2021 Volume 86 Issue 3 Pages 170-180
Hydraulic fracturing（HF）is an essential technology in shale oil and gas development while how the fracture mechanism works and how much propagation occurs in-situ conditions are not clear yet, because the geometry of HF networks in shale formations becomes complex affected by its geological heterogeneities such as natural fractures and bedding planes. To understand the hydraulic fracture propagation mechanisms under in-situ conditions, JOGMEC conducted i）laboratory scale HF experiments with rectangular shale samples（65 mm × 65 mm × 130 mm）and ii） semi-field-scale HF experiments at an outcrop in the range of tens of meters. In this paper, we focus on the result of the semi-field test. JOGMEC conducted the preliminary HF test on the Unosaki coast of the Oga Peninsula, Akita Prefecture（northern Japan）in 2018 and 2019. The test results in 2018 indicate HF succeeded at dolomite concretion sections while a breakdown didn’t happen at the siliceous mudstone section. In 2019, JOGMEC decided to modify the HF test system including packer with shorter intervals, usage of high rate pumping, high viscosity fluid, and diverter to confirm whether a crack could form in the siliceous mudstone section or not. Calcite precipitation was observed on some siliceous mudstone samples from the success section through the result of QEMSCAN. Therefore, carbonate concentration could be an important factor for HF success while detailed analysis is required to select the target section before the HF experiment.
JOGMEC learned a lot from two years of semi-field scale HF experiments including know-how of both target selection and operation. It also has been recognized that the prediction of an adequate interval for hydraulic experiments is very difficult in the Onnagawa Formation due to its complex geological characteristics.
