|Publisher||Society of Petroleum Engineers||Language||English|
|Content Type||Conference Paper|
|Title||Combination of Dual-Energy Gamma Ray/Venturi Multiphase Flowmeter and Phase Splitter for Application in Very High Gas Volume Fraction Environment|
|Authors||E. Delvaux, B. Germond, N.K. Jha, Schlumberger|
Abu Dhabi International Conference and Exhibition, 10-13 October 2004, Abu Dhabi, United Arab Emirates
|Copyright||2004. Society of Petroleum Engineers|
In mature fields, operators are confronted with wells producing high water cut at low pressure with consequently very high gas volume fraction (GVF). Under these conditions, the net oil flow rate is low and therefore, permanent or periodic testing becomes critical to determine profitability and manage the field production.
To optimize and monitor the oil production under these conditions, operators are looking to utilize multiphase flowmetering technologies. Accuracies achievable by inline multiphase flowmeters have greatly improved in recent years, but liquid and water-cut measurement accuracies decrease when the GVF is very high.
At low pressure to reduce the GVF, it is necessary to separate a large portion of the gas upstream of the multiphase flowmeter, thus enabling optimum measurement of the liquid and water cut under lower-GVF conditions.
Market drivers generally dictated by operator requirements have resulted in the formation of an project team with specific Middle East focus to deliver an operational prototype for a production well testing campaign on a fast track basis. The package comprises a partial separation unit and a dual-energy gamma ray/Venturi meter.
The selection of a partial separation design was based on a review of the commercially available solutions capable of handling the large operating range required for use in periodic well testing applications in terms of flow rates and pressure rating. The design comprises gas liquid cylindrical cyclone with tangential inlet. The capacity of each device to ensure a dry gas phase with minimum pressure loss over the complete required operating range was critical in the selection process.
This paper presents test results validating that a gas liquid cylindrical cyclone located upstream of a dual-energy gamma ray/Venturi meter is an effective partial separation system. With an inlet GVF of 99% and 90% of the inlet gas extracted by the partial separation system, the GVF at the multiphase flowmeter condition is below 90%, and accurate measurement of the 3 phases is achieved.
In the Middle East, there are a number of mature oil fields that produce either close to or below the bubblepoint and are pressure maintained using water and/or gas injection. These reservoirs are commonly produced with the assistance of artificial lift systems such as gas lift or electrical submersible pumps. Under these production methods, the effluents at surface are often characterized by low pressure, very high GVF, and high water cut. It is not uncommon to have wells producing with a net oil flow rate of less than 10% of the total flow rate (10% oil volume fraction).1-4
The revenue to the operator is derived mainly from the oil production, and quantifying to a high degree of confidence the oil flow rate is an important piece of information that can determine whether a well is economically viable, especially in environments in which injection gas allocation is critical.
To optimize and monitor the oil production under these conditions, operators are looking to utilize multiphase flowmetering technologies. Inline multiphase flowmeters in very high-GVF environments show an increased uncertainty in the accuracy of the water cut measurement, which is required to obtain the water and oil flow rate from the measured total liquid flow rate. A number of multiphase flowmeters have been tested to assess meter performances against stated requirements5 and the number of meters qualified was limited. One of the qualified meters uses a partial separation device upstream of the multiphase flow measurement and many in the industry have adopted the approach of partial separation upstream of a multiphase flowmeter6-11 . The presence of the partial separation reduces the GVF at the multiphase flowmeter conditions and therefore improves the accuracy of the water cut, hence of the net oil. It does however introduce other drawbacks.
To achieve the objective of minimizing the net oil uncertainty under very high GVF and high water cut, a study was initiated to determine which gas extraction technology combined with a dual-energy gamma ray/Venturi multiphase flowmeter best suits the operational requirements and metering needs for this production well testing application.
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