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21 pages, 23614 KiB

Open AccessArticle

Effect of Acid Fluid on Deep Eocene Sweet Spot Reservoir of Steep Slope Zone in Lufeng Sag, Pearl River Mouth Basin, South China Sea

by Kai Zhong, Lihao Bian, Shijie Zhao and Kailong Feng

Processes 2024, 12(5), 895; https://doi.org/10.3390/pr12050895 - 28 Apr 2024

Viewed by 340

Abstract

The Paleogene system of the Zhuyi Depression exhibits a pronounced mechanical compaction background. Despite this compaction, remarkable secondary porosity is observed in deep clastic rocks due to dissolution processes, with well-developed hydrocarbon reservoirs persisting in deeper strata. We conducted a comprehensive study utilising [...] Read more.

The Paleogene system of the Zhuyi Depression exhibits a pronounced mechanical compaction background. Despite this compaction, remarkable secondary porosity is observed in deep clastic rocks due to dissolution processes, with well-developed hydrocarbon reservoirs persisting in deeper strata. We conducted a comprehensive study utilising various analytical techniques to gain insights into the dissolution and transformation mechanisms of deep clastic rock reservoirs in the steep slope zone of the Lufeng Sag. The study encompassed the collection and analysis of the rock thin sections, XRD whole-rock mineralogy, and petrophysical properties from seven wells drilled into the Eocene. Our findings reveal that the nature of the parent rock, tuffaceous content, dominant sedimentary facies, and the thickness of individual sand bodies are crucial factors that influence the development of high-quality reservoirs under intense compaction conditions. Moreover, the sustained modification and efficient expulsion of organic–inorganic acidic fluids play a main role in forming secondary dissolution porosity zones within the En-4 Member of the LF X transition zone. Notably, it has been established that the front edge of the fan delta, the front of the thin layer, and the near margin of the thick layer of the braided river delta represent favorable zones for developing deep sweet-spot reservoirs. Furthermore, we have identified the LF X and LF Y areas as favourable exploration zones and established an Eocene petroleum-accumulation model. These insights will significantly aid in predicting high-quality dissolution reservoirs and facilitate deep oil and gas exploration efforts in the steep slope zone of the Zhuyi Depression. Full article

(This article belongs to the Special Issue Organic–Inorganic Interactions and Their Significance for Hydrocarbon Generation in Deep Formations)

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10 pages, 2131 KiB

Open AccessArticle

Generation Potential and Characteristics of Kerogen Cracking Gas of Over-Mature Shale

by Lin Zhang, Zhili Du, Xiao Jin, Jian Li and Bin Lu

Processes 2024, 12(3), 528; https://doi.org/10.3390/pr12030528 - 6 Mar 2024

Viewed by 465

Abstract

To investigate the characteristics and generation potential of gas generated from over-mature shale, hydrous and anhydrous pyrolysis experiments were carried out on the Longmaxi Formation in the Anwen 1 well of the Sichuan Basin of China at temperatures of 400–598 °C and pressures [...] Read more.

To investigate the characteristics and generation potential of gas generated from over-mature shale, hydrous and anhydrous pyrolysis experiments were carried out on the Longmaxi Formation in the Anwen 1 well of the Sichuan Basin of China at temperatures of 400–598 °C and pressures of 50 Mpa, with (hydrous) and without (anhydrous) the addition of liquid water. The results show that in the presence of water, the total yield of carbon-containing gases (i.e., the sum of methane, ethane, and carbon dioxide) was increased by up to 1.8 times when compared to the total yield from the anhydrous pyrolysis experiments. The increased yield of carbon dioxide and methane accounted for 89% and 10.5% of the total increased yield of carbon-containing gases. This indicated that the participation of water could have promoted the release of carbon from over-mature shale, like we used in this study. The methane generated in the hydrous pyrolysis experiments was heavier, with a δ¹³C value of −21.27‰ (544 °C) compared to that generated in the anhydrous pyrolysis experiments, which showed a lighter δ¹³C of −33.70‰ (544 °C). It is noteworthy that the δ¹³C values of the methane from hydrous pyrolysis at >500 °C were even heavier than that of the kerogen from the over-mature shale, although the δ¹³C values of the methane show an overall increasing trend with increasing temperature both in hydrous and anhydrous pyrolysis. The carbon dioxide from hydrous pyrolysis was less enriched in ¹³C relative to that from anhydrous pyrolysis. Specifically, the δ ¹³C values of the carbon dioxide increased with the increasing temperature in anhydrous pyrolysis, whereas they remained nearly constant with increasing temperature in hydrous pyrolysis. The overall lighter δ¹³C values of the carbon dioxide generated in the hydrous pyrolysis experiments likely indicate that water tends to prompt the release of lighter carbon and/or suppress the release of heavier carbon from over-mature shale in the form of carbon dioxide, especially at higher temperatures, for example, of >510 °C. Full article

(This article belongs to the Special Issue Organic–Inorganic Interactions and Their Significance for Hydrocarbon Generation in Deep Formations)

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21 pages, 9558 KiB

Open AccessArticle

Paleo-Sedimentary Environments and Controlling Factors for Enrichment of Organic Matter in Alkaline Lake Sediments: A Case Study of the Lower Permian Fengcheng Formation in Well F7 at the Western Slope of Mahu Sag, Junggar Basin

by Gangqiang Chen, Yuantao Tang, Yuhang Nan, Fan Yang and Dongyong Wang

Processes 2023, 11(8), 2483; https://doi.org/10.3390/pr11082483 - 18 Aug 2023

Viewed by 961

Abstract

The Lower Permian Fengcheng formation is a significant source of rocks and a reservoir for the Mahu Sag in the Junggar Basin. Recently, the paleo-environment deposition factors of the P₁f formation have become a popular research topic. This research was conducted [...] Read more.

The Lower Permian Fengcheng formation is a significant source of rocks and a reservoir for the Mahu Sag in the Junggar Basin. Recently, the paleo-environment deposition factors of the P₁f formation have become a popular research topic. This research was conducted using data from the F7 well of Mahu Sag, based on the geochemical analysis results of TOC (total organic carbon), REE (rare earth elements), and major and trace elements of 53 samples from P₁f (Lower Permian Fengcheng formation), and some deposition factors are discussed. The P₁f deposition process was classified into four stages based on paleo-environment elemental indicators. This research describes the deposition process of the evolution of alkaline lakes. The early and preliminary stages of alkali lake evolution are considered as late P₁f₁ to middle P₁f₂; the paleoclimate of this process was dry, the reduction conditions increased, and the paleo-productivity and lake salinity were enhanced. The terminal stage of alkali lake evolution is considered as late P₁f₂ to middle P₁f₃; in this period, the paleoclimate changed with seasonal cycles, resulting in a decrease in water salinity and an increase in oxidation; the paleo-productivity of the alkaline lake was at a medium level. Until the end of P₁f₃, the salinity of the lake decreased, and the water body became anoxic and weakly alkaline. Furthermore, the research on TOC and sedimentary parameters confirmed that the deposition of P₁f organic matter is affected by multiple types of factors. A relatively warm climate, lack of oxygen, fresh water–brackish water, suitable debris flow, and high primary productivity conditions promoted organic matter deposition. Full article

(This article belongs to the Special Issue Organic–Inorganic Interactions and Their Significance for Hydrocarbon Generation in Deep Formations)

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17 pages, 9439 KiB

Open AccessArticle

Hydrocarbon Generation History of the Eocene Source Rocks in the Fushan Depression, South China Sea: Insights from a Basin Modeling Study

by Bang Zeng, Zhenghuan Lu, Taotao Yang, Yang Shi, Hao Guo, Xin Wang, Feiyan Liao and Meijun Li

Processes 2023, 11(7), 2051; https://doi.org/10.3390/pr11072051 - 10 Jul 2023

Viewed by 948

Abstract

Reconstruction of hydrocarbon generation history is essential to understanding the petroleum system. In this study, basin modeling was employed to investigate the primary source rocks in the Fushan Depression (FD), a significant oil-bearing basin situated in the South China Sea. The research findings [...] Read more.

Reconstruction of hydrocarbon generation history is essential to understanding the petroleum system. In this study, basin modeling was employed to investigate the primary source rocks in the Fushan Depression (FD), a significant oil-bearing basin situated in the South China Sea. The research findings indicate that different tectonic zones within the FD underwent distinct hydrocarbon generation stages. The step-fault zone and the central sag zone experienced one hydrocarbon generation stage at 10–0 Ma and 30–0 Ma, respectively. The slope zone, on the other hand, experienced two hydrocarbon generation stages, 40–23.5 Ma and 10–0 Ma, controlled by tectonic movements and heat flow variations. Furthermore, critical times for the process of the petroleum system have been determined based on this work and previous literature. The slope zone in the eastern FD is considered a favorable area for conventional hydrocarbon exploration due to the high maturity of source rocks promoted by volcanic heating and two significant oil charges. The central sag zone is identified as an excellent prospect for unconventional resources because of the substantial retention of hydrocarbons in in-source unconventional reservoirs long after hydrocarbon generation. These findings provide a valuable guide for further exploration. Full article

(This article belongs to the Special Issue Organic–Inorganic Interactions and Their Significance for Hydrocarbon Generation in Deep Formations)

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12 pages, 5720 KiB

Open AccessArticle

Experimental Study about Shale Acceleration on Methane Cracking

by Jingkui Mi, Xianming Xiao, Jinhao Guo, Kun He and Xingzhi Ma

Processes 2023, 11(7), 1908; https://doi.org/10.3390/pr11071908 - 25 Jun 2023

Viewed by 726

Abstract

The temperature or maturity limit of methane (CH₄) cracking is very useful for the determination of the most depth or the highest maturity in natural gas exploration owing to the composition of over mature gas. In this work, three series of [...] Read more.

The temperature or maturity limit of methane (CH₄) cracking is very useful for the determination of the most depth or the highest maturity in natural gas exploration owing to the composition of over mature gas. In this work, three series of CH₄ cracking experiments were conducted under different conditions of N₂ + CH₄, N₂ + CH₄ + montmorillonite and N₂ + CH₄ + shale, respectively, in a gold tube system. The experimental results show that some heavy gas with negative carbon isotope composition could be generated in the three series experiments and that shale has more intense catalysis for CH₄ cracking than montmorillonite. The catalysis of metal elements distributed in the minerals of shale is attributed to CH₄ cracking acceleration. The shale catalysis makes the maturity threshold of CH₄ substantial cracking decrease from 6.0%R_o under no catalysis, to 4.5%R_o under a shale system in a geological setting. Nevertheless, we suggest not to lightly practice natural gas exploration in shale with the maturity range of 3.5–4.5%R_o, as the maturity threshold of gas generation from oil prone organic matter distributed extensively in shale is 3.5%R_o. Full article

(This article belongs to the Special Issue Organic–Inorganic Interactions and Their Significance for Hydrocarbon Generation in Deep Formations)

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13 pages, 3249 KiB

Open AccessArticle

Generation Time and Accumulation of Lower Paleozoic Petroleum in Sichuan and Tarim Basins Determined by Re–Os Isotopic Dating

by Jie Wang, Liangbang Ma, Cheng Tao, Wenhui Liu and Qingwei Dong

Processes 2023, 11(5), 1472; https://doi.org/10.3390/pr11051472 - 12 May 2023

Viewed by 1033

Abstract

With the targets of petroleum exploration transferred to the deep and ancient strata, abundant oil and gas resources have been found in Lower Paleozoic and older strata in central and western China. Due to complex evolutionary processes including multiple episodes of hydrocarbon accumulation [...] Read more.

With the targets of petroleum exploration transferred to the deep and ancient strata, abundant oil and gas resources have been found in Lower Paleozoic and older strata in central and western China. Due to complex evolutionary processes including multiple episodes of hydrocarbon accumulation and ubiquitously accompanied by secondary alterations, significant uncertainties remain concerning the generation time and accumulation processes of these revealed petroleum sources. In this paper, relative pure Re and Os elements existing in the asphaltene fractions of Lower Cambrian solid bitumen collected from the Guangyuan area, western Sichuan Basin, SW China and Middle–Lower Ordovician heavy oils in the Aiding area of the Tahe oilfield in the Tarim Basin, NW China were successfully obtained by sample pretreatments, and Re–Os isotopic analysis was subsequently carried out for the dating of these. The Re–Os isotopic composition indicates a generation time of Guangyuan bitumen to between 572 Ma and 559 Ma, corresponding to the late Sinian period of the Neoproterozoic era. By the means of Re–Os isochron aging, initial ¹⁸⁷Os/¹⁸⁸Os ratios, and carbon isotopic compositions, the Lower Cambrian bitumen is supposed to originate from source rocks of the Doushantuo Formation in the Sinian strata and subsequently migrated into the reservoirs of the Dengying Formation. This previously reserved petroleum was transformed into its present bitumen state by the destruction of reservoirs caused by tectonic uplift. The Re–Os dating results of Middle–Lower Ordovician heavy oil of Tarim Basin suggest that it was formed between 450 Ma to 436 Ma, corresponding to the Late Ordovician–Early Silurian system, and the generated petroleum likely migrate into the Middle–Lower Ordovician karst reservoirs to form early oil reservoirs. With tectonic uplift, these oil reservoirs were degraded and reformed to the heavy-oil reservoirs of today. Full article

(This article belongs to the Special Issue Organic–Inorganic Interactions and Their Significance for Hydrocarbon Generation in Deep Formations)

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20 pages, 8287 KiB

Open AccessArticle

Differential Enrichment of Trace and Major Elements in Biodegraded Oil: A Case Study from Bohai Bay Basin, China

by Haifeng Yang, Deying Wang, Feilong Wang, Yanfei Gao, Guomin Tang, Youjun Tang and Peng Sun

Processes 2023, 11(4), 1176; https://doi.org/10.3390/pr11041176 - 11 Apr 2023

Viewed by 1580

Abstract

Inorganic elements in crude oil have been used in the reconstruction of the sedimentary environment and oil–oil (source) correlations; however, the effect of biodegradation on these elements has not been investigated sufficiently. In this study, 14 crude oils from the Miaoxi Sag of [...] Read more.

Inorganic elements in crude oil have been used in the reconstruction of the sedimentary environment and oil–oil (source) correlations; however, the effect of biodegradation on these elements has not been investigated sufficiently. In this study, 14 crude oils from the Miaoxi Sag of the Bohai Bay Basin, eastern China, were analyzed using molecular markers, trace elements, and major elements to determine the effect of biodegradation on inorganic elements. The molecular markers indicated that the oils are in the low maturity stage and are derived from similar parent materials in lacustrine source rocks. The high-sulfur oil came from a more reductive and saltier environment compared with the low-sulfur oil. The oils were subjected to varying degrees of biodegradation. The concentrations of Mg, Ca, Mn, Fe, Be, Sc, Rb, Sr, Zr, Pb, Th, and U increased significantly throughout the biodegradation process, while the concentrations of Na, K, Ti, Al, Cr, Zn, Cs, Nb, Ba, Hf, and Tl increased considerably only during the intense biodegradation stage (PM < 4). The concentrations of P, Li, V, Co, Ni, Cu, Ga, Sn, and Ta were not correlated with the level of biodegradation. The V/Ni, V/Co, Ni/Co, Cr/V, Sc/V, and Th/U ratios were affected by biodegradation when PM ≥ 4. Several ratios, including Mg/P, Ca/P, Mn/P, and Fe/P, are proposed as favorable indicators of the level of biodegradation. Differential enrichment of these elements is associated with the effects of organic acids generated by biodegradation on the oil–water–rock interactions in the reservoir. Full article

(This article belongs to the Special Issue Organic–Inorganic Interactions and Their Significance for Hydrocarbon Generation in Deep Formations)

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15 pages, 10893 KiB

Open AccessArticle

Effect of Clay Minerals and Rock Fabric on Hydrocarbon Generation and Retention by Thermal Pyrolysis of Maoming Oil Shale

by Kang Li, Qiang Wang, Hongliang Ma, Huamei Huang, Hong Lu and Ping’an Peng

Processes 2023, 11(3), 894; https://doi.org/10.3390/pr11030894 - 16 Mar 2023

Cited by 1 | Viewed by 1315

Abstract

In traditional kerogen pyrolysis experiments, the effects of minerals and rock fabric on the pyrolysis products were ignored. To further clarify the role of the mineral matrix and rock fabric on hydrocarbon generation and retention, a closed anhydrous pyrolysis experiment was conducted on [...] Read more.

In traditional kerogen pyrolysis experiments, the effects of minerals and rock fabric on the pyrolysis products were ignored. To further clarify the role of the mineral matrix and rock fabric on hydrocarbon generation and retention, a closed anhydrous pyrolysis experiment was conducted on core plugs, powdered rock and kerogen from a clay-rich sample of Maoming oil shale within a temperature range of 312 °C to 600 °C, at a fixed pressure of 30 Mpa. The experiment’s results showed that the yields of heavy hydrocarbons (C₁₄₊) generated from the core plugs and powdered rock were obviously lower than that of kerogen, which may be caused by the retention effect of clay minerals in raw shale. The yields of gaseous hydrocarbons generated from core plugs were lower compared with powdered rock due to the retention of C₂₊ hydrocarbons by the intact rock fabric and the preferential generation of methane. Light hydrocarbon (C_6-14) yields generated from the core plugs and powdered rock were higher than kerogen, which may be the consequence of the cleavage of extraction bitumen and the interactions with kerogen. Moreover, the ratios of iso to normal paraffin (iC₄/nC₄, iC₅/nC₅) of the core plugs and powdered rock were higher than kerogen. Our experimental results show that kerogen pyrolysis in a confined system may overestimate the hydrocarbon generation potential due to the negligence of the retention effect of minerals and the rock fabric, especially in the source rocks rich in clay minerals. Full article

(This article belongs to the Special Issue Organic–Inorganic Interactions and Their Significance for Hydrocarbon Generation in Deep Formations)

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