Polymer engineering adapts to frontier environments
As oil and gas exploration reaches into more extreme regions such as deepwater and arctic areas, polymer technology must adapt and improve to meet performance requirements.
Surrounded by Alaska, Canada, Greenland, Norway, and Russia, the Arctic Ocean is believed to contain more than 20% of the globe’s undiscovered recoverable oil and gas reserves. A four-year US Geological Survey study found that the region contains up to 90 Bbbl of oil and almost a third of the world’s undiscovered natural gas – about 1,670 tcf. Of these projected reserves, more than 84% are expected to come from offshore. Roughly 4,000 m (1,312 ft) deep, the Arctic Ocean is better known for the 2-3 m (6.5-9.8 ft) thick ice floes floating on the water. In addition, temperatures are near 0º C (32º F) in the summer but fiercely cold in winter dropping as low as -30º C (-22º F). Ice, ice flow, and the ultimate definition of cold – permafrost – pose daunting challenges to drilling in this region.
Changing technology
Frozen conditions, soils that contain ice, and fiercely cold weather all impact the design of equipment used in the arctic. Drilling equipment, drill bits, and a host of related hardware have been or are being redesigned for colder climates. Even building foundations and workers’ outerwear are developed to withstand the bitter cold and shifting elements. But what about the insulation of key components? It has to be flexible and fully operational in extreme cold. Known as "cold bend," plastics and rubber materials, or polymers, either simply do not bend or else crack to expose critical equipment worse yet pose hazards to workers using electrical equipment.
For example, polymers in the wire cable used to monitor or power equipment can be very temperature sensitive. Impact behavior or the likelihood of a polymer becoming brittle to the point of breaking depends upon the material used for insulation. Engineered polymers have a "glass transition temperature" or Tg. When the temperature is above a given polymer’s Tg, that material continues to exhibit the expected bend and toughness. However, when temperatures fall below the Tg of a polymer, the material begins to act more like glass. It can become very rigid, difficult to bend, and extremely brittle, resulting in a break. The cold bend and impact property of a polymer are critical during normal operation when vibrating or moving equipment or a tool strikes cause a crack or break in the cable resulting in failure.
Balancing properties, performance
Altering polymers may sound simple but requires careful examination of which performance properties are most important. For example, cable outer sheath formed from polymers is usually a balancing act to combine "opposite" or "counteracting" properties. Among the requisite outer sheath performance criteria are cold properties, oil/mud resistance, and physical properties without halogen and produced efficiently enough to be cost competitive. Trying to improve one polymer property often sacrifices one or more of the other properties.
After defining the ideal performance properties, a design process to combine various polymers and other ingredients in the right combination and quantities is required to ensure that the enhanced performance is achieved without sacrificing other important properties.
Once modified, the cable requires internal and external testing by an independent agent for certification.
One example of developing new technologies for challenging drilling conditions comes from Draka. The company has provided wire and cable for offshore drilling operations for more than 30 years and recognizes the potential of the Arctic and that such challenging conditions would mean having to re-engineer part of their products.
Working with vendors and suppliers, Draka identified use for a cable that could operate in temperatures below -30° C (22° F). Using -40° C (-40° F) as a target, Draka went to work with its polymer vendors to create a new product that would perform in the extreme arctic temperatures. After two years of development including extensive testing of cold bend and cold impact, and manufacturing improvements added to the usual requirements of low smoke, zero halogen, and certification, Draka developed an arctic grade cable.
"Our new arctic grade cable combines cold impact and cold bend requirements down to -40° C with excellent mud and oil resistance at the same time," says Eivind Nesset, global innovations leader for Draka Industrial’s Offshore unit.
Following IEC guidelines, the new arctic grade cables are flame retardant and flame resistant, and come in a range from 250 V up to 30 kV, depending upon power, instrumentation, or control cable needs. These cables have been type tested according to relevant IEC and NEK606 specifications. They are DNV certified under DNV Rules for Certification of Ships, High Speed & Light Craft, and Offshore Standards.
Put to work off Sakhalin
One of the better known Arctic projects is Sakhalin-1 which consists of three offshore fields – Chayvo, Odoptu, and Arkutun Dagi. Exxon Neftegas Ltd. (ENL) is the operator for the Sakhalin-1 Consortium (ExxonMobil, interest 30%; RN-Astra, 8.5%; and Sakhalinmorneftegas-Shelf, 11.5%), the Japanese consortium SODECO (30%); and India’s state-owned oil ONGC Videsh Ltd. (20%).
Sakhalin-1 potential recoverable resources are 2.3 Bbbl oil and 17.1 tcf of gas (or 307 million tons of oil and 485 bcm of gas).
"We have been developing this product for a couple of years now, and in late 2008 were satisfied with the technical performance of the product," says Nesset. "We have been awarded a contract by Tyco Fire & Integrated Solutions to supply arctic grade cables for use by the Sakhalin Island project.
"These high performance cables are to form part of a Fire Alarm system that Tyco has been commissioned to provide Fluor Engineering. These HCF cables have the capability to withstand high heat temperatures ranging from 750° C (1,382º F) to 1,100° C (2,012º F)," adds Nesset. "Along with our arctic grade cables, Draka is able to provide products that work from cold to heat extremes and every condition in between."
Temperature dependence
A thermoplastic is a polymer that turns liquid when heated and freezes to a very glassy state when cooled sufficiently. Most thermoplastics are high-molecular-weight polymers whose chains associate through weak Van der Waals forces (polyethylene); stronger dipole-dipole interactions and hydrogen bonding (nylon); or even stacking of aromatic rings (polystyrene). Thermoplastic polymers differ from thermosetting polymers (Bakelite; vulcanized rubber). They can, unlike thermosetting polymers, be remelted and remolded. Many thermoplastic materials are addition polymers; e.g., vinyl chain-growth polymers such as polyethylene and polypropylene.
Thermoplastics are elastic and flexible above a glass transition temperature.
Tg, specific for each one – the midpoint of a temperature range in contrast to the sharp melting point and melting point of a pure crystalline substance like water. Below a second, higher melting temperature, Tm, also the midpoint of a range, most thermoplastics have crystalline regions alternating with amorphous regions in which the chains approximate random coils. The amorphous regions contribute elasticity and the crystalline regions contribute strength and rigidity, as is also the case for non-thermoplastic fibrous proteins such as silk. (Elasticity does not mean they are particularly stretchy; e.g., nylon rope and fishing line.) Above Tm, all crystalline structure disappears and the chains become randomly inter dispersed. As the temperature increases above Tm, viscosity gradually decreases with no distinct phase change.
