ThEOR2017
THERMAL EOR INTERNATIONAL WORKSHOP.
KAZAN, RUSSIA. JUNE 19-23, 2017

Incremental Oil Recovery from Depleted Oilfields
in a Low Oil Price Environment


Maximizing recovery from mature depleted oil reservoirs in a low oil price environment presents several significant challenges, with oil content, reservoir pressure and energy, and return on investment being among them.

Waterflooding these reservoirs can be challenged by low unit displacement efficiency. In instances where these fields have historically been waterflooded, chemical EOR has sometimes be used as a follow-up process. This is a very complex technology requiring a high level of expertise and experience. Reservoir temperature and water salinity impose constraints as to applicability, and screening criteria regarding oil saturation have stipulated minimums as high as 45%.

Unless the formation is thick enough for gravity drainage to be significant, stimulation processes, of any kind, will not be effective due to low expulsion drive energy. Also, CO2 injection is currently being considered in several jurisdictions because of the environmental benefit. It is important to note that miscibility would not be attainable at pressures less than around 8,200 kPa (1,200 psig).

This presentation provides a systematic technical and financial evaluation of the potential of air injection for incremental oil recovery from these reservoirs. Several process controls are shown to be available for achieving profitability at oil prices around $40/bbl. These include pattern cumulative air-oil ratio before air injection capacity is diverted to new patterns, implementing wet combustion, well spacing, and pattern development schedule. Oil prices less than $40/bbl can tolerated if legacy wells are available for use.

The methodology employed in this analysis is described, and recommended for screening reservoirs for air injection EOR. It provides useful mechanistic insights. Oil viscosity, for example, is shown to have a significant impact on profitability.



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