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The application of surface geochemical methods to finding petroleum is based on the detection of hydrocarbons in the soil that have leaked from a petroleum reservoir at depth. While the seal over the deposit was once considered impermeable, surface geochemistry data now show that such leakage is a common occurrence. Despite its simplicity and low costs, surface geochemistry remains controversial because, until now, there was no objective and in-depth treatment of the various methods of surface geochemistry for oil exploration. Written by a successful oil finder, this practical guide: * surveys a broad array of surface geochemistry techniques, from soil gases to microbiology, and provides clear strategies for applying them to the high-stakes art of petroleum exploration * offers numerous case studies, both successes and failures, to show the strengths and weaknesses of different approaches * examines statistical and spatial variation, surveys and models in surface geochemistry, demonstrating how each analytical tool can be used to optimize accuracy * integrates surface geochemistry data interpretation with data from conventional methods of oil exploration, and considers the economics of surface geochemical approaches * discusses key topics that have been neglected in the literature, such as grid design and the effects of soils. Geologists, geophysicists, geological engineers and exploration managers involved in petroleum exploration will gain valuable insights from this volume. By presenting and evaluating each method of surface geochemistry in a neutral tone, this book enables the reader to select and employ these methods with greater confidence.

Inhaltsverzeichnis

Frontmatter

Introduction

Frontmatter

1. History of Surface Geochemistry

Abstract
The history of surface geochemical exploration is filled with misconceptions, unsupported claims, misrepresentations, and a poor understanding of the soil and subsurface environments. Surface geochemical methods have not been readily accepted by the United States petroleum industry, but foreign oil industries with limited American influence have pursued this technology aggressively. Recently, economic pressures associated with higher finding costs and lower success rates have caused American companies to reexamine surface geochemical applications in a variety of geologic environments and exploration scenarios.
Steven A. Tedesco

2. Organic Geochemistry

Abstract
Organic geochemistry as used here is essentially organic chemistry as applied to petroleum exploration. This chapter will present some fundamentals of organic chemistry that are applicable to surface geochemistry: the basic organization and composition of organic compounds and the various reactions and processes these compounds undergo in the earth environment.
Steven A. Tedesco

3. Soils and Their Formation

Abstract
Understanding soil characteristics and formation is an important but often overlooked aspect of surface geochemical exploration. This chapter describes soil profiles and the influence of climate, parent material, biological activity, time, and topographic relief. Comprehending the relationship between soils and migrating hydrocarbons is critical to the proper collection, analysis, and interpretation of surface geochemical data.
Steven A. Tedesco

4. Concepts of Microseepage

Abstract
Vertical migration is the mechanism that is used to explain hydrocarbon seepage to the surface. It is the process that causes the surface geochemical manifestation by which we can detect petroleum accumulations using various shallow methods (Fig. 4–1; see color plate).
Steven A. Tedesco

Methods of Microseepage Detection: Direct vs. Indirect

Frontmatter

5. Soil Gas

Abstract
The most common method for detecting and delineating a surface geochemical anomaly associated with a petroleum reservoir is measuring vapor or liquid hydrocarbons that have migrated to the surface or near-surface. The media in which these measurements occur are the soil, atmosphere, ocean water column, ocean bottom sediments, and groundwater or surface fresh water.
Steven A. Tedesco

6. Radiometrics

Abstract
The use of radiometrics predates the use of other geochemical methods. The technique dates back to at least 1926, when the Soviets observed anomalously low gamma counts over existing oil fields (Armstrong and Heemstra, 1972, 1973). The U.S. petroleum industry began applying radiometric methods about 1943. Since that time, there have been numerous articles and increasing curiosity and application by the industry, especially during widespread economic recession. When petroleum prices are low, the industry has sought inexpensive exploration methods, especially radiometrics. This method has proved that it can be an excellent tool for petroleum exploration, but environmental influences and a preponderance of primitive collection techniques have continued to cause confusion and have limited its acceptance. The consistent association between soil-gas anomalies and radiometric anomalies has never been clearly explained. Only a small percentage of all radiometric anomalies found have been confirmed by soil-gas techniques as being related to petroleum seepage.
Steven A. Tedesco

7. Halogens

Abstract
The halogen group is composed of chlorine, fluorine, bromine, and iodine. Halogens are important components of many types of compounds, especially when bonded with hydrogen. Halogens closely associate themselves with petroleum-derived organics; iodine specifically has been used in the search for hydrocarbons. All the halogens have been employed to delineate ore deposits of zinc, cooper, and gold (Boyle, 1987; Levinson, 1980). However, only iodine has been used consistently to delineate petroleum deposits (Ku-del’sky, 1977; Gallagher, 1984; Allexan et al., 1986; Singh et al., 1987; Gordon and Ikramuddin, 1988; and Tedesco and Goudge, 1989).
Steven A. Tedesco

8. Major and Minor Elements

Abstract
Trace and major elements, certain isotopes, and the compounds in which they are incorporated have been used to identify petroleum microseepage. Applying these forms is a departure from typical surface geochemical methods and represents an attempt to find more reliable techniques, other than soil gas, to target petroleum accumulations. The results have been encouraging and have added information to the understanding of microseepage and the changes it causes in the near-surface. However, the results have not been sufficiently reliable, repeatable, or cost-effective to warrant replacing soil gas, radiometrics, or iodine.
Steven A. Tedesco

9. Microbiological Methods

Abstract
Bacteria that digest hydrocarbons have been used by several investigators to find petroleum accumulations. Early work was done by European and Russian scientists, but it was not until the 1940s that the U.S. scientific community recognized the existence of bacteria that thrive by using petroleum as their sole source of carbon. Microbes are also used effectively in the search for other natural resources such as gold (Parduhn, 1991). Many microbial families, genera, and species have a specific, critical, or unique element or compound that they have adapted to their metabolic requirements. The volume of certain bacteria populations increases in conjunction with the rise in concentration of methane or other hydrocarbons that enter the soil substrate. Three methods were developed by the Soviets for microbial detection. They are: (1) microbial soil surveys, (2) microbial surveys of drill cuttings or cores from nondevelopment wells, and (3) groundwater microbial surveys. The third has become the most common microbial method used in the former Soviet Union, but only the first method will be discussed here because it is the dominant one used in the United States.
Steven A. Tedesco

10. Helium Methods

Abstract
Anomalous accumulations of helium have been identified in association with petroleum deposits both in the reservoir itself and at the surface. Historically, there have been intermittent periods when helium has been used as a prospecting tool for petroleum. This technique has been useful in finding fault and fracture systems associated with a trap.
Steven A. Tedesco

11. pH/Eh Methods

Abstract
Many of the techniques presented in the previous chapters are in some way affected by Eh and pH conditions of the soil and rock strata that are sampled. Only in recent years has research for soil science concentrated intensely on Eh and pH and how they affect chemical and biological processes in the soil substrate. Surface geochemical surveys typically do not measure Eh and pH as standard procedure. Petroleum microseepage into the soil substrate, which causes several chemical reactions and microbial oxidation of hydrocarbons, also causes decreases in Eh and pH. All changes should be measurable depending on such factors as soil mineralogy, clay composition and absorption capacity, amount of organic matter present, humic/fulvic acids present, type of parent material, moisture content, the original Eh and pH, bacterial activity, and climate.
Steven A. Tedesco

Survey Design and Data Analysis

Frontmatter

12. Statistical Analysis and Spatial Variation

Abstract
Several statistical techniques are useful in the evaluation of surface and near-surface geochemical data. The numerous statistical methods available to the reader are in a sense limitless in manipulating data for evaluation. However, the present level of understanding of surface geochemical exploration for petroleum precludes using several of the statistical methods and instead focuses on a few simple methods that aid interpretation. Because there may be multiple variables from a surface geochemical survey, analysis typically does not extend beyond (1) simple profiles; (2) use of means, modes, and standard deviations; and (3) contouring of the data. Usually, the raw data from the lab analysis indicate the presence or absence of an “anomaly” without statistical manipulation. Implementing statistical analysis requires obtaining sufficient data to identify that part (if any) of the population that is related to microseepage, and then determining how best to conclude confidently that it is indeed “anomalous” and is the part of the population being explored. Investigators typically use simple statistics.
Steven A. Tedesco

13. Grids, Surveys, Models, and Economics

Abstract
Survey design is one of the most important aspects of an effective surface geochemical program. The basic objective is to optimize target identification by interpreting changes in diagnostic elements and compounds. There are several factors that enter into survey planning that will influence exploration decisions and affect the outcome. A series of questions outlining objectives that the survey needs to address should be prepared prior to data acquisition. These questions will serve as the framework for designing and conducting the survey effectively. When objectives and requirements are decided before data collection is begun, the survey has an increased chance of success. Success is defined as determining whether or not a geochemical anomaly exists.
Steven A. Tedesco

14. Summary

Abstract
Surface geochemistry is still an evolving exploration tool. Gains in its acceptance have resulted from an expanding data base, supplemented by increasing success, rather than from any significant technological breakthrough. This book was written to bring together several related techniques and present them in an objective format, supported with case histories and methods to improve analytic interpretation. The conclusion is that these techniques can increase and enhance the success of an exploration program. The methods have often been criticized on the grounds that most published American studies have been written by contractors or promoters, whose published work may lack objectivity and whose motivation may be self-interest. University researchers have published reviews or investigated new geochemical concepts but, for the most part, their work has contradicted or ignored field results. End users or explorationists have either not published or the surveys they presented are unconvincing for lack of hard data.
Steven A. Tedesco

Backmatter

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