| Title | Casing failure analysis and proposed repair for well OW-740A in Olkaria Geothermal Field |
|---|---|
| Authors | Nahashon Karanja Nzioka, Kristinn Ingason, Málfríður Ómarsdóttir |
| Year | 2023 |
| Conference | World Geothermal Congress |
| Keywords | Thermal stresses, casing caliper, casing failure, workover, discharge tests, tie-back cementing, coiled tubing, cement plug, LCM, compressive strength. |
| Abstract | Geothermal wells experience extreme temperature changes during production and if the wells are not properly designed and the casings cemented in place properly, the wells are likely to experience failure during production (Kaldal et al., 2015). Well OW-740A is an example of this failure where casings have parted in three locations i.e., 187, 198, and 318 m. The well started developing steam leakage between 20” and the 13-3/8” casings after about one year of being shut-in after drilling and testing. A quenching operation was conducted to try and reduce the wellhead pressure and to replace the leaking master valve followed by a caliper logging to establish the condition of the casing string. This is where the casing failure was detected at the three locations. The main cause of these multiple failures in the casing string is largely unknown but the most logical hypothesis points to faults in cementing of the production casing and thermal stresses induced in the well due to acute changes in temperatures during quenching from a high of about 300 °C to around 26 °C. These stresses must have taken a huge toll on the K55 grade material of the casing leading to plastic deformation followed by snapping of the casing during cooling. Currently, the well is under vertical discharge through a 10” blowpipe at a discharge pressure of 6 barg, and from the analysis in this study, the well formation has enough containment pressure to prevent a blowout. Therefore, the safety of the well and surface equipment is ensured when the well is discharging. In this study, an analysis is done on the well including the drilling data, pressure-temperature analysis, casing caliper logs, and cementing of the well. This will form a basis to compare the casing design to the Africa code of standards for geothermal drilling through a casing failure evaluation. Establishing the root cause of the failure helps to find the best intervention procedure and forms a basis in designing future geothermal wells in Olkaria. A remedial operation procedure is proposed for repairing well OW-740A. |