Heavy oil accounts for more than twice the world’s resources of conventional oil. Yet, because it is highly viscous and difficult to produce, heavy oil provides only about 12% of the world’s crude supplies today.
To recover the many different types of heavy oil, a variety of production processes are being developed and used. These include cold production, steam-assisted gravity drainage (SAGD), and cyclic steam stimulation (CSS). Cold production, considered to be the most simple extraction method, uses an electric submersible pump that can draw the thick fluids. The SAGD method, considered to be state-of-the-art in steam enhanced oil recovery (EOR), involves reducing the viscosity of the heavy oil with steam for easier recovery. CSS is a multistep process that uses steam injection to mix the heavy oil with steam and then recovers the lower viscosity oil.
Heavy oil in the Middle East
Most heavy oil today comes from sandstone reservoirs. But, large discovered heavy oil resources exist in complex carbonate formations, which are often naturally fractured with widely varying permeability and porosity within the same formation. The majority of these carbonate reservoirs are located in the Middle East and, yet, few are being produced because of production challenges.
A unique application of technology applied to the Issaran field, a complex carbonate formation in Egypt, has improved heavy oil production and enhanced its viability.
Egypt’s Issaran field—an industry challenge
Issaran is one of the first heavy oil carbonate reservoir fields in which steam EOR has been used. Discovered in 1981, production did not begin until 1998 because of the particular challenges involved.
Early on, the cold production recovery method was used, which brought total field production to 900 bbl/d. The SAGD method, typically effective in thick and relatively homogenous reservoirs with high vertical permeability, was not considered applicable—the producing zones in Issaran contain impermeable stringers that create breaks in vertical permeability. So, in 2007, CSS with four cycles was implemented in a pilot well, and by mid-year, the field was producing more than 6,000 bbl/d of oil.
Impact of production logging data on field development
The complex, highly fractured carbonate formations in Issaran make it difficult to keep the heat in the oil zones, and water channelling has been a persistent problem. Production logging tools designed especially for this operation have provided valuable data on sources of water channelling and steam breakthrough and have identified water-bearing zones based on a resistivity cutoff.
This information has now led to a change in field development strategy, from one based on openhole completions to the use of cased hole wells and selective perforating within oil zones. The data helped ensure that steam was not injected into highly fractured zones. Results from test wells confirmed that the new completion strategy significantly increased oil production.