开发地质培训英文教材-标准化文件发布号：（9456-EUATWK-MWUB-WUNN-INNUL-DDQTY-KIIProduction GeologyTable of Contents1.Introduction2.Non-marine clastic depositional systemsa.Introductionb.Low sinuosity fluvialc.High sinuosity fluviald.Eoliane.Alluvial fan3.Shallow and deep marine systemsa.Deltasb.Shore-zonec.Deep marine4.Sequence Stratigraphya.Introductionb.Fundamental concepts and terminologyc.Systems tractsd.Application5.Reservoir Geophysicsa.Introductionb.Terminology and fundamental conceptsc.Seismic acquisitiond.Seismic processinge.Seismic framework interpretationf.Acoustic impedance, attribute analysis, direct hydrocarbon indicators, and 4Dseismic6.Fractured Reservoirsa.Introductionb.Key conceptsc.Types of fracturesd.Character of the fracture planee.Detecting and quantifying fracturesf.Fracture porosity, permeability, and productivityg.Data gathering and reservoir characterization7.Capillary Pressurea.Introductionb.Buoyancy and capillary forcesc.The capillary pressure equationd.Determining capillary pressuree.Displacement pressure and saturation distributionsf.The Leverett J-functiong.Reservoir sealsh.Hydrostatic versus hydrodynamic reservoirsi.Examples of how capillary pressure controls the location of oil-water contacts8.Reservoir Heterogeneities and the Use of Geostatisticsa.Introductionb.Types of heterogeneitiesc.Steps to identify heterogeneitiesd.Importance of capturing the appropriate heterogeneitiese.Why geostatistics is neededf.How to calculate a variogramg.Variogram modelingh.Kriging versus conditional simulationi.Object modelingj.Sequential Gaussian simulation9.Geocellular Modelinga.Introductionb.Project scopingc.Data import and quality checkingd.Framework constructione.Three-dimensional griddingf.Property modelingg.Volumetrics and net payh.Realization assessmenti.Upscaling and exportj.Numerical simulation and reserves1. IntroductionProduction geology is a geological sub-discipline that focuses on identifying and producing hydrocarbons from known accumulations. The responsibilities of the production geologist are to 1) determine development well locations that target remaining hydrocarbons, 2) help explain the performance of existing wells by understanding the reservoir quality and lateral continuity of producing horizons, 3) determine the volume of hydrocarbons-in-place and the uncertainties associated with this value, and 4) look for additional opportunities including missed pay behind pipe in existing wells, shallower and deeper pay, and step-out wells that expand the existing field or discover new fields.The primary objective of this course is to provide participants with insights and tools to help them become an effective production geologist. Production geologists differ from exploration geologists, who often work with little data and generate broad play concepts that are sharpened into prospects. The production geologist typically has more data, generates more detailed descriptions, and must be prepared to answer many specific questions that exploration geologists do not consider. A comprehensive list of these questions is included in Table 1-1. While this class will not address all of these questions, it will provide participants with fundamental skills and a philosophy of how to conduct their work, so that the goal of answering all of these questions can be reached.A secondary objective of this course is to help participants understand how to build geocellular models, including how to incorporate information from other disciplines, and how long it should take to build these models. Figure 1-1 is generic geocellular modeling workflow, showing different tasks and how they inter-relate. Although this workflow must be modified for each individual project, it nonetheless provides a basic template for carrying-out geocellular modeling work.Geocellular models have become the primary tool used by geologists to capture their data and interpretations. These models also contain information provided by petrophysicists, geophysicists, and reservoir engineers. The models are used for development planning, reservoir visualization, and geosteering wells. In order to construct these models, geologists must be experts in many critical areas including the six listed below:Depositional systems: to understand the likely geometry, lateral continuity and reservoir quality of sandbodies in the reservoirSequence stratigraphy: to understand the nature of key surfaces, how they should be correlated through the reservoir, and their role as baffles and barriers to fluid flowReservoir geophysics: to determine reservoir structure, faulting, and variations in properties in interwell areasGeostatistics: to use appropriate stochastic techniques for distributing petrophysical parameters including facies types, porosity, and permeabilityCapillary pressure: to distribute water saturation in the model and relate this to variations in rock qualityGeocellular modeling: to understand the techniques and workflows used to build models, and how the results are used by reservoir engineers and othersThis course focuses on these six areas, explaining the fundamentals concepts of each and illustrating these concepts with diagrams, photographs, and exercises.2. Non-Marine Clastic Depositional Systems2a. Introduction. Non-marine clastic depositional systems include low-sinuosity fluvial, high-sinuosity fluvial, eolian, and alluvial fan depositional environments (Figure 2a-1). High sinuosity fluvial systems make excellent reservoirs due to their high net-to-gross ratios, coarse grain size, and sheet-like distribution. Low-sinuosity fluvial systems often have lower net-to-gross ratios than high-sinuosity systems and sandbodies of limited size and lateral extent. Eolian reservoirs are excellent reservoirs because of their clean, well-sorted nature. In contrast, alluvial fan reservoirs are relatively rare due to extreme variations in grain size, sorting, and clay content.This chapter explains how sands and shales in each of these environments are deposited and preserved, and how to recognize them from cores and logs. It also discusses the size, shape, and continuity of different sandbody types, and the key heterogeneities contained within them that impact reservoir fluid flow.2b. Low-sinuosity Fluvial Systems. A low-sinuosity fluvial system is a deposit of sand and gravel, generally with lesser amounts of silt and mud, produced by a series of low to moderately sinuous braided rivers traversing a coastal plain. It differs from a high-sinuosity system in that there are multiple river channels, and it differs from an anastamosing system in that there are no permanent islands between the river channels (Figure 2b-1).Sand and gravel deposited in this fluvial system are concentrated in bars including longitudinal, lateral, and transverse bars (Figure 2b-2). Longitudinal bars have their long axis oriented parallel to flow whereas transverse bars are oriented transverse to the flow direction and migrate downstream. Lateral bars form along the channel margins and are submerged during flood events when coarse material is deposited on their surface. In addition to these basic types of bars, many others have been recognized and classified (Figure 2b-3). These bars are not stable, but instead migrate, and can be destroyed or enlarged with time (Figure 2b-4). The upstream portions of the bars accumulate coarser-grained sand and gravel with a blocky log signature whereas the downstream portions accumulate finer-grained sand and silt with a fining-upward log signature (Figure 2b-5).Low-sinuosity fluvial systems are composed primarily of massive-appearing, sheet-like or tabular sandstone bodies of relatively high lateral continuity. These are separated by discontinuous silty sandstone intervals or less commonly by thin and discontinuous shales. The most common classes of shales are floodplain shales, channel-fill shales, and thin shales that drape various bars. The most important of these are floodplain shales which can extend laterally for hundreds of meters. The major control on shale continuity is their subsequent erosion by fluvial processes, resulting in laterally discontinuous permeabilitybaffles instead of permeability barriers. Typical reservoir characteristics of low-sinuosity fluvial systems are summarized in Table 2b-1.A significant portion of the world’s oil reserves are contained within low-sinuosity fluvial sandstone reservoirs. It is estimated that there are at least 30 billion stock tank barrels of remaining proven oil reserves and 40 trillion cubic feet of remaining proven gas reserves. An excellent example of one of these reservoirs is the Prudhoe Bay field on the North Slope of Alaska, which is the largest oilfield in North America (Figure 2b-6). It has 12 billion barrels of recoverable oil reserves and a gas cap containing 47 trillion cubic feet of gas. The lower part of the reservoir contains heterogeneous delta-front and lower delta-plain sandstones whereas the upper part consists of more homogeneous low-sinuosity fluvial sandstones and conglomerates interbedded with floodplain, abandoned channel, and drape shales. An important heterogeneity in addition to shales in this reservoir is open-framework conglomerates. These were deposited as laterally extensive gravel bars and now serve as “thief” zones which receive most of the injected water or gas during secondary recovery operations.2c. High-sinuosity Fluvial Systems. A high-sinuosity fluvial system is one in which the ratio of the channel length to the down-valley distance exceeds . Higher sinuosity is favored by relatively low slopes, a high ratio of suspended to bed load sediment, cohesive bank material, and relatively steady discharge. The lateral distance across the active river channel system is referred to as the channel belt width, and the channel belt itself is contained within a larger floodplain (Figure 2c-1). With time, the channel belt migrates across the floodplain, cutting off portions of the active river channel (Figure 2c-2).The most important reservoir sandbody in a high-sinuosity channel belt is the point bar (Figure 2c-3). Point bars develop on the inner portion of each meander loop where the flow is slower allowing the sand to drop out. The opposite side, where the water flows faster and causes erosion, is referred to as the cut bank. Point bars are characterized by a sharp base, a fining-upward character, and are often overlain by rooted soil horizons (Figure 2c-4). Within the sandbody itself, there is commonly an upward transition from coarse gravel to trough cross-bedded, parallel-laminated, and rippled sandstone (Figure 2c-5).A secondary type of sandbody associated with high-sinuosity fluvial systems is the crevasse splay(Figure 2c-6). A crevasse splay is formed when a river breaks through a levee at floodstage and deposits its material on the floodplain. Crevasse splays typically are formed by the deposition of suspended sediment and are therefore finer-grained and siltier than point bars. The overall shape of a crevasse splay is lobate, such that they appear lenticular in sections normal and oblique to the flow direction, but triangular in sections parallel to the flow direction (Figure 2c-7).In addition to point bars and crevasse splays, other elements of high-sinuosity fluvial systems include levees, swamps, oxbow lakes, and floodplain deposits. Levees are elevated areas adjacent to the river channel containing overbank deposits of siltstone and very fine sand. They grade laterally into finer grained silts and clays of the floodplain and black organic-rich muds characteristic of swamps(Figure 2c-8). Floodplain sediments aredistinguished in core by their red, oxidized nature whereas swamps appear as rooted mudstones or coals. Oxbow lakes are crescent-shaped bodies of standing water in the abandoned channel (oxbow) of a meander loop (Figure 2c-9). Fine-grained silts and clays referred to as abandoned channel-fill eventually fill these lakes.Within a high sinuosity fluvial system, permeabilities are highest in the point bar and channel fill sands (Figure 2c-10). Crevasse splay permeabilities are typically 1-2 orders of magnitude lower, whereas levee and floodplain deposits are considered non-pay. A key element in determining whether these types of reservoirs can be drilled and produced is the degree to which reservoir sandbodies are connected. In a low net-to-gross reservoir, sandbodies may not be connected, or may only be connected in a few places along the length of the channel belt (Figure 2c-11).As the net-to-gross ratio increases, connectivity will increase such that not only will all the sandbodies be in pressure communication, but it will also be possible to effectively sweep them using secondary recovery processes such as waterflooding. The key is for the system to be sufficiently sand-rich and for there to be enough accommodation space so that sandbodies will erode into each other to form amalgamated channel belts across a broad area (Figure 2c-12). These creates more sand-prone areas that can be imaged from seismic and targeted with wells (Figure 2c-13). Most high sinuosity fluvial systems are complex, ranging from amalgamated, areally extensive sandbodies to isolated single sandbodies. A good example of this is the Stratton Field of southeast Texas which contains multiple sandbody types that are being delineated with the help of seismic data. (Figure 2c-14). Table 2c-1 summarizes the typical reservoir characteristics of high-sinuosity fluvial systems and how to recognize them from other depositional systems, including low-sinuosity fluvial systems. It should come as no surprise that low-sinuosity and high-sinuosity systems are end members, and that some fluvial systems show characteristics of each (Figure 2c-15). Only through the integration of sufficient core, log, and seismic data can the true nature of each system be known.2d. Eolian Systems.Eolian sand dunes produce hydrocarbons from the Permian Rotliegendes Formation of the North Sea, Jurassic strata in the Gulf of Mexico, and numerous other locations. Eolian reservoirs are commonly not as thick as those of other depositional systems, but can be of very high quality due to their clean, well-sorted nature. Deserts cover approximately 20% of the earth’s land surface, but eolian dunes (Figure 2d-1) only cover about one-quarter of the deserts while the rest of the area consists of alluvial fans, plays, stony plains, and eroding highlands. These dunes come in many shapes and forms as a function of wind direction and velocity (Figure 2d-2).In eolian systems, sand is transported by three major processes: saltation, suspension and surface creep (Figure 2d-3). By far, the dominant process is saltation which accounts for approximately 90% of sand transport. Saltation is a complex process of downwind grain movement by collision and bouncing. Saltating grains form a relatively dense layer that moves up the shallow-dipping (stoss) side of each sand dune and is deposited on the steeply-dipping (lee) side of the dune. Saltating grains are deposited by four processes:grainfall, wind ripple migration, avalanching, and adhesion (Figure 2d-4). In general, avalanche and wind ripple deposits are the main dune bedding structures that are preserved. Most eolian dune stratification is dominated by large-scale cross bedding (Figure 2d-5). A cross section through a series of migrating dunes (Figure 2d-6) shows that the preserved portion only represents a fraction of the original dune height. Planar surfaces separate the preserved dune bedsets which are generally one to two meters thick. A major control on stratification within dune systems is the level of the water table at the time of deposition (Figure 2d-7). Changes in the height of the water table preserve the dunes and can produce horizontal truncation surfaces of regional extent called supersurfaces. At times when the water table is at or above ground level, fine grained silts, algal mats, and evaporate deposits may accumulate in lakes and other wet portions of interdune areas (Figure 2d-8). Depending upon changes in the height of the water table and the amount of sand, wet eolian systems can become dry or visa-versa (Figure 2d-9)Eolian systems demonstrate contrasts in reservoir properties ranging from the core-plug scale to the entire reservoir. At the core plug scale, variations in grain size and sorting can result in large variations in porosity and permeability. Figure 2d-10shows a permeability value from a core plug compared with mini-permeameter values from the same core. The mini-permeameter values range from less than millidarcies to millidarcies, showing that a single core plug does a poor job of capturing the permeability variation inherent in these types of rocks. At a bedding scale, grain size variations in dune sheets and interdune deposits create both high quality reservoir intervals and permeability baffles (Figure 2d-11). This presence of these baffles creates complex fluid flow patterns within the reservoir (Figure 2d-12). Table 2d-1 summarizes the typical reservoir characteristics of eolian systems and how to recognize them from other depositional systems.2e. Alluvial Fan Systems. Alluvial fans are directional landforms that begin at a point source along a mountain front and spread-out downdip with an accompanying decrease in grain size and an increase in sorting. The most distinctive feature of alluvial fans is their form. Their characteristic shape results from sediment-charged flows exiting the mountain front at a point source and spreading out along a wide arc (Figure 2e-1). Their relatively steep slope (typically 2-12 degrees) produces topographic relief of 300 to 2000+ meters across the fan. Types of fans include fan-deltas which terminate into a standing body of water, terminal fans which form where topographically confined rivers drain into an unconfined lowland (Figure 2e-2), and bajadas which are a series of coalescing alluvial fans along a mountain front. Reservoir quality sand is most commonly located along the margins of these fans, while basin-margin faulting and downdip pinchouts of these sediments provide excellent trapping mechanisms. (Figure 2e-3).Alluvial fans begin to form when steep slopes of bedrock erode to produce loose masses of soil and rock fragments called colluvium. As water from rainfall or snowmelt is added, the masses become unstable and slide downhill. This process mixes the sediment, entraining air and water and transforming the slide into a gravity flow. The flow races down the fan until dewatering and a decrease in slope cause the shear strength of the mixture to exceed thedownhill pull of gravity, inducing deposition. The resulting deposit is poorly-sorted and generally massive or planar-stratified due to rapid deceleration of the flow.Alluvial fans are formed by two major types of gravity flows; debris flows and fluidal flows. Debris flows contain sand to boulder-sized clasts that are supported by a clay + water slurry (Figure 2e-4). Large debris flows can be up to 6 feet thick and may cover the entire fan. Debris flow fans have constant slopes of 5-15 degrees and downlap onto basin floor deposits (Figure 2e-5). Debris flow processes dominate fans in rugged, semi-arid regions containing glacial or volcaniclastic rocks.Fluidal flows contain sand and gravel carried downslope as bedload or suspended sediment that is deposited as sheetfloods or streamflows (Figure 2e-6). Sheetflood fans are characterized by catastrophic, turbulent, unconfined water flows that expand as they move downfan. Steamflow fans contain channel-fill and associated overbank deposits associated with a semi-permanent channel system. These types of fans typically have slopes of 2-8 degrees that decrease downdip. Their distal portion fines into a sandskirt that interfingers with basin floor deposits (Figure 2e-7). Streamflood and streamflow processes dominate fans with year-round discharge from highlands containing resistant rocks.A good example of a modern streamflow alluvial fan is the Scott glacial outwash fan in Alaska which shows a downfan reduction in gradient and an accompanying decrease in grain size as the fan transitions into a low-sinuosity fluvial system (Figure 2e-8). Another good example is the Kosi fan of Nepal and India which shows a downfan progression from gravelly braided, to straight, to slightly sinuous channel geometries (Figure 2e-9).Debris flow deposits are typically clast-supported, massive conglomerates. Sheet flood deposits are commonly interbedded gravel and sand deposited in couplets 10-30 cm thick. Streamflow deposits contain coarse-grained channel fill, longitudinal bars, and accretion bedding. As might be expected, most alluvial fans are not easily classified as “end members” but instead contain facies types that represent various types of deposits (Figure 2e-10). Alluvial fan deposition is characterized by infrequent, catastrophic events separated by long intervals during which secondary processes are active. In a subaerial environment, ponding, rooting, burrowing, and subaerial erosion produce siltstone lenses, soils, bioturbated horizons, and thin lags of winnowed clasts over the surface of the fan. These are preserved if succeeding flows do not completely erode them. Subaqueous fans contain reduced green or black shales, marine trace fossils, and grade distally into turbidites.The best candidates for hydrocarbon reservoirs are fan-deltas that have been reworked by marine processes to improve their reservoir quality. Figure 2e-11 shows a sequence formed from a progradational fan-delta that includes fine-grained shelf sands grading upwards into sand and gravel of the fan-delta plain. A good example of a modern fan delta is the Copper River delta in Alaska (Figures 2e-12 and 2e-13). The margin of this fan has been extensively modified by both tidal current and waves. There are numerous example of fan-delta reservoirs, including the Miocene Potter Sandstone of California (Figure 2e-14). Debris flow and turbidite sands in this reservoir are steamflooded to recover heavy oil. The reservoir also contains numerous baffles and barriers of muddy sandstone and siltstone. Theseformed over the entire surface of the fan-delta during periods when little sand was being supplied, and then were subsequently eroded by channeling and slumping as shown in the depositional model in Figure 2e-14.Table 2e-1summarizes the reservoir characteristics of alluvial fan systems and includes observations regarding their vertical profile, their sandbody geometry and lateral continuity, and their reservoir quality.3. Shallow and Deep Marine Depositional Systems3a. Introduction. Shallow marine depositional systems include deltas and shoreface sands whereas deep marine depositional systems are characterized by submarine fan sandbodies. Deltas are deposits of sediment formed where a river empties into a body of water. They form if the rate of amount of sediment that is supplied exceeds the ability of waves and tides to disperse it. Shoreface systems are primarily derived from the reworking and transport of deltaic sand along the shoreline. Shoreface sands are found in the narrow, high energy environment extending from wave base (water depth of about 10 meters) to the landward limit of marine processes. Deep marine systems consist of sands that have been transported beyond the edge of the continental shelf into deep water by sediment gravity flows.This chapter explains how sands and shales in each of these environments are deposited and preserved, and how to recognize them from cores and logs. It also discusses the size, shape, and continuity of different sandbody types, and the key heterogeneities contained within them that impact reservoir fluid flow.3b. Deltaic Depositional Systems. A delta forms where a fluvial system enters a standing body of water, producing a bulge in the shoreline (Figure 3b-1). Because fluvial systems carry most of the sediment that is deposited in a basin, deltas are very important locations for the accumulation of thick sediments. The facies types within deltas depend upon the influence of the river, waves, and tides. As such, there are river dominated, wave dominated, and tide dominated deltas, as well as combinations of these (Figure 3b-2). The primary locations of sand deposition in a delta are distributary channels, distributary mouth bars, and crevasse splays (Figure 3b-3). Non-pay facies include silts and muds associated with interdistributary bays and abandoned distributary channels.A cross-section through a prograding, river dominated delta (Figure 3b-4) shows that the upper delta plain contains point bar and crevasse splay deposits similar to a high-sinuosity fluvial system. In the lower delta plain, where the river is influenced by marine processes, the system is dominated by channel fill and mouth bar deposits. Mouthbars form due to the rapid decrease in water velocity as the river terminates into a lake or ocean, resulting in the deposition of a broad apron of sand. As the delta builds seaward (progrades), the distributary channel commonly incises its associated mouthbar (Cross-section B-B’, Figure 3b-4).Distributary mouthbars are characterized by a coarsening, thickening upward profile on logs (Figure 3b-5). They are commonly more poorly-sorted than distributary channel sands because the sediment is dumped into the standing body of water. They also can containsignificant amounts of organic material that has been transported down the river. Distributary channel-fill deposits are characterized by a sharp, eroded based and a blocky to fining-upward character on the logs (Figure 3b-6). There is typically an upward transition from trough cross-bedded sands to planar laminated and ripple sands at the top. The sands can be interbedded with thin shales that form during periods of low river discharge. Crevasse splays are similar to those found in high sinuosity fluvial systems (Figure 3b-7). They consist of finer-grained, siltier, and thinner sands than those found in mouthbars or distributary channels. As a result, their permeabilities are 1-2 orders of magnitude less than mouthbar or distributary channel sands. Crevasse splays form when a river breaches its levee, depositing sand in the adjacent interdistributary bay. Because of this, crevasse splays sands are encased by black or gray interdistributary bay fill shales.In a wave or tide dominated delta, distributary channel-fill and mouthbar deposits are transformed into shoreface sands or tidal bars. Whereas fluvial-dominated deltas have a “bird’s foot” geometry, wave-dominated deltas are elongated parallel to the shoreline and tidally-dominated deltas contain sandbars oriented perpendicular to the shoreline. Figure 3b-8is a diagram of the Niger Delta which is influenced by both waves and tides. These processes tend to result in cleaner, better sorted sandstones, but they can also destroy a delta by transporting the sand along the shoreline or seaward into the deep ocean.As a delta progrades, mouthbar sands are deposited on prodelta siltstones and shelf mudstones (Figure 3b-9). This progradation creates a geometry consisting of topset beds, inclined strata, and bottomset beds (Figure 3b-10). This is referred to as a clinoform geometry and is typically of prograding deltas. This demonstrates that deltas do not consist of flat, sheet-like sandstones, but instead consist of sands that thin seaward onto the underlying shelf deposits. Any attempt to correlate these sands should reflect this geometry. A good example is a correlation framework generated for the Romeo interval of the Prudhoe Bay Field in Alaska (Figure 3b-11). It shows that the sands consist of a series of en echelon, off-lapping, fluvially-dominated deltaic wedges.Deltaic depositional systems are recognizable by their lobate shape and the inclusion of distributary channel, mouthbar and crevasse splay sandstones. Most of the sand is contained within mouthbars that shingle in a down-dip direction. Reservoir quality is best where these sands are winnowed by wave or tidal action. Distributary channel belts range from narrow ribbon-like sandbodies formed during rapid progradation (when sediment supply is greater than basin subsidence), to more sheet-like sandbodies that form during aggradation (when sediment supply and basin subsidence are balanced).Distributary channels typically have good lateral continuity along depositional dip, with poorer continuity along depositional strike. However, in areas where distributary channels have incised their associated mouth bars, lateral continuity should be good in both the depositional strike and dip directions. Table 3b-1 summarizes this aspect, and other deltaic reservoir aspects important to the production geologist.3c. Shore-zone Depositional Systems.Shore-zone depositional systems are found in the narrow, high energy environment extending from wave base to the landward limit of marine。
