The Evaluation of Using Micronized Barite as a Completion Fluid Weighting Material in HPHT Wells

Abstract

Completion and workover fluids are one of the prominent factors that play a great role in the success of completion and workover operations. Since these fluids have a great impact on personnel safety, environment, wells productivity, and the total cost of the operation, great efforts should be put into selecting the optimal fluid to accomplish the required job Completing high pressure high temperature wells is one of the challenging jobs that require formulating a special type of fluids due to the complexity and the critical downhole conditions of high pressure high temperature wells. This complexity and the new technical developments on drilling and completion operations pushed the industry towards the development of new formulations and implementation of advanced technologies to meet all the requirements and the use of conventional drill-in fluids, barite-weighted fluids, was discontinued. However, some of the proposed fluids have environmental issues while others are costly. Since conventional drill-in fluids have high density, are environmentally friendly and relatively inexpensive, this work aims to evaluate micronized barite as a weighting material to resolve the problems associated with conventional drill-in fluids, i.e. formation damage and fluid stability, in order to use these fluids as completion and workover fluids in HPHT wells. In addition to the commercial sample of barite, different sizes of barite, i.e. 106-75 μm, 75-40 μm, and less than 40μm, were prepared using sieve analysis. Moreover, a sample of micronized barite was prepared by reducing barite particle size to a few microns using ball milling machine after optimizing the operating parameters of ball milling machine. Afterwards, solubility tests were conducted to study the effect of particle size on barite removal using a recently developed formulation, DTPA with potassium carbonate as a catalyst. The effect of barite particle size on the rheological properties of the drill-in fluids was investigated at 120 and 250°F. Barite particle size effect on fluids stability was also investigated using zeta potential measurements and static sag test. Furthermore, a new formulation using different proportions of bridging agent (calcium carbonate) was designed to mitigate the resulted formation damage by minimizing fluid filtrate and solid particles invasion into the formation. The new formulation was evaluated to ensure its capability to properly accomplish the required job. As a result of barite particle size reduction, solubility test results showed a good enhancement in barite removal due to the increase of chemical reaction surface area, and HPHT filtration test confirmed these results and showed an improvement of around 5% in filter cake removal efficiency. Moreover, reducing barite particle size showed a thickening behavior in rheology of completion fluids and as the temperature increases, the thickening behavior becomes more noticeable. Finally, zeta potential measurements showed a good enhancement in stability with micronized barite for a pH range greater than 8, while the other sizes of barite were lying in the unstable range, i.e. -30 to +30 mv. While, in contrast, sag test showed insignificant enhancement in fluid stability as barite particle size was reduced to micronized size with a sag factor of 0.546 as compared to 0.563 for the normal size at 230°F.