EOR for Carbonate Reservoirs Under Extreme Conditions: From R&D to Field Implementation

Carbonate reservoirs contain more than 50% of world’s conventional hydrocarbon reserves and on average have ”ultimate” recovery factors between 30-40%. With the insight that the growth rate of “easy oil” supplies (conventional oil and natural gas that are relatively easy to extract) will struggle to keep up with future demand, enhanced oil recovery (EOR) becomes increasingly important to maintain and extend the production from existing oil reservoirs.

Carbonate reservoirs in the Middle East are highly heterogeneous and have complex pore systems, often with triple porosity systems (matrix-vug-fracture) and mixed to oil-wet matrix characteristics. Both geological heterogeneity and wettability have strong impact on remaining oil saturation and its distribution and hence on oil recovery and sweep efficiency and on the choice of EOR options to be applied in such reservoirs. In addition to geology and wettability, the specific properties of the reservoirs in Abu Dhabi makes EOR challenging. Chemical EOR options have large potential to either target remaining oil saturation in waterflooded areas or bypassed oil in low permeability layers or small pores. However, the reservoirs are at high temperature (~100-130 oC), the formation brine is of high salinity (~200,000 ppm) and contains high concentrations of divalent ions (~18,000 ppm of Ca++ and Mg++). Such harsh conditions of the carbonate reservoirs in Abu Dhabi (high temperature and salinity) pose a major challenge to chemical EOR. Hence there is a general lack of experience or analogue in the industry on EOR in general and chemical EOR in particular for such carbonate reservoirs.

ADNOC has recently developed an EOR roadmap in which we have reviewed the available EOR concepts, their maturity and applicability to Abu Dhabi carbonate reservoirs. A large R&D program has been developed to mature EOR concepts for such harsh reservoir conditions in addition to designing innovative hybrid EOR options to target large volumes of by-passed oil in such reservoirs. This presentation will discuss the journey of bringing EOR from R&D to field implementation for carbonate reservoirs under high-temperature and high-salinity conditions.

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