The typical gas wells drilled in heavily explored Panola County of East Texas encounter the highly abrasive Travis Peak and Cotton Valley formations at around 6,300 ft. The Travis Peak is normally reached at 6.300 - 6.500 ft, followed by the Cotton Valley from 8,000-8,300 ft to TD. The Travis Peak and Cotton Valley are each about 1,700-2,000 ft in length. Until recently, the extremely abrasive sections in these formations severely limited the life of the IADC Class 537 through 737 roller cone bits used to drill these wells. Between severe gauge and cutting structure wear, the bits run previously were normally pulled after about 600 ft of drilling. The shortened life meant six to 10 bits were required to complete the two intervals. This paper describes the design and application of new hard formation rock bits that are drilling up to 50% more footage than the 627 and 737 types run previously. The new IADC Class 647 and 747 roller cone bits incorporate new insert geometries and quantities. along with improved carbide grades and diamond-enhanced gauge protection. Today, the Travis Peak and Cotton Valley are being drilled with four bits, averaging more than 850 ft per bit. Along with the new bits, a revised mud program consisting of low-solid polymers contributed to the improved performance realized in recent Panola County wells. The authors will review the design process of the new bits. as well as presenting case studies of typical Travis Peak and Cotton Valley wells in Panola County and elsewhere in East Texas. Introduction The East Texas field was discovered in 1930 with the Joiner-Daisey oil well, Drilling had focused primarily on the shallower and highly productive oil bearing formations. While gas wells have been producing from the Travis Peak for more than 50 years, and gas sands were discovered in the Cotton Valley in 1937, it was not until 1968 that the first producing Cotton Valley gas well came on stream in Panola County. The Natural Gas Policy Act of 1978 and the Federal Energy Regulatory Commission's (FERC) tight gas sand policy of 1980 spawned interest in the gas reserves of the Travis Peak and Cotton Valley. Today, the focus of East Texas exploration is the marginal gas reserves. Fig. 1 outlines the East Texas area where most of the gas drilling takes place. Stratagraphically, the lower Cretaceous Travis Peak comprises fine-grained to very fine-grained sandstones, muddy sandstones and sandy mudstones The sandstones are highly cemented and consist primarily of quartz with quartz cementation. Owing to the extremely cemented nature of Travis Peak sandstones, as confirmed in laboratory tests, the rock fails by fracturing the individual quartzitic sand particles, which accounts for the extremely abrasive nature of the formation. P. 595
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