Comparisons of Pore Structure for Unconventional Tight Gas, Coalbed Methane and Shale Gas Reservoirs

Summary Shales and some tight-gas reservoirs have complex, multimodal pore-size distributions, including pore sizes in the nanopore range, causing gas to be transported by multiple flow mechanisms through the pore structure. Ertekin et al. (1986) developed a method to account for dual-mechanism (pressure- and concentration-driven) flow for tight formations that incorporated an apparent Klinkenberg gas-slippage factor that is not a constant, which is commonly assumed for tight gas reservoirs. In this work, we extend the dynamic-slippage concept to shale-gas reservoirs, for which it is postulated that multimechanism flow can occur. Inspired by recent studies that have demonstrated the complex pore structure of shale-gas reservoirs, which may include nanoporosity in kerogen, we first develop a numerical model that accounts for multimechanism flow in the inorganic- and organic-matter framework using the dynamic-slippage concept. In this formulation, unsteady-state desorption of gas from the kerogen is accounted for. We then generate a series of production forecasts using the numerical model to demonstrate the consequences of not rigorously accounting for multimechanism flow in tight formations. Finally, we modify modern rate-transient-analysis methods by altering pseudovariables to include dynamic-slippage and desorption effects and demonstrate the utility of this approach with simulated and field cases. The primary contribution of this work is therefore the demonstration of the use of modern rate-transient-analysis methods for reservoirs exhibiting multimechanism (non-Darcy) flow. The approach is considered to be useful for analysis of production data from shale-gas and tight-gas formations because it captures the physics of flow in such formations realistically.

Download Full-text

A new application of atomic force microscopy in the characterization of pore structure and pore contribution in shale gas reservoirs

Journal of Natural Gas Science and Engineering ◽

10.1016/j.jngse.2021.103802 ◽

2021 ◽

Vol 88 ◽

pp. 103802

Author(s):

Shangbin Chen ◽

Xueyuan Li ◽

Si Chen ◽

Yang Wang ◽

Zhuo Gong ◽

...

Keyword(s):

Atomic Force Microscopy ◽

Pore Structure ◽

Shale Gas ◽

Gas Reservoirs ◽

Force Microscopy ◽

Atomic Force ◽

Shale Gas Reservoirs

Download Full-text

Flow Units: From Conventional to Tight Gas to Shale Gas Reservoirs

10.2118/132845-ms ◽

2010 ◽

Cited By ~ 21

Author(s):

Roberto Aguilera

Keyword(s):

Shale Gas ◽

Tight Gas ◽

Gas Reservoirs ◽

Flow Units ◽

Shale Gas Reservoirs

Download Full-text

The characteristics and developmental control factors of microscopic pore structure in shale gas reservoirs in the Lower Cambrian Qiongzhusi Formation

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/565/1/012076 ◽

2020 ◽

Vol 565 ◽

pp. 012076

Author(s):

Wei Yang ◽

Yuanyuan Qin ◽

Tingshan Zhang

Keyword(s):

Pore Structure ◽

Shale Gas ◽

Lower Cambrian ◽

Gas Reservoirs ◽

Developmental Control ◽

Control Factors ◽

Shale Gas Reservoirs

Download Full-text

Nano-Pore Structure and Fractal Characteristics of Shale Gas Reservoirs: A Case Study of Longmaxi Formation in Southeastern Chongqing, China

Journal of Nanoscience and Nanotechnology ◽

10.1166/jnn.2021.18721 ◽

2021 ◽

Vol 21 (1) ◽

pp. 343-353

Author(s):

Wei-Dong Xie ◽

Meng Wang ◽

Xiao-Qi Wang ◽

Yan-Di Wang ◽

Chang-Qing Hu

Keyword(s):

Fractal Dimension ◽

Pore Structure ◽

Shale Gas ◽

Fractal Dimensions ◽

Gas Reservoirs ◽

Longmaxi Formation ◽

Shale Gas Reservoirs ◽

Fractal Characteristics ◽

Temperature Liquid ◽

Menger Sponge

Pore structure and fractal dimensions can characterize the adsorption, desorption and seepage characteristics of shale gas reservoirs. In this study, pore structure, fractal characteristics and influencing factors were studied of the Longmaxi formation shale gas reservoir in southeastern Chongqing, China. Scanning electron microscopy was used to describe the characteristics of various reservoirs. High pressure mercury intrusion and low temperature liquid N2 and CO2 adsorption experiments were used to obtain pore structure parameters. V–S model, FHH model and Menger sponge model were selected to calculate the micropore, mesopore and macropore fractal dimensions, respectively. The results show that organic matter pores, inter-granular pores, intra-granular pores and micro-fractures are developed within the shale, and the pore morphology is mostly ink pores and parallel plate pores with aperture essentially in the 1–2 nm and 2–50 nm ranges. Moreover, macropores are the most complex in these samples, with mesopores being less complex than macropores, and the micropores being the simplest. D1 (micropore fractal dimension) ranges from 2.31 to 2.50, D2 (mesopore fractal dimension) ranges from 2.74 to 2.83, D3 (macropore fractal dimension) ranges from 2.87 to 2.95, and Dt (comprehensive fractal dimension) ranges from 2.69 to 2.83 of fractal characteristics. D1 and D2 are mainly controlled by TOC content, while D3 and Dt are mainly controlled by brittle and clay mineral content. These results may be helpful for exploration and the development of shale gas in southeastern Chongqing, China.

Download Full-text

Study on the Spontaneous Imbibition Characteristics of the Deep Longmaxi Formation Shales of the Southern Sichuan Basin, China

Geofluids ◽

10.1155/2021/3563095 ◽

2021 ◽

Vol 2021 ◽

pp. 1-13

Author(s):

Chao Qian ◽

Xizhe Li ◽

Weijun Shen ◽

Wei Guo ◽

Yong Hu ◽

...

Keyword(s):

Pore Structure ◽

Shale Gas ◽

Inhibitory Effect ◽

Spontaneous Imbibition ◽

Structure Evolution ◽

Gas Wells ◽

Fracturing Fluid ◽

Gas Reservoirs ◽

Longmaxi Formation ◽

Shale Gas Reservoirs

Deep shale gas reservoirs are a significant alternative type of shale gas reservoir in China. The productivity of deep shale gas wells is lower than that of shallow shale, and the imbibition characteristics of deep shale have a significant effect on the retention and backflow of fracturing fluid and the productivity of shale gas wells. In this study, the pore structure characteristics of organic-rich deep shale in the Lower Silurian Longmaxi Formation of Weiyuan-Luzhou play were analyzed by low-temperature nitrogen adsorption experiments, and then the imbibition characteristics and factors influencing deep shale were extensively investigated by spontaneous imbibition and nuclear magnetic resonance experiments. The results show that mainly micropores and mesopores are growing in the deep organic-rich shale of the Longmaxi Formation. The spontaneous imbibition curve of deep shale can be divided into an initial spontaneous imbibition stage, an intermediate transition stage, and a later diffusion stage, and the imbibition capacity coefficient of deep shale is lower than that of shallow shale. The transverse relaxation time (T2) spectrum distributions suggest that clay hydration and swelling produce new pores and microcracks, but then some pores and microfractures close. Deep shale reservoirs have an optimal hydration time when their physical properties are optimal. The increasing pore volume and the decreasing TOC content can enhance the imbibition capacity of shale. An inorganic salt solution, especially a KCl solution, has an inhibitory effect on the imbibition of shale. Higher salinity will result in a stronger inhibitory effect. It is crucial to determine the optimal amount of fracturing fluid and soaking time, and fracturing fluid with a high K+ content can be injected into the Longmaxi Formation deep shale to suppress hydration. These results provide theoretical guiding significance for comprehending the spontaneous imbibition and pore structure evolution characteristics of deep shale and enhancing methane production in deep shale gas reservoirs.

Download Full-text