Gas Reservoir Engineering Research Articles

UNRAVELING THE COMPLEX DYNAMICS OF FLUID FLOW IN POROUS MEDIA: EFFECTS OF VISCOSITY, POROSITY, AND INERTIA ON THE MOTION OF FLUIDS

This study investigates novel solitary wave solutions of the Gilson–Pickering ([Formula: see text]) equation, which is a model that describes the motion of a fluid in a porous medium. An analytical scheme is applied to construct these solutions, utilizing the extended Khater method in conjunction with the homogenous balance technique. The derived expressions for the solitary wave solutions are exact and are presented in terms of hyperbolic functions. The [Formula: see text] equation is valuable for a wide range of applications, including oil and gas reservoir engineering, groundwater flow, and flow in biological tissues. Additionally, this model is employed to describe the behavior of waves in various physical systems such as fluids and plasmas. Specifically, it models the propagation of dispersive waves in a media that exhibits both dispersion and dissipation. To ensure the accuracy of the constructed solutions, a numerical scheme is employed. The properties of the solitary wave solutions are analyzed, and their physical implications are explored. The results of this investigation reveal a rich variety of solitary wave solutions that exhibit interesting behaviors, including oscillatory and non-oscillatory behavior, which are elucidated through various types of distinct graphs. Consequently, this study provides significant insights into the behavior of fluid flow in porous media and its applications in various fields, including oil and gas reservoir engineering and groundwater flow modeling. The analytical and numerical methods employed in this investigation demonstrate their potential for studying nonlinear evolution equations and their applications in the physical sciences.

Analysis of development performance characteristics of strong heterogeneous carbonate gas reservoirs——the Deng 4 gas reservoir in the GM block

The Deng 4 gas reservoir in the GM block of Anyue gas field is an important area of natural gas production during the "13th Five-Year Plan" period. A correct understanding of its production dynamics is the key to scientific development of gas reservoirs and long-term stable production. Using gas reservoir engineering, production statistics, well test analysis, etc.，combined with gas reservoir geological characteristics, produced fluid properties, oil pressure production decline, gas well productivity, and single well controlled reserves, analyzed and summarized the Dengying Group gas in the block. The dynamic characteristics of production provide a reference for later efficient development.

Shale gas exploration and development in the Sichuan Basin: Progress, challenge and countermeasures

China's shale gas production in 2020 exceeds 200 × 108 m³, which creates a miracle in the history of natural gas development in China. The Sichuan Basin has already been and will be the main battlefield of shale gas exploration and development in China. In order to further promote the large-scale efficient development of shale gas in China, under the new situation of global COVID-19 spread and domestic “carbon peak and carbon neutrality” goal, this paper analyzes the progress and challenges of shale gas exploration and development in the Sichuan Basin from four aspects, including resource exploration, gas reservoir engineering, drilling and production engineering and industry regulation, and puts forward countermeasures and suggestions for achieving large-scale efficient development of shale gas. The following research results are obtained: First, the large-scale efficient development of shale gas in the Sichuan Basin has to take the sustainable and stable production of middle–shallow shale gas and the large-scale productivity construction of deep shale gas as the base. Second, compared with the shale gas exploration and development in the North America, the Sichuan Basin has its own characteristics in terms of geographical setting, geological condition, drilling and production technology and industry regulation, which makes it difficult to copy the development pattern of large scale, high density and continuous well deployment from the North America, so it is necessary to adopt the strategy of “high production with few wells”. On the one hand, continue to apply the geology and engineering integration technology to carry out “integrated research, integrated design, integrated implementation and integrated iteration” in the whole life cycle of shale gas well; and on the other hand, carry out problem-oriented continuous researches from the aspects of geological evaluation, development policy, engineering technology and industry regulation, so as to improve geological evaluation theory and technology, innovate gas reservoir engineering theory and method, research and develop engineering technology for cost reduction and efficiency improvement, improve shale gas industry regulation, and form a new pattern of collaborative promotion of technical and non-technical elements. In conclusion, the research results provide important reference and guidance for the large-scale efficient development of shale gas in the Sichuan Basin and even the whole country.

Optimization and utilization of peak-shaving capability for water drive gas storage

To determine the reasonable gas injection and production quantity and to minimize the influence of water invasion on the operation of underground gas storage is one of the key factors to decide whether the water drive gas storage can fully exert its peak shaving ability. At present, gas reservoir engineering method is mainly used in China, which mainly reflects the operation of underground gas storage under the condition of less water invasion at the end of gas production, it cannot really reflect the influence of water invasion on the operation of underground gas storage under the condition of large injection-production volume. Through the numerical simulation and the research of the injection-production performance, it is clear that the main geological factors affecting the reasonable injection-production rate of the gas storage are the pressure of the gas storage, the properties of the reservoir, the distribution of gas and water and the radius of well control. Based on the reservoir changes of pressure, water yield, gas-water ratio, gas-water interface and saturation, and according to the influence of multi-period water invasion on the operation of gas storage, the optimization technology of peak shaving capacity of water drive gas reservoir is established, which successfully guides the optimization of injection-production operation of an underground gas storage in China. The result shows that after 5 cycles of operation, the gas injection displacement effect is successful, the gas production capacity is improved gradually, and the peak shaving capacity is 6.85 X 108m3 in 2019. The conclusion is that the optimization technology of peak shaving capacity is applicable to some extent, which provides theoretical basis and operating experience for the design of injection-production operation of the same type gas storage in China.

COMPRESSIVE STRESSES IN HYDRAULIC FRACTURES

In hydraulic fracturing of producing formations in oil and gas reservoir engineering, as well as in coal gas drainage, hydraulic fractures are propped by solid particles—proppant that prevents closure of fractures under the action of compressive stresses in rocks. It is shown that alongside with lateral earth pressure, the compressive stresses in fractures are governed by additional compression generated by fracturing and by compression of rock in depression zone formed in the reservoir fluid inflow to the fracture. The compressive effect in the depression zone can be adjusted by reducing the rate of depression growth in time. This method of compression decrease in fractures is the most efficient in reservoir engineering and in shallow coal seam gas drainage. The compressive stresses in the depression zone are comparable with the lateral earth pressure, thus, the differential pressure step-up can make it possible to keep the stress–strain behavior of rock in the neighborhood of a hydraulic fracture within the limits of elastic deformation and to prevent the fracture closure with irreversible pressing-in of proppant in rock.

A FRACTAL SCALING LAW BETWEEN TORTUOSITY AND POROSITY IN POROUS MEDIA

Hydraulic tortuosity is one of the key parameters for evaluating effective transport properties of natural and artificial porous media. A pore-scale model is developed for fluid flow through porous media based on fractal geometry, and a novel analytical tortuosity–porosity correlation is presented. Numerical simulations are also performed on two-dimensional Sierpinski carpet model. The proposed fractal model is validated by comparison with numerical results and available experimental data. Results show that hydraulic tortuosity depends on both statistical and morphological characteristics of porous media. The exponents for the scaling law between tortuosity and porosity depend on pore size distribution and tortuous fractal dimension. It has been found that hydraulic tortuosity indicates evident anisotropy for asymmetrical particle arrangements under the same statistical characteristics of porous media. The present work may be helpful to understand the transport mechanisms of porous materials and provide guidelines for the development of oil and gas reservoir, water resource and chemical engineering, etc.

A dynamic prediction model of pressure-control production performance of shale gas fractured horizontal wells and its application

For clarifying the inherent relation between relieving fracture closure and improving the EUR by adopting the pressure-control production system for shale gas fractured horizontal wells, and the significance of pressure-control production for gas reservoir engineering, a dynamic formation–fracture coupling prediction model for production performance of fractured horizontal wells was established and solved, with the finite conductivity fracture as basic flow unit and the variable stress sensitivity coefficient introduced. Through a comparison of the calculated results from the established model, classical model and numerical modeling by the Saphir software, the effect of characteristic parameters of stress sensitivity and pressure-control production system on the production performance of fractured horizontal wells was analyzed and verified in two wells. The results show that (1) the calculated results from the established model are basically consistent with those from the classical model and the numerical modeling by the Saphir software; (2) the existence of stress sensitivity makes the fracture conductivity decline with the production of gas wells, which leads to the decrease of cumulative gas production; the greater the stress sensitivity, the greater the decrease of cumulative gas production; (3) although the initial gas production and cumulative gas production of shale gas gained by the pressure-control production system are low compared with those by the pressure-release production system, the ultimate cumulative gas production is higher. Thus, it is more reasonable to adopt a long-term pressure-control production system for shale gas fractured horizontal wells. In conclusion, the research results provide a theoretical support for the popularization of pressure-control production system of shale gas wells.

The application of modified isochronal well test in a low-permeability condensate gas field

ABSTRACTThe modified isochronal well test is a deliverability test method suitable for gas wells in low-permeability gas reservoirs. Generally, the absolute open flow of gas wells is determined by modified isochronal well test, thereby establishing a reasonable working system for gas wells. It is also possible to obtain gas layer physical parameters, gas reservoir engineering parameters, heterogeneity, boundary characteristics, etc. In this paper, the actual test data of a condensate gas field are applied. By modified isochronal well test analysis, not only the deliverability equation of the gas well is obtained, but also the absolute open flow is determined. At the same time, the formation parameters such as reservoir permeability and skin factor are obtained and the acidification effect is evaluated.

A Global Search Algorithm for Determining Water Influx in Naturally Fractured Reservoirs

The determination of water influx in naturally fractured reservoirs is always a significant and difficult task in gas reservoir engineering. To improve this situation, this paper presents a new global search algorithm to determine water influx in the naturally fractured gas reservoirs. In the methodology, a dimensionless water influx derivative curve is first introduced in this paper. It is used to identify flow regimes of water invasion by combining with the water influx characteristic curve. Following that, a sensitivity analysis is performed to study the impacts of key factors on flow regimes. Finally, based on the sensitivity study and material balance equation, a global search algorithm is proposed to obtain water influx. Results show that there are two steps in the dimensionless water influx curve and a “V-shape” in the derivative curve. The smaller the aquifer and gas reservoir radius ratio is, the earlier and more obvious the “V-shape” appears. The smaller the storativity ratio is, the earlier the “V-shape” appears. The smaller the interporosity flow coefficient is, the more obvious the “V-shape” is. Results of the field application demonstrate the method applicability, which provide a good reference for further work about determination of water influx.

Influencing factor analysis of water invasion in condensate gas reservoir with bottom water based on fuzzy comprehensive evaluation and orthogonal experiment

ABSTRACTCondensate oil and water invasion coexist in the condensate gas reservoir with bottom water. Because of influences of condensate oil pollution and water invasion, gas recovery obviously decreases. There are many factors influencing water invasion in a condensate gas reservoir with bottom water, including static petrophysical properties and dynamic operational conditions. Various factors play different roles in the process of water invasion, and the comprehensive effects of them on water invasion are difficult to be determined because these factors interfere with each other. With gas reservoir engineering method and numerical simulation technology, the factors including acuifer size, height of water avoidance, permeability, effective gas pay thickness, condensate oil saturation and gas well production rate on water invasion are researched. Water breakthrough time, stable production period and gas recovery are calculated for different cases under different parameter combinations through fuzzy comprehensive evaluation and orthogonal experiment design. Then sensitivities of these factors are analyzed and main factors influencing water invasion are selected and sequenced. The research supply theoretical basis for preventing and controlling water invasion thus improves development effect of condensate gas reservoir with bottom water.

What’s Conventional and What’s Special in a Reservoir Study for Underground Gas Storage

The development of an underground gas storage (UGS) project and its subsequent management must ensure technical feasibility, commercial value and long-term efficiency. The UGS industry has borrowed much of its knowledge from other disciplines (primarily oil and gas reservoir engineering), but it has also developed its own technology. This paper provides a methodological approach based on current practices and available methods for designing and safely operating a UGS (including the so-called “delta-pressure” option to enhance UGS performance) and highlights what is special in UGS compared to oil and gas reservoirs.

The Researches on Reasonable Well Spacing of Gas Wells in Deep and low Permeability Gas Reservoirs

This Gs64 gas reservoir is a condensate gas reservoir which is relatively integrated with low porosity and low permeability found in Dagang Oilfield in recent years. The condensate content is as high as 610g/m3. At present, there are few reports about the well spacing of similar gas reservoirs at home and abroad. Therefore, determining the reasonable well spacing of the gas reservoir is important for ensuring the optimal development effect and economic benefit of the gas field development. This paper discusses the reasonable well spacing of the deep and low permeability gas reservoir from the aspects of percolation mechanics, gas reservoir engineering and numerical simulation. considering there exist the start-up pressure gradient in percolation process of low permeability gas reservoir, this paper combined with productivity equation under starting pressure gradient, established the formula of gas well spacing with the formation pressure and start-up pressure gradient. The calculation formula of starting pressure gradient and well spacing of gas wells. Adopting various methods to calculate values of gas reservoir spacing are close to well testing' radius, so the calculation method is reliable, which is very important for the determination of reasonable well spacing in low permeability gas reservoirs.

Permeability and elastic parameters under different pressures of tight gas sandstones in eastern Ordos basin, China

The porosity, permeability and elastic parameters are important to the design and engineering of tight gas sandstone wells. Based on experimental tests of sandstones sampled continuously from newly drilled well cores, the porosity, permeability, and elastic parameters were characterized with a discussion of their controlling factors. The porosity lies in a range of 0.1%–13.8%, with 96.6% of all the samples being lower than 10%. The permeability is generally under 0.1 mD, with 43.4% clustered <0.01 mD. The permeability is much more sensitive to the confining stresses than the porosity is, which endured almost five times damage as the confining stresses increased from 500 to 5000 psi. The Young's modulus (E) and Poisson' Ratio (υ) values were tested by uniaxial (UA), triaxial (TA) and acoustic velocity measurement methods. Different methods show different scales and also different variation trend. The E values are similar between the UA and TA methods in a range of >2000 Psi, however, the TA results are generally higher than the UA results in E < 2000 MPa range. The υ values of UA are higher than the TA results in υ > 0.175, vice versa in υ < 0.175. The compressive strength values both from TA and UA methods show a linear relationship, with the TA results three times of the UA results. In general, the dynamic υ values increase sharply (>10%) as with the axial stress increases, while the E values show less of an increase (approximately 5%). The permeability is relatively high at a depth of 1700 m, and then decreases in deeper strata; this is likely caused by the higher stress conditions and complex clay compositions. The elastic parameters show no clear relationship with depth, as they are mainly affected by the combined influences of rock compositions and the diagenesis effect. The results improve the understanding of tight gas sandstone properties and will be useful in gas reservoir engineering.

A FRACTAL NETWORK MODEL FOR FRACTURED POROUS MEDIA

The transport properties and mechanisms of fractured porous media are very important for oil and gas reservoir engineering, hydraulics, environmental science, chemical engineering, etc. In this paper, a fractal dual-porosity model is developed to estimate the equivalent hydraulic properties of fractured porous media, where a fractal tree-like network model is used to characterize the fracture system according to its fractal scaling laws and topological structures. The analytical expressions for the effective permeability of fracture system and fractured porous media, tortuosity, fracture density and fraction are derived. The proposed fractal model has been validated by comparisons with available experimental data and numerical simulation. It has been shown that fractal dimensions for fracture length and aperture have significant effect on the equivalent hydraulic properties of fractured porous media. The effective permeability of fracture system can be increased with the increase of fractal dimensions for fracture length and aperture, while it can be remarkably lowered by introducing tortuosity at large branching angle. Also, a scaling law between the fracture density and fractal dimension for fracture length has been found, where the scaling exponent depends on the fracture number. The present fractal dual-porosity model may shed light on the transport physics of fractured porous media and provide theoretical basis for oil and gas exploitation, underground water, nuclear waste disposal and geothermal energy extraction as well as chemical engineering, etc.

New explicit correlation for the compressibility factor of natural gas: linearized z-factor isotherms

The compressibility factor (z-factor) of gases is a thermodynamic property used to account for the deviation of real gas behavior from that of an ideal gas. Correlations based on the equation of state are often implicit, because they require iteration and are computationally expensive. A number of explicit correlations have been derived to enhance simplicity; however, no single explicit correlation has been developed for the full range of pseudo-reduced temperatures $$\left( {1.05 \le T_{pr} \le 3} \right)$$ and pseudo-reduced pressures $$\left( {0.2 \le P_{pr} \le 15} \right)$$ , which represents a significant research gap. This work presents a new z-factor correlation that can be expressed in linear form. On the basis of Hall and Yarborough’s implicit correlation, we developed the new correlation from 5346 experimental data points extracted from 5940 data points published in the SPE natural gas reservoir engineering textbook and created a linear z-factor chart for a full range of pseudo-reduced temperatures $$(1.15 \le T_{pr} \le 3)$$ and pseudo-reduced pressures $$(0.2 \le P_{pr} \le 15)$$ .

The status quo and technical development direction of underground gas storages in China

UGS (underground gas storage) construction in China has stepped into a new development stage after years of exploration. The eleven UGSs that have been put into production play an important role in domestic natural gas peak shaving safety and supply guarantee, with designed working gas volume of 180 × 108 m3, but there are still various difficulties in UGS construction in China. Firstly, the increasing speed of working gas volume is slower than that of peak shaving demand volume. Secondly, the UGS building engineering is difficult in technologies and high in investment costs. Thirdly, safe operation is under high pressure and it is hard to identify and control risks. Fourthly, there are fewer candidate UGS sites in China and UGS building conditions are complicated. And fifthly, it is difficult for those UGSs to realize economic benefits only based on their own operation under the existing natural gas price systems. To sum up, the currently available UGS operation modes and building technologies in China are not sufficient to cope with the challenges resulted from markets and complex geologic conditions. Facing all these challenges, it is necessary not only to explore market driven operation modes, but also to strengthen technology tackling and carry out core technological research and development, including geologic evaluation, gas reservoir engineering, drilling and completion engineering, UGS injection and gas recovery engineering, surface auxiliary technologies and UGS integrity evaluation, so that UGS building efficiency can be increased greatly.

Evolution of the transport properties of fractures subject to thermally and mechanically activated mineral alteration and redistribution

AbstractStrong feedbacks link temperature (T), hydrologic flow (H), mechanical deformation (M), and chemical alteration (C) in fractured rock. These processes are interconnected as one process affects the initiation and progress of another. Dissolution and precipitation of minerals are affected by temperature and stress, and can result in significant changes in permeability and solute transport characteristics. Understanding these couplings is important for oil, gas, and geothermal reservoir engineering, for CO2 sequestration, and for waste disposal in underground repositories and reservoirs. To experimentally investigate the interactions between THMC processes in a naturally stressed fracture, we report on heated (25°C up to 150°C) flow‐through experiments on fractured core samples of Westerly granite. These experiments examine the influence of thermally and mechanically activated dissolution of minerals on the mechanical (stress/strain) and transport (permeability) responses of fractures. The evolutions of the permeability and relative hydraulic aperture of the fracture are recorded as thermal and stress conditions' change during the experiments. Furthermore, the efflux of dissolved mineral mass is measured periodically and provides a record of the net mass removal, which is correlated with observed changes in relative hydraulic fracture aperture. During the experiments, a significant variation of the effluent fluid chemistry is observed and the fracture shows large changes in permeability to the changing conditions both in stress and in temperature. We argue that at low temperature and high stresses, mechanical crushing of the asperities and the production of gouge explain the permeability decrease although most of the permeability is recoverable as the stress is released. While at high temperature, the permeability changes are governed by mechanical deformation as well as chemical processes, in particular, we infer dissolution of minerals adjacent to the fracture and precipitation of kaolinite.

New progresses in safe, clean and efficient development technologies for high-sulfur gas reservoirs

In China, there are a lot of high-sulfur gas reservoirs with total proved reserves of over 1 trillion m3, most of which were discovered in the Sichuan Basin. Most high-sulfur gas reservoirs in China, distributed in marine carbonate zones, are characterized by great buried depths, complex geologic conditions, high temperatures, high pressures, high H2S and CO2 content, presenting various challenges in gas field development engineering and production safety. Since the development of Sinian high-sulfur gas reservoirs in the Weiyuan area of the Sichuan Basin started in the 1960s, Wolonghe, Zhongba and other medium to small-scale gas reservoirs with medium to low sulfur content have been developed. Ever since 2009, successful production of Longgang and Puguang in the Sichuan Basin, together with some other high-sulfur gas reservoirs highlighted the breakthroughs in development technologies for high-sulfur gas reservoirs in China. This paper reviews the progress made in gas reservoir engineering, drilling and completion engineering, gas production, pipeline transportation, corrosion control, natural gas purification, HSE and other aspects with consideration of specific requirements related to safe, clean and high-efficient development of high-sulfur gas reservoirs since the “12th Five-Year Plan” period. Finally, considering the challenges in the development of high-sulfur gas reservoirs in China, we summarized the trend in future technological development with the following goals of reducing risks, minimizing environmental damages, and enhancing the efficiency of high-sulfur gas reservoir development.

An Identified Method for Lacustrine Shale Gas Reservoir Lithofacies Using Logs: A Case Study for No. 7 Section in Yanchang Formation in Ordos Basin

Unconventional reservoirs are keys to oil and gas exploration and development, especially shale gas reservoirs. Discriminated shale gas reservoir lithofacies are, in particular, a primary problem in shale gas reservoir engineering. The mineral composition will affect both absorbed and free gas contents, therefore their identification is important. The mineral composition is one part of lithofacies. The shale content has always been used in previous lithological identifications: this method is effective in sand reservoirs; however, it is not suitable for use in shale gas reservoirs. This paper takes No.7 section in Yanchang formation in Ordos basin as an example. Through a lithological analysis, it was concluded that overlap method and cross-plot method are not also inappropriate for shale gas reservoirs. The Ordos basin shale gas reservoir is divided into seven lithofacies. We form a mathematical method and apply it to shale gas reservoirs using the shale volume and ΔlgR which are available from conventional well logging and reflect organic matter in the processed dataset. Decision tree is used here. However, there were too many parameters to discriminate all lithofacies precisely. Principal component analysis (PCA) is a technique used to reduce multidimensional data sets to lower dimensions for analysis. This technique can be useful in petro-physics and geology as a preliminary method of combining multiple logs into a single entity or two logs without losing information. Combining PCA and a decision tree algorithm, the lithofacies of a shale gas reservoir were accurately discriminated.

Reservoir simulation of free and adsorbed gas production from shale

Shale gas has become a key natural gas resource and has been a great success in the USA and a few other countries. The gas production behaviour from shale is different to that from conventional gas reservoirs or coal seam reservoirs, primarily because of the different gas storage and flow behaviours in shale. Gas is stored in shale mainly as adsorbed gas in the pores of organic matter and clay minerals and as free gas compressed in other pores. Thus to understand how free and adsorbed gas contribute to the total gas production is a key question for shale gas reservoir engineering. One method to answer this question is by using reservoir simulation; however, this will require a reservoir simulator representing the shale gas storage and flow behaviours. In this work, a triple porosity model was applied in the reservoir simulator SIMED II, which was designed for dual porosity coal seam reservoirs, to account for both gas storage mechanisms of adsorption and free gas. A unique aspect of this new development is that the adsorbed gas, matrix free gas and fracture free gas are identified as different gas types but having the same gas properties. Thus the flow and production of gases with different storage mechanisms are directly identified in the simulation and output. The developed simulator was validated through history matching production data of a vertical well from the Barnett Shale. Then a series of parameter sensitivity analyses was carried out to investigate the impact of reservoir properties on adsorbed and free gas production. The results show that the contribution of adsorbed gas on the total gas production is generally low and is dependent on many factors such as the reservoir permeability, porosity and adsorption behaviour, and hydraulic fracturing effect.