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EQT Production has implemented a new technique for drilling horizontal wells in the hard formations of the Appalachian Basin.Air percussion drilling has been adopted for use horizontally in the Berea sandstone, a hard and abrasive sandstone reservoir that had been traditionally drilled with roller cone bits. The evolution of the technology started with a packed-hole assembly that was trialed on three wells using stabilizer placement to provide directional control in the horizontal. The results were promising as penetration rates increased, but many trips were required to keep the wellbore in the desired target zone. To improve directional control, a percussion BHA with a bent housing positive displacement motor (PDM) was implemented. The introduction of the positive displacement motor with the air hammer produced the same penetration rates seen in the packed-hole assembly while providing the directional control needed. Since mid 2009, the PDM percussion assembly has become the standard practice for drilling Berea horizontal wells, replacing the roller cone BHA. Through June 2010, over 40 wells have been drilled using the assembly. The lateral portion for a majority of the wells is now drilled in one run, reducing total drilling time from 22 to 13 days, dry hole costs by over one half and total well costs by about one third.

In Figure 1 the results of the evaporation test for lignite creosote specimen I are compared with results of a similar test done by Vaughan (12) on coal-tar creosote. The purpose of these tests was to obtain some idea of the probable permanence of the preservative.

This paper presents the first use of a Rotary Steerable System (RSS) using air as the drilling fluid. The case history is in an ongoing unconventional gas development in the Appalachian Basin of the northeast United States. The RSS has been integral to increasing lateral lengths and corresponding increases in production while reducing development costs. Since 2006, EQT Production has developed Devonian reservoirs in Kentucky, Virginia and West Virginia using underbalanced, horizontal drilling techniques. The low (200-500 psi) bottom hole reservoir pressure does not allow drilling with fluid. Typical horizontal wells have had 3,000 ft laterals drilled with air, positive displacement motors, and electromagnetic telemetry (EM) MWD systems; that remains the predominate drilling technique. The air compatible RSS was employed to increase lateral length and production. Well 568478, in Letcher County, Kentucky became the first well to have a horizontal section drilled underbalanced using RSS with dry air. To date, eight wells have been drilled with lateral lengths from 3,800 -6,000 ft. Preliminary results show that the reserves developed are proportional to the lateral length drilled. The rates of penetration (ROP) with the RSS in the additional footage were similar to or greater than those in shorter laterals drilled with a motor. The RSS, with an integral EM MWD, has proven to be a technically feasible option in air drilling environments. The comparable ROP and resulting lower lateral costs per foot achieved with the RSS allows drilling horizontal wells with air beyond their previous limits, enabling greater production footage from fewer wellbores. It further allows drilling portions of the reservoir previously unreachable due to surface constraints such as topography. Many of the learnings to implement the RSS technology also applied to the use of the positive displacement motors (PDMs) previously used. These learnings were applied to the motors and significant improvements were made in drilling horizontals with these tools. Motor capability was pushed beyond limits previously established in the areas being drilled. As a result of the success with RSS and PDMs on extended laterals, EQT Production is extending the lateral length from 3,000 ft to 5,500 -7,000 ft on a plurality of the future wells drilled in the Devonian section.