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An effective drilled cuttings lifting from the bottomhole to the surface improves drilling performance. The transportation of drilled cuttings becomes more challenging when drilling a high angle or horizontal well. A sufficiently high annular mud velocity is essential to prevent drilled cuttings from settling and forming stationary beds on the low side of a hole. This can cause several drilling problems such as high torque and drag, stuck pipe, etc. This problem has been addressed via an experimental work which studied the effect of annular mud velocities on drilled cuttings removal using water-based mud with polypropylene beads in vertical, deviated, and horizontal holes. It was accomplished using a 3.96 m long flow loop which comprised 50.8 mm transparent acrylic section with a simulated drill string. The annular mud velocity was varied from 0.27 m/s to 1.06 m/s at ambient condition. The experimental results showed that increase in annular mud velocity has improved hole cleaning, i.e., cuttings transport ratio experienced an improved performance in the turbulent flow than in laminar flow. The findings further demonstrated that the presence of polypropylene beads in water-based mud has contributed positively to the performance of drilled cuttings lifting in a vertical hole by 9% in a turbulent flow. Index Terms-Annular drilling mud velocity, cuttings transport ratio, polyethylene beads, water-based mud, wellbore cleaning.

Experiments have been carried out at atmospheric temperature and confining pressures up to 5 kb in which rocks, of different porosities, and fitted with flexible jackets, have been deformed up to 6 per cent axially while containing pore water under undrained conditions. Application of a confining pressure and axial compressive stress creates a pore pressure, which weakens and embrittles the rocks under these conditions. The initial pore pressure may take any value up to that of the confining pressure, depending on the amount of water available inside the jacket and sample. Dilatancy produced by crack propagation during shear deformation resulted in dilatancy hardening which prevented or delayed mechanical instability (as manifested by stress drops). The greatest amount of dilatancy occurred during the fracturing process, but dilatancy decreased as the effective confining pressure increased. Only a small amount of dilatancy occurred during subsequent movement on faults, and the diIatancy tended to reach a stable value at deformations of -5 per cent (-1-5 mm of movement on a major fault surface). There is evidence of small quasicyclic variations of dilatancy at greater deformations, which produce small stress drops of -50 b. The implications for crustal faulting and earthquake premonitory effects are discussed.

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