A New Thermal Insulating Fluid and Its Application in Deepwater Riser Insulation in the Gulf of Mexico

Abstract

Summary Undesired heat loss from the production tubing, or uncontrolled heat transfer to outer annuli, contributes to the formation of gas hydrates and causes the deposits of paraffin and asphaltene materials that reduce the production rate. The successful application of thermal-insulating fluids in the last several years has demonstrated that such fluids can control heat loss effectively. In some cases, heat loss from the produced fluids caused by conduction and convection can be reduced by more than 90% when compared with traditional packer fluids. Recently, a new thermal-insulating-fluid system with superior thermal properties has been developed. Compared with the existing insulation fluids, the new insulating-fluid system provides high viscosity at a low-shear-rate range to reduce the fluid-convection rate. It also provides lower viscosity at high-shear-rate range to facilitate fluid placement. The new fluid, with improved insulation properties, has proved to be an attractive alternative to the current insulation method for deepwater risers. This paper highlights the development of this new thermal-insulating fluid and its application in deepwater-riser insulation in the Gulf of Mexico (GOM). Laboratory data and field cases are also presented to demonstrate the effectiveness of this fluid system. Introduction Understanding and controlling the thermal environment for oilfield operations has been a concern and research topic since the mid-1960s, when heavy interest was raised in enhanced oil recovery by steam injection. Much of the early attention was focused on steam-injection operations and is well documented in the cited references. 1--3 For applications where the packer annulus was gas-filled, wellbore refluxing was identified as a major reason for heat loss. Wellbore heat losses from the refluxing annulus were 3 to 6 times higher than anticipated for insulated tubing, and were only 30 to 40% less than would be obtained if the injection tubing was not insulated. 3--6 Silicate foams were among the first fluids to be documented as insulating packer fluids in steam-injection applications. 1 In field operations, a solution of sodium silicate is placed in a packed-off annulus and then steam is injected down the tubing. The hot tubing causes the silicate solution to boil, leaving a coating of insulating material---silicate foam from 1/4 to 1/2 in. thick---on the hot tubing surface. Silicate solution that remains in the annulus after steaming for several hours is removed from the annulus by displacing it with water, which is removed by gas lifting or swabbing. The foam is an excellent insulator, with thermal conductivity of about 0.017 Btu/(hr-ft 2 -degree F/ft). However, difficulties have been encountered in boiling off the solutions to form the foam. "Hot spots" were also observed developing adjacent to the uninsulated couplings. 7,8 To prevent thermal refluxing, an insulating fluid that fills the entire annulus was elected as an alternative to the gas-filled annulus. 9 Oils appeared to be suitable material for this application because of their relatively low thermal conductivity [0.08 Btu/(hr-ft 2 -degree F/ft)]. However, natural convection became just as critical and increased heat transfer of oil by a factor of 10 to 20 over molecular conduction. Willhite and his coworkers 9,10 developed an oil-based fluid with reduced apparent-thermal-conductivity value through increasing the viscosity of the base oil, thereby reducing molecular motion. Unfortunately, this two-phase system suffered from long-term suspended-solids settling. Thermal stability was also questionable at the working temperatures. Alternative gelatinous oil-based fluids 11--14 have been developed for the geothermal and oil-recovery applications. The relative thermal conductivity of this type of fluid is approximately 13% that of water. However, the current and future environmental restrictions could limit its application. Furthermore, the long-term incompatibility with various elastomer elements is a critical concern. As an alternative to chemical methods, Purdy and Cheyne 15 applied vacuum-insulated tubing to solve the problem of paraffin deposits in the production tubing in wells near the Arctic Circle. On the basis of a reservoir temperature of 82degreeF and crude oil with a cloud point of 55--57degreeF, computer simulation predicted that the vacuum-insulated tubing could raise the flowing-tubing temperature at the wellhead above the cloud point of the crude oil, thereby solving the historic waxing problems. Installation of th. vacuum-insulated tubing proved to be an apparent technical success. However, the savings on well dewaxing maintenance did not economically justify the installation of the vacuum-insulated tubing. While insulated tubing is an effective method for wellbore insulation, actual heat losses were still observed to be significant. Heat loss through couplings and other internal structures, such as centralizers and valves, was seen to account for up to 50% of the total heat loss. 3,4 To fully achieve the potential of insulated tubing, selected rubber-insulated couplings were tested along with a thermal pipe coating. Although improved thermal performance was obtained, maintaining the dryness of the annulus over a long period is difficult. Heat loss through refluxing could still occur because of damaged and scraped coating and downhole centralizers, valves, and gauges. This problem can be controlled effectively by the use of specially designed aqueous-based (oil-free)-insulating- packer fluids. To secure the insulation of the wellbore so that the heat transfer from the production tubing to the surrounding wellbore, internal annuli, and the riser environment is reduced, Javora et al. 16 have developed a specialized aqueous-based-insulating-fluid (ABIF) system. This fluid is solids free, nondamaging, environmentally friendly, and highly insulating. Fluid viscosity is designed to provide a fluid that is easy to blend and pump into the annulus. Fluid density is controlled by the amount and type of dissolved salt, which provides positive control of wellbore pressure without the risk of solids settling and separation. This wellbore insulating-fluid system has been a success in field applications in the past several years. It has been demonstrated that such fluids, added into either an annulus or a riser, can effectively reduce undesired heat loss from the production tubing or heat transfer to outer annuli.

High-Performance Water-Based Insulating Packer Fluids

“…17 More recently, Javora et. el [18][19][20][21][22] have developed a specialized aqueous-based insulating fluid system. The system is solids-free, nondamaging, environmentally-friendly, and highly insulating.…”

A New Yield Power Law Analysis Tool Improves Insulating Annular Fluid Design

“…In order to benchmark the YPL-WTP engineering tool, results were compared against the published literature, particularly the excellent recent publications by Vollmer, Fang, Wang, Javora, and their colleagues. 8,9 There was very little difficulty in matching their results ( Figure 1); however, "reasonable" assumptions had to be made for some of the inputs to YPL-WTP.…”

“…[1][2][3][4][5][6][7] The solutions depend on the physical properties of the annular fluids, sea floor, wellbore geometry, and geological boundary conditions, and the fluids' configuration in the wellbore. The following parameters were studied: Many previously published algorithms for solving this type of problem [1][2][3][4][5][6][7][8][9][10][11][12][13] are based on mathematics that assumes that fluids involved have Newtonian or power law (PL) rheological properties. Key studies [8][9][10][11][12][13] on convective heat transfer for insulating fluids emphasize the use of non-Newtonian fluids with high yield stress.…”

“…The following parameters were studied: Many previously published algorithms for solving this type of problem [1][2][3][4][5][6][7][8][9][10][11][12][13] are based on mathematics that assumes that fluids involved have Newtonian or power law (PL) rheological properties. Key studies [8][9][10][11][12][13] on convective heat transfer for insulating fluids emphasize the use of non-Newtonian fluids with high yield stress. Algorithms used in developing YPL-WTP, are based on essentially the same mathematics 11,14,15 ; however a significant distinction is that Herschel-Bulkley (or yield power law) fluids can also be simulated for non-Newtonian fluids with a high yield stress.…”

Water-Based Insulating Fluids for Deepwater Riser Applications

“…Recent articles by Javora et al (2002) and Wang et al (2005) detail the advances made in formulation and use of water-based insulating fluids.…”