Activity in the Fayetteville Shale Gas play on the northern Arkansas side of the Arkoma Basin is gaining momentum and is now rated as the second largest shale gas play in the USA. The Fayetteville prospect is attractive because the thickest part (up to 200ft) of the Mississippian reservoir is encountered at relatively shallow depths (less than 7,000ft). It is also appealing because of its large areal extent estimated at approximately 9,000 square miles. Recently, the operator completed several high-flowing gas producers in White County that highlight the prolific nature of the shale deposit.
The multiple wells required to efficiently develop the gas reserves are usually drilled from one pad. To reduce costs and hel p maintain hole verticality, the operator is drilling the surface and vertical intermediate hole sections with percussion air tools. The advantages of drilling with air as the circulating medium rather than mud are significant. Percussion drilling delivers faster penetration rates (ROP) compared to rollercone and reduces mud costs and incidence of lost circulation
Challenges in the intermediate section include potential hole deviation from vertical and lithology/formation issues. The overburden is composed of highly interbedded shale and hard and abrasive sandstone which can significantly reduce bit life. The sandstone section is responsible for dulling the hammer bit’s cutting structure, reducing its ability to accumulate additional footage while slowing ROP. Historically, the hole section has required up to four bits to reach section TD.
To extend hammer bit life and increase total footage capabilities, an innovative overlapping/adjacent gauge row layout was designed and manufactured. The new hammer bit was run with outstanding results. An engineering analysis was performed comparing the average footage drilled with the new-style bit on 73 runs to 196 runs with conventional hammer bits. Utilizing the new bit technology enabled the operator to drill approximately 58% more footage at high ROP. The increased durability has reduced the number of bits/trips required to complete the interval. The authors will give an overview of the area, outli ne application challenges and document the operator’s time and cost savings.