Plugging of horizontal wellbores can lead to significant loss of productivity and can nullify, the benefit of a horizontal wellbore that is expensive to create. Cleaning horizontal wellbores is a formidable challenge. The problem is particularly complex for heavy oil formations that show asphaltene, sand and other difficultto- remediate problems. This papers aim is to develop a new technique that can effectively clean up a horizontal wellbore without requiring expensive workovers. The technique involves the use of ultrasonic treatment coupled with foam treatment. Initial experiments show that ultrasonic treatment can reduce plugging in two waysthe first is the reduction in oil viscosity (especially in the presence of asphaltic crudes) and the second is the ability of ultrasound to keep particles in suspension. The second effect can be due to generation of microbubbles. The process is coupled with in situ generation foam. In order to generate foam, a particular fYPe of surfactant is chosen from a selection of a wide range of surfactants supplied by the service companies. While the design of the device that couples both these effects need to be optimized, initial series of experiments show goodpromises.
Crude oils produced in many parts of the world contain asphaltenes. Asphaltenes are known to deposit in the vicinity of production wells during miscible floods, after acid stimulation, during thermodynamic changes, and in the pipelines during transportation or during pressure changes in a mature field with an asphaltic crude. Asphaltene deposition leads to production loss and involves expensive corrective measures. This study proposes a new technique for cleaning asphaltenes with an ultrasonic device. The same method can be used to clean a horizontal wellbore that usually suffers from solid deposits, leading to significant reduction in productivity. The principle behind this new technique is ultrasonic irradiation, coupled with foam treatment. Even though ultrasonic treatment has been used in other disciplines for cleaning purposes, the petroleum industry has used the technique for remote sensing'" and material characterization4. Recently, ultrasonics have been used to reduce cuttings size5. This is possibly the first application of ultrasonics in reducing environmental impact due to drilling activities. Several other potential applications of ultrasonics have been investigated, but did not reach commercial level, both in the areas of asphaltene removal6 and the removal of fines and mud solids from new wellbores7.
The ultrasonic treatment has been proven to reduce viscosity to facilitate flow in pipelines. The preliminary experiments conducted by the principal author showed that the same ultrasonic technique can be used to clean asphaltene clogged sections of oil wells and reservoirs8. Little has been reported, however, on the optimization of amplitude, power generation, time required for cleaning and viscosity reduction. The effect of ultrasonication on adsorption properties of the reservoir rocks and fluids is another area that lacks investigation.
Recently, Smordal and Islam9 demonstrated that the combination of ultrasonic treatment with a jet reactor can be attractive.
