RU2086752C1 - Method for back-cementation of casing string in well - Google Patents

Abstract

FIELD: oil and gas production industry. SUBSTANCE: this is used in cementation of casing strings in wells. It cuts time and use of materials, permits injection of plugging compound of any density at any velocity and under any pressure. Mounted on lower end of casing string to be run into well is spring-loaded non-return valve of plate-type. It is made for possible opening under action of axial vertical force directed downwards for example under action of flushing tube string. Holes are made in lower part of string. Annular space between casing string and flushing tube string is filled with liquid. Back pressure is created. During injection of plugging solution into annular space, effected at well head is regulation of back pressure value. Moment of stopping injection of plugging solution into annular space of well is defined at appearance of plugging solution of required composition at well head. EFFECT: high efficiency. 4 dwg

Description

 The invention relates to the construction of wells, in particular to the technology of cementing casing strings in wells, and is intended for use when fastening wells in any geological conditions, including the presence in the wellbore of highly permeable absorbing and / or developing formations with different characteristics, t .e. in conditions of intensive absorption of flushing fluid and / or formation water formation.

 A known method of reverse cementing a casing string in a well, including lowering a casing string with a controlled non-return valve in its lower part, lowering a flush pipe string with a landing cone and a push rod at the lower end, flushing pipe string equipment at the wellhead flow line, injection of cement slurry into the annulus of the well and establishing the moment of its completion [1] The required volume of cement slurry is injected into the annulus of the well at the landing position th column cone drilling pipes, raised above the landing seat of the check valve casing when the locking element - a ball check valve is pressed down, the pusher rod and the circulation passage at the valve seat of the check valve is open. Establishment of the moment of completion of the injection of grouting fluid into the annulus of a well is made by the exit to the mouth of the signal fluid, forced by the drilling fluid in an amount equal to the internal volume of the casing string. After that, the flushing pipe string is lowered to the stop, while its seating cone sits in the seating seat of the casing check valve, closing its circulation channel and stopping the access of the cement slurry into the casing. Then, through the casing string and the radial openings of its landing cone, the excess cement slurry is removed from the casing.

 However, high-quality cementing in this way is achieved in no more than 70 cases out of 100, and in difficult mining and geological conditions, high-quality cementing is generally not guaranteed due to dilution with produced water or absorption of grout during injection into the borehole.

 There is also known a method of reverse 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, which can open it from the action of vertical axial force from top to bottom, for example, from the action of a flushing string pipes, lowering the latter into the well, equipping them at the mouth with a flow line, filling the annulus in the casing and flushing pipes with liquid, lowering flushing the flushing pipe string onto the check valve until it is fully open, injecting the grouting solution into the annulus of the well and determining the moment of its completion [2] To open the flap valve, the free lower end of the flushing pipe string is inserted into the stop ring hole with which the casing is equipped above check valve. When the check valve is open, the first buffer fluid is injected into the borehole annulus, then the drilling fluid and the second buffer in an amount equal to the internal volume of the wash pipe string, after which the grouting fluid is injected, the end of which is established at the end of the first buffer fluid at the wellhead, after which the column of flushing pipes is lifted, the check valve closes.

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

 The purpose of the invention is the reduction of time and material costs and means for cementing the casing string in the well while improving the quality of cementing in any mining and geological conditions by providing the ability to pump cement slurry of any density, at any feed rate and at any pressure in the annulus as with low and with a high specific permeability of the intervals of its trunk, eliminating the need to make their preliminary isolation.

 This goal is achieved by the fact that in the known method of reverse cementing the casing in the well, including preparing the well, lowering the casing into it with a spring-loaded poppet type check valve in its lower part, made with the possibility of opening it from the effect of vertical axial force from top to bottom, for example, from the influence of the casing string, the descent of the latter into the well, their equipment at the mouth with a flow line, the filling of the annulus in the casing and the casing string flushing pipes with liquid, lowering the flushing pipe string to the check valve until it is fully open, injecting grouting mortar into the well annulus and establishing the moment of its completion, the flushing pipe string with holes in its lower part, and after filling the annular space in the casing and flushing casing pipes with liquid in them create back pressure, while during the injection of cement slurry in the annulus of the well at the flow line of the column of flushing pipes at the wellhead Ichin backpressure, and establishing the end of the injection of cement slurry in the annulus of the well is set on the appearance at the flowline column flushing pipe wellhead plugging desired composition solution.

 Figure 1 shows the stage of washing the annular space of the casing string and flushing pipe, which is carried out after flushing the well during its preparation for cementing; figure 2 the stage of filling the column with washing liquid and annular space of the casing and creating back pressure in them before injection into the annulus of the cement slurry; in FIG. Stage 3 injection of cement slurry in the annulus of the well with an open spring-loaded controlled check valve and grouting fluid outlet at the wellhead through the wash pipe string and its flow line; in Fig.4 the beginning of the stage of removal to the surface (at the wellhead) of the column of flushing pipes of the remaining cement slurry therein after filling the well annulus and closing the spring-loaded check valve at the lower end of the casing.

 The proposed method was tested in the field.

In its implementation, the following materials and equipment were used:
cement slurry, which was a cement mortar with a density of 1.85 g / cm ³ with the addition of 2% calcium chloride;
buffer liquid industrial water;
cementing unit CA-32OM 5 pcs.

 cement mixing machine SMN-20 3 pcs.

 manifold block BM-700 1 pc.

 hydromechanical packer GMP-195 1 pc.

Testing of the method was carried out by cementing a casing string in a borehole with a depth of 1592 m and a bore diameter of 216 mm. The wash liquid used in drilling clayless polymer solution density of 1.03 g / cm ^3, viscosity at 16 IVS-5 with a fluid loss of 10 cm ^3/30 min.

Before the casing was launched, hydrodynamic studies of the entire wellbore were carried out by injection. Two permeable sections were identified in the intervals: 975-991 m with a specific injectivity coefficient K 0.47 m ³ / h / atm and 1411-1433 m K 0.89 m ³ / h / atm. Insulation work in these permeable sections of the wellbore was not carried out.

On the lower end of the casing 1, a shoe and a spring-loaded controlled poppet type check valve 2 were installed. After that, the casing 1 was lowered into the well to the bottom, a wellhead sealant was installed on the casing and the flushing pipe 3 was lowered inside the casing, three radial holes 4 with a diameter of 25 mm each were made in the lower part of it. At the wellhead, the flushing pipe string 3 was equipped with a flow line 5, on which a valve and pressure gauges were installed. The annulus 6 and the annulus 7 of the casing were sealed. The well was washed. The column of flushing pipes 3 and the annular space 7 of the casing 1 was filled with flushing fluid 8 and created a back pressure of 10 ATM. By lowering the column of flushing pipes 3 downward, a spring-loaded controlled poppet type 2 check valve was opened and, holding it in the open position (Fig. 3), by pumping flushing fluid into the annulus 6 of the well, reverse circulation was established with the outlet to the wellhead through the column of flushing pipes 3. After of this, 6 m ^{3 of} buffer fluid (industrial water) was injected into the annulus 6 of the well, and then, under a pressure of 15 atm, the annular cement 6 began to be injected into the annulus 6 with a density of 1.85 g / cm ³ , prepared of 61 tons of cement cement with the addition of 2% calcium chloride, while producing on the flow line 5 columns of flushing pipes 3 at the wellhead, control of the back pressure within 10 20 atm. The cement mortar was injected into the annulus 6 until its outflow was established from the flow line 5 at the wellhead, and cement cement was discharged at the wellhead from the wash pipe string 3 and from its flow line 5.

Once the wellhead from flowline 5 column flushing pipe 3 was prepared cement slurry density of 1.84 g / cm ^3, produced a closing spring-operated check valve 2, which washing column tube 3 lifted by the amount of opening of said valve. Then the cement slurry was washed from the wash pipe string 3 (Fig. 4) by supplying wash water from the wellhead through the annulus 7 of the casing 1 of the wash liquid 1, after which the wash pipe string 3 was lifted from the well, leaving the well waiting for cement to harden.

A complex of geophysical studies carried out after 48 h to determine the quality of cementing showed that satisfactory cementing quality was 98% throughout the bore, while with the known method of cementing similar wells in this area, this figure did not exceed 74%
The total time of fixing the well by the casing string during the implementation of the proposed method compared to the known one was reduced by 112 hours, while material costs and cementing resources were reduced by 19%.

 To implement the proposed method, conventional equipment is used. The structural elements introduced into it are simple in design, reliable and easy to operate, allowing both direct and reverse cementing.

Claims (1)

 A method of reverse 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, which can open it from the action of vertical axial force from top to bottom, for example, from the action of the flushing pipe string, lowering the latter into the well, equipping them at the mouth with a flow line, filling the annulus in the casing and flushing pipes with liquid, lowering the washing pipes to the check valve until it is fully open, injecting the grouting solution into the annulus of the well and determining the moment of its completion, characterized in that the washing pipe string is made with holes in the lower part, and after filling the annular space in the casing and the washing pipe string with liquid they create counter pressure, while during the injection of cement slurry in the annulus of the well on the flow line of the column of washing pipes, at the wellhead, the amount of back pressure is adjusted and the establishment of the moment of completion of the injection of grouting mortar into the well annulus is established by the appearance on the flow line of the column of washing pipes, at the wellhead, grouting mortar of the required composition.

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