Value of a Multi-Discipline, Life of Field Approach to Subsea Well Intervention Planning
Authors: Byrd Michael , Ketelaars Frank , Leung Hong , O'Connell Eamonn , Saucier Brian , Siegmund Mark 
Published: June 2014

Abstract
As our industry continues to move into the deeper waters of the Gulf of Mexico, we are finding more and more complex geologic structures, which present increasingly challenging drilling and completions requirements. Due to the geologic complexity, intervention will become an integral part of the reservoir development plan in order to achieve target recovery factors. After first oil, as the development moves into day-today production operations, subsea well interventions will play a significant role in maximizing production rates to keep the facility at maximum capacity. However, increased interventions will also carry additional OPEX impact. A significant challenge for any deepwater development is to identify the types, frequencies, and cost impact of intervention requirements over the life of the field. Since the ramifications of these issues are so diverse, it is crucial that the team which addresses this issue during the define stage of the project be representative of the stakeholders involved. They must take a holistic, or "Life of Field," approach to evaluating and modeling the anticipated intervention program, in order to achieve an optimum balance between CAPEX and OPEX considerations. Reservoir modeling, intervention modeling techniques, impact on well design, equipment selection, and drilling and intervention vessel strategy will be addressed, as each are related to and affected by the Life of Field approach.

Introduction
Deepwater developments traditionally pit CAPEX vs. OPEX, and it generally comes down to a simple equation of greater than vs. less than. For example, what is the future benefit in reduced intervention cost from a large initial investment (such as from a TLP, Spar, or semisubmersible), as compared to a lower CAPEX solution (such as a subsea system) that has greater anticipated intervention and availability costs? Of course, other factors may also be considered on the basis of inherent strategy decisions or key infrastructure targets as part of the corporate business plan. However, in the end, the lower up-front CAPEX with a manageable OPEX risk condition typically wins the battle and is the implemented solution.
The increasing geologic complexity inherent in Gulf of Mexico (GOM) deepwater developments brings with it increasing risk that is not adequately factored by the prior traditional model. Rather, the method presented here seeks to achieve the optimized field solution in terms of lowest overall cost (CAPEX and OPEX), through a multi-disciplined evaluation of several competing drivers. This "Life of Field" approach to subsea well intervention planning will greatly impact overall life-cycle field economics.
For example, consider the decisions made during the well construction and subsea systems design phase of project development. These key decisions are made early in project life and have tremendous impact on overall CAPEX and OPEX economic and risk models for the field. Decisions based solely on CAPEX have the potential of limiting operational or intervention flexibility later in field life and possibly eroding project value.