Abstract

This paper presents a case study of improving the gas metering facilities and operation in the Indian Basin Field, New Mexico. Chevron operates 12 gas wells, each producing 3 to 6 MMSCFD, in the field. The wellhead meters, built about thirty years ago, basically consisted of 3" orifice meters with upstream out-of-plane elbows and other fittings that measured wet gas. Chevron began to examine the production and metering conditions three years ago to improve the measurement accuracy. Since the old meter piping system does not fit the specified configurations in the API 2530/A.G.A. 3 standard, the only way to ascertain the flow condition was to survey the velocity profiles inside the meter. Thus, a directional pitot probe was used to traverse the pipe and no significant swirls were observed. However, the wet gas condition and internal roughness of the old meter tubes were serious concerns. A dehydration unit was constructed to lower the moisture content of the gas and a new orifice meter with electronic measurement was installed downstream of the existing facility. A comparison of the two orifice meters showed that the wet gas measured by the old 3" meter with out-of-plane elbows was approximately 3% lower than the drier gas measured by the new meter. Possible reasons for this metering deviation are discussed in the paper.

Introduction

This paper presents a case study of improving the gas metering facilities in the Indian Basin Field, Eddy County, New Mexico. The Indian Basin Field is a gas field with approximately 30 production wells and has been producing for more than 30 years with current typical production of 3 to 6 MMSCFD for each well. The basic surface facilities used in controlling, treating, and metering the gas production were constructed identically for every well in the Indian Basin Field. In the original setup, the gas from the well flows to a gas production unit that consists of a 16" by 10' horizontal separator operating at 600 to 650 psig. The liquid stream of gas condensate and water then flows to a 36" by 8' low-pressure, vertical separator where the oil and water outflows are metered separately before being transported to a nearby processing plant. The gas flows from the high pressure separator and is measured by a 3" dual-chamber orifice meter. A chart records the pressure and temperature tracings by which Chevron ultimately sells the gas.

Chevron began to examine the production and metering conditions three years ago to improve the measurement accuracy for the 12 wells that it operates. To improve the measurement accuracy, it was decided to examine if the measurement accuracy was compromised by installation effects. At the same time, the wellhead pressure was lowered by installing compression to increase production. With increased production came a larger volume of liquid condensate in the gas stream which then impacted the measurement accuracy. To mitigate the higher loading of liquid in the gas system, a new dehydration and metering system was installed at one of the gas wells to study their effectiveness.

The results of three aspects of improving the wellhead metering operation at Bogle Flats Unit Well No. 1 in the Indian Basin Field are discussed in this paper. Figure 1 is a schematic of the new wellhead facility at the well showing the new compressor, dehydrator and meter installed downstream of the old gas production unit. The first part of the paper presents the diagnostics procedures performed to detect any installation effects that may impact the orifice meter in the existing gas production unit. The second part describes the new facilities installed to treat the larger wet gas flow. The third part presents the performance of the newly installed metering system as compared to the existing metering system.

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