Research

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17 pages, 1585 KiB

Open AccessArticle

Experimental Optimization of High-Temperature-Resistant and Low Oil—Water Ratio High-Density Oil-Based Drilling Fluid

by Zhenzhen Shen, Heng Zhang, Xingying Yu, Mingwei Wang, Chaoli Gao, Song Li and Haotian Zhang

Processes 2023, 11(4), 1129; https://doi.org/10.3390/pr11041129 - 06 Apr 2023

Cited by 1 | Viewed by 2311

Abstract

Problems such as well loss and collapses in deep shale gas drilling are most often due to the development of cracks in the shale formation, resulting in significant leaks of drilling fluid, the sticking and burrowing of drilling tools, and other engineering accidents. [...] Read more.

Problems such as well loss and collapses in deep shale gas drilling are most often due to the development of cracks in the shale formation, resulting in significant leaks of drilling fluid, the sticking and burrowing of drilling tools, and other engineering accidents. In addition, the horizontal sections of wells are very long and issues of friction, rock transport, and formation contamination loom large. As a result, the performance of drilling fluids directly affects drilling efficiency, engineering accident rates, and reservoir protection effects. We first analyze the mechanisms of each emulsifier in an oil-based drilling fluid formulation and the filtration reduction mechanisms, taking into account the collapse-prone and abnormally high-pressure characteristics of shale formations. We undertake an experimental evaluation and optimization of polymeric surfactants, such as primary and secondary emulsions for high-performance oil-based drilling fluids. The design of rigid and deformable nano-micron plugging materials with a reasonable particle size range was achieved, and we obtained a low Oil—Water ratio and high-density oil-based drilling fluid system, with temperature resistance of 200 °C, an Oil—Water ratio as low as 70:30, compressive fracturing fluid pollution of 10%, and a maximum density of 2.6 g/cm³. The reuse rate reached 100%. The developed oil-based drilling fluid system with strong plugging, a high density, and a low Oil—Water ratio suitable for deep shale gas can effectively seal the well wall, reduce liquid invasion, prevent the wall from collapsing, reduce mud leakage, reduce the consumption of oil-based drilling fluid, improve the utilization rate of old mud, and reduce drilling costs. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas Reservoirs Seepage Theory, Numerical Simulation and Application Technology)

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11 pages, 3441 KiB

Open AccessArticle

The Study of Multi-Scale Specific Surface Area in Shale Rock with Fracture-Micropore-Nanopore

by Rongrong Hu, Chenchen Wang, Maolin Zhang, Yizhong Zhang and Jie Zhao

Processes 2023, 11(4), 1015; https://doi.org/10.3390/pr11041015 - 27 Mar 2023

Cited by 2 | Viewed by 1121

Abstract

The specific surface area is an important parameter to characterize pore structure and adsorption properties, however, it is difficult to calculate accurately in shale rock due to its multiscale pore structure. In this paper, the representative 3D gray images of a microfracture sample, [...] Read more.

The specific surface area is an important parameter to characterize pore structure and adsorption properties, however, it is difficult to calculate accurately in shale rock due to its multiscale pore structure. In this paper, the representative 3D gray images of a microfracture sample, micropore subsample and nanopore subsample in shale rock were obtained with computed tomography (CT) scanning and focused ion beam-scanning electron microscopy (FIB-SEM) scanning. The multi-threshold segmentation algorithm with improved maximum inter-class variance method was introduced to construct the platform of multi-scale digital rock. Then, based on the fracture, micropore and nanopore digital rocks, the corresponding network models were extracted to obtain different-scale pore structures, respectively. Finally, based on the digital rock at different scales, the corresponding pore percentage, matrix percentage and specific surface area were calculated respectively. It was found that the specific surface areas of both microfractures and micropores are small, and their specific surface areas are 2~3 orders of magnitude smaller than that of nanopores, and the specific surface area of the shale formation is mainly contributed by nanopores. This paper provides an effective method to calculate the multi-scale specific surface area accurately in shale rock and has an important influence on the adsorption characteristics and swelling properties of the shale matrix. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas Reservoirs Seepage Theory, Numerical Simulation and Application Technology)

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15 pages, 1768 KiB

Open AccessArticle

Experiment on Gas–Liquid Sulfur Relative Permeability under High-Temperature High-Pressure Sour Gas Reservoir Condition

by Xiao Guo, Pengkun Wang, Jingjing Ma and Tao Li

Processes 2022, 10(10), 2129; https://doi.org/10.3390/pr10102129 - 19 Oct 2022

Cited by 1 | Viewed by 1185

Abstract

In the development of high temperature sour gas reservoirs, gas–liquid sulfur two phase percolations exist, which have a significant impact on the gas permeability and gas well productivity. There are currently few reports on experimental studies on gas–liquid sulfur relative permeability. This study [...] Read more.

In the development of high temperature sour gas reservoirs, gas–liquid sulfur two phase percolations exist, which have a significant impact on the gas permeability and gas well productivity. There are currently few reports on experimental studies on gas–liquid sulfur relative permeability. This study improves the experimental equipment and process, and it proposes an experimental method for measuring the gas–liquid sulfur relative permeability curve. Several typical core samples from a sour gas reservoir in Sichuan Basin, China were selected for experimental study, and the gas–liquid sulfur relative permeability under high temperature and high pressure (HTHP) was measured. The results show that, first, the critical flowing saturation of liquid sulfur was 40%, and the gas–liquid sulfur co-flow zone was narrow. With the increase in the liquid sulfur saturation, the gas relative permeability decreased rapidly. Second, the better the physical properties of the core, the greater the damage of liquid sulfur to the core properties. The residual liquid sulfur saturation of the fractured core was higher than matrix core, and as liquid sulfur saturation increased, so did the damage to gas permeability. Third, temperature had an effect on the gas–liquid sulfur relative permeability. Gas relative permeability decreased as the temperature rose, while the liquid sulfur relative permeability remained essentially constant. Fourth, the rock effective stress had a significant impact on the gas–liquid sulfur relative permeability. The relative permeability of gas and liquid sulfur decreased as the effective stress increased, and the fractured core was more sensitive to stress. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas Reservoirs Seepage Theory, Numerical Simulation and Application Technology)

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21 pages, 4310 KiB

Open AccessArticle

Numerical Simulation of Sulfur Deposition in Wellbore of Sour-Gas Reservoir

by Xiao Guo, Pengkun Wang, Jingjing Ma and Changqing Jia

Processes 2022, 10(9), 1743; https://doi.org/10.3390/pr10091743 - 01 Sep 2022

Cited by 1 | Viewed by 1327

Abstract

Sulfur deposition has an important effect on the productivity of sour-gas wells. Accurately predicting the occurrence of sulfur deposition and the location and amount of sulfur deposition in wellbore can effectively guide the production of gas wells. In this paper, the wellbore sulfur [...] Read more.

Sulfur deposition has an important effect on the productivity of sour-gas wells. Accurately predicting the occurrence of sulfur deposition and the location and amount of sulfur deposition in wellbore can effectively guide the production of gas wells. In this paper, the wellbore sulfur deposition model, pressure model, and transient temperature model are established for various well types. Then, numerical simulations of sulfur deposition in the sour-gas well were conducted by coupling these models. Examples show that the proposed methodology has high accuracy, and the average relative error of the calculated results is 3.61%. Based on the model, a sensitivity analysis was performed on the factors affecting sulfur deposition. The results show that with the increase of wellbore inclination angle, the critical sulfur carrying velocity first increased and then decreased, and the maximum critical velocity is about 30% larger than that of the vertical section. The amount of wellbore sulfur deposition increases with increased production time and decreased wellbore pressure, and the amount of wellbore sulfur deposition decreases with increased gas production rate, H₂S content, and inclination angle. The results suggest that the sour-gas reservoir should be developed with the horizontal or deviated well, timely adjust the production system, and keep the gas-well production higher than the critical flow rate as much as possible. At the same time, wellbore heating and insulation, pre-cleaning technology, and the closely implemented sulfur deposition prevention technology in the middle and late stage of development can be adopted to reduce the occurrence of sulfur deposition to ensure the safe and efficient development of high-sulfur gas wells. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas Reservoirs Seepage Theory, Numerical Simulation and Application Technology)

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19 pages, 7001 KiB

Open AccessArticle

Numerical Simulation Investigation on Fracture Propagation of Fracturing for Crossing Coal Seam Roof

by Yanchao Li, Jianfeng Xiao, Yixuan Wang and Cai Deng

Processes 2022, 10(7), 1296; https://doi.org/10.3390/pr10071296 - 30 Jun 2022

Cited by 1 | Viewed by 948

Abstract

The fracturing crossing coal seam roof is a technology that fulfills the fracturing of a coal seam through the vertical propagation of fractures. Geological conditions are the key factors determining the effect of this kind of fracturing, but there is hardly any research [...] Read more.

The fracturing crossing coal seam roof is a technology that fulfills the fracturing of a coal seam through the vertical propagation of fractures. Geological conditions are the key factors determining the effect of this kind of fracturing, but there is hardly any research on this aspect. To determine the favorable geological conditions for through-roof fracturing, based on a 3D fracture propagation model, and considering the interlayer vertical fracture toughness and leak-off heterogeneity, a mathematical model of fracturing through a horizontal well in a coal seam roof was established, and the calculation method of fractures crossing layer propagation was determined. In this method, the effect of fracture communication with the coal seam is evaluated by taking the area and the area ratio of fractures in the coal seam as the objective functions. The effects of parameters such as in situ stress combination profile, coal seam fracture toughness, and fluid loss coefficient on fracturing results were evaluated. The reasonable distance from the horizontal well to the coal seam’s top surface was determined in this work. The study results show that: (i) the fracturing effect is better when the coal seam is lower in in situ stress; (ii) the distance between the horizontal well and the top surface of the coal seam is recommended to be less than 4 m to obtain the ideal fracturing effect; and (iii) the combination of the in situ stress profile is the key factor, and the fracture toughness and fluid loss coefficient of the coal seam, fluid viscosity, and the number of perforations in one cluster are the secondary factors affecting the fracturing effect. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas Reservoirs Seepage Theory, Numerical Simulation and Application Technology)

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14 pages, 3987 KiB

Open AccessArticle

Discussion on the Reconstruction of Medium/Low-Permeability Gas Reservoirs Based on Seepage Characteristics

by Guangliang Gao, Wei Liu, Shijie Zhu, Haiyan He, Qunyi Wang, Yanchun Sun, Qianhua Xiao and Shaochun Yang

Processes 2022, 10(4), 756; https://doi.org/10.3390/pr10040756 - 13 Apr 2022

Cited by 1 | Viewed by 1161

Abstract

The construction of underground gas storage mostly focuses on depleted gas reservoirs. However, the depleted gas reservoir used to build underground gas storage in China is located far from the main gas consumption economic zone. It is necessary to reconstruct underground gas storage [...] Read more.

The construction of underground gas storage mostly focuses on depleted gas reservoirs. However, the depleted gas reservoir used to build underground gas storage in China is located far from the main gas consumption economic zone. It is necessary to reconstruct underground gas storage using nearby reservoirs in order to meet the needs of economic development. The complex three-phase seepage characteristics encountered in the process of reconstruction of underground gas storage reservoirs seriously affect their storage and injection production capacities. Combined with the mechanism of multiphase seepage and the multicycle injection production mode during the process of gas storage construction, the feasibility of rebuilding gas storage in medium- and low-permeability reservoirs was evaluated through relative permeability experiments and core injection production experiments. The results showed that the mutual driving of two-phase oil–water systems will affect the storage space and seepage capacity, that the adverse effect will be weakened after multiple cycles, and that increasing the gas injection cycle can enhance the gas-phase seepage capacity and improve the crude oil recovery. Therefore, we found that it is feasible to reconstruct underground gas storage in medium- and low-permeability reservoirs, which lays a foundation for the development of underground gas storage in China. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas Reservoirs Seepage Theory, Numerical Simulation and Application Technology)

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18 pages, 2925 KiB

Open AccessArticle

An Approach for Predicting the Effective Stress Field in Low-Permeability Reservoirs Based on Reservoir-Geomechanics Coupling

by Yuyang Liu, Xiaowei Zhang, Wei Guo, Lixia Kang, Rongze Yu and Yuping Sun

Processes 2022, 10(4), 633; https://doi.org/10.3390/pr10040633 - 24 Mar 2022

Cited by 4 | Viewed by 1582

Abstract

Low-permeability reservoirs are important to the future growth of oil and gas reserves and production in China. Predicting the effective stress, σ_e, in reservoirs is vitally important due to its considerable impact on reservoir development through hydraulic fracturing. This paper presents [...] Read more.

Low-permeability reservoirs are important to the future growth of oil and gas reserves and production in China. Predicting the effective stress, σ_e, in reservoirs is vitally important due to its considerable impact on reservoir development through hydraulic fracturing. This paper presents methods for predicting the σ_e field in ultralow-permeability reservoirs through reservoir–geomechanics coupling, which involve the simulation and coupling of the tectonic stress σ and pore pressure P_p fields based on three-dimensional (3D) geological models. First, 3D geological models were constructed based on basic data for the oilfield where the reservoir of interest is located. Then, finite element and finite difference simulations were performed to construct the σ and P_p fields, respectively, in the reservoir. Different types of initial σ_e were coupled based on 3D geological models. Subsequently, a dynamic σ_e field in the reservoir was established based on oilfield production data in conjunction with the transformation, optimization, and coupling of specific grid property parameters obtained from different numerical methods. Finally, the proposed methods were tested on real-world data acquired from well area X in an oilfield in Shaanxi Province, China. The results show that the proposed methods can be used to establish the σ and P_p fields in a reservoir based on 3D geological models combined with different numerical methods, and subsequently predict the σ_e value in the reservoir. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas Reservoirs Seepage Theory, Numerical Simulation and Application Technology)

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Review

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15 pages, 638 KiB

Open AccessReview

Review on the Mechanism of CO₂ Storage and Enhanced Gas Recovery in Carbonate Sour Gas Reservoir

by Xiao Guo, Jin Feng, Pengkun Wang, Bing Kong, Lan Wang, Xu Dong and Shanfeng Guo

Processes 2023, 11(1), 164; https://doi.org/10.3390/pr11010164 - 05 Jan 2023

Cited by 2 | Viewed by 1457

Abstract

Carbonate gas reservoirs in the Sichuan Basin have many complex characteristics, such as wide distribution, strong heterogeneity, high temperature, high pressure, high H₂S and CO₂ content and an active edge or bottom water. In the late stage of exploitation of [...] Read more.

Carbonate gas reservoirs in the Sichuan Basin have many complex characteristics, such as wide distribution, strong heterogeneity, high temperature, high pressure, high H₂S and CO₂ content and an active edge or bottom water. In the late stage of exploitation of carbonate sour gas reservoirs, the underground depleted reservoirs can provide a broad and favorable space for CO₂ storage. If CO₂ is injected into the depleted carbonate sour reservoirs for storage, it will help to achieve the goal of carbon neutrality, and the CO₂ stored underground can perform as “cushion gas” to prevent the advance of edge or bottom water, to achieve the purpose of enhanced natural gas recovery. Injecting CO₂ into low permeability reservoirs for oil displacement has become an important means to enhance oil recovery (EOR). However, the mechanism of EOR by injecting CO₂ into carbonate sour gas reservoirs is not clear and the related fundamental research and field application technology are still in the exploration stage. This paper reviews the main scientific and technical perspectives in the process of injecting CO₂ into carbonate sour gas reservoirs for storage and enhancing gas recovery. Full article

(This article belongs to the Special Issue Unconventional Oil and Gas Reservoirs Seepage Theory, Numerical Simulation and Application Technology)

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