AUTHOR=Cai Mingliyang , Li Ming , Zhu Xiaoshuan , Luo Hao , Zhang Qiang 

TITLE=Comprehensive Evaluation of Rock Mechanical Properties and in-situ Stress in Tight Sandstone Oil Reservoirs

JOURNAL=Frontiers in Earth Science

VOLUME=10

YEAR=2022

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2022.911504

DOI=10.3389/feart.2022.911504

ISSN=2296-6463

ABSTRACT=<p>Comprehensive research on reservoir rock mechanics and <italic>in-situ</italic> stress properties combined with petrophysical experiments, logging models and numerical simulation is an important means to achieve efficient development of tight sandstone oil reservoirs. In this study, a large number of rock mechanics and acoustic experiments, full-wave train array acoustic wave tests, hydraulic fracturing data and three-dimensional finite element simulations were used to study the rock mechanical properties and <italic>in-situ</italic> stress characteristics of continental tight oil reservoirs in the Yanchang Formation. The results show that under uniaxial conditions, the tight sandstone samples mainly suffer from tensional ruptures. With the increase of confining pressure, the tight sandstone samples undergo obvious shear ruptures. When the confining pressure is loaded to 35 MPa, a typical vertical shear fracture will be formed. The hydraulic fracturing calculation results show that the <italic>in-situ</italic> stress state of the target layer satisfies <italic>σ</italic><sub>v</sub> (vertical principal stress)&gt;<italic>σ</italic><sub>H</sub> (maximum horizontal principal stress)&gt;<italic>σ</italic><sub>h</sub> (minimum horizontal principal stress). Based on the results of rock mechanics and acoustic tests, we have constructed the dynamic and static mechanical parameter conversion models of tight oil reservoirs and the logging interpretation model of current <italic>in-situ</italic> stress. Furthermore, the finite element method is used to simulate the three-dimensional structural stress field of the target layer. The simulations show that the horizontal principal stress distribution in the work area is consistent with the applied environmental stress. The <italic>σ</italic><sub>H</sub> of the target layer is mainly distributed in 32–50 MPa, and the <italic>σ</italic><sub>h</sub> is mainly distributed in 20–34 MPa. Both <italic>σ</italic><sub>H</sub> and <italic>σ</italic><sub>h</sub> are relatively high in the southern uplift of the work area; among them, <italic>σ</italic><sub>H</sub> is usually greater than 44 MPa, and <italic>σ</italic><sub>h</sub> is usually greater than 24 MPa. The northern part of the study area developed several grooved areas with relatively low stress values. The regions with high stress values are often distributed in bands, which may be related to the compression caused by the deformation of the strata. For shear stress, left-handed and right-handed regions usually alternate with each other. However, the extent of the left-handed area in the southern uplift area is larger than that of the right-handed area, indicating that the tight oil reservoirs in the study area are mainly affected by left-handed activities.</p>