Case Study on Polymer Gel to Control Water Coning for Horizontal Well in Offshore Oilfield

Abstract

Abstract This paper describes polymer gel with different gelation time for water coning control in horizontal well located in Weizhou 11-4 offshore oilfield, CNOOC, China. The selected horizontal well was shut in with zero oil production and 100% water cut before treatment. This paper also reports the detailed information about the treatment, including production history of this horizontal well, gelants formulas with different gelation time optimization, operational procedure and reservoir performance after treatment. In addition, a method is built up to control water coning for horizontal well in offshore oilfeild. The gelants formulas are 0.30%HPAM +0.60%phenol formaldehyde resin, 0.40%HPAM+0.10%Na2Cr2O7+0.20%(NH2)2CS and 0.40%HPAM+0.20%Na2Cr2O7+0.40%(NH2)2CS, with corresponding gelation time of 3.5 day, 2.0 day and 1.0 day separately at 75 degrees celsius. The above gelants were successively injected with injection volumes of 384 m3, 256 m3 and 128 m3. The overdisplacing fluid was used to displace gelants away from percolation area. Then the well was shut in for 4 days in order to form gel that could be used as packer between oil-water interface to control water coning. At the same time, real-time monitoring data about injection pressure and rate were also recorded. The treatment resulted in an oil increase of 16.3~27.4 t/d and average water cut decrease of 6%~9% in one year after treatment. Introduction Excess water production from oil well has become a serious problem for oil & gas field due to long term of water flooding. High level of water production leads to increase corrosion and scale, increase load of fluid-handling facilities, increase environmental protection concerns and eventually shut-in well, especially in offshore oilfield. Consequently, producing zone is often given up in an attempt to avoid excess water produce, even when the intervals still have large volumes of remaining hydrocarbons. Therefore, controlling water production has become more and more important to oil industry in the world. It is widely reported that polymer gel treatment is a cost-effective method to improve sweep efficiency in reservoirs and to reduce excess water production during oil & gas production. The gelant formed by polymer and cross-linker is injected into target formation which is high water cut zone and react to form gel to fully or partially seal the formation at reservoir temperature(Sydansk, 1992 and Fulin, 2001, 2006).