Research On Coal Of Hydraulic Fracture Propagation Extended Regularization

The mechanical properties of coal rocks are quite different from other rocks.Due to the large amount of cutting and natural fractures in the coal rock,the main structures are low strength and elastic modulus,high Poisson's ratio and fragile.Compared with the conventional oil and gas reservoirs,the fractures of coal fractures are more complicated,so the theoretical results of the existing hydraulic fracturing of coal and rock are different from the actual situation that can't be better Analysis of Fracture Morphology of Hydraulic Fracturing.In this paper,coal rock mechanics parameter acquisition experiment and hydraulic fracturing crack expansion experiment are carried out.Firstly,the internal friction angles of horizontal and vertical coring are calculated according to Mohr-Coulomb criterion by measuring the mechanical parameters such as tensile strength,elastic modulus and Poisson's ratio of different coal under different confining directions and confining pressures by cohesion experiments.According to the theory of strength stress factor,the fracture toughness of coal rock is obtained by using the chevron groove test.The experimental results show that the fracture toughness value in vertical direction is larger than in horizontal direction,and the fracture toughness of coal rock is positively correlated with the tensile strength.Secondly,in order to simulate and analyze the hydraulic fracturing expansion of coal rock,the hydraulic fracturing test of whole coal sample is carried out.Through the test,using fracturing curve,coal anatomy and industrial CT scan describes the coal rock crack propagation.The results show that the hydraulic fractures of coal rock are mainly vertical joints,and extend along the direction of maximum horizontal stress.When a hydraulic fracture encounters a fractured system,steering will occur.Through the analysis of the characteristics of hydraulic fracturing expansion of coal rock,the hydraulic fractures are mostly vertical joints,which are in accordance with KGD model.Based on the KGD model and considering the comprehensive filtering loss of fracturing fluid,the calculation model of single fracture geometry is obtained,and the results are in close proximity to the results of the laboratory tests.Considering a large number of fractured systems in the rock have influence to the expansion of hydraulic fractures,this paper regards coal facies cutting as a special natural fracture,and constructs a two-dimensional model of hydraulic fractures through natural fractures and along natural fractures.When the hydraulic fracture is extended along the natural fracture,the stress intensity factor is introduced,and the calculation model of the new crack initiation angle is obtained by the maximum circumferential stress.And combined it with the experiment,the results are similar.Based on the expansion model of coal rock hydraulic fractures,the software is compiled by Visual Basic 6.0.Using the software,the hydraulic fractures of coal rock are calculated and the influencing factors are predicted and analyzed.The results show that the elastic modulus,Poisson's ratio,working net pressure and fracturing fluid filtration have different effects on the fracture morphology.The hydraulic fractures are easy to pass through the natural cracks in the range of high approximation angle and high horizontal stress difference.In the low approximation angle and low horizontal stress difference,the hydraulic fracture tends to extend along the natural cracks,and when the hydraulic fractures extend to the end of the natural fractures,the new fractures are initiated and the initiation angle is related to the approaching angle,the net pressure and the horizontal stress difference.