Study Uses Engineered Vesicles for Cement-Integrity Applications
Authors: Carpenter Chris 
Published: April 2020

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 193538, “Engineered Vesicles for the Controlled Release of Chemical Additives and Application for Enhanced Oil-Well-Cement Integrity,” by Elizabeth Q. Contreras, SPE, Kenneth D. Johnson, and Diana Rasner, SPE, Aramco, et al., prepared for the 2019 SPE International Conference on Oilfield Chemistry, Galveston, Texas, 8–9 April. The paper has not been peer reviewed.

Encapsulation-based systems are of interest for the industry in applications such as chemical-additive preservation, small molecule release, particle delivery, and self-sealing materials. Many methods are used to encapsulate relevant chemical additives for the controlled release of contents such as polymeric vesicles, inorganic shells, and mesoporous materials. In the complete paper, a novel system that uses engineered features of permeable polymeric shell walls for the controlled release of encapsulated cargo is described.

Introduction

Competent cement systems are designed to allow the placement of cement behind the casing at a set time by using chemical additives. The function of these chemical additives is extensive and used to control cement properties such as setting time, rheology, fluid loss, gas migration, density, and enhanced mechanical properties. Challenges arise when additives are depleted promptly or manifested prematurely before cement has been placed behind the casing. Additives are used to accelerate the set time of the cement only after being placed downhole properly during the construction of a well.

To ensure cement quality, innovative polymers based on a family of polymers known as aromatic polyamides, or aramides, are used here as a single additive in cementing. The vesicular design of the polymer offers unique delivery-system features, providing chemical reagents when needed. In this way, the polymer is designed to produce a vast array of encapsulants for controlling the release of additives downhole during cementing operations. The application of using vesicles for the development of right-angle-set cements is shown in the paper. Thereafter, the spent vesicles remain embedded as an elastomer and the robustness of the shell imparts beneficial mechanical properties to the cement sheath. 

Experimental

An emulsion template is used to form vesicles for the modified release of additives (Fig. 1). Interfacial polymerization consisting of two immiscible solvents—a chloroform/cyclohexane mix and water—are stirred to form an emulsion. Droplets are captured by a semi-permeable polymer shell. The dispersed phase contains the accelerant calcium chloride to serve in the design of right-angle-set cements. The general procedure for polyamide synthesis is provided in the complete paper.

Cement Mixing and Curing Procedure. Cement samples are prepared using Class G cement. A cement slurry consists of six components: water, cement, dispersant, cement retarder, applied polymer at 3 wt% of cement, and antifoamer. The polyaramide vesicles are added as a single additive.

The slurry is mixed at 4,000 rev/min for 15 seconds and then increased to 12,000 rev/min for 35 seconds. The cement slurry is poured into a cement consistometer for measurement of slurry-thickening time. After the slurry is brought to the fill line in the slurry cup, the cup is assembled with a paddle and capped and a thermocouple is inserted. Cement viscosity is recorded up to 100 Bearden units of consistency (Bc) at 100 and 300°F at 3,000 psi.