The "Art" of in Situ Fluid Sampling and the Remarkable Compositional Variations in the Wellbore Fluid of VC-2B, Valles Caldera, New Mexico

Abstract

In situ fluid sampling operations were conducted at VC-2B in January 1990 using two flow through tools of different designs. Of eight attempts, no runs obtained samples from their intended depth of collection or, if they did, the tools gained additional fluid by inward leakage during their trips back to the surface. Interpretation of the salinity and mass of the fluid samples indicates that they were collected from apparent depths of about 204 to 1045 m, at collection temperatures of about 125° to 240°C. The data shows a remarkable two fold increase in fluid salinity (>9000 versus about 4000 mg/kg C1) near the top of the well and a relatively thin, dilute "cap" of condensed steam at the top of the water column. Various criteria suggest that these salinity gradients are caused by boiling and condensation of steam in the wellbore during a seven month period of logging, stimulation, flow testing and other in hole experiments.