A simple and straight forward process to overcome the problem of excessive water production due to water coning in oil producing wells has been jointly developed by the Alberta Oil Sands Technology and Research Authority (AOSTRA), the Alberta Energy Company Ltd. (AEC) and Westcoast Petroleum Ltd. The Anti-Water Coning Technology (AWACT) Process, in its basic application involves the stimulation of a producing well with a natural gas slug and a chemical blend to inhibit the influx of formation water to the wellbore. The effectiveness of this treatment has been successfully demonstrated in the South Jenner field and treatments in other Alberta reservoirs are underway or planned to further refine the process and define its limitations.
This paper outlines the development of AWACT and the results of laboratoryinvestigation, numerical simulation and field trials which suggest the probable mechanisms. Typical AWACT field implementations are described as well as the economic benefits which warrant its widespread utilization to alleviate a common oilfield problem.
Excessive water production due to bottom water coning is a widespread oilfield problem and is especially prevalent where the water mobility greatly exceeds the oil mobility. If unchecked, the problem may result in poor oil recoveries because pumping high water: oil ratios ultimately becomes uneconomical. Faced with the prospect of suspending or abandoning high water cut oil wells, operators can resort to a number of remedial methods to inhibit water influx including cement squeezes, polymer, foam or other chemical injection. Unfortunately the success of most of these treatments has been mixed and there has not apparently been a universal treatment which could be applied to the wide spectrum of reservoirs in which the problem is observed.
AWACT is presented as a solution to the problem of water coning with potential application to a range of reservoir characteristics. The AWACT process may be tailored to suit the specifities of most reservoirs. Unlike other remedial methods, which depend upon decreasing water mobility in absolute terms, AWACT relies upon decreasing water mobility in relative terms. Absolute terms are modified individually and hence either permeability is reduced (i.e.cement squeezes) or water viscosity is increased (i.e. polymers). AWACT affects the relative permeabilities of the reservoir fluids, favoring the movement of oil, not water, to the wellbore.
AWACT treatments have the advantages of being simple, low cost and non-damaging. Routine oilfield practices, equipment and materials are used and a typical turnaround time is one week. Natural gas is compressed into the wellhead to chase a slug of chemical blend into the reservoir. Injection rates and volumes tend to be reservoir specific and AOSTRA, through licensing the technology, has taken an active role in the optimization of the process variables.
The results of AWACT treatments in the South Jenner Pool have shown that the process is very cost effective with respect to the production of incremental oil from wells whose high producing water cuts have made them candidates for abandonment. The economics have looked favorable enough for AEC to plan to treat 120 wells to improve Suffield oil recovery by 300,000 cubic meters.1