The Study Of Horizontal Wells Optimization Design In CBM Reservoirs

CBM is treated as a clean energy resource in the21st centry and can release thenarrow condition about the use of conventional energy resource. Not only can the highefficient development and utilization of CBM reinforce the supply of the energy andrelease the serious conflict that China faces, but it can also release the Greenhouseeffect.However, horizontal wells and hydraulic fracturing technology as domestic andoverseas excellent CBM production stimulation measures.Especially, the two kinds oftechnology combind，the result is less than satisfactory, because of being restricted bypoor national theory knowledge and pratical experience, backward technology andequipment etc. Therefore, it is necessary to do further optimizing research on CBMhorizontal wells and the fracturing horizontal wells.This paper based on the superiority of the Southern Qin Shui basin, which isChina’s first CBM exploration and development test and the best promising area,discusses the reservoir characteristics, adsorption and desorption feature about CBM inthe southern part of the Shizhuang South Area. Using the method about CBM reservoirnumerical simulation, and make a systematical analyzation about the adaptability of theCBM horizontal wells development and the influence factors. Furthermore, this paperdiscusses the feasibility of horizontal well fracturing, and optimizes the fracturingfracture parameters. Based on the discussion about the feasibility of dual branchhorizontal wells commingled production, the author predicted commingled productioneffect of Shizhuang South block Nos.3and15coal seams.The whole stratum of the southern part of the Shizhuang is a westward dippingmonoclinal structure.The main stable developing coal layers are No.3of the Shanxiformation and No.15of the Taiyuan formation. By means of the coal samples isothermal adsorption experiments and injection pressure-drop well test analysis inShizhuang Southern District, combined with the well logging interpretation, singlewell basic data, the author analyzed the large difference between coalbed methanereservoirs and conventional gas reservoirs, pointing that the most essential difference isthe CBM adsorption and desorption phenomena. Through the analysis of the study areacoal seam isothermal adsorption experiments, show that the seam has a strongadsorption capacity of methane gas, as well as there are great potential of CBMresources for development in Shizhuang South block.The author makes a demonstration for the adaptability of CBM development usinghorizontal wells from the advantages and disadvantages of different drilling well types,adaptive conditions, increase production ability etc. Then discusses the influence oftwo major aspects of the geological and engineering factors to increasing production,those factors are seam thickness, permeability, anisotropy, as well as the length andorientation of the horizontal section. And drawn some optimization conclusion: firstly,horizontal well productivity is affected greatly by seam thickness, average permeability,which is separately positively correlated with horizontal well productivity; the largerpermeability anisotropy ratio is, the smaller the horizontal well productivity is.Secondly, the horizontal well cumulative production gradually increases with thelength increase of the horizontal section, but the amplitude of variation for cumulativeproduction gradually becomes smaller; Finally, for the anisotropic gas reservoir, theorientation of the horizontal section should be perpendicular to the direction of thenatural fractures development; For the Shizhuang south block, the length of horizontalsection should be1000m, the orientation of horizontal section should be approximatelynorth-south direction.The author established fractured horizontal well numerical simulation model ofCBM based on the optimization of horizontal wells, then analyzed the necessary andfeasibility of fracturing for horizontal wells, and optimized the fracturing fractureparameters. The optimization results of Parameters are as follows: fracture half-lengthis120m, conductivity is15.61μm2.cm and the number of fractures is5to7, then thereis better development effect.Evaluated the feasibility and sensitive factors of commingled producing two coalseams, furthermore, Forecasted the Nos.3and15coal seams production performancein Shizhuang South Block.The analysis shows that different coal permeability,reservoir pressure and gas-saturation etc. influence commingled production greatly, andthe sensitivity parameters of which should not has such great differences that exploit the multi-layer with poor effect. The simulation analysis shows that the difference of Nos.3and15coal seam parameters is very small, so they commingled produce well.By means of the horizontal well optimization design of CBM reservoir inShizhuang South Block, It obtains a more clear understanding of influential factors andkey parameters for exploiting CBM using different types of horizontal wells.Theresearch content provides theoretical basis and guidance for future similar CBMdevelopment, particularly provides reliable basis for CBM horizontal welldevelopment program.