scholarly journals Fracture, Dissolution, and Cementation Events in Ordovician Carbonate Reservoirs, Tarim Basin, NW China

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-28 ◽  
Author(s):  
Vinyet Baqués ◽  
Estibalitz Ukar ◽  
Stephen E. Laubach ◽  
Stephanie R. Forstner ◽  
András Fall
Keyword(s):  
Tarim Basin ◽  
Oil And Gas ◽  
Hydrocarbon Generation ◽  
High Porosity ◽  
Late Permian ◽  
Gas Reservoirs ◽  
Near Surface ◽  
Principal Source ◽  
Igneous Activity ◽  
Karstic Features

Ordovician carbonate rocks of the Yijianfang Formation in the Tabei Uplift, Tarim Basin, contain deeply buried (>6000 m), highly productive oil and gas reservoirs associated with large cavities (>10 m). Previous workers inferred that large cavities are paleocaves (paleokarst) formed near the surface and subsequently buried. Alternately, caves may have formed by dissolution at depth along faults. Using 227 samples from 16 cores, we document textures and cement compositions bearing on cavity histories with petrographic, high-resolution scanning electron microscopy (SEM), isotopic, and fluid inclusion microthermometric observations. Results show that dissolution occurred at depth and was caused by (1) acidic fluids derived from Middle-Late Silurian and/or Devonian-Permian hydrocarbon generation and maturation, (2) high-temperature fluids, of which some were associated with Late Permian igneous activity, and (3) Mg-rich fluids that accompanied Jurassic-Cretaceous deformation and the formation of partially open fractures and stylobreccias (fault breccias). The relative paragenetic sequence of the structure-related diagenesis suggests seven stages of fracturing, dissolution, and cementation. Mottle fabrics in the Yijianfang Formation contain argillaceous carbonate-rich silt and are bioturbation features formed within the marine environment. Those mottled fabrics differ from clearly karstic features in the overlying Lianglitage Formation, which formed by near-surface dissolution and subsequent infilling of cavities by allochthonous sediment. Mottle fabrics are crosscut by compacted fractures filled with phreatic-vadose marine cements and followed by subsequent generations of cement-filled fractures and vugs indicating that some fractures and vugs became cement filled prior to later dissolution events. Calcite cements in fractures and vugs show progressively depleted values of δ18O documenting cement precipitation within the shallow (~220 m), intermediate (~625 m), and deep (~2000 m) diagenetic environments. Deep (mesogenetic) dissolution associated with fractures is therefore the principal source of the high porosity-permeability in the reservoir, consistent with other pieces of evidence for cavities localized near faults.

scholarly journals Fluid geochemistry of the Jurassic Ahe Formation and implications for reservoir formation in the Dibei area, Tarim Basin, northwest China

2018 ◽  
Vol 36 (4) ◽  
pp. 801-819 ◽  
Author(s):  
Shuangfeng Zhao ◽  
Wen Chen ◽  
Zhenhong Wang ◽  
Ting Li ◽  
Hongxing Wei ◽  
...  
Keyword(s):  
Natural Gas ◽  
Tarim Basin ◽  
Oil And Gas ◽  
Northwest China ◽  
Source Rocks ◽  
Coal Measure ◽  
Hydrocarbon Generation ◽  
Gas Reservoirs ◽  
Isotopic Analyses ◽  
Jurassic Coal

The condensate gas reservoirs of the Jurassic Ahe Formation in the Dibei area of the Tarim Basin, northwest China are typical tight sandstone gas reservoirs and contain abundant resources. However, the hydrocarbon sources and reservoir accumulation mechanism remain debated. Here the distribution and geochemistry of fluids in the Ahe gas reservoirs are used to investigate the formation of the hydrocarbon reservoirs, including the history of hydrocarbon generation, trap development, and reservoir evolution. Carbon isotopic analyses show that the oil and natural gas of the Ahe Formation originated from different sources. The natural gas was derived from Jurassic coal measure source rocks, whereas the oil has mixed sources of Lower Triassic lacustrine source rocks and minor amounts of coal-derived oil from Jurassic coal measure source rocks. The geochemistry of light hydrocarbon components and n-alkanes shows that the early accumulated oil was later altered by infilling gas due to gas washing. Consequently, n-alkanes in the oil are scarce, whereas naphthenic and aromatic hydrocarbons with the same carbon numbers are relatively abundant. The fluids in the Ahe Formation gas reservoirs have an unusual distribution, where oil is distributed above gas and water is locally produced from the middle of some gas reservoirs. The geochemical characteristics of the fluids show that this anomalous distribution was closely related to the dynamic accumulation of oil and gas. The period of reservoir densification occurred between the two stages of oil and gas accumulation, which led to the early accumulated oil and part of the residual formation water being trapped in the tight reservoir. After later gas filling into the reservoir, the fluids could not undergo gravity differentiation, which accounts for the anomalous distribution of fluids in the Ahe Formation.

Geological origins of seismic bright spot reflections in the Ordovician strata in the Halahatang area of the Tarim Basin, western China

2018 ◽  
Vol 55 (12) ◽  
pp. 1297-1311 ◽  
Author(s):  
Wei Yang ◽  
Xiaoxing Gong ◽  
Wenjie Li
Keyword(s):  
Tarim Basin ◽  
Oil And Gas ◽  
High Amplitude ◽  
Hydrothermal Activity ◽  
Hydrocarbon Exploration ◽  
Western China ◽  
Bright Spot ◽  
Gas Reservoirs ◽  
Seismic Section ◽  
Bright Spots

Anomalously high-amplitude seismic reflections are commonly observed in deeply buried Ordovician carbonate strata in the Halahatang area of the northern Tarim Basin. These bright spots have been demonstrated to be generally related to effective oil and gas reservoirs. These bright spot reflections have complex geological origins, because they are deeply buried and have been altered by multi-phase tectonic movement and karstification. Currently, there is no effective geological model for these bright spots to guide hydrocarbon exploration and development. Using core, well logs, and seismic data, the geological origins of bright spot are classified into three types, controlled by karstification, faulting, and volcanic hydrothermal activity. Bright spots differing by geological origin exhibit large differences in seismic reflection character, such as reflection amplitude, curvature, degree of distortion, and the number of vertically stacked bright spots in the seismic section. By categorizing the bright spots and the seismic character of the surrounding strata, their geological origins can after be inferred. Reservoirs formed by early karstification were later altered by epigenetic karstification. Two periods of paleodrainage further altered the early dissolution pores. In addition, faults formed by tectonic uplift also enhanced the dissolution of the flowing karst waters. Some reservoirs were subsequently altered by Permian volcanic hydrothermal fluids.

Jurassic source rocks of hydrocarbon fluids in the Eastern part of the Fukan depression (Junggar oil and gas basin)

2020 ◽  
pp. 55-63
Author(s):  
Yang Houqiang ◽  
E. V. Soboleva
Keyword(s):  
Organic Matter ◽  
Oil And Gas ◽  
Research Area ◽  
Molecular Composition ◽  
Source Rocks ◽  
Hydrocarbon Generation ◽  
Gas Reservoirs ◽  
Eastern Side ◽  
Oil And Gas Reservoirs

In recent years, significant successes have been achieved in the search and exploration of oil and gas reservoirs in the Jurassic deposits on the eastern side of the Fukang depression, which is the least studied part of the Junggar oil and gas Basin. In order to find out the source of hydrocarbon generation, we studied source rocks, oil and oil-bearing sandstones (24 samples from 13 wells) from the Badaowan, Sangonghe, Xishanyao, Toutunhe and Qigu production beds of the Fukang depression research area. Based on these studies, the composition of the organic matter of the Jurassic source rocks, the properties and molecular composition of oils, as well as the characteristics of the composition of biomarkers in them are examined in detail. The results of research and interpretation of the data showed that the mudstones of the Badaowan formation were source rocks of oil from the Gumudi zone, the Fukan depression, the Bajiahai ledge and the Shaqi ledge.

scholarly journals Phase States of Hydrocarbons in Chinese Marine Carbonate Strata and Controlling Factors for Their Formation

2012 ◽  
Vol 30 (5) ◽  
pp. 753-773 ◽  
Author(s):  
Jin Zhijun ◽  
Liu Quanyou ◽  
Qiu Nansheng ◽  
Ding Feng ◽  
Bai Guoping
Keyword(s):  
Heat Flow ◽  
Tarim Basin ◽  
Sichuan Basin ◽  
Oil And Gas ◽  
Ordos Basin ◽  
High Heat ◽  
Hydrocarbon Generation ◽  
Oil Accumulation ◽  
The Ordos Basin ◽  
Accumulation History

Chinese marine strata were mainly deposited before the Mesozoic. In the Tarim, Sichuan and Ordos Basins, the marine source rocks are made of sapropelic dark shale, and calcareous shale, and they contain type II kerogen. Because of different burial and geothermal histories, the three basins exhibit different hydrocarbon generation histories and preservation status. In the Tarim Basin, both oil and gas exist, but the Sichuan and Ordos Basins host mainly gas. The Tarim Basin experienced a high heat flow history in the Early Paleozoic. For instance, heat flow in the Late Cambrian varied between 65–75 mW/m2, but it declined thereafter and averages 43.5mW/m2 in the current time. Thus, the basin is a “warm to cold basin”. The Sichuan Basin experienced an increasing heat flow through the Early Paleozoic to Early Permian, and peaked in the latest Early Permian with heat flows of 71–77 mW/m2. Then, the heat flow declined stepwise to the current value of 53.2 mW/m2. Thus, it is a generally a high heat flow “warm basin”. The Ordos Basin has a low heat flow for most of its history (45–55 mW/m2), but experienced a heating event in the Cretaceous, with the heat flow rising to 70–80 mW/m2. Thus, this basin is a “cold to warm basin”. The Tarim Basin experienced three events of hydrocarbon accumulations. Oil accumulation formed in the late stage of Caledonian Orogeny. The generation and accumulation of oil continued in the Northern and Central Tarim (Tabei and Tazhong) till the late Hercynian Orogeny, during which, the accumulated oil cracked into gas in the Hetianhe area and Eastern Tarim (Tadong). In the Himalaya Orogeny, oil cracking occurred in the entire basin, part of the oil in the Tabei and Tazhong areas and most of the oil in the Hetianhe and Tadong areas are converted into gas. In the Sichuan Basin, another triple-episode generation and accumulation history is exhibited. In the Indosinian Orogeny, oil accumulation formed, but in the Yanshanian Orogeny, part of the oil in the eastern Sichuan Basin and most of the oil in the northeastern part was cracked into gas. In the Himalayan Orogeny, oil in the entire basin was converted into gas. The Ordos Basin experienced a double-episode generation and accumulation history, oil accumulation happened in the early Yanshanian stage, and cracked in the late stage. In general, multiple phases of heat flow history and tectonic reworking caused multiple episodes of hydrocarbon generation, oil to gas cracking, and accumulation and reworking. The phases and compositions of oil and gas are mainly controlled by thermal and burial histories, and hardly influenced by kerogen types and source rock types.

Emplacement of intrusions of the Tarim Flood Basalt Province and their impacts on oil and gas reservoirs: A 3D seismic reflection study in Yingmaili fields, Tarim Basin, northwest China

2017 ◽  
Vol 5 (3) ◽  
pp. SK51-SK63 ◽  
Author(s):  
Zhongbo Gao ◽  
Wei Tian ◽  
Lei Wang ◽  
Yongmin Shi ◽  
Mao Pan
Keyword(s):  
Tarim Basin ◽  
Seismic Reflection ◽  
Oil And Gas ◽  
Northwest China ◽  
Lower Permian ◽  
Magmatic Activity ◽  
3D Seismic ◽  
Gas Reservoirs ◽  
Oil And Gas Reservoirs ◽  
Northern Tarim Basin

A basaltic dike-sill network is emplaced into the shallow subsurface of the Yingmai-2 dome, northern Tarim Basin, northwest China. The 3D seismic reflection imaging suggests that these dikes and sills are fed from an intrusion at the focal area of the dome. This basaltic intrusion has a width of approximately 3000 m and thickness of approximately 1000 m, and it is connected with a much larger Early Permian igneous body in the northern Tarim Basin. An unconformity between the Permian basalt lava flows and the base Triassic conglomerates truncates the dome, meaning that the dome must have developed prior to the Triassic. The basaltic intrusion that emplaced beneath the dome likely pushed the surrounding middle Cambrian salts away and instigated uplift of the overlying upper Cambrian to the lower Permian strata. In most cases, igneous activity plays a negative role on formation of oil and gas reservoirs. However, in the Yingmai-2 case, intrusive magmatic activity has caused “forced folding” of the overburdened strata and controlled the formation of a large commercial oil trap. We suggest that the magmatic activity thus also acts as a positive role on the local formation of a producing petroleum system.

scholarly journals Diversity and abundance of <i>n</i>-alkane-degrading bacteria in the near-surface soils of a Chinese onshore oil and gas field

2013 ◽  
Vol 10 (3) ◽  
pp. 2041-2048 ◽  
Author(s):  
K. Xu ◽  
Y. Tang ◽  
C. Ren ◽  
K. Zhao ◽  
Y. Sun
Keyword(s):  
Microbial Communities ◽  
Oil And Gas ◽  
Gas Reservoirs ◽  
Surface Soils ◽  
Gas Field ◽  
Near Surface ◽  
Degrading Bacteria ◽  
Oil And Gas Field ◽  
Oil And Gas Reservoirs ◽  
Alkb Genes

Abstract. Alkane-degrading bacteria have long been used as an important biological indicator for oil and gas prospecting, but their ecological characteristics in hydrocarbon microseep habitats are still poorly understood. In this study, the diversity and abundance of n-alkane-degrading bacterial community in the near-surface soils of a Chinese onshore oil and gas field were investigated using molecular techniques. Terminal restriction fragment length polymorphism (T-RFLP) analyses in combination with cloning and sequencing of alkB genes revealed that Gram-negative genotypes (Alcanivorax and Acinetobacter) dominated n-alkane-degrading bacterial communities in the near-surface soils of oil and gas reservoirs, while the dominant microbial communities were Gram-positive bacteria (Mycobacterium and Rhodococcus) in background soil. Real-time quantitative polymerase chain reaction (PCR) results furthermore showed that the abundance of alkB genes increased substantially in the surface soils above oil and gas reservoirs even though only low or undetectable concentrations of hydrocarbons were measured in these soils. The results of this study implicate that trace amounts of volatile hydrocarbons migrate from oil and gas reservoirs, and likely result in the changes of microbial communities in the near-surface soil.

scholarly journals 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

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.

scholarly journals Reservoir forming conditions and exploration potential of Lower Paleozoic carbonate rocks in Gucheng area, Tarim Basin

2021 ◽  
Vol 329 ◽  
pp. 01057
Author(s):  
Liu Zheng ◽  
Yan Liping ◽  
Sun Guoxin ◽  
Ding Hansheng ◽  
Li Yanjie
Keyword(s):  
Tarim Basin ◽  
Oil And Gas ◽  
High Energy ◽  
Gas Reservoirs ◽  
Lower Paleozoic ◽  
Gas Accumulation ◽  
Yingshan Formation ◽  
The North ◽  
Exploration Target ◽  
Potential Reservoir

The Gucheng region is oil and gas accumulation area of Tarim Basin，dominated by beach controlled lithologic oil and gas reservoirs，which has superior oil and gas accumulation conditions and broad exploration prospects. The lower Paleozoic strata in the Gucheng region are the Carboniferous, Ordovician, and Cambrian systems from top to bottom. The Silurian, Devonian, and Permian systems are missing. The lower Ordovician – Cambrian are the main exploration target layers in the area. There are four reservoirs: the Ordovician group, the Yingshan group, the Penglaiba group and the Cambrian group in The Gucheng region, The upper part of the Yijianfang formation and Yingshan formation are limestone reservoir, which is a set of potential reservoir. The lower part of the Yingshan formation, the Penglaiba formation, and the Cambrian formation developed three sets of dolomite reservoirs. The distribution of oil and gas in Gucheng region was mainly found in Yijianfang formation, Yingshan formation, Penglaiba formation and Cambrian of the Ordovician. The Yingshan group and the Hanwu group were the main exploration target layers. Yingshan formation and Cambrian are the main exploration targets, and Yijianfang formation and Penglaiba formation of Ordovician can be used as the concurrent exploration targets. Gucheng region can form two major realistic exploration areas: dolomite reservoir of Ordovician and reef beach of Cambrian. The Ordovician dolomite reservoirs are mainly searched for the inner shoal of the platform edge high-energy facies belt, and the Cambrian system is mainly search for the high-energy reef beach far away from the platform edge facies belt in the north of cherchen fault.

scholarly journals Diversity and abundance of <i>n</i>-alkane degrading bacteria in the near surface soils of a Chinese onshore oil and gas field

2012 ◽  
Vol 9 (10) ◽  
pp. 14867-14887
Author(s):  
K. Xu ◽  
Y. Tang ◽  
C. Ren ◽  
K. Zhao ◽  
Y. Sun
Keyword(s):  
Bacterial Community ◽  
Oil And Gas ◽  
Gas Reservoirs ◽  
Surface Soils ◽  
Gas Field ◽  
Near Surface ◽  
Ecological Characteristics ◽  
Degrading Bacteria ◽  
Oil And Gas Field ◽  
Oil And Gas Reservoirs

Abstract. Alkane degrading bacteria have long been used as an important biological indicator for oil and gas prospecting, but their ecological characteristics in hydrocarbon microseep habitats are still poorly understood. In this study, the diversity and abundance of n-alkane degrading bacterial community in the near surface soils of a Chinese onshore oil and gas field were investigated using molecular techniques. Terminal restriction fragment length polymorphism (T-RFLP) analyses in combination with cloning and sequencing of alkB genes revealed that trace amount of volatile hydrocarbons migrated from oil and gas reservoirs caused a shift of the n-alkane degrading bacterial community from Gram-positive bacteria (Mycobacterium and Rhodococcus) to Gram-negative genotypes (Alcanivorax and Acinetobacter). Real-time PCR results furthermore showed that the abundance of alkB genes increased substantially in the surface soils underlying oil and gas reservoirs even though only low or undetectable concentrations of hydrocarbons were measured in these soils due to efficient microbial degradation. Our findings broadened the knowledge on the ecological characteristics of alkane degrading community in hydrocarbon microseeps and may provide a new approach for microbial prospecting for oil and gas (MPOG).

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