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...ies in 3D space with geologic models as a template. Geologic models are constructed by distributing facies within a sequence stratigraphic framework using the systematic distribution of ...facies within a depositional model as a guide. There are many types of ...facies, and ...
Reservoir models are constructed by distributing petrophysical properties in 3D space with geologic models as a template. Geologic models are constructed by distributing facies within a sequence stratigraphic framework using the systematic distribution of facies within a depositional model as a guide. There are many types of facies, and facies selection is normally based on the question to be answered. Water depth and changes in sea level are key questions when building a sequence stratigraphic model, and fossil and other grain types together with depositional textures are keys to estimating water depth. Thus, numerous "depositional" facies are commonly described from core material.
... the definition of the internal stratigraphic layering (bedding geometry) and the definition of the facies. In this step, the sedimentary model must be defined in terms of sequence stratigraphy. Once the 3...The layering schemes define lines of correlation inside the model and are used to laterally connect facies and, ultimately, the petrophysical properties. Fig. 3--Internal bedding geometries for two reservo...ration and internal layering, but the volume still is empty (Fig. 4). The next step is to model the facies and simulate their 3D spatial distribution. ...
A reservoir characterization study is a part of the development of a reservoir model. This article describes each of the basic elements involved in a reservoir characterization study. The result of reservoir characterization is the creation of the shared-earth model. The shared-earth model provides for efficient updating of the critical information necessary for 3D modeling. At the basic interpretation stage, the discipline expert interprets the primary data, whereas the geologist and geophysicist collaborate on the structure model and sequence definition.
...t: Flooding surfaces are widespread interfaces that contain evidence of an upward, water-deepening facies dislocation, such as contact between the following: A ravinement surface is a specific type of flo...rface that suggests that transgressive passage of a surf zone has eroded underlying shallower-water facies. Maximum flooding surfaces are interfaces that contain evidence of a widespread, upward, water-dee...pening facies dislocation that is associated with the inferred, deepest water ...
Interpreting seismic data requires an understanding of the subsurface formations and how they may affect wave reception. This article discusses some of the key stratal interfaces and their implications for interpreting the data received. All instantaneous seismic attributes (amplitude, phase, frequency) can be used in interpretation. In practice, most interpreters use instantaneous amplitude, or some variation of an amplitude attribute, as their primary diagnostic tool. Amplitude is related to reflectivity, which in turn is related to subsurface impedance contrasts.
...thofacies from one well to the next by assuming a degree of horizontality and continuity of similar facies. This approach leads to images with highly continuous lithofacies and porosity zones. Many depositi...onal facies, however, are known to be highly discontinuous laterally and vertically, and correlating similar li...formance of carbonate reservoirs. Fig. 1.9 – Generalized block diagram illustrating carbonate-ramp facies patterns and topography. In arid climates, evaporite deposits may form by precipitation of gypsum ...
The efficient extraction of oil and gas requires that the reservoir be visualized in 3D space. Engineers need a conceptual model of reservoirs, an integral part of the decision-making process, whether it be selecting perforations or forecasting future production. However, most engineering measurements made on reservoirs have little or no spatial information. For example, a core measurement has no dimensional information, wireline logs and continuous core measurements are 1D, and production data and pressure information are volumetric but with unconstrained spatial information. Geologic information, on the other hand, contains valuable spatial information that can be used to visualize the reservoir in 3D space. Therefore, engineers should understand the geologic data that can improve their conceptual model of the reservoir and, thus, their engineering decisions. The first and most important geologic information is the external geometry of the reservoir, which is defined by seals or flow barriers that inhibit the migration of hydrocarbons, forming a hydrocarbon trap. The buoyancy force produced by the difference in density between water and hydrocarbons drives migration. Migration will cease, and a hydrocarbon reservoir will form, only where hydrocarbons encounter a trap. Traps are composed of top, lateral, and bottom seals; the geometry of traps can have structural, sedimentary, or diagenetic origins. The second most important geologic information is the internal reservoir architecture. A reservoir is composed of rock types of varying reservoir quality that are systematically stacked, according to stratigraphic and diagenetic principles.
...t. The combination of organic activity, ocean currents, topography, and eustasy produces a typical facies progression from land to basin during highstand, as shown in Fig. 3: The peritidal ...facies, composed of tidal-flat-capped cycles, normally defines the most landward position of an HFC. The c...te sediment onto the mud flat with tidal and storm currents. Tidal-flat sediments are key indicator facies because they define sea level. The tidal-flat environment is divided into the intertidal zone overl...
Carbonate sediments are commonly formed in shallow, warm oceans either by direct precipitation out of seawater or by biological extraction of calcium carbonate from seawater to form skeletal material. The result is sediment composed of particles with a wide range of sizes and shapes mixed together to form a multitude of depositional textures. The sediment may be bound together by encrusting organisms or, more commonly, deposited as loose sediment subject to transport by ocean currents. A basic overview of carbonate-reservoir model construction was presented by Lucia, and much of what is presented herein is taken from that book. Depositional textures are described using a classification developed by Dunham. The Dunham classification divides carbonates into organically bound and loose sediments (see Figure 1). The loose sediment cannot be described in simple terms of grain size and sorting because shapes of carbonate grains can vary from spheroid ooids to flat-concave and high-spiral shells having internal pore space.
...most favored locales for eolian accumulation. Eolian environments can be divided into the following facies: Dunes are large bed forms that come in an array of forms. Barchans, barchanoid ridges, and transv...tional and may fill a small basin. The combination of fluvial and marine processes creates a unique facies assemblage and reservoir architecture. Deltaic sediments are deposited as: Together, these ...facies compose a delta lobe, which is a fundamental building block of a delta system. Delta systems are di...
Siliciclastic (commonly referred to as clastic) rocks are composed of terrigenous material formed by the weathering of pre-existing rocks, whereas carbonate rocks are composed principally of sediment formed from seawater by organic activity. This difference effects hydrocarbon recovery and therefore is important to understand. Clastic sediments are composed of grains and clay minerals, and siliciclastic sediments are first classified according to grain type. Second, siliciclastics are described in terms of grain size (Figure 1b). Mixtures are described with a modifying term for a less-abundant size, such as clayey sandstone, sandy siltstone, or muddy sandstone (Figure 1c).
...(cumulative distribution function, or cdf)--remain constant within a given geologic interval and/or facies, from realization to realization. Typically, the structural and stratigraphic model (major structur...e, the results are different at unsampled locations, producing local changes in the distribution of facies and petrophysical properties in the interwell space. Note that selection of the same random seed al...oals and on data types and their availability. The pixel-based method works best in the presence of facies associations that vary smoothly across the reservoir, as often is the case in deltaic or shallow ma...
A pixel-based model assumes that the variable to be simulated is a realization of a continuous (Gaussian) random function. Using the spatial model, search ellipse, and control data, a pixel-based method simulates values grid node by grid node. Some of the most popular pixel-based algorithms are: turning bands, sequential Gaussian, sequential indicator, truncated Gaussian, and simulated annealing. Each method can produce a range of realizations that capture the uncertainty of an regionalized variable (RV), and so the method choice here will be based on the goals and on data types and their availability. The pixel-based method works best in the presence of facies associations that vary smoothly across the reservoir, as often is the case in deltaic or shallow marine reservoirs.
...%. In the first part of the calibration method, the shaly-sand sequence is classified into several facies according to the clay distribution. Initially, 10 ...facies are identified in the cores, but they are reduced to four petrophysical ...facies consisting of: The electrical continuity of the shale components increases with each ...
This article presents brief summaries of detailed petrophysical evaluations of several fields that have been described in the SPE and Soc. of Professional Well Log Analysts (SPWLA) technical literature. These case studies cover some of the complications that occur when making net-pay, porosity, and water saturation (Sw) calculations. Prudhoe Bay is the largest oil and gas field in North America with more than 20 billion bbl of original oil in place (OOIP) and an overlying 30 Tscf gas cap. In the early 1980s, the unit operating agreement required that a final equity determination be undertaken. In the course of this determination, an extensive field coring program was conducted, which resulted in more than 25 oil-based mud (OBM) cores being cut in all areas of the field and some conventional water-based mud (WBM) and bland-mud cores in other wells.
...thofacies from one well to the next by assuming a degree of horizontality and continuity of similar facies. This approach leads to images with highly continuous lithofacies and porosity zones. Many depositi...onal facies, however, are known to be highly discontinuous laterally and vertically, and correlating similar li...aphic units between chronostratigraphic surfaces, which are sometimes defined by unconformities and facies shifts. A key premise is that the surfaces are formed in response to eustatic sea-level changes of ...
An understanding of the geology of the reservoir is essential to its development, production, and management. This include both the external geology of the reservoir -- what created the hydrocarbon trap -- and the internal geology of the reservoir -- the nature of the rocks in which the hydrocarbons exist. This article focuses on what an engineer needs to know about the external and internal geology to understand the reservoir from which he or she is planning to produce hydrocarbons. The efficient extraction of oil and gas requires that the reservoir be visualized in 3D space. Engineers need a conceptual model of reservoirs. Conceptual models are an integral part of the decision-making process, whether that process involves selecting perforations or forecasting future production. However, most engineering measurements made on reservoirs have little or no spatial information. For example, a core measurement has no dimensional information, wireline logs and continuous core measurements are 1D, and production data and pressure information are volumetric but with unconstrained spatial information.