OPTIMAL SELECTION AND PRINCIPLES OF PRODUCTION TUBING IN DEEP-WATER GAS FIELDS

During the exploitation of deep-water gas fields, the complex deep-water environment conditions result in extremely harsh requirements for the tubing selection. In this paper, the authors studied the selection of tubing in a deep-water gas field. Based on the specific practices in the deep-water gas reservoir A, they suggested the algorithm of the size selection and material selection of tubing. Assuming the flow pressure at the wellhead is 7.5 MPa, the optimized size of the tubing is selected from the most commonly used tubing sizes 5-1/2 '', 7 '', and 9- 5/8 ''. The selection of the tubing size is determined by the comprehensive analysis of the tubing sensitivity, liquid-carrying capacity, and fluid erosion rate. Based on the analysis results, as well as the safety and economy issues, the 7 '' tubing size is regarded as the most suitable. The selection of the tubing material is determined by the analysis of the gas composition in the reservoir, the formation water characteristics, and the acid gas corrosion. The safety of the selected tubing material and the final strength of the optimized tubing are verified by the WellCat software. The results show that the strength of the 13Cr L80 tubing is satisfactory to meet the requirements for operations in the initial gas reservoir stage, the production stage, the well shut-in stage, the well killing stage, and for tubing leak situations under the conditions of different water-gas ratios. In this paper, the selection principles of the tubing size and material are summarized. The conclusions may be vitally important for improving the production safety and efficiency of the tubing, which is important in promoting the development of production technologies in the deep-water oil and gas reservoirs.