Coriolis Mass Flowmeters Used To Measure Bulk Condensate In Gas Field

Natural gas production creates a byproduct of natural gas liquids (or NGL), often referred to as “condensate.” The physical properties of condensate vary with the hydrocarbon constituents and differing fluid vapor pressures depending on the deposit at the location from which they are drawn. This constituent variation and the presence of water or natural gas in the flow stream discharge from the separator compromises the integrity of the measurement.

The Bureau of Land Management (BLM) Onshore Order #4, “Oil and Gas Measurement,” regulations point to positive displacement flowmeter or tank gauging technology as best practices for the measurement of liquid hydrocarbons departing Federal Leases.

Several technical shortcomings exist with mechanical meters in liquid hydrocarbon measurement service where condensate is at “un-weathered” conditions. Such condensate applications are challenging with gas breakout, and the liquid readily cavitates due to the low fluid vapor pressure. Positive displacement flowmeters exhibit no short-term ill effects but erroneously over-measure when vaporization occurs. Over time, mechanical wear leads to undetected drift from baseline conditions between physical proving sessions.

Since mechanical positive displacement flowmeters do not measure process density, sampling is required. This leads to a higher cost of ownership due to additional apparatus needed to comply with API practices. The economic realities of mechanical meter measurement expose an operator to greater uncertainty in measurement of liquid hydrocarbons. Monthly correction of improper or failed measurements leads to questioning of the reported volume. Finally, the methodology of monthly proving or mechanical flowmeter exchange poses a significant health, safety and environmental impact in practice.

Shell Exploration and Production Co. understood the technical limitations of positive displacement technology and proposed a new approach for bulk condensate measurement using Coriolis flowmeters for the Pinedale Anticline natural gas field in Wyoming. The producing company requested and obtained conditional approval of a variance from the BLM (part of the U.S. Department of the Interior) for bulk separator measurement of condensate by Coriolis flowmeters prior to comingling the production streams from other leases. The benefits of Coriolis mass flowmeter measurement include: