Increasing Production Through Selective Acid Stimulation With Coiled Tubing and Self-Aligning Dynamic Divergent Tool: Mexico Offshore Region Case History
Authors: Steffani Michelle Octavio , Inda David A. , Ramirez Marcos , González Julián Javier , Vazquez Jorge , Hernandez Jovanny Alberto , Sors Pedro Alfredo , Narvaez Ivan Ernesto 
Published: February 2016

An operator wanted to perform an acid stimulation in offshore Mexico because of two previous bullheading stimulations did not achieve the target oil rate that resulted in high production with accelerated decline, leading to short well life. Post-analysis supposed indicated that the fluid injection were not affecting detected in the preferential all the potential zones. The operator needed to change this behavior; therefore, based on the petrophysical properties along the openhole section, an unconventional selective treatment was designed to distribute the injection fluids and overcome reduced well geometries present in this region. Normally, the main restriction is the tubing, with the subsurface safety valve and other accessories, having a small restriction of approximately 2.562 in.

This article discusses the results of this intervention wherein the fluid was injected into the formation through coiled tubing (CT) and the self-aligning tool (SAJ) to stimulate 14 specific perforation clusters in a single run. It also discusses alternatives for operators to help optimize or reduce treatment volumes using a dynamic divergent tool that can be applied in large carbonate openhole intervals under these conditions.

Breaking usual paradigms, CT was the chosen method to perform the acid stimulation, but with a difference—a self-aligning jetting tool was used that acted as a "mechanical" divergent by providing focused acid placement at the desired zone. The advantage of combining these variables was avoiding zones with higher permeability or loss circulation zones (highly fractured), where the majority of the treatment could enter if a bullheading intervention was selected. This application does not require existing completions to be removed before the treatment. No workover rig is necessary.

This mechanical divergent tool overcomes the "standoff" distance so that the tip of the tool directly faces the openhole section. This occurs because the self-aligning design allows placing the treatment directly into the matrix, allowing the generation of wormholes at wellbore walls and inducing deeper matrix penetration. Using this method, an accurate treatment was designed to help optimize the volumes necessary.

The results were impressive. Before the stimulation treatment, the well experienced no production. After intervention, well production returned to 3,546 BOPD. A 27% increase in production was realized compared to previous stimulation efforts. Additionally, a 77% decrease in treatment volume and a 63% decrease in the operator's total costs were experienced.

In the offshore region of Mexico, the stimulations are normally performed with bullheading technique; however, there are some cases where it is complicated to stimulate uniformly, especially when the openhole section is large and presents fractures; this technique is a solution alternative with opportunity for the optimization of stimulations in Mexico and globally. Techniques normally used are based on chemical divergence to stimulate large carbonate reservoirs. A problem associated with this practice is the use of large treatment and divergent material volumes, leading to space limitations on the platform and the use of a stimulation vessel. Interventions with CT were not an option previously because of openhole concerns.