Optimizing Underground Thermal Reserves By Insulating The Wellbore Monitoring And Modeling Wellbore Temperature In The Kharyaga Field's Arctic Tundra Environment

摘要

The Kharyaga oil field is located beyond the polar circle in northeastern Europe, and since 1999, has needed first-class thermal insulation for its ESP-lifted wells to produce. In these Arctic conditions, the permafrost typically reaches thickness of up to 300 meters. And with the wax appearance temperature (WAT) or pour point as high as 50°C and 30°C for some geological objects, managing wells in order to minimize wax scraping operations is a real challenge. Especially during shut-in periods, as the produced fluids cool down the risk of wax totally plugging the tubing is significant. To combat that risk, the production or injection annuli are systematically filled with gelled diesel. Permanent real-time temperature monitoring by fiber optic sensors has been deployed in the production annulus of six wells so far, to measure temperature distribution along the wellbore across the permafrost layer, down to the reservoir. And thermal modeling, using the Enthalpy Balance thermal model, shows a good match with the temperatures thus measured. It also confirms the fine thermal quality, as per expectations, of the gel deployed. For the purposes of further development of the Kharyaga field, which includes wells with liquid expected rates less than 1,000 bpd, well modeling flags up the necessity for additional thermal insulation. Using 3?” instead of 4?” tubing is a first solution: trials on two wells have shown a gain of up to 12°C. The benefit and design of field proven double-wall tubing was also assessed for the many additional development producers planned. One set of vacuum-insulated tubing (double-wall tubing with vacuum inside) is already on the spot ready for a field trial on a future work-over in the Kharyaga environment.