Method of setting a balanced cement plug in a borehole

Claim 1

A method of conditioning a borehole penetrating a subterranean formation from the earth's surface prior to the cementing thereof, said method comprising the steps of: identifying the locations in said borehole where the intended top of cement (TOC) and where the intended bottom of cement (BOC) shall be; introducing a conduit into said borehole and positioning the bottom of said conduit at said TOC; injecting at least two streams of drilling fluid from said conduit into said borehole at said TOC wherein said streams of said drilling fluid are injected at high velocity from said bottom of said conduit in at least one plane wherein said plane is substantially parallel to the cross section of said borehole, whereby said streams impact the walls of said borehole in said at least one plane; continuing said injecting of said streams and establishing circulation of said drilling fluid from the bottom of said conduit to the top of said borehole by way of the annular space between said conduit and the walls of said borehole; moving said conduit, while continuing said circulation, from TOC to a termination location which is at least the location of said BOC; continuing said circulation from said termination location; discontinuing said circulation of said drilling fluid when the properties of said drilling fluid are desirable for cementing and when at least one volume of drilling fluid equivalent to the annular volume between the conduit and the borehole wall from the surface to said termination location has been circulated from said termination location to the surface of said borehole whereby said conditioning of said borehole is completed.

Claim 2

A method of conditioning a borehole penetrating a subterranean formation from the earth's surface prior to the cementing thereof, said method comprising the steps of: identifying the locations in said borehole where the intended top of cement (TOC) and where the intended bottom of cement (BOC) shall be; introducing a conduit into said borehole and positioning the bottom of said conduit at said TOC; injecting at least two streams of drilling fluid from said conduit into said borehole at said TOC wherein said streams of said drilling fluid are injected at high velocity from said bottom of said conduit in at least one plane wherein said plane is substantially parallel to the cross section of said borehole, whereby said streams impact the walls of said borehole in said at least one plane; continuing said injecting of said streams and establishing circulation of said drilling fluid from the bottom of said conduit to the top of said borehole by way of the annular space between said conduit and the walls of said borehole; moving said conduit, while continuing said circulation, from TOC to a termination location which is at least the location of said BOC; continuing said circulation from said termination location; discontinuing said circulation of said drilling fluid when the properties of said drilling fluid are desirable for cementing and when at least one volume of drilling fluid equivalent to the annular volume between the conduit and the borehole wall from the surface to said termination location has been circulated from said termination location to the surface of said borehole whereby said conditioning of said borehole is completed.

Claim 10

A method of forming a kickoff plug in a borehole, said method comprising preparing said borehole for cementing in a first phase and placing hydraulic cement in said borehole in a second phase; said first phase is comprised of the steps of: identifying the interval in said borehole where said kickoff plug is to be formed, removing gelled mud and mud cake from the walls of said borehole in said interval and preparing drilling fluid for cementing operations; wherein the top of cement (TOC) is at the upper end of said interval, the bottom of cement (BOC) is at the lower end of said interval and said removing and preparing steps comprise injecting at least two streams of said drilling fluid into said borehole at said TOC wherein said streams of said drilling fluid are injected at high velocity from the bottom of a conduit disposed in said borehole in at least one plane wherein said plane is substantially parallel to the cross section of said borehole, whereby said streams impact the walls of said borehole in said at least one plane, continuing said injecting of said streams and establishing circulation of said drilling fluid from the bottom of said conduit to the top of said borehole by way of the annular space between said conduit and the walls of said borehole, and moving said conduit, while continuing said circulation, from TOC to a termination location which is at least the location of said BOC; said second phase is comprised of the steps of; positioning the bottom of said conduit at said BOC, placing a balanced plug of a slurry of hydraulic cement in water in said interval comprising, introducing said slurry into said annular space from the bottom of said conduit at BOC until the level of said slurry in said annular space and in said conduit are the same; wherein said slurry is introduced by injecting at least two streams of said slurry at high velocity in at least one plane wherein said plane is substantially parallel to the cross section of said borehole; withdrawing said conduit from said borehole at a controlled rate until the bottom of said conduit is at least above TOC; wherein said controlled rate is the smaller of the rate at which said slurry in said annular space and in said conduit flow into the volume created by the withdrawal of said conduit or at a rate which will minimize mixing of said slurry and drilling fluid caused by said withdrawal; and then permitting said slurry to set to thereby form said kickoff plug.

Claim 11

A method of forming a kickoff plug in a borehole, said method comprising preparing said borehole for cementing in a first phase and placing hydraulic cement in said borehole in a second phase; said first phase is comprised of the steps of: identifying the interval in said borehole where said kickoff plug is to be formed, removing gelled mud and mud cake from the walls of said borehole in said interval and preparing drilling fluid for cementing operations; wherein the top of cement (TOC) is at the upper end of said interval, the bottom of cement (BOC) is at the lower end of said interval and said removing and preparing steps comprise injecting at least two streams of said drilling fluid into said borehole at said TOC wherein said streams of said drilling fluid are injected at high velocity from the bottom of a conduit disposed in said borehole in at least one plane wherein said plane is substantially parallel to the cross section of said borehole, whereby said streams impact the walls of said borehole in said at least one plane, continuing said injecting of said streams and establishing circulation of said drilling fluid from the bottom of said conduit to the top of said borehole by way of the annular space between said conduit and the walls of said borehole, and moving said conduit, while continuing said circulation, from TOC to a termination location which is at least the location of said BOC; said second phase is comprised of the steps of; positioning the bottom of said conduit at said BOC, placing a balanced plug of a slurry of hydraulic cement in water in said interval comprising, introducing said slurry into said annular space from the bottom of said conduit at BOC until the level of said slurry in said annular space and in said conduit are the same; wherein said slurry is introduced by injecting at least two streams of said slurry at high velocity in at least one plane wherein said plane is substantially parallel to the cross section of said borehole; withdrawing said conduit from said borehole at a controlled rate until the bottom of said conduit is at least above TOC; wherein said controlled rate is the smaller of the rate at which said slurry in said annular space and in said conduit flow into the volume created by the withdrawal of said conduit or at a rate which will minimize mixing of said slurry and drilling fluid caused by said withdrawal; and then permitting said slurry to set to thereby form said kickoff plug.