Limited Storage and Recovery of Adsorbed Gas in Shale Reservoirs - Insights from Experiments and Production Modeling

According to hydraulic-fracturing practices conducted in shale reservoirs, effective stimulated reservoir volume (ESRV) significantly affects the production of hydraulic fractured well. Therefore, estimating ESRV is an important prerequisite for confirming the success of hydraulic fracturing and predicting the production of hydraulic fracturing wells in shale reservoirs. However, ESRV calculation remains a longstanding challenge in hydraulic-fracturing operation. In considering fractal characteristics of the fracture network in stimulated reservoir volume (SRV), this paper introduces a fractal random-fracture-network algorithm for converting the microseismic data into fractal geometry. Five key parameters, including bifurcation direction, generating length ([Formula: see text]), deviation angle ([Formula: see text]), iteration times ([Formula: see text]) and generating rules, are proposed to quantitatively characterize fracture geometry. Furthermore, we introduce an orthogonal-fractures coupled dual-porosity-media representation elementary volume (REV) flow model to predict the volumetric flux of gas in shale reservoirs. On the basis of the migration of adsorbed gas in porous kerogen of REV with different fracture spaces, an ESRV criterion for shale reservoirs with SRV is proposed. Eventually, combining the ESRV criterion and fractal characteristic of a fracture network, we propose a new approach for evaluating ESRV in shale reservoirs. The approach has been used in the Eagle Ford shale gas reservoir, and results show that the fracture space has a measurable influence on migration of adsorbed gas. The fracture network can contribute to enhancement of the absorbed gas recovery ratio when the fracture space is less than 0.2 m. ESRV is evaluated in this paper, and results indicate that the ESRV accounts for 27.87% of the total SRV in shale gas reservoirs. This work is important and timely for evaluating fracturing effect and predicting production of hydraulic fracturing wells in shale reservoirs.

Download Full-text

Investigating Influential Factors of the Gas Absorption Capacity in Shale Reservoirs Using Integrated Petrophysical, Mineralogical and Geochemical Experiments: A Case Study

Energies ◽

10.3390/en11113078 ◽

2018 ◽

Vol 11 (11) ◽

pp. 3078 ◽

Cited By ~ 4

Author(s):

Zhuoying Fan ◽

Jiagen Hou ◽

Xinmin Ge ◽

Peiqiang Zhao ◽

Jianyu Liu

Keyword(s):

Shale Gas ◽

Total Porosity ◽

Organic Content ◽

Absorption Capacity ◽

Influential Factors ◽

Gas Absorption ◽

Gas Content ◽

Adsorbed Gas ◽

Shale Reservoirs ◽

Gas Volume

Estimating in situ gas content is very important for the effective exploration of shale gas reservoirs. However, it is difficult to choose the sensitive geological and geophysical parameters during the modeling process, since the controlling factors for the abundance of gas volumes are often unknown and hard to determine. Integrated interdisciplinary experiments (involving petrophysical, mineralogical, geochemical and petrological aspects) were conducted to search for the influential factors of the adsorbed gas volume in marine gas shale reservoirs. The results showed that in shale reservoirs with high maturity and high organic content that the adsorbed gas volume increases, with an increase in the contents of organic matter and quartz, but with a decrease in clay volume. The relationship between the adsorbed gas content and the total porosity is unclear, but a strong relationship between the proportions of different pores is observed. In general, the larger the percentage of micropores, the higher the adsorbed gas content. The result is illuminating, since it may help us to choose suitable parameters for the estimation of shale gas content.

Download Full-text

Using well-log data to modeling factors influencing the amount of adsorbed gas in transitional shale reservoirs

Interpretation ◽

10.1190/int-2019-0049.1 ◽

2020 ◽

Vol 8 (2) ◽

pp. T249-T258

Author(s):

Rui Liu ◽

Shaobin Guo ◽

Kun Ji

Keyword(s):

Adsorption Capacity ◽

Mineral Composition ◽

Ordos Basin ◽

Well Log ◽

Isothermal Adsorption ◽

Adsorbed Gas ◽

Upper Paleozoic ◽

Rapid Changes ◽

Shale Reservoirs ◽

Experimental Values

Traditional isothermal adsorption experiments often fail to accurately estimate the adsorption capacity of reservoirs with rapidly changing lithology. Temperature, pressure, and mineral composition can influence the adsorption capacity of shale reservoirs. We have examined the influence of these factors on the amount of gas adsorbed in samples from well Yu-88. Samples consist of marine-continental transitional coal-bearing strata from the Upper Paleozoic Shanxi-Taiyuan Formation of the Ordos Basin of China. Shales occur as frequently interbedded, thin, and single layers that exhibit large cumulative thickness and rapid changes in mineral composition. Our experiments on samples B1 and B2 indicated that Langmuir constant [Formula: see text] varied inversely with temperature, but Langmuir pressure [Formula: see text] did not. The [Formula: see text] exhibits good correlation with illite as well as illite/smectite content but did not clearly correlate with the total organic carbon (TOC). The [Formula: see text] correlated positively with TOC and negatively with illite/smectite content. These relationships enabled modeling of [Formula: see text], [Formula: see text], and mineral composition. Novel step-by-step modeling methods of well logs generated optimized estimates for well-log parameters including mineral composition. According to the actual temperature of the reservoir, we corrected the Langmuir constant [Formula: see text]. We calculated a profile for the amount of gas adsorbed in shale intervals of well Yu-88. Comparisons with experimental values indicate relatively high reference values.

Download Full-text

Analytical analysis of gas diffusion into non-circular pores of shale organic matter

Journal of Fluid Mechanics ◽

10.1017/jfm.2017.180 ◽

2017 ◽

Vol 819 ◽

pp. 656-677 ◽

Cited By ~ 10

Author(s):

Mehran Mehrabi ◽

Farzam Javadpour ◽

Kamy Sepehrnoori

Keyword(s):

Organic Matter ◽

Dirichlet Boundary ◽

Gas Diffusion ◽

Gas Production ◽

Dirichlet Boundary Conditions ◽

Dissolved Gas ◽

Gas Reservoirs ◽

Solid Diffusion ◽

Adsorbed Gas ◽

Shale Reservoirs

The total of the gas in shale gas reservoirs is sourced from a combination of free, adsorbed and dissolved/diffused gas. The mechanisms of production of free and adsorbed gas have been studied by numerous researchers. In contrast, the evolution of the dissolved gas and its contribution to the total gas production is not well understood. In this study we model the effect of pore micro-structure in organic matter (OM) on the rate of gas production in shale reservoirs. In this regard, first, we solve the gas-in-solid diffusion equation over a general doubly connected spatial domain with external Neumann and internal Dirichlet boundary conditions. The obtained solution is applied systematically to multi-pore porous OM domains and then the effect of pore morphology on the rate of gas production is studied. Our model results show that pore geometry has a slight effect on the gas diffusion process, while total organic carbon, and OM porosity, pore size distribution and specific surface area, are dominant parameters. An abundance of very small pores in OM tremendously increases the diffuse gas contribution in the total gas reserve and production.

Download Full-text

Effect of reservoir pressure and total organic content on adsorbed gas production in shale reservoirs: a numerical modelling study

Arabian Journal of Geosciences ◽

10.1007/s12517-021-09416-x ◽

2022 ◽

Vol 15 (2) ◽

Author(s):

Moataz Mansi ◽

Mohamed Almobarak ◽

Christopher Lagat ◽

Quan Xie

Keyword(s):

Numerical Modelling ◽

Shale Gas ◽

Organic Content ◽

Gas Production ◽

Reservoir Pressure ◽

Adsorbed Gas ◽

Total Organic Content ◽

Simulation Results ◽

Shale Reservoirs ◽

The Impact

AbstractAdsorbed gas plays a key role in organic-rich shale gas production due to its potential to contribute up to 60% of the total gas production. The amount of gas potentially adsorbed on organic-rich shale is controlled by thermal maturity, total organic content (TOC), and reservoir pressure. Whilst those factors have been extensively studied in literature, the factors governing desorption behaviour have not been elucidated, presenting a substantial impediment in managing and predicting the performance of shale gas reservoirs. Therefore, in this paper, a simulation study was carried out to examine the effect of reservoir depth and TOC on the contribution of adsorbed gas to shale gas production. The multi-porosity and multi-permeability model, hydraulic fractures, and local grid refinements were incorporated in the numerical modelling to simulate gas storage and transient behaviour within matrix and fracture regions. The model was then calibrated using core data analysis from literature for Barnett shales. Sensitivity analysis was performed on a range of reservoir depth and TOC to quantify and investigate the contribution of adsorbed gas to total gas production. The simulation results show the contribution of adsorbed gas to shale gas production decreases with increasing reservoir depth regardless of TOC. In contrast, the contribution increases with increasing TOC. However, the impact of TOC on the contribution of adsorbed gas production becomes minor with increasing reservoir depth (pressure). Moreover, the results suggest that adsorbed gas may contribute up to 26% of the total gas production in shallow (below 4,000 feet) shale plays. These study findings highlight the importance of Langmuir isothermal behaviour in shallow shale plays and enhance understanding of desorption behaviour in shale reservoirs; they offer significant contributions to reaching the target of net-zero CO2 emissions for energy transitions by exhibiting insights in the application of enhanced shale gas recovery and CO2 sequestration — in particular, the simulation results suggest that CO2 injection into shallow shale reservoirs rich in TOC, would give a much better performance to unlock the adsorbed gas and sequestrate CO2 compared to deep shales.

Download Full-text

Experimental Study on the Characteristics of Adsorbed Gas and Gas Production in Shale Formations

Geofluids ◽

10.1155/2021/2448044 ◽

2021 ◽

Vol 2021 ◽

pp. 1-12

Author(s):

Zhiming Hu ◽

Xianggang Duan ◽

Nan Shao ◽

Yingying Xu ◽

Jin Chang ◽

...

Keyword(s):

Shale Gas ◽

Physical Simulation ◽

Gas Production ◽

Production Optimization ◽

Gas Reservoirs ◽

Tight Sandstone ◽

Free Gas ◽

Adsorbed Gas ◽

Shale Gas Reservoirs ◽

Shale Reservoirs

Adsorbed gas and free gas both exist in shale reservoirs simultaneously due to the unique nanoscale pore structure, resulting in the complex flow mechanism of gas in the reservoir during the development process. The dynamic performance analysis of shale reservoirs has mostly been conducted by the numerical simulation and theoretical model, while the physical simulation method for relevant research is seen rarely in the literature. Thus, in this paper, an experiment system was designed to simulate the degraded development experiments of shale, coal, and tight sandstone to reveal the output law of gas in different occurrence states of shale reservoirs and clarify the pressure propagation rules of different reservoirs, and then, adsorption gas and free gas production laws were studied by theoretical models. Research indicated the following: (1) The gas occurrence state is the main factor that causes the difference of the pressure drop rate and gas production law of shale, coal, and tight sandstone. During the early stage of the development of shale gas, the free gas is mainly produced; the final contribution of free gas production can reach more than 90%. (2) The static desorption and dynamic experiments confirm that the critical desorption pressure of adsorbed gas is generally between 12 and 15 MPa. When the gas reservoir pressure is lower than the critical desorption pressure in shale and coal formation, desorption occurs. Due to the slow propagation of shale matrix pressure, desorption of adsorbed gas occurs mainly in the low-pressure region close to the fracture surface. (3) The material balance theory of closed gas reservoirs and the one-dimensional flow model of shale gas have subsequently validated the production performance law of adsorbed gas and free gas by the physical simulation. Therefore, in the practical development of shale gas reservoirs, it is recommended to shorten the matrix supply distance, reduce the pressure in the fracture, increase the effective pressure gradient, and enhance the potential utilization of adsorbed gas as soon as possible to increase the ultimate recovery. The findings of this study can help for a better understanding of the shale reservoir utilization law so as to provide a reference for production optimization and development plan formulation of the shale gas reservoirs.

Download Full-text

Abstract: Preliminary Quantification of Adsorbed Gas in Monterey Shale Reservoirs at Elk Hills, Kern County, California

AAPG Bulletin ◽

10.1306/522b46db-1727-11d7-8645000102c1865d ◽

1997 ◽

Vol 81 (1997) ◽

Author(s):

MCINTYRE, JANA L, THOMAS J. HAMPTON

Keyword(s):

Kern County ◽

Adsorbed Gas ◽

Shale Reservoirs

Download Full-text