Abstract
Efficient removal of drilled cuttings from a wellbore during the drilling process is critical to the success of any drilling operation. The negative consequences of inefficient hole cleaning can range from the occurrence of significant Non Productive Time due to time and resource consuming remedial operations, to the potential sticking of the drilling BHA and potential loss of the entire wellbore. These can carry very significant financial consequences ranging from tens of thousands to millions of dollars (USD).
While hydraulic hole cleaning during the drilling of vertical wells is a relatively straight-forward matter, the cleaning of deviated wellbores presents entirely different challenges which have been well documented. The Illah field, located offshore the Niger Delta region of Nigeria, presents specific challenges which result in the requirement for significantly deviated wells, which present numerous hole cleaning difficulties. Some of these challenges include but are not limited to:
Vertically stacked and laterally offset objective reservoirs.
Multiple completion objectives and strategies per wellbore requiring complex well designs.
It is a well-documented fact that cuttings removal in inclined wellbores becomes more difficult as the hole inclination increases. In the medium to horizontal deviation scenarios the tendency for cuttings to accumulate into "beds" comes into play and these cuttings beds will increase in severity in the critical angle range depending on other factors such as particle/cutting size. Some other factors which could contribute to the accumulation of cuttings in inclined boreholes include; drilling fluid rheology and density, flow rates, drill string RPM and mechanical wellbore instability.
This paper which is a case study of drilled wells in the Illah field, concentrates on the effects of the application of a mechanical cleaning device; Hole Cleaning Tubulars, to the problem of down hole accumulated drilled cuttings whilst drilling deviated wells.
