DETERMINATION OF VIRGIN FORMATION TEMPERATURE

• US 20040190589A1
• Filed: 03/13/2003
• Published: 09/30/2004
• Est. Priority Date: 03/13/2003
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Zazovsky, Alexander, Haddad, Sammy S.
• Granted Patent: US 6,905,241 B2
• Time in Patent Office: Days
• US Class Current: 374/136
• CPC Class Codes: E21B 47/07 Temperature
• CPC Class Codes: E21B 49/00 Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells

Abstract

A method for determining virgin formation temperature of earth formations surrounding a borehole is provided. The time duration of drilling fluid circulation and the time after cessation of drilling fluid circulation at the borehole depth regions of interest are tracked. At a particular borehole depth region of interest, fluid flows from the formations into a device in the borehole, and the temperature of the fluid as a function of time with respect to initiation of fluid flow is measured. The thermal history of formations surrounding the particular borehole depth region is modeled for a cooling phase during drilling fluid circulation, a temperature build-up phase after cessation of drilling fluid circulation, and a formation fluid flow phase after initiation of fluid flow. The model and temperature measurements are used to determine a trend of temperature evolution and the virgin formation temperature by extrapolation from the trend.

Claims

1. A method for determining virgin formation temperature of earth formations surrounding a borehole that is drilled using drilling fluid, comprising the steps of:

keeping track of the time duration of drilling fluid circulation at borehole depth regions of interest;

keeping track of the time after cessation of drilling fluid circulation at said borehole depth regions of interest;

at a particular borehole depth region of interest, causing flow of fluid from the formations into a device in the borehole, and measuring the temperature of said fluid as a function of time with respect to initiation of said fluid flow;

modeling the thermal history of formations surrounding the particular borehole depth region, said modeling including a cooling phase during drilling fluid circulation, a temperature build-up phase after cessation of drilling fluid circulation, and a formation fluid flow phase after initiation of fluid flow;

using said model and said temperature measurements, determining a trend of temperature evolution at said particular depth region; and

determining the virgin formation temperature by extrapolation from said trend.

2. The method as defined by claim 1, wherein said step of causing flow of fluid from the formations into a device in the borehole and measuring the temperature of said fluid as a function of time comprises positioning a formation testing device at the particular depth region of interest, drawing fluid from the formations into said device, and measuring, in said device, the temperature of said fluid.

3. The method as defined by claim 2, further comprising repeating the steps of the method for determining virgin formation temperature determination for other depth regions of interest.

4. The method as defined by claim 3, further comprising producing a log of the determined virgin formation temperatures as a function of depth.

5. The method as defined by claim 1, wherein said step of modeling the thermal history of said formations comprises formulating model equations that include a function of the unknown virgin temperature, T_o, and a function of the unknown average borehole temperature during frilling fluid circulation, (T_W).

6. The method as defined by claim 5, further comprising repeating the steps of the method for determining T_o and for determining T_W.

7. The method as defined by claim 6, further comprising producing logs of T_o and T_W as a function of depth.

8. The method as defined by claim 1, wherein said step of determining a trend of temperature evolution at a particular depth region includes performing an inversion to obtain a trend of measured temperature versus dimensionless temperature.

9. The method as defined by claim 1, wherein said model includes, during said formation fluid flow phase, a representation of heat conduction and heat convention during fluid flow.

10. The method as defined by claim 1, wherein said step of modeling the thermal history includes inputting to the model, the density and specific heat of the drilling fluid, and the following physical parameters of the formations:

thermal conductivity, specific heat of rock, specific heat of fluid permeability, porosity, rock density, fluid density, bulk modulus, and fluid viscosity.

11. The method as defined by claim 9, wherein said step of modeling the thermal history includes inputting to the model, the density and specific heat of the drilling fluid, and the following physical parameters of the formations:

thermal conductivity, specific heat of rock, specific heat of fluid permeability, porosity, rock density, fluid density, bulk modulus, and fluid viscosity.

12. In a method for determining virgin formation temperature of earth formations surrounding a borehole that is drilled using drilling fluid, that includes the steps of:

keeping track of the time duration of drilling fluid circulation at borehole depth regions of interest;

keeping track of the time after cessation of drilling fluid circulation at said borehole depth regions of interest; and

, at a particular borehole depth region of interest, causing flow of fluid from the formations into a device in the borehole, and measuring the temperature of said fluid as a function of time with respect to initiation of said fluid flow;

the improvement comprising;

modeling the thermal history of formations surrounding the particular borehole depth region, said modeling including a cooling phase during drilling fluid circulation, a temperature build-up phase after cessation of drilling fluid circulation, and a formation fluid flow phase after initiation of fluid flow;

using said model and said temperature measurements, determining a trend of temperature evolution at said particular depth region; and

determining the virgin formation temperature by extrapolation from said trend.

13. The method as defined by claim 12, further comprising repeating the steps of the method for determining virgin formation temperature determination for other depth regions of interest.

14. The method as defined by claim 13, further comprising producing a log of the determined virgin formation temperatures as a function of depth.

15. The method as defined by claim 12, wherein said step of modeling the thermal history of said formations comprises formulating model equations that include a function of the unknown virgin temperature, T_o, and a function of the unknown average borehole temperature during frilling fluid circulation, (T_W).

16. The method as defined by claim 15, further comprising repeating the steps of the method for determining T_o and for determining T_W.

17. The method as defined by claim 16, further comprising producing logs of T_o and T_W as a function of depth.

18. The method as defined by claim 12, wherein said step of determining a trend of temperature evolution at a particular depth region includes performing an inversion to obtain a trend of measured temperature versus dimensionless temperature.

19. The method as defined by claim 12, wherein said model includes, during said formation fluid flow phase, a representation of heat conduction and heat convention during fluid flow.

20. The method as defined by claim 12, wherein said step of modeling the thermal history includes inputting to the model, the density and specific heat of the drilling fluid, and the following physical parameters of the formations:

thermal conductivity, specific heat of rock, specific heat of fluid permeability, porosity, rock density, fluid density, bulk modulus, and fluid viscosity.