Charles D. Masters

Resource Constraints in Petroleum Production Potential

Geologic reasons indicate that the dominant position of the Middle East as a source of conventional petroleum will not be changed by new discoveries elsewhere. The share of world crude oil production coming from the Middle East could increase, within 10 to 20 years, to exceed 50 percent, under even modest increases in world consumption. Nonconventional resources of oil exist in large quantities, but because of their low production rates they can at best only mitigate extant trends. Increased production of natural gas outside the United States, however, offers an opportunity for geographically diversified energy supplies in the near future.

Use of Sedimentary Structures in Determination of Depositional Environments, Mesaverde Formation, Williams Fork Mountains, Colorado

Rock-stratigraphic units composing the Mesaverde Formation of northwestern Colorado were deposited in offbeach, beach, lagoon, swamp, and floodplain environments of deposition. The vertical distribution of these rock-stratigraphic units reflects the lateral distribution of environments at the time of deposition. In a similar manner, the vertical distribution of sedimentary structures within the rock-stratigraphic units reflects the lateral distribution of processes at the time of deposition. Therefore, an understanding of modern processes and the distribution of their resultant sedimentary structures will permit prediction, through the principle of uniformitarianism, of the vertical distribution of stratification within the depositional products of ancient environments. > It is possible to subdivide the products of the various nearshore marine and nonmarine deposits into a series of subenvironments based on types of stratification. In a regressive suite of rocks, beginning with the offbeach environment, the rocks are characterized by parallel laminae and low-angle cross-laminae reflecting deposition from suspension and from low-energy traction currents. Landward, through the beach environment, varying processes and energy levels result in a sequence of sedimentary structures characteristic of the offshore-beach, submarine-bar, and foreshore-beach subenvironments. The beach zone may be overlain by rocks of the lagoonal, swamp, or floodplain environments. The lagoonal environment comprises sedimentary structures indicative of processes in tidal-delta, ti al-channel, lagoon-pond, and tidal-flat subenvironments. The swamp environment is characterized predominantly by lithology--coal and carbonaceous sediments--rather than by stratification. The floodplain environment comprises stratification characteristic of the channel and interchannel subenvironments.

Distribution and quantitative assessment of world crude-oil reserves and resources

The enumeration of world crude-oil reserves and resources is a difficult undertaking. One must rely on data gathered by others and, through various spot-check and cross-check mechanisms, distinguish the reasonable from the unreasonable. Estimating techniques vary; standards of measurement vary; classification of the reported elements differ; and, in some cases, even the recognition of what is being reported is obfuscated by language and nomenclatural ambiguities. Therefore, to improve understanding of world petroleum resources, it is prudent to describe the methodologies and measurement standards explicitly, to disaggregate the data as much as possible to gain insight into the source of the differences, and to standardize the classification and nomenclature scheme to establish unambiguous communication.

Probabilistic Assessment of World Petroleum Resources and Reserves at Fourteenth World Petroleum Congress: Abstracts from World Petroleum Congress, Stavanger, 1994 World Petroleum Assessment and Analysis

The occurrence and quantity of world petroleum resources appears to be well understood. The numbers are so great, however, that even minor variants in the total picture can be responsible for enormous localized industrial activity. Specific knowledge of the widespread local occurrences of oil and gas, therefore, is important to economic development and to the free market distribution of energy. It is also clear, however, that a large proportion of the recoverable petroleum resources are found in only a few selected localities. We believe that, worldwide, recoverable conventional oil and gas exist in ultimate quantities approximating 2300 billion barrels (370 Gm3) of oil and 12 000 trillion cubic feet (340 TM3) of gas. These values are limited by our concepts of world petroleum geology and our understanding of specific basins; nonetheless, continued expansion of exploration activity, around the world, has resulted in only minimal adjustments to our quantitative understanding of ultimate resources. Reserves reporting has been one of the greatest hindrances to a thorough understanding of world resources because we are just now gaining an understanding of field growth and what is actually being calculated and reported from various localities. Unconventional resources are present in large quantities, in particular in the Western Hemisphere, and are of a dimension to substantially contribute to world reserves should economic conditions permit.

United States Assessment Procedures and World Energy Resources Program: ABSTRACT

Resource assessment is a people-oriented endeavor. At every stage of the exercise, good judgment is essential to satisfactory results. There is no single procedure that can guarantee an approximation of truth, but clearly there are procedures and techniques to be selected from within the context of the problem to be solved that serve to lessen subjectivity in the final outcome. The U.S. Geological Survey has had the responsibility of determining petroleum potential, especially for basin size areas. This determination assists in the decision process relative to lease sales, wilderness areas, and international relations. Our requirement is basin understanding, not exploration well siting. Considering the dimension of the objectives, the time frame of need, and the resources available (both people and data), volumetric analysis at the level of the play (group of prospects) is rarely practical. Rather, as described in U.S. Geological Survey assessment documents, we have utilized a variety of volumetric/analogy techniques, sometimes comparing with Klemme classifications, with specific United States or foreign basins, or internally within the basin being assessed, which in effect is a degree of maturity analysis. The petroleum geology of the basin and the results of the various number-generating processes are then subjected to the Delphi process, as reported elsewhere, for the group assessment. The assessment so determined is the hypothesis of the petroleum potential of the area. Because the hypothesis derives from an analysis of petroleum parameters such as source rock, reservoir rock, traps, and seals (which data are published), it is subject to testing as exploration proceeds or as new data are made available. The advantage of the assessment is only partly in the number. In addition, the organization of data permits the recognition of anomalies in the exploration process or in resource reports, thus permitting ongoing adjustments in the assessment or its analysis. End_of_Article - Last_Page 504------------

Environmental Interpretation of Upper Part of Mesaverde Formation, Northwestern Colorado, from Outcrop, Core, and Subsurface Study: ABSTRACT

Various lines of evidence, such as the vertical succession of gross lithologic character, textures, and sedimentary structures, the fauna, and the geometry of rock stratigraphic units, indicate that the upper part of the Hayden Gulch outcrop section of the Mesaverde Formation in northwestern Colorado is a sequence of former barrier islands and lagoons intertonguing with overlying offbeach marine shale of the Lewis Formation. The collective criteria used to recognize the different depositional environments at the outcrops were readily apparent in a core taken along depositional End_Page 730------------------------------ strike from the outcrop section; the nearly perfect vertical sequence of lithology in a core compensates for the loss of lateral exposure in outcrop. Correlation of the outcrop section with electric logs permitted mapping of the distribution of the rock-stratigraphic units, and the resultant geometric interpretation precluded a delta interpretation for this particular stage of Mesaverde deposition in this area. End_of_Article - Last_Page 731------------

Stratigraphic Analysis Through Determination of Depositional Environments: ABSTRACT

The Mesaverde Formation of the Western Interior Cretaceous seaway includes rock units representative of off-beach, beach, lagoon, swamp, and floodplain environments of deposition. Because of migration of the shoreline by transgression and regression, the sedimentary products of various environments are arranged vertically in the geologic record in the same succession as they occurred laterally at the time of deposition. The detailed distribution of the potential reservoir beach sandstone bodies in a regressive sequence follows different patterns, depending on variations in the relative rate of submergence during progradation. These variations are reflected in the character of the back-beach environment. A mainland beach-floodplain progradation, reflecting a low rate of su mergence, results in a tabular sheet of beach sandstone which intertongues only slightly with the overlying floodplain End_Page 2036------------------------------ rocks; a barrier island-lagoonal progradation, reflecting a high rate of submergence, comprises a series of discrete sandstone lenses arranged en echelon, each lens intercalating landward with lagoonal deposits and seaward with off-beach marine shale. During transgression, because of the step-like topography of a barrier island-lagoonal terrain, shoreline sandstone bodies are developed only discontinuously, giving rise to asymmetrical cycles. Because of the general paucity of organic remains in the Mesaverde, the determination of depositional environments commonly must be accomplished by the evaluation of stratification. Though there are no single stratification features peculiar to particular environments, sequences of stratification may be diagnostic. Stratification in rocks occurs in response to physical-depositional processes; the vertical sequence of stratification in a regressive suite of rocks reflects the lateral distribution of processes operative at the time of deposition. Beach stratification, from bottom to top, includes laminae deposited in the transition zone between off-beach shale and offshore beach sandstone, the submarine bar zone, the fore-shore beach, and the back-shore beach. A vertical sequence of lag on stratification may reflect deposition in a tidal delta, lagoon pond, tidal channel, wave flat, and salt marsh. The character of the stratification in the different sub-environments may be determined by study of modern environments and processes; the great variety of processes present within these modern environments yields perspective on the variety of stratification to be expected in the geologic record. End_of_Article - Last_Page 2037------------