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u <br />~II:, InBlonket <br />f.\ ~ tLJt ~~: <br /> <br />Figure 6. Progression of Cas~:ry washing Using Srationary Pipe Techniti <br />Movable Pipe Technique <br />This procedure consists of washing the cavity in a series of horizontal layers. The vertical <br />extent of each layer is limited on the bottom by saturated brine and on. the top by an inert blanket. <br />Figure 7 shows the typical advance made in cavity formation using this technique. <br />It affords a higher degree of control than [he [wo previous methods since the layers can be <br />made very thin rendering almost any shape possible. However, this greater accuracy is obtained <br />at the expense of more [ime consuming pipe manipulations. Moreover, precise pipe positioning is <br />very critical. <br />Any one of the aforementioned systems may be used for the construction of relatively simple <br />shapes such as cones or cylinders. Cylinders can also be formed by the direct circulation method <br />bu[ with less economical use of the circulating water. For more complex shapes, such as <br />spheres, the layer [echnique, described below, was found to be most satisfactory. <br />Layer Technique <br />In order to visualize this process, consider the volume element formed by revolving the <br />quadrilateral ABCD (Fig. 8a) about the vertical axis X. A series of area strips can then be re- <br />volved about [his same axis, as in Fig. bb to form concentric thin-walled segments around the <br />original volume element. If [hese strips are such that their widths are eery small, making the <br />number of strips revolved very large, and the horizontal and vertical progressions are controlled, <br />it is possible to obtain a geometric shape that closely resembles a sphere (Fig. Sc). <br />By utilizing this process over a wide range of flow rates and pipe settings, a cavity is formed <br />through expanding the frustum of a conic section. The greatest diameter of [he frustum of the cone <br />always coincides with the blanket-water contact. Leaching begins with the blanket (air, natural <br />gas or a liquid hydrocarbon) at the top of the proposed cavity. As the cap ity is enlarged, the blan- <br />ket is gradually lowered by an amoun[ dictated by the geometry of the projected shape so tha[ [he <br />blanket-water interface always coincides with the surface of [he projected shape. Almost any de- <br />sired shape can be cons[ructed in [his manner as long as the sides of the cavity below the blanket <br />are confined within the limits of the superimposed shape. <br />302 <br />.~ <br />