The present disclosure generally relates to the production of fluids from a subterranean formation, and, more specifically, to subsurface well systems having multiple drain wells and methods for use thereof.
Multiple, interlinked wells are commonly used in subterranean operations to maximize the production of hydrocarbon fluids from a subterranean formation. The use of multiple, interlinked wells may result in higher production than can be obtained from multiple, non-interlinked wells. Interlinked wells can be particularly advantageous in lenticular pay zones (also commonly referred to in the art as compartmentalized reservoirs), for example, where there can be multiple, non-contiguous hydrocarbon-bearing subterranean zones. FIG. 1 shows a schematic of an illustrative lenticular pay zone 1 having isolated hydrocarbon-bearing subterranean zones 2 located therein. Hydrocarbon-bearing subterranean zones 2 can vary widely in size and shape. It can be difficult to penetrate a sufficient number of hydrocarbon-bearing subterranean zones in a lenticular pay zone while using only a single well, particularly a substantially vertical well. Even when multiple wells, optionally having lateral branches, are used to penetrate a greater number of hydrocarbon-bearing subterranean zones, the formation pressure may not be sufficiently high to enable free fluid flow from the well. In either case, production from the lenticular pay zone may not be economically feasible, even though significant amounts of hydrocarbon fluids may be present therein.
In cases where the formation pressure is insufficient to enable free fluid flow from a well, a lifting mechanism can be employed to assist in the production of a hydrocarbon fluid to the earth's surface. From an operational standpoint, it can often be desirable to have a substantially vertical production well when using a lifting mechanism to assist in fluid production. In a lenticular pay zone, this preference for a substantially vertical production well can make contact with multiple hydrocarbon-bearing subterranean zones problematic when using a single production well.
When multiple hydrocarbon-bearing subterranean zones are being simultaneously penetrated by several wells, the wells can be configured as drain wells to channel hydrocarbon fluid flow toward a few interlinked production wells. For example, the drain wells can be discharged into a collection well which directs the hydrocarbon fluid flow to the production wells. Use of one or more collection wells can be advantageous from the standpoint of pooling the hydrocarbon fluids into a larger volume that is more easily produced to the earth's surface. Pooling of hydrocarbon fluids into a larger volume can also make production more economically viable. In addition, directing the hydrocarbon fluid flow to a few production wells avoids having to control production and maintain a separate lifting mechanism at a large number of separate production wells.