Well downhole condition signalling

Abstract

A downhole tool 10 includes means for detecting a downhole condition, a capacitor bank, and a sparker. The technique is particularly useful for detecting casing collars. As the tool is passed along the well bore 11, it detects collars 12. On each detection, a part of the capacitor bank is discharged through the sparker. This generates an acoustic pulse which is transmitted through the ground (wave 14) to detectors 15, 16. The movement of the tool 10 is also monitored by a movement detector 20. The position of the tool 10 is correlated with the positions of the collars 12 by a computer 22 fed via interfacing circuitry 21. If desired, the pulses may be coded by strength, number, time spacing, etc.

Description

BRIEF DESCRIPTION OF THE DRAWING

The following description and drawings set forth in detail certain illustrative implementations of the invention, which are indicative of several exemplary ways in which the principles of the invention may be carried out. Various objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings, in which:

FIG. 1 is a sectional side view illustrating a CCL locating system embodying the invention.

BRIEF DESCRIPTION OF A PREFERRED EMBODIMENT

One or more exemplary implementations of the present invention are hereinafter illustrated and described, wherein like reference numerals are used to refer to like elements throughout and wherein the illustrated structures are not necessarily drawn to scale.

An embodiment of the invention and its manner of operation will now be described by way of example and with reference to the drawing FIG. 1, which shows the present system in a well.

In the present system, joint detection is achieved as follows. A battery is used to power a high voltage (1500-3000 V) DC-DC converter, which charges a capacitor bank in the downhole tool 10 while it is still on the surface. The tool is then lowered into the well bore 11.

As the tool traverses along the well bore, the collar locating circuitry in the tool 10 monitors its surroundings, ie the well bore around it, for a casing collar. (Several such collars 12 are shown.) If it detects such a casing collar, it sends a signal to the capacitor bank to discharge the bank across the sparker electrodes. The spark vaporises the fluid around it, and the creation and collapse of the resulting bubble sends a pressure wave 13 up through the ground, as ground wave 14, to a well detector 15 and/or a ground detector 16 at the surface.

At the surface, the relative motion of the conveying means (drill pipe, coiled tubing etc.) is detected using some form of linear to rotary detector 20. The surface motion is plotted against the signal received from below ground by a computer 22 via interfacing circuitry 21. This log can be compared to a correlation log made on a previous occasion.

If desired, the sparker capacitor bank can be split into sections which can be fired (discharged) independently. This will enable the positions of several successive casing collars to be detected, and/or differently coded signals (eg by amplitude, or by pulse sequence) to be generated. If desired, a time delay can also be provided between the detection of a casing collar and the firing of the sparker.

Since a sparker has higher, more concentrated output energy than a pressure pulse created by a flow diversion or a solenoid, higher energy pulses can generally be transmitted satisfactorily, directly through the rock formation. A continuous liquid column to surface is not required. In horizontal wells in particular, the surface signal receiver can be located above the well bore away from the rig, and it is therefore does not have to have hazardous area certification in this configuration.

Claims

1. Downhole condition signalling apparatus comprising: detection means for detecting a downhole condition; andsparker means responsive to the detection means to generate an acoustic signal.

2. The apparatus according to claim 1 including signal processing means coupling the detection means to the sparker means.

3. The apparatus according to claim 2 wherein the signal processing means codes the sparker signals by strength.

4. The apparatus according to claim 2 wherein the signal processing means codes the sparker signals by number.

5. The apparatus according to claim 2 wherein the signal processing means sparker signals are coded by time spacing.

6. The apparatus according to claim 2 wherein the signal processing means delays the sparker signals from the detection of the condition.

7. The apparatus according to claim 2 wherein the detection means detects the passage past a casing collar.

8. A downhole condition detection system comprising: a downhole condition signalling apparatus comprising: detection means for detecting a downhole condition, andsparker means responsive to the detection means to generate an acoustic signal; andsurface means remote from the well head for detecting signals from the sparker.