The 10 most-cited articles in AAPG Bulletin, 2023

Abstract With several superimposed petroleum systems and a proven reserve of 200 billion bbl of oil and 160 TCF of gas, the Songliao Basin in northeastern China is considered a super petroliferous basin. This paper outlines the basin’s tectonic units, its tectono-stratigraphy, and the essential elements of each petroleum system and reviews the distribution of hydrocarbon plays and opportunities for future unconventional shale oil exploration. The Songliao Basin developed during an Early Cretaceous rifting event that resulted in localized petroleum systems with the limnic, swampy, coal-bearing Shahezi shale as the source rock for 156.4 TCF of gas discovered in synrift volcaniclastic reservoirs. Continued thermal subsidence during the Late Cretaceous resulted in two rapid flooding events, which resulted in the deposition of the organic-rich Qingshankou and Nenjiang Formations. The first member of Qingshankou shale (K2qn1), with a total organic carbon content ranging from 1 to 7 wt. % and a thickness of 50 to 100 m (165 to 330 ft), reached the oil window at 80 Ma and is the dominant…

Abstract Natural fractures are effective reservoir spaces and the main seepage channel for tight sandstones, which control the migration, enrichment, and productivity of oil and natural gas. This paper systematically reviews the formation and distribution of natural fractures in the deep tight sandstone reservoirs of China over the past three decades. Based on geological origins, multiscale characteristics, effective evolution, and primary controllers of natural fractures, a quantitative method of natural fracture prediction was proposed. Four origins of natural fractures were identified in tight sandstone reservoirs, namely tectonic, diagenetic, tectonic-diagenetic, and overpressure origins. According to the scale and control boundary, natural fractures can be divided into four scales: large scale, mesoscale, small scale, and microscale. The multiscale natural fractures are influenced by paleotectonic stress, differences of rock mechanical property, and thickness. Controlling factors for the growth and evolution of natural fractures in tight sandstones are summarized as internal…

Abstract The Pannonian Basin complex has approximately 13 billion BOE cumulative production to date. As to the remaining resources, various estimates place the combined conventional and unconventional hydrocarbon potential in this very mature basin complex in the >5 billion BOE range. The Pannonian Basin, as with many other super basins, is characterized by several source rocks, stacked reservoirs, greater than 6-km-thick basin fill, mature infrastructure, established service sectors, large amounts of subsurface data, multiple operators, and direct access to markets. Due to the removal from the Alpine collision zone, the overthickened lithosphere of the Pannonian region collapsed during the Middle Miocene and evolved to a large and diffuse back-arc basin system. During the Late Miocene–Pliocene, postrift thermal subsidence caused the sedimentation of an unusually thick basin fill locally exceeding 8 km thickness compared to the typically much thinner synrift sequence not more than 2 km thick. The most prolific petroleum systems are found in the Neogene basin fill (65%), whereas the…

ABSTRACT Linkage of fault segments is a critical process during the formation of strike-slip faults, and it influences the generation and distribution of related structures. In this study, we investigate the linkage processes and formation mechanism for the strike-slip faults in the Shunbei area of the Tarim Basin based upon newly acquired three-dimensional seismic data. The seismic interpretations suggest that the northeast-trending SB-1 fault and the approximately north-trending SB-5 fault are strike-slip faults with the development of superimposed flower structures in the cross-section views. In the plan view, segments of these faults show a step-like arrangement. We infer that the main activities of these strike-slip faults took place in the Middle and Late Ordovician. The linkage underwent two phases. The first phase was the linkage of R and P shears along with different segments by forming principal displacement zones. The second phase was the linkage of different segments by forming overstepped zones, culminating in the flower structures. Overall, under the influence of the…

Abstract Cavern and vug porosities in the Ordovician carbonates in the Halahatang oil field are currently hot targets for hydrocarbon exploration in the Tarim Basin of northwestern China. However, crucially, the formation of cavern and vuggy porosities have not been fully understood due to multiphase tectonic-driven (e.g., faults, unconformities) diagenetic alterations. Here, we integrated petrology observations and geochemical analyses (C, O, Sr isotopes, trace and rare earth elements [REE], clumped isotopes, and laser-based U-Pb dating), aiming at determining the timing for tectonic-driven calcite precipitation, which is closely tied to karstic reservoir development. Vug-filling calcites were emplaced in the late Caledonian (460.8 ± 3.4 and 448.6 ± 5.3 Ma) and early Hercynian (335 ± 19 Ma), and the U-Pb ages for fracture-filling (ca. 364 ± 53 and 282.9 ± 5.4 Ma) and megacrystalline (from 324 ± 23 to 300.9 ± 4.8 Ma and 244.13 ± 13 to 240.5 ± 4.1 Ma) calcites predominantly fell within the Hercynian. In addition, the latest fracture-filling calcites show a slightly younger U-Pb age…

Abstract Some Precambrian carbonate rock bodies host economic petroleum reserves. Here, we present a case study of the deeply buried (>5 km) upper Ediacaran Dengying Formation (ca. 551–541 Ma) to document the formation of a microbialite gas field. Detailed petrological and geochemical data are presented and placed in context with porosity and permeability analyses. This approach leads to a better understanding of Ediacaran microbialite textures, diagenetic pathways, and reservoir properties in general. Microbialite facies yield a positive correlation between sorting coefficient and porosity. Compared with other microbial fabrics, thrombolites have well-connected pore networks and large pore-throat radii. Fibrous dolomite cement was precipitated in a marine pore water environment at an early diagenetic stage. Maximum porosity (∼4%–6%) and permeability values (∼0.01–10 md) are established in spatially confined stratigraphic intervals. Meteoric diagenesis correlates with transient subaerial seafloor exposure and affects carbonates. Meteoric diagenesis is typified by dolostone with low…

Abstract The Anglo-Polish Super Basin forms an important petroleum province that stretches across northwestern Europe. It contains many giant gas fields, primarily located beneath a thick upper Permian (Zechstein Group) evaporite canopy and a smaller amount of oil and gas in Mesozoic reservoirs in the suprasalt section. Although exploration activity continues in the super basin, discoveries have diminished in size; many fields have been decommissioned; and it is beginning a transformation from an area with a rich petroleum heritage to a new, low-carbon energy hub. Given its favorable geology, infrastructure, and the location of major industrial emitters in adjacent land areas, offshore parts of the super basin are being evaluated and repurposed for renewable technologies like wind and geothermal energy, and as possible sites for subsurface carbon dioxide, hydrogen, compressed air, and methane gas storage. The use of a rich, dense, and high-fidelity seismic, well log, core, and pressure data sets acquired during petroleum exploration and production activities provide the basis for a…

ABSTRACT This study aimed to quantitatively characterize pore structure of middle- and high-ranked coal reservoirs in northern China. A total of 51 coal samples from the three coalbed methane (CBM) exploration areas including Anhe, Huaibei, and Huainan coalfields in northern China were investigated using proximate analysis, coal petrology, low-temperature nitrogen adsorption, mercury intrusion porosimetry, nuclear magnetic resonance (NMR), and x-ray computed tomography. The results show that the coalification of the Anhe and Huaibei coalfields is greatly influenced by igneous intrusion, with the maximum vitrinite reflectance (Ro,max) ranging from 1.41% to 2.90% and from 0.59% to 2.12%, respectively. In contrast, the Huainan coalfield has a narrow range of coal rank, with the Ro,max ranging from 0.59% to 0.87%. Of the coal samples studied, those from the Anhe coalfield have the greatest vitrinite content (average 83.81%) and the largest micropores, corresponding to the highest methane adsorption capacity and relatively low pore connections. In the Huaibei coalfield, coals are…

Abstract Carbon capture and storage (CCS) in underground structures depends on the quality of the geological reservoirs. Factors including interconnectivity in the pore spaces, natural fractures, reservoir thicknesses/depths, preexisting fluid (water or hydrocarbon), traps, and overburden integrity express the CO2 storage potentials of the geological reservoirs. This study presents the CO2 storage efficiency factors considering the associated geological parameters involving basalt, shale, carbonate, and siltstone. It evaluates the basalt–sedimentary rock interactions and their impact on the complex, heterogeneous, and unconventional reservoir systems in the Paraná Basin concerning CO2 storage. It considers the reservoir porosity, thickness, and area for CO2 storage with the associated uncertainties based on the efficiency factors EΦ, Eh, and Ea, respectively, to propose the algorithm for capacity estimation. Including water saturation and water salinity-based efficiency parameter in the CO2 storage capacity estimation expression depends on the percentage of water in the reservoirs…

ABSTRACT Lacustrine organic-rich Eocene shales are well developed within the faulted lake basin in the Bohai Bay Basin in eastern China. It is crucial to comprehend the sedimentation of these shales for the study of depositional processes, paleoenvironment reconstruction, and shale oil exploration. This research investigates the sedimentary characteristics and formation mechanisms of lacustrine shales in the upper fourth member and lower third member of the Eocene Shahejie Formation (Es4s–Es3x shale), based on thin sections and field-emission scanning electron microscopy observations of well cores, with x-ray diffraction analysis, electron probe microanalysis, and geochemical elements analysis. The Es4s–Es3x shale is deposited in a hypoxic saline lake with laminated, massive, and lenticular sedimentary structures, wherein laminated shale is the dominant lithofacies. Eight laminae units have been identified: micritic calcite laminae (MCAL), sparry calcite laminae (SCAL), quartz–feldspar–clay mixed laminae (QFCL), organic-rich clay laminae (OCL), clay laminae (CL), organic matter…