Journal of Petroleum Geology最新文献

{"title":"Geological and Geochemical Characterization of Transitional Shale of the Permian Shanxi Formation in the Eastern Ordos Basin, North China","authors":"Yansong Wang,&nbsp;Yifan Gu,&nbsp;Guangyin Cai,&nbsp;Xingtao Li,&nbsp;Hongzhan Zhuang,&nbsp;Yuqiang Jiang","doi":"10.1111/jpg.70016","DOIUrl":"https://doi.org/10.1111/jpg.70016","url":null,"abstract":"<div>\u0000 \u0000 <p>The Lower Permian Shanxi Formation in the Eastern Ordos Basin, North China, is a key exploration target for transitional shale gas. Based on facies markers and elemental characteristics, the Shanxi transitional organic-rich shale are divided into estuary shale and lagoon shale. Various techniques (low-temperature N₂/CO₂ physisorption, etc.) are applied to reveal pore structure differences between estuary shale and lagoon shale. The results indicate that the estuary shale exhibit better macroscopic characteristics (organic matter [OM] component, mineral composition, porosity, and gas content) and nanoscale pore structure than those of lagoon shale. The OM enrichment model reveals the differences in OM components, and estuary shale is supplied by both terrestrial and marine OM. During the hydrocarbon generation and evolution process, the marine-origin sapropelinite has the capacity to generate more organic pores. Organic pores still occupy an important position in estuary organic-rich shale. Lagoon shale is greatly influenced by terrestrial sources, with most of the OM components being terrestrial OM, along with is primary OM showing poor pore-forming abilities. Estuary shale reservoir belongs to a pore-fracture type comprising organic pores, inorganic pores, and microfractures, while lagoon shale reservoir is microfractures type.</p>\u0000 </div>","PeriodicalId":16748,"journal":{"name":"Journal of Petroleum Geology","volume":"49 1","pages":"142-159"},"PeriodicalIF":1.7,"publicationDate":"2025-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145970219","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multiscale Reservoir Characterization of the Sarvak Formation in the Abadan Plain, Iran: Linking Diagenetic Overprints to Hydraulic Flow Units and Sequence Stratigraphy","authors":"Sepideh Darvishi,&nbsp;Hamzeh Mehrabi","doi":"10.1111/jpg.70014","DOIUrl":"https://doi.org/10.1111/jpg.70014","url":null,"abstract":"<div>\u0000 \u0000 <p>The Sarvak Formation, a major Cretaceous carbonate reservoir in the Zagros Basin, Iran, exhibits significant heterogeneity controlled by variations in depositional facies characteristics, diagenetic alterations, and accommodation spaces. This study integrates core analysis, petrography, well logs, hydraulic flow units (HFUs), and sequence stratigraphy to unravel multiscale controls on reservoir quality in the Abadan Plain. Petrographic analyses identified eight sedimentary microfacies deposited across shallow to deep settings of a carbonate platform, with diagenetic processes (dissolution, dolomitization, cementation, compaction, fracturing) tightly linked to sequence boundaries and systems tracts. Two third-order sequences (Cenomanian and Turonian) were interpreted, each comprising transgressive and regressive systems tracts (RSTs). Dissolution, concentrated beneath Cenomanian–Turonian and mid-Turonian unconformities in RSTs, generated vuggy and cavernous porosity, correlating with high-quality flow units and pore-size classes (PSCs). Dolomitization, associated with stylolites in mud-dominated facies of transgressive systems tracts (TSTs), enhanced intercrystalline porosity. Cementation and compaction degraded reservoir quality in low-energy facies. Ten HFUs and seven PSCs were classified using flow zone indicator and Winland R35 methods, whereas velocity deviation log subdivided the reservoir into 14 zones in well-A and 9 zones in well-B, highlighting vertical heterogeneity. Fracturing, primarily micro-scale and cement-filled in the Abadan Plain, showed limited permeability impact compared to tectonically active regions. The study establishes predictive links between sequence stratigraphic surfaces and systems tracts, diagenetic processes, and reservoir properties, emphasizing targeting dissolution-prone RSTs beneath unconformities and dolomitized TSTs near maximum flooding surfaces. This integrated approach reduces exploration risk in carbonate reservoirs and provides a framework applicable to analogous basins globally.</p>\u0000 </div>","PeriodicalId":16748,"journal":{"name":"Journal of Petroleum Geology","volume":"49 1","pages":"97-128"},"PeriodicalIF":1.7,"publicationDate":"2025-10-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145986933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Organic Matter Thermal Maturity Versus Variability of the Present-Day Thermal Gradient of the Eastern Part of Polish Outer Carpathians—The Key to the Success or Failure of Hydrocarbon Generation Processes","authors":"Anna Filipek,&nbsp;Rafał Kudrewicz,&nbsp;Daniel Zaszewski,&nbsp;Maciej Łoziński,&nbsp;Krzysztof Czuryłowicz,&nbsp;Radosław Staniszewski,&nbsp;Adam Baranowski,&nbsp;Kamil Kobyliński,&nbsp;Marcin Barski,&nbsp;Anna Wysocka","doi":"10.1111/jpg.70013","DOIUrl":"https://doi.org/10.1111/jpg.70013","url":null,"abstract":"<div>\u0000 \u0000 <p>This study presents an integrated analysis of organic matter (OM) maturity proxies, including Rock-Eval pyrolysis, vitrinite reflectance, and the spore color standard (SCS), in conjunction with a pre-existing 3D numerical model of the present-day temperature field. Our research, focused on the eastern Polish Outer Carpathians, aimed to unravel the potential distribution of the mature source rocks in the region. Specifically, we sought to verify the timing of maturation (pre- or post-orogenic), delineate extensively uplifted areas, assess the role of the current thermal structure in catagenesis, and understand the origin of thermal anomalies. The 3D thermal model, derived from over 500 well thermal logs, was re-evaluated using isotherm depth maps (80°C, 130°C, and 160°C) to characterize catagenesis stages. The SCS method was introduced as a robust and cost-effective tool for OM maturity determination, offering the unique advantage of tracing multi-sourcing and redeposition. Our findings reveal relatively low maturity in the Silesian and Skole Units, generally mirroring the present-day thermal field. We infer that the mature source rocks responsible for existing hydrocarbon accumulations are likely situated deeper, beneath the basal thrust of the topmost nappes. Localized “hot spots” in the present-day thermal gradient, coinciding with anomalously high OM maturity, indicate irregular heat transfer within the study area. A prominent high heat-flow zone in the southeastern Silesian and Dukla Units (Bieszczady and Bystre Subunit areas) may be linked to significant tectonic uplift or a deep-seated heat source, potentially of magmatic origin. This analysis demonstrates that understanding present-day thermal gradient irregularities can effectively highlight regions of elevated paleotemperatures, indicative of mature source rocks. The presented integration of diverse methods offers a powerful approach for enhanced source rock maturity assessment, benefiting the Carpathian petroleum industry.</p>\u0000 </div>","PeriodicalId":16748,"journal":{"name":"Journal of Petroleum Geology","volume":"49 1","pages":"229-249"},"PeriodicalIF":1.7,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145969887","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Microbial Gas Production Potential of Source Rocks in the Outer Carpathian Mountains (Poland)","authors":"Andrzej Borkowski,&nbsp;Anna Filipek,&nbsp;Anna Wysocka","doi":"10.1111/jpg.70010","DOIUrl":"https://doi.org/10.1111/jpg.70010","url":null,"abstract":"<div>\u0000 \u0000 <p>This study investigated the microbiological susceptibility of rocks from the Outer Carpathians. We hypothesized that source rocks differ significantly in their ability to be colonized by microorganisms, which in turn may affect the potential use of unconventional techniques for microbial enhancement of gas recovery. To test this, we combined geochemical analyses with the isolation of a hydrocarbon-degrading microbial community and respirometric experiments, in which gas production from rock samples was monitored using an automated system. The results showed that, despite their high hydrocarbon generation potential, rocks of the Menilite Formation may not support microbial activity. In contrast, samples from the Krosno Formation, Upper Istebna Sandstones and Spas-Veřovice Shales displayed much more favourable microbiological properties. The key factors influencing microbial activity in the tested rocks were porosity, total organic carbon and the contents of quartz, aluminosilicates and carbonates.</p>\u0000 </div>","PeriodicalId":16748,"journal":{"name":"Journal of Petroleum Geology","volume":"49 1","pages":"215-228"},"PeriodicalIF":1.7,"publicationDate":"2025-09-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145970109","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Modeling the Influence of Mud Rheology on Drill Bit Behavior in Algerian Borehole: A Numerical Study Using CFD Approach","authors":"Abdellah Mekedeme,&nbsp;Samir Benammar,&nbsp;Haroun Ragueb,&nbsp;Belkacem Manser,&nbsp;Kong Fah Tee","doi":"10.1111/jpg.70011","DOIUrl":"https://doi.org/10.1111/jpg.70011","url":null,"abstract":"<div>\u0000 \u0000 <p>The drill bit is a crucial device in oil companies, and it is quite expensive. Therefore, studying its mechanical behavior is essential for preserving this device and reducing its maintenance costs. The drilling mud is among the practical things that influence the bit's performance during the drilling operation. This article presents a numerical study of mud rheology in Algerian oil and gas wells using computational fluid dynamics (CFD) analysis. This study aims to optimize the rheological and dynamic properties around the polycrystalline diamond compact (PDC) drill bit of 244 mm diameter in the Algerian borehole. The drilling mud used is a mixture of water, 0.15% of hydroxyethyl cellulose (HEC), and an Algerian bentonite base. The Herschel–Bulkley model has been used to characterize the rheological behavior of this drilling mud because it is a non-Newtonian fluid. The three-dimensional (3D) model of the PDC drill bit was meticulously designed using SolidWorks (version 24, 2016). Additionally, the dynamic behavior of the PDC drill bit in the presence of drilling mud was modeled and simulated using ANSYS Fluent software (version 19.0, 2018). The results indicate that although mud density has minimal impact on annular velocity, it significantly affects the pressure drop across the drill bit. In contrast, the drill bit's rotational speed directly influences annular velocity, which plays a critical role in mitigating stick–slip phenomena. This mitigation is achieved through the enhancement of cuttings transport from the bottom hole to the surface, thereby preventing accumulation around the drill bit, a primary contributor to stick–slip vibrations. These findings support previous studies that have established the influence of mud density on pressure drop and the critical role of rotational speed in mitigating stick–slip phenomena. The numerical results for fluid parameters at the nozzle, obtained using ANSYS Fluent, were validated against established oilfield empirical correlations, demonstrating satisfactory agreement.</p>\u0000 </div>","PeriodicalId":16748,"journal":{"name":"Journal of Petroleum Geology","volume":"49 1","pages":"82-96"},"PeriodicalIF":1.7,"publicationDate":"2025-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145983875","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Textural and Compositional Controls on Reservoir Quality of the Cretaceous Caballos Formation in the Putumayo Basin, Colombia","authors":"Edison Joan Duarte Gomez,&nbsp;Agustín Cardona Molina,&nbsp;Sergio Hernando Lopera Castro","doi":"10.1111/jpg.70009","DOIUrl":"https://doi.org/10.1111/jpg.70009","url":null,"abstract":"&lt;div&gt;\u0000 \u0000 &lt;p&gt;The evaluation of geological attributes such as mineralogical composition, sedimentary texture, diagenetic processes, and petrophysical properties is crucial for understanding the storage, flow, and recovery potential in hydrocarbon reservoir rocks. This study focuses on the Cretaceous Caballos Formation in the Putumayo Basin, a foreland basin that borders the intramontane Upper Magdalena Valley basin to the west and the Llanos Orientales basin to the northeast. The main objective is to determine how compositional, textural, and diagenetic characteristics influence petrophysical properties, specifically porosity, permeability, and capillarity. Surface exposures of clastic rocks associated with this formation were analyzed at the asymmetric and faulted Santa Ana anticline, near the Costayaco field. Core samples were collected, and thin sections were prepared for detailed sedimentological analysis, focusing on mineral composition, grain size, sorting, roundness, and sphericity. Additional analyses investigated compaction processes, pseudomatrix formation, dissolution, and cementation by silica, carbonates, and iron oxides. Subsequently, petrophysical tests were performed on both the lower and upper segments of the formation. Variations in porosity and permeability were correlated with geological attributes through statistical analysis using the Pearson correlation coefficient, quantifying the relationships between textural characteristics (grain size, shape, and sorting) and petrophysical properties. The results indicated a significant positive correlation between porosity and permeability in both segments, at the individual sample level and within the regional context supported by well data. Additionally, a relationship between pore throat size and grain size significantly influencing permeability was observed. Diagenetic and compositional analysis revealed that the presence of clay matrix and pseudomatrix, resulting from sedimentary lithic deformation and glauconite alteration, negatively impacted pore space connectivity, thus reducing reservoir quality. Furthermore, a progressive quartz enrichment from the lower to upper segments was identified, suggesting greater compositional maturity attributed to tropical humid conditions during the Albian–Aptian. This enrichment facilitated the preservation of petrophysical properties in specific petrofacies, enhancing hydrocarbon storage and flow potential. Recognizing surface analogues, as addressed in the introduction, becomes essential due to the frequent lack of detailed subsurface information. Surface analog studies provide valuable insights into reservoir characteristics and diagenetic processes, thereby significantly improving the certainty and reliability of subsurface reservoir models used in hydrocarbon exploration and production. Ultimately, integrating surface analogues into geological modeling contributes substantially to reducing uncertainties and optimizing explor","PeriodicalId":16748,"journal":{"name":"Journal of Petroleum Geology","volume":"49 1","pages":"56-81"},"PeriodicalIF":1.7,"publicationDate":"2025-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145993856","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Palynofacies Analysis Illustrates the Source Rock Potential of the Menilite Beds, Polish Outer Carpathians","authors":"Filipek Anna,&nbsp;Barski Marcin,&nbsp;Wysocka Anna,&nbsp;Jankowski Leszek","doi":"10.1111/jpg.70005","DOIUrl":"https://doi.org/10.1111/jpg.70005","url":null,"abstract":"<div>\u0000 \u0000 <p>The deposition of the Menilite Beds began during the reorganization of the sea ways and the extensional stage of the Carpathian Basin evolution in the early Oligocene. The beginning of their sedimentation is considered to be isochronous throughout the entire marine basin, which formed a part of the Paratethys and was likely isolated from the global ocean due to tectonic movements. However, the changes in the Carpathian region were likely also influenced by processes associated with the Eocene–Oligocene Transition. The present study focuses on the investigation of the Menilite Beds from two Outer Carpathians (OC) main tectonic units: the Skole (Krościenko section) and Silesian (Korzenna section), using a coupled palynofacies, Rock-Eval pyrolysis, and sedimentological framework. This approach permitted the observation of lateral variations in lithology, sedimentary structures, and palynofacies, recording the changes that took place in the early Oligocene, during the deposition of the Menilite Beds, in regions that are currently separated by great distances. In both sections, the palynofacies of the Menilite Beds are predominantly composed of amorphous organic matter (AOM), suggesting that the Menilite Beds were deposited under strongly oxygen-depleted conditions. The presence of spherical bacteria and AOM with alveolar structures in the Korzenna section indicates that microbial mats were probably locally present at the sediment–water interface during the deposition of the Menilite Beds. Analyses of microplankton with organic walls indicate that brackish conditions were present during the deposition of the lower Menilite Beds. Identified microplankton notably included <i>Botryococcus</i> sp. (Krościenko, Korzenna), <i>Campenia</i> sp. (Krościenko, Korzenna), <i>Leiosphaeridia</i> sp. (Krościenko, Korzenna), <i>Pterospermella</i> sp. (Krościenko, Korzenna), and <i>Cymatiosphaera</i> sp. (Korzenna). These results indicate that some lower Menilite Beds, which are located directly above the Eocene deposits (Krościenko—Complex II, III, and IV; Korzenna—Complex I, II, IV, VI), contain horizons with palynological compositions favorable to hydrocarbon generation, including <i>Botryococcus</i> sp. and <i>Leiosphaeridia</i> sp., which are characterized by a high ability to synthesize and accumulate hydrocarbon. We demonstrate that the integration of sedimentological, palynofacies, and organic matter analyses under UV light supported by Rock-Eval pyrolysis can facilitate the identification of potential hydrocarbon horizons—characterized by elevated algal abundances—within the differentiated lithostratigraphic profile of the Menilite Beds. The formation of these deposits was influenced by a complex interplay of paleogeographical, paleoclimatic, and tectonic factors.</p>\u0000 </div>","PeriodicalId":16748,"journal":{"name":"Journal of Petroleum Geology","volume":"48 4","pages":"352-391"},"PeriodicalIF":1.7,"publicationDate":"2025-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145013123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Conceptual Model of Hydrocarbon Migration Conduits in the Outer Carpathian Fold-and-Thrust Belt in Poland: An Interplay Among Fractures, Faults and Rock Properties","authors":"Barbara Rybak-Ostrowska,&nbsp;Małgorzata Kozłowska,&nbsp;Michał Wyglądała,&nbsp;Anna Haluch,&nbsp;Joanna Uroda,&nbsp;Mirosław Ludwiniak,&nbsp;Sara Wróblewska-Janc,&nbsp;Marcin Barski,&nbsp;Andrzej Konon","doi":"10.1111/jpg.70006","DOIUrl":"https://doi.org/10.1111/jpg.70006","url":null,"abstract":"<div>\u0000 \u0000 <p>The hydrocarbon migration conduits in the Outer Carpathian fold-and-thrust belt (OCFTB) are related to the dynamic development of the structural framework combined with changes of rock properties during the deformation process. Application of an integrated methodology, including fieldwork coupled with analysis of cores and thin sections as well as geophysical and petrophysical data from eight wells, made it possible to describe the relationships between the structural framework and the porous sandy rocks of the Cretaceous-to-Oligocene succession during the evolution of the OCFTB. The results indicate that the folding and thrusting, along with the associated rock fracturing during sustained horizontal contraction, resulted in the complex structure of the Silesian Nappe (part of the OCFTB). Structural deformation of lithified rocks created a system of conduits for hydrocarbon migration. The presence of bitumen in the thrust fault zones, normal faults and longitudinal joints (L), parallel to the anticline axes, transversal joints (T) and shear joints (D₁ and D₂) indicates permanent hydrocarbon migration through complex conduits formed by the subsequent structural deformation of the Silesian Nappe. The assembled evidence points to the existence of an interconnected system of a structural framework combined with porous carrier beds contributing to the formation of conduits for hydrocarbon migration during the progressive deformation of the OCFTB.</p>\u0000 </div>","PeriodicalId":16748,"journal":{"name":"Journal of Petroleum Geology","volume":"48 4","pages":"325-351"},"PeriodicalIF":1.7,"publicationDate":"2025-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145013240","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Petrophysical Implications From a Microtectonic Evaluation of Villeta Formation Cores in the Putumayo Basin (Colombia)","authors":"Eduardo A. Rossello,&nbsp;Marcos E. Mozetic","doi":"10.1111/jpg.70008","DOIUrl":"https://doi.org/10.1111/jpg.70008","url":null,"abstract":"<div>\u0000 \u0000 <p>The HC-producing Putumayo Basin is located in Southwestern Colombia, forming the northern part of the Ecuadorian Oriente Basin. Traditional reservoirs are sandstones of the Caballos Fm. (Aptian–Albian) and also the ‘U and M2 Sandstones’ of the Villeta Fm. (Late Albian–Maastrichtian). To provide a frame for our observations, a review of the main tectosedimentary aspects and petroleum systems considered in the literature was carried out. To evaluate the potential of the carbonate layers as reservoirs, in addition to the traditional ones, a microtectonic study was carried out on some available carbonate-bearing cores from wells drilled in the Villeta Fm. Although not properly oriented in space when acquired, when available, dipmeter logs have contributed to the approximate 3D positioning of these cores. The recognized microstructures belong to two main tectonic events progressively superimposed in time from Upper Cretaceous to Recent and in space from West to East: (i) early features due to vertical compaction by overburden following deposition that develop gently deformed stratification and lamination surfaces around more competent objects generated by differential compaction, steep-angle normal faulting in competent levels with slickensides, subhorizontal stylolites and subvertical calcite veins with cuneiform patterns; (ii) later features due to ENE–WSW subhorizontal convergence by the action of the post-Eocene Andean convergence producing dextral transpressional reactivations on the pre-existing N–S normal faulting. The early compaction is usually associated with the onset of HC maturation and subsequent migration towards contemporaneous potential traps. The carbonate veins confirm that dissolution and precipitation processes have decreased the primary porosity and permeability of the reservoirs by calcareous cementation, especially in the deeper parts of the basin. If the Villeta Fm. is to be considered a potential unconventional or tight reservoir, the more efficient direction for future drilling is subhorizontal NNW–SSE. These studies on available cores are only complementary to the usual, more thorough and expensive methodologies of petrophysical reservoir analysis and mainly aspire to extract additional information considering the high costs of obtaining them.</p>\u0000 </div>","PeriodicalId":16748,"journal":{"name":"Journal of Petroleum Geology","volume":"49 1","pages":"40-55"},"PeriodicalIF":1.7,"publicationDate":"2025-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145970224","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"New Insights Into the Geochemical Characteristics of Petroleum Source Rocks and Oils From Southern Nigerian Sedimentary Basins","authors":"Abdulkareem Toyin,&nbsp;Falilat Omotolani Idris,&nbsp;N'Guessan Francois De Sales Konan,&nbsp;Olabisi Adekeye","doi":"10.1111/jpg.70007","DOIUrl":"https://doi.org/10.1111/jpg.70007","url":null,"abstract":"<div>\u0000 \u0000 <p>The Anambra and the Niger Delta Basins are well-known hydrocarbon-producing sedimentary basins in Southern Nigeria. In the present research, bulk geochemical analysis, which includes total organic carbon (TOC) and rock pyrolysis, molecular markers, and bulk and compound-specific carbon isotopes (CSIAs), in addition to organic petrological analysis was carried out on source rocks of Cretaceous age from the Anambra Basin and oils (both Anambra and Niger Delta Basins) in order to provide information on why there was a sudden seizure in liquid hydrocarbon production in the ANAR oilfield of the Anambra Basin and also to shed more light on the unending debate on the source of Cretaceous Niger Delta oils. From the results, bulk geochemical data and maceral abundances revealed that Nkporo shales from well-x and outcrop Mamu shales are dominantly of Types II and III organic matters and are capable of producing oil and gas upon attaining appropriate thermal maturity, whereas outcrop Mamu coals are of Types II and II/III organic matter, with good potential for oil generation but with minor gas, especially in the deeper section of the basin. Organic matter richness as deduced from TOC revealed that the Mamu coals are the richest (average TOC: 50.74 wt%), whereas Mamu shales are richer (average TOC: 2.89 wt%) than Nkporo shales (average TOC: 1.66 wt%). The hydrocarbon generative potentials of the analyzed source rocks as obtained through the hydrogen index are highest in the Mamu coals (average: 329.25 mg HC/g TOC), and are followed by Mamu shales (average: 130.89 mg HC/g TOC), whereas the least was obtained in Nkporo shales (average: 69.73 mg HC/g TOC). The maximum temperature (<i>T</i>_max) and the vitrinite/huminite reflectance values of the source rocks are 396–443°C, 417–430°C, and 417–421°C, and 0.38%–1.51%, 0.23%–0.42%, and 0.22%–0.46% in Nkporo shales, Mamu shales, and coals, respectively. The values revealed that Nkporo shales are in immature to early–late hydrocarbon generation stages, whereas Mamu shales and coals are dominantly thermally immature. Further, the analyzed source rocks were deposited under sub-oxic-to-oxic conditions based on molecular indices and petrographic evidence. In the Nkporo shales, there was dominant input from lacustrine organic matter, as evident from the high abundance of C₂₈R sterane, higher C₂₁TT, and <i>n</i>-alkane maxima at <i>n</i>-C₂₀ and <i>n</i>-C₂₃. In contrast, the Mamu shales and coals and crude oil from the Anambra Basin received major input from terrigenous organic matter (high C₂₉ R sterane, C₂₉/C₂₇ ratios, wax index, terrigenous/aquatic ratio (TAR), C₁₉ + ₂₀TT, and <i>n</i>-alkane maxima at <i>n</i>-C₂₇–<i>n</i>-C₂₉). The oils (crude oils and condensates) from the Niger Delta are dominated by C₂₉ R steranes, whereas C₂₇ and C<su","PeriodicalId":16748,"journal":{"name":"Journal of Petroleum Geology","volume":"48 4","pages":"280-306"},"PeriodicalIF":1.7,"publicationDate":"2025-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145012789","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}