Well Productivity Enhancement of High Temperature Heterogeneous Carbonate Reservoirs

Acidizing is one of the most popular techniques for well productivity enhancement during oil and gas production. However, the treatment method is not very effective when the wellbore penetrates through multiple layers of heterogeneous reservoirs. Uneven acid distribution always results in productivity enhancement under expectation. When such a well is drilled, the temperature of the well could be too high to keep the acid reaction under control. The acid used in the treatment fluid, most commonly HCl, would react with the tubular and the formation at a very high rate. Rather than creating long wormholes to bypass the damaged area, face dissolution, loss of pipelines, and potential damage are the outcomes after the treatment. Thus, several new techniques were proposed in this study to solve the issues discussed above.

To address the heterogeneity of the reservoir, viscoelastic surfactants (VES) were used as diverting agents during acidizing treatments. A recently developed chelating agent, L-glutamic acid-N,N-diacetic acid (GLDA), was evaluated as a possible alternative for the traditional HCl. Coreflood tests and measurements of rheology properties of the treatment fluids were used to investigate the performance of the treatment fluids based on the two new systems.

In total, two VES were evaluated for their diverting abilities. The first VES was based on amine oxide. It was found that the live VES-based acids had the highest apparent viscosity when the concentration of HCl was 5 wt%. During the coreflood tests, the VES-based acid was only able to build up pressure drop across the core at injection rates less than 1 cm_(3)/min. A significant amount of the VES was left inside the core after the treatment, which reduced the efficiency of production enhancement.

The other VES, based on carboxysulfobetaine, can tolerate high temperatures up to 325?F. According to the viscosity measurements of the spent VES-based acid, the addition of various corrosion inhibitors lowered the fluid viscosity at temperatures above 150?F. Mutual solvent was able to break the wormlike micelles formed by the VES in the presence of calcium chloride. The diverting ability of the VES was proved through coreflood tests.

For the GLDA-based treatment fluids, two additives were added into the system in effort to improve the efficiency of the treatments. Polymers and VES were added into the GLDA to achieve even fluid distribution during treatment. A significant viscosity increment was observed with the help of the viscosifier, which could expand the application of the GLDA.