Horizontal wells in an Improved Oil Recovery (IOR) project can potentially improve sweep efficiency, and the overall economics. In cases of marginal economics, the use of horizontal wells can make IOR more viable. Due to these advantages, many operators are beginning to apply horizontal wells in their IOR projects. Much valuable experience is being gained from these projects.
This state-of-the-art review document is written for the benefit of engineers, planners and managers, who are new fo the application of horizontal wells in IOR projects. It is emphasized that in order to optimize sweep and drainage of oil using horizontal wells, one has to engineer an IOR project around the specific reservoir conditions prevailing in target locations and the interactions between horizontal wells and the main recovery mechanisms of the IOR project. Several limitations of the current technology together with their corresponding economic risks are pointed out. Based on a review of these, some project design considerations and guidelines for the use of horizontal wells in IOR projects are presented.
It is recommended that these considerations be reviewed from time to time as more experience is gained on the performance of horizontal wells in various IOR projects and as innovations in technology mitigate some of the limitations of the current technology, thereby reducing technical and economic risks.
Most of the current horizontal wells have been drilled to improve returns/ reserves of pools producing under primary mechanisms. When these operations reach their economic limits under the current phase, industry would have amassed a large inventory of depleted or watered/ gassed out horizontal wells. Some of these horizontal wells may be extremely valuable during the Improved Oil Recovery (IOR) phase, where the focus will be on improving volumetric sweep as well as, on accelerated production. Due to these considerations, the use of horizontal wells in IOR projects (using not only the existing horizontal wells, but also new injectors and producers, whenever warranted) is receiving increasing attention.
Horizontal wells may not be able to correct all the maladies leading to poor oil recoveries in IOR projects using conventional vertical wells. However, in many cases, they may be able to sufficiently lower impediments to proper drainage by enabling injectant to more efficiently sweep/displace oil. Such impediments could be due to coning, insufficient injectivity/ productivity, heterogeneities, fractures, anisotropies, poorly connected or ‘compartmentalized’ reservoirs, viscous fingering, recovery processes affected by severe gravity over-ride, etc. With the removal of these obstacles, there is a potential to lower unit injection/production costs as well as, overall capital costs as fewer new horizontal wells (as opposed to several new vertical wells) may be needed in a given IOR project. As a result, IOR is becoming viable in certain oil pools where it was otherwise unattractive. In a recent review of the IOR potential of Saskatchewan's oil pools' (jointly conducted by PRI and CERI), it was concluded that the economic viability of IOR at a number of Saskatchewan pools is significantly improved by the use of horizontal wells.