(a) Demonstrate the analogy between the reservoir rock and a number of capillary
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Question
(a) Demonstrate the analogy between the reservoir rock and a number of capillary tubes of different diameters, and (b) Explain the water saturation distribution with depth in an oil reservoir using the schematics of capillary tubes. (c) Based on your diagram of capillary tubes, make link to the free water line of a reservoir. (d) What's a profile of initial water saturation distribution look like? (e) What are the parameters (in words) you need to predict the water saturation distribution after a period of waterflooding operation?Explanation / Answer
1. An analogous for the reservoir rock is one in the same geographic area that is formed by the same, or very similar geological processes as, a reservoir it regards sedimentation, diagenesis, pressure, temperature, chemical and mechanical history, and structure. It also has the same or similar geologic age, geologic features, and reservoir rock and fluid properties whereas Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. The effect can be seen in the drawing up of liquids between the hairs of a paintbrush, in a thin tube, in porous materials such as paper and plaster, in some non-porous materials such as sand and liquefied carbon fiber, or in a cell. It occurs because of intermolecular forces between the liquid and surrounding solid surfaces. If the diameter of the tube is sufficiently small, then the combination of surface tension and the adhesive force between the liquid and container wall act to propel the liquid.
2. Water saturation distribution with depth in oil reservoir with analogy comes with two phases problem firstly, Static problems, involving only the static balance between capillary force sand those due to the difference in densities of the fluids; i.e., gravitational forces. Dynamic problems, involving analysis of the motion of mixtures of immiscible fluids in porous media under the influence of forces due to gravity, capillarity, and an impressed external pressure differential. Under this heading, the static type of problem will be discussed and the results of experimental investigations on the capillary properties of unconsolidated sands will be presented. Although the discussion of this section is, in a sense, prefatory to the treatment of problems of mixture flow, the concepts developed here have considerable intrinsic importance apart from their application to flow problems. For, it is reasonable to postulate that the reservoir fluids are, owing to their long existence in undisturbed mutual contact prior to exploitation, in substantial equilibrium. It follows that their distribution in the reservoir at the time of tapping should be entirely predictable from the theory of capillary equilibrium, provided certain experimentally measurable properties of the reservoir rock are known. Knowledge of the distribution of the several fluids in the reservoir is, of course, helpful in the estimation of the reserve, and in other problems.
It is to be emphasized that throughout the discussion of capillary statics it is assumed that the fluids are in equilibrium from the capillary standpoint.Thus, water, where it is referred to as being in a reservoir, will be understood to be interstitial water, present at the time of drilling the reservoir, commonly termed "connate" water only problems involving clean, unconsolidated sands can be made to yield numerical solutions, since only such sand have been adequately investigated experimentally. Experimental evaluation of the pertinent properties of natural reservoir rocks will permit the extension of the numerical treatment of problems involving these materials. We shall now consider in some detail the static equilibrium of fluid mixtures in porous solids; that is, the manner in which the reservoir fluids are distributed vertically when the forces due to capillarity are just balanced by those due to gravitation.
3. The capillary tube makes water through free water line is Irreducible water saturation sometimes called critical water saturation defines the maximum water saturation that a formation with a given permeability and porosity can retain without producing water. This water, although present, is held in place by capillary forces and will not flow. Critical water saturations are usually determined through special core analysis. The critical water value should be compared to the reservoir's in-place water saturation calculated from downhole electric logs. If the in-place water saturation does not exceed the critical value, then the well will produce only hydrocarbons. These saturation comparisons are particularly important in low permeability reservoirs, where critical water saturation can exceed 60% while still producing only hydrocarbons. Capillary pressure is equal to the product of the height above the free water surface and the density difference between the two fluid phases at reservoir conditions. In a reservoir, the relationship between water saturation and height above an oil-water or gas-water contact is, of course, strongly dependent on the rock pore system, as well as on the wettability and interfacial tension properties of the rock-fluid system.
4. The initial water distribution saturation distribution look's like as Irreducible Water Saturation.
5. We Need the Following parameter
for oil reservior -
where:
k = permeability
q = flow rate
m = fluid viscosity
Dp = pressure differential
L = length
A = cross-sectional area
Furthermore, we find that the total flow rate (Qt,) is expressed by the equation:
Qt = (Qo + Qw),
Popularly Known As Darcy's equation.
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