Modeling Studies of Pressure Cycling Associated with Seismicity in Mutnovsky Geothermal Field, Kamchatka, Russia

Abstract

Two alternative models are presented to explain pressure cycling in the Mutnovsky high temperature two-phase hydrothermal system. A non-linear well fracture (W-F) model describes an open observation well in terms of a lumped parameter model, with well discharge specified as a function of liquid saturation. Two conditions were found necessary to create cycling 1. a hysteretic saturation switch for well discharge ("well off" liquid saturation less than "well on" liquid saturation), 2. heat exchange between the well and surrounding rock (to maintain a pressure gradient from the recharge area to the well). The sensitivity of cycling parameters (cycling period and pressure amplitude) was determined from model parameters. Cycling parameter estimations were found in reasonable agreement with pressure data from an observation well at the high temperature Mutnovsky geothermal field, Kamchatka, Russia. An alternative model considering a wellbore intersected by two fractures was also shown capable of generating cyclic behavior, due to an interplay between the different time scales for pressure and thermal equilibration.