Abstract

In February 2012, Access Energy through its parent company Calnetix Technologies, initiated a 125 kW Organic Rankin Cycle (ORC) unit on a well in St Mary Parish, Louisiana for the purpose of extracting geothermal heat energy for power production. The unit was on location in January but due to cold weather concerns, unit start-up was postponed till February. The well is operated by Hilcorp Energy Company however the power was produced for Cleco Power LLC. The well is listed as a gas and condensate well by SONRIS and was spudded in June 1979. The well was completed in December 1979 at a TD of 17,300 feet (5,273 m) with production in Lower Miocene sands just above the TD. As of the end of May 2011, production from this well was listed by IHS Enerdeq with 769,646 bbls oil, 26,691,789 mcf of gas, and 24,877,655 bbls water.

The power production system is comprised of a high-speed permanent magnet generator in conjunction with a centrifugal expansion turbine supported on magnetic bearings (Carefree^TM Integrated Power Module), and linked to a power electronics (PE) package for the production of electricity from waste heat energy. The permanent magnet generator and the magnetic bearings represent the heart of the IPM. When the IPM is connected to the PE package, electrical output power for grid connectivity ranges from 50 Hz and 400 V or 60 Hz and 480 V. Normal operating speed is 26,500 rpm but can output a reduced power level down to 20,000 rpm. This is important because the energy available from many waste heat sources can vary considerably throughout the day or on a day to day basis. This is especially true in the case of coproduced geothermal energy where fluid production volume from a well can vary dramatically. The rotordynamcs and magnetic bearing controls are sufficiently robust to allow stable and smooth operation at any speed from 0 rpm up to the 25% overspeed of 33,125 rpm. This represents an important improvement over existing ORC systems that operate at much lower rpm and lower efficiencies.

The IPM is a flow-through design, which means it can be installed in the middle of a straight run of pipe. Superheated refrigerant enters the IPM and is directed into an annular space by the diverter cone. A typical inlet condition might be 121°C (250°F) and 1.72 MPa (250 psi). The gas then flows radially inward through a nozzle into the turbine. Expansion across the turbine results in a temperature drop and an 8:1 pressure drop. The exhaust then passes through the generator rotor/stator air gap and around the outside of the generator stator to provide cooling for the generator. The system can produce 125 kW gross electrical output with an overall efficiency of heat-to-electric grid power of approximately 12 - 16%, depending on the temperature of the waste heat stream and the condensing wet bulb temperature. At a typical example for a waste heat gas stream of 980 kWt (3.34 MBtu/h), evaporating temperature of 121°C (250°F), and condensing temperature of 21°C (70°F), the system will deliver a gross 125 kW to the grid. The unit has been designed to work with input heat source temperatures of 82°C (180°F) to 177°C (350°F).

Beta units were first installed in 2008 with first production installation in 2009. Since then, over 100 units have been installed worldwide for capturing heat from digester gas, landfill gas, various biomass gas, and solar thermal operations. More recent efforts were initiated for capturing waste heat found within the oil and gas industry that includes coproduced geothermal heat, heat from natural gas compression facilities, heat from flared gas, and amine gas treaters. The coproduced geothermal operation in Louisiana is the first move of this technology for oil and gas industry benefit.

The well that was targeted for coproduced geothermal production is the MA 13 RA SUA Maryland #010 located in St. Mary Parrish, Louisiana. This well is part of the Garden City Field composed of 150 wells; of these 61 wells are operated by Hilcorp (as of January 19, 2012), with 9 wells designated as oil producing and the remainder as natural gas wells (according to IHS Enerdeq). The field produces from various Lower Miocene sands. The oldest listed producing Hilcorp well dates to 1959 with first `production dates’ on some wells as recent as March 2011. The Hilcorp wells in the field range in total depth (TD) from 4,203 m (13,790 feet) to 6,623 m (21,430 feet) and with cumulative production in the field being 13,946,297 bbls of oil, 1,026,762,650 mcf of gas, and 119,498,870 bbls of water.

Of the Hilcorp wells in the field four have produced water at over 4,000 bbls/day (117 gpm). Three of these wells were drilled to around 15,500 feet (4,724 m) while one well was drilled to 17,300 feet (5,273 m), with upper perforations at 16,972 feet (5,173 m). This fourth well, the MA 13 RA SUA Maryland #010, was chosen to be used for the coproduced geothermal production well. The well was drilled in 1979 and began production as a designated gas well in 1980. The production zone is Lower Miocene from the MA 13 RA reservoir sands. The MA stands for sands defined by the Marginulina ascensionensis benthic microfossil and the MA 13 represents one of the multiple pay sands in the field. As the field is faulted, the MA 13 is broken into separate reservoirs, of which RA represents “reservoir A” (Art Johnson, personal communication). In a stratigraphic chart compiled by the Louisiana Geological Survey these Miocene age sands are part of the Fleming Formation (Johnston, III, 2000).

Water production has ranged from 3,000 to 5,000 bbls/day (88 to 146 gpm) with water temperature varying between 121°C (250°F) and 129°C (265°F). Gross power output has also been variable, ranging from 50 to 65 kW (or 30 to 50 kW net power for utility use). This represents a parasitic load of around 17 kW. Variability of electrical output was a result of changes in water volume availability and the fact that the unit was not online 100% of the time, as the well is primarily a natural gas well. Power production ceased for a time in May and June when flooding occurred related to the Mississippi River. The IPM was temporarily removed during this time but was reinstalled and continued production in July. Unfortunately brine water unexpectedly left in the heat exchanger cause a corrosion problem and flooded the IMP near the end of July at which point the unit failed in its operation. This situation has been rectified and a new unit reinstalled for continuing power production.

This is the first such unit on a producing O&G wells as coproduced geothermal energy for commercial purposes. A similar project is underway in conjunction with the DOE, the University of North Dakota, and Continental Resources, Inc. in the Cedar Creek Field water flood in the Williston Basin. We are looking to expand upon this initial success and provide oil and gas companies with the means to capture geothermal energy within the oil field, along with other opportunities for waste heat-to-electrical production.