Direct evidence for fluid overpressure during hydrocarbon generation and expulsion from organic-rich shales

Wang, Miao; Chen, Yong; Bain, Wyatt M.; Song, Guoqi; Liu, Keyu; Zhou, Zhenzhu; Steele‐MacInnis, Matthew

doi:10.1130/g46650.1

Cited by 49 publications

(22 citation statements)

References 24 publications

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“…Fluid inclusions directly record the paleofluid, and is the main method to study paleofluid activities (Wang et al, 2020). In this paper, fluid inclusion analysis was used to describe the fluid evolution of reservoir, and then to analyze the fluid activities in source rocks.…”

Section: Samples and Methodsmentioning

confidence: 99%

The Fluid Evolution of Ancient Carbonate Reservoirs in Sichuan Basin and Its Implication for Shale Gas Exploration

2021

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Sichuan Basin is the only successful basin for shale gas exploration in China. In addition to the main shale in the Lower Silurian Longmaxi formation, the lower Cambrian Qiongzhusi shale is an important potential formation. However, it was once considered that shale gas is difficult to enrich because of its poor sealing conditions and hydrocarbon migration to adjacent reservoirs. With the increasing research on hydrocarbon generation and reservoir in shale of Qiongzhusi Formation in recent years, it has become an important exploration target in Sichuan Basin. The enrichment of oil and gas is closely related to fluid activities. Limited by the degree of exploration, there is little analysis of fluid activities in Qiongzhusi Formation, and there is little analysis of shale gas enrichment potential from the perspective of fluid. The hydrocarbon generated from Qiongzhusi shale in the rift could migrate laterally to the uplift area and form a reservoir in Dengying Formation. The fluid activities from source rock to reservoir are basically the same. Therefore, this paper reconstructed the history of hydrocarbon activities in Dengying reservoirs based on fluid inclusion analysis. Then the fluid activity process in Qiongzhusi shale was studied, and its enrichment conditions of shale gas was discussed. The results show that the hydrocarbon activities of Dengying Formation can be divided into three stages: 1) oil charging stage, 2) oil cracking gas generation stage and 3) gas reservoir adjustment stage. The first stage is under normal pressure, and the second and third stages developed overpressure with pressure coefficients of 1.3 and 1.2, respectively. High pressure coefficient is an important indicator of shale gas enrichment. Because the source rock of Qiongzhusi Formation has always been the main source rock of Dengying Formation, it can supply hydrocarbon to Dengying Formation only with overpressure in gas generation stage. Therefore, overpressure in the last two stages of gas generation indeed existed. As long as the sealing condition of shale itself is not particularly poor, shale gas “sweet points” would be formed. Therefore, the thick shale in Deyang-Anyue rift is the focus of shale gas exploration in Qiongzhusi Formation.

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Section: Samples and Methodsmentioning

confidence: 99%

The Fluid Evolution of Ancient Carbonate Reservoirs in Sichuan Basin and Its Implication for Shale Gas Exploration

2021

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“…Other diagenesis, such as hydrocarbon generation overpressure in shale, also belongs to positive diagenesis. The generated gas will make the laminated shales open more in the bed-normal direction, which favors incipient vein opening between laminae, even in the absence of deviatoric stress [3]. Veins filled with brittle minerals, such as quartz or calcite veins, are more conducive to the generation of fractured media, which is highly significant for the production of shale gas [4] and the immiscible two-phase flow (in oil zone with a gas cap) displacement [5].…”

Section: Introductionmentioning

confidence: 99%

Study on Hydrocarbon Accumulation Periods Based on Fluid Inclusions and Diagenetic Sequence of the Subsalt Carbonate Reservoirs in the Amu Darya Right Bank Block

et al. 2022

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In order to provide paleofluid evidence of hydrocarbon accumulation periods in the Amu Darya Right Bank Block, microexperiments and simulations related to the Middle-Upper Jurassic Callovian-Oxfordian carbonate reservoirs were performed. On the basis of petrographic observation, the diagenetic stages were divided by cathodoluminescence, and the entrapment stages of fluid inclusions were divided by laser Raman experiment and UV epifluorescence. The hydrocarbon generation (expulsion) curve and burial (thermal) history curve of source rocks were simulated by using real drilling data coupled with geochemical parameters of source rocks, such as total organic carbon (TOC) and vitrinite reflectance ( R o ). The above results were integrated with microthermometry of fluid inclusions by inference the timing of hydrocarbon migration into the carbonate reservoirs. The horizon-flattening technique was used to process the measured seismic profile and restore the structural evolution profile. Four diagenetic periods and three hydrocarbon accumulation periods were identified. (i) For Syntaxial stage, the fluid captured by the overgrowing cement around particles is mainly seawater; (ii) for (Early) Mesogenetic burial stage, the calcite cements began to capture hydrocarbon fluids and show yellow fluorescence under UV illumination; (iii) for (Late) Mesogenetic burial stage, two sets of cleavage fissures developed in massive calcite cements, and oil inclusions with green fluorescence were entrapped in the crystal; (iv) for Telogenetic burial stage, blue fluorescent inclusions along with hydrocarbon gas inclusions developed in dully luminescent calcite veins. Based on the accurate division of hydrocarbon migration and charging stages, combined with the structural evolution history of the traps, the hydrocarbon accumulation model was established. Because two of the three sets of source rocks are of marine origin, resulting in the lack of vitrinite in the kerogen of those source rocks, there may be some deviation between the measured value of R o and the real value. Some systematic errors may occur in the thermal history and hydrocarbon generation (expulsion) history of the two sets of source rocks. Due to the limitations of seismic horizon-flattening technique—such as the inability to accurately recover the inclined strata thickness and horizontal expansion of strata—the final shape of the evolution process of structural profile may also deviate from the real state in geological history. The accumulation model established in this study was based upon the fluid inclusion experiments, which can effectively characterize the forming process of large condensate gas reservoirs in the Amu Darya Right Bank Block and quantify the timing of hydrocarbon charging. However, the hydrocarbon migration and accumulation model does not take the oil-source correlation into account, but only the relationship between the mature state of source rocks and the timing of hydrocarbon charging into the reservoirs. Subsequent research needs to conduct refined oil-source correlation to reveal the relationship between gas, condensate, source rocks, and recently discovered crude oil and more strictly constrain and modify the accumulation model, so as to finally disclose the origin of the crude oil and oil reservoir forming process in the Amu Darya Right Bank Block, evaluate the future exploration potential, and point out the direction of various hydrocarbon resources (condensate gas and crude oil).

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“…These are the most commonly encountered structures in shales than in limestones in sedimentary basins around the globe (Chen, Steele‐MacInnis, Ge, Zhou, & Zhou, 2016; Cobbold, Zanella, Rodrigues, & Loseth, 2013). Previously, it was suggested that tectonics is responsible for the formation of fractures, in which the fibrous calcite veins are formed (e.g., Ma, Dong et al, 2016; M. Wang et al, 2018, 2020; Worden, Benshatwan, Potts, & Elgarmadi, 2015). While some authors argued that hydrocarbon generation is a key mechanism in the formation of fibrous sparry calcite (Cobbold et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

“…While some authors argued that hydrocarbon generation is a key mechanism in the formation of fibrous sparry calcite (Cobbold et al, 2013). Fibrous sparry calcite is abundant in many shales worldwide (Cobbold et al, 2013; Cobbold, Zanella, Fourdan, Neraudeau, & Gouttefangeas, 2015; M. Wang et al, 2018, 2020; Zanella, Cobbold, & Boassen, 2015; Zanella, Cobbold, & Rojas, 2014; Zanella, Cobbold, Ruffet, & Leanza, 2015). According to Ramsay (1980), fibrous calcite is formed due to the crack‐seal mechanism.…”

Section: Introductionmentioning

confidence: 99%

Tracing forming mechanism of the sparry calcite growth in the lacustrine shale of east China: A glimpse into the role of organic matter in calcite transformation

et al. 2022

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The formation of sparry calcite is very common in fine‐grained sedimentary rocks worldwide. Sparry calcite is formed from the diagenetic calcite crystals having a grain size > 50 μm. It is also widely distributed in the Es3x shale of the Eocene Shahejie Formation in the Zhanhua Depression, Bohai Bay Basin. The detailed investigations of the Es3x shale show that the sparite crystals start appearing at a burial depth > 3,000 m and the total organic carbon content (TOC) is >3 wt%. It indicates that the sparry calcite formed at high depths and in the most organic‐rich intervals of the studied shale. The presence of organic matter (OM) laminae parallel to the sparry calcite laminae, and sparry calcite along the edges of the OM show a direct physical relationship between sparry calcite and OM. It suggests that the diagenetic system was not influenced by hydrothermal fluids and only the OM is possibly responsible for the formation of sparry calcite in the studied shale. Sparry calcite forms in the thermally mature oil window, and oil generation in the Es3x shale causes the dissolution of micrite, providing the ions source for sparry calcite formation. Therefore, the geothermal gradient, as well as oil generation and kerogen maturation, are responsible for sparry calcite growth in the studied shale. The proposed model shows that the sparry calcite can form in the pores formed by elastic deformation as well as in the microfractures in the study area. In laminated shale, sparry calcite followed three stages of its formation, including (a) formation of laterally discrete calcite crystals, (b) lateral intergrowth of equant calcite crystals and (c) lateral intergrowth of fibrous calcite. Likewise, the genesis of sparry calcite in the non‐laminated shale also followed the same three phases; however, elastic deformation played a dominant and an important role in this variety of shale. Based on the detailed interpretations, we suggest that the OM, microfractures and elastic deformation act as major contributors in the formation and maturation of sparry calcite. We expect that this study also highlights the growth mechanism and maturation of sparry calcite in the Zhanhua Depression as well as other similar rift‐related basins around the globe.

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Direct evidence for fluid overpressure during hydrocarbon generation and expulsion from organic-rich shales

Cited by 49 publications

References 24 publications

The Fluid Evolution of Ancient Carbonate Reservoirs in Sichuan Basin and Its Implication for Shale Gas Exploration

The Fluid Evolution of Ancient Carbonate Reservoirs in Sichuan Basin and Its Implication for Shale Gas Exploration

Study on Hydrocarbon Accumulation Periods Based on Fluid Inclusions and Diagenetic Sequence of the Subsalt Carbonate Reservoirs in the Amu Darya Right Bank Block

Tracing forming mechanism of the sparry calcite growth in the lacustrine shale of east China: A glimpse into the role of organic matter in calcite transformation

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