Application of Optical-Fibre Temperature Logging (DTS) in Monitoring Subsurface Transient Temperature Changes Resulting from Fluid Flow

A. Forster, J. Schrotter, and D. F. Merriam

The DTS technique is a temperature sensing method that recently has tested successfully in boreholes of the North American Midcontinent (Kansas). The method is based on the Raman effect of the backscattering of light along an optical fibre and allows the measurement of temperature instantaneously over the entire length of the cable by real-time surface data readout. Consequently, temperature changes resulting from transient effects can be monitored for a long time because the DTS cable can be left in place and temperatures are not affected by lowering a probe. Here, we report the results from a fluid-flow experiment in a borehole that was logged previously under thermal equilibrium conditions, in which fluid flow was simulated by inputting 520 gallons (about 2000 liters) of water heated to a temperature of 120°F (48.9°C). Through temperature monitoring in minute intervals over a span of hours, the elevated water table was observed until returned to static conditions, thus allowing a determination of the rate of stimulated flow (5 liter/minute) into the carbontate aquifer at the bottom of the well. The monitoring shows the cooling of hot water remaining in the uppermost part of the water column while temperatures below the cold/warm water interface decrease because of active down-hole water flow. The experiment clearly indicates the potential of the technique to monitor subsurface temperature changes, for example in connection with natural or artificially stimulated fluid-flow conditions in oil and gas reservoirs undergoing secondary or tertiary recovery.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California