The Development of Corrosion-Resistant Tubing

Abstract

Abstract Corrosion problems of deep well tubings and their control measures are discussed. As one of the economical solutions, metal-lined tubings are proposed. It is shown that the metal liner can be tightly fitted by the newly developed thermo-hydraulic fit method. The selection of corrosion-resistant material for the liner is discussed. Some designs of the tubing joint and their manufacturing methods pre proposed. Introduction With the seriousness of an energy shortage, the drillings of oil and gas wells have become more active. In the last few years, the number of drilled wells has increased rapidly as shown in Fig. 1. It should be noted that eighty percent of these wells were drilled in the United States. Fig. 2 shows the depth distribution of oil and gas wells drilled in the United States in 1977. It can be seen that the numbers of oil and gas wells are about the same, but, in general, there are more gas wells at deeper depths than oil wells. As shown in Fig. 3, well depth increases each year, and recently an exploratory well deeper than 10,000 m has been drilled. As the well depth increases, the down hole pressure and temperature rise. For instance, in some severe wells at a depth of 6,000 m, the pressure and temperature are more than 1,000 bar and 200°C respec. tively. Therefore, the strength of the tubings used in such severe conditions is a very important factor for deep wells because they have to sustain their ownweight also. Figure 4 diagrammatically illustrates the transitions of design conditions with the increaseof well depth. Figure 5 shows the relationship between well depth and axial and hoop stresses of API standard tubings with various pipe 'dimensions. It isknown roughly that the strength of class P-I05 is required for the tubing of a 6,000 m well. Another substantial problem in deep oil and gas wells is corrosion. This is mainly due to H2S and C02 which are contained in crude oil and natural gas The density of these contaminants is increased with well depth, and, together with high pressure and high temperature, the corrosion reaction is accelerated. To solve all the above problems in deep wells, a new type of economical, high strength tUbing which has high corrosion resistance is expected. At present a super Ni alloy tubing, which is extremely expensive, tends to be used. As a solution, the authors propose the Tight Fit Tubing (hereinafter referred to as TFT) which is lined inside with corrosion-resistant alloy to meet the above three requirements for the tubing of deep wells. The thermo-hydraulic fit method used here for TFT has been developed to produce the corrosionresistant pipe, TFP, for corrosive flow lines as reported in Ref. 1.