In the summer of 2001, the first multi-stage completion in a deep, hot, and naturally fractured volcanic rock of the Minami-Nagaoka Field, Niigata Prefecture, Japan, was successfully completed using six propped fracture treatment stages.
Successful proppant placement in the northern part of the Minami-Nagaoka Field in Japan has proved to be extremely difficult in the past1-2 . During two propped fracture treatments pumped more than a decade ago, treatments failed miserably with only about 20% of the designed proppant placed before job termination due to premature screen-outs. Post-frac evaluation showed extremely high levels of net pressure of order 4000 psi prior to pumping any proppant – indicating that proppant placement problems were mainly occurred due to simultaneous propagation of very narrow multiple hydraulic fractures. Detailed pressure build-up tests and production data analysis confirmed the diagnosis of narrow multiple hydraulic fractures, which resulted in extremely poor propped fracture conductivity and non-economic gas production.
As successful development of the northern part of the Minami-Nagaoka reservoir could significantly impact Japan's domestic natural gas production, another attempt at propped fracture stimulation was justified. In the summer of 2001, the first multi-stage completion in a deep, hot, and naturally fractured volcanic rock of the Minami-Nagaoka Field was successfully completed using six propped fracture treatment stages. The new treatments in Minami-Nagaoka focused on the ability to mitigate the adverse effects of multiple hydraulic fracture propagation and the accompanying severe near-wellbore fracture tortuosity. A major equipment mobilization was required for this treatment to be possible as part of this concerted effort. Many unconventional changes, including completion changes to obtain highest possible injection rates to enhance proppant placement, aggressive proppant slug strategy, extensive fluid testing, real-time fracture treatment analysis, careful perforation placement, quality control, extreme overbalance perforating, and use of small-grained proppant, resulted in successful stimulation and favorable production response. This paper discusses all these design changes in detail, and provides final results regarding the fracture geometries obtained and post-fracture production response.