One of the biggest ongoing challenges to the successful production of many natural gas reserves is the ability to improve drilling efficiency. In many of these applications, in order to drill the interval safely, it is necessary to drill through gas producing formations using high mud weight. As is well known in the industry, drilling with high mud weight poses significant challenges to drilling efficiency. Generally speaking, high mud weight equates to high solids content in the mud, and slow ROP for the drill bit, which means high hours to drill the section and frequent bit trips. Further to that, high hours and high solids equate to wear and erosion problems with bits and downhole equipment, leading to higher costs.
A new line of steel bodied drill bits has recently been introduced that has shown dramatic improvements in drilling efficiency in Western Canadian foothills natural gas applications. The hydraulic configuration (blade shape & height, void volume, junk slot area, nozzle orientation and TFA flexibility) of the drill bit is of paramount importance in applications with high mud weight. Bit balling is very common in these types of applications, and is very detrimental to drilling efficiency. The ability to utilize a steel body, and to protect it from the typical erosion and wear that is seen in high solid environments, is critical to maximizing hydraulic performance.
The new technology developed for these drill bits allows higher ROP in high mud weight applications, increased mechanical efficiency during the drilling process, and greatly enhanced wear / erosion resistance. Runs have been recorded in intervals with = 1750 kg/m3 mud weight and > 85 cP viscosity showing dramatic increases in ROP, with absolutely no erosive wear to the body of the bit, even after drilling for ~ 160 hours. This significant increase in ROP is a major breakthrough as less time spent in the hole means less wear and erosion on all downhole components.
Introduction
In one particular gas play in Western Canada, the Hinton field, drilling performance has been greatly hampered by the necessity to drill with high MW through highly interbedded formations. The Hinton field is located alongside the Canadian Rocky Mountains, approximately 290 kilometers straight west of Edmonton, Alberta, Canada and has a reputation of being a very challenging area for drilling. High bottom hole pressures, steep formation dip angles, hole instability, hard abrasive sandstone and siltstone formations and unpredictable and highly transitional / faulted formation layers are common. The application of study starts off after the 222mm intermediate hole section is completed and cased at an approximate depth of 3000m. The 156mm (6–1/8") main hole section is approximately 600m in length (approximately 3000m to 3600m), and is drilled utilizing an oil based mud system and a bent housing BHA (primarily to maintain verticality). Bottom hole pressures can frequently exceed 60,000 kPa and the interval is very faulted, with inconsistent transition layers of shale, sand, silt and coal seams with compressive strengths varying between 10000psi – 25000psi. The 156mm interval starts off in the Dunvegan, and drills down through the Shaftesbury, Base Fish Scales, Peace Rivier, and finishes in the Mannville.
