Continental shale oil and gas have emerged as an important contributor to petroleum reserve growth and production addition in China. However, their efficient development of multiple reservoirs simultaneously in a three-dimensional space, that is, cube development, requires fine-scale geological sweet spot evaluation. The Lucaogou Formation in the Jimusar Sag, Junggar Basin represents one of China’s three major demonstration areas of shale oil production capacity construction. This study aims to ascertain the shale oil resource prospects and sweet spot distribution of the Lucaogou Formation to provide theoretical support for its future cube development. Based on a detailed analysis of the geological characteristics of the formation, we assess its “four key properties”, that is, oil-bearing property, oil mobility, reservoir property, and fracability. Accordingly, the concept of sweet spot index is proposed to quantitatively assess the resource quality of shale oil plays. Furthermore, we systematically identify the lithofacies and lithofacies assemblages of shales, quantitatively evaluate the resource potential of varying lithofacies assemblages, and determine the vertical distribution of sweet spot layers. The results indicate that 11 lithofacies can be identified in the Lucaogou Formation based on variations in mineral composition, organic matter abundance, and sedimentary structures. These lithofacies can be further classified into four lithofacies assemblages according to the source rock-reservoir configurations. The most favorable lithofacies for shale oil exploration is identified as the lamellar organic-rich argillaceous siltstone within two lithofacies assemblages: (1) an assemblage consisting of lamellar organic-rich mudstones and limy dolomites and lamellar organic-rich siltstones and (2) an assemblage composed of lamellar organic-rich mudstones and limy dolomites, lamellar organic-rich siltstones, and massive organic-rich to organic-lean siltstones and mudstones. Within the lithofacies assemblage of lamellar organic-rich mudstones and limy dolomites, parts of lamellar organic-rich felsic mudstones and lamellar organic-rich mixed mudstones exhibit considerable potential for shale oil exploration. Shale oil hosted in oil plays characterized by adjacent and integrated source rock-reservoir configurations represents a favorable exploration target in the Lucaogou Formation within the Jimusar Sag. This formation contains multiple sweet spot layers with significant resource potential. Overall, the study area holds promising resource prospects. For continental shale oil systems with multiple superimposed sweet spot layers, the cube development should be adopted based on a fine-scale geological sweet spot evaluation to reducing costs.

Whether clay-rich shale reservoirs with low-medium maturity can serve as primary exploration targets remains a focal point of debate in the academic community. Clarifying the exploration potential of clay-rich shale reservoirs is crucial for the future exploration and development of lacustrine shale. The Triassic Yanchang Formation in the Ordos Basin has been one of most productive lacustrine shale oil systems in China, with substantial oil production capacity already established. While the primary productive layers are currently fine-grained siltstone interbeds, however, it remains a highly debated issue whether the volumetrically more significant clay-rich reservoirs can become viable exploration targets in the near future. To address this issue, we examined the exploration potential of different lithofacies assemblages in Member 7 (Mbr 7) of the Triassic Yanchang Formation, using a borehole in the Tongchuan area of the southern Ordos Basin as an example. We identified favorable exploration targets and assessed whether clay-rich reservoirs formed predominantly-freshwater conditions can become viable exploration targets. The results indicate the presence of six lithofacies in clay-rich reservoirs of Mbr 7 of the Yanchang Formation, with two main lithofacies assemblages: laminated organic-rich shale and massive mudstone. From the perspective of sandstone distribution, the sandstone interlayers within laminated organic-rich shale are primarily formed by gravity (hyperpycnal) flows, while sandstones deposited in delta front environments are typically associated with massive mudstone. Laminated organic-rich shale deposition occurred in an anoxic, deep-water environment characterized by high primary productivity, whereas massive mudstone formed in environments with high sedimentation rates and substantial terrigenous debris influx. Currently, the exploration potential of sandstone interlayers exceeds that of clay-rich reservoirs, with the greatest potential observed in the sandstone interlayers associated with laminated organic-rich shale formed by gravity (hyperpycnal) flows. Comparative analysis reveals that clay-rich reservoirs with low to medium maturity present great challenges for exploitation, making interlayer-type reservoirs the main focus of exploration at this stage. Nevertheless, clay-rich reservoirs in closed systems with high thermal maturity and organic matter content also hold considerable potential.

Research has identified and increasingly explored the micro-migration phenomenon in shaly strata, which is currently one of the key scientific issues affecting shale oil accumulation and efficient development. Recently, qualitative and quantitative methods for characterizing hydrocarbon fractionation related to shale oil micro-migration have been proposed, which brought promising prospects to oil micro-migration research. Three key techniques in this field are summarized in this minireview, and the outlook for shale oil micro-migration characterization is prospected. Fourier transform ion cyclotron resonance mass spectrometry can be employed to distinguish subtle composition differences related to short-distance migration; core-flooding extraction experiments can be utilized for the quantitative characterization of micro-migration in organic-rich shale; and semi-open thermal simulation experiments are useful to analyze the chemical composition and structural evolution of expelled and retained oil. These three methods have different focus and advantages, while they provide different viewpoints and means for the characterization of shale oil micro-migration and have all achieved good results in different regions. Studies regarding the latest technologies deepen our understanding of the short-distance migration of shale oil, as well as improve our knowledge of the mechanisms of shale oil micro-migration, which is of great practical significance to the evaluation of shale oil content and mobility and further optimizes the identification of sweet spots and the effects of fracturing development.