Reversible Invert Emulsion Drilling Fluids: Controlling Wettability and Minimizing Formation Damage

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractNovel emulsifiers in reversible invert emulsion drilling fluids offer a unique opportunity for operators to control the wettability properties of the mud. Reversibility of the invert emulsion will provide economic advantages in drilling and completion and increased productivity. Optimal drilling performance and formation damage control are usually achievable by oil wetting the drill solids, formation and drillstring. On the other hand, optimal completion of a wellfiltercake removal and cement bonding --and disposal of drilled cuttings are best achieved by maintaining all surfaces water-wet. Filtercake removal is especially critical in the completion of horizontal openhole wells.The reversible invert emulsion drilling fluids can be readily and reversibly converted from a water-in-oil emulsion to an oil-in-water emulsion and back to a water-in-oil emulsion using an acid-base chemical switch. This drilling fluid system is simple and easy to run without any drastic changes in current invert-emulsion technology. A novel surfactant package forms an invert emulsion in the presence of lime and a direct emulsion in the presence of acid. Reversible emulsion technology uses new emulsifiers that allow the drilling fluid to cycle between oil-wetting and water-wetting as frequently as one desires. Protonation and deprotonation of the surfactant is used to control the emulsion phase without drastic and uncontrollable viscosity swings.The reversible invert emulsion drilling fluid has been successfully run in a North Sea well. The paper presents field data illustrating the economic benefits of this system and discussion on how the ability to change wettability can influence drilling and completion performance.

Phase Inversion of Pickering Emulsions by Electrolyte for Potential Reversible Water-in-Oil Drilling Fluids

“…3,84 In those cases, the reversible emulsions are stabilized by surfactant emulsifiers, and the viscosity normally decreases near the transitional point. 4,85,86 However, the smooth transition of the rheological properties at the approximate transitional inversion point seen in our case is crucial for safety in the drilling process, since complex problems such as Barite sedimentation, cuttings suspension, or flow impedance could occur if the emulsion rheology deteriorated and emulsion stability failed. Moreover, both W/ O emulsions and O/W emulsions exhibit reasonable gel structures as well as shear-thinning stability with relatively low viscosity for a base Pickering emulsion, which makes it possible to obtain an entire range of desired properties by adjusting the composition of the drilling fluid through the addition of various agents.…”

Cleanup characteristics and mechanisms of reversible invert emulsion drilling fluid

“…Is there another way for the RIEM to reduce the formation permeability besides plugging the pores? It is generally believed that the surfactants in the oil-based mud that invades the rock matrix are capable of changing the natural wetting state from water-wet to oil-wet, thus impeding the flow of hydrocarbons through the rock matrix during production (Chen et al, 2006;Cuiec, 1989;Gant and Anderson, 1988;McDonald and Buller, 1992;Patel and Growcock, 1999;Skalli et al, 2006;Yan et al, 1993;Yan and Sharma, 1989).…”

“…A limited number of publications on this topic can be found in the literature. Several authors (Ali et al, 2004(Ali et al, , 2006Green et al, 2001;Patel, 1999;Patel and Growcock, 1999;Patel and Ali, 2003) reported that low pH promotes the transformation of RIEMs from a water-in-oil type to an oil-in-water type, inducing the water wetting condition of the surfaces of the pipes and the drilled formation. Bryant et al (2006) has demonstrated that the adsorption of ethoxylated alkylamines affects the wettability of mica surfaces.…”

“…During drilling, the drilling fluid can be used as an invert emulsion with all the performance benefits associated with oil-based muds (OBMs). During and after the completion stage, the emulsion can be reversed by adding a water-soluble acid, thus providing excellent filter-cake cleanup, better cementing, improved production in well completion, efficient cutting cleanup, and waste minimization (Ali et al, 2004(Ali et al, , 2006Green et al, 2001;Patel, 1999;Patel and Growcock, 1999;Patel and Ali, 2003). Because the unique attribute of RIEM in the completion of a well is supported by the pH-responsiveness of ethoxylated alkylamine emulsifiers, it is important to explore how pH levels influence the interfacial gathering behaviors of the emulsifiers and thus the completion performance of RIEM.…”