Generation of Electricity from Water Produced by Oilfield Operations

Title: Generation of Electricity from Water Produced by Oilfield Operations
Authors: Lyle A. Johnson and Everett Walker, Rocky Mountain Oilfield Testing Center
Publication: The Outcrop, April 2009, p. 4, 12

INTRODUCTION

Several oilfields in the USA produce large volumes of hot water/brine with the oil. At many production facilities, the waste stream is below 220 °F, considered low temperature for geothermal power production. However, these low temperature waste streams have been projected to be capable of generating up to 5,000 MW of power for facility consumption. To evaluate power generating capability of this low temperature oil field waste stream, the U.S. Department of Energy (DOE) entered into a Cooperative Research and Development Agreement  (CRADA) with Ormat Nevada, Inc. to demonstrate an air cooled, skid mounted standard design organic Rankine cycle (ORC) power plant. Ormat ORC power plants have been used for over 25 years for on-site power generation from conventional geothermal resources. The power system being tested has an air-cooled condenser for the working fluid because this field like most oil fields does not have a sufficient source of cooling water.

 The project is being conducted by the DOE Rocky Mountain Oilfield Testing Center (RMOTC) at Teapot Dome oilfield, also known as the Naval Petroleum Reserve No. 3 (NPR-3). The field is thirty-five (35) miles north of Casper, Wyoming and is operated by DOE as both a producing oil field and a test site for new and developing oil and gas, and renewable energy related technologies. The field is a 9,481-acre operating stripper well oil field offering a full compliment of associated facilities and equipment on-site. Of the 1,319 wells drilled, 730 remain open with 300 used for producing oil from one of nine producing reservoirs ranging in depth from 250 to 5,500 feet. The remaining open wells are temporarily shut-in or are test wells.

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Figure 1. NPR-3 Geothermal Potential

At NPR-3, sufficient hot water (190 to 210° F) is or could be produced from two formations, Tensleep and Madison, to generate low-temperature geothermal energy (Figure 1). The current water production from these formation is 45 MBWPB, Figure 1. It is projected that with minor work on present wells, the rate for the combined Tensleep and Madison produced water would be between 126 and 210 MBWPD. The water resource in both the Tensleep and Madison formation are continuously recharged by outcrops in mountains to the west.

The Ormat supplied power unit (figure 2) was installed in August 2008. The design of the unit was based on a relatively low produced water temperature of 170 ° F and an average ambient temperature of 50 ° F, Table 1. At design conditions, the nominal 250 kW unit would produce a gross power of 180 kW. However, between initial design and installation, two major changes were made. On the equipment design, the pump for the working fluid, isopentane, was incorporated into the turbine-generator package. By incorporating this feature, the parasitic electrical load of the unit was decreased. On the field side, the Tensleep production facility was upgraded and an insulated, produced water storage tank installed. This change kept the produced water temperature in the 195 to 198 ° F range. The higher water temperature permits the system to operate nearer the maximum net power output of 225 kW. Since the system was put into full-time service on September 2, 2008, the net power output has ranged from 80 to 280 kW. The power fluctuation mirrors the ambient temperature when a constant hot water inlet volume is used, Table  1. In its first 4.5 months of operation (through January 17, 2009), the unit has produced over 450 megawatt hours of power from 2.4 million barrels of water.

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Figure 2. Ormat 250 kW Low Temperature Geothermal Power Generation Unit at NPR-3.
Design Operational
Flow Rate, bpd 40,000 12,000 to 40,000
Inlet Water Temperature, ° F 170 195 to 198
Outlet Water Temperature, ° F 152 80 to 170
Average Ambient Temp, ° F 50 -7 to 85
Generator Gross Power, kW 180 305 to 105
Net Power Output, kW 132 280 to 80

Table 1. Design and Operational Data

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