CWC

A Grip on Oil Flow Rates With Neftemer

It is statistically insignificant to sequentially feed the flow from each oil wellhead 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; it 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.

Neftemer™ is a non-intrusive clamp-on Multiphase Meter that measures unseparated crude oil flow in well flowlines and oil-flow pipelines. It provides measurement of oil, produced water and associated gas in the following units: liquid mass flow, tons/day; gas volumetric flow, m3/day and water cut, mass fraction. Preferably, Neftemer is installed on a vertical section of pipeline with flow upward. When in operation, its parts do not come in contact with the product fluids, do not change its direction, do not produce extra hydraulic resistance, nor does it influence the hydrodynamic characteristics of the flow or the physical and chemical properties of the product fluids. The measurements are taken without conditioning the flow (i.e. without homogenization or separation).

This clearly eliminates the persistent issues associated with back allocation for obvious fiscal reasons. The oil rate is accurately measured directly at the wellhead; the gas flow is not diverted to the flare where bulk of the gas may or may not be measured but the Neftemer measures this volume upstream of the well; also, it accurately captures the water flow rate.

At the separator where BSW is determined, back allocation of gas volume and water rate remain problematic. Moreover, in practice, total Flow-Station rates (fluid flow), are seldom 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.

This practice simply does not make room for a representative and accurate determination of oil, gas and water rates simultaneously; a task required for optimal tuning of the well, and effective reservoir management practices.

How does the Neftemer Multiphase Meter achieve all this seamlessly? The secret is in its construction. It comprises of a gamma-ray attenuation transducer which is located near the wellhead in a hazardous area with secondary equipment comprising a data processing unit located in a safe area in a control or equipment room. A user display (personal computer) and printer may be used for setting this up. The gamma-ray attenuation meter comprises a gamma radiation source mounted in a source housing and a flameproof gamma radiation detector all mounted on a special mounting bracket. The density and composition of the unseparated well fluids as well as gas flow velocities, are determined from the attenuation of gamma radiation.

As a clamp-on device, it can be mounted without cutting the flow line; upstream of the pipeline. The length of straight pipe both upstream and downstream of the gamma ray beam should be not less than 0.5m. It also has other plush parameters including two communication links (see Fig. 1). The DCS link is used to provide measurement results to the customer. Output data will be: oil, water and gas flow rates, water cut, average density of flow. The auxiliary link is intended for downloading data archives by a service engineer.

Finally, 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. This practice also leads to endless disputations between the field operator and regulators over what volumes royalty calculations should be based upon. With Neftemer™, however, impactful reservoir management and peace of mind is assured.

This is a paid post, sponsored by Geotrex

 



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