Technical Paper: Reservoir Surveillance - Fluid Contact Monitoring in Fractured Carbonate TA-GOGD Project

Society: SPE
Paper Number: 145554
Presentation Date: 2011
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TA-GOGD is suited for heavy oil in fractured formations. Steam is injected into the fractures serving two purposes; applying a gas gradient across the carbonate blocks so that the oil in the carbonate drops down by gravity, and heating the carbonate blocks so that the reduced viscosity oil drips out faster. The reservoir has two fluid systems; gas/oil/water levels in the fractures, and gas/oil/water contacts in the carbonate. Oil extracted from the carbonate accumulates in the fractured oil rim, where it is produced by wells intersecting the fractures. It is essential to manage the oil rim position and thickness. Wireline interventions with gradio manometer are not safe where steam is injected at 55 bars and 271°C. This temperature is too hot for permanent electronic gauges, but is within the operating range of optic fiber used to measure distributed temperature.

A new measurement to determine the fluid levels was developed using differential thermal relaxation. Cold water was pumped around a U tube containing an optic fiber and clamped outside the perforated tubing across the open hole until the temperature at the reservoir depth inside this U tube was considerably less than the hot surrounding gas, oil and water. With the pump stopped, the rate at which the cooler water inside this U tube reached thermal equilibrium with the warmer well bore fluids was measured with rapidly repeated distributed temperature surveys. Gas, oil and water have different specific heat capacities and thermal conductivities, so each surrounding fluid took a different length of time to heat the cooler water inside the U tube. The differences caused sharp discontinuities on the initial temperature logs of the warming water inside the U tube at the depths of the fluid contacts. The fluid levels measured with this method are sufficiently accurate to manage the oil rim.

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