Hydrocarbon Production Optimisation
Upheaval Buckling and Backfill
Deep Water Pipelines
Professor A.C. Palmer
Professor P. King
Petroleum engineering is now two years old in the Department, and the scale of its activity has increased. Peter King of BP has taken up his appointment as Royal Academy of Engineering Visiting Professor. 1997-98 was the first year of operation of the Petroleum Engineering module in Part IIB, and it attracted 17 students. It benefited from generous support from BP, whose staff contributed a field trip to the Wytch Farm field and a number of lectures. In its second year, the number of students has increased to 42.
The number of PhD research students has further increased, and is now four. Seven students are carrying out MEng dissertation projects in petroleum. Research activities at first concentrated on initially centered on pipelines and ice mechanics, a central factor in offshore petroleum development in the Arctic but of broader interest as an example of an extremely brittle structural material. Research has begun in related areas, particularly through Professor King's interest in geostatistics, reservoir simulation and geostatistics.
An important development has been the preparation for the BP Amoco fluids institute made possible by a £20 million benefaction by BP. It will be an inter-departmental venture jointly between Engineering, Earth Sciences, Chemical Engineering, Applied Mathematics and Chemistry, with an initial staff of six and a new building on the Bullard Laboratory site. The director has been appointed, a new Professor of Petroleum Science will be elected in the summer of 1999, and the building will be complete in 2000.
The Petroleum Engineering Group attaches great importance to its links with industry, which have been beneficial in both research and teaching. In addition to its close links with BP, it has active ongoing collaboration with Schlumberger, Coflexip Stena Offshore (CSO), Science Applications International, Shell, C-CORE and others.
Current approaches to modelling hydrocarbon production usually start by making a detailed numerical model of the geological structures that affect flow. These detailed models typically contain up to 15 million grid blocks of dimensions 10's of metres laterally and a few metres vertically. These models are then coarsened (or upscaled in the jargon of the oil industry) to around a few tens of thousands of gridblocks before detailed numerical flow simulations can be carried out. This is a very time consuming process which can take many man months and hours of cpu time. In addition lack of precise knowledge means that there is a great deal of uncertainty in the predictions. In collaboration with a group in the Physics Department at Boston University we are working on using percolation theory to try to estimate production and its associated uncertainty directly from the knowledge of the statistics of the underlying heterogeneities.
In addition some work has been done (again with Boston and also at the Cavendish Laboratory) in understanding better the physics of the sedimentary process and so enabling us to produce improved geological models. These are based on granular flow models that lead to segregation of coarse and fine particles when bedforms avalanche.
Research has also been carried out to improve upscaling techniques and to understand better where the errors arise.
Hydrocarbon Production Optimisation
Oil and gas production from clusters of many fields can be very complicated with many decisions to be made about sizing of facilities, scheduling of production and so on. There can be a large number of possible variables that could be chosen that it is impractical to vary them all to choose the optimal production strategy (optimal in the sense of maximising some economic criterion like net present value). Instead stochastic search algorithms such as simulated annealing or genetic algorithms have been used to greatly improve value (up to 50% or $500million in one practical case). This was done for a deterministic model, where it was assumed that one knew in detail the reservoir properties. Ongoing research is to extend these techniques where the uncertainty is significant (as it always is).
Upheaval Buckling and Backfill
A persistent problem for both underwater and land pipelines is buckling, which can make a pipeline arch upwards or bend sideways. Pipelines are often stabilised by trenching and burial, most economically by replacing over the pipeline the seabed soil originally excavated from the trench. However, the mechanical and thermal performance of the backfill is often disappointing, and this has caused serious problems in several projects. Research supported by CSO has focused on a better understanding on the mechanics of heavily remoulded loose backfill, and has wider implications for geotechnics of very weak seabed materials. A new rig for tests a nearly field scale has been built, and tests make it possible to investigate the details of the uplift process. An important new result is that the mobilisation distance required to develop the uplift resistance is much smaller than the industry has assumed. The investigation is continuing towards another new phenomenon, pipeline flotation in trenches as a result of the dynamics of the backfill process.
Deep Water Pipelines
The offshore petroleum industry is moving rapidly into very deep water. The first deep-water projects west of Shetland have been far surpassed by the Mensa project in 1640 m in the Gulf of Mexico and the Roncador project in 1870 m off the coast of Brazil. Conventional practice is to lay the pipeline air-filled. The pipe then has to withstand the high external pressure of the sea. This requires the pipe wall to be very thick, which is expensive and wasteful, most of all because the extra wall thickness is only actually used for a few weeks while the pipe is constructed: once it is commissioned, the internal pressure is almost always larger than the external pressure, and there is no risk of collapse.
As part of continuing research on pipelines, a radical departure in pipeline design and construction practice has been investigated(I8,I10). The pipeline is laid filled with water (or with a lighter liquid such as pentane), and this make possible spectacular cost savings without overloading construction equipment.
Another deep-water problem is construct a steel production riser to connect a seabed manifold to a floating production system, and to make it flexible enough to withstand large movements at the top end (typically 30 m vertically and horizontally). An MEng student, Henry Ward, carried out model tank tests on a radically-new riser concept, in which the relative motion is taken up by a very large helical `bedspring' section of the riser. The results are encouraging(I2).
Further work has been carried out to examine the effect of liquid fill on the deformations induced by impact on pipelines. This is one of a group of investigations related to aspects of the Piper Alpha disaster. A paper on the breakup of firewalls caused by the explosion has been published(I8), and a wider programme on explosion response has been started, and will develop coupled CFD and structural models.
Professor John Dempsey (Clarkson University) joined the Department as Senior Research Fellow on August 1, and will work for a year on fracture mechanics aspects of the LOLEIF (low-level ice forces) program, a major research program supported by the EU and led by the Hamburg Ship Research Institute, in which the Department joins with other institutions in Finland, Norway, Sweden and France. He is principally concerned with scaling, with interactions between ice response and the hydrodynamics of the water during icebreaking, and with lead formation.
Concern about the implications of ice gouging for the safety of subsea installations in the Arctic has generated more research on alternative strategies to determine safe trenching depth(I9).
I1. Alessio, H., King, P.R., Jones, A.D.W. Capturing effective behaviour of capilliary influenced flow. Proceedings, 6th European Conference on the Mathematics of Oil Recovery, Peebles (September 1998).
I2. Bruton, D., McShane, B., Palmer, A.C., Ward, R.H. Large diameter rigid riser for operation in high motion environments. Proceedings, 3rd International Conference on Advances in Riser Technologies, Aberdeen (June 1998).
I3. Dokholyan, N.V., Buldyrev, S.V., Havlin, S., King, P.R., Lee, Y., Stanley, H.E. Distribution of shortest paths in percolation. Proceedings, International Conference on Percolation, Giessen, Germany (July 1998).
I4. Dokholyan, N.V., Lee, Y., Buldyrev, S.V., Havlin, S., King, P.R., Stanley, H.E. Scaling of the distribution of shortest paths in percolation. Journal of Statistical Physics, 93, (3-4), 603-613 (1998).
I5. Harding, T.J., Radcliffe, N.J., King, P.R. Hydrocarbon production scheduling with genetic algorithms. SPE (Society of Petroleum Engineers) Journal, 3, (2), 99-107 (June 1998).
I6. King, P.R., Andrade, J.S., Buldyrev, S.V., Dokholyan, N.V., Lee, Y., Havlin, S., Stanley, H.E. Predicting oil recovery using percolation. Proceedings, International Conference on Percolation, Giessen, Germany (July 1998).
I7. Palmer, A.C. Alternative paths for determination of minimum burial depth to safeguard pipelines against ice gouging. Proceedings, Ice Scour and Arctic Marine Pipelines Workshop, 13th International Symposium on Okhotsk Sea and Sea Ice, Mombetsu, Japan (February 1998).
I8. Palmer, A.C. Breakup of the firewall between the B and C modules of the Piper Alpha platform: I: analysis by hand calculation. Engineering Failure Analysis, 5, (1), 57-67 (March 1998).
I9. Palmer, A.C. Geotechnical evidence of ice scour as a guide to pipeline burial depth. Canadian Geotechnical Journal, 34, (6), 1002-1003 (December 1997).
I10. Palmer, A.C. Pipelines in deep water: interaction between design and construction. Proceedings, Workshop on Subsea Pipelines, Rio de Janeiro, Brazil, 157-165 (December 1997).
I11. Palmer, A.C. A radical alternative approach to design and construction of pipelines in deep water. Proceedings, 30th Annual Offshore Technology Conference, Houston, TX, USA, 4, 325-331 (May 1998).
[Table of Contents]
Last modified: October 1999