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Air Injection for Sand Control
This article discusses application of air injection for sand control. It references some laboratory work and subsequent field tests that were performed by the Gulf Research and Development Company in 1964.
While the concept might seem strange to the uninitiated, low-temperature oxidation of heavy oils has the ability to form insoluble (in the native oil) coke that cements the sand grains together. Let us review the requirements for an effective sand-control treatment:
- Sand production must be prevented
- Oil productivity of the well must be maintained.
- The completion should last the life of the reservoir with no remedial work.
Gulf’s laboratory work involved the injection of warm air into unconsolidated sand-packs saturated with a heavy crude oil. This caused the oil to be oxidized and become more viscous. Continued oxidation of this very viscous oil formed an insoluble coke or resin which was observed to cement the sand grains together.
Figure 1 shows that for certain combinations of air injection rate and rate of heating of the sand-pack sand consolidation would occur. For other combinations, the crude oil would ignite (i.e. high-temperature combustion would result)Ignition of the crude is undesirable from a sand control perspective. Figure 2 shows that the compressive strength of the coked sand has a maximum, which is a function of the oxidation temperature. Higher temperatures result in low sand compressive strengths. Ignition of the coke residue was found to be avoidable by proper control of the air injection rate and of rate of temperature increase of the sand-packs.
Other experimental observations were:
Lower temperature limit to form satisfactorily coked sand was 300oF, and
The maximum reduction in sand-pack permeability was 28%.
Gulf field tested this sand consolidation method in a field that was uneconomical to produce because of sand production problems.
Six different wells were treated in reservoirs from 400 to 700 ft deep. Completions types included single-point entry notching, slotted gravel-packed liner, and jet perforating the casing. Following treatment, the wells produced oil at rates up to 150 bbl/d. None produced appreciable quantities of sand. Subsequent water and cold air injection into the wells had no adverse effect on the sand consolidation.
The authors commented that if the reservoir oil is not heavy enough, other oils not native to the reservoir could be injected to replace the reservoir oil. Usually crude oils with gravities of less than 20o API are suitable for sand consolidation by this method.
Terwilliger, P.L., Smith, F.M. and Goodwin, R.J.: Warm-Air Coking – A New Completion Method for Unconsolidated Sands", Jour. of Pet. Tech. (April 1964) pp. 367-371.