| Guizhou Guizhou Province is rich in CBM resources and has great potential for CBM exploration and development.However,due to the combined influence of high regional crustal stress,poor permeability of coal seams,weak water yield of coal measures and other factors,the geological conditions for CBM development are complex,and the geological adaptability of CBM development mode and development process is not clear,leading to the high proportion of low yield wells and low efficiency wells in the current CBM exploration and production process.This article takes the Wenjiaba block in the Zhina Coalfield,which is widely recognized by domestic scholars as the research area for the high production of coalbed methane in Guizhou.The main research object is the constructed coalbed methane wells in the area.By comprehensively applying coalbed methane geology and development theory,geological and engineering data analysis,sampling testing,coal reservoir evaluation,and numerical simulation of coal reservoirs are adopted,and the following understanding and achievements have been achieved:1)The Longtan Formation(P3l)is the main coal bearing formation in the area,with the main target coal seams 16 #,23 #,27 #,and 30 # having characteristics of high gas content,high gas saturation,high porosity,low to medium permeability,and reservoir pressure ranging from under pressure to normal,providing favorable reservoir conditions for coalbed methane development.Affected by this,the use of vertical single well in-situ mining,cluster well group in-situ mining,and multi branch horizontal well continuous water injection surge mining in the block has achieved good gas production results.2)On the one hand,the high production of coal-bed gas wells in the study area is affected by the concentration of structural stress in the axial part of Argong Syncline,the enrichment of coal-bed gas under the action of hydraulic plugging and sealing,and on the other hand,it is closely related to the high original permeability of the coal reservoir and the strong removability of the reservoir under the conditions of shallow burial and low ground stress.The difference in gas production efficiency between wells in the C1 well group is mainly related to the enhanced liquid supply capacity caused by F16 fault water transmission and the flow of formation water towards the C1-3 well with lower target points under the background of inter well interference.Each well in the well group exhibits a gas water production relationship of "low water and high gas production;high water and low gas production".3)Reasonably control the scale of hydraulic fracturing construction during coal reservoir renovation,while increasing the scope of fracturing renovation,avoid communication between fracturing fractures and water conducting faults or occurrence of inter well flow within cluster well groups.During the fracturing construction process,the injection rate of pre fluid is rapidly increased,and efficient fracture formation is achieved.During the fracture formation stage,non continuous slugs are injected,and during the sand carrying fluid support stage,fractures are effectively supported to improve the effectiveness of coal reservoir fracturing transformation.4)During the loading process,the dimensionless gas logging permeability kgi/kg0 of the coal sample has a negative exponential relationship with the effective stress;In the unloading process,the dimensionless gas logging permeability kgi/kg0 and effective stress show a power function relationship,and the stress sensitivity damage of gas logging permeability is irreversible.The sensitivity damage rates of gas measurement velocity after correction for slip effect were 47.17%,83.33%,72.09%,and 47.70%,respectively,with corresponding critical flow rates of 3.95 m L/s,0.33 m L/s,0.25 m L/s,and 9.43 m L/s,respectively.5)Due to the shallow burial depth,good gas bearing properties,weak water rich properties,and significant differences in reservoir sensitivity of the main target coal seams,it is necessary to maintain a low casing pressure extraction condition of less than0.5MPa for a long time during the coalbed methane well combined extraction process,shorten the duration of pressure holding,extend the duration of production increase to improve the fracturing fluid flowback rate before stable production,and ensure the continuity of the extraction process to avoid irreversible damage to the permeability of the coal reservoir,In the stage of increasing gas production,the upper production layer is actively and slowly exposed,extending the stable production time of coalbed methane wells developed in a combined layer.6)Further clarified the principles of drainage and production control for high yield,stable production,high flowback rate,weak inter well interference,and low reservoir damage.The combined drainage and production process was divided into 8 drainage and production stages,and the daily decrease of bottom hole flow pressure in each stage was optimized.COMET3 was used to predict the gas production effect.The simulation results of the reservoir indicate that the better the fracturing transformation effect of the coal reservoir,the easier the reservoir fluid flows out,the more obvious the reservoir pressure drop,forming a pressure drop funnel,and the easier the desorption and diffusion of coalbed methane.The corresponding resource recovery rate is higher,and the overall gas production effect is better.This thesis has 60 images,26 tables,and 120 references. |
