Drilling the Severnaya Truba field in Aktobe, Kazakhstan, has been costly and time consuming. In combination with a drilling-fluid-powered percussion hammer (FPPH), a fit-for-application polycrystalline-diamond-compact (PDC) bit with depth-of-cut (DOC) -control features was used to minimize the exposure of the cutting structure and prevent breakage. The mechanical lifting and falling action creates a rapid variation in weight on bit (WOB), allowing the bit’s DOC to fluctuate while overcoming different stresses. These variations, along with the percussion pulse created with each stroke, led to increased rates of penetration (ROPs).
Drilling with an air hammer is a technique whereby gases (typically compressed air or nitrogen) are used to operate a pneumatic hammer, to cool the drill bit, and to lift cuttings out of the wellbore. Air forced down the drillstring actuates the percussion tool, which, in turn, creates an axial percussion force directed down to a specially designed drill bit.
The advantages of air drilling are that it is usually much faster than using drilling fluid and may eliminate lost-circulation problems. The disadvantages are the inability to control the influx of formation fluids into the wellbore and the destabilization of the borehole wall in the absence of wellbore pressure typically provided by the mud column. Air hammers are also limited to a lower WOB and will stop working if that weight is exceeded.
An FPPH is the next step in performance drilling. Using the same flow rates and operating WOB of a conventional assembly, the tool offers the benefit of an axial percussion force to facilitate the cutting action of the bit. Like an air hammer, the axial percussion force is generated near the bit to give the cutting structure more energy and overcome the formation’s compressive strength....
Hydraulic Percussion Drilling System Boosts Rate of Penetration, Lowers Cost
15 November 2015