Doublets and other allied well patterns

Whenever a liquid is injected into an infinite reservoir containing liquid with the same flow properties, the equations of flow are well known. The pressures in such a system vary over time and distance (radius) in ways that depend on the formation and liquid flow properties. Such equations are well known--they form the basis for the voluminous well-testing literature in petroleum engineering and ground water hydrology. Suppose there are two wells--one an injector and one a producer--with identical rates. The behavior of this system can be calculated using superposition; which merely means that the results can be added independently of each other. When this is done, the remarkable result is that after a period of time there is a region that approaches steady state flow. Thereafter, the pressures and flow velocities in this region stay constant. The size of this region increases with time. This ``steady state`` characteristic can be used to solve a number of interesting and useful problems, both in heat transfer and in fluid flow. The heat transfer problems can be addressed because the equations are identical in form. A number of such problems are solved herein for doublet systems. In addition, concepts are presented to help solve other cases that flow logically from the problems solved herein. It is not necessary that only two wells be involved. It turns out that any time the total injection and production are equal, the system approaches steady state. This idea is also addressed in these notes. A number of useful multiwell cases are addressed to present the flavor of such solutions.