Energies, Vol. 18, Pages 6023: Method for Interpreting In Situ Stress Based on Pump Shutdown Pressure Drop Curves in Deep Coal Seams

Energies, Vol. 18, Pages 6023: Method for Interpreting In Situ Stress Based on Pump Shutdown Pressure Drop Curves in Deep Coal Seams

Energies doi: 10.3390/en18226023

Authors:
Huaibin Zhen
Haifeng Zhao
Zhaojie Jia
Fengyin Xu
Yanqi Sun
Wenting Zeng
Qi Zhu

The G-function can obtain the formation ground stress information by identifying the fracture closure point after fracturing, but the main fracture closure period of the deep coal seam volume fracture network is long, and the on-site pump stop time is short, and only the branch fracture closure can be observed. In order to explore the relationship between the closure pressure of branch fractures and the horizontal in situ stress, taking the deep coal seam in Daning–Jixian area as the background, the numerical simulation of the pump-stopping pressure drop of a complex fracture network with different complexity and different approximation angles was carried out using a finite element method, and the relationship between the closure pressure corresponding to the fracture closure point and the in situ stress was explored. The results show that when the crack approximation angle is greater than 60°, it can be approximately considered that the closure pressure of the first crack closure point tends to the maximum horizontal in situ stress. Furthermore, the minimum horizontal in situ stress can be obtained by formula conversion. The above-outlined method is applied to the in situ stress prediction of the X well area in Daning–Jixian County. The calculation results are compared with the test fracturing results, and the relative difference is within 5%, which shows that it has good accuracy and feasibility. The research results can provide guidance for the optimization of deep coalbed methane scheme design.