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.

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.

Openhole sidetracking is most commonly applied in three drilling scenarios: 1) to drill a horizontal lateral from the main wellbore in unconventional reservoir exploration 2) to drill lateral in a multilateral well 3) to detour around a stuck fish. In most drilling operations, the risk and the economics associated with openhole sidetracking dictates that all commercially available methods and technologies be evaluated thoroughly to achieve the objective and re-establish normal drilling operations. The evaluation is more challenging in medium to hard formations or in highly deviated wells or a combination of both. Recently, the most requested application for the system has been for exploratory wells drilled in unconventional reservoir plays that are recent developments where little or no offset well data exists. In such fields there is significant risk in drilling a horizontal lateral because reservoir characteristics are not well known. The logical step therefore is to rely on the conventional methodology or on the historical experience of field engineers working the region. Traditionally, the predominant openhole sidetracking methodology started with setting a cement plug followed by a directional BHA once the cement hardens. The success of the plug setting operation depends on formation compressive strength, degree of downhole temperature/pressure, wellbore deviation, cement plug depth, quality of cement and cure time. The consequences of plug failure are extra trip time, a new cement plug, loss of drilling days and reconfiguration of drilling trajectory. A recent R&D effort has identified a new method and associated tools that can be effectively utilized to increase operational reliability in openhole sidetracking and to save costs in terms of time and materials.Single trip retrievable openhole sidetrack system: The system is designed for multilateral wells where access to the main bore is a requirement. The system is equally applicable in situations where cement plugs are ineffective such as in medium to hard formation or in highly deviated holes. No cementing operation is required.Cementing openhole system with anchor: The system is designed for unconventional reservoir exploration where the bottom hole is required to be plugged with cement once the pay zone has been identified and kick-off point for a lateral is confirmed. With the anchor firmly holding the system in place, the operator does not have to wait until the cement is fully cured. The solid ramp encased in the cement is used for sidetracking.Cementing openhole system without anchor. This system is designed for wells where there is a hard bottom available. The cement holds the system firmly at the bottom while a solid ramp encased in the cement is used for sidetracking purpose. The paper discusses mechanical and operational features of above system along with their respective field performances. The paper will also describe challenges faced in field runs, how those were overcome, the lesson learned and potential system modifications.

Openhole sidetracking is most commonly applied in three drilling scenarios: 1) to drill a horizontal lateral from the main wellbore in unconventional reservoir exploration 2) to drill lateral in a multilateral well 3) to detour around a stuck fish. In most drilling operations, the risk and the economics associated with openhole sidetracking dictates that all commercially available methods and technologies be evaluated thoroughly to achieve the objective and re-establish normal drilling operations. The evaluation is more challenging in medium to hard formations or in highly deviated wells or a combination of both. Recently, the most requested application for the system has been for exploratory wells drilled in unconventional reservoir plays that are recent developments where little or no offset well data exists. In such fields there is significant risk in drilling a horizontal lateral because reservoir characteristics are not well known. The logical step therefore is to rely on the conventional methodology or on the historical experience of field engineers working the region. Traditionally, the predominant openhole sidetracking methodology started with setting a cement plug followed by a directional BHA once the cement hardens. The success of the plug setting operation depends on formation compressive strength, degree of downhole temperature/pressure, wellbore deviation, cement plug depth, quality of cement and cure time. The consequences of plug failure are extra trip time, a new cement plug, loss of drilling days and reconfiguration of drilling trajectory. A recent R&D effort has identified a new method and associated tools that can be effectively utilized to increase operational reliability in openhole sidetracking and to save costs in terms of time and materials. Single trip retrievable openhole sidetrack system:The system is designed for multilateral wells where access to the main bore is a requirement. The system is equally applicable in situations where cement plugs are ineffective such as in medium to hard formation or in highly deviated holes. No cementing operation is required.Cementing openhole system with anchor:The system is designed for unconventional reservoir exploration where the bottom hole is required to be plugged with cement once the pay zone has been identified and kick-off point for a lateral is confirmed. With the anchor firmly holding the system in place, the operator does not have to wait until the cement is fully cured. The solid ramp encased in the cement is used for sidetracking.Cementing openhole system without anchor.This system is designed for wells where there is a hard bottom available. The cement holds the system firmly at the bottom while a solid ramp encased in the cement is used for sidetracking purpose. The paper discusses mechanical and operational features of above system along with their respective field performances. The paper will also describe challenges faced in field runs, how those were overcome, the lesson learned and potential system modifications.

Conventional wellbore departure and drilling systems generally require the operator to make multiple downhole trips to achieve a specific objective. For example, a window milling bottom hole assembly (BHA) is run in hole to create an exit path in the existing casing and drill sufficient rathole for the next drilling assembly. In the subsequent trip, a directional drilling BHA is run to extend the rathole and drill laterally to the target. The industry requires an economical solution to accomplish the above objective in a single trip with good downhole dynamics control and overall BHA drillability. The re-entry system should be able to mill a window in the existing casing sufficiently large enough for obstruction free entry of the BHA and new liners. Once the BHA has exited the casing, the new system would be required to drill a full gauge lateral wellbore to the target with good directional control and minimal vibration. To solve the challenge engineers analyzed several key technological/operational issues including: Dynamic simulation of the BHA to study the nature and magnitude of the vibrationsControlling vibrations and feed rate to reduce premature cutter damage during window milling operationsUtilizing the latest force balance software for selection of shapes, sizes, number and location of cutters for maximizing on-bottom timeExplored hybrid cutting structures on bit/mill to maintain gaugeCombined knowledge and experience of subject matter experts (SME) from different engineering and operational groups within the organization including directional/geosteering personnel, fishing/remedial group and drill bit design team The evolution of the system and the associated technology occurred in three phases over several years. In all phases a window was milled in the existing casing and a lateral was drilled to various depths. During the first phase the system was run on a conventional rotary BHA in soft and medium formations. The second phase included testing on a positive displacement motor with bent sub or bent housing. The third phase, which is currently under extensive full-scale yard testing, includes a push-the-bit type rotary steerable system. The results obtained from all three phases indicate that a functional single-trip system for milling a window and drilling a lateral borehole is commercially feasible. The versatile system will contribute substantially to the technology required to efficiently and economically mill a window in the existing casing and then drill an extended length lateral wellbore to the target formation without tripping for equipment/bit change out. The wellbore departure and drilling system, which will be optimized with a sophisticated dynamic analysis software program, will incorporate the rate of penetration and footage benefits of polycrystalline diamond compacts (PDC) bit technology combined with the latest directional drilling tools. The paper will include field run details of phase one/two as wells as results of ongoing full-scale yard tests along with key observations and conclusions. The authors will also include an overview of the software used for analysis and plans/capabilities of the final version of the system.