Oil and gas exploration and production activities in the deepwater blocks in the Gulf of Mexico are frequently impacted by unpredictable and high-energy ocean currents. The strength of these events makes them an important consideration in the design and operation of offshore structures in deepwater, warranting continuous monitoring. This paper provides details of the development of new techniques for measurement of currents through water depths of up to 3000m using Acoustic Doppler Current Profiler (ADCP) systems.
The process of integrating a number of ADCPs deployed off a structure, in the water column and on the sea bed to obtain a profile of the currents through the whole water column is a simple concept, however the implementation of this concept for both exploration and production systems is challenging. The constraints, limitations and requirements for exploration and production are widely dissimilar and lead to different technical solutions. Examples of types of systems and their integration, from assessment of requirements through implementation of a real time networked system are presented.
This paper provides details of the development of new techniques for the measurement of currents through water depths of up to 3000m using ADCP systems including quality control, dissemination and management of the data.
Exploration and production of oil and gas reserves continue to venture into the ultra deep-water areas of the Gulf of Mexico. This presents complex problems for moorings and MODU station keeping in both the strong currents associated with the Loop Current/Loop Current Eddies, and the increased significance of the forces encountered on both exploration and production risers in deepwater. This has led to an increased awareness and greater requirements for accurate current monitoring throughout the water column.
The measurement of full current profiles has been carried out for many years in deepwater using stand alone moorings consisting of a combination of traditional single point current meters and upward and/or downward looking ADCPs. Data are downloaded from each instrument only when the mooring is recovered. The measurement of full current profiles in real time began with the commissioning of seabed mounted ADCPs in the late 1980's for ports, harbors, shallow water offshore production units and MODUs. Power and RS422 data signals were hardwired between each subsea instrument and the control PC running data acquisition software enabling data to be displayed in real time and stored for further analysis. Recent technical advances in both measurement instrumentation and subsea communication makes the monitoring of real time current profiles through the water column in ultra deepwater commercially viable for both exploration and production.
Combining an RD Instruments 38kHz ADCP with multiple deepwater rated 75kHz ADCPs in the lower part of the water column, allows complete current profiles to be obtained in water depths up to 3000m. Acoustic telemetry or long range data communications using copper and/or fiber optics allows transmission of data between the seabed and sea surface in real time.
