Abstract

As gas is injected into or withdrawn from a reservoir in the aquifer, changes in pressure or in head occur in the water beneath and around the gas storage bubbles. These changes in pressure, or in head cause flow that is partly pressure, or in head cause flow that is partly controlled by the permeability of the reservoir rock, the compressibility of the water-saturated reservoir rock, and partly by gravitational effects. From this flow, formation behavior can be predicted during the injection and withdrawal season.

Introduction

The Red Field Underground Storage Field is located approximately 32 miles west of Des Moines, Iowa. In 1953 Northern Natural Gas Co. proposed a study of this area. After two years, with exploratory wells and seismic surveys, the existance of anticlinal structure was verified (Fig.1). This structure is some 7 miles by 4 miles in size and contains two sandstones aquifers suitable for gas storage development - the St. Peter and the Mt. Simon formation, with a thickness of 35 feet and 100 feet respectively.

Gas injection started in 1957 and the first seasonal withdrawal occurred in the winter 1959–60. In 1967 Redfield reached the proposed Federal Power Commission capacity of 120 BCF; 70 BCF into Mt. Simon formation, and 50 BCF into St. Peter formation.

This paper will deal with the Mt. Simon and the St. Peter reservoir system for injection and withdrawal season.

THEORY

How does water flow in the reservoir around and beneath the storage bubbles as gas is seasonally injected and withdrawn? How is water displaced by gas? How does the storage gas bubbles behave in such an aquifer? All these questions could be solved in a successful operation if the water movement is controlled. Therefore, it is necessary to understand what occurs in the reservoir in order to achieve these goals. It is necessary to determine what measurements are obtainable, and then predict how these variables are influenced by the predict how these variables are influenced by the movements of fluids within the reservoir. These variables are influenced by the movements of fluids within the reservoir. These variables include static bottom-hole pressure, static well-head pressure, water levels, temperature, and gas pressure, water levels, temperature, and gas injection and withdrawal rate.

At the beginning of the injection and withdrawal season, Reynold's number becomes nearly insignificant. Therefore, the flow is Laminar and the highest velocity and the lowest pressure in the pipe is at the perforation zones.

In some cases Reynolds number may be enormous, many millions, and no turbulance will exist because of the presence of some other influence like rotation, density stratification, or for conducting fluids, magnetic fields.

These buoyancy effects are easiest to understand. If the fluid at the bottom of the perforation zone is less dense than that at the top of the perforation zone, convective activity sets in and can greatly increase the turbulance present - or even prod turbulance when none would otherwise exist. On the otherhand, if the fluid on the top of the perforation zone is less dense, turbulance is inhibited, because the buoyance effect operates in the other directions and take energy out of the turbulance.

Hence injection and withdrawal should start with a Laminar flow rate building up to a turbulant flow rate regardless of the turbulance at the perforation zone (if any).

In the study of formation behavior in a homogeneous Isotropic medium, pressure at the datum level has been calculated and used for plotting the flow.

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