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Delivering Impactful Reservoir Management

The Neftemer Multiphase Flow Meter measures the void fraction of the dispersed fluid phase within the continuous physical mixture of oil, gas and water …

The current, industry-wide practice of sequentially feeding the flow from each well once a month, to a central test separator so as to evaluate the well production performance and determine the flowrate of each phase (oil, gas and water) after separation, is unrepresentative and inaccurate. Wells seldom flow at constant rates and the ‘one-day’ test separator rate is a random sample of one out of thirty possible rates. This is statistically insignificant.

Furthermore, of the total flow station phase flows, only the oil rate is accurately directly measured for obvious fiscal reasons. The gas flow will usually be diverted to the flare where the bulk gas may or may not be measured. The water rate is rarely measured. Instead the samples are frequently taken either at wellhead or at separator and sent to the lab for BSW determination. The results are rarely available within six weeks! Consequently, when and if flow station flows are used for back allocation to the various wells, only the oil rate has a chance of being accurate to the extent of the limitation of the ‘one-day’ separator test rate practice mentioned above. Back allocation of the gas and water rate remain problematic.

In practice, total flow station flow rates are rarely used even when the oil rate injected into a bulk export line is accurately metered e.g. via an available LACT unit. Rather each contributory flow station is assigned a volume based on a so-called reconciliation factor, determination of which is opaque in most cases. Genuine line and other losses (theft!) are shared in a manner not entirely satisfactory to all parties leading to endless disputes between terminal owners, operators and regulators. Clearly using these reconciled rates for back allocation to the wells is a formidable challenge the industry has faced almost since the beginning. The practice simple does not make room for the representative and accurate determination of oil, gas and water rates simultaneously required for optimal tuning of the well, and effective reservoir management practices. Operators are forced to move in the blind for much of the time!

Production engineers need to know if the well is operating within its performance envelope or not and tune it appropriately. Reservoir engineers need accurate oil, gas and water rates to carry out meaningful material balance calculations and determine total underground withdrawal for each reservoir; run realistic reservoir simulation models and generate meaningful medium and long term production forecasts for the business. Current operations practice and use of ‘one-day’ test separator rates simply do not allow for these essential and critical calculations to be accurately carried out. The practice also leads to endless disputations between the operator and the regulator over which volumes royalty calculations should be based.

One alternative to the use of test separators is the use of Multiphase Flow Meters. The key information required from a Multiphase Flow Meter includes the flow rate of oil, gas and water. The ideal way to obtain these measurements is by direct and independent measurement at the wellheads before separation.

The Neftemer Multiphase Flow Meter measures the void fraction of the dispersed fluid phase within the continuous physical mixture of oil, gas and water to determine first, the flow regime of the mixture and then determine the flowrate of each phase in a non-intrusive, continuous and consistent manner over a long period of time. It can be used to compliment or even replace test separators.

They are cheap (costing below one fifth of a conventional multiphase meter), are non-intrusive, immune to sand particles and wax deposition. They are also portable, a fact which makes them ideal for offshore applications and rerouting from well to well on a needs basis.

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