM resources in stabilization regionafter mining yet.This paper combines the method of theoretical research and caseanalysis, inheritance and innovation, summarized innovative methods to study on the reservoir andresource evaluation technique of CBM in mining stabile region in the following aspects:(1) Paper proposed definition of mining stable region from the perspective ofmining influence,defined the concept of CBM reservoirs combined with the traditionalconcepts of reservoirs and the characteristic of mining stable region, and discuss thedescription of mining stable region of coalbed methane reservoir:The CBM reservoir in mining stable region has dual attributes of natural andartificial. Natural attribute refers to the carrier is still the coal and rock, artificialattributes refer to its size associates with the mine production activities closely. Thegeometry&boundary conditions and structure of reservoir&fracture are the twokey contents for reservoir in mining stable region different from the traditional coalreservoir, and the effective unloading fissure field in rocks, difficulty for research, is animportant part to stable region reservoir.(2) The prime location and the spatial behavior characteristics of stable area CBMreservoir were studied by analyzing the experimental data and two-dimensional numerical simulation:The CBM reservoir,which is controlled by the key strata in height and affected bythe stope size&surrounding rocks in width, mainly lies in “caving zone and fracturedzone” in coal seam roof and "gas conductive fracture zone" in floor. Its space formshows “column cap” generally, but can be simplified as “prism form” inengineering.(3)The paper summed up calculation methods for the CBM reservoir instabilization region after mining, using the four parameters such as gas (water) fractureangle in stope roof, the height of roof fracture zone, bottom pressure boundary angleand floor crack depth, based on “coal mining under three circumstances”,“miningprotection layer theory”and “the key strata theory”. The rationality of methods wereverified by the field test and numerical simulation subsequently.(4) On the basis of analyzing the relation and difference between mining stablezone coalbed methane reserves evaluation and traditional coal seam gas reservesevaluation, the two kinds of evaluation models, direct addition and indirect subtraction,for coalbed methane reserves in stable region mining were built, with the calculation orvaluation method for each key parameter. The two models are applicable in differentsituations due to the complete degree of mine production and geological data. Besides,the application condition of models was formed according to the modeling method,the traditional cover theory and coal mining theory under three circumstances.(5) According to the gas producing interval selection principles of traditional gasreservoir reserves evaluation, the main selection principles and basic steps for CBMresources evaluation in mining stable region was picked up, combining with thecharacteristics of mining stable region reservoir. At last, the thesis estimated the coalbedmethane resources in a test area in Shihao mine by using “the direct addition”resource evaluation method, which confirmed the operability of evaluation technology.