RU2235860C1 - Method for cementation of casing string in the well - Google Patents

Abstract

FIELD: oil and gas extractive industry.

SUBSTANCE: method includes preparation of well, lowering of casing column into it having locking device in lower section, made with possible closing from effect of vertical axial force upward along column of backfill material in behind-column space, sealing of behind-column space, pumping of backfilling material into behind-pipe space, raising of washing pipes for small height and removing backfilling material from there be means of forward or backward washing. Washing pipes after their mounting to locking device and partial unloading are immediately raised a bit. Inter-pipe space is sealed and backfilling solution is pumped through these into behind-column space. After appearance of backfilling material on well mouth its circular circulation is performed until receiving solution stability in matter of thickness. Then through washing pipes backfilling material is pushed by calculated volume of pushing liquid with certain volume left in these. Pumping pressure is dropped and after that remaining backfilling material is removed from these.

EFFECT: higher cementation quality, simpler technology and higher ecological safety.

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Description

The invention relates to the oil and gas industry, in particular to the technology of cementing casing strings in oil and gas wells.

A known method of cementing a casing string in a well, including preparing a well, lowering a casing string into it with a spring-loaded poppet type check valve in its lower part, made with the possibility of opening it from a vertical axial force from top to bottom, for example, from a flushing pipe string, a descent the latter into the well, equipping them at the mouth with a flow line, lowering the column of flushing pipes to the check valve until it is fully opened and pumping grouting mortar into the shutter It is the well (1).

The disadvantage of this method is the high cost of time for its implementation, a significant expenditure of material costs and resources and insufficient quality of cementing, especially in difficult mining and geological conditions.

The closest in technical essence to the proposed one is a method of cementing a casing string, including preparing a well, lowering a casing string into it with a locking device in its lower part, made with the possibility of closing it from the impact of vertical axial force from the bottom up of the grouting column in the annulus, sealing annular space, descent into the casing of flushing pipes, landing them on the locking device and partial unloading, sealing the annulus areas, injection of grouting mortar into the annulus, raising the washing tubes to a small height and removing grouting mortar from them by direct or reverse washing (2).

The disadvantages of the method are:

- the need to replenish the well during the descent of the casing string;

- the possibility of contamination of the well from the outflow of clay during the casing;

- at medium and high casing descent speeds, hydraulic fracturing is possible;

- the need to create backpressure at the wellhead during flushing and injection of cement slurry;

- the valve of the locking device does not allow to manufacture all parts from the drilled materials, which may complicate further deepening of the well.

The objective of the invention is to provide a method simpler in terms of technological design, which meets the requirements of environmental safety and improves the quality of cementing.

This problem is solved by the proposed method, including the preparation of the well, lowering the casing into it with a locking device in its lower part, made with the possibility of closing it from the impact of the vertical axial force from the bottom up of the grouting column in the annulus, sealing the annulus, lowering into the casing columns of flushing pipes, landing them on the locking device and partial unloading, sealing the annular space, pumping grouting mortar into the annular space, lifting the washing pipes to a small height and removing grouting mortar from them by direct or reverse washing.

What is new is that washing pipes, after landing them on the shut-off device and partially unloading, immediately lift, seal the annulus and pump the grout into the annulus and, after the grout appears at the wellhead, circulate it until the solution is stable in density then, through the flushing pipes, grouting mortar is pushed with the estimated volume of the squeezing fluid, leaving a certain volume in them Ie, the injection pressure is relieved and then the remaining cement slurry is removed from them.

The drawing shows a longitudinal section of a locking device lowered into the well as part of a casing string used in the implementation of the proposed method (an independent application for the alleged invention has been submitted for the design of the locking device in FIPS).

The device is a stop ring made in the form of a pipe 1 blanked from the bottom with an annular ledge 2 on the outer surface. The pipe 1 is provided with longitudinal grooves 3 and radial channels 4. The blanked section 5 of the pipe 1 is made on the outside with a conical surface 6, the small base of the cone of which is facing the upper part, and its diameter is equal to the outer diameter of the pipe 1. Telescopically to the pipe opposite the longitudinal grooves 3 a support ring 7 is installed, equipped with shear elements 8, the free ends of which are included in the longitudinal grooves 3. In the lower end of the ring 7, a conical bore 9 is made on the inside, adequate to the conical surface 6 of the pipe a 1. The device is equipped with seals 10.

The method is carried out in the following sequence.

After the preparation of the well, the casing 11 is lowered into it to the design depth, the shoe 12 is installed at the lower end of the well, and a locking device is installed above the sleeve 13 and the annulus is sealed. Then, into the casing string, the flushing pipe string 14 is lowered, placed on the locking device and partially unloaded. Under the influence of the load, the shear elements 8 are destroyed, after which the wash pipes are lifted, the annular space is sealed at the mouth and the well is flushed. After that, grouting solution is pumped through flushing pipes 14 into the annulus of the well, which, after it is exited to the mouth, is sent to the capacity of the filling unit and circular circulation is carried out, constantly monitoring the density of the mortar at the inlet and outlet of the well. After the cement slurry is stabilized by density (this moment occurs after about one hour of circulation), the circular circulation is stopped and the calculated volume of the squeezing liquid is pumped through the washing pipes 14, leaving about 100 L of the solution in the washing pipes. Injection pressure is relieved. Under the influence of the pressure drop created by the column of cement slurry in the annular space and directed from the bottom up, the plugged pipe 1 moves upward relative to the ring 7 and wedges at the contact point of the conical surfaces 6 and 9, reliably blocking the casing from the annular space. Moreover, the greater the pressure on the muffled section of the pipe 1, the stronger and more reliable its fixation and sealing. Subsequently, by direct or reverse washing through the annular space and the washing pipes, the remaining cement slurry is removed from the washing pipes and the well is left on the BCP (waiting for cement to harden).

Due to the circular circulation of the grout, a significant increase in the quality of cementing is provided, this achieves the cleaning of the walls of the borehole from the clay cake and the creation of a cement cake in its place, the removal of the clay solution from the caverns and the uniformity of the composition of the cement slurry by volume are achieved. All these factors contribute to the achievement of high tightness of the annulus, which ultimately will increase the life of waterless wells and reduce the amount of repair and insulation work, reduce the likelihood of inter-reservoir flows and ensure the protection of the subsoil and the environment.

The method is simpler to use and does not pose a risk of fracturing during casing descent.

Information used

1. Analog: A.S. No. 1774986, cl. E 21 B 33/14, 1992.

2. Prototype: RF patent No. 2086752, class. 6 E B 33/14, 1997.

Claims (1)

A method of cementing a casing string in a well, including preparing a well, lowering a casing string into it with a shut-off device in its lower part configured to close it from the impact of vertical axial force from bottom to top of the grouting column in the annulus, sealing the annulus, lowering the inside of the casing columns of flushing pipes, landing them on the locking device and partial unloading, sealing the annular space, pumping grouting mortar into the annular the environment, raising the washing pipes to a small height and removing cement slurry from them by direct or reverse washing, characterized in that the washing pipes are immediately lifted after they are seated on the shut-off device and partially unloaded, the annulus is sealed and the cement grout is pumped through them into the annulus the space and after the appearance of the cement slurry at the wellhead, it is circulated circularly until the solution is stable in density, then through the flushing Pipes are selling grouting mortar with the estimated volume of grouting fluid leaving a certain volume in them, the injection pressure is relieved, and then the remaining grouting mortar is removed from them.