A novel experimental approach for fracability evaluation in tight-gas reservoirs

Wang, Daobing; Ge, Hongkui; Wang, Xiaoqiong; Wang, Jianbo; Meng, Fanbao; Suo, Yu; Han, Peng

doi:10.1016/j.jngse.2015.01.039

Cited by 75 publications

(27 citation statements)

References 13 publications

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“…A rock with higher brittle mineral content also has higher brittleness (Liu and Sun 2015). Wang thought that brittle rocks generally comprise a high content of quartz and carbonates and the lowest clay content (Wang et al 2015). However, shale brittleness is not totally intrinsic, but varies with environmental conditions.…”

Section: Introductionmentioning

confidence: 99%

Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production

et al. 2017

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Brittleness and ductility of shale are closely related to shale gas exploration and production. How to predict brittleness and ductility of shale is one of the key issues in the study of shale gas preservation and hydraulic fracturing treatments. The magnitude of shale brittleness was often determined by brittle mineral content (for example, quartz and feldspars) in shale gas exploration. However, the shale brittleness is also controlled by burial depth. Shale brittle/ductile properties such as brittle, semibrittle and ductile can mutually transform with burial depth variation. We established a work flow of determining the burial depth interval of brittle-ductile transition zone for a given shale. Two boundaries were employed to divide the burial depth interval of shale brittle/ductile properties. One is the bottom boundary of the brittle zone (BZ), and the other is the top boundary of the ductile zone (DZ). The brittle-ductile transition zone (BDTZ) is between them. The bottom boundary of BZ was determined by the overconsolidation ratio (OCR) threshold value combined with pre-consolidation stress which the shale experienced over geological time. The top boundary of DZ was determined based on the critical confining pressure of brittle-ductile transition. The OCR threshold value and the critical confining pressure were obtained from uniaxial strain and triaxial compression tests. The BZ, DZ and BDTZ of the Lower Silurian Longmaxi shale in some representative shale gas exploration wells in eastern Sichuan and western Hubei areas were determined according to the above work flow. The results show that the BZ varies with the maximum burial depth and the DZ varies with the density of the overlying rocks except for the critical confining pressure. Moreover, the BDTZ determined by the above work flow is probably the best burial depth interval for marine shale gas exploration and production in Southern China. Shale located in the BDTZ is semi-brittle and is not prone to be severely naturally fractured but likely to respond well to hydraulic fracturing. The depth interval of BDTZ determined by our work flow could be a valuable parameter of shale gas estimation in geology and engineering.

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Section: Introductionmentioning

confidence: 99%

Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production

et al. 2017

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“…Tight sandstone bearing abundant natural gas is widely distributed in China and has attracted more attention in recent years. 6 Higher fracability indicates that larger SRV will be obtained. After injecting a large amount of fracturing fluid with high pumping rate, natural fractures can be easily connected by hydraulic fracture, and complex fracture networks are generated.…”

Section: Introductionmentioning

confidence: 99%

“…5 Fracability is a key parameter that has been used to evaluate whether the reservoir can be easily fractured and produce a large SRV. 6 Higher fracability indicates that larger SRV will be obtained. In recent years, there have been many reports on fracability evaluation.…”

Section: Introductionmentioning

confidence: 99%

A comprehensive approach for fracability evaluation in naturally fractured sandstone reservoirs based on analytical hierarchy process method

Yang

et al. 2019

Energy Science & Engineering

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The tight sandstone gas reservoir in southern Songliao Basin is naturally fractured and is characterized by its low porosity and permeability. Large‐scale hydraulic fracturing is the most effective way to develop this tight gas reservoir. Quantitative evaluation of fracability is essential for optimizing a fracturing reservoir. In this study, nine fracability‐related factors, particularly mechanical brittleness, unconfined compressive strength (UCS), mineral brittleness, cohesion, internal friction angle (IFA), natural fracture, fracture toughness, horizontal stress difference, and fracture barrier were obtained based on a series of petrophysical and geomechanical experiments. Taking above factors into consideration, a modified comprehensive evaluation model is proposed based on analytic hierarchy process (AHP) method. The UCS and IFA were removed from the AHP model based on the results of factor correlation analysis. The transfer matrix in the weighting procedure was applied to improve the consistency of judgment matrix, and the fuzzy matrix was employed to promote the objectiveness of final decision. The fracability evaluation of four reservoir intervals in Jinshan gas field was analyzed. Field fracturing tests were conducted to verify the feasibility of the proposed evaluation model. Results showed that the tubing pressure curve is more fluctuated in the reservoir interval with more developed natural fractures, and gas production is higher in the reservoir interval with greater fracability coefficient. The field test data coincide with the results of the proposed evaluation model.

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“…However, the definitions of brittleness are still ambiguous, an agreement of the measurement standards of brittleness has not yet been reached (Kahramana, 2002;Altindag, 2003;Goktan and Yilmaz, 2005;Wang and Gale, 2009;Wang et al, 2015;Zhang et al, 2016). Current approaches include stress-strain curves upon loading and failure, pre-peak and post-peak behaviors or mechanical properties from tri-axial tests can be used to evaluate brittleness.…”

Section: Introductionmentioning

confidence: 99%

Brittleness index prediction in shale gas reservoirs based on efficient network models

Shi

Lei

Cheng

et al. 2016

Journal of Natural Gas Science and Engineering

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A novel experimental approach for fracability evaluation in tight-gas reservoirs

Cited by 75 publications

References 13 publications

Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production

Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production

A comprehensive approach for fracability evaluation in naturally fractured sandstone reservoirs based on analytical hierarchy process method

Brittleness index prediction in shale gas reservoirs based on efficient network models

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