Abstract
The Auca field, located in the Amazonian region of Ecuador, started production in 1970, reaching a peak of 75,000 BOPD in March 2015. By the end of 2015, production declined to 65,000 BOPD due to water cut increase, reservoir pressure loss, and progressive formation damage. In January 2016, Petroamazonas EP (PAM) and Schlumberger (SLB) initiated the Shaya Project with the objective of increasing production and reserves through infill drilling, secondary recovery, and well interventions. The Auca field produces from the Hollín Formation and the Napo U and T sandstones. The latter two normally suffer from pressure depletion due to weak aquifer support, whereas the Hollín formation maintains reservoir pressure due a strong aquifer acting from the bottom. In general, formation damage in the Auca field is caused during drilling and pulling activities due to invasion of drilling or control fluids, but it also happens naturally in form of scale precipitation which has been physically proved, and possibly fines migration which remains a theory yet to be verified. Several workflows, procedures, and research on the nature of the damage have been put in place to resolve the production loss and decline issues associated with the varios potential causes. The selection of the most appropriate damage-removal technique depends on the reservoir and fluid properties, reservoir architecture, production behavior, water diagnosics, well intervention history, well geometry, artificial lift system, and, most importantly, the nature of the formation damage. From the reservoir and production engineering perspective, understanding formation damage and identifying its root cause is a key for designing the appropriate solution. After 18 months of intensive activity with drilling and workover operations, the production of the Auca field is close to 72,000 BOPD. If the operator had decided to stop activities, the production baseline would be at 35,000 BOPD. This means that, at present, the project has contributed a net incremental of 37,000 BOPD, of which approximately 30% corresponds to damage-removal jobs. This is a case study on one of the largest producing oilfields in the Oriente Basin that shows the typical productivity issues to deal with siliciclastic reservoirs and provides an example of how to select the most appropriate damage-removal techniques.
