Abstract
The Perla-7 well experienced lost circulation while drilling the naturally fractured carbonate reservoir. To cure the losses, 285 bbl of various lost-circulation materials (LCMs) were pumped. This plugged the 300-micron slotted liner and resulted in an impairment of production. This paper describes a study of the solids retention by a 300-micron slotted liner and the design, testing, and application of a delayed-release acid system to remediate the plugged well and recover productivity.
The well was closed while spotting the delayed-release acid treatment; gas was filling the well from the previous well testing. Coiled tubing (CT) was used along with a proven fluidic oscillator technology that enables better control when matching fluid rates to the most desirable frequency and amplitude of the pressure pulses. When the pressure began rising from the last recorded surface pressure, the well was bled off on the surface to maintain a balanced condition. After the treatment, the well was opened and cleaned out using well testing equipment, flaring hydrocarbons, and spent acid.
Logistical considerations resulted in the selection of the in-situ acid-release system instead of conventional treatments. The pumped LCMs dissolved successfully, helping to swiftly recover well productivity. The acid-release treatment was split into two stages, with a 30-minute soaking time between the pumping of the two designed engineered pills. A total of 270 bbl of the delayed-release acid were pumped at a 25% volume/volume concentration. No special tanks were necessary for this operation; the acid-release treatment is neutral on surface and is easily handled until required. The well test interpretation was developed based on a pressure buildup period before and after the treatment. The results returned a fairly good reservoir property, with a Kh of approximately 10 000 md-ft with a consistent skin reduction from 14 to four. There was also a corresponding reduction in the drawdown of 120 psia, which was necessary to achieve the same gas rate of 50 million scf/D.
The Perla field is the largest offshore gas reservoir discovered to date in Latin America. The Perla-7 well was drilled in the Cardon IV block, located in the shallow water eastern part of the Gulf of Venezuela. The in-situ acid release treatment is now an alternative option through which to support offshore operations where logistics can be challenging, especially when well remediation is required.
