TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractThis paper discusses the planning and drilling of Big Prize #2-20 well, drilled by BP America in South Panola Field of the Arkoma Basin in Oklahoma. Wells previously drilled in the field have been prone to problems with lost circulation and stuck pipe, high drillstring torque and drag, low ROP, and directional control. The primary causes of these problems are the hard and fractured formations, steeply dipping formation beds, and small geologic targets. To reduce drilling time and cost, major changes were made to standard drilling practices in the area. The major changes were contracting a state-ofthe-art land rig, modifying the drilling fluids program and surface treatment, using steerable motors from surface to total depth (TD), replacing mud-pulse MWD with electromagnetic (EM) MWD for the first time in the field, and employing premium drill bits. The result was substantial reduction of drilling time and cost. The Big Prize #2-20 well was drilled to a TD of 15,850 ft measured depth (MD) in 70 days compared to 96 days for the offset well drilled on the same pad to a similar depth, which represented an improvement of 26 %.

This paper discusses changes in horizontal drilling practices that have proven to increase production rates, improve return on investment and provide better reservoir drainage for the Hunton formation in various fields in Lincoln County, Oklahoma.An area summary comparison of past and present is included to support the benefit of drilling horizontal wells. Development of the Hunton formation for dewatering purposes began in about 1996 in this field.Wells drilled in the early life of the project were all vertical wells and resulted in a wide range of initial rates.The field has been developed on 160-acre drilling and spacing units.However, due to low permeability in some areas and apparent vertical fracturing, increased density wells have been drilled in most cases to more effectively drain the reservoir. Horizontal drilling was first attempted in 2000.There are several theories on the primary mechanism of production1 from the Hunton formation, but the most common thought is that the reservoir contains matrix porosity and highly conductive pathways combined with vertical fracturing.The process of dewatering the reservoir allows the hydrocarbons to drain into these pathways and break out of the water to be produced. The Hunton reservoir is under-pressured and is known to be subject to severe lost circulation intervals during horizontal drilling.The problems associated with lost circulation and directional drilling tools has resulted in early termination of many horizontal projects.Standard mud pulse MWD equipment is severely limited in its ability to function during times of lost circulation.Clear pulse signals cannot be returned to the surface and the amount of lost circulation material that can be used is limited as well.In addition, there is an increased risk of losing drilling tools during times of lost circulation that might cause an operator to call TD prior to the intended target.Altex Resources has been an active operator in this area since 1989 and through joint use of improved drilling practices, application of new technology, drilling team cooperation and EM-MWD telemetry has made significant improvements in the success of horizontal drilling projects.The results of these efforts have been to change the primary development methods from vertical drilling to horizontal drilling for hydrocarbon recovery from these fields. The process changes described within the paper could be applied to other fields where similar formations are drilled.The end result could be recovery and production of more hydrocarbons per well reducing the time to reach payout and increasing the return on the capital investments. Area Geology The Hunton formation is Devonian-Silurian in age but in this area is comprised of Silurian age rocks primarily within the Chimney Hill Subgroup.This Subgroup is made up of the Clarita, Cochrane and Keel formations. The Hunton was deposited within an intra-continental basin in a relatively stable period of time where carbonate sediments were deposited in calm, fairly shallow shelf environments.Episodic cycles of deposition, erosion and local fluctuations in sea level led to many disconformities within the Hunton.During late Devonian time the Hunton strata was tilted and exposed to sub aerial erosion.This affected the Carney area where most of the younger (Devonian) sediments were removed by erosion and exposed the remaining Chimney Hill section.Secondary dolomitization occurred along joints, fractures, and faults where meteoric waters migrated along these pathways. The two dominant reservoirs within this area are again the Clarita (primarily dolomitic limestone) and the Cochrane (comprised of mainly low porosity, fractured, vuggy fossiliferous limestone.