Method for measuring the thermal conductivity of well casing and the like

• US 3,981,187 A
• Filed: 07/07/1975
• Issued: 09/21/1976
• Est. Priority Date: 03/25/1974
• Status: Expired due to Term

• Current Assignee: Atlantic Richfield Company (BP PLC)
• Original Assignee: Atlantic Richfield Company (BP PLC)
• Inventors: Howell, Eddie P.
• Primary Examiner(s): Goldstein, Herbert
• Application Number:
  US05/593,282
• Time in Patent Office: 442 Days
• Field of Search: 73/15 A, 73/15 R, 73/154, 73/432
• US Class Current: 73/152.13
• CPC Class Codes: E21B 47/07 Temperature
• CPC Class Codes: G01K 3/10 in respect of time, e.g. reacting only to a quick change of temperature

Abstract

A method for measuring the thermal conductivity of well casing in situ. The instrument consists of a probe several feet in length lowered into a well and decentralized so that it maintains contact with the casing wall. Two temperature sensors situated adjacent opposite ends of the probe are thermally insulated from an electrically heated intervening portion of the probe body. The probe is moved from one depth to another at a constant predetermined velocity, and the sensors continuously measure the temperature of the casing wall before and after passage of the heated probe portion thereover. The effective thermal conductivity of the casing is directly proportional to the flux applied by the heater and inversely proportional to the temperature change as the heater passes a point along the casing.

Claims

1. The method of measuring the earth heat flux at a selected depth adjacent an uncased borehole comprising the steps of:

a. measuring the temperature of the well bore at said depth,

b. thereafter applying a known constant heat flux to the well bore at said depth for at least a predetermined time interval sufficient to establish a linear relation between the corresponding temperature rise and the earth thermal conductivity at said depth,

c. measuring the correponding rise in temperature of the well bore at said depth,

d. measuring the temperature gradient in the unheated well bore between two positions separated therein by a predetermined vertical distance at approximately said depth, and

e. calculating a value for the earth heat flux in the vicinity of said depth as a function of the earth thermal conductivity at said depth and of said temperature gradient, wherein the steps are performed in part by moving past said depths at a constant logging speed a well logging probe carrying a pair of vertically spaced apart temperature sensors responsive to the temperature of said bore hole at their respective levels, means for electrically heating a portion of the probe intermediate said sensors, and means for decentralizing the probe so that it is urged into thermal conductive contact with said bore hole, the value of said logging speed being equal to or less than the quotient formed by dividing the length of effective heated interface between said heating means and the bore hole by said predetermined time.

2. The method of claim 1 wherein said earth heat flux is determined in accordance with the formula Q_E = K_E Δ

T_E where

Q_E = earth heat flux in cal./cm² /sec.,

K_E = earth thermal conductivity in cal./cm/sec.°

C,

Δ

t_e = temperature gradient in °

C.