scholarly journals Production Analysis for Fractured Vertical Well in Coal Seam Reservoirs with Stimulated Reservoir Volume

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Chen Li
Keyword(s):  
Analytical Solution ◽  
Coalbed Methane ◽  
Outer Region ◽  
Natural Fracture ◽  
Finite Conductivity ◽  
Stimulated Reservoir Volume ◽  
New Model ◽  
Vertical Well ◽  
Reservoir Volume ◽  
Coalbed Methane Reservoir

The development and utilization of coalbed methane is of great significance to reduce carbon dioxide emission. Through the research, this paper presents a fast analytical solution method for the productivity of coalbed methane reservoir with finite-conductivity fractured well and stimulated reservoir volume region. Based on the dual-porosity flowing mechanism, combined with the Langmuir adsorb equation, Fick diffusion law, and Darcy law, a mathematical model considering diffusion in matrix and transport in natural fracture system is established, using spherical matrix to describe the transient steady-state sorption, and using cubic matrix to describe the pseudosteady-state sorption. Then, combined with the inner system and outer system, the analytical solution was obtained. Furthermore, the accuracy of the solution was validated against a numerical simulation. According to the Duhamel principle, the effect of wellbore storage and skin factor was got. Due to the SRV region, the linear flow and radial flow will appear before the pressure wave reach the outer region. And then, based on the pressure analysis result, we will have made the sensitivity analysis with different influence parameter. The result reveals that storage coefficient and conductivity factor mainly influence the early time; the permeability ratio and dimensionless SRV region radius mainly influence the property of SRV region. Finally, the analytical solution of the new model was applied to field history match. This model takes into account the adsorption and desorption characteristics of coalbed methane, as well as the SRV zones generated during fracturing. The calculation speed of the new model is increased while the calculation accuracy is retained, and the intensity of software application is reached. The model achieves the purpose of rapid evaluation and accurate prediction of gas well productivity and obtains a set of productivity evaluation method suitable for coalbed methane reservoir with fractured vertical well, which provides a basis for the development and productivity evaluation of coalbed methane reservoir in domestic and international cooperation.

scholarly journals Productivity Analysis of Volume Fractured Vertical Well Model in Tight Oil Reservoirs

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Jiahang Wang ◽  
Xiaodong Wang ◽  
Wenli Xu ◽  
Cheng Lu ◽  
Wenxiu Dong ◽  
...  
Keyword(s):  
Outer Region ◽  
Fracture Network ◽  
Oil Reservoirs ◽  
Finite Conductivity ◽  
Tight Oil ◽  
Productivity Analysis ◽  
Type Curves ◽  
Stimulated Reservoir Volume ◽  
Vertical Well ◽  
Tight Oil Reservoirs

This paper presents a semianalytical model to simulate the productivity of a volume fractured vertical well in tight oil reservoirs. In the proposed model, the reservoir is a composite system which contains two regions. The inner region is described as formation with finite conductivity hydraulic fracture network and the flow in fracture is assumed to be linear, while the outer region is simulated by the classical Warren-Root model where radial flow is applied. The transient rate is calculated, and flow patterns and characteristic flowing periods caused by volume fractured vertical well are analyzed. Combining the calculated results with actual production data at the decline stage shows a good fitting performance. Finally, the effects of some sensitive parameters on the type curves are also analyzed extensively. The results demonstrate that the effect of fracture length is more obvious than that of fracture conductivity on improving production in tight oil reservoirs. When the length and conductivity of main fracture are constant, the contribution of stimulated reservoir volume (SRV) to the cumulative oil production is not obvious. When the SRV is constant, the length of fracture should also be increased so as to improve the fracture penetration and well production.

scholarly journals A numerical investigation on the performance of hydraulic fracturing in naturally fractured gas reservoirs based on stimulated rock volume

2020 ◽  
Vol 10 (8) ◽  
pp. 3333-3345
Author(s):  
Ali Al-Rubaie ◽  
Hisham Khaled Ben Mahmud
Keyword(s):  
Hydraulic Fracturing ◽  
Hydraulic Fracture ◽  
Natural Fracture ◽  
Shear Stresses ◽  
Individual Element ◽  
Natural Fractures ◽  
Gas Reservoirs ◽  
Stimulated Reservoir Volume ◽  
Reservoir Volume ◽  
Naturally Fractured

Abstract All reservoirs are fractured to some degree. Depending on the density, dimension, orientation and the cementation of natural fractures and the location where the hydraulic fracturing is done, preexisting natural fractures can impact hydraulic fracture propagation and the associated flow capacity. Understanding the interactions between hydraulic fracture and natural fractures is crucial in estimating fracture complexity, stimulated reservoir volume, drained reservoir volume and completion efficiency. However, because of the presence of natural fractures with diffuse penetration and different orientations, the operation is complicated in naturally fractured gas reservoirs. For this purpose, two numerical methods are proposed for simulating the hydraulic fracture in a naturally fractured gas reservoir. However, what hydraulic fracture looks like in the subsurface, especially in unconventional reservoirs, remain elusive, and many times, field observations contradict our common beliefs. In this study, the hydraulic fracture model is considered in terms of the state of tensions, on the interaction between the hydraulic fracture and the natural fracture (45°), and the effect of length and height of hydraulic fracture developed and how to distribute induced stress around the well. In order to determine the direction in which the hydraulic fracture is formed strikethrough, the finite difference method and the individual element for numerical solution are used and simulated. The results indicate that the optimum hydraulic fracture time was when the hydraulic fracture is able to connect natural fractures with large streams and connected to the well, and there is a fundamental difference between the tensile and shear opening. The analysis indicates that the growing hydraulic fracture, the tensile and shear stresses applied to the natural fracture.

Characterizing the Stimulated Reservoir Volume During Hydraulic Fracturing-Connecting the Pressure Fall-Off Phase to the Geomechanics of Fracturing

2018 ◽  
Vol 85 (10) ◽  
Author(s):  
Erfan Sarvaramini ◽  
Maurice B. Dusseault ◽  
Robert Gracie
Keyword(s):  
Hydraulic Fracturing ◽  
Fracture Network ◽  
Natural Fracture ◽  
Breakdown Pressure ◽  
Pressure Derivative ◽  
Stimulated Reservoir Volume ◽  
Reservoir Volume ◽  
Flow Capacity ◽  
Pressure Fall

Microseismic imaging of the hydraulic fracturing operation in the naturally fractured rocks confirms the existence of a stimulated volume (SV) of enhanced permeability. The simulation and characterization of the SV evolution is uniquely challenging given the uncertainty in the nature of the rock mass fabrics as well as the complex fracturing behavior of shear and tensile nature, irreversible plastic deformation and damage. In this paper, the simulation of the SV evolution is achieved using a nonlocal poromechanical plasticity model. Effects of the natural fracture network are incorporated via a nonlocal plasticity characteristic length, ℓ. A nonlocal Drucker–Prager failure model is implemented in the framework of Biot's theory using a new implicit C0 finite element method. First, the behavior of the SV for a two-dimensional (2D) geomechanical injection problem is simulated and the resulting SV is assessed. It is shown that breakdown pressure and stable fracturing pressure are the natural outcomes of the model and both depend upon ℓ. Next, the post-shut-in behavior of the SV is analyzed using the pressure and pressure derivative plots. A bilinear flow regime is observed and it is used to estimate the flow capacity of the SV. The results show that the flow capacity of the SV increases as ℓ decreases (i.e., as the SV behaves more like a single hydraulic fracture); however, for 0.1m≤ℓ≤1m, the calculated flow capacity indicates that the conductivity of the SV is finite. Finally, it is observed that as ℓ tends to zero, the flow capacity of the SV tends to infinity and the SV behaves like a single infinitely conducting fracture.

scholarly journals Transient Pressure Analysis of a Multiple Fractured Well in a Stress-Sensitive Coal Seam Gas Reservoir

Energies ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3849 ◽  
Author(s):  
Zuhao Kou ◽  
Haitao Wang
Keyword(s):  
Fluid Flow ◽  
Coalbed Methane ◽  
Radial Flow ◽  
Outer Region ◽  
Stress Sensitivity ◽  
Natural Fracture ◽  
Radial Fracture ◽  
Transient Pressure ◽  
Fractured Well ◽  
Adsorption Desorption

This paper investigates the bottom-hole pressure (BHP) performance of a fractured well with multiple radial fracture wings in a coalbed methane (CBM) reservoir with consideration of stress sensitivity. The fluid flow in the matrix simultaneously considers adsorption–desorption and diffusion, whereas fluid flow in the natural fracture system and the induced fracture network obeys Darcy’s law. The continuous line-source function in the CBM reservoir associated with the discretization method is employed in the Laplace domain. With the aid of Stehfest numerical inversion technology and Gauss elimination, the transient BHP responses are determined and analyzed. It is found that the main flow regimes for the proposed model in the CBM reservoir are as follows: linear flow between adjacent radial fracture wings, pseudo-radial flow in the inner region or Stimulated Reservoir Volume (SRV), and radial flow in outer region (un-stimulated region). The effects of permeability modulus, radius of SRV, ratio of permeability in SRV to that in un-stimulated region, properties of radial fracture wings, storativity ratio of the un-stimulated region, inter-porosity flow parameter, and adsorption–desorption constant on the transient BHP responses are discussed. The results obtained in this study will be of great significance for the quantitative analyzing of the transient performances of the wells with multiple radial fractures in CBM reservoirs.

scholarly journals Multiporosity and Multiscale Flow Characteristics of a Stimulated Reservoir Volume (SRV)-Fractured Horizontal Well in a Tight Oil Reservoir

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2724 ◽  
Author(s):  
Long Ren ◽  
Wendong Wang ◽  
Yuliang Su ◽  
Mingqiang Chen ◽  
Cheng Jing ◽  
...  
Keyword(s):  
Horizontal Well ◽  
Oil Reservoirs ◽  
Natural Fracture ◽  
Tight Oil ◽  
Fracture System ◽  
Stimulated Reservoir Volume ◽  
Discrete Fracture Model ◽  
Reservoir Volume ◽  
Fractured Horizontal Well ◽  
Tight Oil Reservoirs

There are multiporosity media in tight oil reservoirs after stimulated reservoir volume (SRV) fracturing. Moreover, multiscale flowing states exist throughout the development process. The fluid flowing characteristic is different from that of conventional reservoirs. In terms of those attributes of tight oil reservoirs, considering the flowing feature of the dual-porosity property and the fracture network system based on the discrete-fracture model (DFM), a mathematical flow model of an SRV-fractured horizontal well with multiporosity and multipermeability media was established. The numerical solution was solved by the finite element method and verified by a comparison with the analytical solution and field data. The differences of flow regimes between triple-porosity, dual-permeability (TPDP) and triple-porosity, triple-permeability (TPTP) models were identified. Moreover, the productivity contribution degree of multimedium was analyzed. The results showed that for the multiporosity flowing states, the well bottomhole pressure drop became slower, the linear flow no longer arose, and the pressure wave arrived quickly at the closed reservoir boundary. The contribution ratio of the matrix system, natural fracture system, and network fracture system during SRV-fractured horizontal well production were 7.85%, 43.67%, and 48.48%, respectively in the first year, 14.60%, 49.23%, and 36.17%, respectively in the fifth year, and 20.49%, 46.79%, and 32.72%, respectively in the 10th year. This study provides a theoretical contribution to a better understanding of multiscale flow mechanisms in unconventional reservoirs.

Study on the Feasibility of SRV in Coal Reservoir

2014 ◽  
Vol 986-987 ◽  
pp. 734-737
Author(s):  
Lin Lin Cheng ◽  
Yuan Fang Cheng ◽  
Chong Chen ◽  
Dong Feng Zhu ◽  
Wen Biao Deng
Keyword(s):  
Coalbed Methane ◽  
New Technology ◽  
Gas Content ◽  
Stimulated Reservoir Volume ◽  
Reservoir Volume ◽  
Surface Development ◽  
Low Efficiency ◽  
Weak Structure ◽  
Coal Reservoir ◽  
Rock Brittleness

In our country there is plenty of CBM (coalbed methane), but the state of CBM itself, unique output mechanism and low saturation, low permeability, low reservoir pressure and high gas content, et al. determine the low efficiency of it, so in order to improve CBM recovery, combined with the successful experience of north American shale gas reservoir by SRV(stimulated reservoir volume), the writer summarizes the implementation of SRV, deeply analyzes effectiveness and limitations of this new technology in CBM development. The results of practical research and theoretical analysis show that SRV in the coal reservoir can achieve the desired effect on the condition that there are great quantity of natural fractures, joints and bedding, weak structure surface development in the reservoir, the rock brittleness index is greater than 40 and horizontal principal stress difference is relatively smaller. Finally, simulating a well’s condition by the MEYER software, the result shows that SRV is feasible in coal reservoir, which will create important guiding significance and practical value for the exploration of CBM.

scholarly journals Study of Cyclic Fracturing in Vertical CBM Wells

2017 ◽  
Vol 10 (1) ◽  
pp. 108-117 ◽  
Author(s):  
Ting Li ◽  
Ji-fang Wan
Keyword(s):  
Hydraulic Fracturing ◽  
Economic Benefits ◽  
Natural Fracture ◽  
Coal Bed ◽  
Coal Bed Methane ◽  
Plastic Behavior ◽  
Natural Fractures ◽  
Stimulated Reservoir Volume ◽  
Reservoir Volume ◽  
Coal Rock

Background:Coal-bed methane productivity of single well is very low, and has been the bottleneck of the coal-bed methane industry in China.Objective:Although hydraulic fracturing is the only stimulation measure to develop CBM, it cannot increase production effectively, conventional fracturing method to create opening fractures should be improved. How to make good use of natural fractures, which are plentiful in CBM reservoirs, is also an important subject for hydraulic fracturing.Method:In this paper, the plastic deformation of coal rock is analyzed by harnessing a pseudo-Maxwell creep phenomenon, which is normally present in rock. The Kelvin-Voigt model is utilized to describe pseudo-plastic behavior of coal rock to determine pressurization and decay cyclic time for cyclic fracturing design. The mechanical requirement for shearing natural fractures is also analyzed, and shearing distance between the faces of natural fracture can be calculated by Westergaard stress function. Ultimately, the cyclic fracturing method is proposed according to theories about stress alteration and shearing of natural fractures. This method includes such periods as fracturing, pumping shut-down and so on.Conclusion:A complex fracture system can be created, which consists of opened and sheared fractures, then, large SRV(stimulated reservoir volume)and flowing drainage area can be acquired. In comparison with conventional fracturing method, this new way can make full use of the characteristics of CBM reservoirs and is more suitable to CBM. This method will lead to a significant increase of CBM production, and will achieve huge economic benefits.

scholarly journals Research of Network Fracturing Method for Coalbed Methane Reservoirs

2016 ◽  
Vol 9 (1) ◽  
pp. 247-256 ◽  
Author(s):  
Ting Li ◽  
Jifang Wan
Keyword(s):  
Hydraulic Fracturing ◽  
Coalbed Methane ◽  
Hydraulic Fractures ◽  
Natural Fractures ◽  
Stimulated Reservoir Volume ◽  
Matrix Permeability ◽  
Reservoir Volume ◽  
Present Technique ◽  
Net Pressure ◽  
Main Flaw

The application of conventional hydraulic fracture treatment is not ideal in coalbed methane reservoirs, which influences the industry development in China, thus, the present technique should be improved. From two aspects of net pressure and stress sensibility of permeability, it is analyzed and considered that permeability around hydraulic fractures is damaged severely, so this is the main flaw of conventional hydraulic fracturing in CBM. It is proposed to shear natural fractures by fracturing treatment, which are plentiful in coalbed methane reservoirs, and the mechanical condition to generate sheared fractures is presented, in the meanwhile, it is verified that the permeability of sheared fractures is much larger than coal matrix permeability. When the angle between natural and hydraulic fractures is small in coalbed methane reservoirs, the natural fractures will shear easily at low net pressure, so network fractures can be formed. In comparison with conventional hydraulic fracturing, this new methodology can make natural fractures shear at low net pressure to form transverse network fractures, hence, the stimulated reservoir volume is larger, and damage to coal permeability is avoided. This new technique is advantageous in both stimulated reservoir volume and permeability improvement, and it is more adaptable for coalbed methane reservoirs, thus, it has a wide application prospect and significant value.

Numerical Modeling of Fracture Propagation During Temporary-Plugging Fracturing

SPE Journal ◽  
2019 ◽  
Vol 25 (03) ◽  
pp. 1503-1522 ◽  
Author(s):  
Yushi Zou ◽  
Xinfang Ma ◽  
Shicheng Zhang
Keyword(s):  
Influence Factors ◽  
Injection Pressure ◽  
Natural Fracture ◽  
Hydraulic Fractures ◽  
Pumping Rate ◽  
Stimulated Reservoir Volume ◽  
Reservoir Volume ◽  
Interaction Behavior ◽  
Before And After ◽  
Horizontal Differential Stress

Summary Temporary-plugging fracturing (TPF) is becoming a promising technique for maximizing the stimulated-reservoir volume in tight reservoirs by injecting diverting agents to plug the preferred perforations and/or hydraulic fractures (HFs). Previous work has developed diverting agents and evaluated their blocking efficiency. However, the mechanism and dominant influence factors of HF growth during TPF remain poorly understood to date, which restricts the application of this technique. To understand the problem and help improve the TPF design, this study simulated the HF-propagation process during TPF in a naturally fractured formation using a previously developed 3D discrete-element-method (DEM) -based complex fracture model. Plugged fracture elements with negligible permeability were incorporated into the model to characterize the blocking intervals of diverting agents within HFs. Parameters, including horizontal differential stress (Δσh), natural-fracture (NF) properties, the number of pluggings, plugging positions, and pumping rate, were investigated to determine their effects on the HF/NF-interaction behavior and the resulting HF geometry. The change in injection pressure before and after plugging under different conditions was also recorded in detail. Modeling results show that the HF/NF-interaction behavior might surprisingly change before and after plugging the preferred HF, ranging from HF crossing of NFs to HF opening of NFs. Notably, Δσh is still the most influential geological parameter that governs the HF-growth behavior during TPF. For a moderate Δσh (=8 MPa), the growth of a single planar HF before plugging can be changed easily into a complex HF network (HFN) through opening of NFs after plugging in the target stimulated region (TSR). In this case, the complexity and covering area of the resulting HFN is closely related to the NF density (positive correlation) and plugging positions. However, for a high Δσh (=12 MPa), opening (usually partially) the NFs after plugging is difficult even in formations with a high density of NFs. In such a case, a large volume of fluid, a high pumping rate, and several repeat pluggings during TPF are necessary. The results of this study help to understand the HF-growth mechanism during TPF and help to optimize the treatment design of TPF and to adjust it in a timely manner.

scholarly journals Production analysis for fractured vertical well in rectangular coal reservoirs

2018 ◽  
Vol 73 ◽  
pp. 62
Author(s):  
Chen Li ◽  
Zhenzhen Dong ◽  
Xiang Li
Keyword(s):  
Coal Seam ◽  
Analytical Solutions ◽  
Methane Production ◽  
Coalbed Methane ◽  
Finite Conductivity ◽  
Storage Coefficient ◽  
Vertical Well ◽  
Production Analysis ◽  
Coalbed Methane Production ◽  
And Diffusion

As one kind of unconventional natural gas, coalbed methane is an important energy resource that is subject to active research. Gas exists in coalbed methane reservoirs in two forms: free gas and adsorbed gas. In the course of coalbed methane production, the reservoir experiences pressure decrease, desorption, diffusion, and seepage. Previous models of coalbed methane production were mainly concerned with circular boundaries. However, field tests revealed that some fractured wells possess the characteristics of rectangular boundaries. For fractured rectangular coalbed methane reservoirs, it is necessary to deal with the four boundaries with mirror image theory, which complicates calculations. In addition, the desorption and adsorption process of coalbed methane exerts a strong effect on the seepage process. Furthermore, the complexity of the rectangular coal seam embedded with the finite-conductivity fracture results in a significant computational challenge. For the first time, this paper presented a fast analytical solution for a finite-conductivity fractured vertical well model with either rectangular closed or constant-pressure boundaries in the coal seam. On the basis of the Fick diffusion law and the Darcy seepage law, a mathematical model that considers diffusion in matrix and seepage within natural fractures was established. Then, we integrated the fracture conductivity function method with the hydraulic fracture model to greatly increase computational efficiency. The analytical solutions were validated against a numerical simulation. Parameter sensitivity analysis reveals that interporosity coefficient and storage coefficient, respectively, affect the appearance time and degree of desorption and diffusion. Desorption coefficient mainly describes the capacity of desorption and diffusion. Well storage coefficient, conductivity factor, and skin factor mainly affect the early stage of production. Finally, the proposed solutions were applied to field history match. The model developed is applicable to production analysis and well testing for coalbed methane reservoirs. The new proposed model extended flow mechanism of coalbed methane, and provided a better production and pressure forecast for coalbed methane reservoirs. In addition, the analytical solutions can be used to generate type curves for fractured vertical wells with finite conductivity and in the rectangular boundary, and provide a sound theoretical basis for well tests in the coal seam. The model is also applicable to other types of unconventional gas reservoirs, such as gas shales, in which the same processes are present.

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