Chemical Transients During Production of High Gas Wells at the Northern Geysers Steam Field, California, USA

Abstract

Non-condensible gas and stable isotope data from the extreme northwest end of The Geysers steam field indicate that this part of the reservoir consists of a deeper zone. below about feet where gas concentrations are as high 100,000 and a shallower zone with steam containing 15,000 ppm-wt gases, conforming to stratification of the reservoir previously reported from a production arca several miles to the east. Production wells may tap the shallow zone. the deep zone, or both, depending upon positions of their production zones with respect to the interface. In addition to high gas content, deeper zone is characterized by anomalously high temperatures, of (and perhaps hydrogen) in the steam, and high total carbon the gases. Shifts of gas composition during production can be interpreted in terms of dilution of steam in the shallow zone by boiling of reservoir liquid. and mixing bctween decp and shallow steam. Reservoir steam saturation after years of production is calculated to about 0.3 in the shallow zone, and about 0.9 in the deep zone. There is some problcm with saturation calculations which involve concentration of hydrogen. which yields deep zone saturation values as high as 2.5, which is impossible. This is discussed in relation to the possible presence of "excess" hydrogen in the steam.