When drilling in the production zone the control of fluid-loss must be obtained without damaging the formation. The use of non damaging fluids is of great importance for:
the production zone of new wells,
re-entry when drilling through damaged well bores,
extended wells where large areas need to be protected,
reaming to expose new production surfaces.
Formulations of non-damaging fluids are of growing importance especially because of the increasing number of horizontal wells being drilled. In horizontal wells, the drilling fluid is in contact with the reservoir formation for a long period of time and there are generally long, exposed zones of production which are difficult to clean up. Horizontal wells are often completed open hole without perforated casing, with therefore increased susceptibility to formation damage and reduced production.
A novel polymeric additive derived from a natural polymer which has been modified to optimise its performance is proposed. This optimisation is achieved by introducing hydrophobic attachment to the polymer backbone. This increased hydrophobicity improves dramatically the fluid loss control without increasing viscosities, in particular through the formation of a thin and impermeable filter cake which protects the production zone from fluid invasion. This thin filter cake is easily removed at low production pressures and allows excellent productivity. In simulated well conditions, such as long core formation damage test, an extremely low formation damage was shown with high return permeability values.
This new polymeric additive is especially advised for use in the preparation of drill-in fluids, in fresh water or brine, in combination with biopolymer and calcium carbonate.