Investigation of Various Pressure Transient Techniques on Permeability Measurement of Unconventional Gas Reservoirs

Permeability anisotropy of shale and tight gas reservoirs is critical for applications in unconventional gas recovery, but laboratory measurements are still limited. This paper presents an experimental method for determining permeability anisotropy of shale and tight reservoirs. The method uses gas production data from a canister and an analytical solution of continuity equation in anisotropic core sample. Axial permeability and transverse permeability of the core are estimated by matching experimental data with analytical solution. The proposed method is verified by comparing with true values and calculated values through numerical simulations that cover variations in rock permeability. The method is applied to real data measured in canister degassing tests (CDT) involving two different directional shale core samples. Then, the experimental results are compared with the results from pulse pressure decay (PPD) method. Both the verification from numerically calculated results and the comparison between PPD results and CDT results exhibit the practicality of the proposed method. At last, the effects of permeability anisotropy, porosity, initial gas pressure, rock dimensions, and adsorption on the profiles of gas production are investigated.

Section: Comparison Between Cdt Results and Ppd Resultsmentioning

confidence: 99%

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confidence: 99%

A method for simultaneously determining axial permeability and transverse permeability of tight reservoir cores by canister degassing test

Zhao

Wang

2019

“…However, a limited number of publications 17-20 could be found for coal permeability measurements by using the PDM, and there are some shortcomings when the PDM is applied to coals and other organic-rich reservoir rocks. [18][19][20] The influence of gas sorption effect on permeability measurements was not fully considered in the conventional PDM, and thereby, considerable errors may result when testing unconventional reservoir rocks, especially for rocks with strong sorption potential. In the previous study, a detailed comparison between Brace et al's technique and Dicker and Smits's technique was made for San Juan basin coal, and the conclusion that these two methods can be both valid when the reservoir pressure less than 1200 psi was drawn.…”

Section: Introductionmentioning

confidence: 99%

“…The PDM has long been widely used for permeability measurements of conventional gas reservoirs. However, a limited number of publications [17][18][19][20] could be found for coal permeability measurements by using the PDM, and there are some shortcomings when the PDM is applied to coals and other organic-rich reservoir rocks. Different pulse-decay techniques are presented in Table 1 based on the experimental results reported by Feng et al 18 .…”

Section: Introductionmentioning

confidence: 99%

“…21,22 During reservoir depressurization, desorption of gas adsorbed on the inner pores leads to coal matrix shrinkage and then widens cleat aperture. [18][19][20] The influence of gas sorption effect on permeability measurements was not fully considered in the conventional PDM, and thereby, considerable errors may result when testing unconventional reservoir rocks, especially for rocks with strong sorption potential. 23 The amount of gas sorption has been experimentally investigated and empirically described by the Langmuir model.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of the vertical stress on CO₂ flow behavior and permeability variation in coalbed methane reservoirs

Ding

Jia

Feng

2019

Self Cite

Given that in situ stress evolution is of great importance in characterizing coalbed methane reservoirs during gas production, CO2 sequestration, and reservoir fracturing, a series of laboratory measurements were conducted to investigate the role of the vertical stress on gas flow behavior and permeability evolution of San Juan Basin coal. Due to the difficulty in maintaining a steady‐state flow when testing coals with tight structure, the pressure transient technique was employed and experiments were conducted under different boundary conditions: uniaxial strain condition and lateral stress‐controlled condition. The results indicated that the vertical stress has a negative role in permeability enhancement. To verify this finding, one more set of experiments under the vertical stress‐controlled condition was carried out. In addition, the application of CO2 injection on reservoir fracturing was theoretically analyzed. The results indicated that both CO2 injection and the vertical stress can exert positive effects on reservoir fracturing. This study contributes to the understanding of the effect of the vertical stress on permeability variation during CO2 injection, which has practical significance for permeability modeling and reservoir fracturing operation in the field.

A simplified transient technique for porosity and permeability determination in tight formations: Numerical simulation and experimental validation

Feng

et al. 2020

Self Cite

A simplified pulse decay method (PDM) with only a single downstream reservoir is proposed to replicate the in situ conditions for reservoir fluid flow, where the pore pressure at any location declines as production continues. The proposed PDM also allows determining the effective porosity and permeability for the core sample under replicated in situ conditions. A mathematical model is firstly established to closely represent the experimental design and verify the feasibility of the method. The analytical solutions of the model are derived to calculate the effective sample porosity and permeability. A series of experiments are then conducted under triaxial stress condition, and a detailed comparison is also made between the PDMs with a single upstream reservoir and a single downstream reservoir. The experimental results showed that accurate measurements on effective sample porosity and permeability can be achieved by the single downstream reservoir PDM due to its capability of better replicating the in situ fluid flow behavior, which extends the application of the transient technique. It is also found that the pore pressure along the sample changes linearly, and its gradient varies with time, indicating the applicability of the single‐reservoir PDMs in permeability determination. This method also lays a foundation for studying flow behavior when a second fluid phase evolves during pressure decline, which occurs in many reservoirs.