TY - JOUR
T1 - The mechanical contrast between layers controls fracture containment in layered rocks
AU - Douma, Lisanne A.N.R.
AU - Regelink, Jaap A.
AU - Bertotti, Giovanni
AU - Boersma, Quinten D.
AU - Barnhoorn, Auke
PY - 2019
Y1 - 2019
N2 - Open natural fractures allow fluids to flow, which is necessary for the production of low-permeable geothermal and petroleum reservoirs. These reservoirs often consist of lithological layers with significant variation in rock strength, which makes it difficult to predict fracture containment within the rock succession. In this paper, fractures are classified as contained, when they do not cross the layer interface of the adjacent layer, so that formation and growth are inhibited in the adjacent layer. This study concerns the impact of the differences in rock strength (i.e., mechanical contrast) between two adjacent brittle layers on the fracture containment in finely-layered rocks. Laboratory deformation tests and 2D finite element modelling were performed on three-layered samples with varying mechanical contrasts to examine the behaviour of fractures at different stress conditions. Fractures initiate as shear fractures in weak layers, and propagate with a steeper angle (tensile fracture) through the adjacent stronger layer. The mechanical contrast within a layered rock does not always act as a containment barrier, meaning that fractures do not cross the layer interface of the adjacent layer. This is due to differences in differential stress between the weakest layer and strongest layer. The mechanical contrast combined with the magnitude of the confining pressure has a significant influence on fracture containment. An increase in mechanical contrast and confining pressure prevents fractures from propagating into stronger layers. The results contribute to predict natural fracture containment in brittle sequences at shallow depth in the subsurface.
AB - Open natural fractures allow fluids to flow, which is necessary for the production of low-permeable geothermal and petroleum reservoirs. These reservoirs often consist of lithological layers with significant variation in rock strength, which makes it difficult to predict fracture containment within the rock succession. In this paper, fractures are classified as contained, when they do not cross the layer interface of the adjacent layer, so that formation and growth are inhibited in the adjacent layer. This study concerns the impact of the differences in rock strength (i.e., mechanical contrast) between two adjacent brittle layers on the fracture containment in finely-layered rocks. Laboratory deformation tests and 2D finite element modelling were performed on three-layered samples with varying mechanical contrasts to examine the behaviour of fractures at different stress conditions. Fractures initiate as shear fractures in weak layers, and propagate with a steeper angle (tensile fracture) through the adjacent stronger layer. The mechanical contrast within a layered rock does not always act as a containment barrier, meaning that fractures do not cross the layer interface of the adjacent layer. This is due to differences in differential stress between the weakest layer and strongest layer. The mechanical contrast combined with the magnitude of the confining pressure has a significant influence on fracture containment. An increase in mechanical contrast and confining pressure prevents fractures from propagating into stronger layers. The results contribute to predict natural fracture containment in brittle sequences at shallow depth in the subsurface.
KW - Fracture containment
KW - Fracture propagation
KW - Layered rocks
KW - Mechanical contrast
KW - Refraction
UR - http://www.scopus.com/inward/record.url?scp=85068625374&partnerID=8YFLogxK
U2 - 10.1016/j.jsg.2019.06.015
DO - 10.1016/j.jsg.2019.06.015
M3 - Article
AN - SCOPUS:85068625374
SN - 0191-8141
VL - 127
JO - Journal of Structural Geology
JF - Journal of Structural Geology
M1 - 103856
ER -