Exploring for subsurface hydrocarbons by sea floor temperature gradients preferably using a multiplexed thermistor probe
First Claim
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1. A method of exploring the sea floor for subsurface hydrocarbons comprising the steps of:
- selecting measurement sites arrayed along the sea floor in a pattern selected as a function of available geological information;
measuring substantially continuous temperature gradients at a plurality of depths within several meters into the sea floor at each of said sites by taking temperature readings at each of said sites, correcting said temperature readings for transient disturbances by ascertaining the temperature at each site at the same depth for a period of time and extrapolating from the temperatures so ascertained corresponding equilibrium temperatures which would be measured if taken after an infinitely long time in an unchanging environment and from said extrapolated equilibrium temperatures determining said temperature gradients;
determining the contribution to said temperature gradients caused by heat propagation through said sea floor resulting from long term bottom water temperature variations; and
differentiating any fluid advection contribution in the measured actual values of temperature when adjusted for the contributions due to said long term buttom water temperature variations at the respctive measurement sites;
calculating the surface heat flow at each site from the corresponding temperature gradient at said site while, eliminating the long term bottom water and fluid advection contributions determined at said site; and
producing a map of said surface heat flow, said map being indicative of characteristics of subsurface hydrocarbon convection through nearby subsurface formations and thereby the location of said subsurface hydrocarbons.
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Abstract
Disclosed are a method and a system for measuring the sea floor temperature gradient several meters into the formation at each of an array of measurement sites, and using these gradients to explore for and characterize hydrocarbon deposits. The measurements can be taken with a special lance driven into the otherwise undisturbed sea floor.
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Citations
19 Claims
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1. A method of exploring the sea floor for subsurface hydrocarbons comprising the steps of:
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selecting measurement sites arrayed along the sea floor in a pattern selected as a function of available geological information; measuring substantially continuous temperature gradients at a plurality of depths within several meters into the sea floor at each of said sites by taking temperature readings at each of said sites, correcting said temperature readings for transient disturbances by ascertaining the temperature at each site at the same depth for a period of time and extrapolating from the temperatures so ascertained corresponding equilibrium temperatures which would be measured if taken after an infinitely long time in an unchanging environment and from said extrapolated equilibrium temperatures determining said temperature gradients; determining the contribution to said temperature gradients caused by heat propagation through said sea floor resulting from long term bottom water temperature variations; and
differentiating any fluid advection contribution in the measured actual values of temperature when adjusted for the contributions due to said long term buttom water temperature variations at the respctive measurement sites;calculating the surface heat flow at each site from the corresponding temperature gradient at said site while, eliminating the long term bottom water and fluid advection contributions determined at said site; and producing a map of said surface heat flow, said map being indicative of characteristics of subsurface hydrocarbon convection through nearby subsurface formations and thereby the location of said subsurface hydrocarbons. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 19)
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16. A method of making geothermal measurements comprising establishing thermal contact between a thermistor and a geological formation whose temperature is to be measured and relating, through a circuit arrangement, (i) the log of the ratio of the resistance of the thermistor at a first temperature to the resistance at a second temperature and (ii) a difference between said temperatures, in a manner allowing said relating to remain substantially linear throughout a temperature range of several decades of °
- C. of expected temperatures and said circuit implementing a product of (i) said first temperature plus an offset, and (ii) said second temperature plus an offset, wherein said offset is selected, for a given thermistor or set of thermistors, to be at a level satisfying said linearity.
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17. A method of making geothermal measurements which comprises establishing thermal contact between at least two thermistors and a geological formation whose temperature is to be measured and relating, through a circuit arrangement, (i) the log of the ratio of resistance of a first thermistor at a first temperature to its resistance at a second temperature and (ii) the log of the ratio of the resistance of a second thermistor at a third temperature to its resistance at the second temperature, in a manner allowing said relationship to remain substantially linear throughout a temperature range of several decades of °
- C. of expected temperatures said circuit implementing a product of (i) said first temperature plus an offset, and (ii) said second temperature plus an offset, wherein said offset is selected, for a given thermistor or set of thermistors, to be at a level satisfying said linearity.
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18. A method of determining at a geological surface level strata heat flow emanating through the strata from below surface geothermal sources comprising:
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measuring a substantially continuous temperature gradient in the strata at a site from the surface at a plurality of depths within several meters below the surface by taking temperature readings at said site, correcting said temperature readings for transient disturbances by ascertaining the temperature at the same depth for a period of time and extrapolating from the temperatures so ascertained corresponding equilibrium temperatures which would be measured if taken after an infinitely long time in an unchanging environment and from said extrapolated equilibrium temperatures determining said temperature gradient; determining the contribution to said temperature gradient at said site in the strata from the surface to the depth of said several meters caused by above-surface heat propagation through said strata; and
differentiating any fluid advection contribution in the measured actual values of temperature when adjusted for the contribution due to above-surface heat propagation; andcalculating heat flow from said temperature gradient, while eliminating said above-surface heat propagation and fluid advection contributions during said heat flow calculation.
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Specification