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USGS2010

Future petroleum energy resources of the world

Is the world running out of oil? Where will future oil and gas supplies come from? To help answer these questions, in 2000 the U.S. Geological Survey completed a new world assessment, exclusive of the United States, of the undiscovered conventional oil and gas resources and potential additions to reserves from field growth. 2 One hundred and twenty-eight provinces were assessed in a 100 manyear effort from 1995-2000. The assessed provinces included 76 priority provinces containing 95% of the world's discovered oil and gas and an additional 52 "boutique" provinces, many of which may be highly prospective. Total Petroleum Systems (TPS) were identified and described for each of these provinces along with associated Assessment Units (AU) that are the basic units for assessing undiscovered petroleum. The assessment process coupled geologic analysis with a probabilistic methodology to estimate remaining potential. Within the 128 assessed provinces were 159 TPS and 274 AU. For these provinces, the endowment of recoverable oil—which includes cumulative production, remaining reserves, reserve growth, and undiscovered resources—is estimated at about 3 trillion barrels of oil (TBO). The natural gas endowment is estimated at 2.6 trillion barrels of oil equivalent (TBOE). Oil reserves are currently 1.1 TBO; world consumption is about .028 TBO per year. Natural gas reserves are about 0.8 TBOE; world consumption is about 0.014 TBOE per year. Thus, without any additional discoveries of oil, gas or natural gas liquids, we have about 2 TBOE of proved petroleum reserves. Of the oil and gas endowment of about 5.6 TBOE, we estimate that the world has consumed about 1 TBOE, or 18%, leaving about 82% of the endowment to be utilized or found. Half of the world's undiscovered potential is offshore. Arctic basins with about 25% of undiscovered petroleum resources make up the next great frontier. An additional 279 provinces contain some oil and gas and, if considered, would increase the oil and gas endowment estimates. Whereas petroleum resources in the world appear to be significant, certain countries such as the United States may run into import deficits, particularly oil imports from Mexico and natural gas from both Canada and Mexico. The new assessment has been used as the reference supply case in energy supply models by the International Energy Agency and the Energy Information Agency of the Department of Energy. Climate energy modeling groups such as those at Stanford University, Massachusetts Institute of Technology, and others have also used USGS estimates in global climate models. Many of these models using the USGS estimates converge on potential oil shortfalls in 2036-2040. However, recent articles using the USGS (2000) estimates suggest peaking of oil in 2020-2035 and peaking of non-OPEC (Organization of Petroleum-Exporting Countries) oil in 2015-2020. Such a short time framework places greater emphasis on a transition to increased use of natural gas; i.e., a methane economy. Natural gas in turn may experience similar supply concerns in the 2050-2060 time frame according to some authors. Coal resources are considerable and provide significant petroleum potential either by extracting natural gas from them, by directly converting them into petroleum products, or by utilizing them to generate electricity, thereby reducing natural gas and oil requirements by fuel substitution. Non-conventional oil and gas are quite common in petroleum provinces of the world and represent a significant resource yet to be fully studied and developed. Seventeen non-conventional AU including coal-bed methane, basin-center gas, continuous oil, and gas hydrate occurrences have been preliminarily identified for future assessment. Initial efforts to assess heavy oil deposits and other non-conventional oil and gas deposits also are under way.

International Geology Review↗
USGS2000

USGS World Petroleum Assessment 2000: New Conventional Provinces

The USGS has completed a new assessment of the undiscovered oil and gas resources of the world. One hundred and five geologic provinces were analyzed for assessment. Assessment units (AU) that comprise Total Petroleum Systems (TPS) were identified and described for each of these provinces. The AU served as the basis for assessing undiscovered petroleum within these provinces, 157 TPS and 270 AU were assessed. Some of data included in the assessment include the cumulative percent of world known petroleum volume by ranked oil and gas provinces; undiscovered NGL; reserve growth of the worlds largest oil and gas fields; and world potential reserve growth for oil/gas/NGL.

Conference Paper↗
USGS2010

Oil shale resources of the Uinta Basin, Utah and Colorado

The U.S. Geological Survey (USGS) recently completed a comprehensive assessment of in-place oil in oil shales of the Eocene Green River Formation of the Uinta Basin of eastern Utah and western Colorado. The oil shale interval was subdivided into eighteen roughly time-stratigraphic intervals, and each interval was assessed for variations in gallons per ton, barrels per acre, and total barrels in each township. The Radial Basis Function extrapolation method was used to generate isopach and isoresource maps, and to calculate resources. The total inplace resource for the Uinta Basin is estimated at 1.32 trillion barrels. This is only slightly lower than the estimated 1.53 trillion barrels for the adjacent Piceance Basin, Colorado, to the east, which is thought to be the richest oil shale deposit in the world. However, the area underlain by oil shale in the Uinta Basin is much larger than that of the Piceance Basin, and the average gallons per ton and barrels per acre values for each of the assessed oil shale zones are significantly lower in the depocenter in the Uinta Basin when compared to the Piceance Basin. These relations indicate that the oil shale resources in the Uinta Basin are of lower grade and are more dispersed than the oil shale resources of the Piceance Basin.

Colorado, Utah↗
USGS2014

Histograms showing variations in oil yield, water yield, and specific gravity of oil from Fischer assay analyses of oil-shale drill cores and cuttings from the Piceance Basin, northwestern Colorado

Recent studies indicate that the Piceance Basin in northwestern Colorado contains over 1.5 trillion barrels of oil in place, making the basin the largest known oil-shale deposit in the world. Previously published histograms display oil-yield variations with depth and widely correlate rich and lean oil-shale beds and zones throughout the basin. Histograms in this report display oil-yield data plotted alongside either water-yield or oil specific-gravity data. Fischer assay analyses of core and cutting samples collected from exploration drill holes penetrating the Eocene Green River Formation in the Piceance Basin can aid in determining the origins of those deposits, as well as estimating the amount of organic matter, halite, nahcolite, and water-bearing minerals. This report focuses only on the oil yield plotted against water yield and oil specific gravity.

Colorado↗
USGS2000

Reserve growth effects on estimates of oil and natural gas resources

Many scientists think that the supply of economically recoverable oil and natural gas is geologically limited. However, as recently as early 1999, we experienced a glut of oil on the world market and the lowest inflation-adjusted price of gasoline in history. What is going on? While we cannot provide a comprehensive answer to that question here, we can describe one process that significantly affects the domestic oil and gas industry, a process that also will affect the global industry at some point—reserve growth (also known as field growth).

Fact Sheet↗
USGS2015

Introduction to special section: China shale gas and shale oil plays

In the last 10 years, the success of shale gas and shale oil productions as a result of technological advances in horizontal drilling, hydraulic fracturing and nanoscale reservoir characterization have revolutionized the energy landscape in the United States. Resource assessment by the China Ministry of Land and Resources in 2010 and 2012 and by the U.S. Energy Information Administration in 2011 and 2013 indicates China’s shale gas resource is the largest in the world and shale oil resource in China is also potentially significant. Inspired by the success in the United States, China looks forward to replicating the U.S. experience to produce shale gas to power its economy and reduce greenhouse gas emissions. By 2014, China had drilled 400 wells targeting marine, lacustrine, and coastal swamp transitional shales spanning in age from the Precambrian to Cenozoic in the last five years. So far, China is the leading country outside of North America in the viable production of shale gas, with very promising prospects for shale gas and shale oil development, from the Lower Silurian Longmaxi marine shale in Fuling in the southeastern Sichuan Basin. Geological investigations by government and academic institutions as well as exploration and production activities from industry indicate that the tectonic framework, depositional settings, and geomechanical properties of most of the Chinese shales are more complex than many of the producing marine shales in the United States. These differences limit the applicability of geologic analogues from North America for use in Chinese shale oil and gas resource assessments, exploration strategies, reservoir characterization, and determination of optimal hydraulic fracturing techniques. Understanding the unique features of the geology, shale oil and gas resource potential, and reservoir characteristics is crucial for sweet spot identification, hydraulic fracturing optimization, and reservoir performance prediction. Even though China shale gas and shale oil exploration is still in an early stage, limited data are already available. We are pleased to have selected eight high-quality papers from fifteen submitted manuscripts for this timely section on the topic of China shale gas and shale oil plays. These selected papers discuss various subject areas including regional geology, resource potentials, integrated and multidisciplinary characterization of China shale reservoirs (geology, geophysics, geochemistry, and petrophysics) China shale property measurement using new techniques, case studies for marine, lacustrine, and transitional shale deposits in China, and hydraulic fracturing. One paper summarizes the regional geology and different tectonic and depositional settings of the major prospective shale oil and gas plays in China. Four papers concentrate on the geology, geochemistry, reservoir characterization, lithologic heterogeneity, and sweet spot identification in the Silurian Longmaxi marine shale in the Sichuan Basin in southwest China, which is currently the primary focus of shale gas exploration in China. One paper discusses the Ordovician Salgan Shale in the Tarim Basin in northwest China, and two papers focus on the reservoir characterization and hydraulic fracturing of Triassic lacustrine shale in the Ordos Basin in northern China. Each paper discusses a specific area.

Interpretation↗
USGS2011

Reserve growth in oil pools of Alberta: Model and forecast

Reserve growth is recognized as a major component of additions to reserves in most oil provinces around the world, particularly in mature provinces. It takes place as a result of the discovery of new pools/reservoirs and extensions of known pools within existing fields, improved knowledge of reservoirs over time leading to a change in estimates of original oil-in-place, and improvement in recovery factor through the application of new technology, such as enhanced oil recovery methods, horizontal/multilateral drilling, and 4D seismic. A reserve growth study was conducted on oil pools in Alberta, Canada, with the following objectives: 1) evaluate historical oil reserve data in order to assess the potential for future reserve growth; 2) develop reserve growth models/ functions to help forecast hydrocarbon volumes; 3) study reserve growth sensitivity to various parameters (for example, pool size, porosity, and oil gravity); and 4) compare reserve growth in oil pools and fields in Alberta with those from other large petroleum provinces around the world. The reported known recoverable oil exclusive of Athabasca oil sands in Alberta increased from 4.5 billion barrels of oil (BBO) in 1960 to 17 BBO in 2005. Some of the pools that were included in the existing database were excluded from the present study for lack of adequate data. Therefore, the known recoverable oil increased from 4.2 to 13.9 BBO over the period from 1960 through 2005, with new discoveries contributing 3.7 BBO and reserve growth adding 6 BBO. This reserve growth took place mostly in pools with more than 125,000 barrels of known recoverable oil. Pools with light oil accounted for most of the total known oil volume, therefore reflecting the overall pool growth. Smaller pools, in contrast, shrank in their total recoverable volumes over the years. Pools with heavy oil (gravity less than 20o API) make up only a small share (3.8 percent) of the total recoverable oil; they showed a 23-fold growth compared to about 3.5-fold growth in pools with medium oil and 2.2-fold growth in pools with light oil over a fifty-year period. The analysis indicates that pools with high porosity reservoirs (greater than 30 percent porosity) grew more than pools with lower porosity reservoirs which could possibly be attributed to permeability differences between the two types. Reserve growth models for Alberta, Canada, show the growth at field level is almost twice as much as at pool level, possibly because the analysis has evaluated fields with two or more pools with different discovery years. Based on the models, the growth in oil volumes in Alberta pools over the next five-year period (2006-2010) is expected to be about 454 million barrels of oil. Over a twenty-five year period, the cumulative reserve growth in Alberta oil pools has been only 2-fold compared to a 4- to- 5-fold increase in other petroleum producing areas such as Saskatchewan, Volga-Ural, U.S. onshore fields, and U.S. Gulf of Mexico. However, the growth at the field level compares well with that of U.S. onshore fields. In other petroleum provinces, the reserves are reported at field levels rather than at pool levels, the latter basically being the equivalent of individual reservoirs. ?? 2010 by the Canadian Society of Petroleum Geologists.

Bulletin of Canadian Petroleum Geology↗
USGS1971

Subsurface waste disposal by means of wells - A selective annotated bibliography

Subsurface waste disposal by means of wells is the practice of using drilled wells to inject unwanted substances into underground rock formations. The use of wells for this purpose is not a new idea. As long ago as the end of the last century, it was common practice to drill wells for the express purpose of draining swamps and small lakes to reclaim the land for agricultural purposes. A few decades later in the 1920's and 1930's many oil companies began using injection wells to dispose of oil-field brines and to repressurize oil reservoirs. During World War II, the Atomic Energy Commission began using injection wells to dispose of certain types of radioactive wastes. More recently, injection wells have been drilled to dispose of a variety of byproducts of industrial processes. The number of such wells has increased rapidly since Congress passed the Clean Streams Act of 1966, which restricted the discharge of waste into surface waters. Many scientists and public officials question the propriety of using the term "disposal" when referring to the underground injection of wastes. Their reasons are that underground injection is not, as many advocates claim, "a complete and final answer" to the waste-disposal problem. Rather, it is merely a process wherein the injected wastes are committed to the subsurface with uncertainty as to their ultimate fate or limits of confinement. In effect, the wastes, undiminished and unchanged, are removed from the custody of man and placed in the custody of nature. Although the concept of waste-injection wells is relatively simple, the effects of waste injection can be very complex, particularly when dealing with the exotic and complex components of some industrial wastes. Besides the physical forces of injection, there are many varied interactions between the injected wastes and the materials within the injection zone. Because these changes occur out of sight in the subsurface, they are difficult to assess and not generally understood. In addition, the various aspects of the problem involve a wide spectrum of science and engineering. Hence, articles published on the subject are widely dispersed in the technical and scientific literature.

Water Supply Paper↗
USGS2012

The systematic geologic mapping program and a quadrangle-by-quadrangle analysis of time-stratigraphic relations within oil shale-bearing rocks of the Piceance Basin, western Colorado

During the 1960s, 1970s, and 1980s, the U.S. Geological Survey mapped the entire area underlain by oil shale of the Eocene Green River Formation in the Piceance Basin of western Colorado. The Piceance Basin contains the largest known oil shale deposit in the world, with an estimated 1.53 trillion barrels of oil in place and as much as 400,000 barrels of oil per acre. This report places the sixty-nine 7½-minute geologic quadrangle maps and one 15-minute quadrangle map published during this period into a comprehensive time-stratigraphic framework based on the alternating rich and lean oil shale zones. The quadrangles are placed in their respective regional positions on one large stratigraphic chart so that tracking the various stratigraphic unit names that have been applied can be followed between adjacent quadrangles. Members of the Green River Formation were defined prior to the detailed mapping, and many inconsistencies and correlation problems had to be addressed as mapping progressed. As a result, some of the geologic units that were defined prior to mapping were modified or discarded. The extensive body of geologic data provided by the detailed quadrangle maps contributes to a better understanding of the distribution and characteristics of the oil shale-bearing rocks across the Piceance Basin.

Colorado↗
USGS2019

Controls on organic matter distributions in Eocene Lake Uinta, Utah and Colorado

The Green River Formation deposited in Eocene Lake Uinta in the Uinta and Piceance Basins, Utah and Colorado, contains the largest oil shale resource in the world with an estimated 1.53 trillion barrels of oil in-place in the Piceance Basin and 1.32 trillion barrels in the Uinta Basin. The Douglas Creek arch, a slowly subsiding hinge-line between the two basins, created separate deep depocenters with shallow water conditions near the crest of the arch. Lake Uinta was a saline lake throughout its history with a lower saline to hypersaline layer (monimolimnion) and an upper less saline layer (mixolimnion). Most of the organic matter in the Green River Formation was derived primarily from algae that lived in the photic zone of the lake and is very hydrogen-rich and oil-prone. In many modern large and deep lakes, rates of organic matter production are highly variable due to differences in nutrient supply. However, cyclonic circulation often leads to winnowing out organic and mineral matter in the mixolimnion leading to organic and fine-grained mineral matter being deposited in increasing amounts toward hydro-dynamically dead zones in the center of the circulation producing concentric bands of increasing organic matter content. Organic matter transport through the dense, hypersaline monimolimnion may have been facilitated by low density organic matter attaching to more dense clay mineral particles. Most of the oil shale intervals deposited in Lake Uinta display similar patterns in their organic matter distributions, increasing in very regular fashion toward the central areas of the lake’s two depocenters. This concentric feature is particularly prominent in the most laminated oil shale zones. Here, we propose that cyclonic circulation was present in Lake Uinta. Each basin appears to have had its own circulation currents, separated by shallow water conditions near the Douglas Creek arch, as well as one hydro-dynamically dead zone. Sediment gravity flow processes were also very active in some strata of Lake Uinta, leading to the reworking and redepositing of sediments. Two general types of sediment gravity flows are recognized: (1) organic-rich sediment gravity flows that reworked and may have concentrated organic-rich material closer to the two deep depocenters, and (2) sandstone and siltstone-rich organic-poor mass movement deposits that originated on marginal shelves. Mass movements could have been triggered by various natural processes and/or possibly by the movement of dense brines that evolved on marginal shelves and moved along the bottom of the water column toward the deep part of the lake. The uppermost, poorly consolidated sediment layer was incorporated in sediment gravity flows as they moved, and in many cases sediment gravity flows scoured down significantly into the more consolidated underlying sediment producing large rip-up clasts of laminated sediments. Truncation of more than 100 ft occurs at the base of a sequence of sediment gravity flows in one well, indicating a significant incised channel. Coarser-grained sediment gravity flows terminated before reaching the lake’s deepest areas, forming thick concentric buildups of organically-lean sediment near the base of the marginal slopes. Intervals dominated by organic-rich fine-grained sediment gravity flows have tightly concentric bands of increasing organic matter toward the deepest parts of the lake and can be organically richer than the richest laminated intervals. There is some evidence that the hydro-dynamically quiet zones did not always correspond closely to the deepest areas of the lake, extending in some cases into shallower areas.

Colorado, Utah↗
USGS2021

Estimates of water use associated with continuous oil and gas development in the Permian Basin, Texas and New Mexico, 2010–19, with comparisons to the Williston Basin, North Dakota and Montana

The Permian Basin, in west Texas and southeastern New Mexico is one of the largest conventional oil and gas reservoirs in the United States and is becoming one of the world’s largest continuous oil and gas (COG) reservoirs. Advances in technology have enabled oil and gas to be extracted from reservoirs that historically were developed using conventional, or vertical, well drilling techniques. Conventional oil and gas reservoirs have discrete deposits that are well defined and are typically trapped by an overlying geologic formation or caprock, whereas COG reservoirs contain deposits that are distributed evenly throughout the geologic formation, typically have much lower permeability (the capacity of a porous rock to transmit a fluid) than the con­ventional deposits, and require specialized horizontal extraction techniques. The methods to extract the oil from the two different reservoirs require differing amounts of water, and the horizontal extraction methods typically require substantially more water. In 2015, the U.S. Geological Survey started a topical study to quantify water used during COG development. The Permian Basin, which contains both types of reservoirs (continuous and conventional), was the second basin in the United States in the U.S. Geological Survey’s topical study to quantify water used during COG development.

Montana, New Mexico, North Dakota, Texas↗
USGS2005

United States geological survey's reserve-growth models and their implementation

The USGS has developed several mathematical models to forecast reserve growth of fields both in the United States (U.S.) and the world. The models are based on historical reserve growth patterns of fields in the U.S. The patterns of past reserve growth are extrapolated to forecast future reserve growth. Changes of individual field sizes through time are extremely variable, therefore, the reserve growth models take on a statistical approach whereby volumetric changes for populations of fields are used in the models. Field age serves as a measure of the field-development effort that is applied to promote reserve growth. At the time of the USGS World Petroleum Assessment 2000, a reserve growth model for discovered fields of the world was not available. Reserve growth forecasts, therefore, were made based on a model of historical reserve growth of fields of the U.S. To test the feasibility of such an application, reserve growth forecasts were made of 186 giant oil fields of the world (excluding the U.S. and Canada). In addition, forecasts were made for these giant oil fields subdivided into those located in and outside of Organization of Petroleum Exporting Countries (OPEC). The model provided a reserve-growth forecast that closely matched the actual reserve growth that occurred from 1981 through 1996 for the 186 fields as a whole, as well as for both OPEC and non-OPEC subdivisions, despite the differences in reserves definition among the fields of the U.S. and the rest of the world. ?? 2005 International Association for Mathematical Geology.

Conference Paper↗
USGS2013

Microbial production of natural gas from coal and organic-rich shale

Natural gas is an important component of the energy mix in the United States, producing greater energy yield per unit weight and less pollution compared to coal and oil. Most of the world’s natural gas resource is thermogenic, produced in the geologic environment over time by high temperature and pressure within deposits of oil, coal, and shale. About 20 percent of the natural gas resource, however, is produced by microorganisms (microbes). Microbes potentially could be used to generate economic quantities of natural gas from otherwise unexploitable coal and shale deposits, from coal and shale from which natural gas has already been recovered, and from waste material such as coal slurry. Little is known, however, about the microbial production of natural gas from coal and shale.

Fact Sheet↗
USGS2004

Natural bitumen and extra-heavy oil

Crude oil is found in sedimentary rocks throughout the world, except, thus far, in Antarctica. In many places the oil has been degraded, so that it is represented by viscous black oil that is difficult to recover, transport, and refine. Depending upon the degree of degradation the result is extra-heavy oil or, in the extreme case, natural bitumen. Except in Canada, precise quantitative reserves and oilin-place data on a reservoir basis are seldom available because most countries and companies consider such information to be proprietary. Natural bitumen is the oil contained in clastic and carbonate reservoir rocks, most frequently in small deposits at, or near, the earth’s surface. These rocks are commonly referred to as tar sands or oil sands and have been mined since antiquity for use as paving. Occasionally such deposits are extremely large in areal extent and in contained resources, most notably those in northern Alberta, Canada. In 2003 only the Alberta bitumen deposits were being exploited as a source of crude oil. Similarly, reservoirs containing extra-heavy oil are geographically widespread but only one such deposit is sufficiently large to have a major supply and economic impact. That deposit is the Orinoco Oil Belt in Eastern Venezuela. Nowhere else in the world is such a concentration of extra heavy oil known or likely to exist. Definitions of terms used in this commentary may be found immediately prior to Table 4.1. The resource definitions are those of the World Petroleum Congress-Society of Petroleum Engineers-American Association of Petroleum Geologists, with minor additions. One such addition, e.g. is the term Original Reserves, comprised of Proved Reserves plus Cumulative Production, which tends to place new and mature reservoirs on a more nearly comparable basis than either term alone

Conference Paper↗
USGS2002

Global petroleum resources: A view to the future

It is necessary to periodically reassess petroleum resources, not only because new data become available and better geologic models are developed; but also because many non-geologic factors determine which part of the crustal abundance of petroleum will be economic and acceptable over the foreseeable future. In 2000, the U.S. Geological Survey completed an assessment of the world's conventional petroleum resources, exclusive of the United States. This assessment is different from those before it: Overall the 2000 assessment of potential petroleum resources is higher than previous assessments, largely because it is the first USGS world assessment to include field growth estimates. Based on a thorough investigation of the petroleum geology of each province, the assessment couples geologic analysis with a probabilistic methodology to estimate remaining potential. Including the assessment numbers for the United States from USGS and the Minerals Management Service (MMS), the world's endowment of recoverable oil - which consists of cumulative production, remaining reserves, reserve growth and undiscovered resources - is estimated at about 3 trillion barrels of oil. Of this, about 24 percent has been produced and an additional 29 percent has been discovered and booked as reserves. The natural gas endowment is estimated at 15.4 quadrillion cubic feet (2.5 trillion barrels of oil equivalent), of which only about 11 percent has been produced and an additional 31 percent has been discovered and booked as reserves. The USGS assessment is not exhaustive, because it does not cover all sedimentary basins of the world. Relatively small volumes of oil or gas have been found in an additional 279 provinces, and significant accumulations may occur in these or other basins that were not assessed. The estimates are therefore conservative.

Geotimes↗
USGS2005

Comparison of methods used to estimate conventional undiscovered petroleum resources: World examples

Various methods for assessing undiscovered oil, natural gas, and natural gas liquid resources were compared in support of the USGS World Petroleum Assessment 2000. Discovery process, linear fractal, parabolic fractal, engineering estimates, PETRIMES, Delphi, and the USGS 2000 methods were compared. Three comparisons of these methods were made in: (1) the Neuquen Basin province, Argentina (different assessors, same input data); (2) provinces in North Africa, Oman, and Yemen (same assessors, different methods); and (3) the Arabian Peninsula, Arabian (Persian) Gulf, and North Sea (different assessors, different methods). A fourth comparison (same assessors, same assessment methods but different geologic models), between results from structural and stratigraphic assessment units in the North Sea used only the USGS 2000 method, and hence compared the type of assessment unit rather than the method. In comparing methods, differences arise from inherent differences in assumptions regarding: (1) the underlying distribution of the parent field population (all fields, discovered and undiscovered), (2) the population of fields being estimated; that is, the entire parent distribution or the undiscovered resource distribution, (3) inclusion or exclusion of large outlier fields; (4) inclusion or exclusion of field (reserve) growth, (5) deterministic or probabilistic models, (6) data requirements, and (7) scale and time frame of the assessment. Discovery process, Delphi subjective consensus, and the USGS 2000 method yield comparable results because similar procedures are employed. In mature areas such as the Neuquen Basin province in Argentina, the linear and parabolic fractal and engineering methods were conservative compared to the other five methods and relative to new reserve additions there since 1995. The PETRIMES method gave the most optimistic estimates in the Neuquen Basin. In less mature areas, the linear fractal method yielded larger estimates relative to other methods. A geologically based model, such as one using the total petroleum system approach, is preferred in that it combines the elements of petroleum source, reservoir, trap and seal with the tectono-stratigraphic history of basin evolution with petroleum resource potential. Care must be taken to demonstrate that homogeneous populations in terms of geology, geologic risk, exploration, and discovery processes are used in the assessment process. The USGS 2000 method (7th Approximation Model, EMC computational program) is robust; that is, it can be used in both mature and immature areas, and provides comparable results when using different geologic models (e.g. stratigraphic or structural) with differing amounts of subdivisions, assessment units, within the total petroleum system. ?? 2005 International Association for Mathematical Geology.

Conference Paper↗
USGS2002

Worldwide estimates of deep natural gas resources based on the U.S. Geological Survey World Petroleum Assessment 2000

The U.S. Geological Survey recently assessed undiscovered conventional gas and oil resources in eight regions of the world outside the U.S. The resources assessed were those estimated to have the potential to be added to reserves within the next thirty years. This study is a worldwide analysis of the estimated volumes and distribution of deep (>4.5 km or about 15,000 ft), undiscovered conventional natural gas resources based on this assessment. Two hundred forty-six assessment units in 128 priority geologic provinces, 96 countries, and two jointly held areas were assessed using a probabilistic Total Petroleum System approach. Priority geologic provinces were selected from a ranking of 937 provinces worldwide. The U.S. Geological Survey World Petroleum Assessment Team did not assess undiscovered petroleum resources in the U.S. For this report, mean estimated volumes of deep conventional undiscovered gas resources in the U.S. are taken from estimates of 101 deep plays (out of a total of 550 conventional plays in the U.S.) from the U.S. Geological Survey's 1995 National Assessment of Oil and Gas Resources. A probabilistic method was designed to subdivide gas resources into depth slices using a median-based triangular probability distribution as a model for drilling depth to estimate the percentages of estimated gas resources below various depths. For both the World Petroleum Assessment 2000 and the 1995 National Assessment of Oil and Gas Resources, minimum, median, and maximum depths were assigned to each assessment unit and play; these depths were used in our analysis. Two-hundred seventy-four deep assessment units and plays in 124 petroleum provinces were identified for the U.S. and the world. These assessment units and plays contain a mean undiscovered conventional gas resource of 844 trillion cubic ft (Tcf) occuring at depths below 4.5 km. The deep undiscovered conventional gas resource (844 Tcf) is about 17% of the total world gas resource (4,928 Tcf) based on the provinces assessed and includes a mean estimate of 259 Tcf of U.S. gas from the U.S. 1995 National Assessment. Of the eight regions, the Former Soviet Union (Region 1) contains the largest estimated volume of undiscovered deep gas with a mean resource of343 Tcf.

Natural Resources Research↗