System Of Firefighting And Blow-out Protection For A Drilling Operation

Abstract

A system of fire fighting and blow-out protection for a drilling operation comprising valves and flow conduits interconnecting a low pressure and a high pressure source of inert gas to the interior of a blow-out preventer assembly. A pneumatically actuated valve connected to the blow-out preventer outflow conduit is moved to the closed position upon a predetermined pressure being effected by the flow of inert gas therewithin. Gaseous hydrocarbons leaking from the blow-out preventer are rendered noncombustible by admixing an inert diluent therewith by moving a flow control valve to a first position. Should the situation deteriorate into a more dangerous condition, the valve can be further opened whereupon a high pressure source of inert gas is flow conducted into the blow-out preventer while at the same time the outflow valve from the blow-out preventer is moved to the closed position, thereby setting the rubber of the blow-out preventer assembly and increasing the effective hydrostatic head of the borehole, as well as lowering the inflammable limits of the escaping gaseous hydrocarbons.

Description

BACKGROUND OF THE DISCLOSURE

Throughout this disclosure, the term "BOP" refers to and will relate to a "blow-out prevention apparatus" of the type described herein.

In drilling operations it is customary to provide one or more blow-out prevention apparatus which are connected to the well casing with the drill string extending therethrough. Should a gas pocket or a high pressure gaseous formation be encountered while making hole, the BOP, when actuated, will prevent "losing control of the well" from a well "blow-out."

Some BOP's are manually actuated by mechanically forcing an annular body of resilient material to be tightly compressed between the interior body of the BOP and exterior surface of the drill string, thereby effecting a seal means for preventing fluid from flowing up the casing annulus. Other BOP's include pneumatically or motor driven resilient bodies which are forced towards one another and about the drill string so as to form a closure member at the upper extremity of the casing annulus.

During the drilling operation, from time to time a high pressure gas pocket may be encountered, whereupon gaseous hydrocarbons are returned to the surface of the earth along with the drilling fluid. The flow of gaseous hydrocarbons in proximity of the drilling operation is dangerous because the mixture, when admixed with atmospheric air, becomes explosive in nature and for this reason it is desirable to be able to admix an inert gas with the escaping hydrocarbons so as to adjust the percentage composition of the resultant mixture to a value which is noncombustible.

At other times the pressure in the gas pocket may be of sufficient magnitude to cause potential loss of control over the well, that is, the well will make sufficient gas so as to percolate the drilling fluid from the borehole, sometime carrying therewith the entire tubing string and portions of the derrick. Sometimes death and destruction accompanies a serious blow-out, and 99 percent of destructive rig fires are caused by this phenomenon.

In BOP's of the prior art, 30 to 60 seconds are required for shutting in the well. When a high pressure gas formation is encountered and a blow-out occurs, ignition of the escaping gaseous hydrocarbons can melt the rig to the ground in as little as three minutes. When a blow-out occurs and the hydrocarbons completely engulf the rig area, it is usually understood that a condition has been encountered where "it's every man for himself."

However, a blow-out seldom occurs instantaneously. There is often sufficient warning to enable an alert driller to shut-in the well by several well known expedients. In the initial stages of the blow-out it would be desirable to be able to sufficiently dilute the flow of gaseous hydrocarbons to preclude combustion thereof. Moreover, it would be desirable for the inflow of the inert gas to be of sufficient magnitude to effectively increase the hydrostatic head of the well, thereby greatly aiding the driller in rapidly attaining a shut-in condition.

It is furthermore desirable to be able to provide deep wells and off-shore drilling platforms with reliable, safe, low cost equipment which would shut-in a well in less time than is required for workmen to abandon the rig.

Summary of the Invention

The present invention encompasses both method and apparatus which provides an inert gas fire fighting and blow-out protection system for drilling apparatus.

The invention is carried out in conjunction with a drilling operation wherein a cased borehole has a BOP affixed thereto with drill tubing axially extending through the BOP and into the casing, with an annular axial flow passageway extending from the casing annulus longitudinally through the BOP.

A rotating seal means at the upper marginal end of the BOP annulus prevents fluid flow from the upper extremity thereof while a drilling fluid outflow passageway enables drilling fluid to flow from the borehole annulus, into the BOP, through the outflow passageway, and to the mud pit.

An inert gas inlet passageway is flow connected to the annulus of the BOP and has associated therewith means by which inert gas can be admixed with any gases contained within the BOP annulus whenever desired.

The system includes means responsive to a high flow rate of inert gas into the BOP which causes the outflow valve to automatically assume the closed position while subsequently or simultaneously the high pressure source of inert gas which is conducted to the annulus of the BOP effectively increases the hydrostatic head of the well.

A primary object of the present invention is to provide an inert gas fire fighting and blow-out protection system for drilling operations.

Another object of the invention is to provide a method of increasing the effective hydrostatic head of a borehole.

A further object of this invention is to provide a method of shutting-in a well during a drilling operation.

A still further object of this invention is to disclose and provide a method and apparatus for reducing the combustibility of hydrocarbon gases flowing from the borehole of a drilling operation.

Another and still further object of this invention is to provide an inert gas flow system used in conjunction with a drilling operation to enable a combustible mixture of hydrocarbons to be rendered incombustible.

These and various other objects and advantages of the invention will become readily apparent to those skilled in the art upon reading the following detailed description and claims and by referring to the accompanying drawing.

The above objects are attained in accordance with the present invention by the provision of a method of fire fighting and blow-out protection for a drilling operation for use with apparatus fabricated in a manner substantially as described in the above abstract and summary.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematical presentation in the form of a flow sheet which sets forth the method of the present invention;

FIG. 2 is an enlarged, part cross-sectional, part schematical representation of a portion of the apparatus disclosed in FIG. 1; and

FIG. 3 is a reduced top plan view of the apparatus disclosed in FIG. 2.

Detailed Description of the Invention

FIG. 1 illustrates a borehole 10 sunk into the ground and having drill string 13 therein to which a drill bit may be attached for making hole.

A drilling rig (not shown) has the usual deck or floor 14 for rotatably supporting a turntable 15 thereon. Disposed below the turntable there is schematically represented two series connected BOP's, 16 and 17, which may be arranged in the disclosed manner, or if desired, the relationship thereof can be reversed. The BOP 16 is not essential for practicing the present invention.

The BOP 17 of the present invention has an outflow valve 18 through which mud or drilling fluid can flow from the borehole to the mudpit (not shown).

Inert gas inlet 19 is connected to inflow conduit 20. Control flow valve 21 is preferably remote controlled from the rig floor so that it forms an inflow control device. The valve is interposed between a source of inert gas 22 and inflow connection 19. Check valve 21' permits flow in the indicated direction but precludes flow from occurring towards remote control flow valve 21.

A high pressure source of inert gas 23, preferably at least 2,000 cu. ft. of gas at 1,500 to 2,500 psi, is conveniently disposed in close proximity of the low pressure source of gas, preferably at least 500 cu. ft. gas at below 250 psi. Valve 24 is normally open and series connected relative to check valve 25 so as to provide a low pressure source of inert gas at junction 26 when the system is in the stand-by configuration.

Motor control valve 27 is normally closed and series connected relative to normally open valve 28 so that when valve 27 is moved to the open position, the high pressure source of inert gas flows from storage 23 to junction 26.

Junction 29 interconnects flow conduit 30 with junction 26 so as to provide a source of pressure at the illustrated motor valves 27, 31. Motor valve 31 normally is in the open position so that drilling fluid from the BOP is free to flow to the mud pit along conduit 32.

The BOP illustrated in FIGS. 2 and 3 includes a massive body member 33 having a circumferentially extending flange 34 which can be bolted onto the terminal end of the borehole casing. The upper marginal end portion 35 of the body is proviced with a rotating seal member, which includes a barrel 36 rotatably received within member 35. Journals 37, 38 preferably are tapered roller bearings set at an angle relative to one another in the usual manner so as to secure the barrel against axial movement.

Seal member 39 is removably affixed to the barrel and precludes fluid flow between the barrel and member 35. The seal can take on any number of different forms so long as this intended purpose is attained. A drilling rubber in the form of a resilient deformable member 40 has a lower terminal end portion 41 which terminates within the BOP annulus and slidably and telescopingly receives the drill string therethrough with the inside peripheral wall portion 42 sealingly bearing against the outer peripheral wall surface of the string. The resilient seal member includes a circumferentially extending seal portion 44 which is removably affixed to the barrel.

The outflow conduit includes passageway 45 which flow communicates with the annular BOP passageway 46, which in turn flow communicates with the casing annulus 112. A plurality of inert gas inflow passageways, one of which is illustrated by numeral 47, flow communicates with annulus 46 and an inflow conduit 19 so that increased pressure can be effected at the seal chamber annulus 43.

Inert gas generator 122 provides additional embodiments of the invention, and can be in the form of a combustion chamber wherein gaseous hydrocarbons are completely combusted into CO.sub.2 and N.sub.2 with the water of combustion being removed by a conventional knock-out drum. Alternatively, the generator 122 can be the exhaust of an internal combustion engine with arrangements being made for precluding ingestion of atmospheric air into the system.

Pump 123 compresses the effluent from 122 so that makeup inert is always available at 23. Constant pressure regulator valve 124 provides a continuous source of low pressure inert gas at 22.

In operation, while making hole with the drilling apparatus, outflow valve 31 is normally open, inflow valve 21 is normally closed, valve 24 is normally open, valve 27 is normally closed, and valve 28 is normally open. Accordingly, valve 21 can be moved to the open position whereupon flow occurs from the low pressure source, through the normally open valve 24, through one-way check valve 25 to junction 26, through the partially open valve 21, through the one-way check valve 21', and into the annulus 43, 46 whereupon the inert gas admixes with and flows along with any gaseous products from the BOP.

The pneumatically actuated valves 27, 31 are set to respond at a pressure in excess of any arbitrarily selected meaningful pressure differential normally effected between the annulus 43 and ambient. For example, valve 31 may be set to close at a pressure of 30 psi above the normal pressure effected within passageway 45, while valve 27 is set to open at a pressure 60 psi above the pressure normally encountered in passageway 47.

As valve 21 is more fully opened to a second position, the pressure within passageway 45 increases, thereby reflecting an increased pressure at 29, whereupon the motor of the valve, such as the diaphragm, causes the valve 31 to assume the closed position. Since the mud pumps are still running, pressure at junction 29 is further increased, thereby causing motor valve 27 to assume the opened position, whereupon the high pressure inert gas 23 flows through normally open valve 28, through valve 27, to junction 26 and on to the annulus 46 and 43, thereby effecting a tremendous pressure within the BOP annulus 43. It will be appreciated that a pressure source of gas at 1,000 psi, for example, is equivalent to about 2,000 feet increased hydrostatic head within the well bore.

This action of the high pressure inert gas causes the inner peripheral wall surface of the rubber to be forced against the outer peripheral wall surface of the drill string with a tremendous force which is proportional to the pressure within the BOP annulus.

Seal 39 wears rapidly and usually is the first interface to cause leakage of hydrocarbons to occur from the borehole into the atmosphere. Progressive wear about this member enables gaseous hydrocarbons to flow from annulus 46, about the seal, and between the interface formed between the barrel and the housing. When leakage is noted, or should ignition of the escaping gases occur, the danger is obviated by admixing inert gas therewith so that the drilling operation can proceed uninterrupted until another trip into the hole becomes necessary, whereupon the seal can be easily replaced with no down-time.

Accordingly, should the well commence making gas, the valve 21 can be partially opened so as to render leakage from the BOP incombustible, that is, the percentage composition of hydrocarbons in the resultant mixture is incombustible in atmospheric air. Should the well commence unequal flow distribution of drilling fluid, or should any other indication of potential loss of control evidence itself, the valve 21 can be further opened, thereby rapidly causing the well to assume the "shut-in" configuration.

The response time for actuation of the motor valves 27, 31 can be regulated to any desired time interval, but it is preferred to have valve 21 arranged to enable shut-in of the well within two to five seconds. Hence, the roughnecks are secure in the knowledge that the well can be shut-in more rapidly than they are capable of abandoning the rig.

Hence, the present invention is useful in preventing combustible mixtures of hydrocarbons from accumulating in proximity of the drilling rig as well as enabling the well to assume the "shut-in" configuration.

Claims

1. In a drilling operation having a blowout preventer affixed to a casing; with the casing extending downhole in a borehole; drill tubing extending through the blowout preventer and into the casing; an annular flow passageway extending from the casing annulus and through the blowout preventer; a flow passageway extending from the annular flow passageway to an outflow pipe; and a seal member for preventing fluid from flowing from the upper extremity of the annular flow passageway; the method of extinguishing fires comprising:

flow connecting a source of inert gas to said annular flow passageway;

interposing an inflow control device between the source of inert gas and said annular flow passageway;

flowing inert gas into the annular flow passageway at a rate which renders any resulting gaseous mixture formed within the outflow pipe incombustible in atmospheric air;

interposing an outflow control device in said outflow line so that the inert gas effects an increased pressure within the annular flow passageway;

actuating the outflow valve to the closed position in response to flow occurring through said inflow control device; and

increasing the inert gas pressure within the annular flow passageway so as

2. The method of claim 1 and further including the steps of:

actuating the inflow control device to the open position when it is desired to attain a first flow of a non-combustible mixture of gases into the blowout preventer;

pneumatically actuating the outflow valve to the closed position when it is desired to attain a second flow of a non-combustible mixture of gases into the blowout preventer; and

pneumatically connecting a high pressure source of gas to the blowout

3. The method of claim 1 wherein said inert gas is selected from the group

4. The method of claim 1 wherein said inert gas is flue gases derived from

5. The method of claim 4 wherein said flue gases are obtained from the exhaust system of an internal combustion engine and further including the step of:

compressing said flue gases so as to provide said source of high pressure

6. The method of claim 5 and further including the step of interconnecting the high pressure source of inert gas with the low pressure source of inert gas by means of a pressure regulator valve.