Law of imbibition effect on shale gas occurrence state

Hu, Zhiming; Mu, Ying; Gu, Zhaobin; Duan, Xianggang; Li, Yalong

doi:10.1016/j.ngib.2020.05.003

Cited by 10 publications

(9 citation statements)

References 8 publications

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“…Water molecules occupy the adsorption sites on the pore surface, forcing adsorbed methane to desorb into free methane, and the proportion of adsorbed gas in the reservoir decreases . In addition, water trapped in shale pores further compresses the occurrence space of free gas, and some free gas escapes from shale pores, further weakening the gas storage capacity of the reservoir . This also means that the gas pressure in the pore increases significantly and the formation energy is supplemented.…”

Section: Resultsmentioning

confidence: 99%

Occurrence Characteristics of Methane and Water in the Matrix Near-Wellbore Area during the Development of Marine Shale

Niu

et al. 2023

Energy Fuels

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During drilling and fracturing of shale gas wells, huge amounts of drilling fluid and fracturing fluid are kept in marine shale reservoirs, forming a water invasion layer. Gas−water displacement and gas production experiments, water absorption, and gas driving water experiments were used in this work to replicate the hydraulic fracturing−soaking−gas production process in shale gas development. Methane and water in marine shale are detected and quantitatively investigated using nuclear magnetic resonance technologies, and their occurrence characteristics are obtained. The results show that fluids, such as drilling fluid and fracturing fluid, are first adsorbed on the surface of pores and fractures to form bound water. With the increase of the water content, capillary pores are filled to form capillary water and then aggregated into free water on large-scale pores. Bound water film promotes the adsorbed gas to desorb, namely gas−water replacement, which improves the development effect of gas wells. Easily produced free gas makes the gas well have the characteristics of an early high yield, and the continuous desorption of adsorbed gas ensures the long-term stable production of gas wells. The flow of gas is accompanied by the discharge of water. Airflow initially removes the capillary water column and some free water. The thickness of the bound water film steadily decreases with the adsorbed gas released and the airflow carried. Capillary water and free water make up most reflowing fluids. Bound water, sensitive to microforces, is challenging to transport out of the reservoir, which results in the low flowback ratio of shale gas wells. This study offers a fresh perspective on the characteristics of competitive adsorption, water absorption, and flowback law in shale reservoirs.

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Section: Resultsmentioning

confidence: 99%

Occurrence Characteristics of Methane and Water in the Matrix Near-Wellbore Area during the Development of Marine Shale

Niu

et al. 2023

Energy Fuels

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“…As shown in Figures and , gas will be trapped in pores after water imbibition during fracturing, which can be extracted until fracturing fluid in fractures and pore entrances connected with the fractures is discharged. The main trapping mechanism is: first, the imbibed fracturing fluid will compete to control the adsorption sites of adsorbed gas owing to the stronger adsorption capacity of water molecules; thus, when the adsorbed gas is affected by the imbibed water, it desorbs as free gas; − second, because of the limited pore length in shale and the high imbibition pressures generated mainly by the capillary pressure and the displacement pressure, the imbibition of water compresses the free gas until the increasing gas pressure is equal to the water phase pressure, , as shown in Figure . The following equations can be proposed for the gas–water equilibrium state For circular pores, the capillary pressure is Gas pressure in circular pores can be obtained by the following gas-state equation …”

Section: Basic Theory and Experimentsmentioning

confidence: 99%

Mechanism of the Production Impact in Shale Gas Wells Caused by Water Invasion during Interwell Interference

Wang

Jiang

et al. 2021

ACS Omega

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Interwell interference is a universal problem in shale gas development and can cause severe reductions in the productivity of producing wells. Studies have attempted to identify the root cause of interference in producing wells, but the mechanisms of production reduction and recovery in impacted wells are still not clear. Thus, an effective preventive strategy is needed for producing wells when fracturing is performed in adjacent wells. According to the mechanism of spontaneous imbibition and water drainage in shale mico- and nanoscale pores, this paper introduces the water–gas distribution during fracturing and production and reveals that water drainage in micro- and nanoscale pores is mainly controlled by the amount of stored gas and follows the order of pore size. Based on this analysis, the mechanism by which interwell interference impacts the production of producing wells is explained for the first time. It is concluded that the secondary water invasion caused by interwell interference completely blocks the pores associated with long-term gas production but has little influence on the pores that have not yet drained or have produced only a small amount of gas, and smaller pores face a greater risk of water blockage. The proportion of drained pores formed during long-term gas production determines the effect of interwell interference on production; when more pores are drained by long-term gas production, greater damage occurs to the productivity of the producing well. The suggestion for preventing interwell interference is to reduce the time interval between fracturing operations at two adjacent wells, thereby diminishing the reduction in production.

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“…Hu et al revealed that when formation water emerges in the reservoir, the mineral nanochannel surface will be occupied by water, and the originally adsorbed gas on the mineral surface is converted to free-status gas, which facilitates shale gas recovery. 16 The formation water comes from primary reservoir water or the water of hydraulic fracturing solution. 17,18 The appearance of formation water plays crucial role influencing methane occurrence.…”

Section: Introductionmentioning

confidence: 99%

“…They found that the proportion of adsorption-status shale gas is mainly controlled by total organic carbon, specific surface area, and pore size distribution, and the proportion of free-status shale gas is mainly controlled by quartz content, gas saturation, and formation pressure. Hu et al revealed that when formation water emerges in the reservoir, the mineral nanochannel surface will be occupied by water, and the originally adsorbed gas on the mineral surface is converted to free-status gas, which facilitates shale gas recovery . The formation water comes from primary reservoir water or the water of hydraulic fracturing solution. , The appearance of formation water plays crucial role influencing methane occurrence.…”

Section: Introductionmentioning

confidence: 99%

Molecular Insight into the Methane Occurrence inside a Shale Nanochannel with Formation Water

et al. 2023

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The occurrence status of shale gas inside a nanochannel of a shale reservoir is crucial for shale gas reserve assessment and exploitation. In this work, adopting molecular dynamics simulations, the methane occurrence inside a shale nanochannel was investigated under different formation water saturations. Moreover, employing three common inorganic minerals including of quartz, calcite, and kaolinite, the influence of mineral hydrophilicity on methane occurrence was also examined. The simulations indicate that there are three occurrence statuses of methane inside nanochannels including a free status located in the internal nanochannel, an adsorption status on mineral and water film surfaces, and a dissolution status inside the water phase. Among them, free-status methane is the dominant contribution to the recoverable reserve assessment and could be feasibly exploited. Without formation water, methane gives two occurrence statuses including an adsorption status on mineral surfaces and a free status. Once the formation water emerges, it will preferentially adsorb onto the mineral surface to form a water film. With the increase of formation water saturation, the proportions of free-status and dissolution-status methanes increase, while the proportion of adsorption-status methane decreases. In three mineral nanochannels with hydrophilicity orders of quartz > calcite > kaolinite, the proportion of adsorption-status methane follows the order of kaolinite > calcite > quartz, and free-status methane gives the order of kaolinite ≈ quartz > calcite. The underlying mechanisms of these occurrence features were discussed at length from the view of microscopic interactions among mineral surfaces, water, and methane. Our work presents the methane occurrence structure inside a shale nanochannel, and the discussion of the three methane occurrence statuses could provide fundamental data and theoretical guidance for shale gas reserve assessment and exploitation.

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Law of imbibition effect on shale gas occurrence state

Cited by 10 publications

References 8 publications

Occurrence Characteristics of Methane and Water in the Matrix Near-Wellbore Area during the Development of Marine Shale

Occurrence Characteristics of Methane and Water in the Matrix Near-Wellbore Area during the Development of Marine Shale

Mechanism of the Production Impact in Shale Gas Wells Caused by Water Invasion during Interwell Interference

Molecular Insight into the Methane Occurrence inside a Shale Nanochannel with Formation Water

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