Well Operability Limits For Managing Production From Deepwater Reservoirs
Authors: Grueschow Eric Russell , Dale Bruce A. , Pakal Rahul , Haeberle David , Wallace Jon , Asmann Marcus 
Published: November 2008

Physics-based well performance modeling technology has been developed that establishes Well Operability Limits (WOLs) to mitigate well failures due to the complex geomechanical loads resulting from compacting reservoirs. This new technology assists in active reservoir management by both limiting the producing drawdown pressure on wells most susceptible to failure and providing confidence in increasing drawdown pressure on wells determined not to be susceptible.

In 2000–2001, ExxonMobil experienced three unexpected reservoir compaction well failures during the start-up of the deepwater Diana/Hoover project in the Gulf of Mexico. This experience led to the development of advanced well performance modeling technology which was used to assess ExxonMobil's worldwide portfolio for potential compaction related well failures. WOLs have now successfully been used to manage nearly 100 deepwater wells without failure since 2001 and are actively used to establish completion and production strategies for wells in many other types of producing assets worldwide. Implementation of this technology has not only prevented well failures and associated production disruption due to reservoir compaction, but also enabled safe increases in well drawdown and accompanying increases in production rates beyond previous industry experience.

This paper focuses on the application of WOL technology to ExxonMobil deepwater wells. The general methodology and development of the reservoir compaction WOL technology will be introduced. Selected case studies will highlight the successful application of the technology as well as illustrate the operating strategies and the subsequent production benefits. WOL technology has significantly improved ExxonMobil's ability to operate wells without incurring costly well failures by more clearly defining the complex limits of compacting reservoirs.

Background

Ensuring long-term well integrity and optimum completion performance is important for the economic development of any field. As fields are developed with fewer wells and in more technically challenging environments, analysis is required to deliver reliable wells that can be operated at the high rates required to meet today's aggressive production targets. Long-term well integrity is essential for commercial deepwater field development. Operators cannot rely on historical industry practices based on aggregate historical data, anecdotal evidence, and simplified analytical models to prevent well failures while simultaneously maximizing well production and reservoir recovery. This is especially true in deepwater environments, where reservoir characteristics are significantly different than in the fields that serve as the basis for historical practices and the cost of well intervention to recover from a failure is substantial.

Well failures due to compaction and subsidence have been experienced for decades in various environments and are summarized briefly below:Wilmington Field - One of the first ExxonMobil experiences with subsidence occurred at the Wilmington field located onshore California. Production began in 1936, and 7 feet of subsidence occurred by 1947, the time of the earliest casing failures. Horizontal movements of 9 inches were documented in three weak shale layers above the producing reservoir (Allen, 1959).