Alaska state requirements as well as sound engineering practice require that oil and gas operators investigate the zonal isolation in the annulus of water injection wells. Conventional cement evaluation can be a time-consuming and expensive process, especially in high-angle or horizontal wells in which the wireline tools must be conveyed with a tractor or on drillpipe. Cased-hole LWD sonic data was acquired in a North Slope, Alaska, well to evaluate the cement bond zonal isolation in the casing by attenuation and transmission analysis. The LWD data was compared with a traditional wireline cement evaluation logs to validate the application. This paper provides a case study of the techniques used to acquire process and interpret logging-while-drilling (LWD) sonic logs for cement evaluation.
In this case study, a horizontal lateral section was drilled after setting and cementing the intermediate casing string. The interval to be evaluated for zonal isolation was behind this intermediate casing. LWD sonic data were acquired for cement evaluation purposes while tripping in the hole to drill out the intermediate casing cement shoe prior to drilling the horizontal section of this well. The ability to acquire cement evaluation data during the normal drilling practice provides significant cost savings over traditional wireline cement evaluation methodologies.
This paper discusses the theoretical basis for using LWD sonic data for cement evaluation, planning procedures, data acquisition, and data processing. A comparison of the LWD sonic cement evaluation data with traditional wireline cement evaluation data that was used to validate this technique is provided. Additionally, the advantage of integrating the LWD cement evaluation option into the drilling process will be described.