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PE Distinguished Seminar Series: Numerical Simulations – Support of a Long-Term Test of Gas Production on the Alaska North Slope
October 10, 2022 @ 4:00 pm - 5:00 pm MDT
Professor and holder of the Robert L. Whiting Chair in Petroleum Engineering
Harold Vance Department of Petroleum Engineering
Texas A&M University
We investigate by means of numerical simulation a planned year-long field test of depressurization-induced production from a permafrost-associated hydrate reservoir on the Alaska North Slope at the site of the recently-drilled Hydrate-01 Stratigraphic Test Well. The main objectives of this study are (a) to assess quantitatively the impact of temporary interruptions (well shut-ins) on the expected fluid production performance from the B1 Sand of the stratigraphic Unit B during controlled depressurization over different time scales, as well as on other relevant aspects of the system response that have the potential to significantly affect the design of the field test, and (b) to investigate possible methods to control water production.
The results of the study indicate that shut-ins obviously reduce gas release and production during and immediately after their occurrence, but their longer-term effects are strongly dependent on the depressurization regime and on the time of observation, covering the entire range of potential outcomes. Shut-ins (a) have a universally strong negative effect when quasi-linear depressurization is involved regardless of the length of the production period, (b) have a strong positive effect in multi-step depressurization schemes that becomes apparent earlier for large initial pressure drops, but (c) can also appear to have practically no effect for slow step-wise depressurization at the end of the year-long production test. The results of the study also indicated the limited options that are available to reduce water production, and their limited effectiveness.
The study confirmed the superiority of multi-step depressurization methods as the most effective strategies for hydrate dissociation and gas production, and showed that two observation wells (located at distances of 30 m and 50 m from the production well) are appropriately positioned and both able to capture the P, T and SG behavior during the fluid production and shut-ins in any of the eight cases we investigated.