Abstract
In a world where oil production declines and where investments in fossil resources are lower and lower, operators are looking for solutions to optimize the production of existing wells. This is the case for horizontal wells in carbonate formations suffering from channeling with strong bottom aquifer. Such problem occurred for well MRS-1H located in France. Its production started in 2001 with high water-cut (80-85%) that increased rapidly with time to reach 99.7% in 2022 for a gross production of 5000 bpd. Even with a barrel at 80 USD, the extraction of oil in such conditions is not economical due to the high OPEX required for pumping and water disposal. A Water Shutoff (WSO) treatment was designed having as target to decrease water production by, at least, a factor of 2, while keeping the volume of oil production at same level.
The bottom aquifer is located in the very permeable Upper Bathonian formation, just below Lower Callovian formation. Oil in place is 36° API with a viscosity of 3.3 cp. Reservoir temperature and pressure are 70 °C and 186 bar respectively. Reservoir water salinity is between 5 to 10 g/L TDS.
The main problem is the presence of a channeling connection between the well and the aquifer by a fracture network localized close to the heel of the horizontal drain. WSO treatment consisted in injecting by bullheading a first slug of microgel followed by a slug of elastic gel followed by a third slug of microgel. The total volume of the chemical treatment was 300m3.
During the injection, wellhead pressure increased and remained stable below 60 bar for an injection rate of 3bpm. The fact that pressure did not build up (especially during the injection of the gel slug) indicates that the treatment penetrated in low resistance flow areas (fractures). After 15 days of shut in, the well was put back on production, showing a dramatic drop of gross production rate, reaching 630 bpd while it was 5000 bpd before the treatment. The oil production reached 17 bpd corresponding to an oil cut of 2.5% (compared to 0.3% initially). The well has kept this behavior with time, making its production economical.
The bullhead treatment combining microgel and gel proves to be a good WSO strategy for wells suffering from strong bottom aquifer channeling and should have many applications in fractured carbonate reservoirs.
