Experimental Study on the Failure Mechanisms in Brittle Shales

Wang, Daobing; Wang, Xiaoqiong; Ge, Hongkui; Sun, Dongliang; Yu, Bo

doi:10.1021/acsomega.0c00278

Cited by 7 publications

(9 citation statements)

References 57 publications

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“…The fracture conductivity of igneous rocks is strong, and the pressure penetration of the drilling fluid along the fracture further affects wellbore stability. 18 , 19 …”

Section: Resultsmentioning

confidence: 99%

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Study on Rock Mechanics and Wellbore Stability of Igneous Formation in the Shunbei Area

et al. 2022

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While drilling into the igneous rock formations of the Shunbei area, problems such as loss of well circulation and borehole collapse occur frequently, seriously hindering the efficient development of oil and gas resources. Aiming to solve this problem, the physicochemical and mechanical properties of igneous rocks are studied through a series of laboratory tests to determine the main factors influencing formation collapse and instability. In addition to the laboratory results, the weak plane effect of fracture mechanics, the seepage effect of drilling fluid, and the hydration effect of the drilling fluid on the borehole wall stability of igneous rock formations are evaluated and analyzed by establishing a mathematical model. The results show that the microfractures in the igneous rock are relatively developed and can be divided into unfilled fractures and calcite-filled fractures. The mechanical strength of the matrix igneous rock is higher than that of the rock samples with microfractures. The compressive strength of calcite-filled and unfilled fracture samples is 1/3–1/4 that of matrix igneous rocks, and immersion in the drilling fluid has little influence on the mechanical strength of igneous rocks. The fracture weak plane effect has the greatest influence on wellbore stability. With the increase of the number of fractures at different angles, the collapse pressure equivalent density of the formation subject to the mechanical weak plane effect increases by 21% compared with that of the homogeneous formation without fractures. The seepage effect of the drilling fluid on borehole stability is secondary, and the equivalent density of the formation collapse pressure increases by 11%. Because of the low content of clay minerals, the hydration effect of the drilling fluid on borehole stability was minimal and the equivalent density of collapse pressure increased by only 2%. During the drilling process, considering the weak plane effect of the microfractures and the seepage effect of the drilling fluid, the drilling fluid density should be controlled at about 1.82 g/cm 3 . The effective plugging ability and rheological properties of the drilling fluid should be improved for the formation with microfractures. The research results can provide a theoretical basis for the safe and efficient development of igneous reservoirs.

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“…The fracture conductivity of igneous rocks is strong, and the pressure penetration of the drilling fluid along the fracture further affects wellbore stability. 18 , 19 …”

Section: Resultsmentioning

confidence: 99%

“…The fractures in igneous rocks are relatively developed, and the mechanical weak plane effect of the fractures is the main factor affecting borehole wall collapse. The fracture conductivity of igneous rocks is strong, and the pressure penetration of the drilling fluid along the fracture further affects wellbore stability. , …”

Section: Resultsmentioning

confidence: 99%

Study on Rock Mechanics and Wellbore Stability of Igneous Formation in the Shunbei Area

et al. 2022

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“…The mechanical failure of different formation rocks such as sandstones, limestones, and shales has been extensively investigated in the literature. − Although the mechanical failure of formation can be successfully estimated, a set of information is required for the prediction of geomechanical properties to understand the behavior of a reservoir rock system. Poisson’s ratio, shear modulus, Young’s modulus, stress intensity factor, and all related formation stress parameters are required to be evaluated to predict the behavior and failure of a reservoir rock. − This can be a long and costly experimental process requiring complex equipment.…”

Section: Introductionmentioning

confidence: 99%

Adhesion and Cohesion of Silica Surfaces with Quartz Cement: A Molecular Simulations Study

et al. 2022

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This study focuses on developing an adhesive and cohesive molecular modeling approach to study the properties of silica surfaces and quartz cement interfaces. Atomic models were created based on reported silica surface configurations and quartz cement. For the first time, molecular dynamics (MD) simulations were conducted to investigate the cohesion and adhesion properties by predicting the interaction energy and the adhesion pressure at the cement and silica surface interface. Results show that the adhesion pressure depends on the area density (per nm 2 ) and degree of ionization, and van der Waals forces are the major contributor to the interactions between the cement and silica surfaces. Moreover, it is shown that adhesion pressure could be the actual rock failure mechanism in contrast to the reported literature which considers cohesion as the failure mechanism. The bonding energy factors for both “dry” and “wet” conditions were used to predict the water effect on the adhesion pressure at the cement–surface interface, revealing that H 2 O can cause a significant reduction in adhesion pressure. In addition, relating the adhesion pressure to the dimensionless area ratio of the cement to silica surfaces resulted in a good correlation that could be used to distribute the adhesion pressure in a rock system based on the area of interactions between the cement and the surface. This study shows that MD simulations can be used to understand the chemomechanics relationship fundamental of cement–surfaces of a reservoir rock at a molecular/atomic level and to predict the rock mechanical failure for sandstones, limestones, and shales.

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“… 1 − 4 It has been reported that China has approximately 36 trillion cubic meters of recoverable shale gas resources and has made an ambitious plan for large-scale gas extraction. 5 , 6 …”

Section: Introductionmentioning

confidence: 99%

“…The successful exploitation of unconventional oil and gas resources (e.g., shale gas) in North America has inspired an energy revolution because of a rapid increase in energy demand on a worldwide scale. − It has been reported that China has approximately 36 trillion cubic meters of recoverable shale gas resources and has made an ambitious plan for large-scale gas extraction. , …”

Section: Introductionmentioning

confidence: 99%

Experimental Study of the Wettability Characteristic of Thermally Treated Shale

Yang

Gu²,

Chen

et al. 2020

ACS Omega

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Extraction of shale gas from shale reservoirs is significantly affected by shale wettability. Recently, thermal recovery technologies (e.g., combustion) have been tested for shale gas recovery. This requires an understanding of the wettability change mechanism for thermally treated shale samples. In this study, the effect of combustion on shale wettability was investigated. Shale samples were first processed to obtain smooth surfaces and then combusted at temperatures of 200, 400, and 800 °C. The initial contact angles and dynamic behavior of water droplets on shale surfaces were recorded using the sessile drop method. It was found that pores and fractures were generated on the shale surfaces following high-temperature combustion. The pore volume and diameter increased with increasing combustion temperature, which improved the connectivity of hydrophilic pore networks. Compared to a raw shale sample, the shale sample combusted at 400 °C showed a smaller initial water contact angle and a more rapid decrease in the contact angle because of the oxidation of organic matter and generation of pore structures. Water droplets were found to completely spread over the surface of the shale sample combusted at 800 °C because of the generation of fractures. Moreover, the van der Waals potential between water droplets and combusted shale samples was determined to be stronger. However, the initial contact angle and dynamic behavior of water droplets did not show a significant change for the shale sample combusted at 200 °C. As a result, high-temperature combustion (≥400 °C) can be used to significantly improve the hydrophilicity of shale.

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Experimental Study on the Failure Mechanisms in Brittle Shales

Cited by 7 publications

References 57 publications

Study on Rock Mechanics and Wellbore Stability of Igneous Formation in the Shunbei Area

Study on Rock Mechanics and Wellbore Stability of Igneous Formation in the Shunbei Area

Adhesion and Cohesion of Silica Surfaces with Quartz Cement: A Molecular Simulations Study

Experimental Study of the Wettability Characteristic of Thermally Treated Shale

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