Water Control - How to Use Oil Soluble Compounds to Selectively Reduce the Water Permeability

Abstract

Abstract We describe a new concept to selectively reduce the water production from watered-out zones in oil wells: Heat an oil soluble compound to a temperature above its melting temperature and inject it into the formation as a liquid. When cooled to reservoir temperature, the chemical compound solidifies and reduces the formation permeability. Because of its oil solubility, the solidified compound is dissolved where oil is flowing. After a clean-up period, the oil permeability is fully regained. In the watered-out zones, the permeability reduction is permanent, simply because the solidified compound is not soluble in water. The concept has a large environmental improvement potential for the oil industry. By reducing production from watered-out zones, it will also reduce unwanted recycling of any injected water. Environmental savings might include power reduction and associated CO2 emission reduction linked to water treatment of produced and injected water, less need of chemicals to treat produced and injected water, and less produced water disposals to sea. Paraffin wax is a promising candidate. A paraffin wax with melting temperature of 61°C was injected at 70°C into a core plug. When lowering the temperature to 50°C, the injected wax resulted in stable permeability reduction. Brine backproduction for extended periods did not help to regain the permeability and the water permeability changed from initially 80 md to 1 md. During oil backproduction the oil permeability regained with less than 10 pore volumes of oil. The core flooding results agree well with bulk experiments of wax solubility in oil. Warmer reservoirs require waxes (or similar compounds) with higher melting temperature. Here we report results from the use of the hard carnauba wax, with melting temperature of 84°C. We confirmed that the wax melting temperature can be lowered, either by dilution of the hard wax in oil or by preparing a paraffin-carnauba blend. Core flood experiments with pure carnauba wax, carnauba wax diluted in oil and paraffin-carnauba blend all revealed excellent injectivity of the melted wax and the flow behavior was understood by two-phase oil-water flood. The water permeability, after a shut-in period, was low and stable while oil partly dissolved the solidified wax. However, the clean-up time for the carnauba-treated cores was significantly longer than for the paraffinic ones. We observed that dissolution rate depends on type of oil. Hexane (C6) revealed more rapid permeability regain than C10 and C16 alkanes. One explanation for the long clean-up period can be that the carnauba-containing waxes contributed to a more severe wetting alteration. Other wax alternatives with high melting temperature exists and are part of ongoing research. A recent experiment shows excellent results with paraffin wax with melting temperature of 82°C. Thinking ahead on oil field operational aspects, the concept seems ideal for low-volumes bull heading injection, where the whole near well area is treated with a limited invasion depth. Temperature control of the wax before entering the porous rock will be paramount.