scholarly journals Role of Gas Viscosity for Shale Gas Percolation

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Xiaoming Wang ◽  
Junbin Chen ◽  
Dazhong Ren ◽  
Zhaolong Shi
Keyword(s):  
Pressure Drop ◽  
Shale Gas ◽  
Double Porosity ◽  
Gas Viscosity ◽  
Important Index ◽  
Bottom Hole ◽  
Fracture Systems ◽  
Bottom Hole Flowing Pressure ◽  
Porosity Model

Viscosity is an important index to evaluate gas flowability. In this paper, a double-porosity model considering the effect of pressure on gas viscosity was established to study shale gas percolation through reservoir pressure, gas velocity, and bottom hole flowing pressure. The experimental results show that when pressure affects gas viscosity, shale gas viscosity decreases, which increases the percolation velocity and pressure drop velocity of the free state shale gas in matrix and fracture systems. And it is conducive to the desorption of adsorbed shale gas and effectively supplemented the bottom hole flowing pressure with the pressure wave propagation range and velocity increasing, so that the rate of pressure drop at the bottom of the well slows down, which makes the time that bottom hole flowing pressure reaches stability shortened. Therefore, the gas viscosity should be fully considered when studying the reservoir gas percolation.

scholarly journals Effect of the Angle between Hydraulic Fracture and Natural Fracture on Shale Gas Seepage

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Xiaoming Wang ◽  
Junbin Chen ◽  
Jianhong Zhu ◽  
Diguang Gong
Keyword(s):  
Numerical Simulation ◽  
Shale Gas ◽  
Hydraulic Fracture ◽  
Natural Fracture ◽  
Reservoir Pressure ◽  
Effective Measure ◽  
Seepage Rate ◽  
Bottom Hole ◽  
Gas Seepage ◽  
Bottom Hole Flowing Pressure

Fracturing technology is an effective measure to exploit shale gas and the fractures improve the seepage ability of shale reservoir after fracturing. In this paper, taking Chang 7 of Yanchang Formation as the study area, a double porosity seepage model considering natural fracture was established and it was solved by finite element method of COMSOL5.5; then, shale gas seepage was analyzed under different angles between hydraulic fracture and natural fracture finally. Meanwhile, angles between hydraulic fracture and natural fracture were optimized by analyzing both the reservoir pressure distribution and bottom hole flowing pressure. Also, a permeability experiment with liquid was conducted to verify the accuracy of the numerical simulation result. Both numerical simulation and permeability measurement experiment get a uniform result that the optimal angle between hydraulic fracture and natural fracture is 90°. Permeability is the highest, shale gas seepage rate is the fastest, bottom hole flowing pressure is the highest, and also it is beneficial to the desorption of adsorbed gas in the matrix system and then effectively supplements reservoir pressure and bottom hole flowing pressure. The research results will provide some theoretical guidance for fracturing design.

scholarly journals Gas Flow Tightly Coupled to Elastoplastic Geomechanics for Tight- and Shale-Gas Reservoirs: Material Failure and Enhanced Permeability

SPE Journal ◽  
2014 ◽  
Vol 19 (06) ◽  
pp. 1110-1125 ◽  
Author(s):  
Jihoon Kim ◽  
George J. Moridis
Keyword(s):  
Shale Gas ◽  
Shear Failure ◽  
Double Porosity ◽  
Gas Production ◽  
Coupled Flow ◽  
Gas Reservoirs ◽  
Shale Gas Reservoirs ◽  
Tightly Coupled ◽  
Secondary Fractures ◽  
Porosity Model

Summary We investigate coupled flow and geomechanics in gas production from extremely low-permeability reservoirs such as tight- and shale-gas reservoirs, using dynamic porosity and permeability during numerical simulation. In particular, we take the intrinsic permeability as a step function of the status of material failure, and the permeability is updated every timestep. We consider gas reservoirs with the vertical and horizontal primary fractures, using the single- and dynamic double-porosity (dual-continuum) models. We modify the multiple-porosity constitutive relations for modeling the double porous continua for flow and geomechanics. The numerical results indicate that the production of gas causes redistribution of the effective-stress fields, increasing the effective shear stress and resulting in plasticity. Shear failure occurs not only near the fracture tips but also away from the primary fractures, which indicates the generation of secondary fractures. These secondary fractures increase the permeability significantly, and change the flow pattern, which, in turn, causes a change in the distribution of geomechanical variables. From various numerical tests, we find that shear failure is enhanced by a large pressure drop at the production well, a high Biot's coefficient, and low frictional and dilation angles. Smaller spacing between the horizontal wells also contributes to faster secondary fracturing. When the dynamic double-porosity model is used, we observe a faster evolution of the enhanced-permeability areas than that obtained from the single-porosity model, mainly because of a higher permeability of the fractures in the double-porosity model. These complicated physics for stress-sensitive reservoirs cannot properly be captured by the uncoupled or flow-only simulation, and, thus, tightly coupled flow and geomechanical models are highly recommended to describe accurately the reservoir behavior during gas production in tight- and shale-gas reservoirs and to design production scenarios smartly.

scholarly journals Double porosity model to describe both permeability change and dissolution processes

2015 ◽  
Vol 2 (5) ◽  
pp. 15-00210-15-00210 ◽  
Author(s):  
Yuichi NIIBORI ◽  
Hideo USUI ◽  
Taiji CHIDA
Keyword(s):  
Double Porosity ◽  
Permeability Change ◽  
Double Porosity Model ◽  
Porosity Model

scholarly journals Nested Recharge Systems in Mountain Block Hydrology: High-Elevation Snowpack Generates Low-Elevation Overwinter Baseflow in a Rocky Mountain River

Water ◽  
2021 ◽  
Vol 13 (16) ◽  
pp. 2249
Author(s):  
Éowyn M. S. Campbell ◽  
M. Cathryn Ryan
Keyword(s):  
Rocky Mountain ◽  
High Elevation ◽  
Third Order ◽  
Relative Temperature ◽  
Local Flow ◽  
Fracture Systems ◽  
Lower Elevation ◽  
Flow Systems ◽  
Longitudinal Sampling

The majority of each year′s overwinter baseflow (i.e., winter streamflow) in a third-order eastern slopes tributary is generated from annual melting of high-elevation snowpack which is transmitted through carbonate and siliciclastic aquifers. The Little Elbow River and its tributaries drain a bedrock system formed by repeated thrust faults that express as the same siliciclastic and carbonate aquifers in repeating outcrops. Longitudinal sampling over an 18 km reach was conducted at the beginning of the overwinter baseflow season to assess streamflow provenance. Baseflow contributions from each of the two primary aquifer types were apportioned using sulfate, δ34SSO4, and silica concentrations, while δ18OH2O composition was used to evaluate relative temperature and/or elevation of the original precipitation. Baseflow in the upper reaches of the Little Elbow was generated from lower-elevation and/or warmer precipitation primarily stored in siliciclastic units. Counterintuitively, baseflow generated in the lower-elevation reaches originated from higher-elevation and/or colder precipitation stored in carbonate units. These findings illustrate the role of nested flow systems in mountain block recharge: higher-elevation snowmelt infiltrates through fracture systems in the cliff-forming—often higher-elevation—carbonates, moving to the lower-elevation valley through intermediate flow systems, while winter baseflow in local flow systems in the siliciclastic valleys reflects more influence from warmer precipitation. The relatively fast climatic warming of higher elevations may alter snowmelt timing, leaving winter water supply vulnerable to climatic change.

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