“Sticky Scale” had been a great obstacle in producing gas at our “Dissolved in water type” gas field. However, it has recently been solved by injecting polyphosphates with concentration of 3 to 4 ppm into wells. The author has written on the field test as follows: 1. The properties of EDTA and polyphosphates. 2. The results of tests with EDTA and polyphosphates. 3. The outline of tests.
The main reservoir rocks in Nagaoka district are volcanic rocks of the Nishiyama and Shiiya formations. Abnormal pressures are observed in the reservoirs of the Fujikawa and Kumoide gas fields in the western margin of this district. On the other hand, hydrostatic pressures are observed in the reservoirs of such fields as the Katagai and Nishi-Nagaoka. This suggests the presence of permeability barriers in the volcanic rocks. On a plot of the mudstone thickness vs the common logarism of excess pressure from hydrostatic pressure, a positive correlative relationship is observed. The abnormal reservoir pressures in this district may be ascribed to the thick mudstone seal and overburden pressure.