The Well Integrity Assessment by EM Wireline Logging in Acidic Geothermal Production Well: Case Study of the Hatchobaru Geothermal Field, Japan
Yuki MAEHARA and Takayuki WADA
Well integrity assessment is very important to maintain the well activity through the entire well lifecycle. If the well integrity is not compliant, the serious incidents are potentially triggered e.g. blowout, formation fluid seepage to surface. This presentation introduces a case study of the assessment by wireline logging in the Hatchobaru geothermal field located in Kyushu Island, Japan. Sidetracking was planned in one of the production wells, which had produced hot acidic fluid for more than 15 years and a lot of metal debris of casing conveyed from the downhole had been observed. Well integrity was one of the major concerns when planning sidetracking and it was decided to conduct casing corrosion assessment by wireline logging. In general, three logging technologies are available for the casing pipe corrosion evaluation, 1) mechanical caliper measurement, which is robust measurement for inner diameter of a casing string, 2) ultrasonic measurement, which enables to measure both casing ID and the thickness of inner casing string, 3) electro-magnetic (EM) field measurement, which is sensitive not only to thickness (or rather its mass) of the inner casing string but also to that of the outer casing strings in a multiple-string configuration. In the case of this particular well, the casing section of interest was filled with air and the static borehole temperature exceeded the logging tool’s temperature limit. Under these environmental constraints, EM field measurement was selected as it would be best suited to fulfill our needs, while the temperature limitation can be overcome by injecting water during logging survey to keep the borehole cool. The data processing and interpretation was conducted after implementing strict QC on the acquisition data. The acquired EM signal was free from noise and of sufficient quality to stand further processing. Integrating the EM data with the auxiliary log data, the downhole condition of the production well was interpreted as follows. - Downhole temperature was sufficiently cooled down by the injection water - Flow regime of injection water was mist flow interpreted by the pressure log - Precipitation of casing scale was indicated by high gamma-ray log at the shallower section - Casing thickness tends to get thinner as it goes deeper - Metal loss of casing mainly occurred inside the casing which was most likely caused by the generic corrosion Based on the well integrity condition interpreted by the logging data, the operator managed to optimize the remedial workover program.
|        Topic: Corrosion and Scaling||Paper Number: 27005|