Unconventional wells in Argentina have evolved from the first vertical wells to Vaca Muerta shale formation in 2013, to the present, where more than 1200 wells have been drilled (mostly horizontal) and around 1000 of them are in production.
During this evolution, diverse challenges have been found at all stages of the confection of the well, such as: drilling issues related to Quintuco formation (preceding Vaca Muerta), casing deformations during completions, paraffin deposition in Shale Oil or sweet corrosion in Shale Gas during production.
The objective of this work is to summarize the different problems related to the casing and tubing strings along shale wells′ life, from drilling to production phases, and their possible solutions.
Well Integrity Issues related to casing and tubing strings were categorized, as follows:
1) Drilling Stage:
– Over pressurized sections, total mud losses, kicks, wellbore instability and stuck pipes.
– Casing Running in extended reach laterals (more than 3000 m): high drag forces, high dogleg curves and buckling of the casing string.
2) Completion Stage:
– Casing deformation during fracking operations: high formation stresses and weak layers, frac hits that affect near wells already in production.
– Sand erosion: high pumping rates, high proppant concentration.
3) Production Stage:
– CO2 corrosion: at early production stage, the combination of CO2 and water presence with high pressures results in a corrosive environment that can put in risk the integrity of the well.
– Paraffin deposition: many shale plays produce oil with high paraffin content, which precipitates at temperatures around 50°C, restricting the flow rate.
Since the beginning of Vaca Muerta operation, the challenge of overcome complex formations during drilling stage of last section was matter of several considerations and techniques such as the use of UBD (Under Balanced Drilling) or MPD (Managed Pressure Drilling). Furthermore, the combination of these techniques with Casing Drilling of vertical sections or the need of a contingency string (casing or liner) to strengthen the well profile were the most applied examples of facing this issue.
