SU1707186A1 - Method of cementing casing strings - Google Patents

Abstract

The invention relates to the mining industry and can be used in the construction of wells. The purpose of the invention is to improve the quality of cementing. In the casing after its descent is placed in the area of the shoe device, by definition, the entry of cement into the casing. Then, buffer fluid and cement mortar are pumped into the annulus from above. An additive, tartaric acid, in an amount of 0.3-0.5 wt.% Is introduced into the first portion of the cement slurry. From the moment the cement mortar penetration is determined inside the casing, the cement mortar injection in the piping space is continued in a volume equal to the volume of the cement mortar with the addition of tartaric acid. After that stop the injection of cement mortar.

Description

The invention relates to the field of drilling for oil, gas, water and other minerals, and in particular to a method for attaching casing strings.

There is a known method of reverse cementing casing, which consists in introducing into the first portion of a cement slurry of fibrous fillers plugging a filter installed in a predetermined interval of the casing.

There is also known a method of reverse cementing casing, in which, before cementing begins, 4-5 m of signal buffer fluid is injected into the annulus of the well, and it is forced into the drilling fluid in a volume equal to the internal volume of the casing.

A common disadvantage of these methods is that low-level cement mortar is placed in the annulus against the complex of productive layers.

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quality. This is because, as it moves downward, the first portion of the cement slurry is saturated with the loose part of the mud cake (or other) mud on the walls of the well. When the first batch of cement slurry mixed with a loose crust of mud is approached to the casing shoe, the cement slurry injection into the annulus stops and the annulus of the well is filled with poor quality gel cement in the priming zone.

The closest technical solution to the present invention is a method in which, in order to increase the reliability of overlapping the casing flow section after pumping the calculated volume of cement slurry, the locking element is designed as a hollow cementing plug secured to the shear elements in the casing shoe and the restriction

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the movement of the cementing plug; in this case, the cementing plug has a seating-gripping seat made of an elastic material.

The disadvantages of this method are filling the annular space against productive formations with low-quality cement mortar, the difficulty of accurately accounting for the volume of the annular space, complicating the design of the bottom casing.

The aim of the present invention is to perform the quality of casing cementing.

The goal is achieved by the introduction of tartaric acid in the amount of 0.3-0.5 wt.% In the first portion of the cement slurry of a certain volume, from the moment the cement slurry is detected, the cement slurry is pumped into the annular pro- the space is continued in a volume equal to the volume of cement mortar with the addition of tartaric acid, then cementation is stopped.

The essential differences of the proposed method from the known technical solutions are as follows:

injection of the first portion of cement mortar of a known volume with the introduction of a reagent that prevents the cement mortar from setting;

the intake and leaving inside the casing only portions of the cement slurry containing reagents that prevent the cement slurry from setting;

filling the annulus space against productive formations with high-quality cement mortar;

interrelated control of the volume of injection of the first portion of cement mortar from above into the annulus, and then into the inside of the casing;

the ability to supply the first batch of cement slurry containing reagents that prevent it from seizing in a wide range of volumes and leaving the same volumes of cement slurry inside the casing without the need for disassembling.

The method is carried out as follows.

The descent of the column is carried out in the usual way. The bottom of the column is equipped with a guide plug, cementing holes, centering lanterns.

After the descent of the column has been completed, the well is washed and the wellhead is manufactured. The cementing head is wrapped onto the casing and through it inside the casing string on the logging cable, the device is lowered to determine the approach of the cement slurry to the casing shoe. As such

the instrument may be a density gauge (for example, a SGDT logging tool). The device is installed near the casing shoe.

Then from the mouth to the annulus

0 is pumped successively a portion of the abrasive solution 5 with a volume of 4-5 m and a buffer fluid in a volume equal to or greater than the internal volume of the casing. A portion of abrasive fluid is pumped with

5 in order to preliminarily remove the loose part of the mud cake from the borehole walls and prevent it from falling in a large volume into the first portion of the cement slurry. Portions of cement mortar or various visco-elastic separators are used as an abrasive solution.

Buffer fluid is pumped to push a portion of the abrasive solution, and

5 also for washing the crust from the walls of the well. As a buffer liquid, use technical waters and aqueous solutions of peptizing reagents (soda ash and caustic soda 2-3 wt.%

0, etc.). Following them, the first portion 7 of a cement slurry of a certain volume with the addition of tartaric acid in the amount of 0.3-0.5 May is pumped into the annulus. % of the amount of cement.

5 Additive in cement mortar tartaric acid in such an amount prevents its seizure. Other reagents (for example, various polymers) are used as such reagents.

0 The purpose of the vssda in the first portion of the cement slurry of a certain volume of tartaric acid is as follows. When moving down the cement slurry, despite the preliminary cleaning of the well stratus from the loose part of the mud cake, some of the crust falls into the first portion of the cement slurry. Therefore, when using the proposed method of reverse cementing

In the first portion of a lower-quality cement slurry of a lower quality, it is forced into the inside of the casing, high-quality cement slurry is installed in the annulus against productive formations, and the cement slurry inside the casing does not set, drilling operations are no longer necessary.

The final cementing works are carried out in the following sequence. The time at which the first batch of cement slurry penetrates through the shoe or the holes into the inside of the casing is determined by the density meter. From this moment on, cement mortar is pumped into the annulus with the mouth in a volume equal to the volume of the first portion of cement mortar with the addition of tartaric acid. The volume of the last portion of the cement slurry is determined and monitored by the instrument of the cementing control station (SCC-2M). Controlling and delivering the last portion of the cement slurry in such a volume ensures that only the first portion of the cement slurry containing reagents that prevent its setting into the inside of the casing string is entered.

The volume of the first portion of cement slurry with the addition of tartaric acid depends on many factors: the depth and diameter of the well, the casing, the type and quality of drilling mud, the lithology of the rocks composing the geological section. Therefore, for each area, this volume is established empirically and can amount to 0.5-1.5 m or more.

By the end of cementing, the solutions are arranged in a subsequent sequence. In the annulus of the well there is a cement slurry, inside the casing - a portion of cement slurry with the addition of tartaric acid, above - a buffer fluid. The portion of the abrasive solution at this point is completely displaced from the cavity of the casing. After the completion of the injection of the last portion of the cement slurry, the taps on the cementing head are closed and the density gauge is raised.

Example. The depth of the borehole is 2500 m, the diameters of the borehole and the casing are 216 and 146 mm respectively. The volume of the first batch of cement mortar is 1 m, the volume of the well annular space, taking into account the volume of cavities, is 53 m, and the volume of the internal cavity of the casing string is 32 m. The amount of cement is taken from the calculation of the preparation of cement mortar with a volume of more than 57m3.

After flushing and equipping the wellhead and lowering the casing string into the casing of the SGDT instrument, 4 m of cement slurry and 33 m of an aqueous solution of soda ash with a concentration of 2 wt.% Are sequentially pumped into the annulus. Then the first portion of cement mortar with a volume of 1 m3 is pumped.

after adding to it 0.5% tartaric acid, i.e. at the rate of 1.3 tons of dry cement, 6.5 kg of ester-stone acid are added to the preparation of 1 m of cement mortar.

After that, the pumping of cement mortar without additives is continued. The cement mortar is pumped under pressure of 10–20 kgf / cm, regulating the back pressure

cranes cementing head,

After fixing the moment the cement mortar approaches the casing shoe with the SGDT device, the cement mortar is further pumped

volume of 1 m, control of the volume of the instrument control station cementing. After the end of the quest of this volume, the taps are closed and the SGDT device is lifted upwards.

The proposed method in comparison with the known has the following advantages:

A quality cement slurry is installed in the annulus against the producing formations;

a portion of the cement slurry in the lower part of the casing does not harden, there is no need to drill the cement plug;

subsoil pollution does not occur;

the loose part of the mud cake is removed from the borehole walls, which improves the contact of the cement stone with the borehole walls;

Labor safety and industrial sanitation conditions are observed.

Claims (1)

The invention of the method of casing cementing. including descending into the casing before cementing and installing near the shoe of the device column to determine the approach of the cement mortar inside the casing, pumping the buffer fluid and cement mortar from above into the tubular space with entering the first portion of the additive, determining the moment of entering the cement mortar inside the casing different with that In order to improve the quality of cementing, tartaric acid in the amount of 0.3-0.5 wt.% is introduced into the first portion of the cement slurry. From the time the cement slurry is determined to enter the inside of the casing, the cement slurry is continued to be pumped into the annulus equal to the volume of cement mortar with the addition of tartaric acid, then stop the pumping of cement mortar