2018 Volume 83 Issue 6 Pages 491-498
Unconsolidated sands often appear as places of unconventional resources under development, but the mechanisms of phenomena occurring during development, such as sand production and hydraulic fracturing, are not well understood yet. This paper experimentally examined the fracture phenomenon accompanying fracturing. To this end, a method to simulate hydraulic fracturing of unconsolidated strata in laboratory experiment was constructed. In the experiments using a specimen made from a mixture of silica sand and kaolin and a fracturing fluid of machine oil, a linearly extending fracture was formed similarly to the case of hard rocks when the proportion of kaolin was large.
However, when the proportion of kaolin is small, fracture was not formed at all. This phenomenon can be interpreted if the fracture is formed by compressive deformation / failure, which is completely different from conventional theory of hydraulic fracturing. That is, since tensile force is not transmitted in unconsolidated sands, gaps are created by pushing the part where the fluid pressure acts and the grains in the vicinity thereof. Also, in the mixture of silica sand and kaolin, as the proportion of kaolin decreases, the interlocking between the grains improves and compressive deformation / failure hardly occurs, so it is considered difficult to form gaps / fracture in hydraulic fracturing.
