Prevention of Barite Sag in Oil-Based Drilling Fluids Using a Mixture of Barite and Ilmenite as Weighting Material

Abstract

Drilling high-pressure high-temperature (HPHT) wells requires a special fluid formulation that is capable of controlling the high pressure and is stable under the high downhole temperature. Barite-weighted fluids are common for such purpose because of the good properties of barite, its low cost, and its availability. However, solids settlement is a major problem encountered with this type of fluids, especially at elevated downhole temperatures. This phenomenon is known as barite sag, and it is encountered in vertical and directional wells under static or dynamic conditions leading to serious well control issues. This study aims to evaluate the use of barite-ilmenite mixture as a weighting agent to prevent solids sag in oil-based muds at elevated temperatures. Sag test was conducted under static conditions (vertical and inclined) at 350 °F and under dynamic conditions at 120 °F to determine the optimum ilmenite concentration. Afterward, a complete evaluation of the drilling fluid was performed by monitoring density, electrical stability, rheological and viscoelastic properties, and filtration performance to study the impact of adding ilmenite on drilling fluid performance. The results of this study showed that adding ilmenite reduces sag tendency, and only 40 wt.% ilmenite (from the total weighting material) was adequate to eliminate barite sag under both static and dynamic conditions with a sag factor of around 0.51. Adding ilmenite enhanced the rheological and viscoelastic properties and the suspension of solid particles in the drilling fluid, which confirmed sag test results. Adding ilmenite slightly increased the density of the drilling fluid, with a slight decrease in the electrical stability within the acceptable range of field applications. Moreover, a minor improvement in the filtration performance of the drilling fluid and filter cake sealing properties was observed with the combined weighting agent. The findings of this study provide a practical solution to the barite sag issue in oil-based fluids using a combination of barite and ilmenite powder as a weighting agent to drill HPHT oil and gas wells safely and efficiently with such type of fluids.

Barite–Micromax mixture, an enhanced weighting agent for the elimination of barite sag in invert emulsion drilling fluids

“…The main principle of the sag test is to measure the weight difference between the top and bottom of the fluid column after the test. The detailed procedure of the static and dynamic sag tests is well explained in the literature (Mohamed et al 2017(Mohamed et al , 2019Basfar et al 2018Basfar et al , 2019.…”

“…Secondly, the particles of Micromax additive have a higher surface area-to-volume ratio compared to barite that makes the lift and drag forces greater than the cohesion and gravity forces (Boyou et al 2019). Thirdly, Micromax additive has a higher surface charge than barite, and as the surface charge increases, the stability of the colloidal system increases (Mohamed et al 2019;Joseph and Singhvi 2019). Moreover, additional enhancement in the sag tendency will be observed in real cases because the high density of Micromax additive reduces the total amount of the weighting agent required to formulate a drilling fluid with the same weight of the base fluid, and thus, it reduces the solids loading in the drilling fluid.…”

“…Several studies were conducted to solve solids sag phenomenon in oil-and water-based muds by training rig personnel (Scott et al 2004), optimizing the rheological properties of the drilling fluid using anti-sagging agents and rheology modifiers (Temple et al 2004;Davis et al 2017;Basfar et al 2018;Elkatatny 2018Elkatatny , 2019Mohamed et al 2020), reducing the particle size of the weighting agent (Mohamed et al 2017;Boyou et al 2019), replacing the weight material, or adding a combination of weight materials (Alabdullatif et al 2015;Abdou et al 2018;Basfar et al 2019;Mohamed et al 2019).…”

Impact of Perlite on the Properties and Stability of Water-Based Mud in Elevated-Temperature Applications

“… 3 This increase of yield point and gel strength indicates the enhancement in the mud capability to keep the solid particles in suspension and reduce the sag tendency at dynamic and static conditions, confirming the sag test results. 26 , 34 , 35 Another advantage of using perlite with high-density mud is enhancing yield point to plastic viscosity ratio (YP/PV). Perlite additive increased the YP/PV significantly from 1.31 to 2.58 to fall within the recommended range as per drilling practices (1.5–3).…”

Prevention of Barite Sag in Water-Based Drilling Fluids by A Urea-Based Additive for Drilling Deep Formations

“…It was concluded that decreasing the barite particle size to micronized size slightly enhances the drilling fluid stability, but it does not eliminate the sag issue. Basfar et al [27] and Mohamed et al [28] studied the effect of using a barite-ilmenite combined weighting material on the properties of water-based and oil-based drilling fluids. It was found that the combined weighting material greatly enhanced the rheological properties and the stability of the drilling fluid and prevented solids sag in both vertical and inclined conditions.…”