Study On The Prediction Of Resources And The Main Control Factors Of Production Capacity Of Vertical CBM Wells In Zhengzhuang Block In Qinshui Basin

The prediction of CBM(Coalbed Methane)resource quantity is the basis of CBM development.The study on the main control factors and stimulation measures of single well productivity is of great significance to improve the production and development efficiency of single CBM well.This paper takes Zheng Zhuang block in southern Qinshui Basin as the research object,on the basis of the test and experiment data of parameters wells and the geological and development data of development wells in Zheng Zhuang block.The geological reserves and the technical recoverable reserves have been predicted and the main control factors of single well production capacity have been clear out.At last,the quantitative prediction methods of production capacity and production-increasing techniques are put forward.The results show that:The buried depth of no.3 coal seam in zhengzhuang block varies greatly,ranging from 383 to1336m.The permeability is low overall,with an average of 0.045md.The gas content is high,with an average of 22.4m~3/t.The thickness distribution is stable,with an average of 5.63m.The average temperature of coal seam is 29.8?and the temperature gradient is about 1.83?/100m.The volume predition method is used to predict the geological reserves of coalbed methane resources in the study area.The low limit of the gas content in the study area is determined to be10m~3/t based on the statistical relationship between the gas content of no.3 coal seam and daily gas production.The area weighting method is used to calculate the thickness and gas content of coal seam.The thickness of coalseam is 5.85m,and the gas content of coal is 23.09 m~3/t.The average density of coal is 1.46 t/m~3 and the geological reserve of coalbed methane is predicted to be 330.53×108 m~3.The Arps production decline method is used to predict the recoverable reserves.The average recoverable reserves of per well from Zheng 1 block to Zheng 4 block are 244.68,211.23,576.02 and 245.9×10~4m~3 respectively.The recoverable reserves of the study area are73.84×10~8m~3,and the recovery rate of the block is only 22%under the current technical conditions.The higher the gas content and permeability are,the higher the daily production is.When the gas content is greater than 15m~3/t,the daily gas production of per well is greater than 600m~3.When the permeability is greater than 0.1md,the daily gas production is greater than 1500m~3.The daily gas production of CBM wells increases first and then decreases with the increase of the burial depth,and the production reaches a peak at the burial depth of about 700m.The daily gas production decreases with the increase of adsorption time and the Langmuir pressure.When the adsorption time is greater than 12d,the daily gas production is less than 800m~3 on the whole,and the relationship with Langmuir volume is not obvious.The relationship between daily gas production and vitrinite reflectance is complex.Under the existing reservoir stimulation technology,the lower the proportion of crushed coal is,the higher the daily gas production of CBM wells will be.When the proportion of crushed coal is lower than 0.6,the daily gas production will reach more than 600m~3.The grey correlation coefficient method is used to screen out 6 main productivity control factors such as pulverized coal ratio,buried depth,Langmuir pressure,thickness,Langmuir volume and vitrinite reflectance.The GM(1,N)model can be used to quantitatively predict the gas production of CBM wells,and the correlation between the predicted value and the measured value of gas production is above 0.8.Acidizing fracturing is performed for vertical Wells with a burial depth of more than 700m and carbonate mineral content of more than 1%.For the vertical wells in the development area of crushed coal,the fracturing in roof and floor formation of coal seam is better,and the average daily gas production incresement is more than 500 m~3 per well.In the area with a permeability of0.01m D in the study area,the daily gas production of the pilot test wells with well space of 200m is nearly 2000m~3 higher than that of the adjacent old well with well space of 300m.In the low permeability zone caused by the crushed coal structure,the use of screen-completion horizontal well development has a good effect,with the average daily production of per well reaching more than 3000m~3.In the low permeability area where fractures do not well develop,the average daily production of a single well can reach more than 8000m~3when the development is carried out by the method of staged fracturing horizontal Wells with casing completion.The paper has 51 maps,19 tables,80 references.