Horizontal wells have added to our ability to increase recoveries duringenhanced recovery operations and from mature reservoirs. Infill horizontalwells can recover oil which has been bypassed by vertical wells; also, horizontal wells can recover oil from those parts of a reservoir which couldnot be accessed with vertical wells. More generally, horizontal wells should bean integral part of any enhanced recovery, be it in conventional oil, heavy oilor gas. In situations where economical recovery is viable only throughhorizontal wells, then horizontal well development should be fully recognizedas being enhanced recovery in its own rights.

Whether horizontal wells constitute the EOR process itself or whether theycontribute to the success of some other EOR process, such as chemical, miscible, or thermal processes, one can group the ultimate advantages of usinghorizontal wells, as compared to vertical wells, into two bread categories:

  1. greater recovery with fewer wells

  2. further recovery from mature reservoirs

If you are new to horizontal wells and wish to ensure your first applicationto be a success, here are the most favorable situations:

  • Thin pay zones which have sufficiently high vertical permeability,

  • Reservoirs which contain enormous numbers of natural vertical fractures butwhere there is poor communication between the fractures,

  • Situations where it is desirable to obtain very large production, injectionor withdrawal rates,

  • Enhanced oil recovery where a significant increase in the sweep efficiencyis wanted, such as promoting solvent spreading,

  • To reduce water coning, particularly in heavy oil reservoirs underlain by alarge, active aquifer.

When planning further recovery from a mature reservoir with combination EORand horizontal wells, one should give consideration to the following:

  • Locate injection wells so as to distribute injected fluids evenly in thereservoir, i.e.- increase the sweep efficiency

  • Locate production wells so as to optimize the capture of the incrementaloil.

As examples, horizontal well applications in miscible, thermal, gravitydrainage of heavy oil, waterflooding, polymer flooding, carbon dioxide floodingare reviewed.

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