TY - JOUR
T1 - Effect of water imbibition on fracture generation in Mancos shale under isotropic and anisotropic stress conditions
AU - Zhang, Shifeng
AU - Sheng, James J.
N1 - Publisher Copyright:
© 2017 American Society of Civil Engineers.
Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2018/2/1
Y1 - 2018/2/1
N2 - During hydraulic fracturing in shale oil and gas reservoirs, hydration swelling due to shale water imbibition is believed to create secondary fractures that improve permeability, as observed at ambient conditions. In this paper, the influence of hydration swelling on fracture generation and permeabilities in Mancos shale at different stress conditions was investigated. Hydration swelling was characterized by swelling strain tests. Generated fractures were observed by computed tomography (CT) scan tests. The permeability of the shale was measured before and after water imbibition. In shale with isotropic confining pressure increased to 2.0 MPa or more, water imbibition can cause fracture closing instead of propagation. As a result, permeability decreased significantly, up to two orders compared with that before water imbibition. On the other hand, the differential stress required to activate shear-induced fractures was greatly reduced after hydration, up to 50% in shale after water imbibition. For shale cores under higher confining pressure, with decreased hydration swelling magnitude, shear-induced fracture generation was reduced. Water permeability of shale with a shear-induced fracture was nearly 100 times higher than that of shale without a fracture. In other words, water imbibition can enhance the generation of shear-induced fractures under anisotropic stress to improve shale permeability, but it can cause fractures to close in shale under isotropic stress.
AB - During hydraulic fracturing in shale oil and gas reservoirs, hydration swelling due to shale water imbibition is believed to create secondary fractures that improve permeability, as observed at ambient conditions. In this paper, the influence of hydration swelling on fracture generation and permeabilities in Mancos shale at different stress conditions was investigated. Hydration swelling was characterized by swelling strain tests. Generated fractures were observed by computed tomography (CT) scan tests. The permeability of the shale was measured before and after water imbibition. In shale with isotropic confining pressure increased to 2.0 MPa or more, water imbibition can cause fracture closing instead of propagation. As a result, permeability decreased significantly, up to two orders compared with that before water imbibition. On the other hand, the differential stress required to activate shear-induced fractures was greatly reduced after hydration, up to 50% in shale after water imbibition. For shale cores under higher confining pressure, with decreased hydration swelling magnitude, shear-induced fracture generation was reduced. Water permeability of shale with a shear-induced fracture was nearly 100 times higher than that of shale without a fracture. In other words, water imbibition can enhance the generation of shear-induced fractures under anisotropic stress to improve shale permeability, but it can cause fractures to close in shale under isotropic stress.
KW - Fracture generation
KW - Hydration swelling
KW - Hydraulic fracturing
KW - Isotropic and anisotropic stress
KW - Permeability
KW - Water imbibition
UR - http://www.scopus.com/inward/record.url?scp=85038390335&partnerID=8YFLogxK
U2 - 10.1061/(ASCE)GT.1943-5606.0001832
DO - 10.1061/(ASCE)GT.1943-5606.0001832
M3 - Article
AN - SCOPUS:85038390335
VL - 144
JO - Journal of Geotechnical and Geoenvironmental Engineering
JF - Journal of Geotechnical and Geoenvironmental Engineering
SN - 1090-0241
IS - 2
M1 - 04017113
ER -