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Fracability evaluation of lacustrine shale by integrating brittleness and fracture toughness

Huang Cheng, Yang Chao and Shen Feng
Fracability evaluation of lacustrine shale by integrating brittleness and fracture toughness
Interpretation (Tulsa) (May 2019) 7 (2): T363-T372

Abstract

Rock brittleness and fracture toughness are important parameters for evaluating rock fracability. The stress-strain curves indicate that the lacustrine shale is strongly brittle. Brittle failure occurs rapidly when the stress of the lacustrine shale reaches its peak value. In addition, the lacustrine shale has different plastic strains before and after peak stress; this can relax the stress concentration of the crack tips. Therefore, the plastic strain that occurs before and after the peak stress can cause decreasing brittleness, which can be used to distinguish the brittleness and fracability in the formation of the lacustrine shale clearly. Moreover, this further enlarges the difference in the brittleness index. Based on the influence of plastic strain on brittleness, we have developed a new brittleness evaluation method that uses the ratio of linear elastic strain energy to the total strain energy before complete rock failure, which can indicate the difference of the lacustrine shale clearly. Fracture toughness is another important parameter that impacts the fracture extension and influences fracability. Based on the impact of brittleness and fracture toughness on the fracability, we have developed a new fracability evaluation method. The brittleness index increases with increases in the quartz content, and it decreases with increases in the albite feldspar and calcite contents. The fracture toughness decreases with increases in the quartz and clay contents, and it increases with increases in the siderite content. In addition, we established an empirical formula that can evaluate the brittleness index and the fracture toughness using mineral contents obtained from elemental logging. Using the new fracability evaluation method to optimize the fracturing stage, the preliminary field test indicates that the new approach was effective in the lacustrine shale formation.


ISSN: 2324-8858
EISSN: 2324-8866
Serial Title: Interpretation (Tulsa)
Serial Volume: 7
Serial Issue: 2
Title: Fracability evaluation of lacustrine shale by integrating brittleness and fracture toughness
Affiliation: Peking University, Department of Energy and Resource Engineering, Beijing, China
Pages: T363-T372
Published: 201905
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 39
Accession Number: 2019-036101
Categories: Economic geology, geology of energy sourcesApplied geophysicsEngineering geology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Technical papers
Illustration Description: illus. incl. 3 tables
Secondary Affiliation: Shaanxi Yanchang Petroleum Company, CHN, China
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 201909
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