Impact of Fluvial Geological Characteristics on EOR Screening of a Large Heavy Oil Field

Abstract Many fields in the Middle East suffer from low recovery and declines in primary production due to low oil gravity (<20 API) and viscosities above 100 cP. The studied field contains well in excess of 1 billion barrels in place with overall recovery expected to be less than 10% without EOR. 75% of the STOIIP comprises 20 API oil with 120–160 CP viscosity while the remainder comprises 17 API with 800 cP viscosity. Complicating matters, the three main sandstone reservoirs vary from braided fluvial streams in Upper formation (A), to thick sheet sands in the middle formation (B) and thinner sands separated vertically by thin shales in the Lower formation C. In this study EOR techniques have been assessed for these three formations in order to recommend suitable development options for the field. Simulation schemes were developed for the following seven recovery mechanisms, including, water flood, chemical EOR – polymer and ASP, thermal EOR – CSS, steam flood, SAGD and in-situ combustion. Due to geological and fluid variation in these three formations, EOR mechanism behaves differently in terms of recovery for each reservoir. The three most promising techniques, ASP, steam flood/CSS and insitu combustion were then developed to optimise pattern spacing and injection rates for each technique and for all three formations in this field. Heterogeneity and geological factors have different impacts on the various EOR mechanisms, including convective methods like ASP and polymer flooding and convective-conductive methods like Thermal EOR. Overall, thermal EOR has been found to be more effective and economically feasible for this field, in particular for the heterogeneous formation with high viscosity oil. Different EOR techniques could be considered for each formation due to the variation in heterogeneity, with recovery also changing from one formation to another due to fluid viscosity. Different thermal schemes, for example varying the number of steam injection cycles before continuous steam injection, have been suggested for each formation in respect to its heterogeneity and oil properties. It is also noted that a SAGD EOR process can be more effective in certain formations in this field.