American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
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" Corrugated" flow in heterogeneous variable-density aquifers causes anomalous gradients in head or in potential. These gradients retard the establishment of equilibrium under and around a gas storage bubble after withdrawal of storage gas. The head under the storage bubble can be less than the head at the same elevation outside the bubble. Thus, gas can be forced into layers deeper than the injection strata.
In a variable-density aquifer certain gravitational effects influence flow (Bond, 1973). The purpose of the present paper is to show:
how these gravitational effects can be used to explain anomalies in indicated flow directions in reservoirs;
how these gravitational effects reduce the response in pumping tests; and
how these effects pumping tests; and
how these effects influence the growth of a gas-storage bubble.
I have shown that in a variable-density aquifer, structure on the top and the bottom of the aquifer can influence the potential or the head in the aquifer. Also, relatively impermeable tilted barriers within the aquifer-barriers that divert flow from horizontal paths-can cause a difference in head. In an aquifer that contains such barriers, flow is diverted down and then up, over and over again, to give an undulatory, "corrugated" flow. That is, if water flows, it flows through a series of irregular U-shaped troughs (Bond, 1973).
In a region where a dense water is being displaced by a lighter water, the dense water in the U-shaped troughs is not necessarily displaced completely. The net result is a series of troughs, or U-tubes, containing light water on the inlet side and dense water on the outlet side of each of the U-tubes. Each U-tube produces a head difference, H 1.00 (in terms of fresh water), equal to (pD-pL) Delta Z, where pD and pL are the relative densities of the dense and light water, respectively, and Delta Z is the depth of the U-tube. In a series of U-tubes, the head differences are additive. Thus, anything within the aquifer that causes flow to deviate from the horizontal can introduce gravitational effects that result in differences in head.
One may argue that, even though barriers to horizontal flow are present, tortuous horizontal paths that permit some flow around these barriers can be found.
