Well-logging evaluation of in-situ stress fields and its geological and engineering significances

Research of the in-situ stress field can provide theoretical guidance and technical support in well design, fracture stimulation of wells and fracture effectiveness evaluation. It is crucial to summarize the in-situ stress field analysis and related loging evaluation methods. The study summarizes the components of in-situ stress field and its well-logging response mechanism, and presents the log suite consisting of sonic transit time, resistivity and image logs as the most sensitive to in-situ stress responses. The time and magnitude of paleotectonic stress field can be determined by acoustic emission experiment. The maximum paleotectonic stress magnitude can be recovered by using resistivity log, sonic transit time log and fracture density. The in-situ stress field can be described in respect of orientation and magnitude. The orientation of in-situ stress field can be determined by using the image logs to pick up borehole breakouts and induced fractures, and the array acoustic logs to derive shear wave splitting. The magnitude of the in-situ stress field can be determined through hydraulic fracturing combined with acoustic emission experiment. The in-situ stress can be calculated through models or methods including the combined spring model built on the in-situ stress field description, realizing in-situ stress field analysis. The analytical results can better help analyze fault properties, evaluate reservoir quality and fracture effectiveness, predict reservoir distribution, as well as be of practical value to the engineering fields like hydraulic fracturing of unconventional hydrocarbon reservoirs.