scholarly journals CO2 Mass Transfer and Oil Replacement Capacity in Fractured Shale Oil Reservoirs: From Laboratory to Field

2022 ◽  
Vol 9 ◽  
Author(s):  
Runwei Qiao ◽  
Fengxia Li ◽  
Shicheng Zhang ◽  
Haibo Wang ◽  
Fei Wang ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Numerical Model ◽  
Production Management ◽  
Effective Diffusion ◽  
Oil Reservoirs ◽  
Diffusion Experiment ◽  
Shale Oil ◽  
Field Scale ◽  
The Matrix ◽  
Shale Oil Reservoirs

CO2-based fracturing is widely introduced to stimulate shale oil reservoirs for its multiple advantages. However, the range of CO2 entering the matrix around fractures and CO2-oil replacement capacity between matrix and fractures cannot be fully explained. To address this issue, a radial constant volume diffusion experiment on shale cores was designed in this study, and the pressure drop curve history was matched through numerical model to determine the composition effective diffusion coefficient. A field-scale numerical model was established, in which a series of certain grids were used to explicitly characterize fracture and quantify the prosess of CO2 mass transfer and oil replacement. Based on the field-scale numerical model, the process of shut-in, flow back, and oil production was simulated. The distribution of CO2 in fractured shale oil formation and its impact on crude oil during shut-in stage and flow back stage were investigated. This study concludes that CO2 gradually exchanges the oil in matrix into fractures and improve the fluidity of oil in matrix until the component concentrations of the whole reservoir reaches equilibrium during the shut-in process. Finally, about 30∼35 mole % of CO2 in fractures exchanges for oil in matrix. The range of CO2 entering the matrix around fractures is only 1.5 m, and oil in matrix beyond this distance will not be affected by CO2. During the process of flow back and production, the CO2 in fracture flows back quickly, but the CO2 in matrix is keeping dissolved in oil and will not be quickly produced. It is conclued that the longest possible shut-in time is conducive to making full use of the CO2-EOR mechanism in fractured shale oil reservoirs. However, due to the pursuit of economic value, a shut-in time of 10 days is the more suitable choice. This work can provide a better understanding of CO2 mass transfer mechanism in fractured shale oil reservoirs. It also provides a reference for the evaluation of the shut-in time and production management after CO2 fracturing.

Effect of Fracture Characteristics on Behavior of Fractured Shale-Oil Reservoirs by Cyclic Gas Injection

2016 ◽  
Vol 19 (02) ◽  
pp. 350-355 ◽  
Author(s):  
T.. Wan ◽  
J. J. Sheng ◽  
M. Y. Soliman ◽  
Y.. Zhang
Keyword(s):  
Oil Recovery ◽  
Gas Injection ◽  
Fracture Network ◽  
Production Performance ◽  
Oil Reservoirs ◽  
Shale Oil ◽  
Well Production ◽  
The Matrix ◽  
Stress Dependent ◽  
Shale Oil Reservoirs

Summary The current technique to produce shale oil is to use horizontal wells with multistage stimulation. However, the primary oil-recovery factor is only a few percent. The low oil recovery and abundance of shale reservoirs provide a huge potential for enhanced oil-recovery (EOR) process. Well productivity in shale oil-and-gas reservoirs primarily depends on the size of fracture network and the stimulated reservoir volume (SRV) that provides highly conductive conduits to communicate the matrix with the wellbore. The fracture complexity is critical to the well-production performance, and it also provides an avenue for injected fluids to displace the trapped oil. However, the disadvantage of gasflooding in fractured reservoirs is that injected fluids may break through to production wells by means of the fracture network. Therefore, a preferred method is to use cyclic gas injection to overcome this problem. In this paper, we use a numerical-simulation approach to evaluate the EOR potential in fractured shale-oil reservoirs by cyclic gas injection. Simulation results indicate that the stimulated fracture network contributes significantly to the well productivity by means of its large contact area with the matrix, which prominently enhances the macroscopic sweep efficiency in secondary cyclic gas injection. In our previous simulation work, the EOR potential was evaluated in hydraulic planar-traverse fractures without considering the propagation of a natural-fracture network. In this paper, we examine the effect of fracture networks on shale oilwell secondary-production performance. The impact of fracture spacing and stress-dependent fracture conductivity on the ultimate oil recovery is investigated. The results presented in this paper demonstrate that cyclic gas injection has EOR potential in shale-oil reservoirs. This paper focuses on evaluating the effect of fracture spacing, the size of the fracture network, fracture connectivity (uniform and nonuniform), and stress-dependent fracture-network conductivity on well-production performance of shale-oil reservoirs by secondary cyclic gas injection.

scholarly journals Evaluation of the Effectiveness of Continuous Gas Displacement for EOR in Hydraulically Fractured Shale Reservoirs

SPE Journal ◽  
2021 ◽  
pp. 1-24
Author(s):  
George Moridis ◽  
Matthew Reagan
Keyword(s):  
Oil Recovery ◽  
Gas Production ◽  
Oil Reservoirs ◽  
Natural Fracture ◽  
Temperature Phase ◽  
Shale Oil ◽  
Early Arrival ◽  
Wide Range ◽  
The Matrix ◽  
Shale Oil Reservoirs

Summary The main objective of this study is to analyze and describe quantitatively the effectiveness of continuous gas displacement as an enhanced oil recovery (EOR) process to increase production from multifractured shale oil reservoirs. The study uses CH4 continuously injected through horizontal wells parallel to the production wells as the displacement agent and investigates the effects of various attributes of the matrix and of the induced and natural fracture systems. This numerical simulation study focuses on the analysis of the 3D minimum repeatable element (stencil/domain) that can describe a hydraulically fractured shale reservoir under production. The stencil is discretized using a very fine (millimeter-scale) grid. We compare the solutions to a reference case that involves simple depressurization-induced production (i.e., without a gas drive). We monitor continuously (a) the rate and composition of the production stream and (b) the spatial distributions of pressure, temperature, phase saturations, and relative permeabilities. The results of the study indicate that a continuous CH4-based displacement that begins at the onset of production does not appear to be an effective EOR method for hydraulically fractured shale oil reservoirs over a 5-year period in reservoirs in which natural or induced fractures in the undisturbed reservoir and/or in the stimulated reservoir volume (SRV) can be adequately described by a single-medium porosity and permeability. Under these conditions in a system with typical Bakken or Eagle Ford matrix and fracture attributes, continuous CH4 injection by means of a horizontal well parallel to the production well causes a reduction in water production and an (expected) increase in gas production but does not lead to any significant increase in oil production. This is attributed to (a) the limited penetration of the injected gas into the ultralow-k formation, (b) the dissolution of the injected gas into the oil, and (c) its early arrival at the hydraulic fracture (HF; thus, short circuiting the EOR process by bypassing the bulk of the matrix), in addition to (d) the increase in the pressure of the HF and the consequent reduction in the driving force of production and the resulting flow. Under the conditions of this study, these observations hold true for domains with and without an SRV over a wide range of matrix permeabilities and for different lengths and positions (relative to the HF) of the gas injection wells.

Use of Interference Tests to Constrain the Spacing of Hydraulically Fractured Wells in Neuquen Shale Oil Reservoirs

2017 ◽  
Author(s):  
T. Chen ◽  
R. Salas-Porras ◽  
D. Mao ◽  
V. Jain ◽  
M. A. Thomas ◽  
...  
Keyword(s):  
Oil Reservoirs ◽  
Shale Oil ◽  
Interference Tests ◽  
Shale Oil Reservoirs

Seismic resolution enhancement in shale-oil reservoirs

Geophysics ◽  
2018 ◽  
Vol 83 (5) ◽  
pp. B281-B287 ◽  
Author(s):  
Xiwu Liu ◽  
Fengxia Gao ◽  
Yuanyin Zhang ◽  
Ying Rao ◽  
Yanghua Wang
Keyword(s):  
Seismic Data ◽  
Resolution Enhancement ◽  
Oil Reservoirs ◽  
Inversion Method ◽  
Shale Oil ◽  
Data Set ◽  
Extension Method ◽  
Seismic Resolution ◽  
Full Band ◽  
Shale Oil Reservoirs

We developed a case study of seismic resolution enhancement for shale-oil reservoirs in the Q Depression, China, featured by rhythmic bedding. We proposed an innovative method for resolution enhancement, called the full-band extension method. We implemented this method in three consecutive steps: wavelet extraction, filter construction, and data filtering. First, we extracted a constant-phase wavelet from the entire seismic data set. Then, we constructed the full-band extension filter in the frequency domain using the least-squares inversion method. Finally, we applied the band extension filter to the entire seismic data set. We determined that this full-band extension method, with a stretched frequency band from 7–70 to 2–90 Hz, may significantly enhance 3D seismic resolution and distinguish reflection events of rhythmite groups in shale-oil reservoirs.

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