Polycrystalline Diamond Compact Bit Proves Effective at South Graham Deese Sand Unit
Authors: Preslar P.L. 
Published: December 2007

In the past 2 years, polycrystalline diamond compact (PDC) bits have gained acceptance in the U.S. with many spot applications in soft to medium-hard formations. PDC bits were chosen by Tenneco's Mid-Continent Div. Drilling Dept. to be used at its South Graham Deese Sand Unit (SGDSU) in southern Oklahoma. Drilling in the field is complicated by a plunging anticline that has caused deviations of more than 20 degrees. Previous wells were drilled in 24 days, excluding completion time, using conventional rotary bits and applying light bit weight to control deviation. By using a PDC bit, similar wells can be drilled in as little as 10 days.

Introduction

The oil industry is going through some very unstable times compared to just 2 years ago. Inflation in the 1981 and 1982 boom years, along with declining oil prices, have caused companies now, more than ever, to reduce their overall cost per foot (CPF) when exploring for hydrocarbons. One method Tenneco has found effective is the use of PDC bits to improve rate of penetration (ROP). Since the development of the Stratapax drill blanks by General Electric Corp. in the early 1970's. PDC bits have made steady advances in the drilling industry. The performance of PDC bits are well documented in the North Sea, Arabian Gulf, and many other areas where rig cost can still be as high as $60,000/D. This paper presents specific applications of PDC bits in Tenneco Oil's SGDSU. The first step in determining if PDC bits could be used was to study logs and offset bit records over the interval to be drilled. The Graham Deese field has 16 productive sands connected by long homogeneous shale sections that seemed ideal for PDC use. The first runs of PDC bits in the field proved that placement of the bit in formations that were either too hard or abrasive proved detrimental to the bit's life. Subsequent runs were more economical because bits were properly placed in the right intervals. Also, PDC use is favored because the smaller rigs used in southern Oklahoma do not have the pump pressure requirements to run downhole motors, which have been used to solve some of the slow ROP's caused by low bit weights with conventional roller cone bits. By using light bit weights with high rpm's, the PDC bit performed better than any previous drilling procedure used at SGDSU, resulting in time and money saved.

Field History

The South Graham Deese field is located in Carter county, approximately 100 mi [161 km] south of Oklahoma City. The field is situated from Sec. 31-T2S-R2W to Sec. 22-T3S-R2W in the Fox-Graham-Wheeler trend, which is part of the Ardmore basin (Fig. 1). It is one of a series of Pennsylvanian anticlines that are productive in this area. The discovery well for the South Graham field was drilled in 1917 near an oil seep at the surface. By 1967, the field comprised 416 total wells-381 producers and 35 dry holes. In Feb. 1969, APCO Oil Co. unitized the area shown in Fig. 1 and began secondary recovery by a line drive water injection flood pattern on 10-acre [40 468-m ] tracts. Before unitization, the area had produced 18.9 million bbl [3x10 M ] oil with minimal water production. As of late 1982, 20 new infill wells have been drilled to recover oil beneath subsurface locations that had been bypassed because of severe deviation problems. The initial potential from these 20 wells totaled 1,750 B/D [278 m /d] oil and 2,454 B/D [390 M /d] water. It is estimated that 9 million bbl [1.4 × 10 M ] oil in place are still recoverable.

Geology

The Graham anticline along the SGDSU is a northwest-southeast-trending, thrusted, asymmetrical anticlinal fold with steep dip on both flanks (Fig. 2). The Deese group is composed of interbedded, fine-grained sands and soft to medium-hard. gray, fissile shales, which were deposited in a shallow marine environment. Deposition and structural growth were contemporaneous; therefore, the formations are thinner over the crest of the structure and thicker on the flanks. The productive zones in the unit area have been divided into 16 separate Deese sands ranging in depth from 1,850 to 7.600 ft [564.9 to 2316.5 m]. They are Lower Fusulinid (1 through 6), Upper Tussy (1 through 4), Lower Tussy (1 and 2), Upper and Lower Carpenter. Morris, and Dornick Hill. These sands are shown on the composite type log of the field (Fig. 3). Deviation begins drastically from 1.000 to 1,200 ft [3 .8 to 365.8 m] deep. This interval is where an angular unconformity between Permian Age rocks and older Pennsylvanian rocks occurs.

JPT

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