The First Successful Fracture Treatment Campaign Conducted in Japan:Stimulation Challenges in a Deep, Naturally Fractured Volcanic Rock

摘要

In the summer of 2001, the first multi-stage completion in arndeep, hot, and naturally fractured volcanic rock of thernMinami-Nagaoka Field, Niigata Prefecture, Japan, wasrnsuccessfully completed using six propped fracture treatmentrnstages.rnWhile successful development of the northern part of thernMinami-Nagaoka reservoir could significantly impact Japan’srndomestic natural gas production, successful proppantrnplacement in this field has proved extremely difficult in thernpast1-2. During two propped fracture treatments pumped morernthan a decade ago, treatments failed miserably with only aboutrn20% of the designed proppant placed before job terminationrndue to premature screen-outs. These treatments exhibited netrnpressures up to 4,000 psi before pumping any proppant - thernhighest net pressure level that we have ever observed,rnindicating extremely complex fracture growth. Post-fracrnevaluation confirmed that proppant placement problemsrnmainly occurred due to simultaneous propagation of veryrnnarrow multiple hydraulic fractures. Detailed pressure builduprnand production test analysis confirmed the diagnosis ofrnnarrow multiple hydraulic fractures, which resulted inrnextremely poor (and vanishing) propped fracture conductivityrnand non-economic gas production.rnThe new treatments in Minami-Nagaoka focused on thernability to mitigate the adverse effects of multiple hydraulicrnfracture propagation and the accompanying severe nearwellborernfracture tortuosity. Major equipment mobilizationrnwas required for this treatment to be possible as part of thisrnconcerted effort. Many unconventional changes, includingrncompletion changes to obtain highest possible injection ratesrnto enhance proppant placement, aggressive proppant slugrnstrategy, real-time fracture treatment analysis, gel testing forrnminimization of proppant damage, careful perforationrnplacement, quality control, extreme overbalance perforating,rnand use of small-grained proppant, resulted in successfulrnstimulation and favorable production response. This paperrndiscusses all these design changes in detail, and provides finalrnresults regarding the fracture geometries obtained.