Through Bit logging: Applications in Difficult Wells, Offshore North Sea

摘要

Through bit logging is a method for data acquisition using thedrill string and bit as a conduit to the well bore.Two case studies are presented demonstrating the uniquecapabilities of this technology to obtain data in difficult andtroublesome well situations. Both cases were recent (early2004) wells, offshore North Sea.Case study 1 concerns an exploration well with a large opensalt interval open above the reservoir. Conventional loggingtools could not pass the squeezing salt interval, and TBL wasused to get past the troublesome interval and successfullyobtain quad combo and pressure data. Subsequently, thecement stinger could not pass the same interval, and the TBLbit was again used, this time to cement through.Case study 2 describes a well drilled into a nearby block,suspected of being depleted. After loosing the BHA, theoperator wanted to reduce the risk of getting stuck with anRFT and decided to use TBL to successfully obtain wirelinepressure data in the subsequent side track.Recent developments include a new type of Side Entry SubSystem to enable easy surface deployment as well asproviding a rapid easy fishing method in case the logging toolswere to get stuck during TBL operations.Compatibility with rotary steering and MWD is underdevelopment, delivering the concept of 'Through BoreDrilling', the ultimate low cost drilling system. This will allowdirectional drilling in combination with open hole logging andother operations through the bit, in a single trip.Conclusion: TBL opens up new low cost/low risk options fordata acquisition (and other through bore operations) duringwell construction. It gives both drilling and petroleumengineers new and low cost options to choose from to optimisewell construction and data acquisition. TBL is a firstsignificant step on the way to Through Bore Drilling and hasalready proven its versatility in a number of 'difficult well'cases.