Temperature anomaly mapping provides a rapid and inexpensive method of finding and evaluating hydrocarbon deposits.

Each of the past 25 years has added knowledge, strength and value to the concept of temperature anomaly mapping for finding hydrocarbons. Examination of data from more than 150,000 well logs and thousands of miles of surface surveys has yielded extreme proof-of-system accuracy.

The method can be used to determine where to drill; when to quit drilling; the deeper drilling potential of producing properties; and whether, and at what price, to buy or sell producing properties. Same-day answers are provided for surveys up to 100 miles (160 km) per day offshore, 300 miles (480 km) per day by surface vehicle and 700 miles (1,120 km) per day by aircraft. It is highly accurate and environmentally friendly, with permitting seldom if ever required, and is considered by some to be fail-safe. It will locate stratigraphic trap reservoirs, and the presence of faulting, halite and basalt are not a problem. Under common circumstances its cost is less than one-tenth of 1% that of a seismic survey. Survey repeatability is shown in Figure 1.

Hydrocarbon deposits are much more thermally insulative than common sediments. Temperatures are lower above and higher below hydrocarbon deposits. After consideration of pore surface area vs. volume within the pay zone, the distance of the measurement from the deposit in question and the effects of possible deeper pay zones, the relationship is quantitative. The greater the anomaly, the greater the pay zone. Fine-grained oil reservoirs have been found to be better insulators than coarse-grained oil reservoirs because, even though they contain more water and less oil, they have a much higher number of interfaces per unit volume that impede both natural connective and conduction boundary effects.
An exhaustive Alberta, Canada, area study has shown that temperatures below oil and gas fields are 15?F to 34? F (-9?C to 1?C) warmer than the same depth average values observed outside the fields.
Five different types of temperatures profile survey methods have been developed. Bottomhole temperatures can be processed to determine an area temperature gradient and identify specific locations of negative departure from area gradient value. Shallow depth temperatures can be taken over the area of interest, ground-surface infrared surveys taken at a fixed distance from ground level, airborne infrared surveys taken at a fixed low level (500 ft to 700 ft or 150 m to 215 m) above ground, and offshore surveys made below any thermocline by towing a suitable sensor at a fixed depth. In wells where multiple log runs have been made, one can commonly pick pay zones from log headings alone without opening a single log, using maps or knowing the geology.

Using surface surveys, shallow pay zones can be identified by a more abrupt shift to negative anomaly values at bed boundaries.

Published values of thermal conductivity are of little help and can even be a hindrance to understanding the simplicity of this oil and gas finding method. A significant amount of literature concerning sedimentary heat transfer is faulty, and it might well benefit our industry to burn a few existing publications and textbooks. Thermal conductivity values are very temperature-sensitive, and it has been reported that the gradients for both carbonates and evaporites more than double with an increase of 100?F from the 200?F level. Going from 80?F to 260?F, the thermal conductivity of halite has been reported to decrease by 42%.
Massive observations prove that geothermal gradients are non-linear and increase significantly with depth, while linear gradients remain in all publications and texts reviewed. Proponents of linear gradients must believe that all subsurface sedimentary materials at any depth have identical heat transfer ability and are immune to changes in temperature, pressure and effects of compaction with time. More than 2,000 data points from Bee County, Texas, show that the temperature gradient increases 300% with increasing depth from 3,500 ft (1,065 m) to 15,500 ft (4,725 m).

Contrary to published literature, the thermal conductivities of sedimentary rocks do not increase with depth through the effects of compaction; natural convection heat flow plays a very important role in sedimentary basins worldwide, and the best common heat transfer material within the earth is water. At standard temperature and pressure (STP) the upward heat transfer value for water is somewhere between 18 and 25 times that of the downward transfer. This ratio increases with increased depth, temperature, viscosity and surface tension effects. As salt content increases within water at STP, thermal conductivity can more than triple.

Most textbook values for thermal conductivity do not document the percentage of rock components, porosity, pore geometry, saturating fluid composition, temperature or pressure at the depth at which the samples were taken. A German study found that an anhydrite core expanded 7% after being brought to the surface. Most samples analyzed are dime-sized, and almost none have downhole fluids present. Most specimens are measured dry or dampened with kerosene. Specimen machining is imprecise and represents only a microscopic fraction of what exists in the subsurface. Laboratory heat source vs. sink geometry cannot closely duplicate underground conditions. The gradient in laboratory models is much greater than that found in the subsurface. There is seldom if ever any single direction flow and always unwanted horizontal direction heat loss in laboratory measurements. Edge (equipment boundary) heat loss from the laboratory specimen does not accurately duplicate subsurface conditions.

Using only published values for thermal conductivity to establish realistic subsurface temperature profiles is equivalent to the differential one would experience by placing a finger 1-in. above a burning candle as opposed to 1-in. horizontally from the flame. Analysts who rely on textbook gradients are likely to get burned.

There are factors that affect recorded temperature such as cloud cover, time since circulation, target surface composition, coloration, elevation, slope, vegetation, atmospheric moisture content, etc. Years have been spent studying them, and no critical interpretation problems have been found outside a rather small but recognizable gray area.

Faced with the reported 80% industry failure/incompetence rate in wildcat ventures, it is time for a change. In addition to geological and geophysical exploration costs, discovery success rates must be factored in, particularly the costs of leasing unnecessary acreage and the drilling of non-commercial wells or dry holes. These alone can account for many times the expense of generating exploration data.
For more information about temperature anomaly mapping, call +1-281-497-1392.

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