Abstract The U.S. Geological Survey (USGS) recently assessed potential volumes of undiscovered technically recoverable conventional oil, natural gas, and natural gas liquids (NGL) of the world, exclusive of the United States (USGS, 2000). Using a geology based methodology, the USGS defined 149 total petroleum systems (TPS) and 246 assessment units (AU) in 128 oil and natural gas provinces worldwide, and quantitatively assessed undiscovered resources in each of the 246 AU. This assessment provides estimates of the quantities of conventional, technically recoverable oil, natural gas, and natural gas liquids, exclusive of the United States, that have the potential to be added to reserves in the next 30 yr (1995 to 2025). These amounts include estimates of undiscovered volumes and the estimated volume of reserve growth for discovered fields. The assessment results are shown in Table 1 , and are summarized as follows: a mean of 649 billion bbl of undiscovered conventional oil with a range of 344–1107 billion bbl of oil; a mean of 4669 tcf of conventional natural gas with a range of 2299–8174 tcf, and a mean of 207 billion bbl of natural gas liquids with a range of 95–378 billion bbl of NGL, exclusive of resources in the United States. Adding these assessment results to estimates of undiscovered oil and natural gas resources of the United States, the cumulative production, remaining reserves, and reserve growth of provinces throughout the world, a total world endowment of conventional oil resource, was estimated by the USGS to be about 3 trillion barrels

Abstract Fossil fuels will remain an important source of energy for much of this century under most energy projections, although their abundance and potential shortages are debated. Their distribution, quantities, and availability will thus continue to be of paramount importance for world economies. Policy decisions made in the U.S. and elsewhere depend on detailed knowledge of petroleum resources and their distribution in the world. Therefore, petroleum resources are periodically reassessed, not just because new data become available and better geologic models are developed, but also because many non-geologic factors such as technologic advances, accessibility to markets, and geographic or societal constraints determine which part of the crustal abundance of petroleum will be economic and acceptable throughout some foreseeable future. Detailed petroleum information was published in a recent world assessment of petroleum resources conducted by the U.S. Geological Survey (USGS) in their World Petroleum Assessment (WPA) 2000 (USGS, 2000). Two major components of world petroleum resources exclusive of the United States were assessed by the U.S. Geological Survey (USGS, 2000): undiscovered conventional resources and reserve (field) growth. This assessment provided estimates of the quantities of conventional technically recoverable oil, natural gas, and natural gas liquids (NGL), outside the United States, that have the potential to be added to reserves (Table 1). Many individuals and groups, such as the International Energy Agency (IEA 2000, 2001, 2002) and the Energy Information Administration of the Department of Energy (EIA, 2000, 2001a,b), Cavallo (2002), and Greene et al. (2003) use the USGS (2000) study as

Abstract Volumes (statistical mean estimates) of undiscovered conventional oil, natural gas, and NGL (exclusive of the U.S.) as assessed in USGS (2000) are: Â∈¢ 649 billion bbl of oil (Figure 9) Â∈¢ 4669 tcf of natural gas (778 billion BOE) (Figure 10) Â∈¢ 207 billion bbl of natural gas liquids (NGL) (Figure 11) Table 1 summarizes the estimates of the ranges of volumes of undiscovered conventional oil, natural gas, and NGL for the world both exclusive and inclusive of U.S. petroleum resources. Lognormal probability distributions for the three commodities, exclusive of the U.S., are shown in Figures 9, 10, and 11. These estimates demonstrate that a significant volume of undiscovered petroleum is yet to be found in the world. The estimates of undiscovered resources of individual assessment units were aggregated into TPS, provinces, regions, and finally the world. Perfect positive dependency among estimates was assumed at the AU, TPS, province, country, and region levels. In aggregating the eight region-level sets of estimates to the world level, a positive dependency of 0.5 was assumed. Dependencies assumed for aggregations are described in USGS (2000) by Charpentier et al. (2000).

Abstract Reserve growth refers to the increases, in estimated sizes of discovered fields, that can occur through time as oil and natural gas fields are developed and produced. In the U.S., which is one of the most intensely explored countries in the world, reserve growth is widely considered to be a major component of remaining oil and natural gas resources ( Arrington, 1960 ; Root and Mast, 1993 ; Attanasi and Root, 1994 ; Root et al., 1995 ; Schmoker and Attanasi, 1996, 1997; Attanas and Schmoker, 1997; Attanasi et al., 1999 ; Verma, 2000; Klett, 2003; Klett and Schmoker, 2003 ). A forecast of world potential reserve growth was therefore a necessary element of the World Petroleum Assessment 2000 (USGS, 2000). The forecast (Table 1) shows that the estimated potential additions to reserves from reserve growth are nearly as large as the estimated undiscovered resource volumes ( Schmoker and Klett, 2000 ). Unlike World Petroleum Assessment 2000 (USGS, 2000), allocations of the world reserve growth were made in this study for the eight regions of the world for liquid petroleum, oil and natural gas liquids, ( Figure 30 ), and natural gas ( Figure 31 ). Reserve growth refers to the increases, in estimated sizes of discovered fields, that can occur through time as oil and natural gas fields are developed and produced. In the U.S., which is one of the most intensely explored countries in the world, reserve growth is widely considered to be a major component of remaining oil and natural gas resources ( Arrington, 1960 ; Root and Mast, 1993 ;

Abstract Although there have been individual analyses of source rock intervals and some elements of the total petroleum system ( Klemme, 1986 ; Tissot et al., 1987; Klemme and Ulmishek, 1991 ; Perrodon, 1992 ; Magoon and Dow, 1994), the USGS (2000) study of world TPS provides many new geologic insights, petroleum volumes associated with the TPS, and a significant database for further studies. Some of these insights are discussed briefly for the elements of the TPS, and supporting data are shown in a series of Figures, maps, and Appendices. In this study a large body of geologic information was assembled and synthesized for the TPS of the world included in the assessment. Eight geologic parameters from the geologic summaries for each of the assessment units (AU) were recorded in a spreadsheet (Appendix 4) and for each TPS (an aggregation of AU into their TPS) in Appendix 5. The geologic parameters are (1) source rock age, (2) source rock character, (3) peak maturation age, (4) reservoir rock age, (5) reservoir rock deposi- tional environment, (6) reservoir rock lithology, (7) seal lithology, and (8) trap type. The data from the eight geologic parameters were examined in terms of frequency of occurrence in the world TPS and their correlation with petroleum resource volumes. Total petroleum resource volumes, in billion BOE, are further distinguished as (1) known (cumulative production plus remaining reserves, [data from Petroconsultants, 1996]); (2) undiscovered volumes (data from USGS, 2000); and (3) conventional endowment, which consists of the sum of known

Abstract To understand where the greatest potential for undiscovered resources lies, a summary of the estimated largest undiscovered fields from the USGS (2000) assessment is included here (Appendices 6, 7). Additionally, analyses of the depth, pressure, and temperature attributes of the world’s oil and natural gas fields provide insights into the world distribution of these parameters. Appendices 6, 7, 8, and 9 present information about possible locations of large, undiscovered fields in the world by assessment units (AU). Because of the extreme skewness of field-size distributions, much uncertainty exists as to the size of the largest undiscovered fields. The procedure used provides a distribution that shows the uncertainty for size of the largest undiscovered field for each AU ( Charpentier and Klett, 2000 ). Because of high uncertainty, the statistics in Appendices 6 through 9 should be viewed for their relative, rather than absolute, value. Appendix 6 presents a ranked list of AU by the estimated size of the largest undiscovered oil field. Appendix 7 shows a similar list for the largest undiscovered natural gas field. Appendix 8 shows the ranking of AU by number of expected oil fields with at least 1024 MMBO. Appendix 9 illustrates AU ranking by number of expected natural gas fields with at least 6144 bcf (1024 million BOE). All four of these appendices show that many of the largest fields remaining to be discovered are expected in Region 2, the Middle East and North Africa. East Greenland is also high on the oil ranking (Appendix 6)

Abstract Economics of onshore petroleum exploration and production are very different from offshore. In the assessment process, allocations of estimated undiscovered volumes were made to onshore and offshore locations (where applicable) in order to enhance the utility of the results for further economic analysis. Offshore areas were deemed those that required offshore infrastructure, in either fresh or salt water. Estimated volumes of onshore and offshore undiscovered oil by region (excluding the U.S.) are shown in Figure 96 ; of undiscovered natural gas, in Figure 97 ; and of NGL, in Figure 98 . Most of the onshore undiscovered resources are expected to be in Regions 1 (Former Soviet Union) and 2 (Middle East and North Africa). Figure 99 shows that, at the world level, approximately equal amounts of each of the three undiscovered commodities are expected to be onshore and offshore. Figure 100 shows that for Regions 3 through 8, about one-fourth of the undiscovered volume of each commodity is expected to be onshore and nearly three-quarters of the potential is offshore. The offshore potential of each assessment unit (AU), total petroleum system (TPS), and province and the water depths associated with the offshore portion for each AU, is documented in USGS (2000). Most offshore provinces extend to water depths of 6562 ft (2000 m) with the exception of areas where exploration has already begun in deeper water depths. For example, the water depth limits of the AU were extended to 13,123 ft (4000 m) in the Campos Basin

Abstract Therefore, the grown endowment of recoverable oil is estimated in the USGS (2000) at about 3 trillion bbl of oil ( Table 1 ; Figure 107 ). The grown natural gas endowment is estimated at about 2.6 trillion BOE ( Table 1 ; Figure 107 ). Oil reserves as of 12/2001 are 1.1 trillion bbl of oil; world consumption is about 0.028 trillion bbl of oil per year. Natural gas reserves are about 0.8 trillion BOE; world consumption is about 0.014 trillion BOE. Without any additional discoveries of oil, natural gas, or natural gas liquids, there are about 2 trillion BOE of proved petroleum reserves. Of the oil and natural gas grown endowment of about 5.6 trillion BOE, the world has consumed about 1 trillion BOE, or 17% leaving about 83% of the grown endowment to be found and/or utilized ( Figures 12 , 13 , 107 ; 1 trillion bbl of oil = 1000 billion bbl of oil, 1 trillion BOE = 1000 billion BOE). The potential additions to reserves from reserve growth are estimated to be nearly as large as the estimated undiscovered resource volumes. The additional remaining reserves and the estimates for reserve growth from these known fields imply that 76% of the world’s grown conventional oil endowment ( Figures 12 , 107 ) and 66.3% of the world’s conventional grown natural gas endowment have already been discovered in the areas assessed ( Figures 13 , 107 ). For these areas, 23.5% of the world’s total conventional grown oil endowment and 11.4%

Abstract The USGS World Petroleum Assessment 2000 (USGS, 2000) provides estimates of the quantities of conventional oil, natural gas, and natural gas liquids outside the United States that have the potential to be added to reserves in the next 30 years (1995 to 2025). Excluding the U.S., the mean estimated volumes of undiscovered resources are 649 billion bbl of oil, 4669 tcf, and 207 billion bbl of NGL. The estimated mean additions to reserves from discovered fields (reserve growth) are 612 billion bbl of oil, 3305 tcf, and 42 billion bbl of NGL. The potential additions to reserves from reserve growth are nearly as large as the estimated undiscovered resource volumes. These estimates imply that 75% of the world’s grown conventional oil endowment and 66% of the world’s grown conventional natural gas endowment have already been discovered in the areas assessed (exclusive of the U.S.). Additionally, for these areas, 20% of the world’s grown conventional oil endowment and 7% of the world’s grown conventional natural gas endowment had been produced by the end of 1995. By way of calibration, the 8 years since 1995 are less than one-third of the 30-yr forecast span (1995–2025) for the assessment. During this period, 18% of estimated oil resources and 27% of the estimated natural gas resources have been added to reserves from new field discoveries and reserve growth for the provinces assessed in USGS (2000). If the entire world is considered, exclusive of the U.S. and Canada, these percentages increase to 23% of

Abstract Presented in this publication are the results of a major study of the petroleum resources of the world as analyzed by total petroleum systems. The distribution and volumes of resources available in these systems are critically important for the future of the world's economies. Geologic insights gained from studying these 149 systems and their constituent assessment units in 128 provinces and 96 countries, exclusive of the United States, allow a new look at petroleum accumulations and the rocks that are intimately associated with them. The geographic distributions of oil and natural gas systems show significant differences. Lists of new areas of potential and new estimates of resources make this a must-have addition to the petroleum geologist's library.

Abstract Analysis of estimated total recoverable oil volume (field size) of 186 well-known giant oil fields of the world (>0.5 billion bbl of oil, discovered prior to 1981), exclusive of the United States and Canada, demonstrates general increases in field sizes through time. Field sizes were analyzed as a group and within subgroups of the Organization of Petroleum Exporting Countries (OPEC) and non-OPEC countries. From 1981 through 1996, the estimated volume of oil in the 186 fields for which adequate data were available increased from 617 billion to 777 billion bbl of oil (26%). Processes other than new field discoveries added an estimated 160 billion bbl of oil to known reserves in this subset of the world's oil fields. Although methods for estimating field sizes vary among countries, estimated sizes of the giant oil fields of the world increased, probably for many of the same reasons that estimated sizes of oil fields in the United States increased over the same time period. Estimated volumes in OPE C fields increased from a total of 550 billion to 668 billion bbl of oil and volumes in non-OPEC fields increased from 67 billion to 109 billion bbl of oil. In terms of percent change, non-OPEC field sizes increased more than OPE C field sizes (63% versus 22%). The changes in estimated total recoverable oil volumes that occurred within three 5-year increments between 1981 and 1996 were all positive. Between 1981 and 1986, the increase in estimated total recoverable oil volume within the 186 giant oil fields was 11 billion bbl of oil; between 1986 and 1991, the increase was 120 billion bbl of oil; and between 1991 and 1996, the increase was 29 billion bbl of oil. Fields in both OPEC and non-OPEC countries followed trends of substantial reserve growth.

Abstract The problem addressed here is the calculation of the mass of hydrocarbons generated by the active source rock pod of a petroleum system. This calculation method follows a four-step sequence: (1) the source rock is identified and its boundaries defined, (2) the mass of organic carbon in the source rocks is calculated (equation 1), (3) the mass of hydrocarbons generated per gram of organic carbon is estimated (equation 2), and (4) the total mass of hydrocarbons generated is determined by multiplication of these data (equation 3). The key idea of the calculation is use of the hydrogen index to quantify the fractional conversion of kerogen to hydrocarbons. The hydrogen index, derived from Rock-Eval pyrolysis, represents the potential of a source rock to generate additional hydrocarbons. The difference between the original hydrogen index prior to any petroleum generation and the present-day hydrogen index thus approximates the decrease in generation potential and is equated here to hydrocarbons generated.