Design and Drilling Performance of Two Exploratory Wells in Argentinean Parva Negra Oeste Shale Gas Field from the Vaca Muerta Formation. Experiences and Lessons Learnt.

Abstract

Parva Negra Oeste field is located 90 km north-west far from Añelo City in Neuquén Province, Argentina. It is considered an unconventional dry gas field targeting Vaca Muerta Formation in exploration phase. It is located on the east flank of Dorso de los Chihuidos with presence of over-pressure and faulting. Several wells were drilled in the area in order to test production and acquire information, which showed a complex drilling scenario and an abandonment rate of 40%. In order to define well architecture, nearby well's events were studied in a radius of 15 km, detecting gas kicks and mud losses at different depths and formations. With this information shoe depth, operative mud window and contingency casing were defined with focus in well integrity and operational hazard control. These problematic events were integrated with the seismic data and zones of structural quietness were selected in order to reduce the probability of occurrence. Both wells were successfully drilled. Although gas kicks were detected, at similar depths to nearby wells and at new zones or formations, with the use of Managed Pressure Drilling (MPD) and appropriate mechanical design, these events overcome successfully in a short period of time. Depth Interval from 1000 to 2000 mts (Agrio and Huitrin Formations) had a higher hardness than expected and abundant carbonates, decreasing rop for this interval of the first well. For second well, with the rock hardness log of the first well, the Bottom Hole Assembly (BHA) and drilling parameters were modified, with better results. A contingency liner was considered in order to isolate Quintuco Formation from Vaca Muerta Formation, but it was not needed. In both cases, all logging information were effectively acquired and 90 mts of core were extracted in the second well, with a recovery factor of 100%. This paper provides experiences and techniques to successfully drill in a zone where information is scarce and neighbor wells were abandoned in a high rate.