Objective

This paper summarizes key engineering discoveries and technical findings observed during the staged development of a volcanic reservoir. Through out the development, 200 hydraulic fracturing diagnostic injection tests and 168 hydraulic fracturing treatments were performed. This program was conducted in one of the few commercially viable thick and laminated volcanic gas reservoirs in the world and were staggered in 5 separate campaigns over an 11-year period.

Method, Procedure, Process

Due to the low permeability of this gas reservoir, hydraulic fracturing was necessary for sustained economic productivity. As this massive laminated reservoir contained between 15 to 40 vertically separated pay sections, a key design consideration was to connect as much pay as possible with the least number of fracturing stages.

Although a conventional plug and perforation frac technique gives full assurance of optimal fractures for every bit of pay, the completion cost would undermine the project's economics. Therefore, the limited entry technique was selected. The uncertainties and risks were evaluated to maximize the probability of success.

Both methodologies were applied in successive campaigns. Staggering the project into 5 successive campaigns enabled adequate time to evaluate results, acquire data and execute. The results from these learnings are summarized in this paper.

Results, Observations, Conclusions

Over 60 DFITs (Diagnostic Fracture Injection Tests), ~90 SRTs and ~50 Mini-Fracs have been conducted. In addition to conventional fracture diagnostics tests, other techniques were applied with successful implementation. One such example was the utilization of multiple step rate tests within the same frac stage to evaluate limited entry efficiency. As a result of the test data, the number of clusters per frac was increased from 3 to 6, increasing the net pay coverage by about 65%.

Another achievement was the reduction of the uncertainty in tubing friction and the evaluation of tubing friction increase due to the addition of proppant. This resulted in a cost effective method of reducing uncertainties in calculated BHPs, thus improving the overall understanding of fracture geometry. This paper also demonstrates that the integration of all of the collected diagnostic data, temperature surveys, frac simulation and geo-mechanic calibration resulted in increased contribution from more zones which was verified with production logs.

This enhanced reservoir understanding greatly helped to save operational time and reduce cost. Completion improvements have resulted in an 80% increase in productivity and a 20% increase in EUR. Screen out rates have dropped from 33% to 5% between the initial and the most recent campaign.

Novel/Additive Information

A holistic workflow for conducting diagnostic injection tests in volcanic pays.

Detailed analysis of limited entry controlled hydraulic fracturing and its efficiency.

Representative case histories including, DFITS, Step rate tests, Mini Fracs, Temperature surveys and production logs to back up the production results.

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