ABSTRACT:
We discuss the first fracture treatment practices carried out in Hailaer Basin, China in igneous extrusive sedimented rocks (tuff). The Hailaer Basin is dominantly a non-marine sedimentary basin with a large sequence of extrusive rocks (basalt and tuff) and tuffaceous conglomerate. Rock mechanics analysis indicated a strong component of reservoir rock plastic behavior for which fluid design and proppant concentration choice in the first two fracture treatment attempts were inadequate and failed. The rock is also sensitive to water; swelling and slaking are observed upon exposure to aqueous fracture fluids, making the fracturing treatment more difficult and complex. After implementing more suitable fracture techniques such as repeated fracturing and new types of fracture fluids, successful treatments were designed and implemented in the tuffaceous reservoir sequence. A total of 190 intervals in 95 wells have been treated to date using the method, with a success rate of 97%.
1 INTRODUCTION
It is usual industry practice to execute massive hydraulic fracturing treatments in low-permeability sandstone reservoirs to stimulate well production, but it is far less common to use such methods to stimulate tight, volcanic-origin reservoirs, as these are quite rare. Several reports of successful hydraulic fracturing treatments in volcanic reservoir rocks can be found; e.g. Weijers et al. (2002) reported fracturing practices in volcanic tight gas reservoirs in the Minami-Nagaoka gas field in Japan. Also, Antoci & Anaya (2001) discussed massive fracture treatments in tight gas zones in the Neuquen Basin (Argentina) where the lower parts of the oil zone are tuffaceous porphyrites. In recent years, tight tuffaceous natural gas reservoirs were discovered through exploration activities by Daqing Oilfield Ltd. in the Hailaer Basin. The basin is dominantly a non-marine basin with a large sequence of extrusive rocks (basalt and tuff).
