The Bandurria Field in Argentina is known for its narrow operational window due to the difference in pressure gradients while drilling through the Quintuco and Vaca Muerta formations. This scenario usually requires managed pressure drilling (MPD) and a robust well design, including four casing sections, which significantly increases the well construction cost. The operator's objective was to design an efficient and cost-effective well aligned to the current economic market conditions.
Using a break-even price target of 43 USD/bbl, high-end technologies resulting in high operational costs are not cost effective and unacceptable. Therefore, the operator selected a new technology and operational method focused on the drilling fluids to increase the pressure-gradient operative window.
An ultra-resistant and flexible technology was used in the open hole section in real-time while drilling. The technology is designed with the drilling fluid system so that new rock drilled would be sealed quickly. Minimizing the interaction between the drilling fluid and the formation would preserve the original formation conditions. Using this technology, it was possible to perform a flawless operation, increasing the operative window and minimizing wellbore instability while drilling through the Quintuco and Vaca Muerta formations which are characterized by interbedded carbonates/shale layers under high-pressure conditions.
The offset wells on the same pad presented severe operations issues, including stuck pipe, lost circulation, and sidetracks, even with the use of MPD. The technique implemented, known as Wellbore Stabilization Technology (WSST), enabled the operator to perform a dynamic formation integrity test (DFIT) while drilling through the transition zone to evaluate the magnitude of the operative window increase and compare those results to the offset wells on the same pad. As measured in the field, the WST allowed an increase of 2-3 lb/gal beyond the fracture gradient window.
The WST was later applied in six additional wells in the same area, where the drilling efficiency significantly improved compared to historical wells. Further, the operator reduced the volume of oil-based drilling fluid (OBM) used per well, minimizing drilling fluid costs and optimizing the drilling operations.
A thorough laboratory analysis was performed to evaluate this novel technology's effectiveness against several high-end technologies. This innovative adoption to the drilling fluid design resulted in a significant cost reduction to drill the Bandurria Sur Field. In addition to presenting field results, including the increase in the fracture gradient window as compared to offset wells, this paper describes the prevention of lost circulation, resulting in a nearly 50% decrease in wellbore instability.