Related Activities in Cambridge
Dr J. Li was appointed to the first lectureship in Engineering made possible by BP's benefaction to the University. His appointment is held jointly between Engineering and the BP Institute. He is a specialist in the computational dynamics of two-phase flows. He was previously at the University of Paris V and Virginia Polytechnic Institute.
Professor King, one of the Department's Royal Academy of Engineering Visiting Professors, was appointed to a Professorship in the Petroleum Engineering group in the TH Huxley School at Imperial College, from March 2000. Professor Palmer was President of the Pipeline Industries Guild for the two years to May 2000.
Professor A.C. Palmer
The group's work has developed into new areas. Several practically important, and at the same time scientifically interesting, problems lie close to the triple point where fluid mechanics, structural mechanics and geotechnics meet, and have often been neglected by specialists in one of the three fields. They typically involve several time and length scales, and it is rarely obvious how the different mechanisms interact.
One of these problems is 'shallow-water flow' (SWF), a misleading term for a phenomenon that has caused severe problems in drilling in the Gulf of Mexico (ironically, in very deep water). The seabed contains layers of overpressured sands, in which the pore pressure is much higher than hydrostatic. If a wellbore penetrates the sand, water flows into the bore and up the hole. The water progressively erodes the sides of the hole, mining a large cavity, within which any casing is unsupported and can easily buckle. On one project, this led to the need to abandon several deep-water wells, at very high cost. It cannot be avoided simply by increasing the mud weight, because in deep water the safety margin against hydraulic fracturing is very small. Control options include elaborate casing programs and increasing the mud pressure at the seabed, but they are all expensive.
Geologists see SWF as a problem in geology and site investigation, and fluid dynamicists see it as a problem in fluids. The geotechnics has been neglected. Our project is supported by Schlumberger Cambridge Research. It sets up a hollow triaxial specimen, in which the radial total stress at the outer boundary, the pore pressure at the outer boundary, and the pore pressure at the inner boundary can all be controlled independently, so that the conditions for initiation can be defined and related to parallel numerical analysis using the discrete-element method. SWF also offers interesting opportunities for creative design to eliminate the problem, perhaps by modestly increasing the cohesion of the sand ahead of the drillbit.
Another of these problems the behaviour of a catenary riser pipe in a floating production system, in the region close to the touchdown point where the riser reaches the seabed(I2,I4). The bending stress there is lower than the stress in most of the suspended span, but when the floater moves in rough seas the stress range is higher than elsewhere, because the touchdown point moves backwards and forwards. The area close to touchdown is therefore particularly prone to fatigue. The soft seabed deforms under the larger loads locally applied by the pipe, and there are unusual structural boundary layers. As the pipe moves in the groove it has excavated, it pumps water in and out, and sediment transport enlarges the hole.
Marine pipeline stability under waves raises similar questions. Conventionally, pipeline design assumes that the seabed itself is stable. Field experiences, consistent with calculations, show that in most locations the seabed is massively unstable long before the design conditions for the pipeline have been reached. Building on previous Department research into sediment transport, we are carrying out wave flume experiments whose objective is to develop a radically different rational approach to pipeline design.
The collaborative EU LOLEIF project on ice forces has been completed, and several publications have presented new work on fracture hot spots and velocity effects(I8). A second ice project, STRICE, is about to begin, and several papers on Arctic pipelines has been published(I3,I6,I7).
The work on uplift resistance of buried pipelines has concluded with a series of tests on pipes buried in rock fragments. Comparisons between centrifuge and 1 g tests, and between tests on soils ranging from fine silt to rock, generate interesting questions about scaling.
The petroleum engineering module in Part IIB continues to attract a large and lively group of students. An innovation this year was the introduction of a petroleum engineering project in Part IIA, in the Easter Term of the third undergraduate year. That project attracted six good students, who completed a remarkable amount of work on the phased exploration and development of the Sherwood Reservoir in the Wytch Farm Field.
BP made a substantial benefaction to the University to found an Institute devoted to fluid flow, a collaborative effort between Engineering and four other Departments. Engineering continues to play an active role in its development. The Director, Peter Smith, was appointed in 1999 and is a member of the Department. Andy Woods, the Professor of Petroleum Science, took up his post in January 2000. The first two of four lectureship appointments were made in the summer of 2000, and Dr Li is assigned to Engineering. The Institute has made a number of post-doctoral appointments, and its new building will be complete in 2001.
I1. Lissaman, J., Palmer, A.C. Decommissioning marine pipelines. Pipes and Pipelines International, 44, (6), 35-43 (November/December 1999).
I2. McShane, B.M., Bruton, D.A.S., Palmer, A.C. Rigid risers for floating production systems in deepwater field developments. Pipes and Pipelines International, 45, 21-34 (January-February 2000).
I3. Palmer, A.C. Are we ready to construct submarine pipelines in the Arctic? Proceedings, 32nd Annual Offshore Technology Conference, OTC 2000, Houston, TX, USA, 3, Paper OTC12183, 737-744 (May 2000).
I4. Palmer, A.C. Catenary rise interaction with the seabed at the touchdown point. Proceedings, Deepwater Pipeline and Riser Technology Conference, Houston, TX, USA (March 2000).
I5. Palmer, A.C. Friction: not as simple as it seems. Pipes and Pipelines International, 45, 30-32 (July-August 2000).
I6. Palmer, A.C. Gouging in the context of critical issues for Arctic offshore pipeline development. Proceedings, 2nd Ice Scour and Arctic Marine Pipelines Workshop, held at 15th International Symposium on Okhotsk Sea and Sea Ice, Mombetsu, Japan, 5-10 (February 2000).
I7. Palmer, A.C., Gudmestad, O.T. Arctic offshore pipelines. In: Basics of Offshore Petroleum Engineering and Development of Marine Facilities; Edited by O.T. Gudmestad et al, Part II, chapter 8, section 3, 229-235 (Izdatel'stvo Neft i Gaz, Moscow, Russia, 1999).
I8. Palmer, A.C., Johnson, I.E. Ice velocity effects and scaling. Proceedings, IUTAM Symposium on Scaling Laws in Ice Mechanics and Ice Dynamics, Fairbanks, Alaska, USA (June 2000).
[Table of Contents]
Last modified: September 2001