Anticlinal Belt Research Articles

Natural Gas Enrichment Processes and Differential Accumulation Models in the Central Anticline Belt of the Xihu Sag, East China Sea Shelf Basin

Natural Gas Enrichment Processes and Differential Accumulation Models in the Central Anticline Belt of the Xihu Sag, East China Sea Shelf Basin

Differential Enrichment Regulation and Genetic Analysis of Tight Sandstone Gas Reservoir

In the deep Paleogene of graben basins in eastern China, not only the tight sandstone oil and gas resources, but also the secondary hydrocarbon generation of source rocks are universal and worth studying. In order to elucidate the laws of oil and gas accumulations in tight sandstone with different phases and explore the diversity of its genetic mechanism, Shahejie Formation in Wendong area was taken as an example in this paper to carry out further research. Firstly, the differential enrichment rules of oil and gas reservoirs are clarified from the aspects of spatial distribution, phase type and fluid properties. Secondly, the reasons for differential accumulation of oil and gas reservoirs were analyzed from multiple perspectives by using a variety of methods, such as source rock thermal evolution simulation, fault activity evaluation and reservoir porosity evolution. A large number of researches have been carried out on hydrocarbon generation and expulsion process of source rocks, paleo-temperature and paleo-pressure changes, the connectivity of skeleton sand bodies, reservoir physical property and densification process, tectonic strength and so on. The results indicate that the deep tight sandstone reservoirs of the Paleogene in the Wendong area have a quasi-continuous distribution characteristic of "planar partition and longitudinal zoning". Secondary kerogen cracking gas, crude oil cracking gas, medium light crude oil, and primary kerogen cracking gas are distributed in a semi-circular manner, from the center of Qianliyuan Sag to Wendong graben and rollover anticline belt at the high structural position. In conclusion, the two periods of hydrocarbon generation and expulsion of source rocks lead to the discontinuity of hydrocarbon accumulation process. Paleo-temperature and paleo-pressure conditions control the phase types of hydrocarbon filling. The lateral connectivity and the difference of physical properties of the skeleton sand bodies limit the distribution range of oil and gas reservoirs. The temporal and spatial availability of faults during the critical accumulation period determines the differential enrichment of oil and gas. The temporal and spatial validity of faults during the critical accumulation period determines the extent of differential enrichment of oil and gas.

Hydrocarbon accumulation conditions and exploration targets of the Sinian Dengying Formation in the Southeastern Sichuan Basin

No breakthrough has been made in petroleum exploration of the Sinian Dengying Formation in the southeastern Sichuan Basin as the major factors controlling the hydrocarbon accumulation of the Dengying Formation have not been well established, including the development period and distribution of the platform margin, the effectiveness of the source-reservoir combination and the reliability of the Cambrian pre-salt structural trap. Based on the interpretation of seismic data and hydrocarbon-source correlation, the distribution of the platform margin of the Sinian Dengying Formation in the southeastern Sichuan Basin was mapped. Moreover, the gas source rocks of the Dengying Formation were clarified according to geochemical characteristics of fluid inclusions, and the pre-salt structures were further confirmed by seismic forward modeling and experiments of prestack depth migration. Results showed that the sedimentary facies of the 4th member of Dengying Formation in the southeastern Sichuan Basin was platform margin of gentle slope type. The platform margin reservoir of the Dengying Formation and the Lower Cambrian source rocks constitute a favorable source - reservoir combination. The carbon isotope characteristics of gas in fluid inclusions indicate that some of the oil/gas in the Dengying Formation were contributed by the Doushantuo Formation source rocks. As the difference in seismic velocities between carbonate rocks and gypsum/salt beds may cause a reduction in the amplitude of pre-salt structures, the low-amplitude structures identified on current seismic profiles are underestimated instead of overestimated. Accordingly, the Sinian structural traps are confirmed to develop in the deep pre-salt sequences in the low-steep anticline belt, southeastern Sichuan Basin. On the basis of the above new understanding, we propose two types of hydrocarbon migration modes for the Sinian Dengying Formation in southeastern Sichuan Basin, including lateral migration of hydrocarbons generated from the Cambrian Qiongzusi Formation and vertical migration of hydrocarbons derived from the Sinian Doushantuo Formation. Lithologic traps at the platform margin and pre-salt structural traps within the platform are favorable targets for natural gas exploration.

The study of reservoir parameters of subsurface rocks based on the core data of anticline belt of Sangachal-deniz–Bulla-deniz

Alongside the geological-geophysical characteristics of the fields being developed and explored, the calculation of hydrocarbon reserves, the modeling of the fields, as well as the specification and direction of a new exploration are of great importance with regard to the study of their reservoir parameters. With this purpose, the geological-geophysical studies carried out in the anticline belt of Sangachal-deniz–Bulla-deniz, and the data of samples of subsurface rocks from well intervals have been analyzed as well. The changes in reservoir parameters of the rocks of various granulometric content in the anticline zone have been investigated and the graphs of parameters depending on the depth have been developed. The studies justify that the sand and sand deposits keep their reservoir parameters even in comparatively large depths. These characteristics indicate the presence of favorable litofacies and structural-petrographic conditions for the accumulation of oil and gas reserves in deep sections.

Characteristics, origin and controlling effects on hydrocarbon accumulation of overpressure in foreland thrust belt of southern margin of Junggar Basin, NW China

Aiming at the differential distribution of overpressure in vertical and lateral directions in the foreland thrust belt in the southern margin of Junggar Basin, the study on overpressure origin identification and overpressure evolution simulation is carried out. Based on the measured formation pressure, drilling fluid density and well logging data, overpressure origin identification and overpressure evolution simulation techniques are used to analyze the vertical and lateral distribution patterns of overpressure, genetic mechanisms of overpressure in different structural belts and causes of the differential distribution of overpressure, and the controlling effects of overpressure development and evolution on the formation and distribution of oil and gas reservoirs. The research shows that overpressure occurs in multiple formations vertically in the southern Junggar foreland thrust belt, the deeper the formation, the bigger the scale of the overpressure is. Laterally, overpressure is least developed in the mountain front belt, most developed in the fold anticline belt, and relatively developed in the slope belt. The differential distribution of overpressure is mainly controlled by the differences in disequilibrium compaction and tectonic compression strengths of different belts. The vertical overpressure transmission caused by faults connecting the deep overpressured system has an important contribution to the further increase of the overpressure strength in this area. The controlling effect of overpressure development and evolution on hydrocarbon accumulation and distribution shows in the following aspects: When the strong overpressure was formed before reservoir becoming tight overpressure maintains the physical properties of deep reservoirs to some extent, expanding the exploration depth of deep reservoirs; reservoirs below the overpressured mudstone cap rocks of the Paleogene Anjihaihe Formation and Lower Cretaceous Tugulu Group are main sites for oil and gas accumulation; under the background of overall overpressure, both overpressure strength too high or too low are not conducive to hydrocarbon enrichment and preservation, and the pressure coefficient between 1.6 and 2.1 is the best.

Source-to-sink analysis of Mesozoic–Cenozoic sandstone-type uranium deposits in the Qaidam Basin

Accurate evaluation of uranium sources and identification of their spatiotemporal correlations with uranium deposits (or sinks) in sedimentary basins are important for exploring sandstone-type uranium deposits. This study examines the source-to-sink system of Mesozoic–Cenozoic sandstone-type uranium deposits in the Qaidam Basin (QB) through a literature review in conjunction with logging and seismic data and yields the following findings. (1) The uranium-supplying capacity of a source rock in the uranium source area depends on primarily its type and to a lesser extent, the tectonic zone where it is located and the episode during which it formed. (2) The initial uranium content, U0, is the core parameter for classifying and evaluating the uranium-supplying capacity of a source rock. At U0 > 1.5 ppm, uranium begins to migrate from a source rock. The uranium variation coefficient, ΔU, and the amount of uranium migration, ΔUt, decrease continuously to –55 % and –5 ppm respectively as U0 increases up to 9.5 ppm, which suggests that at most 5 ppm of uranium in the source rocks can migrate away. As U0 increases beyond 9.5 ppm, ΔU and ΔUt fluctuate around –55 % and –7 ppm respectively, which suggests that approximately 7 ppm of the uranium in the source rocks can migrate away. (3) Of the different types of rocks, silicic igneous rocks (including both intrusive and volcanic igneous rocks) and granitic gneisses have the highest uranium-supplying capacity; intermediate igneous rocks and gneisses come second; mafic–ultramafic igneous rocks and the other metamorphic rocks (except granitic gneiss and gneiss) come third. Of the sub-source areas (tectonic zones), the western segment of the Eastern Kunlun and the Qiman Tagh have the highest uranium-supplying capacity; the Central and Southern Altyn Tagh come second; the others come third. (4) Uranium sources are the fundamental prerequisite for the formation of uranium sinks. Other geological factors control the specific formation process of uranium sinks as well as their spatiotemporal distribution patterns. For QB, the most economic and prospective uranium sink, Neogene formations of Gy anticline, was fed by the source areas which had the highest uranium-supplying capacity. This suggests that the Neogene of WEK anticline belt, Quaternary of Kumukol Basin and Qarqan River Basin are the most noteworthy metallogenic prospective areas. The uranium-source evaluation scheme and “source-to-sink” ore exploration approach introduced in this study have practical value for advancing the exploration of uranium deposits in sedimentary basins in northern China and other parts of the world.

Quantitative Characterization of Excess Pressure Gradient in the Upper Interval of Es4 Member of Dongying Depression and Its Indicative Significance for Oil Migration and Accumulation

Excess pressure is the main driving force of oil migration in the source-reservoir system of overpressured petroliferous basins. It can reflect the change in driving force for oil migration and its influence on oil accumulation in overpressure transport layers. The drilling stem test (DST) data, well logging data, and seismic velocity data are used to describe the plane distribution of the excess pressures in the Es4s member of the Dongying Depression. Then, the values and directions of the excess pressure gradient, which can indicate oil migration and accumulation, are calculated based on the plane distribution of the excess pressure in the Es4s member of the Dongying Depression. The results suggest that overpressure is widely developed in the Es4s member of the Dongying Depression, and the excess pressure gradually decreases from the center to the edge of each sag, while the variation in the excess pressure gradient is characterized by “low-high-low” in a circular band around the sags. The excess pressure in the sag areas exceeds 15 MPa, but the excess pressure gradient is mainly between 0 and 1 MPa/km. The excess pressure in the northern steep slope zone of the Lijin sag and the northern steep slope zone of the Minfeng sag are less than 15 MPa, while the excess pressure gradient ranges from 1 to 7 MPa/km. The excess pressure in the central anticline belt and the gentle slope belt in the south of the Niuzhuang sag are between 0 and 15 MPa, and the excess pressure gradient is from 0 MPa/km to 2 MPa/km. From geochemical evidence, local oil migration directions indicated by the excess pressure gradient are consistent with those indicated by the ratio parameters of carbazole compounds in crude oil samples, indicating that the direction of the excess pressure gradient can indicate the dominant direction of oil migration driven by excess pressure, and the oil from the Es4s source rock is mainly distributed in the areas with a high excess pressure gradient or the areas with a low excess pressure gradient and low excess pressure (area II).

Oil generation model of the liptinite-rich coals: Palaeogene in the Xihu Sag, East China Sea Shelf Basin

Hydrocarbon generation from liptinite-rich coal is an important focus in petroleum geology as well as in coal geology. The confined pyrolysis experiment in gold tubes is an effective approach in assessing the hydrocarbon generation potential of coals. Xihu Sag is one of the most hydrocarbon-rich Cenozoic basins in the East China Sea Shelf Basin, and oil and gas are believed to be generated from Paleogene liptinite-rich coals. Coals from the Pinghu and Huagang formations of the Paleogene have a liptinite content mostly higher than 10%, and contain type II-III organic matter. The HImax values, H/C, and O/C ratios of these coals are in the range of 200–300 mg/g·TOC, 0.97 to 1.42, and 0.08 to 0.20, respectively. All these characteristics demonstrate good potential for these coals to generate oil. Experimental data show that the maximum cumulative yields of oil produced range from 122.74 to 154.09 mg/g·TOC, and the coals in the sag can also generate oil in their immature stage (Ro = 0.36%–0.5%) due to abundant resinite (mostly higher than 5%). To further assess the characteristics and processes of petroleum generation under geological conditions, we reconstructed the liquid hydrocarbon generation history of the coals in three structural units of Xihu Sag, i.e., the West Slope Belt, West Sub-sag, and Central Anticlinal Belt. For the coals in the Pinghu Formation, the West Slope Belt is a favorable oil-forming area, while the West Sub-sag and the Central Anticlinal Belt are less favorable oil-forming areas. For the coals in the Huagang Formation, the West Slope Belt is a favorable asphaltene (ΣC14+)-forming area, while the West Sub-sag and Central Anticlinal Belt are favorable light hydrocarbon (ΣC6-14)-forming areas. Results of this study will contribute to a better understanding of the characteristics and potential of oil generation from the liptinite-rich coals and are of significance for oil exploration in the Xihu Sag.

Oblique strike-slip superimposed structure in Yingxiong range, western Qaidam basin and its response to Altyn Tagh fault and Eastern Kunlun fault

ABSTRACT The Yingxiong Range is the largest anticlinal belt within the triangular overlapping zone between the Altyn Tagh Fault and the Eastern Kunlun Fault and thus records the critical information concerning the strike-slip superimposition between the two large-scale left-slip faults. The detailed structural analysis on the basis of 3D seismic data shows that the Shizigou (SZG) and Youshashan (YSS) structures in the Yingxiong Range are controlled by NE-dipping low-angle thrust faults at shallow depth and three groups of faults including the NW-striking inverted faults, the WNW-striking XI fault and the N–S-striking Shidong fault zone at deep levels. The inverted faults were right-stepping en-échelon sinistral transtensional normal faults in the Eocene. Fracture analysis on cores of the U. Xiaganchaigou Formation shows the existence of syn-sedimentary normal faults which indicate Eocene extension deformation in the Yingxiong Range. The Eocene transtensional normal faults constituted a half-graben structural system and controlled the formation of the SZG sag. In the early Miocene, the XI fault obliquely superimposed the pre-existing Eocene transtensional normal faults, causing the reactivation of these faults in a reverse sense. Simultaneously, the Shidong fault zone started to develop as a dextral tear fault. The oblique strike-slip superimposition from transtension to transpression in the Yingxiong Range reflects the differential controlling effects of the asynchronous initiation of the Altyn Tagh Fault and the Eastern Kunlun Fault on the structural evolution and oil-gas reservoir development in the western Qaidam Basin.

Late Jurassic Structural Deformation and Late Cenozoic Reactivation of the Southern Junggar Fold-And-Thrust Belt, NW China

Because of the influence of the far field effect of the collision between Euro-Asian and India plates during the Late Cenozoic, the Tian Shan orogenic belt underwent intense reactivation, forming the Southern Junggar fold-and-thrust belt (SJ-FTB) to the north and the Kuqa fold-and-thrust belt to the south. Most previous research focuses on the deformation features and mechanisms during the Late Cenozoic. However, little research has been done on deformation features and mechanisms during the Late Jurassic. In this paper, we conducted geometric and kinematic analyses of seismic profiles and outcrop data to reveal the Late Jurassic deformation characteristics in SJ-FTB. Furthermore, we carried out sandbox modeling experiments to reproduce the regional structural evolution since the Early Jurassic. Angular unconformity between the Cretaceous and Jurassic is well preserved in the Qigu anticline belt. This unconformity also exists in the Huoerguosi–Manasi–Tugulu (HMT) anticline belt, which is the second fold belt of the SJ-FTB, indicating that the HMT anticline belt started to become active during the Late Jurassic. The Qigu anticline belt reactivated intensively during the Late Cenozoic, and the displacement was transferred to the HMT anticline belt along the Paleogene Anjihaihe Formation mudstone detachment. Therefore, the present-day SJ-FTB forms because of the two-stage compressional deformation from both the Late Jurassic and Late Cenozoic (ca. 24 Ma).

Origins of overpressure in the central Xihu depression of the East China Sea shelf basin

The origins of overpressure in the central Xihu depression have been accepted to result from disequilibrium compaction and hydrocarbon generation. This study uses organic matter correction of the log data in source rocks and five empirical methods (the multilogging combination method, Bowers’ method, the sonic velocity–density cross-plot method, the porosity method, and the pressure inversion method) to understand the origins of overpressure in the central Xihu depression. Overpressure strata are mainly distributed in the following two areas: 1) the Pinghu Formation on the western slope of the central Xihu depression; 2) the Pinghu Formation and lower part of the Huagang Formation in the western sag and the central Inversion anticline belt. The areas contain two types of pressure profiles: normal pressure–overpressure and normal pressure–overpressure–normal pressure. At the western slope and the western sag, overpressure in source rock and nonsource rock was caused by hydrocarbon generation and pressure transfer, respectively. At the central inversion anticline belt, however, overpressure was caused by hydrocarbon generation and tectonic compression in source rock and by pressure transfer and tectonic compression in nonsource rock. We also propose criteria for confirming the combination of tectonic compression and hydrocarbon generation as the origin of overpressure, where the porosity distribution in the overpressured mudstone is consistent with the normal compaction trend or conforms to a higher level of normal compaction as the depth increases. In the sonic velocity–effective stress diagram, sonic velocity increases with decreasing effective stress, whereas density and sonic velocity both increase with increasing normal compaction in the density–sonic velocity diagram.

Structural Coupling Between the Qiman Tagh and the Qaidam Basin, Northern Tibetan Plateau: A Perspective From the Yingxiong Range by Integrating Field Mapping, Seismic Imaging, and Analogue Modeling

AbstractThe Qiman Tagh and the Qaidam Basin within the northern Tibetan Plateau are contrasting in geomorphological, geological, and geophysical features. The Yingxiong Range is the largest anticlinal belt in the SW Qaidam Basin and holds a key in understanding the relationship between the above two tectonic units. Herein, we investigated the geometry, shortening, timing and mechanism of the structural deformation across the Yingxiong Range by integrating field mapping, interpretation of 3‐D/2‐D seismic reflection data and analogue modeling. The structural interpretation demonstrates that the Yingxiong Range is primarily controlled by NE‐directed basement‐involved reverse faults. These faults likely sole into a décollement layer at depth of ~15 km through the excess area‐depth analysis. This pattern is complicated by the development of a local salt layer that decouples the deformation of underlying and overlying strata, as indicated by analogue modeling. Deformation initially occurred at ~8.1 Ma but strengthened at ~2.5 Ma, with total shortening up to ~5 km in the NW part but decreasing to <2 km to the SE. Together with published results, our findings revealed an NE‐directed thrust system involving the Qiman Tagh and the SW Qaidam Basin, with the Yingxiong Range as the front of this system. We further inferred that this NE‐directed thrust system in the upper crust, together with the previously identified SW‐directed deep reverse fault offsetting the Moho, may form a southwestward tapering tectonic wedge, which likely results from the heterogeneity of lithospheric mantle between the Qaidam Basin and the Qiman Tagh‐East Kunlun Shan.

Geological structures and potential petroleum exploration areas in the southwestern Sichuan fold-thrust belt, SW China

Based on the latest geological, seismic, drilling and outcrop data, we studied the geological structure, tectonic evolution history and deformation process of the southwestern Sichuan fold-thrust belt to find out the potential hydrocarbon exploration areas in deep layers. During key tectonic periods, the southwestern Sichuan fold-thrust belt developed some characteristic strata and structural deformation features, including the Pre-Sinian multi-row N-S strike rifts, step-shaped platform-margin structures of Sinian Dengying Formation, the western paleo-uplift in the early stage of Late Paleozoic, the Late Paleozoic–Middle Triassic carbonate platform, foreland slope and forebulge during Late Triassic to Cretaceous, and Cenozoic multi-strike rejuvenated fold-thrusting structures. The fold-thrust belt vertically shows a double-layer structural deformation controlled by the salt layer in the Middle Triassic Leikoupo Formation and the base detachment layer at present. The upper deformation layer develops the NE-SW strike thrusts propagating toward basin in long distance, while the deeper deformation layer had near north-south strike basement-involved folds, which deformed the detachment and thrusting structures formed earlier in the upper layer, with the deformation strength high in south part and weak in north part. The southern part of the fold-thrust belt is characterized by basement-involved fold-thrusts formed late, while the central-northern part is dominated by thin-skin thrusts in the shallow layer. The Wuzhongshan anticlinal belt near piedmont is characterized by over-thrust structure above the salt detachment, where the upper over-thrusting nappe consists of a complicated fold core and front limb of a fault-bend fold, while the deep layer has stable subtle in-situ structures. Favorable exploration strata and areas have been identified both in the upper and deeper deformation layers separated by regional salt detachment, wherein multiple anticlinal structures are targets for exploration. Other potential exploration strata and areas in southwestern Sichuan fold-thrust belt include the deep Sinian and Permian in the Wuzhongshan structure, pre-Sinian rifting sequences and related structures, platform-margin belt of Sinian Dengying Formation, and Indosinian paleo-uplift in the east of the Longquanshan structure.

ПЕРСПЕКТИВЫ НЕФТЕГАЗОНОСНОСТИ АНТИКЛИНАЛЬНОЙ ЗОНЫ ХАЛИ-НЕФТ ДАШЛАРЫ В СВЯЗИ С ЕЁ ПАЛЕОТЕКТОНИЧЕСКИМИ УСЛОВИЯМИ

Актуальность. Абшеронский нефтегазоносный район, где были проведены исследования, является одним из продуктивных в Азербайджане. Цель поисково-разведочных работ в основном заключается в увеличении добычи углеводородов, а это достигается выявлением новых нефтегазоносных объектов. С этой точки зрения в антиклинальном поясе Хали‒Нефт Дашлары в разрезе палеоген-миоценовых отложений выявление залежей, связанных с антиклинальными и неантиклинальными типами ловушками, имеет важную практическую особенность и это однозначно сыграет немаловажную роль в повышении добычи нефти и газа в республике. Наши исследования были проведены по определяющим нефтегазоносность критериям: геотермическим, литофациальным, тектоническим, палеотектоническим и т. д., по стратиграфическому разрезу палеоген-миоцен и плиоцена для определения новых объектов. Цель: определить с геотермической точки зрения в какой зоне нефтегазообразования в настоящее время находятся отложения продуктивной толщи и, в соответствии с этим, уточнить перспективность зоны, а также исследовать распространенность неантиклинальных ловушек в связи с палеотктоническими особенностями и конседиментационным развитием зоны. Объекты: отдельные структуры, представляющие антиклинальную зону Хали‒Нефт Дашлары, свиты нижнего отдела продуктивной толщи. Методы. Изменения общей мощности и песчанистости отложений продуктивной толщи в исследуемых структурах были проанализированы в локальном и региональном направлениях, были построены соответствующие диаграммы, отражающие закономерности изменения мощности и песчанистости по свитам. Наряду с этим были построены палеопрофили, отражающие палеотектоническое развитие структур антиклинальной зоны Хали‒Нефт Дашлары. Результаты. Построение графика скорости осадконакопления и, в связи с этим, анализ данных, изучение палеотемпературных условий Пираллахи-Келькорской впадины и проведенный анализ позволяют определить время нахождения отложений как продуктивной толщи, так и нижележащих отложений миоцена, палеогена и мезозоя в главной зоне нефтегазообразования, а также сопоставить главные этапы миграции со временем образования структур в пределах данной территории. Результаты всех исследований, проведенных в этом направлении, позволяют утверждать, что область исследований и ее окрестности также являются перспективными с точки зрения нефтегазоносности.

The Evolution of the Complex Anticlinal Belt With Crosscutting Strike‐Slip Faults in the Central Tarim Basin, NW China

AbstractIntegrated 2‐D and 3‐D seismic data sets reveal that a WNW trending complex anticlinal belt (the Tazhong Uplift) was cut roughly perpendicularly by a series of NNE oriented strike‐slip faults in the central Tarim Basin, NW China. Through detailed interpretation of the internal architecture of the Tazhong Uplift and the structural characteristics of the strike‐slip faults, the timing of their movements was determined. Based upon their geometric relationship and coeval movement, we propose an integrated model for the evolution of both the Tazhong Uplift and the strike‐slip fault system. Initially, the Tazhong Uplift formed perpendicular to the NNE oriented compression that responded to the collision between the Tarim block and the western Kunlun terrane in the latest Middle Ordovician. Meanwhile, regional joints formed parallel to the maximum compression, that is, perpendicular to the Tazhong Uplift. In the latest Ordovician, northward compression caused the uplifting climax of the Tazhong Uplift in response to the collision between the Tarim block and the coherent eastern Kunlun‐Altyn Tagh‐Qaidam‐Qilian terrane. Under such a northward compression, the resolved shear stress on the NNE trending joints formed the transpressional strike‐slip faults. Afterward, the Tazhong Uplift tilted northward during the ongoing subduction from the Kunlun Ocean, which lasted until the latest Middle Devonian. The negative flower structures formed along the preexisting transpressional strike‐slip faults due to the dragging of the overlying covers in the latest Middle Devonian. The data and evolution model not only unveil the formation mechanism of the Tazhong Uplift and the associated strike‐slip faults but also provide further constraints on the evolutionary age of the Proto‐Tethys Ocean.

The 2016 Mw 6.0 Hutubi earthquake: A blind thrust event along the northern Tian Shan front

The Tian Shan Range, which trends E-W along the southern margin of the Junggar Basin, is one of the longest and most active intracontinental orogenic belts in central Asia. On 8 December 2016 (05:15:04 UTC), a Mw 6.0 earthquake ruptured the northern Tian Shan front. Here, we use Sentinel-1 radar imagery to investigate the deformation and source parameters related to this event. The co-seismic surface deformation was predominated by uplift without surface rupture. Ascending and descending interferograms indicate that the event triggered small co-seismic deformations with maximum line-of-sight displacements of 22 mm and 24 mm, respectively. Although the north-dipping and south-dipping plane solutions can both fit the observations well, the north-dipping solution with a dip of 58° is preferred in consideration of the relocated aftershocks and regional geological structure. Significant slip is located between depths of 12 km and 17 km, suggesting that the event was caused by a completely blind thrust fault. This blind rupture is characterized largely by a compact thrusting patch with a peak slip of 56 cm at a depth of 13 km. The source model generates a geodetic moment of 6.678 × 1017 N m corresponding to a Mw 5.85 event. Both the interferometric synthetic aperture radar modeling and the aftershock locations indicate that the rupture plane is linked to the Huoerguosi-Manas-Tugulu fault at a depth of ∼16 km, a typical locking depth in the Tian Shan. We suggest that the 2016 Hutubi earthquake more likely occurred on a back-thrust of the Huoerguosi-Manas-Tugulu fault, and the back-thrust is interpreted to represent a preexisting normal fault beneath the Qigu anticline belt that was tectonically inverted during the Cenozoic.

Rupture Directivity of the 18 April 2008 Mt. Carmel, Illinois, Earthquake from Modeling of Local Seismic Waveforms

The 2008 M_w 5.2 Mt. Carmel earthquake is the largest earthquake in the last 50 yrs in southeastern Illinois, near the north termination of the north‐northeast‐trending Wabash Valley fault system (WVFS). The earthquake shows almost pure strike‐slip focal mechanism, but it is still uncertain which nodal plane (NP) is the ruptured fault plane. To resolve the fault plane, we determine rupture directivity of the earthquake via the relative centroid method. We begin with inverting the point‐source solution (strike 297°/dip 84°/rake 1° for NP1, strike 206°/dip 89°/rake 173° for NP2, and centroid depth 16 km) and then determine the relative location between the centroid and hypocenter via regional waveform fitting. Two M 4+ aftershocks are used as reference events, and the waveform time shifts of reference events with respect to the 1D velocity model are used to calibrate the path effects. The results show that the Illinois mainshock ruptured to east‐southeast along the 297° NP for about 2–3 km, consistent with relocated aftershock distribution, and we infer that the sinistral causative fault connects the north‐northwest‐trending La Salle anticlinal belt and the north‐northeast‐trending WVFS.

Paleohydrogeology of a Paleozoic sandstone aquifer within an intracratonic basin: Geochemical and structural controls

The aqueous geochemistry of the St. Peter Sandstone, a major aquifer in the Illinois Basin, an intracratonic sedimentary basin, is extremely complex. There are multiple sources of water, including in situ remnant brines, leakage from overlying and underlying units, and recharge during both the Pleistocene and Holocene Epochs. In our study region, recharge to the St. Peter Sandstone has come from multiple locations, and structural features, primarily the LaSalle Anticlinal Belt but also possibly the Sandwich Fault Zone, are a major control on recharge and groundwater flow. In the northern part of the study region, Holocene recharge has displaced most of the Pleistocene recharge, but in the rest of the study region considerable amounts of Pleistocene recharge still exist. The ion chemistry in the St. Peter Sandstone cannot be accounted for by simple mixing of Pleistocene recharge and in situ brines, and the most likely mechanism that could account for the aqueous chemistry is leakage of fluids from overlying formations via fractures opened by flexural loading during glacial advances. The water chemistry in the Western Region of our study area is clearly different from the Central and Eastern regions, having a more pronounced signature of Pleistocene water and suggesting different flow paths and sources of recharge. The large concentrations of SO42− and relatively high δ34S values in the Western wells suggest an up-gradient source of anhydrite and/or gypsum, possibly from Mississippian evaporite deposits in Iowa.

Tectonic characteristics and distribution of Putaohua oil Reservoir in Changchang area of Songliao basin

Since the Late Jurassic in the Songliao Basin, the tectonic movement of Yanshan and Heshan has experienced a lot of tectonic movement. The tectonic activity has a clearer display on the seismic profile. The tectonic deformation is generally weak in the east, Features. The regional structure of the Chaochang area is located on the Chaoyangou terrace and Changchunling anticline belt in the central depression of the northern part of the Songliao Basin, and across the two tectonic units of the Chaoyanggou terrace and Changchunling anticline. The study area is characterized by a low tectonic pattern in the southwest and northwest. The highest point is located near the Chang72 well in the Changchunling anticline. The elevation is about -100 m, and the lowest point is the Zhou50 Well near the depth of about - 1750 m. Based on the technical means such as splicing, closed difference correction, horizon calibration, seismic interpretation and attribute extraction of 9 seismic blocks in the study area, the seismic interpretation of the top of the Putaohua reservoir is completed, and the next step Style, tectonic evolution characteristics, oil and gas accumulation law and other research work to lay the foundation.

Sequence Stratigraphic Framework Analysis of Putaohua Oil Reservoir in Chaochang Area of Songliao Basin

The regional structure of the Changchang area in the Songliao Basin is located on the Chaoyangou terrace and Changchunling anticline belt in the central depression of the northern part of the Songliao Basin, across the two secondary tectonic units of the Chaoyanggou terrace and Changchunling anticline. However, with the continuous development of oil and gas, the unused reserves of Fuyu oil reservoir decreased year by year, and the oil field faced a serious shortage of reserve reserves. At the same time, during the evaluation process, a better oil-bearing display was found during the drilling and test oil in the Putao depression to the Chaoyanggou terraces, the Yudong-Taipingchuan area, and in the process of drilling and testing oil in the Putaohua reservoir. Zhao41, Zhao18-1, Shu38 and other exploration wells to obtain oil oil, indicating that the area has a further evaluation of the potential. Based on the principle of stratification, the Putao area was divided into three parts by using the core, logging and logging. It is concluded that the middle and western strata of the study area are well developed, including three sequences, one cycle from bottom to top (three small layers), two cycles (one small layer), three cycles (two small layers) Rhythm is positive-anti-positive. From the Midwest to the southeastern part of the strata, the strata are overtaken, the lower strata are missing, and the top rhythms become rhythmic.