Research Of Rock Mechanics Characteristics And Stress Field About Oilfield Formation

Rock mechanics properties and in-situ stress are one of the important basic data of petroleum resources assessment,reservoir simulation,oil and gas well engineering design and construction in the oil industry.This paper has carried on the comprehensive research to oil fields rock mechanics properties and stress field by indoor core test,logging data interpretation,fracturing construction data analysis and finite element simulation of stress field.Static rock mechanics parameters are obtained,analyzing the relation between triaxial parameters and confining pressure,linear fitting equation between peak strength and elastic modulus with confining pressure are given through the triaxial compression test of core under different confining pressure.The dynamic rock mechanics parameters and the relationship between vertical and horizontal wave velocity of the block are obtained according to wave velocity experiment of the core.This paper providing the basis for getting the continuous static rock mechanics parameters in the engineering through analyzing the relationship between dynamic and static rock mechanics parameters.Triaxial compression test and dynamic rock mechanics parameter test are done on sandstone core of vertical and parallel to formation direction,anisotropy coefficient of the rock mechanics parameters are calculated.The fitting formula between depth and anisotropic coefficient of peak strength,longitudinal wave velocity,vertical and horizontal wave velocity ratio and poisson ratio are given through analyzing the influence of confining pressure and depth on anisotropic coefficient.The anisotropic coefficient of peak strength,longitudinal wave speed and vertical and horizontal wave velocity ratio decrease as the depth increases,but the anisotropic coefficient of poisson ratio is opposite.Dependence of dynamic and static elastic modulus with depth is bad,the anisotropy of dynamic elastic modulus is weaker than static elastic modulus.The relationships between strain energy and strain under three confining pressures are fitted by using stress-strain curve of triaxial compression test,which can obtain the energy value of limestone in anyone axial strain.Several energy changing equations of several stages in the compression process are analyzed,so as to explain the more several rock failures under higher confining pressure in consideration of the rock sample doing work to hydraulic oil.Based on crack extension degree affects the value of the Young's modulus,the concept of crack development coefficient F is proposed,and the empirical formula to strike F using ? under the three confining pressures is given,and the real rock mechanical parameters of various stages during the limestone compression are got,the plastic platform appearing near the peak intensity under high confining pressure with changing tendency of F is explained.Indoor core test of in-situ stress magnitude and direction are proceeding including AE experiment,wave velocity anisotropy and paleomagnetic orientation test.The maximum and minimum horizontal main stress of rock core are tested by AE experiment under confining pressure,and the fitting equation of horizontal principal stress and depth are got.The relation between stress values determined by AE test under the uniaxial compression and hydraulic fracturing method are studied,analytical results show that the KE level is not equal to one of the principal stresses or their differences and it is related to the damage created by the combined effects of principal stresses,a rock dependent coefficient k is evaluated base on the KE level obtained during the uniaxial compressive is a linear combination of principal stresses and the k value calculated by AE tests and hydraulic fracturing method approximately exhibited a range between 0.08 and 0.23,the dependencies of the k value on internal friction angle ? is discussed in view of the similarity of Coulomb failure criterion and the AE stress formula and the index correlation coefficient as high as 0.97.The relative orientation of in-situ stress are obtained according to wave velocity anisotropy test of full diameter core,the horizontal principal stress direction are comprehensive determined finally by the orientation between north geographic pole tested by paleomagnetic of rock core and marker line.Rock mechanics parameters and the ground stress are researched by the logging data.Rock mechanics parameters are got according to density and sonic logging data combined with the relationship between the vertical and horizontal wave velocity.Several model methods of estimating the horizontal stress based on the vertical stress are introduced.Logging information are analyzed by LogVision and rose diagram of in-situ stress direction under the corresponding depth are given.The basic mechanics model of hydrofracture are introduced and the formula to calculate horizontal principal stress according to hydraulic fracturing curve is given.Several related parameters with stress measurement are discussed.In-situ stress size of construction layer are calculated by fracturing construction materials and the fitting relation between horizontal principal stress and depth are given.Finally,horizontal principal stress gradient are obtained comprehensive datas of indoor core test and hydraulic fracturing.Finite element modeling of stress field are proceeded.Multiple constrained optimization inversion is done basing on the superposition of linear elastic problems,constrained optimization inversion are done by MATLAB,as difference value between measured value and inversion value of key well point as objective function,as range of stess weighting coefficient as constraint condition.The simulated results are good in the whole block except three well point which spread over periphery of compact district by comparing measured values and ANSYS simulation values.