Abstract

A case history of the drilling practices on southwestern Pennsylvania practices on southwestern Pennsylvania Oriskany wells demonstrates how the use of diamond-enhanced hammer bits have reduced costs per foot and directional control problems. problems.

INTRODUCE

The Oriskany formation in southwestern Pennsylvania has been one of the more Pennsylvania has been one of the more actively drilled plays in the northern Appalachian basin in recent years. These wells are drilled in the complex geology of the Allegheny High Plateau. The drilling prospects are located in narrow fault blocks that are identified using seismic. Many of these features are one or two well fields. Deviation must be controlled to intersect these targets. Wells are usually located on seismic shot points at the highest point on the points at the highest point on the structure. Deviation must be controlled to intersect these features. Uncontrolled deviation from vertical could cause the wellbore to miss the fault block completely or to intersect the reservoir down dip. Down dip wells usually exhibit higher water saturations and lower permeability. Faults and steeply dipping permeability. Faults and steeply dipping beds will be encountered in most boreholes.

Air drilling is used in this area as it is in most of the Appalachian basin. Roller cone bits and standard air rotary drilling techniques have been used in this area. When deviation has been a problem, pendulum assemblies, low problem, pendulum assemblies, low weight-on-bit (WOB), and high rotary speeds have been used to drill. This reduces rate of penetration (ROP) and increases cost per penetration (ROP) and increases cost per foot. If these measures fail to correct the borehole's trajectory, motor runs on air or fluid have been used to turn the borehole. This procedure greatly increases costs.

Various pneumatic hammer and bit combinations have been tried since the late seventies to correct deviation problems. Hammer drilling, in conjunction problems. Hammer drilling, in conjunction with low WOB and pendulum assemblies, will drill extremely vertical well bores but costs per foot were still high due to short bit life. industrial "flat bottomed" bits with tungsten carbide inserts were limited by wear on the inserts and particularly the gauge buttons. This limited their use to short bit runs to correct the wellbore back to vertical or to drilling through known intervals of severe deviation control. Recently, diamond-enhanced hammer bits have been able to significantly increase bit life and ROP and have reduced cost per foot (Ref. 1) while reducing deviation from vertical (Ref. 2).

This paper is a case history of five Oriskany wells drilled in one area and a comparison of costs per foot and directional control for conventional air rotary and air hammer drilling utilizing polycrystalline diamond-enhanced bits. polycrystalline diamond-enhanced bits. P. 271

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