Abstract

Venturi meters, used in combination with relationships published for orifice plates to correct for wetness, can accurately meter wet gas. This allows separators to be omitted from gas field developments where they were used only to remove entrained liquid before the gas was metered. Vortex meters have also been investigated but they do not give predictable readings. A calibration technique based on the tracer dilution technique using gases has been developed to calibrate wet-gas meters.

Introduction

Wet-gas flow measurements play an important role in the economical development of small gas fields in the Netherlands. Traditionally, the Nederlandse Aardolie Maatschappij (NAM), the largest gas producer in the Netherlands, has developed small producer in the Netherlands, has developed small fields by using separators at each production location. This ensures that the gas is dry enough to be metered accurately by conventional techniques before it is combined with gas from other fields for transport to central processing plants where the gas quality is brought up to sales standard. However, with the low gas prices of recent years (the gas price is coupled to the oil price), it is uneconomic to equip small gas fields with separators. Therefore, NAM has recently been developing small fields without separation equipment; the separation has been carried out at the central processing plants. This requires the wet gas to be metered accurately at each gas field because the gas price and indeed the ownership of each field is often different (Fig. 1).

The use of wet-gas flow measurements for gases with low liquid/gas ratios (LGR) was accepted by both the Dutch government and partners, providing NAM can guarantee the accuracy of the measurements. This prompted NAM to begin a joint project with the Koninklijke Shell Exploratie and Produktie Laboratorium (KSEPL) to assess the accuracy of existing wet-gas flow measurements and, if necessary, to develop new measurement techniques. The first objectives of the project were to find a correction for wetness for venturi meters in wet service under typical NAM conditions (pressures between 80 and 100 bar (8 – 10 MPa) and a LGR lower than 200 m3/10(6) normal m3) and to develop a cheap calibration technique for these meters. The ultimate objective was to find or develop a gas meter that is independent of liquid content. With this in mind, the second stage of the project was to evaluate alternative meters in wet service.

This paper presents some of the findings. Firstly, the literature on differential-pressure-type meters is discussed and the results compared with the results from a venturi meter operated at well flowline conditions. Secondly, tests on a vortex shedding meter are presented together with their implications for all meters in which the fundamental measurement is that of gas velocity. This is followed by a discussion of a calibration technique using an inert gas chemical tracer. The remainder of the paper describes same field experiences with wet-gas measurements and considers two examples where such measurements were used in field developments.

DIFFERENTIAL-PRESSURE-TYPE METERS

Literature survey Many investigators (see ref. 1 for a list) have proposed expressions for calculating the flow rate proposed expressions for calculating the flow rate of a multiphase mixture through an orifice plate or a venturi flow meter.

P. 211

This content is only available via PDF.
You can access this article if you purchase or spend a download.