RU2605856C1 - Method of cementing casing string - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention relates to cementing casing strings in a well and, in particular, to cementing the conductor. Method involves washing the well. Flush fluid is pumped into the well. Prepared and pumped is a grouting mortar. For this purpose to the wellhead the grouting mortar is fed via two outlet pipelines, while combining the flow at the wellhead by means of a tee-piece into one supply pipeline. Each outlet pipeline is connected to the corresponding cementing unit providing the mortar supply with a preset speed. Herewith the tee-piece is made with possibility of conversion of the two outlet pipelines flows, in fact laminar, into a turbulent flow in the supply pipeline. For this purpose the diameter of the supply pipeline is approximately 1.4 times larger than the diameter of the outlet pipelines. Angle between branch pipes of the outlet pipelines of the tee-piece arranged in different planes is made smaller than the angle between branch pipes of the outlet pipelines and the supply pipeline. After injection of the grouting mortar into the casing string it is squeezed into the annular space.

EFFECT: reducing time costs and improving the cementing quality due to increased speed of the flow in the annular space.

5 cl, 1 dwg

Description

APPLICATION AREA

The invention relates to the oil and gas industry, in particular to the construction of wells, namely to cementing a casing string, in particular a conductor in the presence of zones with partial absorption.

BACKGROUND

The traditionally used method of cementing the casing consists in flushing the well, supplying buffer fluid to the well, in preparing and supplying grouting mortar to the well, and in selling grouting grout into the annulus (for example, V.M. Muravyov, Sputnik neftehnika, Nedra, 1977).

This method has many disadvantages, in particular, the preparation and supply of grouting mortar into the casing is carried out by cement-mixing machines and two cementing aggregates, where one of the aggregates delivers water for mixing, and the second grouting grout is pumped and forced into the column, i.e. one unit is not involved in the injection of cement mortar. At the same time, when mixing machines are changed when grouting grouting occurs, a technical break occurs, which leads to uneven mixing of the components of the grout, because grinder grout continues to move down the pipe space due to the difference in specific gravities, displacing the flushing fluid from the annulus. Because of this, a situation arises when you have to “catch up” with cement that has come down during a break. This may cause air congestion, water hammer, etc. All of the above leads to a loss of time and a decrease in the quality of cementing. It should be noted that in the presence of absorption zones, this method is not applicable, since the cement slurry easily leaves in the zones even with partial absorption.

A well-known method of well construction, allowing to overcome the absorption zone, providing for the isolation of the absorption zones of the drilling fluid with additional casing pipes, lowering the production string and uncoupling the layers (for example, G. Abdrakhmanov, Isolation of the absorption zones with steel pipes without reducing the diameter of the well. - Oil industry, N 4 1982, p. 26-28).

A known method of construction of wells, providing for the supply at intervals of the absorbing layers of cementitious mixtures with fillers (RU 2061840 C1, 10.06.1996).

A known method of isolation of absorbing layers using aerated buffer fluid (RU 2057900 C1, 04/10/1996).

The disadvantages of these analogues is the low efficiency, which consists in the fact that they require material costs for the implementation of the method and lead to a decrease in the mechanical drilling speed and, as a result, to an increase in the duration and cost of well construction.

The present invention is the provision of a method of cementing casing strings, in particular a conductor, in which time is reduced, the quality of cementing is increased, and the upward flow rate in the annulus is increased.

SUMMARY OF THE INVENTION

This problem is solved by the proposed method of cementing the casing from two points, containing the stages at which the well is washed, the buffer fluid is pumped into the well, the grouting solution is prepared and pumped into the well, the grouting fluid is pushed into the annulus, characterized in that it is grouted to the wellhead the solution is fed through two outlet pipelines, combining the flow at the mouth by means of a tee into one supply piping, with each outlet piping connected to the corresponding cementing unit supplying the solution with a given feed rate.

In this case, the tee is made with the possibility of converting two input (in the general case, laminar) flows into one turbulent one. As is known from the prior art, in the case of the merger of two equally directed flows, turbulent mixing of flows (shock) takes place, while the greatest turbulent turbulence is characteristic when two flows moving at different speeds merge. This shock phenomenon is accompanied by pressure losses resulting from:

a) losses due to turbulent mixing of the two flows;

b) losses at the turn of the stream when it exits from the side branch into the supply pipeline;

c) losses due to expansion of flow in the supply pipeline.

In view of the foregoing, the diameter of the supply pipe is approximately 1.4 times larger than the diameter of the output pipes.

The grouting mortar is sold by means of the aforementioned two outlet pipelines combined at the mouth into a single supply pipeline.

The predetermined feed rate of the first cementing unit is equal to or different from the predetermined feed rate of the second cementing unit.

The target speed is equal to at least the nominal feedrate.

Using the method, acceleration of the cementing process of the casing string, in particular of the conductor, is achieved, while, as indicated above, the fact that the supply is from two points, combining below two laminar flows into one, provides natural turbulence of the flow, contributing to the effect on stagnant zones and on the crust of deposits on the walls of the well and the creation of a disturbance in the flow of the solution, which leads to a more complete displacement of the drilling fluid and replacing it with cement. Thus, when applying this method, it becomes possible not to resort to additional means to create a turbulent flow regime, which in turn leads to a decrease in the metal consumption of the casing string structure and, consequently, to a reduction in costs.

It was found that with the proposed method with a two-point supply of cement slurry, the solution passes zones with partial absorption faster, not having time to penetrate into the pores and cracks in the rock, and after raising the cement slurry the risk of absorption is minimal, since the column height of this mixture is low for the conductor (up to 500 m).

BRIEF DESCRIPTION OF THE DRAWINGS

The presented figure depicts the proposed layout and tying of cementing equipment for conductor cementing.

DETAILED DESCRIPTION OF THE INVENTION

To conduct a conductor cementing operation, preparatory work is necessary. First of all, the placement of grouting equipment is carried out, including 2 cementing units (CA) 1, 3 (for example, CA-320M), each containing a tank 5, 6 for cement mortar, and two cement mixing machines (for example, 2СМН-20) 2 and 4. The equipment is strapped, and the measured tanks 8 and 9 of the cementing units are used as a container of water for mixing cement and are connected to the corresponding cement mixing machines 2 and 4.

After that, in the capacity of cement-mixing machines 2 and 4, water is supplied from the tanks 8 and 9, respectively, and the chemicals are dissolved.

TsA-320 injection lines are pressure tested for 0.25 hours with a pressure equal to one and a half times the maximum design working pressure expected during cementing, but not less than 9.0 MPa.

If there is a clay solution in the well, 6 m ^{3 of} buffer liquid (2% aqueous solution of TPPN (sodium tripolyphosphate)) is fed into the well.

In the case of finding in the process water is pumped downhole mud in an amount of 10-15 m ³ with the addition of up to 10% filler by volume of slurry, and then 6 m ³ buffer liquid.

If the test pressure is not reached at the wellhead during preparation of the wellbore, up to 1.5-2 well volumes of the clay solution are added to the conductor before the buffer fluid with up to 10% filler added to the volume of the clay solution.

Then, the calculated volume of cement slurry with a density of 1830 ± 10 kg / m ³ closed in industrial water or in a 3-4% CaCl ₂ aqueous solution is pumped (if necessary, reduce the time of OZC (waiting for the cement to harden) to 8 hours).

The prepared cement slurry is pumped into the well and pushed through two cementing units from two points continuously. At the same time, pipelines from measuring tanks 5 and 6 are combined into a single supply pipeline by means of a tee 10. This is one of the differences of the proposed method from the traditional method in which one CA was used to pump water into the cement mixing machine, and the other to pump cement into the well .

As mentioned above, due to the proposed approach, the upward flow velocity in the annulus increases, which allows partial cement absorption to raise the cement slurry to the wellhead without loss, and a two-point feed with flow pooling at the wellhead allows for a turbulent flow regime.

Since the feed is carried out from two CAs at the same time, the feed rate exceeds the set speed for each cementing unit by half or less than the speed set for each cementing unit by more than two times. In this case, the set speed for each cementing unit is set equal to at least the nominal pumping speed at which the working discharge pressure is achieved. The working injection pressure should provide a sufficiently fast upward flow, but should not exceed the fracture pressure.

When cementing casing strings, pressure arises due to the difference in the specific gravities of the cement slurry and the drilling fluid (the greater the difference in the specific weights and the depth of the lowering of the string, the greater the pressure) + hydrodynamic resistances. Two units allow to increase the flow rate twice as compared to their passport indicators, which ensures acceleration of the upward flow and, accordingly, a turbulent regime with a decrease in pressure on the reservoirs.

In a private embodiment, in which the cementing unit ЦА-320М was used, the nominal speed was set equal to 11 l / s at a working supply pressure of 2 MPa.

The maximum set speed is limited by the technical characteristics of cementing units.

In the particular case of execution, the maximum set speed was set equal to the highest ideal supply, at which the supply pressure is equal to the maximum supply pressure of the cementing unit.

In the particular case of execution, in which the cementing unit ЦА-320М was used, the highest speed was set equal to 26 l / s at a maximum supply pressure of 2.5 MPa.

However, it should be borne in mind that a twofold increase in the maximum rate of injection of a mortar can adversely affect the quality of cement stone, since too high a rate of ascent of cement slurry can lead to inefficient displacement of drilling mud from the narrowings and extensions in the wellbore and their non-filling with cement mortar.

Thus, it is preferable to set the feed rate for each cementing unit near the nominal.

In order to achieve the largest swirls in the feed stream, it is preferable to set the feed rate of the first cementing unit to be different from the feed rate of the second cementing unit.

For the same purpose, the location of the tee nozzles should be chosen so that the angle between its nozzles connected to the outlet pipelines is less than the angles between the nozzles connected to the outlet pipelines and the nozzle connected to the supply piping. This ratio can be expressed as, for example, 30 ° / 165 ° / 165 °.

In addition, also for greater turbulization, the tee nozzles connected to the outlet pipelines can be located in different planes, while their angle of inclination to the plane of the nozzle connected to the supply pipe can be 20 ° -40 °.

To double the set speed while maintaining the supply pressure corresponding to the set feed rate, and for reliable operation of the equipment, the diameter of the supply pipe is approximately 1.4 times the diameter of the outlet pipelines of the cementing units.

Claims (5)

1. A method of cementing a conductor, comprising the steps of:
- flushing the well;
- injection of buffer fluid into the well;
- preparation and injection of cement slurry into the well;
- selling cement slurry into the annulus,
characterized in that the step of injecting the grouting mortar is carried out as follows: to the wellhead, the grouting grout is fed through two outlet pipelines, combining the flow at the wellhead by means of a tee into one supply piping, with each outlet piping connected to a respective cementing unit supplying the mortar at a given speed supply, while the tee is configured to convert the flows of two output pipelines, essentially laminar, into a turbulent flow in the pipeline under chi, which supply pipe diameter approximately 1.4 times the diameter of the outlet ducts, and the angle between the nozzles tee outlet ducts located in different planes, less than the angle between the nozzles and the outlet ducts supply pipe. 2. The method according to p. 1, in which the grouting grouting is carried out by means of the above-mentioned two outlet pipelines, united at the mouth into one supply pipeline. 3. The method of claim 1, wherein the predetermined feed rate of the first cementing unit is equal to the predetermined feed rate of the second cementing unit. 4. The method of claim 1, wherein the predetermined feed rate of the first cementing unit is different from the predetermined feed rate of the second cementing unit. 5. The method according to claim 1, wherein the predetermined speed is equal to at least the nominal injection speed at which the working discharge pressure is achieved.

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