Experimental Evaluation of the Blockage Efficiency of a Novel Gel System To Mitigate Water-Cut Problem of Producing Wells

Abstract

Abstract Water production is a problem of paramount importance from technical, environmental and oil production points of views. The processing, treatment and disposal of produced water cost millions of dollars for a single field. On the other hand, high water production causes a drastic reduction in oil production. The issue of excessive water production has been addressed by the industry by placing different gel system in the reservoir to block the water flow and facilitate the oil flow. The most commonly used solutions are polymer gels with chromium (Cr3+) as the cross-linking agents in the gel system. Some of the polymer gel systems are not effective at temperature above 70 oC due to the thermal and hydrolytic degradation of the polymer. Moreover, the precipitation of the toxic cross-linking agent with increased temperature and pH is a major environmental concern. This paper describes the water blocking efficiency of an environment friendly and biodegradable gel system to mitigate the water cut problem of producing wells. The newly designed gel system has no cross-linking agent and is stable up to 194ºF (90ºC) temperature. The system is stable in the presence of divalent ions and also in a range of pH conditions. Experimental results indicate nearly 100% reduction in water permeability of 16/30 sand-pack after treatment. Flow test with mineral oil indicate higher oil permeability compared to water. However, oil permeability has been reduced dramatically compared to pre-treatment oil permeability. Hence, it is most suitable for treating the water zone of a reservoir. Introduction Water production is a problem of paramount importance from technical, environmental and oil production points of view. High water cut in producing wells can cause loss of a substantial volume of recoverable hydrocarbon. In the case of gas field, high water production can completely block gas production of gas wells (Aniello Mennella, 1999). Excessive water production not only compromises the profitability of oil and gas producing wells but also reduces the sweep efficiency and ultimate recovery from hydrocarbon reservoirs. The processing, treatment and disposal of produced water to minimise the impact on the surrounding environment costs millions of dollars for a single field. Published data indicates an average of three barrels of water production per barrel of oil from depleting reservoirs (Bailey et al, 2000). The worldwide daily water production is about 210 million barrels for every 75 million barrels of oil production (Gino and Phil, 2002). Water management cost is a big factor in increasing the production cost. Estimated water production cost range from 5 to more than 50 cents for each barrel of water (Bailey et al, 2000). Wells producing oil with 80% water cut can cost about $4/bbl water handing cost. According to Brent et al. (1998) the water disposal cost of Alberta alone is about $1 billion per year. That is why produced water has a major economic impact on the profitability of an oil field. From energy consumption point of view, producing 1 bbl of water requires as much as or more energy than the production of 1 bbl of oil (Larry Eoff et al., 2003). This highlights the enormous economic burden of water production problem for the oil and gas industry. The management of produced water is a vital part of reservoir management and a decisive factor in well productivity and the ultimate reserve of a field (Kuchuk et al. 1999). Although prevention of water production is more effective than treating, it is often treated after production than the prevention of the water production at the first place (Wouter Boterman et al. 2001). The need for the prevention of water production is increasing for deep water, remote and stranded oil and gas fields to minimise platform size or eliminate it altogether, for efficient management of unavoidable part of produced water, to overcome the increasingly strict environmental laws and regulations and for economic exploitation of mature and marginal fields.