The Use of Reversibly Adsorbing Tracers for Characterizing Unconventional-Petroleum Reservoirs at Geothermal-Reservoir Temperatures

Abstract

We conducted a series of laboratory and field tests in order to characterize flow processes during the hydrofracture and production of a Horn River, Canada shale-gas reservoir. The heat from this unconventional-petroleum reservoir was not co-produced with the petroleum, but, if it were, this system, with down-hole measured temperatures of 140 oC, could qualify as a low-temperature geothermal reservoir. Laboratory studies were conducted using a bench-top flow reactor in which we simulated reservoir conditions using drill cuttings from shale formations. In the subsequent field experiment, we injected a combination of conservative and reactive tracers into each of 10 long-reach horizontal wells. Water samples were collected during the flowback portion of the test from each of the wells and the concentrations of the conservative and reversibly adsorbing tracers were measured at EGI. In most cases, within each formation, the gas production rate was proportional to the relative degree of adsorption of the reversibly adsorbing tracer. Using the laboratory-obtained tracer-rock interaction data, a numerical simulation model of the injection/flowback process was built. The model was then used to calculate tracer-contacted fracture-surface area adjacent to each well, which was used to correlate with gas production rate.