The Pickton Field - Review of a Successful Gas Injection Project
Authors: McGraw J.H. , Lohec R.E. 
Published: December 2007

The Pickton field Bacon Lime reservoir, with its thin section, high drilling costs, low relief, high shrinkage oil and dissolved-gas-drive producing mechanism presented a challenge to improve recovery efficiency and provided the opportunity for a reasonable margin of profit where primary operations might have ended in economic failure. Reservoir studies indicated a recovery of only 6.6 million of the 34 million STB oil in place by primary operations. Cooperation of royalty owners and operators at a time when unitization was in its infancy and its legal status was uncertain made possible an increase in recovery to 22 million bbl, including the gasoline plant products.

Introduction

The Pickton field was recognized early as a prime prospect for the application of reservoir engineering technology because of the extremely low recovery anticipated as a result of a number of unique reservoir characteristics. Of added incentive was the prospect of a large and irrevocable loss of oil if primary operations were conducted to their usual economic limit. This presented a challenge to the operating and royalty interests in the field because at that time, the late 1940's, unitization was in its infancy and many operators were concerned over the possible legal problems involved. Most cooperative ventures were directed toward reservoirs substantially depleted of their primary reserves where incentives were clearly defined. Also Article 6008b, relating to voluntary unitizations, was not passed by the Texas legislature until 1949.

History of Development

In Nov., 1944, with the completion of Humble's C. D. Nichols, initial production was obtained from the Pickton field in the East Texas basin located in the northeast corner of the state. The presence of the reservoir had first been indicated by geologic correlation of subsurface data and was later confirmed and isolated by geophysical data. Structurally, Pickton is an extremely low-relief anticline which, of itself, is not unusual for small structures in the East Texas basin. The unique feature of Pickton is the structural low relief in a field large enough to contain 34 million STB oil and to extend over an area in excess of 7,300 surface acres. It has a dip which varies between 1/2 and 1 1/2 degree as indicated by the structure map of the reservoir, Fig. 1. The producing reservoir known locally as the Bacon Lime is a usually non-productive, low porosity, calcareous, oolitic zone occurring at a depth of about 7,900 ft

The field is in the upper portion of the Rodessa member of the Lower Glen Rose formation and underlies the Massive anhydrite zone throughout a large part of the East Texas basin. The saddle-like configuration of the reservoir is shown to an exaggerated vertical scale in Fig. 2, as a northwest, southeast cross-section through the original production area and the extension of the field. The western area of the field was first developed with 57 wells being drilled. The final stage of development began after the discovery of a productive formation more than a mile to the east of the limits of production in the original development area. Until development of this extension area began 5/2 years after completion of the discovery well, and showed considerably more original oil in place, the exact producing mechanism of the field was not definitely known. The preponderance of geological data indicated dissolved-gas drive, but performance persistently exceeded predictions. Eventually the field was fully developed when a total of 166 producing wells had been drilled on 40-acre spacing, and the boundaries of production had been defined by a permeability pinchout to the north and east and by a water table at 7,425 ft subsea to the south and west.

JPT

P. 399ˆ