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

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.

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

Geofluids ◽  
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.

scholarly journals Prediction of Shale Gas Reservoirs Using Fluid Mobility Attribute Driven by Post-Stack Seismic Data: A Case Study from Southern China

2020 ◽  
Vol 11 (1) ◽  
pp. 219
Author(s):  
Jing Zeng ◽  
Alexey Stovas ◽  
Handong Huang ◽  
Lixia Ren ◽  
Tianlei Tang
Keyword(s):  
Shale Gas ◽  
Seismic Data ◽  
Spectral Decomposition ◽  
Southern China ◽  
Gas Reservoirs ◽  
Seismic Attribute ◽  
Longmaxi Formation ◽  
Shale Gas Reservoirs ◽  
The Sichuan Basin ◽  
Shale Reservoirs

Paleozoic marine shale gas resources in Southern China present broad prospects for exploration and development. However, previous research has mostly focused on the shale in the Sichuan Basin. The research target of this study is expanded to the Lower Silurian Longmaxi shale outside the Sichuan Basin. A prediction scheme of shale gas reservoirs through the frequency-dependent seismic attribute technology is developed to reduce drilling risks of shale gas related to complex geological structure and low exploration level. Extracting frequency-dependent seismic attribute is inseparable from spectral decomposition technology, whereby the matching pursuit algorithm is commonly used. However, frequency interference in MP results in an erroneous time-frequency (TF) spectrum and affects the accuracy of seismic attribute. Firstly, a novel spectral decomposition technology is proposed to minimize the effect of frequency interference by integrating the MP and the ensemble empirical mode decomposition (EEMD). Synthetic and real data tests indicate that the proposed spectral decomposition technology provides a TF spectrum with higher accuracy and resolution than traditional MP. Then, a seismic fluid mobility attribute, extracted from the post-stack seismic data through the proposed spectral decomposition technology, is applied to characterize the shale reservoirs. The application result indicates that the seismic fluid mobility attribute can describe the spatial distribution of shale gas reservoirs well without well control. Based on the seismic fluid mobility attribute section, we have learned that the shale gas enrich areas are located near the bottom of the Longmaxi Formation. The inverted velocity data are also introduced to further verify the reliability of seismic fluid mobility. Finally, the thickness map of gas-bearing shale reservoirs in the Longmaxi Formation is obtained by combining the seismic fluid mobility attribute with the inverted velocity data, and two favorable exploration areas are suggested by analyzing the thickness, structure, and burial depth. The present work can not only be used to evaluate shale gas resources in the early stage of exploration, but also help to design the landing point and trajectory of directional drilling in the development stage.

scholarly journals The Impacts of Matrix Compositions on Nanopore Structure and Fractal Characteristics of Lacustrine Shales from the Changling Fault Depression, Songliao Basin, China

Minerals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 127 ◽  
Author(s):  
Zhuo Li ◽  
Zhikai Liang ◽  
Zhenxue Jiang ◽  
Fenglin Gao ◽  
Yinghan Zhang ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Pore Structure ◽  
Fractal Dimensions ◽  
Organic Medium ◽  
Songliao Basin ◽  
Sem Images ◽  
Fractal Characteristics ◽  
Inorganic Mineral ◽  
Nanopore Structure ◽  
High Fractal Dimension

The Lower Cretaceous Shahezi shales are the targets for lacustrine shale gas exploration in Changling Fault Depression (CFD), Southern Songliao Basin. In this study, the Shahezi shales were investigated to further understand the impacts of rock compositions, including organic matters and minerals on pore structure and fractal characteristics. An integrated experiment procedure, including total organic carbon (TOC) content, X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), low pressure nitrogen physisorption (LPNP), and mercury intrusion capillary pressure (MICP), was conducted. Seven lithofacies can be identified according to on a mineralogy-based classification scheme for shales. Inorganic mineral hosted pores are the most abundant pore type, while relatively few organic matter (OM) pores are observed in FE-SEM images of the Shahezi shales. Multimodal pore size distribution characteristics were shown in pore width ranges of 0.5–0.9 nm, 3–6 nm, and 10–40 nm. The primary controlling factors for pore structure in Shahezi shales are clay minerals rather than OM. Organic-medium mixed shale (OMMS) has the highest total pore volumes (0.0353 mL/g), followed by organic-rich mixed shale (ORMS) (0.02369 mL/g), while the organic-poor shale (OPS) has the lowest pore volumes of 0.0122 mL/g. Fractal dimensions D1 and D2 (at relative pressures of 0–0.5 and 0.5–1 of LPNP isotherms) were obtained using the Frenkel–Halsey–Hill (FHH) method, with D1 ranging from 2.0336 to 2.5957, and D2 between 2.5779 and 2.8821. Fractal dimensions are associated with specific lithofacies, because each lithofacies has a distinctive composition. Organic-medium argillaceous shale (OMAS), rich in clay, have comparatively high fractal dimension D1. In addition, organic-medium argillaceous shale (ORAS), rich in TOC, have comparatively high fractal dimension D2. OPS shale contains more siliceous and less TOC, with the lowest D1 and D2. Factor analysis indicates that clay contents is the most significant factor controlling the fractal dimensions of the lacustrine Shahezi shale.

scholarly journals Characteristics of shale gas reservoirs in Wufeng Formation and Longmaxi Formation in Well WX2, northeast Chongqing

2017 ◽  
Vol 2 (4) ◽  
pp. 324-335 ◽  
Author(s):  
Jin Wu ◽  
Feng Liang ◽  
Wen Lin ◽  
Hongyan Wang ◽  
Wenhua Bai ◽  
...  
Keyword(s):  
Shale Gas ◽  
Gas Reservoirs ◽  
Longmaxi Formation ◽  
Shale Gas Reservoirs

scholarly journals Fractal Characteristics of Pores in the Longtan Shales of Guizhou, Southwest China

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Yuqi Huang ◽  
Peng Zhang ◽  
Jinchuan Zhang ◽  
Xuan Tang ◽  
Chengwei Liu ◽  
...  
Keyword(s):  
Organic Matter ◽  
Fractal Dimension ◽  
Pore Structure ◽  
Shale Gas ◽  
Storage Capacity ◽  
Evaluation Criteria ◽  
Fractal Dimensions ◽  
Gas Absorption ◽  
Relative Pressure ◽  
And Storage

The pore structure of marine-continental transitional shales from the Longtan Formation in Guizhou, China, was investigated using fractal dimensions calculated by the FHH (Frenkel-Halsey-Hill) model based on low-temperature N2 adsorption data. Results show that the overall D 1 (fractal dimension under low relative pressure, P / P 0 ≤ 0.5 ) and D 2 (fractal dimension under high relative pressure, P / P 0 > 0.5 ) values of Longtan shales were relatively large, with average values of 2.7426 and 2.7838, respectively, indicating a strong adsorption and storage capacity and complex pore structure. The correlation analysis of fractal dimensions with specific surface area, average pore size, and maximum gas absorption volume indicates that D 1 can comprehensively characterize the adsorption and storage capacity of shales, while D 2 can effectively characterize the pore structure complexity. Further correlation among pore fractal dimension, shale organic geochemical parameters, and mineral composition parameters shows that there is a significant positive correlation between fractal dimensions and organic matter abundance as well as a complex correlation between fractal dimension and organic matter maturity. Fractal dimensions increase with an increase in clay mineral content and pyrite content but decrease with an increase in quartz content. Considering the actual geological evaluation and shale gas exploitation characteristics, a lower limit for D 1 and upper limit for D 2 should be set as evaluation criteria for favorable reservoirs. Combined with the shale gas-bearing property test results of Longtan shales in Guizhou, the favorable reservoir evaluation criteria are set as D 1 ≥ 2.60 and D 2 ≤ 2.85 . When D 1 is less than 2.60, the storage capacity of the shales is insufficient. When D 2 is greater than 2.85, the shale pore structure is too complicated, resulting in poor permeability and difficult exploitation.

scholarly journals An Investigation of Fractal Characteristics of Marine Shales in the Southern China from Nitrogen Adsorption Data

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Jian Xiong ◽  
Xiangjun Liu ◽  
Lixi Liang
Keyword(s):  
Fractal Dimension ◽  
Pore Structure ◽  
Southern China ◽  
Fractal Dimensions ◽  
Nitrogen Adsorption ◽  
Mean Value ◽  
Relative Pressure ◽  
Pore Surface ◽  
Adsorption Sites ◽  
Fractal Characteristics

We mainly focus on the Permian, Lower Cambrian, Lower Silurian, and Upper Ordovician Formation; the fractal dimensions of marine shales in southern China were calculated using the FHH fractal model based on the low-pressure nitrogen adsorption analysis. The results show that the marine shales in southern China have the dual fractal characteristics. The fractal dimensionD1at low relative pressure represents the pore surface fractal characteristics, whereas the fractal dimensionD2at higher relative pressure describes the pore structure fractal characteristics. The fractal dimensionsD1range from 2.0918 to 2.718 with a mean value of 2.4762, and the fractal dimensionsD2range from 2.5842 to 2.9399 with a mean value of 2.8015. There are positive relationships between fractal dimensionD1and specific surface area and total pore volume, whereas the fractal dimensionsD2have negative correlation with average pore size. The larger the value of the fractal dimensionD1is, the rougher the pore surface is, which could provide more adsorption sites, leading to higher adsorption capacity for gas. The larger the value of the fractal dimensionD2is, the more complicated the pore structure is, resulting in the lower flow capacity for gas.

Sign in / Sign up

Export Citation Format

Share Document