Hydrocarbon exploration and exploitation have progressively shifted toward 10000-meter-deep onshore plays, 1000-meter-deep offshore plays, unconventional plays, and residual oil in mature oilfields. The emerging frontiers are characterized by diverse reservoir types, complex geological conditions, and considerable difficulties in exploration and development, posing challenges such as incompatibilities between existing methodological and technical systems and exploration and exploitation targets to research on well logging geology. This study presents a summary of the evolution of research on well logging geology in terms of depth, scale, span, and dimension for hydrocarbon exploration and exploitation. The results indicate that logging geology research is gradually advancing towards in-depth interdisciplinary integration and multidimensional development. The integration of geology, logging, seismology, engineering, and artificial intelligence (AI) can enhance the efficiency of hydrocarbon exploration and exploitation while reducing costs and risks. In the development of deep to ultra-deep onshore plays at depths of about 10000 m, the combination of logging and geology allows revealing the genetic mechanisms of reservoirs and analyzing major factors controlling reservoir quality, thereby achieving a comprehensive reservoir evaluation. For unconventional hydrocarbon reservoirs, research on well logging geology enables the identification of the geological characteristics of millimeter-scale laminae, as well as analyses of subtle variations in oil-bearing properties and oil mobility within micro- to nano-scale pore throats. On the spatial scale, logging technology allows for the detection of wellbores, near-well areas, and far-well regions, achieving the characterization of point-line-plane-volume full-space geological information. On the temporal scale, logging technology enables the analysis of changes in log data before and after fracturing or water injection, thus contributing to fine-scale hydrocarbon development. Driven by AI empowerment, the future integration of multidisciplinary dimensions, that is, geology, well logging, seismology, and engineering, will further expand the application domains and scope of well logging geology, accelerating its development. This will offer robust technical support for future hydrocarbon exploration and exploitation.

High industrial natural flow has been produced from the ultra-deep Cretaceous Bashijiqike sandstones (>6000 m) in the Qiulitage Structural Belt in the Kuqa Depression, Tarim Basin, northwestern China. However, the Cretaceous Bashijiqike reservoirs exhibit strong heterogeneity and significant reservoir quality variations. The complex in-situ stress state plays a critical role in reservoir quality; however, little research has been performed on the relationship between in-situ stress and reservoir quality, which constrains efficient hydrocarbon exploration and development. In order to clarify the in-situ stress-controlled reservoir quality variations, cores, thin sections and well log data are integrated to clarify the depositional microfacies, diagenesis and in-situ stress. The in-situ stress orientation and magnitude characteristics are investigated, and the distribution patterns of stress state are analyzed considering sedimentary environments and diagenesis. The results show that in-situ stress in Zhongqiu 1 gas field of Qiulitage Structural Belt remains unreleased since rare fractures are formed, and horizontal stress differences are greatly varied due to structural patterns, lithology assemblages and variations of geomechanical properties. The current maximum principal stress (S_hmax) orientation is NW–SE, derived by image logs in the Cretaceous Bashijiqike reservoirs of Zhongqiu 1 gas field. Vertical stress (S_v) is determined by integrating bulk density of the overburden rocks, while the maximum horizontal principal stress (S_hmax) and the minimum horizontal principal stress (S_hmin) are calculated by the combined spring model using density and sonic logs. A significant negative correlation relationship is observed between measured porosity and horizontal in-situ stress differences (Δσ = S_hmax−S_hmin). The measured helium porosity is reduced to 9.4% when the Δσ is higher than 40 MPa. Intensive stress compression will contribute to a high compactional porosity loss (COPL), and COPL reaches 34.2% when the Δσ becomes higher than 40 MPa. Layers with lower Δσ values exhibit higher reservoir porosity and also higher natural gas production. Overall, favorable reservoirs are distributed at the center of sandbody in underwater distributary channel microfacies, and the sandstones are fine- to medium-grained and well-sorted with low in-situ stress differences. In-situ stress will control the compaction behaviors and the matrix porosity of sandstones, and also determines the hydrocarbon productivity. The results will provide insights into the reservoir quality variations in ultra-deep sandstones, and have implications for deep buried rocks with complex stress conditions worldwide.

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.