Research On Calculation And Distribution Of In-situ Stress Of Low Porosity And Low Permeability Reservoirs In Huaqing Area

The sandstone and mudstone interbeds of the Yanchang Formation in the Huaqing area of the Ordos Basin are developed.The reservoir has three low characteristics and an extremely low pressure.The rock mechanics of the Chang 6-Chang 8 tight sandstone reservoir is mainly characterized by strong anisotropy.The original isotropic rock mechanics and geostress evaluation methods are not applicable obviously.It is necessary to apply a variety of modeling methods and rock mechanics and geostress experiments to establish feasible methods and models for rock mechanics and geostress parameters.In this paper,the Chang 6,Chang 7 and Chang 8 sections of the Huaqing area are studied.Firstly,the 8 parameters of static rock mechanics under simulated stratum conditions are tested and analyzed.Different angles(0°,45°,90°)The 71 rock samples were subjected to triaxial compression experiments.Secondly,the five full-diameter cores are scanned for circumferential sound velocity,and the horizontal maximum and horizontal minimum principal stress directions are determined according to the wave velocity variation(anisotropic).Then,one rock sample is drilled in this direction and vertically,and 30 sets are taken.The ground stress is measured in a conventional sample.Under the conditions of confining pressure simulation formation,the Kaiser-AE tester was used to test the ground stress,and the magnitude of the three-way principal stress(Sv,SH1 and SH2)was obtained.Then the rock dynamics static and dynamic transformation model and the new model of anisotropic formation ground stress calculation are established through experiments,and the LogCRMS software is used to calculate the rock mechanics and ground stress of multiple well logging data in the work area.Finally,the mechanical parameters are extracted hierarchically and the ground stress contour map is drawn to study the current stress distribution law.Get the following main ideas:(1)The Young's modulus of the Chang6,Chang 7,and Chang8 segments averaged 22.857GPa,29.558GPa,and 27.911GPa,respectively.Comparing the Young's modulus and Poisson's ratio of different core angles,the Young's modulus and Poisson's ratio of the horizontal samples are larger than the vertical samples(EH>EV,PRH>PRV).Fit the vertical and horizontal Young's modulus and Poisson's ratio.The Young's modulus anisotropy coefficient is 1.107,the Poisson's ratio anisotropy coefficient is 1.084,and the rock mechanical parameters show anisotropy.(2)The in-situ stress state of the Chang 6-Chang 8 is Sv>SH1>SH2,the minimum horizontal and maximum principal stress gradient are 1.2-1.7MPa/100m,1.5-2.2MPa/100m,and the horizontal stress ratio is 1.10-1.32,The average is 1.25 and the stress difference is 3-12 MPa.The Chang 7 section is greater than the Chang 6 and the Chang 8 section.(3)The distribution of horizontal minimum principal stress(SHmin)is obvious in all sections of Chang 6,Chang 7,and Chang 8 sections.It has the characteristics of southeast low and northwest high,and an overall change from southeast low value to northwest high value.(4)The Chang 6-Chang 8 sections of 12 Wells in the working area is calculated.The horizontal minimum principal stress is between NW0°-NW50°,and the horizontal maximum principal stress direction is between NE40°-NE90°?Through the above research,a set of comprehensive evaluation software for in-situ stress logging suitable for low-porosity and low-permeability reservoirs has been developed,which improves the calculation accuracy of engineering parameters of low-porosity and low-permeability reservoirs,It is a good way to reveal the distribution law of the in-situ stress of Chang 6 to Chang 8 in Huaqing area,and provide reliable decision-making basis for basin well network deployment,horizontal well drilling and hydraulic fracturing design and implementation.