Abstract

The evolution of fracture stimulation design for the Red oak formation in the Arkoma Basin of Eastern Oklahoma has led to significant improvements manifested not only in greater production but in less expensive treatments. production but in less expensive treatments. Over the past 32 months, over 48 stimulations have been performed ranging from 15,000 gallons to 290,000 gallons of fluid and from 10,000 pounds to 500,000 pounds of proppant. During pounds to 500,000 pounds of proppant. During this period, improvements in fracture fluid, fracture design and treatment implementation have all led to greater success.

Introduction

Since the discovery of the Red Oak Gas Field (Figure 1) in 1960 over 100 wells have been completed to one or more of its productive horizons. Production is extremely dry gas and is mainly from three Atoka sands with the majority of reserves in the field attributed to the Red Oak sand found from roughly 6,550 to 10,050 feet. This paper will deal with the fracturing techniques used on 45 Red Oak completions from March 1986 through October 1988.

Table I summarizes the range of formation properties exhibited by the Red Oak sand in the properties exhibited by the Red Oak sand in the wells of interest. Although a number of treatments dealt with wells having permeabilities exceeding 0.5 md, 28 treatments permeabilities exceeding 0.5 md, 28 treatments designed for wells having less than 0.1 md of permeability, indicating the need for long permeability, indicating the need for long fractures to effectively drain the 320-acre areas.

This analysis will be divided into three major categories of discussion. Comparisons will be made between those treatments using gelled water only and 70 quality (percent) foamed gel which has become the more common fluid. Fracture design techniques which have become useful will also be discussed as will treatment implementation.

FRACTURING FLUID

This section compares the gelled water treatments used during the early periods of the completion program with the 65 to 70 quality carbon dioxide foamed fluids which became dominant in the latter stage of the program.

The 17 treatments which used strictly hydroxypropylguar gels (HPG) were pumped from March 1986 through December 1987. The typical HPG gel treatment used a 40-pound crosslinked gel (40 pounds of gellant per 1000 gallons of water) pounds of gellant per 1000 gallons of water) containing surfactant, bactericide, gel breaker and a 5 percent phase of diesel.

The introduction of 65 to 70 quality foamed carbon dioxide fluids occurred in July 1986 and foam became prevalent in 1987. The base gel approximates that used in the jobs having straight gel except that 50-pound loading was the most common. The higher gel concentration is required for the linear base gel to make a stable foam at the average reservoir temperature of 175 degrees F (79 degrees C). A 40-pound gel loading is only stable to 125 degrees F (52 degrees C) in a carbon dioxide foam. Again surfactants, bactericide, and breaker were added to the gel. In addition, methanol (gel stabilizer), pH buffer, and a foamer were also used to help create a stable, consistent foam.

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