Regression equation analysis of dynamic and static elastic modulus and Poison's ratio of Paleogene sandstone reservoirs in Zhanhua sub-sag, Bohai Bay Basin

• Established a high-accuracy quadratic model( Eₛ = 0.0003 Ed ² − 0.0167 Ed + 9.9553, R² = 0.98) for Paleogene sandstones, and compared with existing linear/power-law models, the prediction error was significantly reduced. • Through comprehensive ultrasonic triaxial testing verification, 20 MPa was determined as the critical confining pressure for microcrack closure to dominate the dynamic static relationship. • It can be directly applied to well logging interpretation, with on-site data verification showing an error of<8 %, supporting wellbore stability and fracturing design for high porosity reservoirs. The static elastic parameters of rocks are the basis for oil drilling, formation fracturing, and fracture prediction. Given the limited research on dynamic-static parameter conversion models for Paleogene continental sandstone reservoirs in the Bohai Bay Basin, this study employs an integrated measurement technique combining ultrasonic pulse transmission and triaxial loading systems to obtain dynamic and static elastic parameters of core samples from the Paleogene sandstone reservoirs in the Zhanhua Sag. The aim is to establish a regional dynamic-static elastic parameter conversion equation, providing a basis for predicting continuous-depth static parameters using acoustic logging data. The experimental results demonstrate that:(1) Rock density exhibits a clear correlation with P- and S-wave velocities, which is typically more pronounced under unconfined pressure conditions.(2) Confining pressure shows a positive correlation with dynamic elastic modulus, particularly when the confining pressure is below 20 MPa, where wave velocities and dynamic modulus exhibit heightened sensitivity to pressure variations.(3) Both static elastic modulus and Poisson’s ratio increase with rising confining pressure We developed a high-accuracy predictive model (R² = 0.98) for static elastic modulus in Paleogene sandstones of the Zhanhua Sag. Integrating ultrasonic and triaxial tests on 8 core samples, we identify a critical confining pressure threshold (20 MPa) where microcrack closure dominates dynamic-static relationships. Compared with linear and power-law models, this model significantly reduces prediction errors and has been validated through well logging data (with an average error of<8 %). The research results provide reliable basis for wellbore stability assessment and hydraulic fracturing design of high porosity reservoirs.