Subsea increased oil recovery draws from kit of tools

Arild Selvig - FMC Technologies

Subsea systems are used increasingly as the primary field development solution for offshore oil and gas fields. Currently, there are around 3,300 producing subsea wells around the world, with an average age of almost seven years. The sizes of new offshore discoveries are getting smaller. These factors drive subsea operators to be increasingly aware of securing the integrity of the producing subsea infrastructure and of maximizing the recovery from the assets.

Ageing subsea wells drive the need for more cost-effective maintenance on both the subsea systems and wells to maintain uptime and to improve production. Many emerging maintenance initiatives aim to answer this call. FMC groups these initiatives under improved oil recovery (IOR).

At the highest level, all IOR aims to enhance the value of an already producing field. In principle, this can be done in two ways, either lower the production cost per barrel or accelerate/increase the revenue from the field. Lowering the cost of production often is overlooked as an avenue for IOR. Every field has a break-even cost where the opex exceeds the production revenue. If an operator lowers that break-even point, it will prolong the life of that field and thus improve the recovery.

Examples from FMC’s IOR “tool box” include remote monitoring services with expert support centers, riserless light well intervention (RLWI), through-tubing-rotary drilling (TTRD), and subsea processing and pumping.

“Check engine” light

Today, FMC monitors and advises operators of 20 producing fields through its expert remote monitoring center in Norway. Accumulated production from the fields is more than 1.2 MMb/d of oil from 420 subsea wells. The center in Norway monitors production from the fields, assists in flow optimization discussions, and advises on flow assurance.

Another emerging technology in the suite of remote monitoring services is the Condition and Performance Management (CPM) system. The purpose of CPM is proactive maintenance of subsea systems, much like the proactive maintenance that has succeeded in other industries. CPM is designed to be a surveillance system that provides proactive monitoring of the integrity of the subsea production infrastructure bundled with a 24/7 collaborative expert environment for diagnosis, problem solving, and advice. Real-time data acquisition from multiple subsea sensors on the equipment, combined with software to turn data into information, lets operators monitor the remaining lifetime of the various systems components and to plan preventive maintenance rather than to react after a problem arises.

With CPM comes a three-step process to maintenance decisions. The first step is to extract raw data from the subsea sensors. Step two is to interpret the data and to understand if the equipment is good, requires follow-up, or requires equipment shut down. The third step is to use this knowledge to understand how the state of the equipment will affect the business as a whole, with regards to overall plant integrity, production time, HSE, etc.

A central part of the CPM system is the Technical Condition Index (TCI) – an indicator to illustrate the remaining life of the monitored component. The TCI operates like a stoplight. When it is green, the equipment is operating optimally; yellow is a warning light that the equipment might soon require attention; and red is an alert that the equipment may require a shut-down.

The TCI is linked into a hierarchy built for each piece of equipment, which includes knowledge of any available back-up or redundancy. With this in place, the system understands that while the sensors might send a red light on the component level, the product actually might be in a yellow or green status because of built in back-up or redundancy. Hence, the TCI concept monitors the various pieces and subassemblies of the equipment and gives an overview of the criticality of the failure. The TCI is integrated into the CPM system as a building block in FMC’s remote monitoring expert center concept.

Light-well Intervention (RLWI) is another tool for IOR. It enables wireline interventions on subsea wells from a vessel rather than a drilling rig. This brings the cost down by 66%, and allows the operator to increase the frequency of wireline interventions.

FMC and Island Offshore have three vessels in the North Sea today; two on the Norwegian continental shelf for Statoil and one West of Shetland for BP. The uptime and performance has been favorable in this harsh environment and has saved the operators significant intervention costs. FMC is working on modifying the RLWI equipment for applications in deepwater markets such as West Africa, GoM, and Brazil.

Sidetracking a subsea well using through tubing rotary drilling (TTRD) without pulling the completion or christmas tree is another recent IOR achievement from FMC. The TTRD equipment is placed on top of the christmas tree during drilling, and the side track well is drilled quicker and less expensively than with traditional drilling equipment and methods. The first two wells were drilled successfully last fall using theStena Don rig on a contract with Statoil.

The last element in FMC’s IOR tool box is subsea processing. This also can retrofit to mitigate the effect of reduced back pressures on the wellhead. The suite of subsea processing equipment includes multiphase pump stations, various subsea separation concepts, and subsea gas compression. In 2006, FMC delivered the world’s first-full scale water removal subsea separation system to Statoil for the Torids field in Norwegian continental shelf.

The future of IOR

As wells age and big discoveries become increasingly difficult to find, IOR will score high on operators’ priority lists. The industry will continue to move more towards the use of remote monitoring and expert centers to secure the integrity of the subsea infrastructure, to enable preventive maintenance campaigns, and to optimize production limited by infrastructure bottlenecks. Operators will rely increasingly on advice from these centers to optimize day-to-day and long-term activities to maximize the value of their producing assets.