Oghena, Andrew (Chevron U.S.A. Inc.) | Zhou, Dengen (Chevron U.S.A. Inc.) | Fitzmorris, Robert (Chevron U.S.A. Inc.) | Chawathe, Adwait (Chevron U.S.A. Inc.) | Colina, Julio De La (Chevron U.S.A. Inc.) | Orribo, Jose (Chevron U.S.A. Inc.) | Gentry, Michael (Chevron U.S.A. Inc.)
Huge oil resources have been discovered in the Wilcox Trend fields of Deepwater Gulf of Mexico (GOM). The Wilcox Trend fields are ultra-high pressure and high temperature, highly undersaturated, low permeability reservoirs typically with moderate to high oil viscosities. As a result of the unfavorable rock and fluid properties coupled with anticipated large well spacing due to high well cost, the estimated primary recovery factor with artificial lift is on the order of 10 – 15%. Incremental recovery factors from water injection are forecast from 2 – 5% due to anticipated limited injectivity increasing the total oil recovery factor (primary plus secondary) to 12 – 20%. Miscible gas was thoroughly studied to determine if it could significantly increase the oil recovery factors forecast for secondary recovery.
We have carried out detailed miscible gas injection studies for six Wilcox Trend fields. Results from these field case studies demonstrate that miscible gas injection has the potential to increase the total oil recovery factor to 15 – 25% or 5 – 10% incremental above that forecast for primary depletion with artificial lift. The increase in the oil recovery from gas injection is from the improved reservoir processing rates and high local recovery efficiency of miscible displacement processes. In addition, the increase in oil recovery is due to higher oil production rates because of gas injection supporting reservoir pressure and providing natural gas lift. The GOM Wilcox field gas injection displacement process will be implemented as a secondary recovery process (before waterflood) rather than tertiary method (after waterflood).
This paper will report a new systematic workflow for integrating ultra-high pressure laboratory PVT and slim tube data and high resolution mega static earth-models into compositional reservoir simulation models for assessing gas injection displacement processes in these reservoirs. Wilcox reservoir simulation performance results will be presented for primary depletion with artificial lift, water flooding, gas injection, and gas followed by water injection and vice versa. The major uncertainties and their effect on incremental oil recovery from gas injection, resolutions to barriers to Deepwater gas injection projects, and key enabling technology developments for the ultra-high pressure miscible gas injection process will be discussed. We will end our presentation with a description of future plans for a number of GOM Deepwater Wilcox trend fields under consideration for gas injection development.