Invasion of CaCO3 particles and polymers into porous formations in presence of fibres

Abstract

Formation damage can occur through migration of drilling fluid particles and polymers into porous formations. A methodology for assessing formation damage was applied to measure invasion of CaCO3 and polymers into porous formations, where the CaCO3 particles size had been selected using established particle size selection methods. Tests were conducted with and without the presence of a cellulose-based additive, to study if the fibres could reduce the fluid loss and limit the formation damage.Input factors such as applied differential pressures, ranging from 6.9 to 34.9 MPa (1000-5000psi), and median pore-throat openings of discs were also varied to investigate which parameters affected the significance of the formation damage.The results showed invasion of CaCO3/ground marble into the formation and that particle size selection methods used to reduce fluid loss also led to formation damage. Further it was discovered that the presence of fibres limited the invasion of both CaCO3 and polymers into the porous formations when the D90 of the fibres were ≥3/2 times the pore-throat size, and that higher applied pressures led to larger formation damage. The fluid loss tests also showed both lower total fluid losses and lower fluid loss rates over time with the fibres added to the fluids, indicating that the filter-cake permeability was reduced with the addition of the fibre particles.