Abstract
The cuttings transport efficiency of various drilling fluids has been studied in several approaches. This is an important aspect, since hole cleaning is often a bottleneck in well construction. The studies so far have targeted the drilling fluid cuttings’ transport capability through experiments, simulations or field data. Observed differences in the efficiency due to changes in the drilling fluid properties and compositions have been reported but not always fully understood. In this study, the cuttings bed, wetted with a single drilling fluid, was evaluated. The experiments were performed with parallel plates in an Anton Paar Physica 301 rheometer. The results showed systematic differences in the internal friction behaviors between tests of beds with oil-based and beds with water-based fluids. The observations indicated that cutting beds wetted with a polymeric water-based fluid released clusters of particles when external forces overcame the bonding forces and the beds started to break up. Similarly, it was observed that an oil-based fluid wetted bed allowed particles to break free as single particles. These findings may explain the observed differences in previous cutting transport studies.
Highlights
As the global demand for the more efficient drilling of oil wells is increasing, long horizontal wells with extended reaches are becoming more common; this comes with intrinsic challenges of the more complex structures, such as a weakened hole-cleaning efficiency, as the drilling cutting particles tend to precipitate inside the wellbore by gravity through a long area [1]
The continuous rotational test, maintaining a constant gap between the parallel plates, undergoes deformation of the cuttings bed shape, stretching to the sides and losing height and, losing contact area; as this occurs, it is not possible to be aware of the real contact area between the cuttings bed and the upper plate where the calculations are made when assuming the area of the plate
As the internal friction coefficient depends on the shear stress (σ) and the normal stress (P), and these two depend on the area, inaccuracy of the area will result in unrealistic internal friction coefficient values, as shown in Figures 3 and 4
Summary
As the global demand for the more efficient drilling of oil wells is increasing, long horizontal wells with extended reaches are becoming more common; this comes with intrinsic challenges of the more complex structures, such as a weakened hole-cleaning efficiency, as the drilling cutting particles tend to precipitate inside the wellbore by gravity through a long area [1]. These drilling cuttings are debris composed mainly by sandstones and shales with specific gravities between 2.2 and 2.7, with an average of 2.6, and sizes varying widely between a couple of microns to tens of millimeters [2,3,4], the most common range being between 0.5 mm to 2.5 mm. The probability of being able to run casing strings or completion strings without excessive problems increases
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