Application of Fractal Geometry in Evaluation of Effective Stimulated Reservoir Volume in Shale Gas Reservoirs

Abstract

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), § Corresponding author. This is an Open Access article published by World Scientific Publishing Company. It is distributed under the terms of the Creative Commons Attribution 4.0 (CC-BY) License. Further distribution of this work is permitted, provided the original work is properly cited. 1740007-1Fractals 2017.25. Downloaded from www.worldscientific.com by 13.66.222.141 on 04/09/19. Re-use and distribution is strictly not permitted, except for Open Access articles.G. Sheng et al. 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 (d), deviation angle (α), iteration times (N ) 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.

Pore-Throat Structure and Fractal Characteristics of Shihezi Formation Tight Gas Sandstone in the Ordos Basin, China

“…from greyscale image analyses 37 to pore structures of porous media, 38,39 and from fracture networks 40,41 to larger-scale sand body macroscopic characteristics. 6,42 It is also important for the evaluation of the reservoir quality. This paper separated pores from throats, as is shown in Fig.…”

“…5,6,8,10 Moreover, studies on the respective effects of fractal features of pores and throats on the effective physical property of tight sands are practically limited. In this paper, the relationships between the fractal dimension of pores and throats of tight sandstones from the Shihezi Formation and the effective porosity and effective gas permeability were analyzed.…”

“…1,3 Exploration and development in such reservoirs are hindered by extreme heterogeneity owing to the fine pores and complex pore characteristics including size, shape, location and connectivity of pores and throats. [4][5][6][7] As one of the most primary factors controlling the exploitation of tight gas sandstones, the pore-throat structure of fine pores has been extensively studied. It is generally believed that the pore-throat structure directly impacts the fluid flow through the reservoir and thus further affects the hydrocarbon recovery.…”

Editorial

“…The branching networks such as tree branches, leaf veins, blood vessels, bronchial tree etc abound in nature, and fractal theory has been used to characterize the topology and transport properties of natural and industrial branching networks. 8 Sheng et al 9 introduced a random fractal algorithm based on Lindenmayer system to generate fracture networks according to the micro-seismic data, and evaluate the effective stimulated reservoir volume in shale gas reservoirs. Lu et al 10 presented a fractal model for the net present value of multi-stage fractured horizontal wells in tight gas reservoir, where a fractal gas permeability model with slippage effect was employed to characterize the apparent permeability of reservoir stratum.…”

Fractal Characteristics of Pores in Taiyuan Formation Shale From Hedong Coal Field, China

“…3,4 The characteristics of pore structure for shale, such as pore geometry, size and pore distribution have significant influence not only on the capacity of gas flow, but also on the capacity of gas storage and adsorption. [3][4][5][6] To evaluate the key factors for pore formation and development, various measuring and testing techniques are used to characterize the pore structure of shale. The direct 2D and 3D imaging technology, such as polarized light microscopy, high resolution scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and CT-scan, can qualitatively observe the pore shape, size and geometry down to nano-scale resolution.…”