Metrology is the science of measurement so it will be no surprise that Subsea Metrology is the science of measuring subsea. One main application for subsea metrology is measuring the relative distance and attitude of two terminating pipeline flanges in order to allow a “spool piece” to be fabricated and set in place to join two pipelines.
Traditionally there have been many different methods of performing accurate measurements. Most are based on either a taught wire or acoustics. Both suffer problems of setup difficulty and expense and accuracy of final measurement.
By exploiting Ring Laser Gyro technology, CDL Ltd. Of Aberdeen, Scotland have pioneered a method for performing spool piece metrology using Inertial Measurement. Their initial method was to use a RDI Workhorse Dopplar Velocity Log aided (to remove velocity errors) and a Paroscientific Digiquartz Depth Sensor (for accurate depth) to aid a dead reckoned position from a Kearfott T16 Ring Laser Gyro. This method was marketed as the CDL MiniSpool system.
The CDL Minipos has another use over spool-piece metrology. SeaView Systems identified the benefit of this system to provide accurate position and attitude in locations in accessible with more conventional navigation means i.e. acoustic positioning. Initially we teamed with Mr. Jeff Snyder of Seavision Underwater Solutions to perform a bathymetric survey under two mothballed aircraft carriers in Newport, RI. From that experience we coined the process “Restricted Access Hydrographic Survey”.
Following up on that experience we deployed the Minipos technology to aid in the remediation of one of the worlds largest uranium mines for the uranium mining company Cameco ( Cigar Lake Mine, in Saskatchewan, Canada).
Since the original MiniSpool system was introduced, CDL has refined the product to include an acoustic link thus tightening accuracy and simplicity of operation.
SeaView believes this technology shows great promise and is an excellent way for a small, competent team running a relatively small but powerful ROV to provide value to the offshore oil and gas industry.
At present, our Falcon DR, capable of diving to 1000m is a good platform for carrying this technology. With the LARS, Winch and ROV all mobilized inside of the one 20’ Control Van/Workshop it represents the cheapest, easiest mobilization package possible. In most waters this package is quite adequate to perform the operations but there are occasions where ocean currents on bottom are in excess of 2 knts. and the Falcon DR, loaded down with equipment will become more difficult to operate.
To answer this limitation SeaView is working on developing the SeaView “Raptor” system. The Raptor is essentially a SAAB Falcon DR but with double the thrusters. We are building in a full extra suite of 5 thrusters into a cradle in which the Falcon DR sits. Expected to come online in Q4, 2011, this enhanced system will result in a very powerful, stable machine that has the capacity to carry payload and operate competently in currents in excess of 3knts.
The chart below compares the Thrust Vs. Surface Area for several different models of ROV on the market. It illustrates how the new SeaView “Raptor” will provide a vehicle with water current handling capability comparable to the most powerful vehicles in the industry but in a compact, easily mobilized spread.
We see a big future for INS aided acoustic spool-piece metrology both in the US and further afield. This work is particularly interesting to us as it’s challenging, interesting work which is well suited to our high quality/low volume business model.