The Well / Aquifer Model (Initial Test Results)   -   6

2.0   BACKGROUND RESEARCH AND PREVIOUS WORK

Prior to design of the well/ Aquifer model, an exhaustive literature search was undertaken on previous works relating to both theoretical and experimental procedures on well screens, gravel packs, and aquifer materials.  Some of the more important investigations have provided guidance in this study, with some major conclusions or hypotheses incorporated into the present research.  A summary of the more important investigations regarding hydraulics of well screens and gravel packs is included in Appendix I.

3.0   MODEL DESIGN AND CONSTRUCTION

3.1  Physical Model Type

The function of the model is to reproduce the operating components of production water wells.  These include well screens, entrance velocities, gravel packs, and aquifers.  These criteria necessitated building an apparatus that would reflect more of a prototype condition than a scaled down model.  Thus, a wedge-shaped model 5 ft high and 12 ft long was conceived which represents a typical section of an aquifer having pure radial flow into a well.  The sides of the prism represent those of an equilateral triangle with the internal angles being 60 degrees, or 1/6 the circumference of a well (see Figure 3).  The physical dimensions of the model were designed to permit testing of commonly used well screens.

Figure 3

With model well screen diameter of 10 in. and a standpipe providing 60 ft of head (or drawdown) on the aquifer, a maximum model flow of 300 gpm is attainable using typical aquifer materials.  This model flow is equivalent to 1800 gpm for a similar well in the field penetrating a 5 ft section of the same aquifer materials.

To achieve the strength required and prevent deflection, the frame was constructed as a welded one-piece tank.  The top and one apex of the wedge are flanged and removable.  They are heavily ribbed to withstand the potential of 150 ton hydraulic forces with minimal deflection.  The three sides of the model are tied together with a network of steel bars spaced every 20 in. to maintain the stiffness required.

In order to prevent water from bypassing the aquifer along the top of the model (a common problem in sand tank models), an inflatable diaphragm was installed between the aquifer and the model top plate.  Water pressure 4 to 6 psi higher than the aquifer system pressure is introduced into the diaphragm to prevent "channeling" along the top of the aquifer.

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