Look to increased subsea data acquisition and use to add options in deepwater plays.

By designing deepwater subsea infrastructures that integrate advanced data acquisition and management technologies with the latest hardware, operators can unlock increased productivity from subsea developments.

With field productivity and process optimization continuing to drive the oilfield, as well as an excellent suite of subsea hardware technologies available to the industry, it is time to embrace the pivotal role of real-time data - its acquisition and application - in achieving subsea goals. We must build systems that enable increased productivity and are better suited to the full lifetime of subsea wells. This can be achieved by adding customized data acquisition and management systems, as well as built-in intervention and control options, to subsea wells and their seafloor production networks.

Data and hardware technologies can be combined into an integrated system that provides improved surveillance and control at each stage in the subsea production chain throughout the life of a field. Reservoir optimization, flow boosting and flow assurance are among the tasks that will benefit from these data-rich systems.

Data and the reservoir

Historically, due to lack of routine intervention, subsea wells have been reported to perform at only 75% of comparable land and platform wells. For subsea wells, the costs and risks of traditional intervention practices often have been found to be prohibitive, yet the target of recovering more of the remaining 25% in performance, which has been calculated to equate to about $10 billion/year in gross industry revenue, is desired.

Subsea wells designed with the built-in capacity from day one to be monitored continually and reliably for key performance criteria promise not only to deliver maximized performance, but also lower traditional intervention costs and minimize associated risks. The benefits of real-time surveillance information will be realized only when the data are fed into a continuous, closed-loop process that includes analysis and decision-making. Core reservoir competency and strong interpretation capabilities are required to create and utilize tomorrow's fast acting models that will be fed by real-time surveillance data. This will allow the long-term, positive impact of a continual data stream to be applied for reservoir optimization, quality control and prolonged field life.

One surmountable obstacle to reaching this integrated well surveillance and control goal is the current practice of bundling all subsea control and monitoring into one seafloor system that is typically capable of offering only extremely low data rates for surveillance style activities. All data going to and from a well must pass through one of these systems, which are designed largely for subsea valve control. With today's goal of high-speed, high-volume data throughput, the need for an expanded seafloor data acquisition system is clear. One major operator has estimated that its subsea wells are delivering a maximum of 10% of the data it is getting from its platform wells, limiting its decision-making capacity. Room for improvement in subsea data delivery clearly exists.

An immediate solution is to separate safety-critical control functions from the subsea monitoring process through the use of a complementary subsea monitoring and control (SMC) module that works in conjunction with the traditional system. This approach allows a surveillance system to be employed without impacting the stability of the subsea control infrastructure, and provides for surveillance package expansion and upgrade without affecting production.

For maximum flexibility, the SMC system developed by Schlumberger supports any data acquisition or control device and is capable of communicating over hard wire or optical media at rates of 100 to 150 megabits/second.

With surface-based systems already in place to securely deliver large volumes of high-bandwidth data around the world, eliminating the current seafloor bottleneck will open up the world of subsea data, improving an operator's ability to make informed productivity decisions concerning its subsea wells throughout their lifetime.

Optimized flow boosting

Subsea flow optimization and assurance are tasks that change over time with varying reservoir dynamics and fluid compositions. Additional complexity is introduced when multiple wells or reservoirs are tied together into a producing network. As subsea technologies improve and an increasing number of the largest offshore reservoirs reach maturity, some operators are maintaining the production plateau by bringing "marginal" reservoirs online via tie-backs to nearby existing production infrastructure.
Long subsea tie-backs can result in higher back-pressures, up to 2,000 psi, on the producing wells. This increased load may subsequently cause these wells to be abandoned early. However, early well abandonments can be eliminated through the use of subsea flow boosting. In addition, flow-boosting systems assist wells to produce with wellhead pressures as low as 50 psi, increasing production rates and extending well life.

Reliable seabed multiphase pumping systems available today are capable of performing with high gas volume fraction and are ideal for reservoir fluids with high bubble-point pressures or artificial gas-lift systems. Seabed multiphase boosting pumps integrated with dual high-voltage, deep-set electric submersible pumps (ESP) provide production efficiency and flexibility. These benefits are in addition to the savings associated with having a single high-voltage power umbilical supplying ESP lift, seabed boosting and pipeline heating requirements.

Bottom line, integrated, cost-effective solutions can be designed to leverage the efficiencies of a multiparty, multiphase, subsea development, while ensuring optimized flow from each well in the network. The design, execution and management of such solutions from a flow boosting perspective will require expertise in downhole pumping and lifting technologies, seafloor multiphase pressure boosting systems, subsea flow metering and the data acquisition and management technologies required to monitor and control all aspects of the resulting system.

In order to meet today's flow assurance requirements, integrated solutions need to include the ability to continually gather real-time data and perform predictive modeling of scale and depositional probabilities. In addition flow-line simulations are required to minimize flow treatments and remediation costs while optimizing production throughput. Prevention and treatment mechanisms include one or a combination of thermal, chemical, or mechanical techniques, all of which benefit from the use of diagnostic measurements to improve the total outcome. These measurements, localized or distributed throughout the subsea infrastructure, can be directly fed into a closed-loop control process, thereby reducing treatment and intervention costs. For example, the over-treatment that occurs when chemical applications are designed for the worst-case scenario can be eliminated through the data monitoring and modeling and subsequent treatment reduction. Similarly, temperature data routinely acquired along a seabed pipeline can be modeled and subsequently result in dynamic pipeline temperature control to avoid production deposits and pinpoint pipeline leaks.

Linking quality control and predictive processes to a long heritage of lab and field expertise, multiplies the benefits of surveillance and modeling technologies, particularly in multiphase, multiparty systems.

Opportunities and solutions

More than 2,000 subsea wells were operating last year, and a further 2,000 are expected to come online during the next 7 years, largely in the Gulf of Mexico, Brazil, the North Sea and West Africa. This activity is expected to involve capital expenditures of more than US $48 billion over the next 5 years. Will applying a portion of these funds for data acquisition and management technologies lead to saving a few percentage points in operational costs and a similar increase in lifetime production? Is it realistic that reliable well performance data will improve our subsea design, planning, reservoir management and system optimization capabilities?

The answers to these questions are in the making. The technologies, processes and expertise are available to make data-rich subsea project designs and installations a reality. The remaining question is: how long will it take us to embrace this approach and reap its promised benefits?