Geothermal Leases Research Articles

A modeling analysis of unitized production: Understanding sustainable management of single-phase geothermal resources with multiple lease owners

A generally acceptable rule is that a geothermal lease is indivisible by its nature. Thus, production from any part of a unit affects all leases within the unit. One serious risk involved in the adequate and sustainable development of geothermal resources originates from multiple lease owners in the same area. Having two or more lease owners for a given resource area situation leads to the potential risk of offset production and interference effects between adjacent developments using the same resource. This can lead to legal entanglements and potential resource sustainability issues.A well-known approach for the multiple lease owners’ problem is unitization. Unitization, in simple wording, is the unit based operation of a geothermal resource by consolidating or merging the entire field or a substantial part of it as a single entity and designating one or more of the parties as operator.This study outlines the importance of unitization on the geothermal resource development. Synthetic examples are used to quantitatively show the benefits of unitization. Lumped parameter models are used for modeling reservoir performance. The results of the lumped parameter modeling approach are discussed for better understanding the reservoir performance in terms of pressure and temperature and to demonstrate the interference effects when more than one lease owners tap the same reservoir. The results help to appreciate the problems of having multiple lease owners in the same area.

The Influence of Basement on Surface Heat Flow in the Cooper Basin

This paper describes the results of an investigation into the surface heat flow distribution around GEL-99, a Geothermal Exploration Lease granted to Scopenergy Limited by the South Australian Government. I collated temperature and thermal conductivity data from a number of sources in order to construct one-dimensional thermal models of 30 petroleum industry wells. The data indicate a marked thermal conductivity contrast between the base of the Eromanga Basin sequence and the Cooper Basin sequence, resulting in a relatively high thermal gradient in the latter. Observed drill stem test temperatures support this prediction.Vertical heat flow within GEL-99 ranges from about 90 mW/m2 to over 110 mW/m2, averaging over 100 mW/m2. Heat flow drops off significantly towards and beyond the edge of the Big Lake Suite granodiorite. Observed values of heat flow cover a range of about 25 mW/m2. This variation can be attributed to a combination of a variable thickness of heat-generating material in the basement, and heat refraction through areas of relatively shallow basement.

Developments in Geothermal Resources in 1982

The total number of geothermal wells drilled in 1982 decreased to 79 from 99 wells in 1981. Total footage drilled in 1982 decreased to 559,326 ft from 676,127 ft in 1981. An increase in average well depth from 6,830 ft in 1981 to 7,080 ft in 1982 indicated that operators are having to drill deeper in their efforts to extend the productive limits of proven geothermal reservoirs. Of the 79 geothermal wells completed in 1982, about 80% (i.e., 63 wells, which accounted for 90% of the total footage) were drilled in California. Two major acquisitions occurred during 1982 in The Geysers geothermal field in northern California. Geothermal Resources International, Inc. (GRI), purchased Thermogenics, Inc. (TGI), including the steam-producing property from which TGI sells steam to the Pacific Gas and Electric Co. (PG&E) Unit 15 geothermal power plant. Additionally, GRI purchased the 50% interest of Aminoil USA, Inc., in about 60,000 acres within and around The Geysers for $26.25 million in the largest transaction negotiated in the geothermal industry during 1982. GRI then entered into agreements for the exploration and development of the acreage with the Central California Power Agency. Geothermal power generation was highlighted at The Geysers by an increase of 110 MWe of electricity. With the start-up of PG&E Unit 17, the total capacity of The Geysers at year end was 1,019 MWe. In the Salton Sea KGRA in the Imperial Valley in southern California, the Southern California Edison Co. 10 MWe single flash demonstration plant became operational in 1982, bringing the total geothermal electricity generation capacity in the Imperial Valley to about 31 MWe. By mid-year, 5 development wells were completed by California Energy Co., Inc., at the Coso Hot Springs KGRA on the China Lake Naval Weapons Center in south-central California. These wells confirmed the dry steam discovery of late 1981 and established the Coso area as another important geothermal resource for electric l power generation. Other achievements included the accelerated federal geothermal leasing program reaching its goal of offering about 600,000 acres in 14 sales held by the U.S. Bureau of Land Management. Five other geothermal lease sales were conducted by 3 state agencies. Private industry paid more than $18.7 million in bonus bids in 1982 for geothermal leases at these competitive federal and state lease sales, an average of $113.20/acre. In 1982, 2 significant technical developments, the Crystallizer Clarifier Processor and the EFP System, were successfully demonstrated and will accelerate the commercial utilization of liquid-dominated geothermal resources in the United States and elsewhere. Finally, the dedication of several district heating projects highlighted the direct-use application of geotherm l resources in 1982.