A systematic review and summary of the developmental history and advances in experimental techniques for carbonate reservoirs reveals that technological progress in experimentation serves as a fundamental driving force behind theoretical and technological innovations in the field. The research results are as follows. (1) The evolution from macro-scale reservoir characterization via visual inspection and magnifying lenses in the 1950s and 1960s to modern digital outcrop acquisition, 3D micro-to-nano pore imaging, and multi-scale reservoir heterogeneity characterization and modeling in the 21st century, underscores the pivotal role of theoretical and experimental technological advancements, particularly in carbonate petrology, sedimentology, sequence stratigraphy, and the deployment of sophisticated experimental equipment. (2) “Geochronology, thermometry, barometry, and fluid property tracing” represent the most cutting-edge geochemical testing techniques for carbonate reservoirs in the 21st century. The iterative upgrading from bulk-rock to in-situ micro-area analysis, from solution-based methods to laser ablation, and from point detection to area mapping defines the future trajectory of the field. Furthermore, digital transformation and intelligent development provide the impetus for these technical upgrades, which will yield more comprehensive and reliable data for investigating the genesis of diagenetic fabrics and diagenetic-porosity evolution. (3) The high-temperature and high-pressure (HTHP) visualization apparatus for reservoir formation simulation across tectonic stages in ultra-deep layers is the core equipment for investigating the genetic mechanisms of ultra-deep reservoirs. It can accurately replicate ultra-HTHP geological environments, enabling dynamic forward modeling of water-rock interaction processes across tectonic stages, and integrates in-situ real-time monitoring of fluid properties and rock permeability. This apparatus provides direct experimental evidence for unraveling the formation mechanisms, preservation conditions, and spatial distribution patterns of secondary porosity in ultra-deep carbonate reservoirs. The elucidation of hydrocarbon accumulation mechanisms in ultra-deep carbonate reservoirs via simulation experiments represents a defining future research trend. (4) Reservoir prediction is the ultimate objective of reservoir characterization, evaluation, genesis, and modeling. Given that geophysical techniques are the primary tools for reservoir identification and prediction, it is highly recommended to strengthen the organic integration of experimental carbonate reservoir techniques with geophysical methods.

To support ongoing hydrocarbon exploration of the marine Mesozoic strata in the Qiangtang Basin, we conduct surveys and reassessments of the regional petroleum geology. Accordingly, several benchmark sections of the basin’s source rocks and reservoirs are established. The results indicate that the Qiangtang Basin contains three dominant source rock sequences (the Bolila, Bagong, and Quse formations), two suites of carbonate reservoirs (the limestone karst of the Bolila Formation and the dolomites of the Buqu Formation), three suites of sandstone reservoirs (the Bagong, Quemocuo, and Xiali formations) dominated by tight-sand reservoirs, and three suites of well-developed regional evaporite cap rocks (the Quemocuo/Quse and Xiali formations). Analysis of oil and gas shows reveals that the marine Mesozoic strata in the Qiangtang Basin experienced the hydrocarbon generation, migration, and accumulation processes. In this basin, oil-generating strata, reservoirs, and cap rocks are well-matched both temporally and spatially, forming two petroleum systems: the Upper Triassic-Lower Jurassic pre-salt system and the Lower-Middle Jurassic intrasalt system. Three hydrocarbon plays are identified in the basin. The first play consists of the source rocks of the Bolila Formation, the karst reservoirs of the Bolila Formation, and the mudstone cap rocks of the lower Bagong Formation. The second one is composed of the mudstone source rocks of the Bolila-Bagong formations, the sandstone reservoirs of the Quemocuo-Bagong formations, and the evaporite cap rocks of the middle-upper Quemocuo Formation. The third one comprises the source rocks of the Quse Formation, the dolomite reservoirs of the Buqu Formation, the sandstone reservoirs of the Xiali Formation, and the evaporite/mudstone cap rocks of the Xiali Formation. Three types of hydrocarbon resources occur in the Qiangtang Basin: conventional, shale, and tight hydrocarbons. In the Maqu area, play fairways cover an area of about 5 × 10³ km². An assessment of the hydrocarbon generation intensity and hydrocarbon accumulation coefficients (HACs) of source rocks in the Bolila-Bagong formations reveals that the Maqu area has conventional hydrocarbon resources of about 0.5 × 10⁹ t when estimated using a minimum resource abundance of 100 × 10³ t/km². Meanwhile, the Bagong Formation contains shale oil resources of approximately 1 × 10⁹ t. In the Biluocuo-Esima area, play fairways with an area of about 8 × 10³ km² are identified. An assessment of the hydrocarbon generation intensity and HACs of source rocks in the Quse and Bagong formations reveals that this area contains conventional hydrocarbon resources estimated at 0.8 × 10⁹ t based on a minimum resource abundance of 100 × 10³ t/km². In this area, the Bagong and Quse formations are identified as play fairways for shale oil exploration, with shale oil resources of approximately 1.6 × 10⁹ t and about 0.8 × 10⁹ t, respectively. In the Shenglihe area, play fairways span an area of 5 × 10³ km², where the Quse Formation holds shale oil resources of about 1 × 10⁹ t.

Presently, large-scale oil and gas fields discovered in deep carbonate rocks are predominantly distributed within porous dolomite reservoirs and fractured-vuggy karst limestone reservoirs. However, recent discoveries in wells Pengshen 12 and Nanchong 2 in the Sichuan Basin confirm the presence of porous limestone reservoirs in the 2nd member of the deep Maokou Formation (also referred to as the Mao 2 Member). This finding challenges the traditional geological understanding of reservoirs, establishing the porous limestone reservoirs as a hot research topic. In this study, geological insights are gained using core and thin section observations, geochemical analysis of reservoirs, and reservoir identification and tracking through well-tied seismic interpretation. The results indicate that porous bioclastic limestone reservoirs are present in the Mao 2 Member. The dominant storage spaces include intergranular pores, biological cavity pores, moldic pores, and dissolved pores, which are formed in sedimentary and supergene environments. Specifically, the reservoir encountered in drilling well Pengshen 12 exhibits a cumulative thickness of 24.80 m, an average measured porosity of 5.1%, and an average measured permeability of 0.05 × 10^-3 μm². Early hydrocarbon charging and the presence of anomalous overpressure (overpressured compartments) are identified as key factors contributing to the deep preservation of pores formed during the sedimentary and early supergene stages. The intermittently distributed porous bioclastic limestones are wrapped by relatively tight micritic limestones, resulting in the formation of local anomalous overpressure within bioclastic shoals under the influence of ultra-high temperatures at great depths. Reservoirs in the Mao 2 Member are sandwiched by the floor of tight micritic limestones of the Mao 1 Member and the roof of tight mudstones interbedded with limestones from the Wujiaping Formation. This configuration facilitates the formation of regional anomalous overpressure in the Mao 2 Member. The mechanisms underlying pore formation and preservation suggest that the large-scale porous limestone reservoirs in the Mao 2 Member are developed under a combination of favorable conditions: intermittently distributed porous bioclastic shoals, early hydrocarbon charging, local anomalous overpressure within individual shoals, and regional anomalous overpressure. These reservoirs exhibit a laterally intermittent distribution. Based on the identification of bioclastic shoals, the roof and floor of the member, it is predicted through well-tied seismic interpretation that favorable bioclastic limestone shoal reservoirs cover an area of 9.5 × 10⁴ km². These insights provide a theoretical foundation for the occurrence of porous limestone reservoirs in deep parts, expanding the exploration targets of deep limestone reservoirs in the Sichuan Basin. Additionally, this study offers a valuable reference for the exploration of deep limestone reservoirs in other basins.

This study systematically reviews and summarizes the history and advances of research on the geneses of dolomites and dolomite reservoirs, and outlines the prospects for future research orientations. The study of dolomites has had a history of over 200 years, while research on dolomite reservoirs has been kicked off since the 1950s. Previous studies established dolomitization models under varying geological conditions represented by seepage reflux and burial-compaction, and explained the geneses of dolomites with varying characteristics and occurrences in nature. Accordingly, the dolomite pores may mainly result from dolomitization as concluded. Over the past decade, progress has been made by incorporating modern sedimentary observations and simulation experiments, and four genetic types of dolomites have been identified, that is, the low-temperature organic precipitation type, the low- and high-temperature metasomatism types, and the high-temperature inorganic precipitation type. Based on this, the plot for identifying the geological and geochemical characteristics of dolomites is developed. It has been revealed that the genesis of dolomites cannot be simply equated with that of dolomite reservoirs. The porosity in dolomite reservoirs is mainly inherited from original porosity followed by modification, featuring more significant facies control and inheritance rather than modification. Although some dolomite pores are the products of burial dissolution, early-stage dolomitization is favorable for pore preservation. Two dolomitization pathways, i.e., dolomitization with protolith texture preserved and burial-based limestone dolomitization, have been identified, with the former exhibiting the optimal reservoir-forming effects. The advancements in experimental techniques have deepened the understanding of the geneses of dolomites, while simulation experiments provide deep insights into the geneses of dolomite reservoirs. In response to hydrocarbon exploration and production, future research should intensify the fine characterization and modeling of dolomite reservoirs, as well as logging-based reservoir identification and seismics-based reservoir prediction using the geological models of reservoirs.

The origin of dolostone in the Middle Jurassic Buqu Formation of the Plateau Basin has been a subject of prolonged debate. This study combines detailed petrological observations with analyses of Mg-C-O isotopes and elements to constrain the origin of dolostones in the Buqu Formation. Petrography and cathodoluminescence (CL) examination identified three types of matrix dolostones: very finely to finely crystalline dolostone (D1), finely to medium crystalline dolostone (D2), and medium to coarsely crystalline dolostone (D3). The analysis of the diagenesis sequence reveals that D1 originated from the dolomitization of grainstone in the early diagenetic phase, whereas D2 and D3 resulted from the recrystallization of D1 during the later burial phase. The presence of high Na (>100 ppm), low Fe (<1000 ppm), low Mn (<250 ppm), positive Ce anomaly, LREE enrichment, stable δ²⁶Mg (−2.28‰ to −2.04‰), and δ¹³C (1.02‰–2.95‰) indicates that the early dolomitization fluid was oxidized seawater. As the crystal size increases (D1→D2→D3), the progressively rising Mn content and significantly negative δ¹⁸O (−10.72‰ to −7.81‰) suggest that the dolostone has experienced modification and alteration by buried pore water in the later stages. The fluctuations in relative sea level during the sedimentary deposition of the Buqu Formation were reconstructed through the utilization of Na, Sr/Cu, Sr/Ba, Rb/Sr, ∑REE, and δ¹³C. It was observed that the δ²⁶Mg of dolostone closely mirrored the variations in sea level. The consistent trend of change confirms that sea level fluctuations control the formation and distribution of early dolostone. Frequent sea level rise and fall prompted the limestone deposited on the carbonate platform to be continuously transformed into dolostone, which accumulates over a long period to form large-scale thick dolostone. After the formation entered the burial stage, under the combined action of high Mg/Ca ratio pore water, high temperature, and high pressure, the early dolostone experienced the adjustment of burial dolomitization. This research offers a typical case study on the application of Mg-C-O isotope and elements to determine the origin of dolostone. This will aid in a more comprehensive understanding of the formation process of dolostone in ancient rock records.