Innovative concept of hydrofracturing for deep stress measurement

For the effective measurement of the reopening pressure in hydraulic fracturing, it is necessary to use the testing equipment with sufficiently small compliance. If not, there is no way to estimate the maximum stress in a plane perpendicular to a borehole, i.e. the maximum horizontal stress assuming a vertical borehole, from the reopening pressure. This limitation makes it difficult to apply the hydraulic fracturing for the measurement of the maximum stress, because the compliance of conventional equipments is generally so large. Taking account of this situation, we propose a new strategy which allows us to do the in-situ tests of hydraulic fracturing for stress measurement at depths more than 1 km. The system consists of two components which are (a) the compact drilling tool with a built-in mudmotor and (b) the packer tool with a built-in pump. Each of them is conveyed in drill pipe on wireline. The compact drilling tool is used to drill an additional hole with 47 mm (AQ size) in diameter and 2-3 m in length at the bottom of an original borehole, and the hydraulic fracturing is carried out in the drilled hole by using the small packer tool.