In the Unconventional Loma Campana Oil Field, located in Neuquen, Argentina, the primary target is the Vaca Muerta shale, and the secondary target is the Quintuco carbonate. Both formations are naturally fractured and present high formation pressures and a narrow mud weight operating window. Those conditions generate operational issues (influx or fluid losses) and are the primary reason for the use of the Under Balanced Drilling (UBD) technology through problematic zones.
When using conventional BHA for UBD operations, after reaching TD, it is necessary to kill the well, by increasing mud weight, in order to pull out of hole and run the casing. This heavier mud exerts high ECD during the cement job causing partial or total loses of returns. In other cases, when the formation pressures are too high to be controlled with the mud weight, it is necessary to unload the well until reservoir pressure decreases to the manageable level. This operation has high impact on both time and cost of the well.
By the use of the casing drilling technology and with the knowledge of the operating window it is possible to perform managed pressure cementing (MPC). This is done by exerting back pressure needed to adjust the ECD within the operating window detected in the region of interest for each stage of the operation. With this technique there is no need to kill the well. The main goal, to reach the desired height of cement, is achieved by minimizing fluid losses and controlling influxes.
This paper contains information that will help develop cementing fluid design, pump schedule, and required back pressure in each stage of cementing job.