In Bohai bay, China, more than 150 highly deviated and horizontal wells are drilled every year. For most of these wells, it is difficult to evaluate the cement quality since a conventional cement bond log (CBL) log cannot be easily performed even with drill pipe conveyance and a tractor. Therefore, the well completion operation cannot always be performed with high enough confidence. This paper describes a new quantitative cement evaluation method using logging-while-drilling (LWD) sonic tools which has been utilized successfully for several wells in Bohai bay. For these highly deviated and horizontal wells, LWD sonic tools can easily overcome the conveyance difficulty and also offer a method to evaluate the cement bond quality in the same manner as a conventional CBL. For LWD sonic tools, due to the presence of a thick steel collar, the conventional amplitude only based approach to determining bond index is insufficient to evaluate both low and high bonding (Kinoshita, 2013) and must be integrated with the attenuation rate based measurement in the form of a hybrid approach (Izuhara, 2017) to cover the full range of bonding. Additionally, the bottom-hole-assembly (BHA) design should be optimized and procedures developed to mitigate noise while running the tool, particularly with the presence of casing scrapers in the logging run, as was done in Bohai bay.

8 wells in Bohai bay have respectively used LWD sonic to evaluate the cement bonding across different oil/water zones after the cementing operation, in both 9 5/8in and 7in casings. Despite the presence of a potentially high noise source casing scraper in the BHA for all runs, the tool signal was clear enough to deliver a bond index measurement in all cases. The bond index curve derived from LWD sonic tools shows that most of these wells have good bonding for the interface between the casing and cement. According to these results the perforation program was optimized and put into practice with a solid reference. The hybrid method of determining a bond index measurement with LWD sonic tools has been deployed in the industry since 2016. The successful applications of this method in 8 wells in Bohai bay have demonstrated its feasibility and its efficiency gains where conventional evaluation methods can be challenged. This complements the theoretical development of this approach and forms solid reference for more applications in other regions cross the world.

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