Wet Gas Metering: Trends in Applications and Technical Developments

Abstract

Abstract Wet gas metering covers a variety of measurements in production streams with high to very high gas volume fractions. There is a need for direct measurement of gas under these conditions in such applications as gas condensate and high GOR fields as well as many production operations where gas from separation systems may contain liquid. More gas will be produced in the future from remote and subsea fields where production, capital investment, and operating costs must be optimized. For example, real time measurement of gas and liquid flow rate are critical in a subsea production system which will improve well allocation, optimize reservoir production, and enhance flow assurance. A number of wet gas metering strategies and systems have been developed to address these needs. This paper reviews the principle of operations of commercially available systems, and evaluates their strength and limitations in various applications. Available data from test loops, pilot and field installations are used to assess the performance and accuracy of these wet gas systems. The field installations are used to identify the types of applications as well as the application trends that have utilized these systems. The paper also assesses the potential benefits from the deployment of a wet gas metering system. The technologies employed in the current systems impose performance and accuracy as well as operational limitations. These limitations are outlined and evaluated in terms of operator expectations and requirements. The analysis is used to outline a list of issues that an operator has to consider in selecting and justifying a system for wet gas measurements in an asset development. New developments that are ongoing or must be undertaken to address the limitations of the current wet gas metering systems are also reviewed. The implications of these developments to extend the future applications of wet gas metering systems are discussed. Introduction More gas will be produced in the future from remote and subsea fields where production, capital investment, and operating costs must be optimized. As an example, gas production from deep waters in the GOM (1) has increased in the last 5 years as shown in Fig. 1. Real time measurement of gas and liquid flow rate are critical in a subsea production system to improve well allocation, optimize reservoir production, and enhance flow assurance. In many of the deepwater reservoirs, the economics developments dictate that several fields be commingled together and processed at a central facility. In such cases, it is critical to be able to measure the produced gas at the wellhead in order to be able to allocate the oil and gas assets to partners in each reservoir (2). These trends have provided much support to the development of more robust and accurate wet metering systems. Wet gas metering covers a wide range of measurements, which is necessitated by the specific applications and the definition of "wet gas". The definition of wet gas can vary depending on whether one is looking at the fluids from the perspectives of reservoir engineering, measurement systems, or commercial sales of the products (3). The lack of a common definition is partly to be blamed for some confusion and misunderstanding when facility engineers, operators and vendors have to communicate across these perspectives. In the following section an attempt is made to establish an acceptable definition, which could be used through the rest of this paper to facilitate our discussion of the wet gas metering systems.