Abstract
Due to the strict environmental regulations particularly with chrome-based drilling fluid additives and due to the challenges faced when drilling HPHT wells in terms controlling the rheological properties and filtration characteristics of water-based drilling fluids, a lot of efforts have been put into the development of an efficient chrome-free based drilling fluid additives. Controlling the fluid loss and rheological properties under high temperature conditions can be very challenging due to the fact that a lot of polymers degrade at such conditions, which could result in poor fluid loss control as well as a dramatic increase or decrease in the rheological properties. This paper presents an extensive development and laboratory evaluation of a new chrome-free lignosulfonate with high thermal stability along with a comparison with some available commercial chrome-free products.
A water-based drilling fluid, which was contaminated with calcium sulfate to simulate the contamination occurring when drilling through thick anhydrite sections, was used as reference point to evaluate the performance of nine different Chrome-Free Lignosulfonate (CFLS) and the performance was compared with two commercially available CFLS. The performance of the new CFLS was evaluated under both low and high temperature. The rheological properties were assessed after aging the reference fluid samples for 24 hours under room temperature conditions and treating it with 8 lb/bbl CFLS. Then, the samples were aged for 16 hours under high temperature conditions (300o F) and both the rheological properties and filtration characteristics were measured. The performance of the CFLS was assessed in terms of the %thinning efficiency as well as the %reduction in fluid loss.
The results showed a significant reduction of 36% in terms of thinning efficiency and up to 42% in terms of fluid loss by the addition of 8 lb/bbls of the newly developed CFLS. On one hand, one of the evaluated commercial CFLS showed a 63% improvement in terms of thinning, however, the fluid loss increased by 33%. On the other hand, the other commercial CFLS resulted in adverse effect on the rheological properties, where the yield point was increased by almost 100% while the fluid loss was reduced by 48%. Based on the results, the newly developed CFLS product was able to maintain both good rheological properties and filtration characteristics under high temperature conditions. The newly developed CFLS outperformed the two commercially evaluated products under high temperature conditions, which shows the great potential of the new product in replacing the available products.
