Back-stress influence on minimum stress calculations in hydraulic fracturing experiments

The analysis of fluid injection pressure variation during hydraulic fracturing is widely used for tectonic stress estimation. However, the models used for that are based on several simplifying assumptions. In this article, based on the results of laboratory experiments, we show that it is necessary to consider some additional parameters for a more adequate assessment of the minimum tectonic stress based on changes in fluid pressure during hydraulic fracturing. We describe scaled laboratory experiments on hydraulic fracturing and compare the fracture closure pressure with the stress applied to the sample, which, according to standard assumptions, should be equal. However, the comparison revealed a discrepancy between these values. To address this discrepancy, we estimate the back-stress effect. This stress arises due to an increase in pore pressure caused by fluid pressure diffusion from the hydraulic fracture into the rocks. The back-stress acts on the fracture boundaries, contributing to its closure. We have estimated the back-stress effect and its influence on the minimum stress calculations. It has been shown that accounting for the back-stress in the minimum stress calculation significantly reduces the difference between the calculated values and the experimental data.