Abstract
The decommissioning of wells and restoration of natural subsurface barriers which prevent hydrocarbon flow to surface, is a critical activity in well life which removes environmental impact for the future after oil/gas production facilities have been removed. Despite reduced rig/equipment costs, abandonment continues to be a substantial expenditure and represents a significant liability for operators in a cash constrained environment. While we see many efforts to reduce scope of abandonment and workover operations, engineered design and execution must comply with regulations as defined in the Code of Federal Regulations (CFR) without compromising safety.
Abandonment and workover activities in the deepwater Direct Vertical Access (DVA) environment are typically conducted with a platform installed rig. However, there exists a significant amount of work involved in rig workover activities (cement plug installation, tubing cutting, circulation to workover fluid, etc) which do not require the physical workover unit itself and therefore can be accomplished "offline" both to save rig days, cost, personnel exposure, etc. In this context, "offline" will be defined as the time associated with activities that may be accomplished without dedicating critical path rig time to abandonment scope, reducing time and cost, assuming this identified rig would not otherwise be idle. Saved time may be used to provide value in a number of capacities from drilling and completing new wells to working over or abandoning another well.
This paper discusses the case histories of two wells accessible via a deepwater Tension Leg Platform (TLP) in the Gulf of Mexico (GoM), both of which were scoped for conventional producer zonal abandonment and recompletion/workover activities. One would be worked over to another target production zone ~7000’ up-hole while the other would be worked over and converted into a new field injector for a major water flood project in the region. Through meticulous pre-planning, engineering design, and contingency development, the engineering and operations teams working on these two wells were able to reduce the critical path time of the work unit by realizing offline opportunities.
These activities utilized conventional intervention techniques of slickline, electric line, and available pumping to both abandon these wells in an unconventional manner and ready the wells for immediate tubing pull once the rig was skidded atop. This was all done with full compliance with the CFR, in a "through-tubing" method, and satisfied abandonment conditions and operational safety requirements of the operator. While both wells noted significant savings either to acceleration of operation timeline or of first oil, the work conducted required decisive challenge management to succeed. The engineering decisions made, scope reductions identified, and trouble time events incurred will be discussed to the detail possible in this manuscript.
