The ability to measure both water and oil continuous phases of a production stream from 0% to 100% water cut has been pursued by a multitude of companies for many years with marginal success in transferring the technology to practical use.
A field worthy technology developed for accurately determining the full range of water-in-oil (0-100% water cut) for production and well testing will be covered. Information about the fluid phase, oil or water continuous, is determined and given in real time. The novel technique used is called oscillator load pull, which detects the permittivity of the fluids. Salinity, temperature, entrained gas, and emulsion type effects will be discussed showing their effects on phase inversion and measurement parameters. Data from installed instruments on location in Alaska and the lower 48 states will be shown. Comparisons to shake-outs and well test logs will be compared. Descriptions of how the real time information of the phase of the fluids has been used to observe and affect well management will be presented.
The accurate measurement of the water content in crude oil has been an ongoing problem in both the low water cut (0-4% water in crude oil) and the full cut range (0-100% water). These problems existed due to the limited sensitivities of earlier measurement methods and the conductivity of salt water which both limits the sensitivities available and makes the determination of the phase of the fluids a necessity.
A typical use for a full range water cut instrument is in well testing. The use of a full range instrument allows the use of only a two phase separator which reduces the size and complexity of the well test equipment while improving the reliability of the measurement. Since the entire fluid stream is measured at once and a totalizer tied to flow meters can give the net oil, the separate tracking of the water and oil legs is eliminated. The separate oil and water tank level controls are eliminated along with the associated errors with oil/water carry over to the water/ oil legs.
An emulsion is a dispersion of one liquid in another where the continuous or external phase is defined as the matrix in which the droplets are suspended. The droplets which are surrounded by the continuous phase are called the discontinuous or internal phase.' The two types of emulsions will be abbreviated OIW for oil-in-water (water continuous) emulsions and W/O for the water-in-oil (oil continuous) case.
Generally, a well begins by producing W/O emulsions until water injection begins and the water cut increases over time to 70% or above. The point at which the well will produce water emulsions depends upon the emulsifier contents of the crude oil. Under laboratory conditions, West Texas crude oil will invert from W/O emulsions to O/W at approximately 88% water at 80 degrees F while injecting 5% salt water.
