Water Occurrence Characteristics of Gas Shale Based on 2D NMR Technology

Mu, Ying; Hu, Zhiming; Shen, Rui; Chang, Jin; Duan, Xianggang; Li, Yanran; Guo, Qiulei

doi:10.1021/acs.energyfuels.1c03870

Cited by 9 publications

(14 citation statements)

References 44 publications

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“…In previous studies, we have developed a quantitative analysis method for water in shale, which is not mentioned here. According to the different relaxation times of the hydrogen nuclear signal, the water in shale can be classified as immovable water, bound water, capillary water, and free water . In comparison of the T 1 – T 2 spectra and T 1 spectra of shale at different water absorption stages (panels a–e of Figure ), it can be found that there is still a certain amount of hydrogen-containing fluid in shale obtained by the conventional drying method.…”

Section: Resultsmentioning

confidence: 99%

“…According to the different relaxation times of the hydrogen nuclear signal, the water in shale can be classified as immovable water, bound water, capillary water, and free water. 44 In comparison of the T 1 −T 2 spectra and T 1 spectra of shale at different water absorption stages (panels a−e of Figure 7), it can be found that there is still a certain amount of hydrogen-containing fluid in shale obtained by the conventional drying method. The hydrogen nuclear signal is concentrated between 0.01 < T 1 < 0.10 ms and 0.01 < T 2 < 1.00 ms.…”

Section: Water Absorption Process 2d Nmr Technology Can Well Characte...mentioning

confidence: 95%

“…In addition, water enters capillary pores and forms a water column under the action of capillary force. With the further increase of the shale water content, free water with strong mobility appears in larger pores and fractures. − …”

Section: Introductionmentioning

confidence: 99%

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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%

Section: Water Absorption Process 2d Nmr Technology Can Well Characte...mentioning

confidence: 95%

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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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“…Only a small amount of fracturing fluid is returned to the wellbore (roughly 25–60%) after hydraulic fracturing is finished . Studying the adsorption and flow capacity of shale gas is made more difficult by the fluctuating water-bearing state of the reservoir, which also makes it more difficult to estimate the geological reserves of gas reservoirs and to predict and develop capacity . Shales from the WCSB block in Canada, the Barnett block in the U.S., and the Alum block in Europe all demonstrated lower methane sorption capacity in equilibrium water circumstances compared to dry conditions, with a reduction of 30 to 70%. − When the gas-water two-phase flow through 100 nm nanopores was investigated, it was discovered that compared to the dry condition, the gas-phase flow capacity was reduced by about 10 for 20% water saturation in the pores and by about 20 for 40% water saturation in the pores. , For the development plan of a gas field and the assessment of development potential, it is crucial to clarify the characteristics of water distribution in the shale pore space.…”

Section: Introductionmentioning

confidence: 99%

Water Distribution in Marine Shales: Based on Two-Dimensional Nuclear Magnetic Resonance and Low-Temperature Nitrogen Adsorption

Guo

et al. 2023

Energy Fuels

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A significant amount of foreign fluid is kept in the marine shale reservoirs after hydraulic fracturing. The water distribution characteristics in the pore space are quite complex because of the shale’s significant inhomogeneity. The change in reservoir water status brings new challenges to studying the adsorption and flow capacity of shale gas, which also brings difficulties to assessing the geological reserves of shale reservoirs and capacity prediction and development. In this study, based on a two-dimensional nuclear magnetic resonance technique and low-temperature nitrogen adsorption technique, clay minerals, organic matter, and marine shale were used as the study objects to get the distribution characteristics of water in shale pores. The results show that after entering the shale reservoir, most of the water is adsorbed on the surface of inorganic pores, mostly clay pores, to create a bound water film with a thickness of around 0.96 nm. Shale pores’ diameter, volume, and surface area are all smaller in the wet state compared to the dry, falling by 10.11, 47.02, and 71.00%, respectively. Small-scale pores (D < 10 nm) are better at absorbing water, and the water in these pores fills the spaces between them to create capillary water besides being adsorbed on the pore surface. Bound water can aid in the development of gas reservoirs and the desorption of adsorbed gas, but the capillary water column obstructs the flow of gas and restricts the flow of shale gas in microscopic pores. This study will lay a theoretical foundation for evaluating the water-bearing characteristics of marine shale reservoirs, which will help analyze the modification effect of fracturing fluid retention on reservoir water-bearing characteristics and then guide gas well development.

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“…The current geological analysis results reveal that under original formation conditions, actual shale reservoirs generally have a certain water saturation [29,30]. The average water saturation of shale gas reservoirs in Barnett, Marcellus, and Woodford formations in the US ranges from 15% to 35% [31], compared to 30%-95% for the marine shale plays found in South China [32].…”

Section: Introductionmentioning

confidence: 99%

Effect of Water Saturation on Gas-Accessible Effective Pore Space in Gas Shales

Chen

Liu

et al. 2022

Lithosphere

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The existence and content of water will certainly affect the effective pore space of shales and therefore is a key point for the evaluation of in-situ gas content and gas flow capacity of shale reservoirs. In order to reasonably evaluate the gas storage and flow capacities of water-bearing shale reservoirs, the effect of water on the effective pore space of shales needs to be understood. In this study, the Upper Permian Longtan shale in the southeastern Sichuan Basin, China, was selected as an example to conduct nuclear magnetic resonance cryoporometry (NMRC) measurements under different water saturation levels. The gas-accessible effective pore spaces in shales under different water saturation levels were quantified, and the effect of water saturation on gas-accessible effective pore space in shales was investigated. The results show that water plays an important role in the gas-accessible effective pore space of shales. When the Longtan shale increases from a dry state to a water saturation of 65%, 75%, and 90%, the gas-accessible effective pore volume decreases by 35%-60% (average 46.3%), 50%-70% (average 58.8%), and 65%-82% (average 75.8%), respectively. Water has an effect on the gas-accessible effective pore space regardless of pore size, and the effect is the strongest in the 4-100 nm range, which may be mainly due to the high content of clay minerals in the Longtan shale. Our studies are of important theoretical significance and application prospects for accurately evaluating the gas-accessible effective pore space of gas shales under actual geological conditions.

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Water Occurrence Characteristics of Gas Shale Based on 2D NMR Technology

Cited by 9 publications

References 44 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

Water Distribution in Marine Shales: Based on Two-Dimensional Nuclear Magnetic Resonance and Low-Temperature Nitrogen Adsorption

Effect of Water Saturation on Gas-Accessible Effective Pore Space in Gas Shales

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