Thermochem - High-Accuracy Well Testing Operations Services

Occasionally production separators are used at production operating pressures with conventional single-phase flowmeters to measure the separated steam and brine flowrates (Figure 2). This system can produce higher accuracy data than the James Tube / weir box method, but it is much costlier, has limited turn-down capability and generally not suitable for initial start-up and warming operations of geothermal wells which must be done at low pressures. Low-pressure steam would overwhelm the capacity of a high-pressure separator. Accuracy of total mass flow measurement by this method should be +/- 5 % or better, with enthalpy on the order of +/-10 kJ/kg.

Thermochem developed an alternative Geothermal Well Testing Facility in 2010 based on a compact atmospheric separator system built around shipping containers. A James Tube is used at the inlet and brine metering manifold at the outlet equipped with high-accuracy Magnetic Flowmeters for brine measurement (Figures 3 - 5). This "Low-Emissions Compact Muffler" (LECM) utilizes baffles in the lower container separator unit and mist pads in the upper container dryer unit to minimize carry-over. A key aspect of the design is the large surface area of the dryer outlet to maintain steam exit velocity bellow a maximum, which if exceeded will result in brine carry-over (Easley, 2018). The James Tube method can produce remarkable accuracy for well testing when reliable brine flow measurement is available, with total mass flowrate accuracies within about +/- 5% or better, comparable to conventional single-phase flowmeters, and total fluid enthalpy accuracies within about +/-12 kJ/kg, comparable to flowing PT survey enthalpy and TFT® measurements (Hirtz, 2001).

The LECM has inherent advantages over the conventional atmospheric cyclone separator design in lower brine droplet emissions at the same flowrate and steam exit velocity, and ease of transport. Commercial stainless-steel mist elimination pads remove fine droplets and aerosols, resulting in very low brine carry-over up to full load. Excessive brine carry-over leads to an under-estimation in brine flow and over-estimation of total enthalpy. This is critically important for high-enthalpy wells. Brine carry-over is also an important environmental and local community impact concern.

The 40 x 40 ft. LECM is fabricated with the same outside dimensions as ISO shipping containers (8 ft. wide), which allows the pre-fabricated mufflers to be transported by standard trucking and ocean freight shipping lines worldwide, even to very remote areas. An equivalent capacity cyclone muffler would need to be at least 25 ft. in diameter, which precludes transport on most public roads, requires fabrication on-site and would still not provide the same efficiency or accuracy as an LECM.