Abstract Different oil operators have faced technical and economical challenges while drilling wells in the Nororiente basin. Drilling in a tectonic active setting creates problems ranging from influxes and stuck pipe incidents to circulation losses and reservoir damage. Operations in Ramon Lista experienced similar problems, especially wellbore instability, lost circulation and influxes. The presence of a salt member increases the drilling risks, with very high pore pressure (up to 19.3ppg) just below this member. Drilling nearby wells has evidenced many catastrophic events, like 120 days to control an influx with simultaneous losses. This article will describe the application of the process used to reduce risks and cost while drilling in the Nororiente basin.
Introduction Pluspetrol and Schlumberger worked together during planning and execution to drill successful development well in this high drilling risk environment. This team effort represented a considerable reduction in cost comparing to the offset well. Minimizing non-productive time associated with wellbore instability reduces the risk of dangerous accidents and is required to complete the well on time and within budget.
It was developed a three-dimensional approach in order to optimize well location and trajectory, focusing on reducing drilling risks and unscheduled events. The three-dimension analysis uses different sources of information, including the 3D seismic, electrical logs (wireline and LWD), drilling event analysis, within the 3D structural and geological model to generate a comprehensive 3D mechanical earth model (MEM). It will be shown that building a mechanical earth model and identifying the drilling risks during the well planning phase and revising it in real time is extremely valuable in delivering complex wells safely while minimizing unplanned well construction costs.
The developed MEM supported drilling decisions that includes:well trajectory,
casing points,
mud window and
potential drilling risks.
It was identified that there was no stable mud weight window to drill the original casing program, with over pressured zones (up to 19.3 ppg) and non-compatible fracture gradients at the same section. It was proposed several options to reduce this drilling risks, including: change the casing depths, stress cage concept, move surface location, open hole FIT below the salt as criteria to define a requirement for an extra casing string, and an inclined trajectory. Some of those recommendations were selected by the team to be successfully implemented while drilling.
Location Noroeste is an asymmetric foreland basin and mainly covers Salta, Jujuy and part of Formosa provinces. The Noroeste basin is bounded on the southeast by the Chaco Paranaense basin, which includes the rest of the Formosa province 1 (Figure 1).
The Ramon Lista area is located in the Noroeste basin, close to El Molino and Palmar Largo fields (approximately 5 km from El Molino and 15 km from Palmar Largo) as shown in figure 2.