Well flow measurement plays an obvious role in offshore production; you can, after all, only be completely sure of output by metering it at the source. Moreover, beyond individual well performance, the provision of accurate real-time data can form the basis of a valuable diagnostic tool for maintenance purposes as well as allowing proper optimisation in the face of changing well activities.
Effective flow surveillance offers the promise of increased production rates and maximised returns, and as the following case studies show, advances across a range of metering technologies now allow oil and gas companies to predict and measure well flow with unprecedented accuracy.
Wireless, offshore Norway
Wireless data transmission has rapidly become a feature of everyday life, but nowhere are its benefits to be more acutely felt than offshore. Reservoir-to-surface transmission has become increasingly commonplace as a consequence, with evident benefits across the whole spectrum of well monitoring, but true duplex communication – though undeniably attractive as a concept – has inevitably proven more challenging to achieve.
Expro's recent operational demonstration of integrated two-way data transmission functionality with the installation, offshore Norway, of a state-of-the-art, cableless telemetry system (CaTS) represents a major development in this field. The company's CaTS mandrel systems were installed in wells A5 and B7 of the Ormen Lange Field early in 2009, and successfully commissioned in the following October, with four further systems scheduled for deployment during 2010-11. As wireless business general manager, Brian Champion explains, "the successful implementation of duplex in-well wireless communications in this deepwater, subsea, high-rate gas well environment, together with the recent successful testing of our FlowCAT wireless flow control valve, marks a key achievement on the way to reaching our future goals in delivering production optimisation solutions."
Delivering a "reservoir-to-beach" two-way communication capability has been described as the most challenging engineering project to date by Steve Hudson, Expro's wireless technology manager, but it clearly has commercial potential in next-generational well management. Aside from the advantages that real-time, cable-free data-flow to and from in situ instrumentation brings to flow measurement and well monitoring, it also opens the door to the wider application of remote control across the entire producing reservoir interval – and that could ultimately come to revolutionise the whole shape of downhole completions.
Optical, offshore Congo
Essentially eliminating downhole electronics, optical technology enjoys a reputation for enhanced robustness and reliability, particularly in comparison with conventional gauges at higher temperatures.
The potential of the approach was reinforced in May 2010, when Tendeka completed the successful installation of a comprehensive and advanced optical reservoir monitoring system at a platform offshore Congo, which offers unprecedented control of well performance. Comprising proprietary distributed temperature sensors allied to four SmartCell optical pressure gauges, the solution facilitates the production of a complete profile of the reservoir in real time, allowing well flow to be optimised. This stream of continuously available, real-time data provides an unparalleled understanding of flow contribution, enabling the interpretation and analysis of both the inflow profile and respective phase contributions along the horizontal interval to be made with significantly greater certainty.
Tendeka's system has already been shown capable of measuring temperatures to a resolution of ±0.01ºC a metre, over a fibre-optic cable of up to 30km in length, while the SmartCell optical gauge technology allows a single string to accommodate multiple instruments. The combination made the package a highly cost-effective solution for this application and, crucially, allowed a number of downhole splice assemblies to be installed without compromising the system's measurement performance.
Ultrasonic, offshore Nigeria
Ultrasonic flow meters offer the prospect of flexible, non-intrusive flow measurement, with a high dynamic range. Widely regarded as both reliable and accurate, with the capability to routinely deliver measurement uncertainties of less than 0.25% over a significant proportion of their range, these devices are extensively used to make custody transfer and allocation determinations.
When the start-up phase of the Ofon field development, offshore Nigeria, was announced in 2007, alongside the installation of a series of new platforms – three drilling, one processing and one accommodation – Total Elf Nigeria selected an ultrasonic flow meter package consisting of 32 Flexim units.
Due to come on stream during 2010, and with additional reserves estimated at over 350 million barrels of oil equivalent, this new phase is expected to increase oil output by more
than double – to around 100,000bpd by the end of the year.
Flexim's flow measurement solution consists of a combination of instruments to quantify produced water and crude oil, chosen for their rugged dependability and suitability for use in this challenging environment. The Fluxus ADM 8127 is a seawater-proof, ultrasonic flow meter purpose-designed for offshore applications, with an entirely stainless steel body, flameproof enclosed electronics, increased safety terminals and ATEX approval for use in explosive hazard zones. The system also includes the company's ADM 8127 flow meter enclosures – equipped with HART communication protocol – for use at temperatures of up to 130°C, on pipes with diameters of between 6in and 40in and Permalok mountings to protect the system's transducers from mechanical damage.
Addressing the particular challenges for mission-critical monitoring equipment inherently presented by the offshore environment, the new Ofon installation stands as a clear example of the lowered technical risk and operating costs achievable through ultrasonic flow measurement technology.
Wet gas, offshore Western Australia
Liquefied natural gas (LNG) presents its own problems for flow metering technologies, not least amongst them being the need to cope with the cryogenic temperatures involved given the intrinsic difficulties of such conditions and the global paucity of suitable testing facilities.
Never-the-less, with ongoing advances in LNG production being tipped by many as the key to realising the potential of isolated gas reserves around the world, accurate flow measurement will have an increasingly important role to play in the coming years.
With LNG consumption predicted to double within ten years in the Asia Pacific region alone, the use of Roxar subsea wet gas meters in the Greater Gorgon fields – one of the largest untapped natural gas fields in the world – gives a glimpse of what may lie ahead.
Situated 130km offshore Western Australia, Gorgon contains an estimated one trillion cubic metres of LNG and a phased subsea development is currently underway that will ultimately see the subsea wells directly tied back to a 15-million-tons-a-year LNG plant on Barrow Island. Operating in depths of 200m to 1,300m, the wet gas metering solution implemented will accurately quantify hydrocarbon flow rates and water production, and provide online detection of formation-water breakthrough.
Providing this real-time data on the onset of formation-water production will enable main operator Chevron Australia to take appropriate remedial action at the earliest opportunity, thus minimising disruption and gaining continuous flow assurance.
Gunnar Hviding, Roxar CEO and president, explains "whether it be production well testing, improved reservoir management, or hydrate and scale prevention, the accurate and real-time measurement of wet gas flow is crucial to today's operators – particularly with subsea tiebacks, as is the case with the Gorgon development."
The offshore industry has been quick to recognise the benefits of novel and improved flow measurement technologies. The rise of multiphase metering is a case in point, with meters now adopted widely across the globe after an early uptake that was largely limited to the North Sea, and analysts at Douglas-Westwood and OTM Consulting predicting the deployment of over 1,000 more by 2015.
Ultimately the successes of all the forms of metering technologies installed at today's high-profile fields, coupled with the industry's continuing mandate to go deeper, further and more remote, will form renewed drivers on further developments in the sector. One thing seems clear; there will be more innovations to come.