Quantitative prediction of complex tectonic fractures in the tight sandstone reservoirs: a fractal method

Self Cite

Preservation conditions are the key factors that determine the effective accumulation of shale gas. The damage of faults formed by differential structures to the roof and floor and the shielding of lateral edges are the direct reasons for the difference in preservation conditions. Taking the organic-rich shale of the Wufeng–Longmaxi Formation in the south of the Sichuan Basin as an example, this paper reveals different types of shale gas-rich structures by using typical seismic profiles and puts forward the main controlling factors of different gas-rich structures and their influence on preservation. The results show that three kinds of gas-rich structures are developed in the Wufeng–Longmaxi Formation in southern Sichuan: positive type, negative type, and fault transformed slope type. The basin is dominated by a wide and gentle syncline, fault spreading fold, and low scope concealed anticlines. Wide and gentle anticline, arc anticline, and fault transformation slope are developed at the basin edge. Fault sealing is the main controlling factor for the preservation of shale gas in wide and gentle anticlines. The main controlling factors for the preservation of circular arc anticlines and hidden anticlines are anticline curvature and the distance between faults. The preservation of shale gas in a syncline is mainly controlled because it includes formation buried depth, foliation development degree, and formation dip angle. The preservation of fault transformed syncline is mainly affected by formation buried depth, dip angle, and fault sealing. Foliation and faults form a three-dimensional migration system, which jointly controls the intensity of gas escape. Positive structures such as wide and gentle anticline and circular arc anticline at the basin edge, and deep buried gentle syncline and low scope concealed anticline in the basin are favorable shale gas-rich structures.

Section: Introductionmentioning

confidence: 84%

Deformation Differences in Complex Structural Areas in the Southern Sichuan Basin and Its Influence on Shale Gas Preservation: A Case Study of Changning and Luzhou Areas

Qin

et al. 2022

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“…The development of fractures affects the physical properties of shale reservoirs and strongly influences the formation and expansion of hydraulic pressure fractures, thus affecting shale productivity. Structural and nonstructural fractures are the main fractures developed in the study area (Zou et al, 2010;Li H. et al, 2021;Li, 2021).…”

Section: ) Fracturesmentioning

confidence: 99%

“…Fractures are important reservoir spaces and migration channels of shale gas, playing an important role in the accumulation, preservation, exploration, and development of shale gas (Li et al, 2019c;Li et al, 2020;Li H. et al, 2021;Li 2021). Investigation of the Lower Paleozoic marine shale gas in the Sichuan Basin and its surrounding areas shows that marine shale has a good material foundation, and gas-bearing can almost be observed in each drilling.…”

Section: Physical Characteristicsmentioning

confidence: 99%

Geological Characteristics and Controlling Factors of Enrichment of Deep Shale Gas in the East Weiyuan–North Rongchang Area, Sichuan Basin, China

Tang

Li³

et al. 2022

The southern Sichuan Basin is the core area of China’s efficient development of deep shale gas (burial depth greater than 3,500 m). Reservoir geological characteristics determine whether shale gas can be preserved, enriched, and produced. Taking the Long 11 sub-member of the Wufeng Formation of the Upper Ordovician and the Longmaxi Formation of the Lower Silurian in the East Weiyuan–North Rongchang area as an example, we used the core, logging, production test, and other data, combining X-ray diffraction analysis, LECO Total Organic Carbon (TOC)-S analysis, optical microscopy, and argon ion polishing field-emission scanning electron microscopy, to study the shale mineral composition, geochemistry, reservoir space, pore structure characteristics, and reservoir physical properties. The following results were obtained: 1) The brittle mineral content, organic matter maturity, and TOC content are high, gradually increase from top to bottom, and reach their maxima at small layer 1 of Long 11. 2) Organic pores, inorganic pores, and fractures are important reservoir spaces, among which organic pores and fractures are important seepage channels for shale gas. 3) The shale pore structure revealed by electron microscopy shows that the pore structure in target layers can be divided into four types: unimodal type (mainly organic pores), bimodal type (both organic and inorganic pores), monoclinic type I (mainly organic pores), and monoclinic type II (mainly inorganic pores). The pore morphology is complex, and circular and oval shapes predominate. 4) Sedimentary facies are the main factor controlling the enrichment of shale gas, and the development of fractures is the key to obtaining high yields of shale gas. 5) The class I favorable target area is mainly distributed in wells W206, W206H1, R234H, and R233H and areas to its south, and some areas in the east of the study area.

“…Fractal geometry theory was proposed by Mandelbrot and can be used to characterize special structures that do not conform to European geometric laws and have certain self-similarity (Mandelbrot, 1978(Mandelbrot, , 1984(Mandelbrot, , 1985. In recent years, it has been widely used in the shale pore structure field (Li et al, 2019a;Liu et al, 2020;Li, 2021;Liu et al, 2021). Pore image data, gas or liquid flow test data (such as nitrogen adsorption and mercury intrusion tests), and NMR data can be used to study the pore fractal characteristics (Yang et al, 2017;Liu J. S. et al, 2018;Tang et al, 2019;Wei et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Pore structure and fractal characteristics of the marine shale of the longmaxi formation in the changning area, Southern Sichuan Basin, China

Jiling²,

Mou

et al. 2022

Self Cite

The pore structure is an important factor affecting reservoir capacity and shale gas production. The shale reservoir of the Longmaxi Formation in the Changning area, Southern Sichuan Basin, is highly heterogeneous and has a complex pore structure. To quantitatively characterize the shale’s pore structure and influencing factors, based on whole rock X-ray diffraction, argon ion polishing electron microscopy observations, and low-temperature nitrogen adsorption-desorption experiments, the characteristics of the shale pore structure are studied by using the Frenkel-Halsey-Hill (FHH) model. The research reveals the following: 1) The pores of the Longmaxi Formation shale mainly include organic pores, intergranular pores, dissolution pores and microfractures. The pore size is mainly micro-mesoporous. Both ink bottle-type pores and semiclosed slit-type pores with good openness exist, but mainly ink bottle-type pores are observed. 2) The pore structure of the Longmaxi Formation shale has self-similarity, conforms to the fractal law, and shows double fractal characteristics. Taking the relative pressure of 0.45 (P/P0 = 0.45) as the boundary, the surface fractal dimension Dsf and the structural fractal dimension Dst are defined. Dsf is between 2.3215 and 2.6117, and the structural fractal dimension Dst is between 2.8424 and 2.9016. The pore structure of micropores and mesopores is more complex. 3) The mineral components and organic matter have obvious control over the fractal dimension of shale, and samples from different wells show certain differences. The fractal dimension has a good positive correlation with the quartz content but an obvious negative correlation with clay minerals. The higher the total organic carbon content is, the higher the degree of thermal evolution, the more complex the pore structure of shale, and the larger the fractal dimension. The results have guiding significance for the characterization of pore structure of tight rocks.