Description
ABSTRACT
The need for alternative sources of energy has become even more acute in light of the recognition of the dwindling conventional world oil reserves. The interest in exploring other avenues of complimenting and/or eventually replacing this resource is growing quite rapidly. A ready alternative to conventional crude oil is oil sands which are abundant and vastly unexplored. The huge deposits of tar sand found in South- Western Nigeria remain untapped due to concerns about the environmental impact. The consequences of the methods in processing tar sand, ranging from water pollution to emission of greenhouse gases, especially in Canada bring in to sharp focus the urgent need for an alternative means of extracting oil from tar sand. A more effective and less environmentally damaging procedure could be the break through needed to open a new chapter in the exploitation of oil sands.
The alternative recovery procedure is supercritical carbon dioxide extraction. Recent supercritical extractions use high temperatures and pressures. The upgrade in this research involves using high pressures and lower temperatures which saves energy and improves the process. The experimental study of the bitumen extraction from Nigerian tar sand by dense CO2 was carried out by high pressure extractor. The samples of tar sand were first heated in an oven at 120 °C to melt. A 50 g sample of melted tar sand with addition of 3 g of ethanol was placed into an extractor and heated to 80 °C to initiate the experiment. Carbon dioxide was injected in to the extractor to create 50 MPa of pressure in static mode for 20 min after which the extract was collected. In the presence of ethanol, the extract had a lighter colour than the usual black. Nigerian tar sand is known to be composed of 84 % sand, 17 % bitumen, 4 % water and 2 % mineral clay. Using this data, an extract of 19.47 % was calculated which makes the recovery achieved very encouraging. The experiment shows that recovery of bitumen from tar sand is possible under relatively low temperatures and can be possibly economically profitable.
TABLE OF CONTENTS
COVER PAGE
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWELDGEMENT
ABSTRACT
CHAPTER ONE
- INTRODUCTION
- BACKGROUND OF THE PROJECT
- PROBLEM STATEMENT
- AIM OF THE PROJECT
- OBJECTIVE OF THE PROJECT
- SCOPE OF THE PROJECT
- PROJECT ORGANISATION
CHAPTER TWO
LITERATURE REVIEW
- DESCRIPTION OF TAR SAND AND ITS ORIGIN
- PROPERTIES OF NIGERIAN TAR SAND
- HISTORICAL BACKGROUND OF TAR SAND
- PRODUCTION OF TAR SAND
- METHODS OF EXTRACTION
- REVIEW OF BITUMEN
- SUPERCRITICAL EXTRACTION OF TAR SANDS AS AN ALTERNATIVE HISTORICAL BACKGROUND OF THE STUDY
CHAPTER THREE
- METHOD AND MATERIAL
CHAPTER FOUR
- RESULT AND DISCUSSION
CHAPTER FIVE
- CONCLUSION
- REFERENCES
CHAPTER ONE
1.0 INTRODUCTION
World energy demand is increasing and the current crude oil is being produced from the light oil deposits which are only one third of all world oil reserves. The other two thirds belong to heavy and extra heavy crude oil group and only one per cent is being exploited. With the increasing prices of crude oil, the production from the heavy and extra heavy oils will become more economically profitable and the scale of their exploitation will increase.
The petroleum formation process exists due to thermal transformation of soluble bitumen and insoluble kerogen dispersed in organic substances. Like most typical thermal transformation reactions, the petroleum generation rate increases with increasing burial depth and consequently with increasing temperature. In shallow oil deposits located near the surface where oil deposits have access to surface waters containing oxygen, biodegradation takes place. Tar sands are the product of biodegradation and chemical changes due to bacteria degradation and water washing.
The tar sand is a sedimentary rock that contains bitumen or other heavy petroleum that, in natural state, cannot be recovered by conventional petroleum-recovery methods. This condition usually applies to oils having a gravity less than 12 °API. The largest world deposits are in Canada, Venezuela, Madagascar, USA, and Russia (Chilingar and Yen, 1978). The recovery of bitumen from tar sand is a difficult process due to its high viscosity. Viscosity reduction is achieved mainly by injecting steam (300-340 °C) and solvents into the sands. These processes use more water and require larger amounts of energy than conventional oil extraction. The most efficient method in use currently is surface mining, where tar sand is excavated, washed with hot water and NaOH is added to the sand to improve bitumen separation from the sands. Wetting agents such as caustic sodium and sodium silicate can be used as processing aids during the hot water digestion of tar sands (Miller and Misra, 1982).
The quartzose tar sands are of fluviatile and lacustrine origins with the highest contents of tar being present in the clean, well sorted fluviatile sands. The maximum tarry-oil content is 18-20 % by weight of saturated sand. In spite of the high energy consumption required in extraction of bitumen from tar sand, it is an economically viable enterprise and it is being undertaken in vast tar sand deposits in Canada. The degree of oil saturation in a formation which is generally measured in weight per cent varies from 0 to as high as 18 %. The Athabasca tar sands, the biggest tar sand deposits in the world have an average degree of saturation between 11-12 % (Chilingar and Yen, 1978).
With the expected increase in crude oil prices in the foreseeable future, interest in tar sand will spread to other countries as well. The current mining technologies use mainly open pit mining and the in situ operations where hot steam is used. This processing procedure leads to environmental problems with the improper disposing of toxic water and the releasing of CO2 into the atmosphere. The main problem with the present extraction methods arise from the contamination of water bodies. There are already lagoons contaminated with the toxic waste from tar sand mining. Another problem is the transport of bitumen through pipelines; due to their high viscosity it is impossible to transport them like conventional crude oil. In order to transport bitumen, it is mixed with conventional crude or chemicals to decrease viscosity which enhances flow. Transported bitumen also contains impurities like sand and other waste which need to be removed at great cost. The problems of impurities in the bitumen and the operational problems from the mentioned methods can be decreased by application of the supercritical carbon dioxide method.
1.1 BACKGROUND OF THE STUDY
Oil sands (called tar sands) are sands or carbonates containing bitumen or other hydrocarbons of such high viscosity to be immobile under normal reservoir temperatures. In order to be utilized, the hydrocarbons must be mined or extracted in site from the rock by the use of heat or solvents.
The largest single hydrocarbon deposit in the world is the Athabasca oil sands of northeastern Alberta, which contains over one trillion barrels of bitumen in place. About ten percent of the deposit is shallow enough to be surface mined. Two open pit mines together produce over 350,000 barrels of synthetic crude per day, equal to about 12 percent of Canadian needs. In situ extraction of bitumen produces about another 150,000 barrels per day from deposits, which are too deep for mining, including much of the Athabasca deposit, and the smaller and deeper Cold Lake, and Peace River deposits (Maurice Dusseault, 2002).
The process of choice for in situ extraction is Steam Assisted Gravity Drainage (SAGD), in which pairs of horizontal wells are drilled near the base of the bitumen deposit. Steam is injected into the injector well, which is placed about 5 meters above the producer well. The steam rises and heats the bitumen, which flows down under the force of gravity to the lower producer well from which it is pumped to the surface. The bitumen is either upgraded at site, or at a regional upgrade, or mixed with diluents and shipped to a refinery. Several pilot projects have tested the SAGD process, and several commercial scale projects are currently in the construction, engineering design and regulatory approval stages (Maurice Dusseault, 2002).
Tar sands are found in several countries around the world, including the former Soviet Union, Venezuela, Cuba, Indonesia, Brazil, Jordan, Madagascar, Trinidad, Colombia, Albania, Rumania, Spain, Portugal, Argentina, and Nigeria. The United States contains scattered deposits of oil sands, mainly in Utah, Kentucky, Kansas, Missouri, California, and New Mexico.
On the basis of the progress made in developing improved technology for recovery of bitumen from tar sands, it is logical to assume that as the world’s supply of light and heavy oil is depleted, production of synthetic oil from the bitumen resources in tar sands will accelerate. As most of the known deposits of tar sands were discovered by accident, there is reason to believe that a worldwide exploration program based on sound geological principles will discover much more of this material. The long lead times required to mine this massive resource into acceptable alternative refinery feedstock at a reasonable price make it imperative that we vigorously pursue the development of recovery technology at this time if we are to avoid shimmies of liquid fuel early in the next century. There is no question that the Light-crude-oil substitute developed from this resource will be more expensive than the Conventional light and heavy crude are being used today. However, there is reason to believe that the differential in costs will narrow as the search for new sources of light oil swings to deeper targets in more remote and hostile environments, such as the southern part of Nigeria (Alvarez, Johannes; Sungyun Han July 2013).
And arctic islands, and more expensive enhance recovery techniques are used to recover the oil now left behind in deep depleted light- and heavy-oil reservoirs. The Petroleum engineers have defined tar sands pragmatically as oil too viscous to flow into a well in sufficient quantities to be produced economically.
This definition, if universally applied, causes problems because oils of Different gravities are included, depending on their depth of burial and the reservoir temperature. Others have defined tar sands as reservoirs containing bitumen i.e., oils heavier than water or with gravity of less than 10”API. A compromise definition proposed by UNFTAR [states that tar sands contain crude bitumen with a gravity of less than 10”API at 60”F or have a viscosity greater than 10,000 mpa. s at original reservoir temperature (Alvarez, Johannes; Sungyun Han July 2013).
No definition of tar sands enunciated to elate is universally acceptable to geologists, petroleum engineer, and refiners. If one were to classify a reservoir as a tar sand only if it contains a semi liquid hydrocarbon that is heavier than water (less than 10”API gravity), has a viscosity of more than 10,000 cp at reservoir temperature, and cannot be produced in significant quantities through a well by prima~ production, some large deposits widely accepted as tar sands, such as the Orinoco belt reservoirs in Venezuela, the Cold Lake deposit in Alabama, the Asphalt Ridge deposit in Utah and Bitumen deposits in western Nigeria would be excluded for failing to meet one or more of the three criteria. Defining crude bitumen as oil with gravity Iess than 10”API at 60”F puts these ultra-heavy oils in a group consistent with their commercial value, regardless of their depth of burial, once they have been produced. It also is a good indication of the amount of “upgrading” necessary to make them into refinery feed stock. Crude oil heavier than water commonly contains significant quantities of asphaltene and usually is contaminated with impurities such as oxygen, nitrogen, sulfur, vanadium, nickel, and iron.
Note that bitumen is found in the same variety of rocks as light oil and includes sandstones, carbonates, and volcanic rocks. Because bitumen is so widely dispersed, it is not surprising that the world’s largest petroleum accumulations and bituminous in nature and the question of its origin has attracted considerable attention since biblical times (Butler, Roger 1991).
The recent realization that the world’s supply of conventional oil is limited, the question of how much bitumen can be extracted economically and converted to a light synthetic crude has assumed new importance. The amount of bitumen in the world has been estimated conservatively at 4.07 trillion bbl. However, remain speculative, as there is no reliable published quantitative information on the resource outside Canada, the U. S., and Venezuela. This gap in our knowledge is, not surprising since, until recently, Little commercial value was assigned to the material and thus there was almost no incentive to embark on a costly drilling and coring program to prove up reserves. This situation should change now that the technology for extracting and upgrading the low-quality hydrocarbon To marketable refinery feedstock is ready economical (Butler, Roger 1991). Observations on the geologic setting of giant tar sand deposits have led to the formulation of generalizations about their occurrence but the most striking feature is the sheer size of the bitumen accumulations. For example, the amount of bitumen in Alberta, Canada, and the Orinoco belt in Venezuela each exceeds 1 trillion bbl in the ground (Butler, Roger 1991).
1.2 PROBLEM STATEMENT
The problem of the old methods in processing tar sand, ranging from water pollution to emission of greenhouse gases, especially in Nigeria bring in to sharp focus the urgent need for an alternative means of extracting oil from tar sand and also A more effective and less environmentally damaging procedure could be the break through needed to open a new chapter in the exploitation of oil sands, and also Transported bitumen also contains impurities like sand and other waste which need to be removed at great cost. The problems of impurities in the bitumen and the operational problems from the mentioned methods can be decreased by application of the supercritical carbon dioxide method.
1.3 AIM OF THE PROJECT
The main aim of this work is to discuss an improve method of oil recovery from tar sand in Nigeria using Dense Carbon Dioxide method. In this work, an experimental study of the bitumen extraction from Nigerian tar sand by dense CO2 was carried out by high pressure extractor.
1.4 OBJECTIVES OF THE PROJECT
This study is fully discussed the following:
- Evaluation of the Dense Carbon Dioxide process applied in tar sand
- Environmental impact evaluation of the
- Economic evaluation of tar sand
- Tar sand market and prospect in
1.5 SCOPE OF THE PROJECT
Tar sand had many other uses in the ancient world. It was mixed with sand and fibrous materials for use in the construction of watercourses and levees and as mortar for bricks.
In Nigeria, development of heavy oil and bitumen in Tar sand reserves is increasing around the western part of the country. The increasing volume of cheaper heavy oil in the supply mix has provided an incentive for refiners to upgrade their equipment to process the poorer-quality heavier crude occurring in tar sand. As the demand for heavy oil and synthetic crude from tar sands remains strong, heavy- hydrocarbon development projects are being initiated in western part of Nigeria. In addition, unsuccessful attempts to find new giant conventional oil fields in recent years have caused some producers to turn to the marginally economic heavy hydrocarbons to replace depleted petroleum reservoirs. Bitumen development in Nigeria is also poised to become Nigerian major foreign exchange earner, second to conventional oil in the coming years (Butler, Roger 1991).
1.7 PROJECT ORGANISATION
The work is organized as follows: chapter one discuses the introductory part of the work, chapter two presents the literature review of the study, chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.
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