The paper describes the improvement in drilling efficiency obtained in five mature North Sea fields, by using a systems approach. The drilling program was managed by a drilling efficiency group consisting of a service company, drilling contractor and operator engineers drawn from several disciplines. All of the well sections were geometrically complex. Data was gathered using downhole pressure and vibration sensors, and acoustic caliper sensors.
MWD annular pressure measurements had shown that conventional steerable motor/bit combinations required extensive circulation and occasional back reaming to ensure adequate hole cleaning. MWD vibration measurements and BHA modeling had proved that particularly high levels of vibration were caused by both circulating and back reaming. This was directly associated with MWD, motor and other downhole tool failures. It was concluded that the basic problem was hole quality and attention was directed to eliminating hole spiraling deduced from MWD logs and calipers.
A new combination of compatible steerable PDM and long gauge bit was designed with input from the operator. This was designed to achieve improved hole quality from long gauge bits without losing the rapid deviation response of conventional motor/bit combinations. The aim was to improve overall drilling system efficiency, particularly poor hole cleaning, excessive torque and drag, and slow ROP when sliding.
The paper discusses the initial data gathering and diagnosis and how measurement and modeling of downhole conditions led to the optimal solution. Comparison between 8 conventionally drilled hole sections and 8 hole sections drilled utilising the new drilling system showed more than 50% reduction in overall drilling time. Significant time savings have been made when drilling in the orientated mode. Other benefits are reduced drilling WOB from 30,000 lb to 3,000 lb, reduced drilling torque and drag, and an overall improvement in hole quality reflected by improved hole cleaning.