Muhammad Abduh (abduh@reksolindo.co.id)
The challenge of higher CO2 content in Natuna Alpha-D reservoir recently has seen an economic barrier to the development of this field. But the raise of crude oil price has made the non-prospective drilling like Natuna Alpha-D become prospective as well as the driver from development of exploration and production technology that become more cost-efficient. One of the key issues in development of oil and gas production is the use of advanced materials in deep water drilling and more hostile environment (higher CO2 and H2S content).
TO LOWER SYSTEM-COST
The ultimate goal for the use of advanced materials in offshore application is to lower system-cost of oil and gas production facilities. The system-cost should be regarded as life-cycle cost (construction and maintenance) rather than capital expenditure cost (construction). Platform owner conservatively tends to push the capital expenditure as low as possible without comprehensively investigating the potential to reduce system-cost by application of advanced material. Conservative material choice also associated largely due to management of change issue since change of ownership of oil and gas production facilities is quite high.
Pilot project for new material application pioneered by Conoco (now StatoilHydro) for their North Sea production Heidrun TLP. Conoco claimed a significant system cost reduction by applying composites to the several risers. Successful new materials application in this region also supported by certification bodies including Det Norske Veritas by issuing technical guidelines for offshore application of non-steel material. However the expanding use of new materials in other region are still reviewed. Mineral Management Service of United States to be waited by industry for the approval of offshore composite application for producing fields in Gulf of Mexico.
Both technical and economic justifications are needed here. Technical justification for the use of advanced material (stainless steel, nickel alloys, aluminum alloys, composites, concrete, titanium alloys, copper alloys) has been provided adequately. And the economic model to propose the cost-benefit of using alternative materials also already proposed. Model incorporating life-cycle approach and risk factor has
already developed by Craig and Swalm. As seen in Figure 1, by taking risk factor into account we can determine economic choice of material selection for length installed pipelines. Future studies with pipeline failure data representatives will improve the model becomes more accurate and comprehensive.
Figure 1 – Probability Limit Curves for Carbon Steel Failure, clad versus carbon steel for 6-inch pipeline, various pipeline length (Craig)
MATERIAL OF CHOICE AND OFFSHORE APPLICATION
Steel (low carbon steel) will be ever dominant materials since it has tremendous advantage of a large experience base and strong link between producers, designers, fabricators, and regulators. However there is a challenge in advanced material application due to demands for deep water drilling, oil reservoir rich in CO2 and sulfur, large capacity platforms, and ocean vessels. Choice of materials and the application in offshore structures are listed in Table-1.
Table- 1 Materials and offshore application
RECOMMENDATIONS
A comprehensive world industry leader workshop in New Orleans Louisiana United States in 1997 has drawn several recommendations for the use of breakthrough materials in offshore application as follow:
a. Mooring Systems
- Adequate engineering basis for synthetic ropes and composite strands and updated and unified design standards to accommodate taut mooring system.
- Requirement of updated reliability based safety factors and a coupled hull-mooring dynamic analysis methods.
- Requirements for verification of carbon fiber ropes (lightweight, high axial stiffness, excellent fatigue properties) and more investigation on fatigue strength behavior of steel rope.
b. Riser Systems
- Collaborative efforts are needed for successful use of advanced materials involving end-users, material suppliers, academia, and government.
- System-cost saving must be assessed and emphasized when advanced materials are considered.
- Development NDE/NDT techniques for the changing materials from steel to non steel.
- Development of reelable composite tubulars to minimize costly metallic connectors.
c. Floaters
- For Steel: Materials with higher tensile strength capacity combined with good fracture toughness, more efficient corrosion protection, improvement for weldability, fabrication, quality control, and corrosion resistance.
- For Concrete: more efficient construction method with less manning, more efficient quality control, light weight properties and easy fabrication.
- For Composite: cost efficient fibers, resin, easy fabrication, general qualification of composites as construction material, fire and toxicity safety perspectives.
- For Aluminum and Titanium: alloys with higher structural capacities (ultimate strength, fatigue, crack resistance), and improvement of weldability.
d. Secondary Structures
The use of corrugated or honeycomb construction for secondary structures is recommended because of its lightweight and maintained strength and structural integrity.
e. Hulls
With so many different hull arrangements and purpose hybrid design should be investigated to utilize the best material for certain situation.
f. Pipeline
- Update design code to include limit state design
- Welding Standard for corrosion resistance alloy
- To establish H2S limits for 13% Cr Steel
g. Process Equipment
- Technical barrier for new materials application including design issues, manufacturing and fabrication and costs
- Technical database should be provided to increase the knowledge
- Testing, verification of materials and prototype evaluation should be developed to establish experience base for fabrication and service history of materials.
BARRIERS AND ROADBLOCKS
Several barriers in many cases and regions including in Indonesia that prevent the use of advanced material are:
- Lack of knowledge about materials
- Lack of codes and standards for new materials
- Little experience in the use of many new materials
These barriers become high roadblocks to the potential of system-cost saving of advanced materials. End-users still don’t have enough confidence, fabricators shy away from using some of these new materials because of their ignorance on the weldability and fabricability, and the lack of experience will add a lot to cost. For the successful application of advanced materials there is a requirement to overcome the barriers by providing sufficient knowledge to the stakeholders, organizing technicaland economic justification and more research, development and pilot project to raise the user confidence of new materials application.
Reference
1. The Influence of Risk Analysis on The Economics of Carbon Steel and CRA Clad FLowlines, B.D Craig and R.S Thompson, Paper for Nickel Development Institute presented at Offshore Technology Conference Houston Texas US May 1-4 1995.
2. International Workshop on Advanced Materials for Marine Construction, Mineral Management Services DOI US and Colorado School of Mines, New Orleans Louisiana US February 4-7 1997
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