The oil and gas fields in the Orenburg region are some of the oldest and largest in Russia. Drilling through carbonates with low mud flow rates is common in this region along with the associated challenges that these conditions present to polycrystalline diamond compact (PDC) drilling. This paper details how these conditions and others, were addressed as part of the design process culminating in a novel bit design with appreciably higher penetration rates and associated cost savings.
Having encountered a series of unusual dull conditions on PDC bits run in Orenburg, a systematic design approach was adopted in order to solve a series of specific regional issues resulting in new design features which lend themselves to other applications worldwide.
The team established that the best practice for drilling a particular vertical section in this region was to use a bent motor due to experiences of uncontrolled deviation close to total depth (TD). The objective was therefore not only to take into consideration the carbonate formation and flow rate issues, but also to establish the effect of the bent housing on PDC bits in order to improve the bit condition and overall performance.
Subsequent 3D CAD modeling and analytical studies enabled a common approach design solution for both bent housing and carbonate type applications. These studies, together with Computational Fluid Dynamics (CFD) analyses, enabled new innovative design features to be introduced into the bit to address hydraulics, formation and eccentric bit rotation. These new features resulted in far superior drilling performance and dull characteristics, which ultimately led to record runs being achieved in the region over a 1200m section of predominantly carbonate, inter-bedded formation.
The features would also prove to be transparent to the drilling contractor should they be running a bit on a straight or bent housing motor with low or high flow rates, thus acting to enhance the existing drilling practices in the region.