scholarly journals Origin and Distribution of Carbonate Cement in Tight Sandstones: The Upper Triassic Yanchang Formation Chang 8 Oil Layer in West Ordos Basin, China

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-13 ◽  
Author(s):  
Jin Lai ◽  
Guiwen Wang ◽  
Jing Chen ◽  
Shuchen Wang ◽  
Zhenglong Zhou ◽  
...  
Keyword(s):  
Organic Acids ◽  
Late Stage ◽  
Ordos Basin ◽  
Source Rocks ◽  
Type I ◽  
Dissolved Carbon ◽  
Carbonate Cement ◽  
Two Generations ◽  
Tight Carbonate ◽  
Ferroan Dolomite

Two generations of carbonate cement as Type I (microcrystalline calcite and dolomite) and Type II (mainly Fe-calcite and Fe-dolomite) are recognized in Chang 8 sandstones, Ordos basin. Carbonate cement in Chang 8 sandstones is closely related to the dissolved carbon from thermal maturation of organic matters. Carbonate cement in the loosely packed framework grains precipitated shortly after deposition, and late-stage ferroan calcite and ferroan dolomite formed with progressive burial. The early diagenetic carbonate cement is partially to completely replaced by late-stage ferroan calcite and ferroan dolomite. Carbonate cement is much more commonly observed in sand bodies adjacent to Chang 7 source rocks. With increasing distance from the Chang 7 oil layers, the carbonate cement content gradually decreases. However, some tight carbonate cemented zones also occur at the sandstone-mudstone interfaces. Dissolution of Ca-feldspars by organic acids-rich fluids, together with clay mineral transformations such as illitization of smectite, would provide Ca2+ and Mg2+ ions for carbonate cementation. Organic acids and CO2 rich fluids would charge into the reservoirs with the hydrocarbons, and when the CO2 and acids were buffered by the framework grain dissolution, carbonate cement would precipitate with a decrease in CO2 concentration.

Liquid hydrocarbon characterization of the lacustrine Yanchang Formation, Ordos Basin, China: Organic-matter source variation and thermal maturity

2017 ◽  
Vol 5 (2) ◽  
pp. SF225-SF242 ◽  
Author(s):  
Xun Sun ◽  
Quansheng Liang ◽  
Chengfu Jiang ◽  
Daniel Enriquez ◽  
Tongwei Zhang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Source Rock ◽  
Ordos Basin ◽  
Depositional Environments ◽  
Source Rocks ◽  
Type I ◽  
Hydrocarbon Generation ◽  
Type Ii ◽  
Thermal Maturity ◽  
Yanchang Formation

Source-rock samples from the Upper Triassic Yanchang Formation in the Ordos Basin of China were geochemically characterized to determine variations in depositional environments, organic-matter (OM) source, and thermal maturity. Total organic carbon (TOC) content varies from 4 wt% to 10 wt% in the Chang 7, Chang 8, and Chang 9 members — the three OM-rich shale intervals. The Chang 7 has the highest TOC and hydrogen index values, and it is considered the best source rock in the formation. Geochemical evidence indicates that the main sources of OM in the Yanchang Formation are freshwater lacustrine phytoplanktons, aquatic macrophytes, aquatic organisms, and land plants deposited under a weakly reducing to suboxic depositional environment. The elevated [Formula: see text] sterane concentration and depleted [Formula: see text] values of OM in the middle of the Chang 7 may indicate the presence of freshwater cyanobacteria blooms that corresponds to a period of maximum lake expansion. The OM deposited in deeper parts of the lake is dominated by oil-prone type I or type II kerogen or a mixture of both. The OM deposited in shallower settings is characterized by increased terrestrial input with a mixture of types II and III kerogen. These source rocks are in the oil window, with maturity increasing with burial depth. The measured solid-bitumen reflectance and calculated vitrinite reflectance from the temperature at maximum release of hydrocarbons occurs during Rock-Eval pyrolysis ([Formula: see text]) and the methylphenanthrene index (MPI-1) chemical maturity parameters range from 0.8 to [Formula: see text]. Because the thermal labilities of OM are associated with the kerogen type, the required thermal stress for oil generation from types I and II mixed kerogen has a higher and narrower range of temperature for hydrocarbon generation than that of OM dominated by type II kerogen or types II and III mixed kerogen deposited in the prodelta and delta front.

The coupled generation of organic acids and hydrocarbons during source rock maturation

2020 ◽  
Author(s):  
Jian Chen ◽  
Jie Xu ◽  
Zhenyu Sun ◽  
Susu Wang ◽  
Wanglu Jia ◽  
...  
Keyword(s):  
Organic Acids ◽  
Source Rock ◽  
Maximum Yield ◽  
Source Rocks ◽  
Type I ◽  
Hydrocarbon Generation ◽  
Pore Waters ◽  
Reservoir Properties ◽  
Type Iii ◽  
Short Period

<p><strong>Introduction: </strong>Organic acids which are commonly detected in oilfield waters, can partially enhance reservoir properties. Previous studies have suggested that cleavage of the oxygen-containing functional group in kerogen is a major source of organic acids. However, this cleavage is assumed to occur before the source rock enters the oil window. If this is correct, then these acids can dissolve only minerals in the source rocks. Presently, no detailed study of the generation of organic acids during the whole thermal maturation of source rocks has been conducted. It is unclear whether organic acids could migrate into reservoirs.</p><p><strong>Aim: </strong>This research simulated the thermal evolution of source rocks in order to build a coupled model of organic acid and hydrocarbon generation, and investigate if organic acids generated in source rocks can migrate into reservoirs.</p><p><strong>Methods: </strong>Three immature source rocks containing type I, II, and III kerogens were crushed to 200 mesh. These powders, along with deionized water, were sealed in Au tubes and heated to 220–360°C for 72 h (EasyRo 0.37-1.16%). All the run products, including organic acids, gas, and bitumen, were analyzed.</p><p><strong>Results: </strong>At all temperatures, the organic acids dissolved in the waters are composed of formate, acetate, propionate, and oxalate. Acetate is the major compound with a modal proportion of >83%. The maximum yield of total organic acids was from source rocks containing type I kerogen (31.0 mg/g TOC), which was twice that from source rocks containing type II and III kerogens (13.3–15.4 mg/g TOC). However, for the type I and II kerogen-bearing source rocks, the organic acids reached a maximum yield (EasyRo = 1.16%) following the bitumen generation peak (EasyRo = 0.95%). Organic acids from type III kerogen-bearing source rocks reached their maximum yield (EasyRo = 0.95%) before the source rock entered the gas window (EasyRo > 1.16%).</p><p><strong>Conclusions: </strong>Our data suggest that the generation of organic acids is coupled with the generation of oil from type I and II kerogen-bearing source rocks, but form earlier than gas from type III kerogen-bearing source rocks. As such, some organic acids dissolved in pore waters are possibly expelled from source rocks containing type I and II kerogen with oils, which can then migrate into reservoirs. Migration of organic acids into reservoirs from source rocks containing type III kerogen is also possible in some situations. For example, when a source rock is rapidly buried for a short period, such as in the Kuqa Depression, Tarim Basin, China, the generation interval of organic acids and gas is short. Both could be expelled outside and migrate upwards into reservoirs. In conclusion, organic acids derived from source rocks can contribute to reservoir alteration.</p>

scholarly journals The impacts of diagenetic facies on reservoir quality in tight sandstones

2020 ◽  
Vol 12 (1) ◽  
pp. 1060-1082
Author(s):  
Dazhong Ren ◽  
Liang Sun ◽  
Rongxi Li ◽  
Dengke Liu
Keyword(s):  
Pore Structure ◽  
Ordos Basin ◽  
Source Rocks ◽  
Reservoir Quality ◽  
Carbonate Content ◽  
Porosity Evolution ◽  
Carbonate Cement ◽  
Pore Structures ◽  
Diagenetic Facies ◽  
The Impact

AbstractThe impact of diagenetic minerals and the characteristics of pore structures on reservoir qualities has been studied separately in the past years. However, the difference in the reservoir quality with different pore structures and having same or similar content of diagenesis minerals has not been ascertained. In this study, based on the core samples derived from Chang 6 member in the Ordos basin, various tests were performed to examine the sandstone diagenesis and investigate the pore structure. The results showed that there were five diagenetic facies by diagenetic and pore structure analyses, and the best reservoir quality rocks were found to have relatively low percentage of illite, carbonate cement, pore-filling chlorite, authigenic quartz, and relatively high proportion of intergranular pores. Smectite-to-illite reaction and chemical compaction were main sources for quartz cementation at 60–120°C, and carbonate content was found to increase toward source rocks. The porosity depth trends significantly affected the diagenetic facies. The diagenetic and the pore structure pathways of various diagenetic facies were reconstructed by integrated petrographic, mineralogical, and pore system data. This study provides insights into the porosity evolution and diagenetic pathways of various diagenetic facies of tight sandstones, and the influence of diagenesis minerals and pore structures on their reservoir quality.

COMPARISON OF SELECTED NON-MARINE PETROLEUM-BEARING BASINS IN AUSTRALIA AND CHINA

1986 ◽  
Vol 26 (1) ◽  
pp. 285
Author(s):  
P.S. Moore D.K. Hobday H. Mai ◽  
Z.C. Sun
Keyword(s):  
Ordos Basin ◽  
Sedimentary Facies ◽  
Alluvial Fan ◽  
Source Rocks ◽  
Local Source ◽  
Type I ◽  
Migration Routes ◽  
Factors Affecting ◽  
Half Graben ◽  
Oil Source

This paper summarises the geology and hydrocarbon potential of two Chinese and two Australian basins (Ordos, Northern Jiangsu, Eromanga, and Surat basins) in order to compare factors affecting the generation, migration, and entrapment of hydrocarbons. In all four basins, hydrocarbons are generated from nonmarine source rocks of lacustrine and fluvial-overbank origin. While the Chinese and Australian basins contain a similar range of sedimentary facies, from alluvial fan to lacustrine, the arrangement and relative thicknesses of these facies vary considerably as a result of different tectonic and palaeoclimatic settings.During the Triassic, the Ordos Basin was dominated by retroarc foredeep subsidence and the development of deep, fresh-water lakes with anoxic bottom waters. This non-bioturbated substrate, with Type I and II kerogen precursors, provided an excellent oil source for adjacent fan-delta, deltaic, and fluvial reservoirs, and for the unconformably overlying Jurassic fluvial valley-fill sandstone reservoirs.The Northern Jiangsu Basin was initiated by back-arc extension and underwent very rapid half-graben subsidence in the Eocene. Alluvial fan, shoreline, and fluvial facies aggraded in a relatively narrow zone along the active, faulted margin, and merged laterally into organic-rich shales which provided a local source for oil.By comparison, the Eromanga/Surat basins developed in response to gentle downwarp and reactivation of older structural trends. Reservoirs are largely restricted to craton-derived quartzose facies such as in the Hutton, Precipice, and Namur sandstones. There is probably a dual source for oil, from the underlying Permian (which may be the dominant source in the Surat Basin), and from shales deposited in shallow, partly oxygenated lakes and overbank facies of Jurassic age (important in the Eromanga, and possibly subordinate in the Surat Basin). Deep lacustrine facies, typical of the Chinese basins, did not develop. The greater abundance of oil in the Chinese nonmarine basins is explained in terms of tectonic and palaeoclimatic factors which yielded thicker and better quality source rocks, more rapid maturation, and a better juxtaposition of source rocks and good-quality reservoirs, thus providing short, highly efficient migration routes.

scholarly journals Climate-Provenance Effect on the Organic Matter Enrichment of the Chang 9 Source Rocks in the Central Ordos Basin, China

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Ling Ma ◽  
Zhihuan Zhang ◽  
Weiqiu Meng
Keyword(s):  
Organic Matter ◽  
Chemical Weathering ◽  
Ordos Basin ◽  
Source Rocks ◽  
Sediment Provenance ◽  
Type I ◽  
Hydrocarbon Generation ◽  
Hydrocarbon Generation Potential ◽  
Primary Producer ◽  
Geochemical Analyses

The Upper Triassic Chang 9 organic-rich sediments have been considered as effective hydrocarbon source rocks for the Mesozoic petroleum system in the Ordos Basin. Previous studies on the Chang 9 member mostly focused on the influence of their paleoproductivity and paleoredox conditions on the organic matter (OM) enrichment, whereas there are few studies on the influence of the paleoclimate condition and sediment provenance on the OM enrichment. In this study, a series of geochemical analyses was performed on the Chang 9 core samples, and their hydrocarbon generation potential, paleoclimate condition, and sediment provenance were assessed to analyze the effect of paleoclimate-provenance on OM enrichment. The Chang 9 source rocks are characterized by high OM abundance, type I−II OM type, and suitable thermal maturity, implying good hydrocarbon generation potential. Based on the C-values and Sr/Cu ratios, the paleoclimate condition of the Chang 9 member was mainly semihumid. In addition, the Th/Co vs. La/Sc diagram and negative δEuN indicate that the Chang 9 sediments were mainly derived from felsic source rocks. Meanwhile, the paleoweathering intensity of the Chang 9 member is moderate based on moderate values of CIA, PIA, and CIW, which corresponds to the semihumid paleoclimate. The relatively humid paleoclimate not only enhances photosynthesis of the primary producer, but also promotes chemical weathering intensity, leading to suitable terrestrial clastic influx to the lacustrine basin, which is beneficial for OM enrichment.

Analysis of Fault Characteristics and Reservoir Forming Control in Middle Fault Depression Belt in Hailer-Tamtsag Basin

2012 ◽  
Vol 616-618 ◽  
pp. 174-184
Author(s):  
Yong He Sun ◽  
Lin Kang ◽  
Feng Xiang Yang ◽  
Xue Song Li
Keyword(s):  
Oil And Gas ◽  
Source Rocks ◽  
Fault System ◽  
Type I ◽  
Weathering Crust ◽  
Gas Migration ◽  
Block Boundary ◽  
System Type ◽  
Fracture Damage ◽  
Buried Hill

In order to reveal in middle fault depression belt of Hailer-Tamtsag Basin buried hill oil and gas migration and accumulation characteristics, we summarize controlling effect of fault on oil and gas migration and accumulation of buried hill, which by analysing genetic mechanism of buried hills based on fault systems formation and evolution. Research shows that three types of fault system in Hailer-Tamtsag Basin: early stretched fault system(Type I), early stretched middle tensile shearing fault system(Type I-II), early stretched middle tensile shearing reverse late fault system(Type I-II-III). Type I-II and I-II-III are stretching by NW tensional stress in Nantun group ,which afford tectonic framework for syngenesis buried hill and epigenetic buried hill. Type I make buried hills complicated .It is also favorable to ancient geomorphological buried hill in the fault less affected zones. Although they formed cracks dense zone easier, Type I-II and I-II-III fault system damage the reservoir which is not conducive to " hydrocarbon-supplying window " formation; Type I fault system have less promotion on the development of the buried hill reservoir, while it is conducive to hydrocarbon accumulation as the block boundary in buried hill hydrocarbon. Fault formed source rocks two kinds for hydrocarbon mode: unidirectional and bidirectional, which formed two reservoir-forming pattern: Unidirectional transportation hydrocarbon of weathering crust or hydrocarbon of fracture damage zones and bidirectional transportation hydrocarbon of weathering crust or hydrocarbon of fracture damage zones.

scholarly journals Light hydrocarbon geochemical characteristics and their application in Upper Paleozoic, Shenmu gas field, Ordos Basin

2016 ◽  
Vol 35 (1) ◽  
pp. 103-121 ◽  
Author(s):  
Wenxue Han ◽  
Shizhen Tao ◽  
Guoyi Hu ◽  
Weijiao Ma ◽  
Dan Liu ◽  
...  
Keyword(s):  
Natural Gas ◽  
Ordos Basin ◽  
Light Hydrocarbon ◽  
Source Rocks ◽  
Higher Plant ◽  
Gas Field ◽  
Gas Source ◽  
Upper Paleozoic ◽  
Methyl Cyclohexane ◽  
Normal Stage

Light hydrocarbon has abundant geochemical information, but there are few studies on it in Shenmu gas field. Taking Upper Paleozoic in Shenmu gas field as an example, authors use gas chromatography technology to study light hydrocarbon systematically. The results show that (1) The Shenmu gas field is mainly coal-derived gas, which is mixed by partial oil-derived gas due to the experiment data. (2) Based on K1, K2 parameter and Halpern star chart, the Upper Paleozoic gas in Shenmu gas field belongs to the same petroleum system and the depositional environment of natural gas source rocks should be homologous. (3) The source rocks are mainly from terrestrial higher plant origins and belong to swamp facies humic due to methyl cyclohexane index and Mango parameter intersection chart, which excluded the possibility of the Upper Paleozoic limestone as source rocks. (4) The isoheptane ranges from 1.45 to 2.69 with an average of 2.32, and n-heptane ranges from 9.48 to 17.68% with an average of 11.71%, which is below 20%. The maturity of Upper Paleozoic gas in Shenmu gas field is low-normal stage, which is consistent with Ro data. (5) The Upper Paleozoic natural gas in the Shenmu gas field did not experience prolonged migration or secondary changes, thus can be analyzed by light hydrocarbon index precisely.

scholarly journals Analysis of the charging process of the lacustrine tight oil reservoir in the Triassic Chang 6 Member in the southwest Ordos Basin, China

2017 ◽  
Vol 54 (12) ◽  
pp. 1228-1247
Author(s):  
Zhengjian Xu ◽  
Luofu Liu ◽  
Tieguan Wang ◽  
Kangjun Wu ◽  
Wenchao Dou ◽  
...  
Keyword(s):  
Ordos Basin ◽  
Source Rocks ◽  
Driving Mechanism ◽  
Tight Oil ◽  
Geological Time ◽  
Tight Sandstone ◽  
Main Production ◽  
The Ordos Basin ◽  
Homogenization Temperatures ◽  
Quartz Grains

With the success of Bakken tight oil (tight sandstone oil and shale oil) and Eagle Ford tight oil in North America, tight oil has become a research focus in petroleum geology. In China, tight oil reservoirs are predominantly distributed in lacustrine basins. The Triassic Chang 6 Member is the main production layer of tight oil in the Ordos Basin, in which the episodes, timing, and drive of tight oil charging have been analyzed through the petrography, fluorescence microspectrometry, microthermometry, and trapping pressure simulations of fluid inclusions in the reservoir beds. Several conclusions have been reached in this paper. First, aqueous inclusions with five peaks of homogenization temperatures and oil inclusions with three peaks of homogenization temperatures occurred in the Chang 6 reservoir beds. The oil inclusions are mostly distributed in fractures that cut across and occur within the quartz grains, in the quartz overgrowth and calcite cements, and the fractures that occur within the feldspar grains, with blue–green, green, and yellow–green fluorescence colours. Second, the peak wavelength, Q650/500, and QF535 of the fluorescence microspectrometry indicate three charging episodes of tight oil with different oil maturities. The charging timings (141–136, 126–118, and 112–103 Ma) have been ascertained by projecting the homogenization temperatures of aqueous inclusions onto the geological time axis. Third, excess-pressure differences up to 10 MPa between the Chang 7 source rocks and the Chang 6 reservoir beds were the main driving mechanism supporting the process of nonbuoyancy migration.

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