Coal Reservoir Characteristics And Hydraulic Fracturing Optimization Design Of Yuwang Block In Laochang

This paper takes the Yuwang block of Laochang as the research object,analyzes the basic geological characteristics of the study area from the aspects of coal-bearing,gas-bearing and reservoir physical properties.The brittleness of coal and rock,the fracture toughness,the difference in elastic modulus between layers,and the effect of ground stress on the fracturing transformation of coal reservoirs were discussed.Based on this,the comprehensive index of coal reservoir compressibility was established,and the fracturing properties of coal reservoirs are analyzed and studied.On the basis of reasonable optimization of the fracturing construction parameters,a fracturing plan suitable for studying the geological characteristics of coal reservoirs was proposed.There are 15 layers of coal mining in the area of Yu Wang,and the total coal mining thickness is 6.47~33.34 m.The main recoverable coal seam is 3#,7+8#,9#,13#,16# and 19# coal.The depth of coal seam is 20.27~1135.16 m,and the total depth from NW to SE gradually deepens.The pore types are mainly small pores and micropores.The pore connectivity is good,the coal seam has strong adsorption capacity and good gas storage capacity.The permeability of the reservoir is poor,and the permeability is less than 0.1mD.The distribution of gas content and gas content in each coal seam is quite different,which is mainly affected by the structure in the area and the depth of coal seam.The gas content of 9#,13# and 19# coal seam is relatively high.Logging interpretation results show that coal structure of 7+8#,16# and 19# coal is good,which is favorable for reservoir reconstruction.Coal brittleness is an important parameter for evaluating reservoir fractureability.The higher the elastic modulus,the smaller the Poisson's ratio,the better the brittleness of coal,and the easier it is to form a seam after fracturing,the stronger the fracturing of coal and rock.Fracture toughness can reflect the ability of cracks to extend forward,and the greater the fracture toughness,the less favorable the extension of cracks.The greater the difference between the elastic modulus of the surrounding rock and the coal seam,the more favorable it is to control the seam height.The size of the ground stress in the study area is related to the structural development.The geostress of the complex complex area is relatively high.For example,in the northern part of the Yuwang block,the high stress area has a large rupture pressure,and appropriate displacement should be selected during the fracturing design.Considering the influence of coal rock brittleness,fracture toughness,interlayer elastic modulus difference and ground stress,the compressible comprehensive index based on the brittle index,fracture toughness index,the ratio of surrounding rock to the elastic modulus of coal seam and the difference of horizontal stress is put forward,and the evaluation of the fracture of the main coal reservoir is evaluated.The results show that 19# coal has better fracturing performance and 7+8# coal takes the second place.For the 19# and 7+8# coal reservoirs,the three-dimensional fracturing software FracproPT was used to simulate the construction parameters.The study found that with the increase of the total liquid volume,the seam length,seam height,and seam width will increase correspondingly.With the increase of displacement,the seam length showed a tendency of increasing first and then decreasing.In general,when the displacement was 3~7m3/min,a higher slit length was maintained;the seam height had a positive correlation with the displacement;the slit width was associated with the row The increase in volume shows a trend of gradual increase after decreasing first.With the increase of the percentage of pre-liquid,the slit length and seam height will increase first and then decrease,and the crack width will gradually decrease.With the increase of sand ratio,the seam height and seam width gradually increase,and the seam length gradually decreases.5%~8%~10%~12%~12%~15% of the sand adding process makes the crack have good diversion ability.Based on the above results,a fracturing scheme suitable for the geological conditions in the study area was proposed.The optimized construction parameters have better hydraulic fracturing effects.