Maximizing recovery factors requires careful assessment of many candidate technologies applied together (hybrid or mixed) or in a series of extraction phases (sequenced). Two major issues arise in sequencing technologies: first, understanding the physics and screening criteria of the options; second, understanding and exploiting the changes that the reservoir has experienced during previous phases.
Sequencing of extraction technologies takes advantage of improvements in transport properties caused by different technologies. CHOPS increases the reservoir permeability, porosity and compressibility, as well as favorably altering the stress fields and shortening the flow path. These major improvements mean that thermal or gravity methods will be far more effective if applied after CHOPS, rather than as a first extraction phase.
High-pressure thermal approaches such as SF, CSS or HCS generate a great deal of reservoir dilation, as well as viscosity reduction (T) and breaching of shaley flow barriers. These effects mean that gravity methods such as IGI and VAPEX have greater chances of success and will achieve increased extraction efficiency if used after these high-pressure steam methods. Once interwell communication is established by an approach such as CSS, conversion to drive methods or combined drive and gravity drainage approaches is feasible. Also, massive dilation during cyclic injection phases means that recompaction drive mechanisms can be counted on to improve recovery rates and recovery factors.
ISC (combustion) in long or short flow path configurations could have far greater chances of success if used as a final "stripping" technology once a reservoir has been dilated, heated, and depleted by other methods.
A possible vertical well sequence is CHOPS _ CSS _ SF _ IGI, perhaps even terminating with a ISC phase. A horizontal well sequence of CP _ HCS _ SAGD _ IGI _ ISC may be feasible. At the very least, a phase of CHOPS, if it can be achieved, will improve reservoir transport properties for most other production technologies. Because CHOPS is limited to vertical wells, this leads to ideas involving combinations of vertical and horizontal well arrays, such as CHOPS and HCS executed simultaneously, followed by conversion to SAGD once communication is established, then IGI and perhaps ISC as stripper phases. In the presence of active water or gas zones, options are more limited because of channeling and coning, but there still remain sequencing possibilities for low Δp (gravity drainage) approaches exploiting reservoir changes.
Planning for sequencing of production options from the beginning of a project will reduce costs in many ways, as well as prolonging the asset life and increasing the ultimate recovery factor.
The impact on technically recoverable reserves estimates in heavy oil will be huge if sequencing is properly implemented. Recoverable reserves increases exceeding a trillion barrels are expected.
Since the early 1980's, a number of new production technologies has been introduced to the oil industry. Under the right set of reservoir conditions and fluid properties, each of these technologies can bring additional value by increasing the Recovery Factor (RF), reducing costs, or accelerating production rate.
