The Fundamentals, Simulation, and Management of Conventional and Unconventional Recoveries
E-Book, Englisch, 488 Seiten
ISBN: 978-0-12-800523-1
Verlag: Elsevier Reference Monographs
Format: PDF
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)
Connects key reservoir fundamentals to modern engineering applicationsBridges the conventional methods to the unconventional, showing the differences between the two processesOffers field case studies and workflow diagrams to help the reservoir professional and student develop and sharpen management skills for both conventional and unconventional reservoirs
Abdus Satter retired from Texaco in 1998 as a senior research consultant after 30 years of service, and he started his own company for engineering consulting and training services. Besides Texaco, he worked for Amoco Petroleum Company, Frank Cole Engineering and taught at the University of Western Ontario and Ahsanullah Engineering College in Bangladesh. He is an expert with 40+ years of experience in reservoir engineering, reservoir simulator development, applications, water flooding an enhanced oil recovery processes. He has taught many reservoir courses in the US and internationally and has authored four other books and many articles. Dr. Satter is a distinguished member of SPE, Legion of Honor and also a Life member. He holds a BS degree in Mechanical Engineering from the University of Dhaka, PE and MS degrees in Petroleum Engineering from the Colorado School of Mines and a PhD in Engineering Science from the University of Oklahoma.
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2 Elements of conventional and unconventional petroleum reservoirs
Abstract
It is important to have a clear understanding of the depositional environment and natural events that shape various characteristics of the petroleum reservoirs through geologic times. Sedimentary rock types, structural and stratigraphic characteristics, and reservoir heterogeneities including the presence of faults and fractures are directly influenced by various processes and events that occur in nature. An overview of petroleum reservoir rock types indicates that conventional reservoirs are mostly composed of sandstones and carbonate rocks. About 60% of the world’s production of oil and gas is based on carbonate rocks, while sandstone reservoirs account for about 30% of production. Worldwide occurrences of petroleum, combined with the temperature range of catagenesis as well as the geothermal gradient of sedimentary basins, suggest that there is an “oil window,” i.e., the depth range where the petroleum reservoirs are most likely to exist. This chapter also presents a comprehensive modeling study of the petroleum system in Alaska. Keywords
sedimentary rocks petroleum basin oil window catagenesis depositional environment basin modeling shale gas shale oil Introduction
It is important for reservoir engineering professionals to have a clear understanding of the basic elements and events of nature that influence petroleum reservoirs from inception until the present day. A detailed knowledge of the origin, migration, and entrapment of hydrocarbons in geologic formations aids in evaluating the characteristics, behavior, and potential of the reservoir. The petroleum industry utilizes the valuable information in the exploration of the new frontiers of oil and gas; a case study demonstrating the above is presented in this chapter. Furthermore, the knowledge aids in the interpretation of geologic events that shaped the petroleum basins, regional geologic trends, extent of the reservoirs, estimates of hydrocarbon volume, and the analysis of subsurface pressure anomalies, among others. There is a new focus on the origin of petroleum due to the fact that the source rock of petroleum plays a direct role in the exploration of unconventional reservoirs. Wells are drilled in the source rock to produce oil and gas wherever geologic and other conditions are favorable. Study of the reservoir elements leads to the following queries: • How are petroleum reservoirs formed? • How, when, and where did oil and gas originate? • What are the types of the reservoir rocks? • How are the fluids accumulated and trapped in a reservoir? • What are the essential rock properties to store and produce petroleum? • Did petroleum fluids originate at the same location as discovered today? • What is a petroleum system? What are its elements? • Is there any distinction between the elements of conventional and unconventional reservoirs? • How do computer models aid in petroleum exploration and production? The answers to these queries can be found in the results of wide-ranging studies pertaining to the petroleum basin, the reservoir, and the rocks. The studies include, but not limited to, geological, geochemical, petrophysical, geophysical, hydrodynamic, and geothermal. The organic matter found in the rocks is also the subject of intense scrutiny. Tools and methodologies involved in the studies range from very basic, such as field observation, to the most sophisticated, including simulation of robust computer models. Reservoir rock types and production of petroleum
Shale is the most abundant rock type in sedimentary basins, comprising about 80% or more of the total rock volume in many instances. However, conventional oil and gas reservoirs are mostly composed of sandstone and carbonate formations, often interbedded with shale. Carbonate reservoirs are highly prolific producers, about 60% of the world’s production of petroleum is based on these reservoirs. Sandstone reservoirs account for over 30% of production. In recent times, however, production potential from shale and other unconventional resources is rapidly gaining intense industry interest since the early years of this century. A sizeable portion of natural gas in the United States is currently produced from unconventional shale gas reservoirs. Certain metamorphic or igneous rocks are known to be producers of petroleum. However, the source of petroleum is believed to be sedimentary rock, mostly shale, from which oil moved to the other rock types mentioned above. Sandstones are widely composed of feldspar and quartz grains with their origin rooted in desert, stream, or coastal environments in prehistoric ages. The grains range from micrometers to millimeters and are typically cemented by silica. Carbonate rocks (limestone or dolomite) are based on the skeletal remains and shells of organisms that chiefly lived in shallow marine environments. Carbonates may have inorganic origin too, where calcite is precipitated in water. Certain limestones transformed into dolomites following postdepositional processes involving the evaporation of marine water, transformation of calcium carbonate to magnesium carbonate, and recrystallization. Shale, the most abundant of reservoir rock types, is composed of clay and silt particles. It is not uncommon to encounter petroleum reservoirs having a combination of the various rock types mentioned above. For example, a sandstone reservoir with appreciable shale content is referred to have a shaley sandstone lithology. Origin of petroleum
Over decades, scientists have proposed several theories regarding the origin of petroleum, including organic, abiogenic, and cosmic. Based on field evidence, laboratory investigations, mathematical modeling, and analyses, the organic origin of petroleum has been largely accepted by the petroleum industry. In the following, the elements of petroleum reservoirs are discussed in brief. Deposition of sediments and organic matters: the process begins
The origin of petroleum is rooted in the transportation and deposition of sediments in marine, shallow marine, deltaic, lagoon, swamps, mud, desert, and various other environments by the natural forces of wind, water, ice, and gravity over long periods in ancient times. Pertaining details for various rock types related to deposition of sediments are presented in Table 2.1. A typical depositional process involving mountains, land, and sea shelf is depicted in Figure 2.1. Table 2.1 Origin of sedimentary rocks [1] Rock type Sediment Transport and accumulation Notes Sandstone Sand Desert dunes – windblown sands (eolian), river channels (fluvial), low gradient stream valleys (alluvial), deltas, shorelines, and shallow seas Light beige to tan in color; sometimes dark brown to rusty red. Composed of grains of quartz, feldspar, etc. and cemented by silica Conglomerate Gravel River channels, alluvial fans, and wind-swept coastlines Grains of sandstone and conglomerate originate from pre-existing rocks and minerals Limestone (calcium carbonate) and dolomite (calcium–magnesium carbonate) Shells, algae, and coral; precipitation of calcite Warm shallow seas Usually light to dark gray in color; exhibits fossil molds and casts; void spaces largely due to dissolution and vugs Chalk (calcium carbonate) Produced by marine plankton Deep seas Fine textured Shale Clay, silt Lakes (lacustrine), tidal flats, river flood plains, deltas, and deep seas Dark brown to black in color; sometimes dark green; composed of fine grains of clay and silt. Exhibits lamination in the horizontal direction Coal Woody plant matter, peat Swamps Chert (silicon dioxide) Produced by marine plankton Deep seas Rock salt Salt Lagoons or marginal seas Figure 2.1 Typical depositional environment of sediments and organic matter in shallow and deep marine.
The accumulation of sand, shale, silt, clay, and carbonates depends on the location, available energy, and other natural processes. The depositional process continued through prehistoric ages. Deposited along with the sediments was organic matter such as marine organisms and remnants of woody plant material, among others. These organic resources ultimately led to the origination of oil and gas found in present day reservoirs in a span of tens to hundreds of millions of years. Types of sediments
Sediments are of clastic, biochemical, and chemical origin as in the following: • Clastic (detrital) rocks such as sandstone and siltstone are formed by the particles or grains of...
