Well Safety and Performance Gains from MPD in Unconventional High Overpressure Reservoirs in Argentina

Abstract

The present paper describes performance improvements and well safety achieved with the use of Managed Pressure Drilling (MPD) in the exploratory block of Parva Negra Este, in Neuquén Basin. Petrobras Argentina S.A (PESA), with the technical support from the Petrobras’ headquarters, in Brazil, drilled two exploratory wells applying MPD and targeting Vaca Muerta shale oil & gas play. High-pressure zones characterized the drilling scenario, reaching, usually, pore pressures higher than 18 lbm/gal in unconventional reservoirs, composed of tight sand and shale. The use of MPD in both well constructions was quite efficient, including well control and plug and abandonment (P&A) operational applications. Those operations proved that MPD can effectively replace the Under-Balanced Drilling (UBD) system, which is standard practice in that area. In the first well, PESA reported significant gains in drilling performance when compared to other wells previously drilled. Drilling with MPD did not record non-productive time (NPT), differing substantially from the previous wells constructed in the surroundings of Parva Negra Este with an average NPT of 20 days. A considerably larger recovery of coring samples was achieved, being also possible to eliminate one well section, by drilling two zones of interest in a singlesection. Additionally, lessons learned were implemented, resulting on higher rate of penetration (ROP) with the support of MPD. In the second well, a high overpressurized pore zone was reached, leading to a very complex well control event followed by a permanent P&A operation. The formation pore pressure was much higher than the expected for the area. Instead of using an 18 lbm/gal drilling fluid, it was necessary to weight the fluid up to 21.3 lbm/gal, adding hematite as weighting material. In that scenario, the use of MPD made the operations of circulation and well cementing safer than with the conventional drilling approach utilized in that vicinity. The application of Dynamic Formation Integrity Tests (DFIT) and Dynamic Pore Pressure Tests (DPPT) ensured a more precise operational window, helping to formulate risk matrices for safely pulling the drilling string out of the hole. In addition, the precise definition of the operational window was a valuable information to plan the best approach for P&A. Besides performing those tests, the MPD system was very useful to evaluate operational parameters and verify how effective was the settlement of the abandonment cement plugs. In summary, MPD supported safer drilling and P&A jobs, better drilling performance and greater information achievement through more efficient well logging and sample coring.