Better Foam Cement with a Liquid Stabilizer: Offshore Case Histories

Abstract

Foam cementing has been widely used for offshore applications where the formation has low fracture gradients, and shallow water flow may occur. One challenge of foam cementing is to ensure that the foamed slurry is stable at the desired foam qualities with low permeability. Therefore, stabilizers are commonly applied along with the foaming agent. This paper describes the comparison testing and several offshore applications of a new liquid foam stabilizer that improves logistics and flexibility on the rig, and prevents excessive viscosity and foaming during mixing. The new liquid foam stabilizer was tested in the laboratory to compare its performance with that of a dry stabilizer used previously in the field. The stabilizer was then used in several offshore wells to assess its performance in real-world operations. In particular, one problem with dry foam stabilizers is that they can promote excessive foaming during mixing, which leads to pump cavitation if not controlled with a defoaming agent. The field operations were arranged to test a new operational procedure for use with the liquid foam stabilizer to avoid cavitation without a defoamer. The laboratory testing determined that the new solids-free liquid foam stabilizer disperses easily in the cement slurry. The new stabilizer was also found to improve the stability of the foam and the density distribution of the set foam cement compared with no stabilizer. Furthermore, several case histories will demonstrate that the combination of the liquid additive and the new operational procedure improved the slurry mixability without any pump cavitation issues. The new liquid foam stabilizer has more predictable and reliable response than conventional dry stabilizers, and the case histories will demonstrate how its use improves cementing flexibility and logistics.

Foamed Cement Applications in Oil Industry Based on Field Experience: A Comprehensive Review

“…It is crucial that the foam remains stable for longer than the time it takes for the cement to harden. 24,25 Frequently used foaming agents include substances such as surfactants, ethoxylated alcohols, and fatty acid derivatives in the form of quaternary ammonium salts. Stabilizers include polymers, mixed surfactants, polyglycol ethers, and sulfate salts or even solids.…”

“…One of the most critical challenges while cementing offshore wells is that the formation fracture pressure gradient is low and flow of shallow water could occur; therefore, it is important to ensure stability of the foamed slurry that will produce a sheath with very low permeability, and hence, injection of stabilizer with the foaming agent is recommended to ensure stability of the slurry while pumping downhole and into the annulus. 25 3.1.2. Laboratory Testing.…”

“…On drilling out the shoe track, a good formation integrity test was obtained, comparable to offset wells completed with the conventional cement. 72 Doan et al 25 suggested the use of a liquid stabilizing agent to produce highly stable foam cement for offshore applications. The use of this liquid stabilizer in three offshore wells in the Gulf of Mexico enabled the production of more stable foamed cement compared to that produced with the dry stabilizer and to the foam cement generated with no stabilizing agent.…”

“…The most important operational challenges of foam cementing are to achieve a stable foamed slurry at the desired foam quality and to generate a cement sheath that has low permeability. 25 Nitrogen solubility plays a minor role in downhole foamed cement quality and is difficult to accurately estimate.…”

“…The chemicals used to create and maintain the foamed cement must function well in high temperature and pressure conditions and in the highly alkaline, calcium-rich environment of the water component of the cement slurry. It is crucial that the foam remains stable for longer than the time it takes for the cement to harden. , …”