BLOWOUT AND LOST CIRCULATION DETECTOR

• US 3,760,891 A
• Filed: 05/19/1972
• Issued: 09/25/1973
• Est. Priority Date: 05/19/1972
• Status: Expired due to Term

• Current Assignee: Sonat Offshore Drilling, Inc.
• Original Assignee: John F. Gadbois
• Inventors: Gadbois, John F.
• Primary Examiner(s): Brown, David H.
• Application Number:
  US05/255,160
• Time in Patent Office: 494 Days
• Field of Search: 175/48,50,40,8 73/155
• US Class Current: 73/152.21
• CPC Class Codes: E21B 21/001 specially adapted for underwater drilling dual gradient drilling E21B21/082
• CPC Class Codes: E21B 21/08 Controlling or monitoring pressure or flow of drilling fluid, e.g. automatic filling of boreholes, automatic control of bottom pressure valve arrangements therefor E21B21/10

Abstract

A method and apparatus for rapidly detecting blowouts and lost circulation in a drilling well, having particular application to a well being drilled at sea from a floating drilling platform. The return rate of flow of drilling fluid which will be affected by a blowout is monitored and transduced into an electrical signal proportional thereto. The magnitude of the electrical signal is monitored and accumulated over selected overlapping intervals of time to form a sequence of accumulated values. Each accumulated value in the sequence is compared with at least one of the previous accumulated value in the sequence and the difference therebetween determined. This difference is compared with preselected values denoting the allowable limits of the return flow rate of the fluid. If the difference between the accumulated values exceed the preselected values, an indication is provided of the commencement of a blowout or lost circulation. This abstract is not intended to define this invention which, of course, is measured by the claims, or to be limiting in any way as to the scope of this invention.

Claims

1. A method of detecting the commencement of blowouts and lost circulation in a well in which a drilling fluid is being utilized, including the steps of:

transducing the rate of flow of the drilling fluid out of the well into an electrical signal proportional thereto;

commencing at a first point in time, accumulating said electrical signal over a first selected interval of time;

commencing at a second point in time occurring a second selected interval of time after said first point in time, accumulating again said electrical signal over said first interval of time;

repetitively performing said step of accumulating said electrical signal over said first selected interval of time to obtain a continuous sequence of accumulated values, each step of accumulation commencing at said second selected interval of time after the commencement of the preceding step of accumulation; and

comparing each of said accumulated values with at least one selected accumulated value preceding it in said sequence to determine the difference in value therebetween, a preselected difference between said accumulated values being indicative of the commencement of one of a blowout and lost circulation.

2. The method according to claim 1, including the step of:

comparing each of said differences in accumulated values with selected limiting values denoting selected limits in transient changes of the return flow rate of the drilling fluid, said preselected limiting values being such that normal changes in the return flow rate produce differences between said acccumulated values that fall within said limiting values and blowouts and lost circulation produce differences between said accumulated values that do not fall within said limiting values.

3. A method according to claim 1, including the step of:

actuating means for indicating the commencement of one of a blowout and lost circulation responsive to any of said differences between said accumulated values falling outside said preselected limiting values.

4. A method according to claim 1, including the steps of:

determining whether each of said accumulated values is greater than or less than the ones of said preceding accumulated values with which it is compared, and assigning an algebraic sign to each of said differences therebetween indicative thereof;

comparing each of the absolute magnitudes of said differences in accumulated values with preselected limiting values denoting selected limits in the transient changes of the return flow rate of the drilling fluid; and

actuating means for indicating the commencement of one of a blowout and lost circulation if any of the absolute magnitudes of said differences exceeds said preselected limits;

said actuating means indicating the commencement of a blowout if said algebraic sign indicates said return rate of flow is increasing and indicating the commencement of lost circulation if said algebraic sign indicates said return rate of flow is decreasing.

5. A method according to claim 1 wherein the step of transducing produces an electrical signal having one of its parameters of voltage and current proportional in magnitude to said return flow rate.

6. A method of obtaining a signal representative of the return flow rate of drilling fluid in a well and free of ambiguities caused by cyclic anD regularly occurring variations, comprising:

transducing said return flow rate into an electrical signal having one of its parameters of voltage and current proportional in magnitude thereto;

repetitively accumulating the magnitudes of said parameter of said signal over a first selected interval of time to obtain a sequence of accumulated values, each step of accumulation commencing at a second selected interval of time after the commencement of the preceding step of accumulation;

comparing each of said accumulated values with at least one selected preceding accumulated value in the sequence to determine the difference in value therebetween;

determining limiting values representative of changes between said accumulated values produced by normal cyclic and regularly occurring variations in the return flow rate;

comparing said difference between accumulated values with said selected limiting values; and

generating an electrical signal responsive to the difference between said accumulated values exceeding said selected limiting values.

7. In a well in which drilling fluid is being utilized, a blowout and lost circulation detector comprising:

means for sensing the rate said drilling fluid flows out of said well;

means connected to the output of said sensing means for transducing said return rate of flow into an electrical signal proportional thereto;

means connected to the output of said transducing means for obtaining a sequence of accumulated values of said transduced electrical signal, each of said accumulated values being obtained over a first selected interval of time and the commencement of obtaining each accumulated value occurring at a second selected interval of time after the commencement of obtaining the preceding accumulated value in the sequence; and

a first comparator connected to the outputs of said accumulating means for comparing each of said accumulated values with at least one selected preceding accumulated value in the sequence and for determining the difference in value therebetween, a preselected difference between said accumulated values being indicative of the commencement of one of a blowout and lost circulation.

8. A detector according to claim 7, wherein:

said means for determining said return flow rate includes a fluid conductor in communication with said drilling fluid and vertically positioned to provide a columnar receptacle for said drilling fluid, and said means for transducing said return rate of flow into an electrical signal includes a pressure-sensitive transducer in communication with said columnar receptacle which transforms the pressure of the drilling fluid therein into an electrical signal having one of its parameters of voltage and current proportional thereto.

9. A detector according to claim 7 wherein said means for obtaining said sequence of accumulated values comprises:

a clock generating a timing signal;

a first switching means connected to the output of said clock and to the output of said transducing means; and

a plurality of accumulators, each of which is connected to the output of said first switching means, said first switching means coupling the output of said transducing means responsive to said timing signal to selected ones of said accumulators, at selected points in time and for selected intervals of time.

10. A detector according to claim 7, including:

said first comparator also determines whether each of said accumulated values is greater than or less than the preceding accumulated values with which it is compared and assigns to said difference an algebraic sign indicative thereof;

a second comparator coupled to the output of said first comparator for comparing the absolute magnitude of each of said differences in accumulated values with preselected limiting values denoting selected limits in transient changes of the return flow rate of said drilling fluid; and

means connected to the output of said second comparator for indIcating the commencement of one of a blowout and lost circulation whenever any of the absolute magnitudes of the differences exceeds said preselected limiting values, said means indicating one of a blowout and lost circulation depending upon said algebraic sign assigned to said difference.

11. A detector according to claim 7, including:

a second comparator connected to the output of said first comparator for comparing each of said differences in accumulated values with preselected limiting values denoting selected limits in transient changes of the return flow rate of the drilling fluid, said preselected limiting values being such that normal changes in the return flow rate produce differences between said accumulated values that fall within said limiting values and blowouts produce differences between said accumulated values that do not fall within said limiting values.

12. A detector according to claim 11, including:

means connected to the output of said second comparator for indicating the commencement of one of a blowout and lost circulation when any of said differences between said accumulated values fall outside said preselected limiting values.