IMPROVEMENT IN STEAM PRODUCTION THROUGH ORIFICE PLATE CLEANOUT IN THE CERRO PRIETO GEOTHERMAL FIELD

Abstract

Since 1997, Latina and Calpine Corporation have been operating a total of 32 production wells in the Cerro Prieto geothermal field in Mexico. The decline in steam production in this field is caused by two mechanisms: a drop in reservoir pressure as well as by flow restrictions created by silica deposition. Based on recent drilling and well work-over results, the effect of the latter on the decline rate is found dominant. Silica precipitation by brine flashing can occur anywhere in the flow system such as reservoir, wellbore and surface equipment. The orifices, which cause a change in velocity profile, are vulnerable to silica deposition. The silica deposition usually reduce the diameter of the orifices. This, in turn, reduces orifice plate area, resulting in a decrease in the steam production rate. In effort to reduce steam decline rate, an aggressive orifice plate diameter cleanout program for the Latina-Calpine production wells was recently implemented.

The results obtained from this cleanout program indicate a significant decrease in overall steam decline rate. The results of decline rate with and without aggressive orifice cleanout are presented in the paper. The total amount of steam recovery per month by orifice cleanout is also discussed.