Criteria For Displacement Of Oil Reservoirs: Gas Versus Water Injection

Description

ABSTRACT

Water and gas injection are two widely used improved oil recovery techniques that can be applied individually or combined as water alternating gas (WAG) or simultaneous gas and water (SWAG) injection. To do reservoir development planning, for possible implementation of these oil recovery schemes, reliable reservoir performance prediction is needed. Most of the existing reservoir simulators are unable to adequately account for all the complex multi-phase and multi-physics processes involved in these oil recovery techniques. That is particularly the case under mixed-wet and low gas-oil IFT (near-miscible) conditions. Performing reliable laboratory experiments is the key to evaluating the performance of these oil recovery techniques under reservoir conditions.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWELDGEMENT

ABSTRACT

CHAPTER ONE

• INTRODUCTION
• SIGNIFICANCE OF OIL RECOVERY
• ECONOMIC COSTS AND BENEFITS OF THE STUDY
• BENEFITS OF WATER INJECTION
• LIMITATIONS OF WATER INJECTION TECHNOLOGY
• APPLICATION IMMISCIBLE GAS INJECTION

CHAPTER TWO

LITERATURE REVIEW

• HISTORICAL BACKGROUND OF WATERFLOODING
• REVIEW OF GAS INJECTION
• REVIEW OF MECHANISMS OF MEOR
• REVIEW OF WATERFLOOD DESIG

CHAPTER THREE

METHODOLOGY

• WATER INJECTION (OIL PRODUCTION)
• SOURCES OF INJECTED WATER
• HOW WATER INJECTION WORKS
• WATERFLOODING
• WATERFLOODING CONSIDERATIONS
• RESERVOIR GEOLOGY CONSIDERATION
• WATER INJECTION FOR SECONDARY RECOVERY
• GAS INJECTION IN OIL RESERVOIRS
• GAS INJECTION WORKING PRINCIPLE
• GAS INJECTION, GAS LIFT & GAS MISCIBLE PROCESS
• CHAPTER FIVE

5.1     CONCLUSIONS

5.2     SUMMARY

5.3     REFERENCES

CHAPTER ONE

1.1                                                        INTRODUCTION

Enhanced oil recovery (abbreviated EOR) is the implementation of various techniques for increasing the amount of crude oil that can be extracted from an oil field. Enhanced oil recovery is also called improved oil recovery or tertiary recovery (as opposed to primary and secondary recovery). According to the US Department of Energy, there are four primary techniques for EOR: thermal recovery, gas injection, water and chemical injection, but in this work we are going to focus on gas and water injection. Sometimes the term quaternary recovery is used to refer to more advanced, speculative, EOR techniques. Using EOR, 30 to 60 percent, or more, of the reservoir’s original oil can be extracted, compared with 20 to 40 percent using primary and secondary recovery.

Discoveries of new reservoirs, is a high-risk business that companies undertake hoping to achieve a correspondingly high return. Sometimes they are successful but more often they are not. In many cases, increasing the recovery of oil from existing reservoirs can be less expensive than exploration and less risky as well. The reservoir will have already been partially developed therefore wells and surface production facilities are already in place.

1.2                                        SIGNIFICANCE OF OIL RECOVERY

Oil Recovery Factor: also called overall hydrocarbon displacement efficiency, the volume of hydrocarbon displaced divided by the volume of hydrocarbon in place at the start of the process measured at the same conditions of pressure and temperature.

Where,

E_v= macroscopic (volumetric) displacement efficiency; and

E_D= microscopic (volumetric) hydrocarbon displacement efficiency.

1.3                         ECONOMIC COSTS AND BENEFITS OF THE STUDY

Adding oil recovery methods adds to the cost of oil —in the case of CO₂ typically between 0.5-8.0 US$ per tonne of CO₂. The increased extraction of oil on the other hand, is an economic benefit with the revenue depending on prevailing oil prices. Onshore EOR has paid in the range of a net 10-16 US$ per tonne of CO₂ injected for oil prices of 15-20 US$/barrel. Prevailing prices depend on many factors but can determine the economic suitability of any procedure, with more procedures and more expensive procedures being economically viable at higher prices. Example: With oil prices at around 90 US$/barrel, the economic benefit is about 70 US$ per tonne CO₂. The U.S. Department of Energy estimates that 20 billion tons of captured CO₂ could produce 67 billion barrels of economically recoverable oil.

It is believed that the use of captured, anthropogenic carbon dioxide, derived from the exploitation of lignite coal reserves, to drive electric power generation and support EOR from existing and future oil and gas wells offers a multifaceted solution to U.S. energy, environmental, and economic challenges. There is no doubt that coal and oil resources are finite. The U.S. is in a strong position to leverage such traditional energy sources to supply future power needs while other sources are being explored and developed. For the coal industry, CO₂ EOR creates a market for coal gasification byproducts and reduces the costs associated with carbon sequestration and storage.

1.4                                         BENEFITS OF WATER INJECTION

• Will significantly help to prevent detonation.
• Will raise the octane of the gas you are using.
• By reducing detonation, this will allow you to increase boost or run lower octane.
• Lowers air intake temperatures which keep the engine cooler from the inside out.
• Will literally steam clean the carbon deposits from within the engine.

1.5                       LIMITATIONS OF WATER INJECTION TECHNOLOGY

Water injection can increase the volume of oil recovered from a reservoir; however, it is not always the best technology to use and it can have complicating factors. When evaluating how best to produce a particular oil reservoir, a petroleum engineer should include water injection in the options that are analyzed, both technically and economically. Those evaluations should include such potentially complicating factors as:

• Compatibility of the planned injected water with the reservoir’s connate water
• Interaction of the injected water with the reservoir rock (clay sensitivities, rock dissolution, or generally weakening the rock framework)
• Injection-water treatment to remove oxygen, bacteria, and undesirable chemicals
• The challenges involved in separating and handling the produced water that has trace oil content, naturally occurring radioactive materials (NORMs), and various scale-forming minerals

1.6                               APPLICATION IMMISCIBLE GAS INJECTION

The decision to apply immiscible gas injection is based on a combination of technical and economic factors. Deferral of gas sales is a significant economic deterrent for many potential gas injection projects if an outlet for immediate gas sales is available. Nevertheless, a variety of opportunities still exist. First are those reservoirs with characteristics and conditions particularly conducive to gas/oil gravity drainage and where attendant high oil recoveries are possible. Second are those reservoirs where decreased depletion time resulting from lower reservoir oil viscosity and gas saturation in the vicinity of producing wells is more attractive economically than alternative recovery methods that have higher ultimate recovery potential but at higher costs. And third are reservoirs where recovery considerations are augmented by gas storage considerations and hence gas sales may be delayed for several years.

Nonhydrocarbon gases such as CO₂ and nitrogen can and have been used.^[4] In general, calculation techniques developed for hydrocarbon-gas injection and displacement can be used for the design and application of nonhydrocarbon, immiscible gas projects. Valuing the use of such gases must include any additional costs related to these gases, such as corrosion control, separating the nonhydrocarbon components to meet gas marketing specifications, and using the produced gas as fuel in field operations.