Barite sagging is one of the common issues while drilling high pressure-high temperature wells. This will cause variation in the mud weight in both vertical and deviated wells. Barite sagging can cause many problems such as; density variations, well-control problems, stuck pipe, downhole mud losses, and induced wellbore instability.
The objective of this study is to assess the effect of adding a new copolymer to the invert emulsion drilling fluid to prevent the sagging issue. Sag test was conducted under static conditions over a wide range of temperature (200°F to 350°F). Sag test was performed using vertical and decline (45° degree) aging cell. In addition, the effect of adding the new copolymer on the rheological properties and the electrical stability of the invert emulsion drilling fluid was evaluated.
The results obtained showed that adding 1 lbm/bbl of the new copolymer had no effect on drilling fluid density (14.5 ppg). The new copolymer slightly enhanced the electrical stability of the invert emulsion drilling mud. The new copolymer had a minor effect on the plastic viscosity, yield point, and gel strength. Adding 1 lbm/bbl of the copolymer prevent barite sagging at 350°F, where the sag factor was 0.55 before adding copolymer, and 0.503 after adding it. The storage modulus (G′) was increased by 40% after adding 1 lbm/bbl of the new copolymer confirming the sag test results. There was no effect of adding the new copolymer in the filtration loss and filter cake thickness.
The novelty of this work is the development of a new drilling fluid formulation that can be used in drilling HPHT wells without any sag issue. This development will help the drilling engineers to safely drill deep wells and maintain the drilling fluid integrity during the drilling operation. In general, this will reduce the overall cost of the drilling operation by reducing the non-productive time in solving many issues such as well control, loss of circulation, or pipe sticking.