Fluid Flow Within a Porous Medium Near a Diamond Core Bit
- L.H. Jenks (Esso Production Research) | J.D. Huppler (Esso Production Research) | N.R. Morrow (Esso Production Research) | R.A. Salathiel (Esso Production Research)
- Document ID
- Petroleum Society of Canada
- Journal of Canadian Petroleum Technology
- Publication Date
- October 1968
- Document Type
- Journal Paper
- 172 - 180
- 1968. Petroleum Society of Canada
- 1 in the last 30 days
- 93 since 2007
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A laboratory coring program using diamond microbits and water-based mud to core in sandstone samples was carried out to investigate pressure and fluid flow behaviour in the rock near a working bit. The work was specifically designed to answer the questions: (1) What effects do borehole-to-formation differential pressure (overbalance) and associated filtrate invasion have on reservoir fluid saturations during the coring process? (2) Under what conditions is it feasible to core for residual oil saturations?
The results of the study indicate that over a considerable range of normally encountered conditions, residual oil values within the core will be reduced during the coring operation. In the system employed, this oil stripping varied directly with overbalance, filtrate production rate, core diameter and core permeability; it varied inversely with penetration rate and was affected by mud properties. Up to 60 per cent of the residual oil was stripped from the rock under severe coring conditions. Pressure gradients and permeability damage were high near the bit and diminished rapidly with distance from the bit.
Trends observed in the laboratory suggest that overbalance pressure is the prime factor in oil-stripping behaviour and should be kept low to minimize stripping in the field. Mud composition, especially particle size control, and penetration rate also appear to be important variables.
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