Abstract
A deep well multi stage fracturing project is under going the Minami Nagaoka gas field. Permeability of the target formation is 10-2md order of tight volcanic rocks, deposited deeper than 4, 000m, which creates a high temperature, and high pressure circumstance. In addition, rock facies changes almost foot by foot, and some regions are highly naturally fractured. These characteristics make it difficult to have successful frac operation by a classical approach. Recent study and feed back from the two premature screen out experiences in the Minami Nagaoka gas field suggested that near wellbore tortuosity, which caused multiple fractures to grow, was estimated to be higher than anticipated. In this condition, the net fracturing pressure became increasing due to individual fracture push each other with the fracture width keeping narrow. Increasing net pressure led to the high surface treating pressure, the injection rate would be limited, finally ended in premature screen out.
To eliminate this phenomenon, the newly drilled well last year was designed for the high-pressure fracture treatment. Several new design concepts such as extremely overbalanced perforation (EOB), step down test, and proppant slug techniques are planned to observe the degree of near wellbore tortuosity and will be tried to reduce these tortuous paths.
