Advanced Casing Design Against Stress Corrosion Cracking of Grade P-110 Casing in Lignosulfonate Mud
- Shoichi Ikeda (Teikoku Oil Co. Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- June 1992
- Document Type
- Journal Paper
- 141 - 147
- 1992. Society of Petroleum Engineers
- 3 Production and Well Operations, 1.14.1 Casing Design, 1.6 Drilling Operations, 1.10 Drilling Equipment, 1.14 Casing and Cementing, 4.2.3 Materials and Corrosion, 4.1.2 Separation and Treating, 4.1.5 Processing Equipment
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Stress corrosion cracking (SCC) of Grade P-110 casing couplings occurred in the hot, deep Minami-Nagaoka gas field. Detailed stress analyses revealed that the dynamic stress changes resulting from temperature caused by operation played a significant role in those failures. From this information, a new casing design was developed.
The Minami-Nagaoka gas field is located in the Niigata Prefecture, about 210 km northwest of Tokyo (Fig. 1). Production Prefecture, about 210 km northwest of Tokyo (Fig. 1). Production and delivery began in 1984. The production rate of each well is approximately 300 000 m /d, and the production zone ranges from 4400 to 4700 m. The bottomhole static temperature is about 175C. The flowing wellhead temperature and pressure are 100C and 380 kgf/cm , respectively. Extraordinary pressures in the annuli of several wells were found in 1987. Surveying showed the communication of pressures among annuli for 8.89-cm tubing, 17.78-cm casing, 24.45-cm casing, and 33.97-cm casing. In 1988, during the first well service, severe coupling failures of 17.78- and 24.45-cm casings were found. The non-API special sour-resistant casing grade with 65,214-N/cm (Grade 95) specified minimum yield strength (SMYS) and API Grade L-80 with premium connection were selected for new casing strings. The hoop stress caused by makeup with premium connection was less than 50% of buttress threads. Fig. 2 is a schematic of the wells before and after well service. The first well service went as follows. 1. The 17.78- and 24.45-cm casings were cut off at the top of cement (1894 and 804 m, respectively) and pulled out of hole. 2. The new casings were run into the hole and connected to the original casings with casing patches. 3. The new casings were cemented through a mechanical stage cementer connected on casing patches. Many longitudinal coupling failures were discovered during well service (Fig. 3). All the coupling failures occurred on Grade P-110 buttress casings. In 17.78-cm casing, 35 of the upper 50 P-110 buttress casings. In 17.78-cm casing, 35 of the upper 50 joints failed from 16 to 591 m. In the 24.45 cm casing, 14 of the upper 24 joints failed from 53 to 274 m.
To elucidate the cause of coupling failure and to find possible solutions, Teikoku Oil Co. Ltd., three oil-country tubular goods (OCTG) manufacturers, and one mud company performed various investigations and tests. The casing materials satisfied API grade specifications. The environments in the annuli were almost identical among the production wells in the Minami-Nagaoka gas field, and the mud investigation showed that H2S was generated from lignosulfonate mud. The literature survey of hoop stress caused by. makeup was also done, together with metallurgical and chemical investigations. Schneider showed the calculated hoop stress caused by the makeup of the buttress thread. The following information was derived from a series of investigations. The cracking was caused not only by the casing materials but also by a combination of environmental factors and hoop stress resulting from makeup of the couplings. Because the SCC caused by H2S from lignosulfonate mud was the primary suspect, the plans detailed below were executed. It is well known that this kind of cracking is caused by a combination of environment, materials, and stress. In regard to the environment and materials, the mud in the annulus was changed during the cementing operation and a non-API special sour-resistant casing grade with premium connection was selected. The following plans to counter stress were considered and executed. Detailed triaxial stress analyses were carried out on all bodies and couplings of the casing strings. The triaxial stress levels on the bodies and couplings were kept smaller than the threshold stress of casings under all possible well situations. The influence of cyclic stress caused by repeated production and shut-in was minimized by increased casing landing weight. The engineering method used to estimate safety factors concerning triaxial stress level against SCC was defined; then the maximum allowable casing landing weight for a wedge-type casing slip without SCC was determined by experiment. These plans against stress are the main focus of this paper.
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