Field Use of Turbine Meters in Sand-Laden Oil

Abstract

Introduction The need for an accurate, reliable device for metering lease crude oil is a natural outgrowth of efforts by the oil industry to modernize producing facilities to improve operating efficiencies. An initial step in this effort was eliminating the traditional, individual-lease, oil-treating facilities, and oil-storage tanks from which "pipeline-quality" oil was transferred to the pipeline after manual gauging and sampling. In may areas, modernization has replaced the traditional tank battery with lease free-water knockouts and emulsion metering equipment. Centrally located oil-treating stations treat commingled emulsion streams from a number of leases before transferring custody to the pipeline through an automatic custody transfer (ACT) unit. In any measurement system it is imperative that the measurement device not only be accurate, but that it remain repeatable between calibration checks. Many parties, including the oil producer, royalty owners, parties, including the oil producer, royalty owners, out-side working interests, and regulatory agencies, have a vital interest in metering accuracy. An operator's policy to deal honestly and equitably with all associates policy to deal honestly and equitably with all associates requires selecting metering equipment of proven accuracy and providing proper calibration, surveillance, and preventive maintenance procedures for this equipment. preventive maintenance procedures for this equipment. Positive displacement (P) meters have been recognized by industry and regulatory agencies for many years as acceptable measuring devises for metering emulsions from the commingled leases. Regardless of make, the PD meter is designed to divide the fluid stream into a number of discrete-volume segments; the movement of these segments is registered on a counter in terms of gallons, barrels, or other desired units. The PD meters are manufactured with tolerances sufficiently close to assure that the discrete-volume segments remain isolated from each other within the meter. The PD meters, with their inherent close tolerances, are susceptible to internal wear, particularly when handling erosive, sand-laden crudes. The internal wear becomes apparent during periodic provings with a master meter. As internal clearances increase because of erosive wear the meter factor gradually increases to the point where the meter becomes an unsuitable measuring device. A number of fields along the Gulf Coast produce from poorly consolidated sand formations, and produced fluids contain sand in varying quantities. To reduce meter drift and high maintenance costs experienced with the PD meter in sandy crudes, a test program was initiated in Dec. 1971 to evaluate turbine program was initiated in Dec. 1971 to evaluate turbine meters in this service. Based on the satisfactory results of the initial test, the use of the turbines has been expanded to include 56 turbine meters installed in seven fields. Turbine-Meter Description A cross-section of a typical turbine meter is shown in Fig. 1. Meters vary among manufacturers by rotor pitch and proportions, bearing design, materials, etc. but the principle is the same for all. Liquid impinges on the principle is the same for all. Liquid impinges on the rotor, resulting in rotory motion whose speed or frequency is proportional to the rate of flow. JPT p. 139