Useful instantaneous source functions for a two-layered reservoir with architecture akin to letter ‘E’ are compiled for all possible external boundary types assuming that each layer of the reservoir has a horizontal well. Both crossflow and no-crossflow interface cases in a normal and inverted architecture are considered.

Results show that sixteen (16) different boundary variations are possible each for normal and inverted architecture. Among these variations only two (2) may have the maximum six (6) similar external boundary combinations of either no-flow or constant-pressure. There are two (2) mandatory infinite-acting external boundaries in each architecture. With the interface considered as a constant-pressure interlayer boundary, the more the number of constant-pressure external boundaries, the fewer the number of uniform flux (sealed boundaries or no-flow) instantaneous source functions that can be written down and vice versa. Only single edged external fluid drive is possible in any architecture irrespective of the nature of the interface. Similarly, only one (1) top and one (1) bottom external fluid drive is possible for crossflow interface. For no-crossflow interface, only the top layer can be subject to top external fluid drive and only the bottom layer can be subject to a bottom external fluid drive.

In the inverted architecture, the heel of the horizontal well becomes the toe and vice versa. The predominant instantaneous source function in all the combinations is the infinite-acting source function of the kind I(x). The influence of this dominant function, and therefore, that of the entire layered reservoir, can be optimized especially where the interface is crossflow. The optimization is possible by completing the well as far away from the sealing boundary as possible to decelerate arrival of pseudosteady state and from a constant-pressure boundary to guarantee prolong clean oil production.

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