Since the mid nineteenth century, over 500,000 wells have been drilled in the Appalachian Basin. While many of these wells have been plugged and abandoned, approximately 185,000 wells are still active producers. A majority of these active wells were drilled during the last ten years at depths averaging approximately 3,200 ft [975.4 m]. The recent decrease in oil and gas prices has made it increasingly difficult for producers to justify new shallow drilling programs. There are, however, deeper programs. There are, however, deeper productive horizons in many existing productive horizons in many existing wells that have remained untapped. A number of unique procedures have been developed which allows the deepening, economically. of existing wells through existing casing as small as 4-1/2 in [114 mm].
The use of improved "slimhole" drilling techniques to deepen existing wells has proved to be an economically viable method of recovering additional reserves, The economics associated with this procedure are, in most cases, more attractive than that for a new well. In addition, this procedure can extend the productive life procedure can extend the productive life of wells which may currently be no longer commercial. There are a number of advantages inherent to deepening existing wells which include:
* No additional title and surveyexpense
* Higher success rate by drilling in proven fields
* Current well depth is "free"
* Surface production equipment and gathering lines are already inplace
* Hydrocarbon purchase agreements are already in place
* Current production can usually flow after deepening is completed
* Finding costs are, in most cases, lower than a new well
* Plugging liabilities are postponed
* Costs associated with drilling and completing the deeper formation qualify for appropriate tax benefits, i.e. intangible drilling costs are deductible
The actual deepening procedure involves the drilling of a new hole through the existing 4-1/2 in (114 mm) casing (minimum size worked). Briefly stated, the existing well bore is first cleaned via sand pumping, bailing, etc. The latchdown baffle and shoe are then drilled out, if required.