Physical production system models help view real challenges, solutions

Stepping beyond digital 3D

Sep 1st, 2000

With the rapid proliferation of 3D computer modeling software, it is becoming rare to find an offshore installation firm that tests designs by building physical models. Yet, almost an entire room at R J Brown Deepwater's offices in Houston is devoted to just such models. - This field development model at RJ Brown Deepwater allows engineers to test different field development solutions.

Models can be more than 20 ft long and 9 ft wide, and strung with dozens of twine lengths and tiny chain, simulating flowlines, umbilicals, anchor lines, and risers for a floating production solution.

The floor under the model is laid out as a grid and represents the seabed in most of the modeling done at RJ Brown. The floor can be tilted to simulate an angled bottom. On what is the sea surface, about 7 ft off the floor, are mock-ups of anchor-handling vessels, floating production vessels, and pipelay vessels. Several of these small, wooden models contain motors to reel in or pay out line. The motors play a role in simulating various dynamic activities related to an installation.

Bob Brown, Director of RJ Brown, said he has built a similar model in every shop he's worked in since the first one was constructed in 1976. At that time, he was working on Panarctic's Drake 76 installation. This was a tricky installation because it was being performed below three meters of ice. Brown found the modeling not only helped generate ideas on how to design the solution, but also helped explain how the solution would work to oil and gas producers, contractors, and those in charge of executing the designs and installing the equipment.

Field complexity

The model graphically illustrates the complexity of modern offshore installations. The various chains, lines, and cords give the effect of a giant spider's web woven inside a heavy-duty aluminum frame. Tolerances in such designs are remarkeably close.

Gene Raborn, President of R J Brown Deep-water, said this is the best way to quickly identify trouble areas in a design. In one case recently, Raborn said a client had a conceptual design for a field layout in which the flowlines were re-routed around the anchor lines to avoid clashing.

Using the 3D model, Raborn said his team was able to solve this problem in a way that allowed the flowlines to be tied back directly to the floating production vessel. This change in the design saved the client 15-20%, he said.

Designs are usually visualized in two dimensions, Brown explains. In fact, the models built at his shop grow out of preliminary two-dimensional drawings. Brown says he starts with an overhead view of a potential layout design. From this, he develops drawings of a side view. "Then we go to the model," Brown said.

There are several employees who have a knack for such things, and Brown said these people actually assemble the model. Other employees install the small motors when required, tying them back to a control panel on the side of the model.

Spotting problems

Once construction is completed, Brown said it typically takes several days to put a model in place, and it becomes easy to see where problems may develop. To illustrate, Brown leans into the model and delicately points out one of the narrow spaces where a flowline must be threaded between anchor lines. While the space looks narrow on a model, it is even trickier to navigate in open water where currents affect lines and the operator cannot see what is taking place.

Using the model, Brown and his team tests alternatives and evaluates the practicality of a design that appears good on paper. Once the team is comfortable with a modeled design, he said he brings in operations personnel and the operator to demonstrate why a particular design is best.

A 3D physical model provides a clear picture of what is involved in a project. Particularly important, Brown said, is that the workers conducting the installation understand what is required of them. He tries to involve the installation crews early in the process, since he must rely on them to take the design from the model stage to the seafloor. If there is a problem from an installation standpoint, then Brown and his team can rearrange the model. Using the motors on the simulated vessels, Brown said different parts of the installation could be simulated.

In addition to modeling complex 3D field development plans, Brown also used the model to plan pipeline and flowline installations on the seabed. These are mainly 2D models in which a simulated pipeline is deflected to tie into a platform or termination skid.

Brown and the team calculate the length of the pipeline and the range of deflection, then test these on the grid. Using plastic tubes, Brown actually simulates the procedure and estimates the envelope of deflection. The tubes are mounted on plastic supports and ballasted with small chains to simulate the actual pipeline. Using a cushion of air, the pipeline can be deflected, as it would on the seabed, floating just off the surface. The model can be adjusted to simulate different currents to match a particular environment.

Transfer to paper

Once Brown is comfortable with a design and the model proves it out, then the installation must be transferred to paper in a series of step-by-step procedures. The model is used to simulate the installation procedure so that the critical order of activities can be worked out. The step-by-step procedures are controlled by matrix scheduling. Every detail is included. The actual installation is invisible from the surface, with the exception of remotely operated vehicle (ROV) cameras. Because of this, everyone involved is required to follow procedures and the plan in exact order. "You have to adhere to what you laid out in the model," Brown said.

While computer modeling is becoming commonplace, Brown said it is difficult to model the 3D relationships between all the anchor lines, flowlines, and catenary ropes in a floating production solution.

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