P.3 ~ Continued - New DTS interpretation improves matrix acidizing offshore Mexico

The Schlumberger ACTive live downhole coiled tubing (CT) was selected for real-time treatment monitoring of subsequent matrix acidizing jobs. The ACTive CT services convey live downhole measurements on fiber-optics, telemetry-enabled CT, and consist of a bottomhole assembly, surface electronics and interpretation software. Downhole data, including internal and external pressures, temperature, casing collar locator, gamma ray and distributed temperature sensing, can be used for various intervention operations independently. However, PEMEX was most interested in how these measurements can be used collectively to optimize acidizing.

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Conclusions

This case history is characteristic offshore Mexico in many wells where the treatment fluid cannot reach a specific interval, either because the formation is altered due to the presence of fissures, fractures or a significantly higher permeability/porosity, or because the treatment program is not fully adapted to the wellbore conditions. The use of ACTive service with DTS profiling to provide a temperature profile of the entire wellbore to monitor fluid placement and well production performance helps bridge this gap.

For instance, had the treatment been pumped as initially planned by simply bullheading all the fluid, the extent of the imbalance between the three perforated intervals downhole would not have been discovered. Furthermore, the team would not have diagnosed that the bottom interval could not be reached by bullheading the fluid, no matter the rate, or that the formation was so tight and that the properties of the middle interval caused all fluid spotted directly with the CT at the lower interval to flow back to it.

Finally, the application of the DTS quantitative method using the inversion algorithm was successful in helping to bring understanding to a level not possible by a simple qualitative interpretation of the temperature traces – how the top and middle intervals both reacted to the treatment, for example.

Although the bottom interval could not be stimulated, valuable information was collected regarding the reservoir dynamics in this field. The analysis helped identify how future interventions might be modified to stimulate bottom, tight zones. While CT conveyance and bullheading techniques together were insufficient in this case, mechanical diversion using inflatable packers may be a better alternative for upcoming interventions.

Ultimately, the joint use of ACTive real-time downhole measurements and distributed temperature surveys were key in tracking the exact placement of treatment fluids to allow comparison of the actual performance versus the design prepared for that intervention. In particular, the technique clearly identified deviations from the expected formation behavior during the design phase, and thus provided valuable information on actions to take during the intervention.

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