Analysis of vertical position relationships between igneous sills and an unconformity surface — Interpretation of seismic profiles from the Northern Tarim Basin, NW China

Sill emplacement mechanisms are very complex, diverse, and regional, and insights from sill reflections are helpful for understanding the emplacement process of magma in the Tarim Basin. This study takes advantage of high-quality 2D seismic data, which are rarely used to study sills in the Tarim Basin, to analyze the sills’ geometric characteristics, plan-view distributions, emplacement timing, and emplacement mechanisms with unconformity surfaces. In the seismic-reflection profiles of the middle-upper Ordovician in the North depression and the southern part of the Tabei uplift in the Tarim Basin, sills with strong positive polarity reflections appear, and they are closely distributed near the Tg52 unconformity surface, which represents the interface between Middle Ordovician limestone and Upper Ordovician mudstone. According to the vertical position of the sills relative to the unconformity, we can divide the sills into saucer-shaped or quasi-saucer-shaped sills above the unconformity surface, sill complexes and saucer-shaped sills on the unconformity surface, and saucer-shaped sills below the unconformity surface. Potential hydrothermal vents and peripheral faults associated with sill intrusion terminate upward in the Middle Permian strata, suggesting that these sills formed in the Middle Permian. Sills with inner flat sheets on the Tg52 unconformity surface formed when the magma ascended and encountered an abrupt change in the fracture toughness and tensile strength between the two adjacent host rock layers. The sills above and on the Tg52 unconformity surface overlap or are vertically linked; therefore, the sills above the Tg52 unconformity surface are the result of the continuous upward expansion of the sills on the unconformity surface, forming sill complexes. Our findings further confirm that unconformities are important interfaces that affect the emplacement of sills.

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New Method for Characterizing Internal Structure of Fault-Karst Reservoirs and Analysis on Acidizing Fracturing Effect: A Case Study in HLHT Oilfield, Tarim Basin, NW China

Lithosphere ◽

10.2113/2021/6784641 ◽

2021 ◽

Vol 2021 (Special 1) ◽

Author(s):

Peng Cao ◽

Shaoying Chang ◽

Yongjin Zhu ◽

Jinlong Shen ◽

Zhanfeng Qiao ◽

...

Keyword(s):

Internal Structure ◽

Tarim Basin ◽

Production Performance ◽

Signal Interference ◽

Data Conversion ◽

Well Test ◽

Seismic Profiles ◽

The North ◽

Internal Structures ◽

Karst Reservoir

Abstract Superimposed tectonic movement and karst erosion resulted in a combination of fractures and irregular caves in deep/ultradeep carbonate rocks, typically along major fault swarms. Outlining these fault-karst reservoirs mainly depends on recognizing the strong reflection in seismic profiles; however, characterizing their internal structures is still difficult, which are represented as weak amplitude in seismic profiles. This study intended to propose a method to dissect the internal structure of fault-karst reservoirs, which contains four steps: (1) elimination of the signal interference by the covering bed with strong energy and recognition of internal reservoirs with low energy based on seismic data conversion, frequency division, and inversion; (2) gradient structure tensor analysis based on an anisotropic Gaussian filter for fault-karst reservoir outlining; (3) internal faults and cave recognition on the basis of wave-based inversion; and (4) reevaluation of the number and scale of these faults and caves based on seismic recognition and well test results and verification of their volumes and hydrocarbon reserves. The method was used in the evaluation of the fault-karst reservoir in the Halahatang (HLHT) oilfield, which is located in the north of Tarim Basin. The results show that the fault-karst reservoirs along major faults and their internal structures are effectively recognized, and the error of the predicted depth of the reservoirs decreases from more than 20 m before to less than 4 m now; the drilling success ratio increases from 70% to 90%. In addition, the method supports the recognition of untapped fault-karst reservoirs around shut-in wells, which provides guidance for sidetracking plans. Further, by comparing the geophysical volume of fault-karst reservoirs and the reserve predicted by production performance, the untapped reserve in a certain reservoir can be evaluated; on this basis, producing wells received high yields by targeted acid fracturing. In summary, the method effectively improves the prediction accuracy and the recovery efficiency of fault-karst reservoirs.

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The 3D seismic characteristics and significance of the strike-slip faults in the Tazhong area (Tarim Basin, China)

Interpretation ◽

10.1190/int-2016-0135.1 ◽

2019 ◽

Vol 7 (1) ◽

pp. T1-T19 ◽

Cited By ~ 1

Author(s):

RenHai Pu ◽

KunBai Li ◽

Machao Dong ◽

ZiCheng Cao ◽

Pengye Xu

Keyword(s):

Tarim Basin ◽

Strike Slip ◽

Late Ordovician ◽

3D Seismic ◽

Seismic Profiles ◽

The North ◽

Tazhong Area ◽

Detailed Interpretation ◽

3D Seismic Data ◽

Stratigraphic Thickness

The eastern part of Tazhong area in the Tarim Basin consists of three sets of vertical strike-slip faults oriented in north–northeast (36°azimuth), east–northeast (68° azimuth), and west–northwest (126°azimuth) directions that cut the strata from Cambrian to Carboniferous. The fault belts indicate significant horizon upwarp and downwarp deformations and variations in their stratigraphic thickness on seismic profiles. Through detailed interpretation of the 3D seismic data, we consider that these phenomena reflect the different stress properties and active stages of the faults. The horizon upwarp and downwarp within the fault belts correlated respectively to the decrease and increase in stratigraphic thickness within the fault belts in comparison to the coeval counterpart of the bilateral fault blocks. For the same fault, different stratigraphic intervals express different types of horizon deformation and thickness changes. The horizon downwarp and the contemporaneous stratigraphic thickening inside the fault belts suggest the transtensional actions of the fault. The horizon upwarp and the contemporaneous thinning within the fault belts suggest transpressional actions of the fault. Based on this, we inferred the active periods of the three sets of strike-slip faults. The north–northeast-striking faults were formed in the late Ordovician Sangtamu Formation. This set of faults experienced four stages, i.e., sinistral transpression, sinistral transtension, static, and transtension. The east–northeast and west–northwest-striking faults initiated in the mid-Cambrian period as coupled transtension. Activity ceased in the west–northwest faults after the mid-Cambrian and in the east–northeast faults during the late Ordovician. The three sets of strike-slip faults all affect the formation of the hydrothermal dissolution reservoirs that are distributed in the Ordovician carbonate rocks.

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Contribution a l'etude stratigraphique et paleontologique du synclinal d'Ancenis (Massif armoricain)

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.s7-v.3.318 ◽

1963 ◽

Vol S7-V (3) ◽

pp. 318-329 ◽

Cited By ~ 1

Author(s):

Pierre Cavet ◽

Jean Pillet

Keyword(s):

Upper Devonian ◽

Upper Ordovician ◽

Basement Complex ◽

Middle Ordovician ◽

The Core ◽

The North ◽

Continental Deposits ◽

The Right ◽

Armorican Massif ◽

Loire River

Abstract The schists and quartzites which form the northern and southern flanks of the Ancenis syncline on the right bank of the Loire river (France), have yielded sandy, micaceous nodules which contain a middle Ordovician trilobite fauna. This discovery indicates a similarity between the quartzites and the Calymenella bayani sandstone of the more northern folds of the Saint-Georges-sur-Loire synclinorium; but the volcanic schists which overlie the C. bayani sandstone are not represented in the Ancenis syncline. Contrary to what has been thought until now, the schists and quartzites rest unconformably on the Brioverian basement complex. The Brulis limestones, present as lenses interbedded in the schist-quartzite band on the south flank, are considered middle or upper Ordovician. The Ecochere jasper and calcareous schist with limestone lenses are directly transgressive on the middle Ordovician and contain a fauna typical of the Frasnian (upper Devonian). The Frasnian Cope-Choux limestone with Hypothiridina cuboides of the north flank seems to be directly related to fissile shales identical to those containing the Ecochere limestones. Continental deposits of the lower Culm, which contain Rhodea hochstetteri, occupy the core of the syncline and are principally Dinantian, but may extend into the lower Namurian. The absence of upper Namurian and Westphalian deposits suggests the intervention of a new orogenic phase (Erzgebirgian?). The Llandeilian trilobites Placoparia zippei, Colpocoryphe aragoi, and Pricyclopyge binodosa are described from the nodules. Pricyclopyge binodosa is the first representative of the Cyclopygidae reported from the Armorican massif.

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Composite Strike-Slip Deformation Belts and Their Control on Oil and Gas Reservoirs: A Case Study of the Northern Part of the Shunbei 5 Strike-Slip Deformation Belt in Tarim Basin, Northwestern China

Frontiers in Earth Science ◽

10.3389/feart.2021.755050 ◽

2021 ◽

Vol 9 ◽

Author(s):

Haowei Yuan ◽

Shuping Chen ◽

Yuan Neng ◽

Huaibo Zhao ◽

Shidong Xu ◽

...

Keyword(s):

Tarim Basin ◽

Plate Tectonics ◽

Oil And Gas ◽

Strike Slip ◽

Petroleum Exploration ◽

Gas Reservoirs ◽

Plan View ◽

Middle Ordovician ◽

Oil And Gas Reservoirs ◽

Slip Deformation

Strike-slip deformation belts are interesting structures in the crust and are of significance in petroleum exploration. The Shunbei 5 fault belt (SB5), a long strike-slip deformation belt in the Tarim Basin, played an important role in the formation of a recently discovered major oilfield known as the Shunbei oilfield. In this study, models of plan view and vertical profile were established to interpret SB5 with multi-cycled tectonic activities. To this end, its structural framework, tectonic evolution, and associated plate tectonics were investigated using 2D and 3D seismic data. SB5 was formed as a dextral simple shear belt at the end of the Middle Ordovician. In the plan view, R-shears and P-shears with local transpressional and transtensional structures were observed. Along the vertical profiles, various structural styles occurred at various depths and strata in response to various stratigraphy mechanisms. Although these structures show clear boundaries between them, they correspond to the same formation time, indicating that they underwent deformation simultaneously. The second activity of SB5 occurred at the end of the late Ordovician, during which it was a dextral transtensional strike-slip deformation belt consisting of left-stepping en echelon R-shears. The R-shears were transtensional during the progressive deformation. Subsequently, SB5 underwent several strike slips of weak strength. Notably, SB5 cut through a deep Middle Cambrian gypsum salt layer and connected the deep Lower Cambrian source rock with deep Lower and Middle Ordovician carbonates to form the oil and gas reservoirs. The established models are of reference value in the interpretation of other subsurface strike-slip deformation belts.

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Geochemistry and Mineralogy of Lower Paleozoic Heituao Shale from Tadong Low Uplift of Tarim Basin, China: Implication for Shale Gas Development

Minerals ◽

10.3390/min11060635 ◽

2021 ◽

Vol 11 (6) ◽

pp. 635

Author(s):

Shihu Zhao ◽

Yanbin Wang ◽

Yong Li ◽

Honghui Li ◽

Zhaohui Xu ◽

...

Keyword(s):

Organic Matter ◽

Tarim Basin ◽

Shale Gas ◽

Organic Matter Content ◽

Matter Content ◽

Mature Stage ◽

Lower Paleozoic ◽

Development Potential ◽

Middle Ordovician ◽

Average Value

Tarim Basin is the largest Petroliferous basin in China, while its shale gas development potential has not been fully revealed. The organic-rich black shale in middle Ordovician Heituao Formation from Tadong low uplift of Tarim Basin has been considered as an important source rock and has the characteristic of large thickness, high organic matter content and high thermal maturity degree. To obtain its development potential, geochemical, mineralogical and mechanics research is conducted based on Rock-Eval pyrolysis, total organic carbon (TOC), X-ray diffraction (XRD) and uniaxial compression experiments. The results show that: (1) the TOC content ranges between 0.63 and 2.51 wt% with an average value of 1.22 wt%, the Tmax values are 382–523 °C (average = 468.9 °C), and the S2 value is relatively low which ranges from 0.08 to 1.37 mg HC/g rock (averaging of 0.42 mg HC/g rock); (2) the organic matter of Heituao shale in Tadong low uplift show poor abundance as indicated by low S2 value, gas-prone property, and post mature stage (stage of dry gas). (3) Quartz is the main mineral component in Heituao shale samples, accounting for 26–94 wt% with an average of 72 wt%. Additionally, its Young’s modulus ranges from 20.0 to 23.1 GPa with an average of 21.2 GPa, Poisson’s ratio ranges between 0.11 and 0.21 (average = 0.15); (4) the fracability parameter of brittleness index (BI) ranges between 0.28 and 0.99 (averaging of 0.85), indicating good fracability potential of Heituao shale of Tadong low uplift and has the potential for shale gas development. This study reveals the shale gas accumulation potential in middle Ordovician of the Tarim Basin, and beneficial for future exploration and production practice.

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Katian (Late Ordovician) conodonts on the northwestern margin of the North China Craton

Journal of Paleontology ◽

10.1017/jpa.2021.11 ◽

2021 ◽

pp. 1-22

Author(s):

Zhihua Yang ◽

Xiuchun Jing ◽

Hongrui Zhou ◽

Xunlian Wang ◽

Hui Ren ◽

...

Keyword(s):

North China Craton ◽

North China ◽

Late Ordovician ◽

Carbonate Platforms ◽

Upper Ordovician ◽

The North ◽

Low Latitudes ◽

Northwestern Margin ◽

Conodont Fauna ◽

Stratigraphic Range

Abstract Upper Ordovician strata exposed from the Baiyanhuashan section is the most representative Late Ordovician unit in the northwestern margin of the North China Craton (NCC). In total, 1,215 conodont specimens were obtained from 24 samples through the Wulanhudong and Baiyanhuashan formations at the Baiyanhuashan section. Thirty-six species belonging to 17 genera, including Tasmanognathus coronatus new species, are present. Based on this material, three conodont biozones—the Belodina confluens Biozone, the Yaoxianognathus neimengguensis Biozone, and the Yaoxianognathus yaoxianensis Biozone—have been documented, suggesting that the Baiyanhuashan conodont fauna has a stratigraphic range spanning the early to middle Katian. The Baiyanhuashan conodont fauna includes species both endemic to North China and widespread in tropical zones, allowing a reassessment of the previous correlations of the Katian conodont zonal successions proposed for North China with those established for shallow-water carbonate platforms at low latitudes. UUID: http://zoobank.org/7cedbd4a-4f7a-4be6-912f-a27fd041b586

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Oxygen isotope (δ18O) trends measured from Ordovician conodont apatite using secondary ion mass spectrometry (SIMS): Implications for paleo-thermometry studies

Geological Society of America Bulletin ◽

10.1130/b35891.1 ◽

2021 ◽

Author(s):

Cole T. Edwards ◽

Clive M. Jones ◽

Page C. Quinton ◽

David A. Fike

Keyword(s):

Mass Spectrometry ◽

Secondary Ion Mass Spectrometry ◽

Matrix Effects ◽

Analytical Techniques ◽

Upper Ordovician ◽

Bulk Analysis ◽

Middle Ordovician ◽

Ion Mass Spectrometry ◽

Oxygen Isotopic ◽

Secondary Ion

The oxygen isotopic compositions (δ18O) of minimally altered phosphate minerals and fossils, such as conodont elements, are used as a proxy for past ocean temperature. Phosphate is thermally stable under low to moderate burial conditions and is ideal for reconstructing seawater temperatures because the P-O bonds are highly resistant to isotopic exchange during diagenesis. Traditional bulk methods used to measure conodont δ18O include multiple conodont elements, which can reflect different environments and potentially yield an aggregate δ18O value derived from a mixture of different water masses. In situ spot analyses of individual elements using micro-analytical techniques, such as secondary ion mass spectrometry (SIMS), can address these issues. Here we present 108 new δ18O values using SIMS from conodont apatite collected from four Lower to Upper Ordovician stratigraphic successions from North America (Nevada, Oklahoma, and the Cincinnati Arch region of Kentucky and Indiana, USA). The available elements measured had a range of thermal alteration regimes that are categorized based on their conodont alteration index (CAI) as either low (CAI = 1−2) or high (CAI = 3−4). Though individual spot analyses of the same element yield δ18O values that vary by several per mil (‰), most form a normal distribution around a mean value. Isotopic variability of individual spots can be minimized by avoiding surficial heterogeneities like cracks, pits, or near the edge of the element and the precision can be improved with multiple (≥4) spot analyses of the same element. Mean δ18O values from multiple conodonts from the same bed range between 0.0 and 4.3‰ (median 1.0‰), regardless of low or high CAI values. Oxygen isotopic values measured using SIMS in this study reproduce values similar to published trends, namely, δ18O values increase during the Early−Middle Ordovician and plateau by the mid Darriwilian (late Middle Ordovician). Twenty-two of the measured conodonts were from ten sampled beds that had been previously measured using bulk analysis. SIMS-based δ18O values from these samples are more positive by an average of 1.7‰ compared to bulk values, consistent with observations by others who attribute the shift to carbonate- and hydroxyl-related SIMS matrix effects. This offset has implications for paleo-temperature model estimates, which indicate that a 4 °C temperature change corresponds to a 1‰ shift in δ18O (‰). Although this uncertainty precludes precise paleo-temperature reconstructions by SIMS, it is valuable for identifying spatial and stratigraphic trends in temperature that might not have been previously possible with bulk approaches.

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Seismic attribute for characterization and prediction of carbonate faulted karst reservoirs in Tarim Basin, China

Interpretation ◽

10.1190/int-2019-0162.1 ◽

2021 ◽

pp. 1-36

Author(s):

Zhiwei Xiao ◽

Li Wang ◽

Ruizhao Yang ◽

Dewei Li ◽

Lingbin Meng

Keyword(s):

Tarim Basin ◽

Oil And Gas ◽

Prediction Method ◽

Strike Slip ◽

Fault System ◽

Bright Spot ◽

Upper Ordovician ◽

Reservoir Prediction ◽

Seismic Attribute ◽

Gas Field

An ultradeep, faulted karst reservoir of Ordovician carbonate was discovered in the Shunbei area of the Tarim Basin. Fractured-cavity reservoirs buried beneath the large thickness of upper Ordovician mudstone were formed along the fault-karst belts. The hydrocarbon accumulation in these reservoirs is controlled by the fault system, and the oil-gas accumulation was affected by karstification and hydrothermal reformation. Previous studies and 2D modeling revealed that the reservoirs had “bright spot” amplitude responses like “string beads,” and they have developed along the strike-slip faults. However, describing such a complex fault-controlled karst system is still a difficult problem that has not been well addressed. We have sought to instruct the attribute expression of faulted karst reservoirs in the northern part of the Tarim Basin. We applied coherence and fault likelihood (FL) seismic attributes to image faults and fractures zones. We then used a trend analysis method to calculate the residual impedance from the impedance of the acoustic inversion, using the fact that residual impedance has higher lateral resolution in reservoir predictions. Finally, we integrated the coherence, FL, and residual impedance attributes into a new seismic attribute, the “fault-vuggy body,” with a certain fusion coefficient. The fault-vuggy body attribute establishes a connection between faults and karst cavities. This method could help in the characterization and prediction of carbonate faulted karst reservoirs. Available drilling data were used to validate that the fused fault-vuggy body attribute was an effective reservoir prediction method. As the seismic sections and slices along the layer help delineate, the distribution of bright spots and strike-slip faults indicates that the main strike-slip fault zones are the most favorable reservoirs in the Shunbei Oil and Gas Field.

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The Sjælland Fjelde Formation: a new Ordovician formation from eastern North Greenland

Rapport Grønlands Geologiske Undersøgelse ◽

10.34194/rapggu.v132.7961 ◽

1986 ◽

Vol 132 ◽

pp. 27-37

Author(s):

J.R Ineson ◽

J.S Peel ◽

M.P Smith

Keyword(s):

Shallow Water ◽

North West ◽

Middle Ordovician ◽

The North ◽

New Formation ◽

North Greenland

The name Sjælland Fjelde Formation is introduced for a varied sequence of shallow-water platform dolomites and dolomitic limestones, about 105 m in thickness, in Kronprins Christian Land, eastern North Greenland. The new formation lies between the previously described Wandel Valley and Børglum River Formations. Conodont faunas indicate that the Sjælland Fjelde Formation is of Middle to earliest Late Whiterockian (early Middle Ordovician) age and that it can be eorrelated with the upper part of the Wandel Valley Formation of Peary Land to the north-west.

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