Research And Application Of Logging Prediction Of Coal And Rock Mechanics Parameters In DQ Block

The original integrity of coal have been destroyed because of weak structural planes,like cleat,thus,the coal bed is easy to creep and broken,even collapse,and then make borehole lose stability.It's crucial to overcome this difficulty to getting curves of rock mechanical parameters of DQ block accurately.Affected by weak structural planes,the application effect of existed evaluation methods of rock mechanical parameters in coal bed were unsatisfactory.Prediction models of rock mechanical parameters had not yet been established based on logging information and available for all kinds of coal beds.Fractal dimension is a general term of figures and structure features which are similar to itself.Studies have shown that the formation was a random self-similar fractal system,structure of rock had typical fractal characteristics,logging curves had characteristic of self-similarity.Prediction models of rock mechanical parameters could be introduced based on the structural complexity of coal and available for all kinds of coal beds.Based on a lot of research and analyses of physical experiments and numerical simulations and preliminary application,the following results were obtained:(1)The density of coal samples mainly distributed in 1.5 g/cm3?1.7g/cm3,and the density of samples which derived from block LaoChang is generally larger than that of block EnHong.The acoustic travel time of longitudinal wave of samples which derived from block LaoChang is 395?s/m,the acoustic travel time of transverse wave of samples which derived from block LaoChang is 793?s/m,and the ratio of VP and VS is 2.02.The acoustic travel time of longitudinal wave of samples which derived from block EnHong is 464?s/m,the acoustic travel time of transverse wave of samples which derived from block LaoChang is 97?s/m,and the ratio of VP and Vs is 2.05.The porosity of coal samples is distributed in 0.85%?9.61%,the average porosity is 4.4%,the porosity of samples which derived from block LaoChang is lower than that of EnHong,and permeability changes in a large range.The pore types of LaoChang are mainly plant stomatal pores,dissolution pores and residual intergranular pores.The pore types of EnHong are mainly plant residual pores,intergranular pores,and dissolution pores are visible and they are a large number of distribution,tensional crack and shear crack are also visible.(2)The failure of coal samples is mainly splitting failure along the structural plane.The failure path of coal become complex,tensile splitting,shear failure along the structure plane are existed while the confining pressure increase to 5 MPa or 6 MPa.The failure way of coal is mainly shear failure while the confining pressure increase to 10 MPa or 12 MPa.The tensile strength of coal is distributed in 0.46 MPa and 2.05 MPa.(3)The box dimension of the coal have good correlation with uniaxial compressive strength and elastic modulus and Poisson's ratio and tensile strength,the relationship between box dimension of the coal and uniaxial compressive strength is negative,the relationship between box dimension of the coal and elastic modulus is negative,the relationship between box dimension of the coal and Poisson's ratio is positive,the relationship between box dimension of the coal and tensile strength is negative.The calculation models of coal mechanical parameters of the coal box dimension were established on the basis of those understandings.(4)Curve AC and Rt have good fractal characteristics.The box dimension of logging curve had a good correlation with the complexity of strata clutter structure and can be used to evaluate it.It is optimal to select window technology which based on two-dimensional division if we calculate the box dimension of logging curve.(5)Prediction models of rock mechanical parameters of coal reservoir based on box dimension of logging curve have been established,their applicability have been proved by compare the prediction results and field data.This paper realized the logging evaluation of mechanical parameters of fractured coal reservoir rock in DQ block,and provides basic information for scientific and efficient fracturing,which is of great significance for enhancing coalbed methane recovery in DQ block.This work also provide reference for the logging evaluation of rock mechanical parameters of other CBM blocks,even all the fractured complex stratum.