Factors Affecting the Application of Anti- Water Coning Technology (AWACT) At the South Jenner Oil Field, Southeast Alberta (1999)

Abstract The Anti-Water Coning Technology (AWACT) was developed to mitigate water coning problems. It has been applied commercially in the Glauconitic Sandstone reservoir, South Jenner field, in southeastern Alberta. The reservoir rock in the study area consists of sandstones with mature texture and excellent porosity and permeability. Ten wells out of 25 have cores with fining upward sequences, with permeability decreasing upwards. Of 35 wells treated with AWACT, at or near the economic limit, 21 had incremental oil recovery, seven had decreases in ultimate oil recovery, and five showed no effects from AWACT treatment. The additional oil recovery was accompanied by a change in production decline characteristics from exponential decline before AWACT to harmonic decline afterwards. This change in decline characteristics indicated a change in fluid flow behaviour in the reservoir. Wells that were treated before January 1989 had larger incremental oil recovery after gas injection, averaging ∼ 8,140 m3 or 25% OOIP. Wells treated after November 1990, on average, had no incremental oil recovery. In the absence of strong correlation with geological and well operational variables, differences in AWACT performance were attributed to well interference effects. That is, the performance of the later wells had been affected by drainage of the reservoir by earlier wells. This led to the conclusion that AWACT treatment would be more effective if the well spacing were greater than the 100 m currently used. Introduction This study evaluates a method to improve oil recovery that has been applied to viscous oil reservoirs with active bottom water drives. Due to early breakthrough of bottom water, referred to loosely as "coning," primary oil recovery is generally less than 10% of the original oil in place (OOIP)(1), and the cost of water handling has an adverse effect on overall field productivity. Several measures have been taken to improve recovery and to reduce water production. These include: infill drilling programs to reduce well spacing, in some cases, to 1 ha(2); attempts to reduce the mobility of water by use of polymers and foams; and attempts to block the influx of water by use of cement squeezes or injection of immiscible gas(3). Injection of immiscible gas with associated additives in wells at or near the economic limit of oil production, followed by back production from the same wells, is reported to provide economic production of additional oil and to reduce water production. This technology, developed by Alberta Oil Sands Technology Research Authority (AOSTRA) with technological and financial support from several oil and gas companies, was patented in 1985 by AOSTRA as the Anti-Water Coning Technology, or AWACT(4). Since the introduction of this technology, several companies have tested more than 40 watered-out wells with AWACT in six different reservoirs in Southern Alberta. Alberta Energy Company Ltd. (AEC) wells in the South Jenner oil pool report incremental oil production following gas injection and are considered successful applications.