Gulf of Mexico Borehole Geothermal Data Integration into the National Geothermal Data Systems, Part 1: Texas Continental Shelf

Seiichi Nagihara¹, Cory Christie¹, Nosakhare Ogiamien¹, Motunrayo Oladokun¹, Olabisi Ajiboye¹, and Sergio Ojeda¹,²
¹Department of Geosciences, Texas Tech University, Lubbock, Texas 79409
²Currently at Concho Resources, Midland, Texas 79701

In 2009, the U.S. Department of Energy initiated the effort to establish the National Geothermal Data System (NGDS). When it becomes accessible by the public via internet in ~2013, the NGDS will be a unified source of geothermal information for the entire United States, its territories, and the surrounding coastal seas. A number of universities, state geological surveys, U.S. Geological Survey, nonprofit organizations, and private entities are participating in the compilation of relevant data for the NGDS. Here, we report progress on the part of this effort to integrate data from the US Exclusive Economic Zone (aka. the federal waters) of the Gulf of Mexico to the NGDS.

Bottom-hole temperatures (BHTs) reported in the wireline log headers are currently tabulated and compiled into a database accessible by a geographic information systems (GIS) interface. BHTs as measured, typically, are of lower temperature than the predrilling formation temperatures at the measured depths, because the drill fluid circulation cools down the well bore and the surrounding formation. Knowledge of the predrilling formation temperatures is more useful in assessing the geothermal setting of an area of interest. It is possible to estimate the pre-drilling formation temperatures from BHTs, if BHTs are measured on multiple logging runs to the same depth: those measured later typically yield higher temperatures, because temperature of the well bore formation gradually rises and recovers toward its pre-drilling state, once the well has been shut. Using a mathematical model of heat transfer around the well bore, one can theoretically extrapolate the temperature recovery trend and estimate the pre-drilling formation temperature. This methodology for estimating the pre-drilling temperature is called the Horner plot technique and is widely used in the geothermal energy field (Lachenbruch and Brewer, 1959; Nagihara, 2004).

Both corrected and uncorrected BHTs, as well as optically scanned copies of the wire-line logs are being cataloged and made available through the NGDS. The current Gulf of Mexico data compilation effort builds on the outcome of an earlier project supported by the Minerals Management Service (currently the Bureau of Ocean Energy Management) in the mid-2000s to map sediment temperatures in the outer continental shelf of the southern U.S. (Nagihara and Smith, 2008; Nagihara 2010). We are currently sweeping the federal waters eastward from the mouth of the Rio Grande along the continental shelf all the way to the western Florida coast.

AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012