Characterization of basement fractured gas reservoir incorporating hydraulic injection and microseismic monitoring
Kazuhiko Tezuka(1), Ryohei Kamitsuji(1), and Tetsuya Tamagawa(1)
Japan Petroleum Exploration Co., Ltd. JAPEX Research Center (email@example.com)
ABSTRACT Microseismic monitoring during a massive hydraulic injection experiment was performed in the Yufutsu gas field in May 2005. The Yufutsu gas reservoir is known as a so-called “fractured reservoir” seated at around 4 km depth in the Southern Ishikari Plain, central Hokkaido, in northern Japan. The objectives of the experiment were to delineate the spatial distribution of the fractures by stimulating the pre-existing fractures. The injection schedule and the anticipated area of stimulation were thoroughly designed and predicted by using an in-house numerical simulator SHIFT, which runs on a Discrete Fracture Network (DFN) model. The DFN model was created on the basis of fracture information obtained from borehole images. Injection of more than 5,600m3 of seawater, without any additives, effectively induced microseismic activity and accordingly improved the injectivity of the well. Over 3,700 seismic events were detected by a network of 4 deep downhole and 3 shallower seismic sensors and for approximately 700 of these events clear onsets of P and S waves were located. The preferential direction of observed microseismic distribution showed a good consistency with the prediction. However, the extent of the observed cloud was larger than the prediction and significant differences in pressure responses were also observed. These mismatches were fed back to the modification of the model, which finally showed a reasonable match. Through the experiment and the modeling study, we successfully demonstrated the feasibility of characterizing the fracture system in the...