Determining the present-day in-situ stresses of tight-oil sandstones by conventional logs: An approach in the Triassic Yanchang Formation, southern Ordos Basin

The present-day in-situ stresses affect the drilling design, well pattern deployment, completion modification, hydraulic fracturing and water injection of tight-oil sandstones. measurement data these are commonly unavailable because their high costs limited core samples, therefore employing conventional logs for stress determination is imperative Firstly, suitable calculation models by were selected according to geological characteristics sixth member Yanchang Formation (Chang 6) in Heshui area southern Ordos Basin, China. Then, dynamic rock mechanical parameters determined logs, corrected static obtained from triaxial tests. Moreover, pore fluid pressure was empirical formula method. Finally, maximum minimum horizontal compressive (σ H σ h ), vertical v ) six wells calculated stresses, respectively. proposed method paper, verified those acoustic emission tests finite-element numerical simulations with relative errors less than 10%. results show that magnitudes , differential H−h study mainly range 32 43 MPa, 23 37 MPa 5 8 magnitude three-dimensional increases increase depth. average gradients H, 0.018, 0.014 0.015 MPa/m, respectively, >σ . In this state, fractures, a trend little expansion towards multiple directions, developed at small angle intersecting direction area.