Canyon Express

Case Study 4 Thermodynamic Inhibition Canyon Express and Ormen Lange Flowlines... 

At start-up in September 2002, the Canyon Express development in the Gulf of Mexico was the world s deepest, with the three field locations in... 

The above two examples serve to illustrate that more severe conditions of gas recovery require large expense in thermodynamic inhibitors. The high pressure and high water production at Canyon Express and the steeply upward sloping lines and subfreezing temperatures of Ormen Lange are harbingers of more severe conditions in the future. There are some cases in which the cost of hydrate inhibitors determine the project viability. 

Forty-six case studies of hydrate plug formation and remediation are recorded in Hydrate Engineering (Sloan, 2000). In every case, hydrate plugs were remediated. In addition, a rule of thumb is that most of the offshore flowline shut-ins are less than the 10 h no touch time, which requires no antihydrate operation before restart (J.E. Chitwood, Personal Communication, August 1, 2003). However, hydrate prevention methods are very expensive, as shown in the above Canyon Express and Ormen Lange examples, or in the fact that deepwater insulation costs are typically U.S.Sl million per kilometer of flowline. 

This strategy was successful in extending the field life by almost 2 years. This is one key example of the risk management philosophy, enabled by operating experience on the platform. The hydrate plug prevention technique in this case study is time-dependent and should be contrasted with thermodynamic (time-independent) inhibition methods in Case Study 4 of Canyon Express and Ormen Lange. 

Hare, S., Case, R., Canyon Express Commissioning and Start-up Experience, in Offshore Technology Conference Proceedings, OTC15097, Houston, TX, May 6 (2003). 

What are the relative contributions of these two sources Two approaches have been taken. One is to establish the geology and hydrology of a basin in great detail. This has been carried out for the Amazon (Stallard and Edmond, 1981) with the result that evaporites contribute about twice as much sulfate as sulfide oxidation. The other approach is to apply sulfur isotope geochemistry. As mentioned earlier, there are two relatively abundant stable isotopes of S, and The mean 34/32 ratio is 0.0442. However, different source rocks have different ratios, which arise from slight differences in the reactivities of the isotopes. These deviations are expressed as a difference from a standard, in the case of sulfur the standard being a meteorite found at Canyon Diablo, Arizona. 

Review of Isotope Concepts. The average relative concentration of the two most abundant stable isotopes of sulfur, 32S and S, are 95.0% and 4.2%, respectively. Ratios of these two isotopes are measured with specialized isotope ratio mass spectrometers, normalized to standard Canyon Diablo meteoritic sulfur, and expressed as a delta value (634S) according to the relation ... 

The continental slope includes up to 40% of the seafloor area it descends down to depths of 2000 m. It is steep and cut by submarine valleys and canyons. Its lower part, located at depths of 1500-2000 m, is referred to as the continental foot in selected cases, the boundary between the slope and the foot is poorly expressed. The floor of the basin (35% of the total area) represents a flat accumulative plain with a surface that gradually declines toward the center of the sea. 

Approximately 0.5 mg of BaS04 was mixed with equal amounts of V2O5 and reacted in an online Elemental Analyzer to a ConHo SIRMS (Finigan Delta -I-). The sulfur isotope ratio is defined as the deviation in %c of the ratio " S/ S between a sample and a standard, expressed in the conventional 5 " S notation relative to Canyon Diablo Troilite (CDT). The accuracy of the measurements based on standard measurements was better than 0.3%c. 

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