... important aspects of the development project along with the results of the qualification testing. chemistry thermal property application offshore technology conference subsea thermal insulation application extreme temperature operation mechanical properties heat capacity iso 12736 coating...

... technology conference pipe wall gas development thermal property operation hydrate plug induction time upstream oil & gas Turner , Douglas J , Mahadevan , Geetch and Jason Labhance , Hydrate Stable Startup and Restart of Oil and Gas Production System , Proceedings...

... and the well integrity. offshore technology conference sediment reservoir characterization hydrate dissociation thermal property gas hydrate dissociation fracture upstream oil & gas well component dissociation effect hydrate well integrity wellbore stability strength integrity...

... followed the objective of first selecting the best solvent (hydrocarbon based), with low cost and good thermal properties and second finding the right association with a very robust network in order to reach a safe, permanent and stable insulation material. In addition to its in-place stability...

... thermal property ian frazer otc 13143 thermal conductivity conductivity otc 13143 flowline burial system upstream oil & gas pipe burial deepwater soil roger osborne subeconomic marginal discovery roger osborne piping simulation piping design flowline burial trench Copyright 2001...

... content offshore pipeline piping simulation thermal property Copyright 2001, Offshore Technology Conference This paper was prepared for presentation at the 2001 Offshore Technology Conference held in Houston, Texas, 30 April 3 May 2001. This paper was selected for presentation by the OTC Program...

...<ing a thermal conduc- tivity for sand and gravel to both be 2.6 W/moC. In reality, a combination of both scenarios is most probable. Fig. 7 illustrates crude production from a Ness field well before and after insulation. The difference is dramatic and demonstrates the success of this method of thermal insula- tion of pipelines. 4.0 THE GULLFAKS - A CASE 4.1 The Problem The problem in this case evolved during the normal decision making processes connected with engineering a new development. The Gull faks field, operated by Statoil with partners Norsk Hydro and Saga Petroleum, is a large oil field in about 135 metres of water. The field has been developed by means of two large integrated platforms, with a third to be insta11 ed duri ng the sumner of 1989, and a number of subsea wells tied back to the .platforms. This case concerns a subsea well, A-9H, developed and controlled through the Gullfaks- Aplatform. The well is characterised by a very high production rate but with a short lifetime, and is representative of the majority of the wells in this field. It was decided to develop the well by means of a 6" flexible flowline (Coflexip) and associated control 1ines. During the engineering stage it was found that the 1ines requi red protecti on from mechanical damage and some form of insulation for the flowline was also necessary in order to maintain the required minimum arrival temperature at the platform, which was calcu- lated to be 25 degrees centigrade. Given that previous trenching in the area had posed huge problems due to a subsoil of very hard boulder clay over a 1arge area, the Operator had to develop an innovative solution to a complex problem. 371 4.2 The Solution Due to the problems foreseen in achieving adequate trenching of the lines, the Opera- tor chose rock dumping to provide mechanical protection. The Operator had previously used rock dumping to good effect in the area and hence had good experience of rock dumping techniques. The rock berm solution moreover had an advantage over trenching of being a single pass operation compared with the need to make two separate trenches for the flow lines and control lines, and was consequently cost effective. To provide thermal insulation, the Operator selected the use of a sand layer, which had been pioneered in a sn~ll pilot project ear- l ier. The deci si on was also based on a study performed on behalf of the contractor by Delft Hydraulics l.aboratory and at a 1ater stage as a result of the very satis- factory outcome of the I~bil Ness project. One major drawback was using a sand layer without a trench. Atrench retains the sand and hence reduces the quantity of insulating sand required. If the sand layer had to be app1ied over the fl ow 1ine on a fl at seabed, the amount required would have been about 150% more than an application into a trenc- hed flow line. The sand dumping operation represents the bulk of the contractor's costs, and hence a solution had to be found to minimise the quantities required. The contractor therefore developed a design consisting of two small berms either side of the flowline, thereby creating an artificial trench and al so giving protection to the control lines (See Fig. 8). After detailed engineel'ing it was proposed that a filter layer should be "sandwiched" in between the insulating sand layer and the protective armour 1aye:r to avoid the sand bei ng washed away through the armour 1ayer by current and wave action. At a later stage however, it was decided to change the sand distribution curve to a much coarser material. This was the equivalent of mixing the sand and the filter layer material and resulted in only two layers being required. The effecti veness of thi s change, brought about by a more practical and economic app- roach during the construction phase, is still the subject of an extensive study by both Operator and Contractor, but a positive effect was definitely observed. 4.3 The Construction Method The configuration chosen for the dual purpose of mechanical protection and thermal THE USE OF A PRECISELY APPLIED SAND MIXTURE AS A METHOD FOR THERMALLY INSULATING SUBSEA FLOWLINES q = Aoko(T - T) (1) OTC 6156 (pc)p = (l-n) (pc) + n (pc) (3) B f hi and ho are the heat transfer coefficients over the interior and exterior surface of the pipe, respectively. In practice the interior heat transfer is very large and its effect on the oil temper- ature can be neglected. The reason for this is that in crude pipelines the flow is nearly always turbulent and hence the heat transfer of the oil is very 1arge and the temperature difference between the bulk temperature of the oil and the temperature at the inner pipe wall can be neglected. The exterior heat transfer expresses the effect of thermal resistance induced by a cover layer and the surrounding soil. The exterior heat transfer can be computed on the basi s of the thermal properti es of the cover layer and soil. In granular materials the heat can be trans- ported by conduction, convection and disper- sion. Conduction is the heat flux due to the exchange of ki neti c energy between the molecules of the considered medium without appreciable displacement of these molecules. Convection is the heat flux due to any flow within the medium. It is the heat which is carried along with the flow. Dispersion in granular material is the phenomenon of spreading of heat (or solute) due to random flow velocities and resulting macroscopic mixture in the pores. The thermal properties of granular materials can be expressed by the heat capacity (pc)p and the thermal conductivity (.1 The heat capacity expresses the capabi~ ity of the medium to store heat. For a saturated granular material the heat capacity is commonly written as: where p is the density, c the specific heat, n the porosity of the granular mate- rial and the subscribes sand f refer to the solid granular phase and fluid phase, respectively. The thermal conductivity is the proportiona- l ity factor between the heat fl ux and temperature gradient. It depends, in general, on the structure of the. granular material as well as on the thermal conduc- tivities and volume fractions of each constituent. The thermal conductiVity is especially very sensitive to moisture content. In dry state granular materials characteristically have low thermal conduc- tivities. This is due to the small contact areas between the grains through which heat mllst flow. At higher moi sture content a 372 18.3 Days 3.8 Days 10.7 Days 2.2 Days Dumping ROV Survey Loading and Transit Weather Downtime where Ri and Ro are the inner and outer radii of the pipe, respectively, .1. i is the thermal conductivity of the pip~ P(which can be determined quite easily on the basi s of the thermal properties and wall thickness of the pipeline material and its coatings) and A total of 19,700 tonnes of sand and 30,850 tonnes of rock were used during the operation. The heat loss of covered subsea flowlines depends on the thermal properties of the pipe itself as well as the thermal properties of the cover material and surrounding soil. In general, the heat loss of acyl indrical tube can be expressed as follows (see Fig. 9): insulation consisted of 0.5 mof cover depth of sand mixture, greater than the Mobil Ness case as a result of the coarser material used, and a protective armour layer of 0.4 mcover depth of graded rock. The operational sequence consi sted of seven stages: Pre-survey using the ROV, Installing the two side berms, Survey over the berms using the ROV, Installing the insulating layer, Post-insulating layer survey using the ROV, Placement of armour layer and post survey of the "as-built" construction, again using the ROV. The total working time was 35 days, comprising of: 1 k = irrr olIn (R /R ) { 0 1R.; -h-R + i 1 1 p 1pe where q is the heat loss per meter pipe lenqth(W/m) , T is the temperature of the oil (OK) and To a reference temgerature, AQ the outer contour of the pipe (m2) and K the overall heat transfer coefficient (W/m2JOK) based on the outer pi pe di ameter. The overall heat transfer coefficient can be expressed as follows: 5.0 SOME THEORY BBiIND THE SAm/ROCK THERMAL INSULATION PROPERTIES 6 OTe 6156 M. VAN TRAA J K. DE RUITER J S. BOER & R. WATSON 7 water film around the grains is effectively increasing the contact area and thus the thermal conductivity. At even higher mois- ture content the water film around the grains in combination with capillary mechanism are forming a more continuous fluid phase. . The thermal conductivity increases further due to water movements in this fluid phase. At the point of saturation any free water movement within the granUlar material will further increase the thermal conductivity of the gra- nular material due to hydrodynamic dispersion induced by the flow. Other properties of the granular material which have also effect on thermal conductivity are: porosity, per- meability, dry density weight, mineral com- position, etc. The thermal diffusivity (m2js) is another parameter which is reflecting the thermal properties of granular materials. K = A / (pc) p p (4) where K is the thermal diffusivity and .:I. the thermal conductivity of the granula~ material, which involves the overall effect of molecular conduction within both phases as well as the effect of dispersion induced by pore flow. The thermal diffusivity is especi- ally ill1>ortant when time dependent heat loss problems are considered. In table 1 some values of the thermal conduc- tivity, together with other properties, are given for different granular materials. A great deal of literature has been publ ished on thermal properties of granular materials and several models...