阅读说明：本技术 一种气井氮气钻井管柱安全起下的方法及气井结构 (Method for safely tripping up and down gas well nitrogen drilling pipe column and gas well structure ) 是由 岳慧 丁士东 胡群爱 张东清 于 2020-04-16 设计创作，主要内容包括：本发明提供了一种气井氮气钻井管柱安全起下的方法及气井结构,该方法包括：步骤一、在气井的直井段和水平裸眼段的连接处钻出井斜角大于90°的上翘段并下套管固井,上翘段的上翘高度大于井眼位于直井段底部的直径,上翘段位于储层所处的目标靶点前；步骤二、通过套管向所述气井中灌入泥浆进行压井,所述泥浆的密度在数值上等于地层压力系数；步骤三、当气井的井口压力为零时,起出或下入管柱。该方法通过钻出上翘段来与直井段构成U型管状的气井结构,利用U型管原理规避气液置换效应,进而可以在气井管柱起下时通过注入泥浆来压井且避免泥浆进入储层产生污染。(The invention provides a method for safely tripping up and down a nitrogen drilling string of a gas well and a gas well structure, wherein the method comprises the following steps: drilling an upwarp section with a well inclination angle larger than 90 degrees at the joint of a straight well section and a horizontal open-hole section of a gas well, and setting a casing for well cementation, wherein the upwarp height of the upwarp section is larger than the diameter of a well hole at the bottom of the straight well section, and the upwarp section is positioned in front of a target spot where a reservoir is positioned; secondly, grouting slurry into the gas well through a casing pipe for killing the well, wherein the density of the slurry is equal to the formation pressure coefficient in numerical value; and step three, when the wellhead pressure of the gas well is zero, tripping out or tripping in the pipe column. According to the method, the upwarp section is drilled to form a U-shaped tubular gas well structure together with the straight well section, the gas-liquid displacement effect is avoided by using the U-shaped pipe principle, and then mud can be injected to kill the well when the gas well pipe column is lifted and lowered, and the mud is prevented from entering a reservoir stratum to cause pollution.)

1. A method for safely tripping a nitrogen well drilling string of a gas well is characterized by comprising the following steps:

drilling an upwarp section with a well inclination angle larger than 90 degrees at the joint of a straight well section and a horizontal open-hole section of a gas well, and setting a casing for well cementation, wherein the upwarp height of the upwarp section is larger than the diameter of the gas well at the bottom of the straight well section, and the upwarp section is positioned in front of a target spot where a reservoir is positioned;

secondly, grouting mud into the gas well through the casing to kill the well, wherein the density of the mud is numerically equal to a formation pressure coefficient;

and step three, when the wellhead pressure of the gas well is zero, tripping out or tripping in a pipe column.

2. A method of safely tripping a gas well nitrogen drilling string as in claim 1 wherein in step one, after the upturned section is drilled, the drilling direction is adjusted to drill a horizontal open hole section and drill to a target point of interest.

3. A method of safely tripping a gas well nitrogen drill string as claimed in claim 2 wherein in step one, the upturned section is drilled using mud drilling and the horizontal open hole section is drilled using nitrogen drilling and drilled to the target point of interest.

4. A method as claimed in claim 3 for safely tripping a nitrogen well drilling string in a gas well, wherein in step one, after the upwarp section is drilled and cased for cementing, the gas well is cleaned with clean water and then drilled with nitrogen gas.

5. A method for safely tripping a nitrogen well drilling string in a gas well according to any one of claims 1 to 4, wherein in the first step, before the upwarp section is drilled, the radius of curvature of the upwarp section is determined according to the drilling friction of the gas well.

6. A method of safely tripping a gas well nitrogen drilling string as in claim 1 wherein in step three, while tripping the string, the gas well is filled with mud in an amount equal to the volume of the tubing string.

7. A method of safely tripping a gas well nitrogen drilling string as claimed in claim 1 wherein the upturned section has an upturned height of 1-2 m.

8. A method of safely tripping a gas well nitrogen drilling string as claimed in claim 1 or 7 wherein the maximum angle of inclination of the upturned section is 95 °.

9. A gas well structure using the method of any one of claims 1 to 8 for tripping a tubular string is characterized by comprising a straight well section, an upturned section and a horizontal open well section containing a target point, which are sequentially communicated, wherein the straight well section and the upturned section are integrally in a U-shaped tubular shape, and the height of the bottom well wall of the horizontal open well section is higher than that of the top well wall at the lowest point of the height of the upturned section.

10. The gas well structure as claimed in claim 9, wherein a casing is lowered into each of the straight well section and the upturned section, and a cement sheath is formed between the casing and the wall of the well by pouring cement.

Technical Field

The invention relates to the technical field of oil and gas exploration and development, in particular to a method for safely tripping up and down a nitrogen drilling string of a gas well and a gas well structure.

Background

Gas reservoirs, especially dense gas reservoirs, are usually in formations with poor drillability, low drilling rate, small pore throat, severe water sensitivity and other problems, and are not suitable for drilling with conventional mud, but generally adopt nitrogen for drilling. Nitrogen drilling is a gas underbalance drilling technology, can greatly improve the drilling speed, and simultaneously can avoid the pollution of mud in the conventional mud drilling to a reservoir stratum, thereby ensuring the productivity of a gas well.

However, the well control safety is difficult when the well is drilled by adopting nitrogen and is taken out after the gas is discharged from the stratum. During well completion, the well can be completed by only adopting a drill rod, namely, a drill rod column is not taken out, gas production is directly carried out by using a casing or the drill rod, the well can not be completed by adopting a system mode comprising an oil pipe, a packer and a safety valve like a conventional gas well, and the safety of a gas production well mouth is difficult to ensure; in addition, it is difficult to ensure safety in tripping the drill string in the middle of tripping operations such as replacing the drill bit. Of course, in the prior art, a mode of tripping the drill after mud killing is adopted is also available, but the pollution to the reservoir is difficult to avoid by adopting mud killing, and the advantage of zero pollution of nitrogen drilling to the reservoir is wasted.

In addition, the shaft of the nitrogen well drilling is not filled with mud and only contains high-pressure gas, so that the safety challenge is brought to the operations such as well logging, testing and the like, therefore, the well logging and the testing operations are generally not considered in the nitrogen well drilling at present, and the safety of the well drilling is also influenced to a certain extent.

Disclosure of Invention

In order to solve the problems in the prior art, the application provides a method for safely tripping up and down a nitrogen drilling string of a gas well and a gas well structure, which can effectively prevent mud from entering a reservoir stratum to cause pollution when mud is used for killing the well.

The invention discloses a method for safely tripping a nitrogen drilling string of a gas well, which comprises the following steps:

drilling an upwarp section with a well inclination angle larger than 90 degrees at the joint of a straight well section and a horizontal open-hole section of a gas well, and setting a casing for well cementation, wherein the upwarp height of the upwarp section is larger than the diameter of the gas well at the bottom of the straight well section, and the upwarp section is positioned in front of a target spot where a reservoir is positioned;

secondly, grouting mud into the gas well through the casing to kill the well, wherein the density of the mud is numerically equal to a formation pressure coefficient;

and step three, when the wellhead pressure of the gas well is zero, tripping out or tripping in a pipe column.

In one embodiment, in the first step, after the upwarp section is drilled, the drilling direction is adjusted to drill a horizontal open hole section and drill to a target point of interest.

In one embodiment, in step one, the upwarp section is drilled using mud drilling, and the horizontal open hole section is drilled using nitrogen drilling and drilled to a target point of interest.

In one embodiment, in the first step, after the upwarp section is drilled and the casing is set for well cementation, the gas well is cleaned by clean water, and then the drilling is continued by using nitrogen drilling.

In one embodiment, in the first step, before the upwarp section is drilled, the radius of curvature of the upwarp section is determined according to the drilling friction of the gas well.

In one embodiment, in step three, the gas well is filled with an amount of mud equal to the volume of the tubing string while the tubing string is tripped out.

In one embodiment, the upturned section has an upturned height of 1-2 m.

In one embodiment, the maximum angle of inclination of the upturned section is 95 °.

The gas well structure utilizing the method comprises a straight well section, an upturned section and a horizontal open hole section containing a target spot, which are sequentially communicated, wherein the straight well section and the upturned section are integrally in a U-shaped tubular shape, and the height of a well wall at the bottom of the horizontal open hole section is higher than that of a well wall at the top of the lowest point of the height of the upturned section.

In one embodiment, a casing is arranged in each of the straight well section and the upturned section, and a cement sheath is formed between the casing and the well wall by pouring cement.

The features mentioned above can be combined in various suitable ways or replaced by equivalent features as long as the object of the invention is achieved.

Compared with the prior art, the method for safely tripping the nitrogen drilling string of the gas well and the gas well structure provided by the invention at least have the following beneficial effects:

according to the method, the upturned section is drilled between the diameter section of the gas well and the horizontal open hole section containing the target point by adopting mud drilling, the upturned section and the diameter section are integrally in a U-shaped tubular shape, and then the horizontal open hole section is drilled by using nitrogen drilling and drilled to the target point. When the tubular column needs to be lifted, slurry is poured into the gas well for killing the well, and according to the principle of a U-shaped pipe, because the produced gas of a gas reservoir exists at the target point, the formation pressure and the produced gas pressure are balanced with the pressure of the slurry column, the pressure of the well mouth is zero, and the tubular column can be safely lifted; meanwhile, the mud only exists in the whole straight well section and part of the upwarping section and cannot enter a target point, and pollution to a reservoir stratum is avoided.

Drawings

The invention will be described in more detail hereinafter on the basis of embodiments and with reference to the accompanying drawings. Wherein:

FIG. 1 shows a schematic flow chart of the steps of the method of the present invention;

FIG. 2 shows a cross-sectional view of a gas well structure of the present invention;

in the drawings, like parts are provided with like reference numerals. The drawings are not to scale.

Reference numerals:

10-gas well, 11-straight section, 12-raise section, 13-horizontal open hole section, 101-casing, 102-cement sheath, 103-mud, 104-drill string.

Detailed Description

The invention will be further explained with reference to the drawings.

Taking the river stratum of the Sichuan basin as an example, the river stratum of the Sichuan basin is a compact sandstone reservoir which has poor physical property, serious water sensitivity and poor rock drillability, adopts a mud drilling machine with extremely low drilling speed, is easy to pollute the stratum and seriously affects the productivity. The nitrogen gas drilling can greatly improve the drilling speed and avoid reservoir pollution, but when the drill rod column is taken out in the drilling process or after drilling and the well completion pipe column is put in after the drill rod column is taken out, the pipe column cannot be taken out due to stratum gas outlet and wellhead pressure. If the mud kill well is adopted, on one hand, the produced gas in the stratum continuously floats upwards and is gushed out due to the gas-liquid displacement effect, so that the well killing is difficult to stabilize; on the other hand, the mud sinks to the reservoir stratum to generate pollution, so that the advantages and the purpose of protecting the reservoir stratum by adopting nitrogen drilling are abandoned.

Example 1

The invention discloses a method for safely tripping a nitrogen drilling string of a gas well, which comprises the following steps of:

drilling an upwarp section with a well inclination angle larger than 90 degrees at the joint of a straight well section and a horizontal open-hole section of a gas well by adopting mud drilling, and setting a casing for well cementation, wherein the upwarp height of the upwarp section is larger than the diameter of the gas well at the bottom of the straight well section, and the upwarp section is positioned in front of a target spot where a reservoir is positioned. And after well cementation, washing the well by using clean water, replacing the clean water by using nitrogen after well washing, then adjusting the drilling direction, drilling a horizontal open hole section by using nitrogen drilling and drilling to a target point.

And step two, when the drill string needs to be pulled out, such as when the drill bit needs to be replaced during drilling to a target point, mud is poured into the gas well through the casing pipe for killing the well, and the density of the mud is equal to the formation pressure coefficient in value.

And step three, when the pressure of the wellhead of the gas well is zero, the filled mud fills the straight well section of the gas well, the pressure of the liquid column of the straight well section is equal to the pressure of the stratum, and the drill string can be safely pulled out. When tripping out the drill string, the gas well is filled with mud in an amount equal to the volume of the drill string.

Specifically, in the first step, the drilled upwarp section and the straight well section are integrally in a U-shaped tubular shape, the joint of the bottom of the straight well section and the upwarp section is the U-shaped bottommost end, the height of the top well wall at the bottommost end is lower than that of the bottom well wall at the target point, and the gas-liquid displacement effect is avoided by utilizing the U-shaped pipe principle.

And in the second step, when the drill bit needs to be replaced in the process of drilling the horizontal open hole section by adopting the nitrogen drilling and drilling to the target point, the drill string and the drill bit need to be taken out. However, as the nitrogen well is adopted for drilling, the shaft is filled with gas, the nitrogen and the gas produced by the stratum can be discharged from the well mouth, the pressure is high, the drilling tool cannot be directly lifted, and at the moment, well killing needs to be carried out firstly, and mud is poured into the gas well for well killing. In the actual operation process of mud killing, mud is filled while air is released and pressure is relieved through the sleeve; or a section of slurry is poured into the reactor, and a section of gas is discharged.

In the third step, along with the filling of the mud, the pressure generated by the mud liquid column gradually tends to be balanced with the formation pressure and the pressure of the gas generated by the formation, and because the density of the filled mud and the numerical value of the formation pressure coefficient, when the straight well section is filled with the mud in the gas well, the pressure generated by the mud liquid column is equal to the formation pressure and the pressure of the gas generated by the formation, and at the moment, the pressure of the well mouth is zero, so that the drill rod column can be safely pulled out. When tripping out the drill string, the gas well is filled with mud in an amount equal to the volume of the drill string in order to maintain pressure balance in the wellbore.

The gas well mainly solves the problem that in the nitrogen drilling process of the gas well, when a drill rod string needs to be pulled out and a drill bit needs to be replaced in the process of drilling to a target spot located in a reservoir stratum, the safety of the drill rod is difficult to be pulled out due to the pressure of a well mouth. The upwarp section and the straight well section in the embodiment form a U-shaped tubular shape, and the gas produced by the stratum is prevented from floating out of a gas well through a gas-liquid displacement effect by utilizing the principle of the U-shaped pipe, so that the stability of mud kill-well is ensured, and mud is prevented from entering a reservoir stratum. And then can adopt mud to stabilize the kill-job when playing out the drilling rod string, guarantee the safety of drilling rod and play, also make the mud in straight well section and the upwarp section simultaneously can't enter into the reservoir stratum of target point department, avoided mud pollution reservoir stratum.

Example 2

The invention discloses a method for safely tripping a nitrogen drilling string of a gas well, which comprises the following steps of:

drilling an upwarp section with a well inclination angle larger than 90 degrees at the joint of a straight well section and a horizontal open-hole section of a gas well by adopting mud drilling, and setting a casing for well cementation, wherein the upwarp height of the upwarp section is larger than the diameter of the gas well at the bottom of the straight well section, and the upwarp section is positioned in front of a target spot where a reservoir is positioned. And after well cementation, washing the well by using clean water, replacing the clean water by using nitrogen after well washing, then adjusting the drilling direction, drilling a horizontal open hole section by using nitrogen drilling and drilling to a target point.

And step two, when a completion string needs to be put into the gas well after the drill string is pulled out, the drilling string is pulled out and simultaneously mud with the same volume as the drill string is poured into the gas well through the casing pipe, and the density of the mud is equal to the formation pressure coefficient in numerical value.

And step three, when the pressure of the wellhead of the gas well is zero, the injected mud fills the straight well section of the gas well, the liquid column pressure of the straight well section is equal to the formation pressure, and the well completion pipe column can be safely put into the well.

Specifically, in the first step, the drilled upwarp section and the straight shaft section are integrally in a U-shaped tubular shape, the joint of the bottom of the straight shaft section and the upwarp section is the U-shaped bottommost end, and the height of the top well wall at the bottommost end is lower than that of the bottom well wall at the target point.

And in the second step, after the gas well is drilled to a target point, a completion pipe column is required to be put in for well completion, and drilling tools such as a drill string, a drill bit and the like are taken out before the completion pipe column is put in. And (3) injecting mud with the volume equal to that of the drill rod into the gas well through the casing pipe while the drill rod string is pulled out, so as to maintain the balance of the pressure in the well bore.

And in the third step, after the drill string is completely pulled out, the completion pipe string is put into the well, the completion pipe string occupies the space in the well bore along with the putting in of the completion pipe string, and the slurry in the well bore is squeezed and is slowly discharged from the well mouth. In the whole process of putting the well completion string, the pressure inside the shaft is balanced, and the pressure of the wellhead is zero.

The embodiment mainly solves the problem that the conventional gas well cannot be completed by adopting a completion string. When the well is completed, because the stratum is gas-out and the wellhead is pressurized, the conventional gas well can only be completed by adopting a drill rod, namely, the drill rod column is not pulled out, the gas production is directly carried out by using a casing or the drill rod, the well completion mode of an oil pipe, a packer and a safety valve cannot be adopted like the conventional gas well, and the safety of the gas production wellhead is difficult to ensure. In the embodiment, when the well is completed after the well is drilled to the target point, the mud is pumped while the drill string is pulled out, and the pumped mud does not influence the stability of the reservoir layer due to the existence of the upwarp section. The well completion pipe string is put in after the drill string is pulled out for well completion, the pressure in the whole process is balanced, the operation is safe, and the problem that the conventional gas well can not be completed by the well completion pipe string is solved. Meanwhile, the embodiment can also realize well logging, the well logging pipe column is lowered into the gas well according to the steps during well logging, and the liquid of the well logging pipe column penetrating through the straight well section and the upwarping section enters the target point.

Example 3

The invention discloses a method for safely tripping a nitrogen drilling string of a gas well, which comprises the following steps of:

drilling an upwarp section with a well inclination angle larger than 90 degrees at the joint of a straight well section and a horizontal open-hole section of a gas well by adopting mud drilling, and setting a casing for well cementation, wherein the upwarp height of the upwarp section is 1-2m, the maximum well inclination angle is 95 degrees, and the upwarp section is positioned in front of a target spot where a reservoir is positioned. And after well cementation, washing the well by using clean water, replacing the clean water by using nitrogen after well washing, adjusting the drilling direction, drilling out a horizontal open hole section by using nitrogen drilling, and drilling to a target point.

And step two, grouting mud into the gas well through a casing pipe for killing the well, wherein the density of the mud is numerically equal to the formation pressure coefficient.

And step three, when the wellhead pressure of the gas well is zero, the filled mud fills the straight well section of the gas well, the liquid column pressure of the straight well section is equal to the formation pressure, and the tubular column can be safely lifted out or put into the well. When tripping out the drill string, the gas well is filled with mud in an amount equal to the volume of the drill string.

Specifically, in the first step, the drilled upwarp section and the straight well section are integrally in a U-shaped tubular shape, the gas-liquid displacement effect is avoided by using the principle of a U-shaped pipe, and the connecting part of the bottom of the straight well section and the upwarp section is the U-shaped bottommost end. In principle, the upwarp height of the upwarp section only needs to be larger than the diameter of the gas well at the bottom of the vertical well section, and the upwarp height can be enlarged to 1-2m (the diameter of the gas well is generally smaller than 1m) in consideration of measurement errors in practical application and can be further enlarged to 5m according to practical conditions. The well inclination angle is an included angle between a tangent line of any point on an axis of a gas well track curve and a plumb line, the maximum well inclination of the upwarp section is at the tail end of one side, close to a target point, of the upwarp section, the maximum well inclination angle of the upwarp section is 95 degrees, namely the upwarp of the upwarp section is relatively gentle, and the reaction on the curvature radius shows that the curvature radius of the upwarp section is relatively large. And then the track of the gas well borehole changes more smoothly from the straight borehole section to the upwarp section, thereby avoiding the excessive friction between the drill string and the borehole wall during drilling.

The problem that the drilling tool generates excessive friction with the well wall due to the U-shaped track in the process from the straight well section to the upturned section is mainly solved. In the embodiment, the radius of curvature of the upwarp section is determined according to the drilling friction of the gas well, and the radius of curvature influences the change rate of the well inclination angle. When the upwarp heights of the upwarp sections are the same, the smaller the curvature radius is, the larger the change rate of the inclination angle is, the larger the maximum inclination angle is, and the steeper the gas well track of the upwarp section is. In this case, the drill string will have more contact and pressure with the borehole wall and more friction during the drilling of the upturned section by the drill bit, and the safety of drilling will not be used. Therefore, in order to reduce the friction degree between the drill string and the well wall, the gas well track of the upwarp section needs to be smoother, so the curvature radius of the upwarp section is properly increased according to the magnitude of the drilling friction resistance. When the upwarp heights are the same, the larger the curvature radius is, the smaller the change rate of the inclination angle is, the smaller the maximum inclination angle is, and the borehole trajectory of the upwarp section of the gas well tends to be smooth. Therefore, the maximum well deviation of 95 degrees of the upwarp section is obtained according to the curvature radius determined by the actual well friction resistance.

Example 4

As shown in the attached drawing fig. 2, the gas well structure of the invention is characterized by comprising a straight well section 11, an upturned section 12 and a horizontal open-hole section 13 at a target point, wherein the straight well section 11 and the upturned section 12 are integrally in a U-shaped pipe shape, and the height of a bottom well wall of the horizontal open-hole section 13 is higher than that of a top well wall at the lowest point of the height of the upturned section 12.

A casing 101 is arranged in the straight well section 11 and the upwarp section 12, and a cement sheath 102 is formed between the casing 101 and the well wall by pouring cement.

Specifically, the gas well structure in this embodiment is drilled according to the method and run-off string is started by using the method, and the gas well 10 integrally comprises a straight section 11, an upwarp section 12 and a horizontal open-hole section 13, wherein the horizontal open-hole section 13 is located at a target point of a reservoir. The whole height of the horizontal open hole section 13 is higher than that of the upwarp section 12, when the mud is used for killing the well, the stratum produced gas is filled in the whole horizontal open hole section 13 and the upper part of the upwarp section 12, the mud is filled in the whole straight well section 11 and the lower part of the upwarp section 12, the pressure in the whole gas well 10 is balanced, and the stratum produced gas cannot enter the straight well section 11 by utilizing a gas-liquid displacement effect according to the principle of a U-shaped pipe. The safe tripping of the nitrogen drilling string can be realized through the gas well structure.

The cement sheath 102 serves to connect the casing 101 to the borehole wall, serves to stabilize the casing 101, and provides a stable path for the drill string 104 and mud to travel within the gas well 10.

In the description of the present invention, it is to be understood that the terms "upper", "lower", "bottom", "top", "front", "rear", "inner", "outer", "left", "right", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are only for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, should not be construed as limiting the present invention.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that features described in different dependent claims and herein may be combined in ways different from those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other described embodiments.