Gas Prospects Research Articles

Geological Structure Analysis of Satellit Gravity Data in Oil and Gas Prospect Area of West Aceh-Indonesia

Estimation of the subsurface geological structures in oil and gas prospect area of West Aceh has been done by utilizing gravity field anomaly of satellite gravity data. This research aim to analyze satellite gravity data in order to get geological features which is include deep and shallow structure or fault around oil and gas prospect area in West Aceh. The satellite gravity data is originally provided as Free Air Anomaly and should be corrected to get Complete Bouguer Anomaly (CBA). Furthermore, CBA was transformed into a horizontal plane and corrected from regional anomalous effects to obtain residual anomaly, horizontal and vertical derivative. From CBA, the gravity anomaly show good correlation with geological boundaries on different rock formation and the anomaly is decrease from NE-SW. Residual anomaly also gives same information with CBA but this anomaly focus on shallow structure. Furthermore, horizontal derivative and vertical derivative also show good correlation with geological structure or fault but in some areas the anomaly related with deep structure cannot be seen on the surface or geological map. Despite the result cannot correlate directly with oil and gas prospect area, satellite gravity can be used to identify gravity anomaly and also fault that related with hydrocarbon anomaly area

Модель геологического строения нижнемеловых и юрских отложений акватории Обской губы Карского моря в связи с перспективами нефтегазоносности

Модель геологического строения нижнемеловых и юрских отложений акватории Обской губы Карского моря в связи с перспективами нефтегазоносности

Перспективы использования газомоторного топлива

Перспективы использования газомоторного топлива

Thermal history of Lower Palaeozoic rocks from the East European Platform margin of Poland based on K-Ar age dating and illite-smectite palaeothermometry

Large-scale shale gas prospecting in the Polish part of the East European Platform did not discover large reserves of this resources. The article presents new research indicating that one of the reasons for the lack of shale gas relates to the thermal history of the Lower Palaeozoic rocks. Illite-smectite palaeothermometry was used to reconstruct the history of the platform and determine the maximum temperatures to which these rocks were subjected. The age of illitisation was also constrained using the K-Ar method. This method allowed precise dating of the maximum age of thermal transformations due to the deposition of numerous pyroclastic horizons (K-bentonite) throughout the entire geological profile from the Cambrian to the Silurian. Isotopic dating was made on over 53 samples of Lower Palaeozoic bentonites and low-grade metamorphic clays. These results were supplemented by analysis of the degree of thermal (smectite to illite) transformation in the profiles of 37 deep boreholes. 11 zones could be distinguished with different tectonic histories within the Polish part of the East European Platform edge. Maximum heating occurred in this region at about 320–340 Ma, corresponding to the Early Carboniferous or the turn of the Early and Late Carboniferous, phase A of the Variscan orogeny, known as the Sudetian phase. In the southern part of study area, the maximum of thermodiagenesis is slightly younger – 270–290 Ma, which responds to the Early Permian, the Asturian phase, the last phase of the Variscan orogeny. This means that the generation of hydrocarbons occurred before significant Mesozoic exhumation of the Polish part of the East European Platform, which led to the escape of a considerable amount of the gas generated. The study also presents the results of an interlaboratory comparison of illite age dating using the K-Ar and Ar-Ar methods. The comparison was conducted to find out what realistic error should be considered when interpreting geological K-Ar dating results.

Geoelectric studies of the oil and gas bearing area on the southern slope of the central Dnieper-Donets Basin part

In 2017 modern synchronous magnetotelluric and magnetovariational investigations were carried out on the Nesseno-Irzhuets—Abramovka profiles in eleven points for the study of the deep structure of the central part of the southern Dnipro-Donets Basin (DDB) board, where the Kirovograd electrical conduction anomaly crosses the Lokhvytsky and Poltava blocks of the DDB. The processing of experimental materials was carried out using known programs PRC_MTMV and PTS. Reliable estimates of the types for periods of geomagnetic variations from 30 to 3700 s and parameters of apparent electrical resistance (amplitude values and phase of impedance) from 40 to 10 000 s are obtained. A joint analysis of complex types and curves of apparent electrical resistance and impedance phases indicates the presence of a surface conductor. Which extends from northwest to southeast and associated with superficial conductivity of the sedimentary strata of the DDB. Also spatially detailed heterogeneity, which is assumed in deep horizons with an upper edge of 20—30 km in the middle part of the profile and corresponds to Kirovograd electrical conduction anomaly. The qualitative interpretation of experimental MT/MV data allows us to clarify the perspective on the oil and gas bearing area in the area of the southern side, which outlines the central part of the DDB between the settlements of Khorol and Reshetilivka. In addition, confirm and detail previously allocated oil and gas prospecting sites, namely Glydinintsiv, with which the anomaly is connected in its southeastern part and extend to the southeast by 20 km. Information about the existence of a deep conductor and its parameters should be the basis for quantitative interpretation and construction of 3D deep geoelectric model.

The history of the Scientific Center for Aerospace Research of the Earth of the Institute of Geological Sciences of the National Academy of Sciences of Ukraine. Earth remote sensing development in the Kyiv department of the Institute of Geology and Fossil

The analysis of the development of methods for remote sensing of the Earth in the oil and gas prospecting industry in the period from 1979 to 1992 in the Kiev Department of the Institute of Geology and Fossil Fuels Development of the USSR Ministry of Petroleum Industry and the USSR Academy of Sciences (KD IG FFD) is presented. The structure and main scientific and methodological problems that were solved by the team of specialists of the KD IG FFD are given. The main scientific and methodological results of the Kiev department are presented: maps, methodological recommendations, successful results of forecasting oil and gas prospecting structures on the territory of Ukraine and oil and gas provinces of the former USSR. The leading role of KD IG FFD in the training of specialists in the use of aerospace methods in the study of oil and gas bearing regions and, in general, nature management is emphasized.

Shale facies from the Wufeng-Lower Longmaxi Formations in the Huangying section of Wulong County, southeastern Sichuan Basin, China

With the increasing interest on shale oil and shale gas around the world, it is essential to discover alternative economic shale gas fields outside the Fuling gas field, which is China’s first large-scale shale gas field with 100 billion cubic meters of reserves in the Sichuan Basin (China). Based on comprehensive analysis of dozens of black shale samples, the Wufeng Formation and the Lower Longmaxi Formation in the Huangying section of Wulong County showed good prospects for shale gas. An integrated study of petrology, organic geochemistry, trace element analysis, and sedimentology reveals that the sea level during the Early Silurian period was relatively high. Consequently, carbon-rich and high-silica lithofacies were deposited, corresponding to argillaceous-siliceous deepwater shelf microfacies. During deposition of the Guanyinqiao bed (latest Ordovician), the sea level was relatively low, resulting in the formation of moderately high carbon and high-silica shale facies, corresponding to argillaceous shallow shelf microfacies. A complete transgressive-regressive third-order sequence was recorded in the Longmaxi Formation. Carbon-rich and high-silica lithofacies, which are associated with carbonaceous deepwater shelf microfacies and siliceous-argillaceous deepwater shelf microfacies, respectively, dominated the transgressive system tract. Compared with the Fuling area with a record of high shale gas productivity, the Wufeng Formation and the transgressive system tract of the Longmaxi Formation in the study area demonstrate great potential for shale gas.

Organic geochemical characteristics, mineralogy, petrophysical properties, and shale gas prospects of the Wufeng–Longmaxi shales in Sanquan Town of the Nanchuan District, Chongqing

Thick marine shales occur in the Wufeng Formation and Longmaxi Formation of Sanquan Town of the Nanchuan District, Chongqing Municipality, which is located on the southeast margin of the Sichuan Basin. However, few details of the characteristics of the Wufeng–Longmaxi shales in this area have been reported. In this study, a well approximately 100 m (∼328 ft) deep was drilled. A high-quality shale (total organic carbon [TOC] >2.0 wt. %, clay <40%) interval that was approximately 24 m (∼79 ft) thick with an average TOC value of 3.0 wt. % mainly occurs in the Ordovician Wufeng Formation (Katian and Hirnantian) and base of the Silurian Longmaxi Formation (Rhuddanian). Shales with higher TOC values commonly have a higher porosity and specific surface area. Tectonic movements may also have been very important factors that influenced the petrophysical properties of the shales. For example, a detachment layer that resulted from complex tectonic movements is extensive in the Wufeng Formation. The cracks and microcracks in the detachment layer can result in good pore connectivity. Consequently, the detachment layer can be an effective migration pathway. The Longmaxi–Wufeng shales of Sanquan Town are also compared with those of the famous Jiaoye 1 well in the Jiaoshiba shale gas field in the eastern Sichuan Basin. Although the shales in Sanquan Town have considerable shale gas generation potential, the shale gas resource potential in Sanquan Town is probably poor because the escape of shale gas may be accelerated by the detachment layer in destroyed anticlines and synclines.

Geochemical, geological, and petrophysical evaluation of Garau Formation in Lurestan basin (west of Iran) as a shale gas prospect

The Garau Formation in western Iran is a potential shale gas play. To evaluate its gas potential, a geochemical, geological, and petrophysical study was conducted on samples from the Baba Ghir 1 well drilled in Lurestan District (W Iran). Organic matter analysis of Garau Formation shows that total organic carbon (TOC) ranges between 0.42 and 2.43 wt% and this formation possesses kerogen type III with a high degree of maturity, reflecting gas window conditions. Mineralogical analyses show that the lithology of Garau Formation in this well is carbonate-dominated and the clay mineral content is less than 4%, and displays several characteristics that are similar to the Eagle Ford shale. Based on the relationship among quartz, carbonate, and clay minerals, the brittleness index is about 25%, a value of importance to select the best stimulation fluid. Petrophysical evaluation shows a porosity of about 5–15%. Estimation of the amount of free gas reserves possesses a good correlation with the reserves that were estimated based on petrophysical interpretation. Because of absence of underground contour maps, calculation of adsorbed gas volumes was not possible but estimates of gas storage capacity (GC) shows an increase with depth. All data indicate that the Garau Formation can be considered as a promising gas shale play.

Crab! How a dispute over snow crab became a diplomatic headache between Norway and the EU

Norway and the European Union (EU) are closely interlinked. However, one issue has arisen where interests have clashed: snow crab. A newcomer to Norwegian Arctic waters, this resource has attracted attention as projections of future profit have soared. Why is the EU pursuing a relatively minor issue over the right to catch snow crab in the Barents Sea? This issue has also brought to the fore the underlying disagreement between Norway and the EU over the status of the maritime zone and related continental shelf around the archipelago of Svalbard, stemming from the 1920 Spitsbergen Treaty. Is the EU using the snow-crab issue to challenge Norway’s Svalbard regime? How are EUropean interests in this resource best understood? At stake are also the prospects of oil and gas, as well as Arctic governance and environmental protection. The EU is a multi-faceted creature, where special interests can hijack the machinery and bring issues to the table, depending on the circumstances. This article outlines these circumstances, as well as the process concerning the dispute over snow crab and the background, which relates to economic interests, but also international politics as well as law. Further, it examines the EU’s interests, drawing on scholarly work on the EU’s position on Svalbard and interviews with Brussels-based decision-makers, officials and politicians.

Comments: The Golden Age of Gas Revisited

Editor's column Seven years ago, the International Energy Agency (IEA) issued a report on the prospects of natural gas titled, Are We Entering the Golden Age of Gas? The answer appears to be not yet, but the growth in supply and trade, and moves to de-link the price of gas from the price of oil could propel the cleanest-burning hydrocarbon forward as the fuel to the future. Gas supplies are plentiful and exports are surging. Most of this is due to the growth of shale in the US, which has led the country to become a major exporter of liquefied natural gas (LNG) along with Australia. Just as the US shale revolution disrupted the global oil market, it is reshaping the world’s gas trade. The US produced 71.1 Bcf/d of gas in 2017, a 1% increase over the previous year and near its all-time high. US output is now 20% of global production. Russia, the world’s second-largest gas producer, reached output of 61.5 Bcf/d last year. US gas exports, in the form of LNG and mostly to Asia, were 1.7 Bcf/d in 2017, while pipeline exports totaled 6.3 Bcf/d, mostly to Mexico. What has hampered the international growth of gas in the past is its lack of tradability and its relation to a global price marker. Gas has long been linked to oil prices—which have shown sharp volatility the past decade—and tied to long-term contracts, both of which contain risks for both buyers and sellers. But the increase of LNG exports has opened the door to more international trade and discussion of establishing global price markers. Companies are increasingly using US Henry Hub prices as a reference point for international gas trade. And CME Group and Cheniere Energy are developing an LNG futures contract linked to physical delivery at Cheniere’s Sabine Pass, Texas terminal. Before now, gas has been traded regionally or through long-term contracts based on the price of oil. US gas was priced off Henry Hub but trade in Europe used a regional trading hub and Asia, one of the largest importers of gas, preferred contracts linked to crude. De-linking the price of gas from oil would protect buyers and sellers from price movements in oil that do not reflect gas market fundamentals. That stability could give rise to more investment in gas production and infrastructure. Gas proponents argue that gas should be the bridge to the future, as the world transitions from one based heavily on oil to a global energy mix that includes more alternative energy sources. China is relying more on gas as it weans itself from heavy coal use. Major gas producing countries—including Iraq, Russia, Qatar, and Venezuela—have discussed forming a gas-type OPEC organization to create market stability. This Gas Exporting Countries Forum’s goal is to increase the share of gas in the global energy supply. These producers so far appear reluctant to embrace the free-market approach that growth in LNG is bringing about. But, as the IEA recently pointed out, half of the global consumption increase in gas in the medium term will come from emerging economies in Asia. And they stand to benefit most from market-based natural gas pricing.

Boost for Kurdish gas prospects

Oil and Energy TrendsVolume 43, Issue 9 p. 8-9 GAS AND POWER Boost for Kurdish gas prospects First published: 27 September 2018 https://doi.org/10.1111/oet.12616Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume43, Issue9September 2018Pages 8-9 RelatedInformation

Cenozoic stage of development of local structures of the Lower Kura Depression and Baku Archipelago related to their oil and gas prospectivity

The South Caspian Basin (SCB), including the Lower Kura Depression (LKD), was one of the deep‐sea basins of Tethys before the Late Palaeogene. During the Late Palaeogene, due to the convergence of the Iranian‐Afghan and Anatolian plates with the Eurasian Plate, the SCB was transformed into a marginal sea. By the end of the Miocene, the Arabian Plate converged between Anatolian and Irano‐Afghan, which contributed to fold deformations of north‐eastern orientation in the north‐western part of the Iranian‐Afghan Plate. It led to the development of the western side of SCB and drainage of Kura Depression; since then, the LKD became a western onshore continuation of SCB. A compressive stress regime, established there since the end of the Miocene, directly influenced the structures development process in LKD and Baku Archipelago (BA). Although LKD is located onshore and its eastern edge belongs to SCB west board, together with BA they form a single structural and tectonic zone, which is evidenced by the evolution, spatial orientation of local structures and anticlinal zones. To establish the correlation of the evolution features of LKD and BA, we performed the palaeoanalysis on the basis of reconstructed palaeoprofiles for several LKD and BA structures. From palaeoprofiles, we constructed diagrams of fold growth intensity. The results of the correlation of these diagrams indicate at the consedimentational and continuous character of the development of structures in both zones (except for the buried structures) but featuring different intensity at different intervals of geological time. During the formation time of the Lower Production Series (LPS), both zones were characterized by a relatively rapid growth of the folds. At the time of formation of the Upper Production Series (UPS), Absheron‐Aghjagil structures growth intensity was roughly the same but lower than that of LPS. The most intense growth of folds in both zones occurred in Quaternary time.

Palynofacies, Organic Thermal Maturation and Source Rock Evaluation of Nanka and Ogwashi Formations in Updip Niger Delta Basin, Southeastern Nigeria

ABSTRACT The oil and gas prospects in the Nigerian inland basins necessitated the palynofacies characterization, thermal maturation and source rock evaluation of the Nanka and Ogwashi formations of the Niger delta basin. The Nanka Formation has dominant terrestrial microflora, brown structured phytoclasts and amorphous organic matter, opaque debris accompanied by dinoflagellate cysts. The Ogwashi Formation has maximum terrestrial microflora, medium to large brown structured phytoclasts, opaque debris with abundance of dark brown amorphous organic matter and a few marine taxa. Palynofacies constituents of the Nanka Formation reflect Kerogen Type II / III which are Gas / Oil prone shown by abundance of marine species, amorphous organic matter in conjunction with terrestrial phytoclasts and non-marine palynomorphs assemblage. The spore/pollen colour range from light brown to dark brown which suggest oil generation to production of wet gas. This corresponds to thermal alteration index (TAI) 2+ to 3+ and vitrinite reflectance index (%Ro) 0.5% to 1.3%. Palynofacies of the Ogwashi Formation has Kerogen Type III (gas prone) linked with overwhelming abundant terrestrial phytoclasts palynomorphs and large amorphous organic matter of terrestrial origin. Spore/pollen thermal alteration colour ranges from light medium brown to dark brown indicative of mature oil generation and transition to dry gas phase. The thermal alteration index and vitrinite reflectance index (%Ro) values of the Ogwashi Formation is consistent with that of the Nanka Formation.

Geological and Geochemical Characteristics and Exploration Prospect of Coal‐Derived Tight Sandstone Gas in China: Case Study of the Ordos, Sichuan, and Tarim Basins

AbstractThis work extensively investigated global tight sandstone gas, and geologically and geochemically analyzed the tight sandstone gas in China's Ordos, Sichuan, and Tarim basins. We compared typical tight sandstone gas in China with that in North America. We proposed six conditions for the formation of China's tight sandstone gas, and illustrated the geological characteristics of tight sandstone gas. In China, gas‐bearing tight sandstones were mainly deposited in continental lake deltas and marine‐terrigenous facies basin environments, associated with coal‐measure strata, and were mostly buried deeper than 2000 m under a formation pressure of 20–30 MPa, with pressure coefficients varying from overpressure to negative pressure. In other countries, tight gas bearing sandstones were dominantly deposited in marine to marine‐terrigenous facies environments, occurred in coal‐measure strata, and were mostly buried shallower than 2000 m in low‐pressure systems. We systematically analyzed tight sandstone gas in the Ordos, Sichuan, and Tarim basins in terms of chemical compositions, geochemical characteristics of carbon isotopes, origins, and sources. Tight sandstone gas in China usually has a hydrocarbon content of &gt;95%, with CH41 content &gt;90%, and a generally higher dry coefficient. In the three above‐mentioned large tight sandstone gas regions, δ13C1 and δ13C2 mainly ranges from –42‰ to –28‰ and from –28‰ to –21‰, respectively. Type III coal‐measure source rocks that closely coexist with tight reservoirs are developed extensively in these gas regions. The organic petrology of source rocks and the carbon isotope compositions of gas indicate that tight sandstone gas in China is dominantly coal‐derived gas generated by coal‐measure strata. Our analysis of carbon isotope series shows that local isotope reversals are mainly caused by the mixing of gases of different maturities and that were generated at different stages. With increasing maturity, the reversal tendency becomes more apparent. Moreover, natural gas with medium‐low maturity (e.g., Xujiahe Formation natural gas in the Sichuan Basin) presents an apparent reversal at a low‐maturity stage, a normal series at a medium ‐maturity stage, and a reversal tendency again at a high‐maturity stage. Finally, we proposed four conditions for preferred tight sandstone gas “sweep spots,” and illustrated the recoverable reserves, proven reserves, production, and exploration prospects of tight sandstone gas. The geological and geochemical characteristics, origins, sources, and exploration potential of tight sandstone gas in China from our research will be instructive for the future evaluation, prediction, and exploration of tight sandstone gas in China and abroad.

Generation, migration, entrapment and leakage of microbial gas in the Dutch part of the Southern North Sea Delta

Understanding the shallow gas system is critical for assessing its potential as an energy source, for evaluating the possible hazard of shallow gas for drilling and wind farm locations and for evaluating the effect of gas emissions at the seabed on marine ecosystems and climate. This paper presents the key elements and processes of the microbial shallow gas system in the Plio-Pleistocene Dutch Southern North Sea Delta based on recent findings from different projects. Geochemical and carbon isotopic composition of shallow gas occurrences in the delta are indicative of a microbial origin of the gas. Shallow gas mainly occurs in stratigraphic traps and stacked anticlinal structures above salt structures, as indicated by identified direct hydrocarbon indicators on seismic, such as bright spots. Organic matter in the delta deposits is of predominantly land plant origin with TOC values varying between <1% and 5%, and mostly between 1 and 2%. Simulations of temperature and burial history in combination with dedicated 1D simulations of microbial gas generation reveal that gas generation in the delta started in Early Pleistocene Calabrian times and is still ongoing. Simulated volumes of gas generation are more than enough to fill published estimated volumes of shallow gas prospects in the delta. The geometry of the E-W prograding delta sequences and the close interbedding of interglacial silty/sandy and glacial clayey/silty sediments focus gas migration updip through the foresets towards the topsets of the delta sequences, and ultimately into the anticlinal stacked traps. Grain-size based calculations of the permeability and capillary seal capacity of clayey/silty seals of the stratigraphic and anticlinal traps provided first estimates of permeability values ranging from 2.8E-20 m2 to 1.1E-18 m2 and capillary seal capacity values between 10m and 24m. Comparison of gas column heights derived from grain-size based calculations, cross plots of neutron and density logs and pressure measurements, with trap heights derived from seismic bright spots suggests that many traps in stacked bright spots are not filled to structural spill point. This suggests that filling of the stacked reservoirs is not related to fill-spill migration, but rather to leakage through the top seal. In absence of fault and fracture zones crossing the seal, this leakage is related to the capillary seal capacity and permeability of the top seal. The leakage extends, locally, to the seabed. The microbial gas system in the delta today is a highly dynamic system driven by ongoing burial of the delta sediments and microbial gas generation. © 2018

Unconventional trade-offs? National oil companies, foreign investment and oil and gas development in Argentina and Brazil

These are turbulent and uncertain times for the global oil and gas industry. This paper examines the industry's emerging new political economy in terms of competition (or a trade-off) both between and within International Oil Companies (IOCs) for rival oil and gas prospects. A qualitative cross-case analysis of Argentinian shale and Brazilian deep-water finds that unconventional and deep-water projects are complementary rather than competing assets of an IOC's portfolio. Further, despite the technical challenges IOCs face in developing these reserves, it is the non-technical risks and uncertainties that are more pressing for these companies and are the greater inhibitors to investment.

Theory, technology and prospects of conventional and unconventional natural gas

Abstract The development of natural gas in China has entered a golden and leap-forward stage, which is a necessary bridge to clean energy. This in-depth study on the status quo, theory, technology and prospect of natural gas development shows: (1) The global remaining proven recoverable reserves of natural gas are 186×1012 m3 and the reserves-production ratio is 52.4, indicating a solid resource base for long-term and rapid development. (2) Ten formation and distribution laws of conventional and unconventional natural gas reservoirs have been proposed. In terms of exploration geology, the theory of conventional “monolithic” giant gas fields with different gas sources, and an unconventional gas accumulation theory with continuous distribution of “sweet areas” in different lithologic reservoirs have been established; in terms of development geology, a development theory of conventional structural gas reservoirs is oriented to “controlling water intrusion”, while a development theory of unconventional gas is concentrated on man-made gas reservoirs. (3) With the geological resources (excluding hydrates) of 210×1012 m3 and the total proven rate of the resources less than 2% at present, the natural gas in China will see a constant increase in reserve and production; by 2030, the proven geological reserves of natural gas are expected to reach about (6 000− 7000)×108 m3 the production of conventional and unconventional natural gas each will reach about 1 000×108 m3 and the gas consumption will reach 5500×108 m3. The dependence on imported natural gas may be 64% by 2030, and 70% by 2050. (4) Ten measures for future development of natural gas have been proposed, including strengthening exploration in large-scale resource areas, increasing the development benefits of unconventional gas, and enhancing the peak adjusting capacity of gas storage and scale construction of liquified natural gas.

Sequence subdivision and development characteristics of low-accommodation non-marine basins: a case study of the Yanchang Formation in the Ordos Basin

ABSTRACTThe third-order sequences of the Yanchang Formation in the Ordos Basin were determined by a comprehensive analysis of surface outcrops, core, logging and seismic data. Natural gamma curves were studied by the band-pass method. The hidden stratigraphic sequence and six lithological cycles were extracted. By examining sequence boundaries and lithological cycles, we identified six third-order (including SQ1, SQ2, SQ3, SQ4, SQ5 and SQ6) and three second-order sequences in the Yanchang Formation. The sequence stratigraphy of the Ordos Basin was found to have the following special development characteristics: (1) the third-order sequence growths were totally stable, and the thickness of the Ordos Basin was relatively stable; (2) thick sand bodies did not form in lowstand systems because of underdeveloped slope breaks; (3) the third-order sequences had diverse features at different sedimentary periods; (4) the distribution of the depositional systems had various characteristics in different tectonic belts, and the entire sequence had the filling characteristics of multiprovenances and multicycles. The low-accommodation Ordos Basin in the Upper Triassic was limited by slow subsidence, gentle basement paleorelief, stable tectonic settings and sufficient sediment supply. The characteristics of the basin included stable developed sequences, limited preserved lowstand systems tracts, multiple depocentres and subsiding centres, development of many delta systems in the north and south of the basin controlled by the gradient of the basement paleorelief, and laterally stretching sediments. Results further indicated that the controlling factors of the third-order stratigraphic sequences of Yanchang Formation in the low-accommodation lacustrine Ordos Basin included sediment supply (provenance), climate and lake-level fluctuation. Overall, our case study indicated that the development characteristics and controlling factors of sequence stratigraphy in a low-accommodation lake basin provided a comprehensive method of establishing the sequence stratigraphic framework of a low-accommodation non-marine basin. Our results also predicted that the SQ3, SQ4 and SQ5 of the Qiaochuan and Zhidan areas favoured oil and gas prospecting of the Yanchang Formation.

Gas-condensate potential of the middle-Jurassic petroleum system in Abadan plain, Southwest Iran: Results of 2-D basin modeling

ABSTRACTThe Jurassic petroleum system has been proven as prolific oil and gas prospects in the southwestern of Iran. During this study, 2-D regional modeling was done on two selected sections (north-south and east-west); furthermore, 1-D models were reconstructed on 7 deeply drilled wells in order to evaluate petroleum generation and source rock maturity histories in the Abadan Plain area in southwest Iran. The results revealed that the Middle Jurassic Sargelu Formation with average present-time TOC and HI values of 2.65wt% and 151 mgHC/gTOC, respectively, can be classified as good to excellent type II source rock. The initial TOC and HI values regarded for modeling are 5wt% and 620 mgHC/gTOC, respectively. The geochemical maturity parameters indicate a wet gas window for the Sargelu Formation. The modeling results show that the maximum temperature and vitrinite reflectance in the Sargelu Formation has reached 150 oC and 1.3%VRo. Generation of hydrocarbon in the Sargelu commenced during the Early Cretaceous, while the main expulsion happened in the Paleogene. 2-D models show that the Jurassic source rock has already reached a high transformation ratio within the studied area and, due to lack of intense tectonic activity, the maturity is the same throughout the studied area. Oil and gas migrated mostly vertically to the overlying traps which are existed in the Jurassic and Cretaceous succession. The results predict the existence of gas-condensate in the Jurassic petroleum system of the studied area.