Reservoir Structures

It is rare to be able to observe elastic deformations (which occur for instance during earthquakes) since by definition an elastic deformation does not leave any record. However, many subsurface or surface features are related to the other two modes of deformation. The composition of the material, confining pressure, rate of deformation and temperature determine which type of deformation will be initiated. 

A secondary feature is the development of rollover anticlines which form as a result of the downward movement close to the fault plane which decreases with increasing distance from the plane. Rollover anticlines may trap considerable amounts of hydrocarbons. 

Growth faulted deltaic areas are highly prospective since they comprise of thick sections of good quality reservoir sands. Deltas usually overlay organic rich marine clays which can source the structures on maturation. Examples are the Niger, Baram or Mississippi Deltas. Clays, deposited within deltaic sequences may restrict the water expulsion during the rapid sedimentation / compaction. This can lead to the generation of overpressures. 

Four mechanisms have been suggested to explain how faults provide seals. The most frequent case is that of clay smear and juxtaposition (Fig. 5.8) 

less frequent fault seals are created by  

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Keywords reservoir structures, faults, folds, depositional environments, diagenesis, geological controls, porosity, permeability... 

Folds are features related to compressional, ductile deformation (Fig. 5.10). They form some of the largest reservoir structures known. A fold pair consists of anticline and syncline. 

If the original field development plan was not based on a 3-D seismic survey (which would be a commonly used tool for new fields nowadays), then it would now be normal practice to shoot a 3-D survey for development purposes. The survey would help to provide definition of the reservoir structure and continuity (faulting and the extension of reservoir sands), which is used to better locate the development wells. In some cases time-lapse 3-D seismic 4D surveys carried out a number of years apart, see Section 2) is used to track the displacement of fluids in the reservoir. 

The In Salah gas project took up operation in Algeria during summer 2004. There as well, a C02-rich natural gas is treated to reach commercial concentrations of C02. After separation in an amine plant, the C02 is stored in the gas-containing reservoir structure. Using the same structure for production and storage of course involves the risk of a breakthrough of C02 into the production wells. 

The basic units of carbohydrates are the monosaccharides or simple sugars. These may be assembled into more complex structures such as disaccharides, polysaccharides, glycoproteins, and glycolipids. Carbohydrates serve as energy sources, energy reservoirs, structural components, and for cellular communication. 

The reservoir structure was updated by shooting a 3D seismic survey. 

Unlike conventional oil and gas reservoirs, structure and stratigraphy often play a secondary role in the accumulation of hydrocarbons within a BCGS, primarily because of the dynamics associated with the abnormal pressure generation (Law 1984a,b, 1985, 1995 Masters 1979, 1984 Nuccio et al. 1992). BCGSs are often not in static capillary equilibrium which is usually manifested by capillary pressure transitions that are more a function of two-phase capillary seals than from structural closure (Iverson 1994 ... 

Microseismic monitoring is currently the best available method for obtaining three-dimensional information about reservoirs and fracture systems at locations remote from boreholes. The primary problem of the method is its location accuracy. When located with conventional location algorithms, the events are frequently seen to be distributed as a cloud with little macro- or microstructure. It is difficult to meaningfully correlate such images with logging data of existing wells. Therefore, information on detailed reservoir structure, fracture orientation, and hydraulic behavior cannot be obtained from the application of conventional microseismic location techniques. 

Fehler, M., Jupe, A. and Asanuma, H. (2001). More Than Cloud New techniques for characterizing reservoir structure using induced seismicity. The Leading Edge, 324-328. 

A review on field applications of steam foams is given in [261]. It is shown that experiments on injection of aqueous steam foam surfactant solutions, conducted earlier gave a relatively low increase in oil recovery, but remained profitable nevertheless. To achieve better results, the reservoir structure must be taken into consideration for the choice of an optimum foam injection regime. 

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