Deepwater production challenges typify many of the present and future field developments offshore Africa and technical solutions need to be found to make these often huge discoveries viable.*
Deepwater production challenges typify many of the present and future field developments offshore Africa and technical solutions need to be found to make these often huge discoveries viable.*
THE TOOLBOX FOR offshore hydrocarbon development is growing as the industry rolls back barriers to better production interlaced with hard-won operating experience and know how.
The choice for offshore operators is now a dazzling one with an array of hardware and software designed to tap deep, extensive and complex oil and gas reservoirs. But how do you start choosing which tools to use when the box of tricks is getting bigger and ever more sophisticated all the time?
This article will look at some of the technologies Emerson Process Management and its Roxar reservoir management solutions can offer to developers of challenging reservoirs, with particular emphasis on subsea technology and corrosion and erosion management for African deepwater fields.
Rush towards technological solutions
As the number of African nations with offshore acreage that can boast offshore hydrocarbon development has been steadily growing, from Angola to Côte d'Ivoire to Guinea Bissau to Nigeria, to name just a few, there has been a
great rush towards technological solutions to penetrate, understand and utilise deepwater hydrocarbon provinces beyond Africa's shorelines.
Emerson has been one among many offering solutions which have answered questions and helped operators solve regional field development issues raised by extreme water depth – typically beyond 1,000 m.
By focusing on reservoirs and their monitoring and management, we have developed products and solutions to achieve those higher production goals - from the subsea environment within the reservoir along production tubing, flowlines and risers up to the surface and on to platform process equipment. Alongside all these stages, we are also providing subsea and topside corrosion and erosion monitoring to assist with asset maintenance.
Producing deepwater subsea developments offshore Africa is complex, challenging and costly. The Emerson suite of subsea products and solutions are helping operators reduce their capital expenditure and ultimately achieve optimal oil and gas production.
Multiphase flow meters
Multiphase flow meters, now in common currency, and intelligent downhole sensors – both offered by Emerson – provide a real time view of reservoir conditions. Our field monitoring software, Roxar Fieldwatch allows desktop visualisation, monitoring and analysis of the wealth of data now available from down the wellbore.
Combined with predictive software and history matching, this system can give operators more intelligence on their hydrocarbon reservoir which in turn provides scope for increased optimisation and automation of production.
Roxar Fieldwatch can take data from subsea meters, reservoir and production system software, control and erosion instruments, downhole networks and instruments, process instruments and topside meters to provide a
comprehensive view of the production cycle from inside the reservoir to the process platform – giving the operator an integrated ‘helicopter view’ of the entire wellstream flow.
Subsea meters are now supplied for wet gas, water cut and multiphase production requirements and are capable of offering up to 12,000 measurements per second on the wellstream flow and coping with water cut rates from 0-100 per cent and 0-100 per cent of gas void fractions. The multiphase meter MPFM 2600 is now in its third generation and we are hoping to develop a subsea version in the near future.
Subsea multiphase meters, subsea sand monitors, and subsea single phase meters, have all been added by Emerson to the field developers' toolbox, empowering them with more data to better manage their assets.
This multiphase meter is based on a cross correlation and venturi system for flow rate measurement. Fraction measurements are determined by using electrical impedences, combined with a robust single energy gammaray densitometer. All these combined provide robust and high measurement accuracy for oil, water and gas rates, thus eliminating the need for expensive test lines and facilities. The lightweight and compact design allows for
easy installation in the jumper, manifold or production tree.
The subsea retrievable canister version MPFM SRC® houses all electronics, signal and power systems within a ROV retrievable canister that allows for intervention without stopping production. Another version of this meter - a choke bridge version - installs directly on to a pipe assembly or module, and can be installed or retrieved as part of that same assembly.
The MPFM can cope with velocities ranging from 1.5 to 35 m per second and are designed for a water depth of 3,000 m and up to 690 bar or 10,000 psi. Each meter is individually sized to best match the production profile for eaxch well during its lifetime.
Subsea sand monitors using an acoustic detection technique can offer quantitative monitoring of sand content within a wellstream – allowing an operator to ‘tune’ or optimise oil and gas production to avoid excessive wear on valves, process equipment and flowlines by selecting the maximum acceptable sand production rate. These monitors also come with the retrievable electronics canister which again can be retrieved by an ROV, if required.
Erosion and corrosion monitoring
Turning to asset maintenance, the energy industry is placing a greater focus on ensuring equipment uptime and early warning of potential failures has been enhanced with more extensive monitoring systems. Emerson offers two types of monitoring - intrusive and non-intrusive, with the latter using sophisticated acoustic and FSM – Field Signature Method - technologies.
Topside intrusive monitoring equipment sees corrosion or erosion probes inserted into the wellstream flow via a hydraulic access fitting. Measurements and data from the probes can be downloaded to hand-held devices or linked directly to a dedicated software package for continuous monitoring by the operator.
The Roxar non-intrusive FSM tools require a matrix of wires to be placed on pins welded across the surface of the target structure and then an electrical current is sent across this wire matrix. Higher resistivity compared to the original electrical signature of the target indicates loss of metal from the structure – such as a pipeline – thereby signalling corrosion. This is ideally suited for not just low temperature offshore productoin but also for sour sersvice or high temperature piping as seen in refineries or chemical plants. One of the major deepwater field development issues that offshore Africa faces
is flow assurance and a subsea chemical injection valve introduced to the market by Emerson in July last year seeks to address this. It provides measurable chemical dosing of the wellstream flow to inhibit hydrate formation by the injection of hydrate prevention fluid – monoethyleneglycol (MEG) – where the formation of hydrates - formed in high pressure and low temperature gas flows - can threaten production by blocking pipework. This is a particular threat in wet gas and deepwater fields.
Built from high grade alloy and ceramic material to be both robust and durable in hostile operating conditions where erosion is a hazard, the subsea injector can be configured for pressure of up to 10,000 psi and for a water depth of up to 3,000 m.
Additionally this new tool has been qualified for work within contaminated environments, for example, where sand particles are present. It also has no moving parts – which reflect the ethos behind its long design life – except where the flow rate needs to be adjusted. And it is ROV retrievable, so intervention is possible. Accuracy is possible to within +/- 5 per cent, and, if fitted with a turbine metre, this accuracy can be raised to +/-1 per cent.
With a design weight of 60 kg in water and 150 kg at the surface, the tool uses standardised communication protocols, and it is possible to link it with other instruments – such as the Roxar wet gas meter which measures any early start of formation water production – which in turn can be managed by adjusting the MEG/water mixture.
Over-dosing the wellstream with MEG brings its own problems. Too much injection is both costly and inefficient and injecting the right amount is preferable and possible. This is something we are achieving with our chemical injection valve, particularly in relation to high flow dosage rates.
Latest developments
Retrievable subsea sensors are also part of Emerson's recent additions to the field developers' armoury: Here you have a particular solution for the retrieval and installation of erosion, corrosion, pressure/temperature or a combination of these instrumentations on trees, manifolds and process systems during production.
This will allow operators to extend the lifetime of operating sensors through regular maintenance without any impact to production, thus improving availability and reliability especially on critical applications.
All of Emerson’s re trievable products are designed so that the whole retrieval process takes place within a controlled leak-proof environment, thus leading to optimum safety and environmental protection.
by Steven Jennings, Emerson Process Management
