Tackling Breakdown and Proppant Placement Issues in a High-Temperature Volcanic Reservoir: Lessons Learned Through Multistage Fracturing in the Minami-Nagaoka Gas Field, Japan
Authors: Kidogawa Ryosuke , Yoshida Nozomu , Kaneko Masayuki , Takatsu Kyoichi , Kubota Ayumi , Kaminoyama Haruki , Boucher Andrew , Shaoul Josef R. , Tkachuk Inna , Spitzer Winston J. , de Pater C. J. 
Published: January 2025

Fracturing treatments are often challenging in high-temperature, tectonically stressed areas with heterogeneous and complex lithology. This study presents case histories of two multistage fracturing operations executed on a tight gas formation in a deep volcanic reservoir onshore Japan. This work begins by highlighting the technical difficulties experienced during the first operation, reviews the countermeasures developed over the course of the decade between operations, and finishes with lessons learned from the execution and evaluation of the second operation.

A root-cause analysis was undertaken to understand the poor treatment results from the first operation, where stages were defined by no formation breakdown, poor injectivity, or early screenout. It included reevaluation of core/petrophysical interpretation, stress model and net pressure history matching, and development of injectivity index diagnostic plots. The findings were used to identify updated technologies and workflows for the second operation with consideration of limitations in the target well drilled 10+ years before and left uncompleted. Finally, details of field execution and post-job logging results are presented to verify the effectiveness of the proposed techniques and extract lessons learned for future operations.

The breakdown and injectivity issues of the first operation appear to be tied to the initiation interval location and facies, where initiating in a massive lava facies was most problematic because of high stress and tortuosity. Uncertainty in the propped height from the net pressure history matches showed room for optimization in treatment design. In the second operation, with mitigation plans for breakdown issues, premature screen-outs, and detection of propped height in place, nine fracture stages were attempted. Eight stages achieved successful breakdown with careful target selection and using weighted brine. Two conventional treatments with crosslinked gel were placed in intervals with high injectivity and, as a field trial, two slickwater treatments with high viscosity friction reducer (HVFR) were placed in intervals with low injectivity. Issues with high apparent net pressure caused by tortuosity continued, comparable to the first well, and investigation of methods to further reduce treating pressures for future operation continues. Logging of the nonradioactive traceable proppant pumped suggested small propped heights while production logging showed contribution from the zones treated with slickwater, indicating that slickwater fracturing may be a viable option for this type of reservoir.

This work highlights a series of technical issues and possible solutions of multistage fracturing in a volcanic reservoir, validated through field execution. Proposed solutions partially solved the challenges, but at the same time, they open further questions for future operations. This study can serve as a reference for fracturing operations in analog reservoirs that have similar challenges.