N. J. Chittim Pilot Waterflood Successful Test Flood of Low Permeability Taylor Age Sands
Authors: Gleeson C.W. , Levine J. 
Published: December 2007

The San Miguel-1 sand in the Sacatosa field is in a low permeability formation and was considered noncommercial. Hydraulic fracturing and waterflooding have turned it into a profitable operation with an anticipated secondary recovery equaling the primary, and a projected life of over 35 years.

Introduction

While conducting a geological investigation of the Chittim Arch anticlinal structure in 1956, Continental Oil Co. discovered the Sacatosa (San Miguel-1) field. It is located in Maverick County, Tex., near the Dimmit and Zavala County lines (see Fig. 1). When the drilling program was completed in the fall of 1968, there were program was completed in the fall of 1968, there were approximately 670 active wells in the field. The field has an areal extent of 11,500 acres, of which 11,000 acres are located on Continental Oil Co.'s N. J. Chittim lease. At first, the field was considered noncommercial. The potential of the discovery well was only 4 BOPD. After stimulation with nitroglycerin, production was increased to 8 BOPD. This low productivity led to an intensive study to determine if the San Miguel-1 could be commercially produced by the use of newer stimulation techniques.

Hydraulic fracturing was tried on two wells drilled during 1957. One well was fractured with 22,500 lb of sand in 16,590 gal of diesel oil; the potential, pumping, was 19 BOPD. The well was later refractured pumping, was 19 BOPD. The well was later refractured with 75,000 lb of sand and 51,240 gal of diesel oil. Following this fracture treatment, the potential, flowing, was 60 BOPD on a 11/64-in. choke. The second well was fractured with 90,000 lb of sand and 67,000 gal of diesel oil and flowed at a rate of 58 BOPD on an 8/64-in. choke. The performance of these three wells was studied to evaluate the feasibility of further development.

These studies indicated that the field could be commercially developed. A development program was begun in 1958 and, prior to the waterflood expansion in the Fall of 1967, a total of 483 production wells had been drilled and completed by Continental Oil Co. in the San Miguel-1 sand.

Geology

The San Miguel-1 sand is a member of the Upper Taylor formation in the Gulf series of the Cretaceous system of Mesozoic age. The Chittim Arch is the controlling geological structure in the Southwest Gulf Coast area. The San Miguel-1 sand pinches out or shales out updip against the flank of this structure, creating stratigraphic traps for oil accumulations. Sacatosa (San Miguel-1) field is the largest of a number of oil and gas fields that resulted from entrapment of hydrocarbons against the arch.

The Sacatosa (San Miguel-1) field is the result of shale-outs or permeability barriers on the south, west and north sides of the field. (See Fig. 2.) An oil-water contact has been established on the east and southeast sides, but it does not appear to be an active drive mechanism.

Minor faulting occurs across the field, which is of importance in only one instance: a fault closure has caused a gas cap to form and two wells have been shut in due to high GOR.

The sands were deposited initially as a beach of an old ocean.

JPT

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