Abstract
The dehydration of oil to meet pipeline water specifications usually involves the resolution of the intractable water in oil emulsions present in the crude oil, and the use of some separation equipments. However, emulsion resolution may be very problematic and challenging when highly stabilized heavy crude oil types are produced. They often require more chemical injection and time to be resolved. One such study was conducted to observe the effect of specific gravity and viscosity reduction on emulsion stability, which in turn is defined by no less than three parameters – Rate of water drop, Oil dryness and interface quality.
Several hours of demulsification bottle testing with a typical 200API heavy crude oil, a light straight run Gasoline as a diluent to reduce the crude's viscosity, and a typical front-end demulsifier chemical for emulsion resolution were carried out. The crude oil was blended with Gasoline at different ratios in six 100ml test bottles. The emulsion blends at its wellhead temperature of 450C were resolved with 2ppm of demulsifier chemical which is a reduced treatment rate from 5ppm. The experiment revealed a number of interesting trends.
Addition of about 5ml of Gasoline in one of the test bottles led to 63% reduction in the oil's absolute viscosity, without the use of any additional heat except that attained at the wellhead of the operator's oilfield. This sample dropped about 96% of its emulsified water after 5 minutes of chemical injection, with a very sharp oil/water interface. The top oil had trace Basic sediment and water BS&W, and the separated water, an improved Total Petroleum Hydrocarbon TPH of about 50ppm. These Data demonstrated a good quality and sellable dry oil, easy to handle and can be pumped with little cost since its viscosity is appreciably reduced. Besides the effluent water is safe for disposal at the operator's terminal. On the basis of this bottle test, this research could result into the following benefits to the Operator:
A 60% reduction in chemical usage and logistics costs
A 45% – 50% reduction in production chemical costs
Reduction in the unavoidable use of heaters in oilfield for emulsion resolution
Production of a high quality and sellable crude oil for export and improved oil in water content of the produced water discharge.
The case study discussed in this paper is that of a heavy crude oil emulsion collected from a major operator's flowstation in the eastern Niger delta area of Nigeria.
