Producing Dry Oil From a Transition Zone: Should This Be Called a Wedge Zone?

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThere is a common mis-understanding about the transition zone in which both water and oil should be mobile. This paper will illustrate that in the transition zone only oil is movable above the Free Water Level (FWL) at normal gravity conditions. Putting wells on production in the transition zone produce dry oil unless the drawdown pressure disturbs the normal gravity conditions.To avoid any confusion among geoscientists and reservoir engineers, we introduce new term called the "Wedge Zone", where the water saturation increases down flank towards the oil-water contact as a result of gradual increase in the micropores with bounded water due to diagenesis and cementation. The intensity of the diagenesis (cementation) is related to the timing of oil migration and entrapment.Four wells that had been drilled in an onshore field in the Middle East in the Wedge Zone and have producing dry oil for the last two years. As result of repositioning the new wells based on the Wedge Zone concept, an extra amount of recoverable oil will be added.The Modeling techniques over this zone have been revised resulting in changing the concept of modeling the transition Zone to that modeling of a Wedge Zone. As a consequence, the model prediction of sweep efficiency is also impacted.