RU2196880C1 - Method of well two-stage cementing - Google Patents

Abstract

FIELD: oil and gas producing industry; applicable in stage cementing of wells with producing formations presented by fissured and high-permeability reservoirs. SUBSTANCE: method includes running into well of casing string with landing adapter, cementing valve, shoe in lower part, and devices for stage cementing located on hollow plugs. Plugs are installed on casing string and their bottom part projects inside casing string, and they have weakened cross-section. Devices are installed above producing formation. Lowered into casing string are tubings with sealing nipple at their end and shearing sleeve which destroys hollow plugs. Sealing nipple is fitted into landing adapter. Cement mortar of the first stage is injected through tubings somewhat above devices. Injection is continued until moment of forcing plug entering into landing adapter. Sealing nipple is withdrawn from landing adapter, and annular space is sealed. Cement mortar is removed. Tubings are lifted to level of sealing nipple position, and cement mortar setting is waited. Then cement mortar of the second stage is injected through tubings and said devices with annular space closed. Small volume of cement mortar is left in wellbore. After forcing of cement mortar, pressure is reduced, and that cement mortar is removed through tubing. Cement mortar setting is waited. EFFECT: provision of required quality of cement stone behind casing string and considerable saving of material means. 5 dwg

Description

 The invention relates to the oil industry and will find application in stepwise cementing of wells, when productive formations are fractured or highly permeable reservoirs.

 A known method of step cementing, which involves the injection of cement mortar of the first stage by direct cementing, and the second stage through the annulus (1).

 The disadvantage of this method is that when the second portion of the cement slurry is injected into the annulus due to the large friction of the slurry against the rock, additional pressure is created on the absorbing formations up to hydraulic fracturing, which creates a risk of cement slurry leaving them. Hence the high cost of cement and low quality cementing casing.

 The closest in technical essence to the proposed one is a step cementing method, including casing descent with step cementing devices installed above the reservoir, landing sub, cement valve and shoe in the lower part, first stage cement mortar injection slightly higher than step cementing devices with using a squeeze plug, removing the cement slurry located above the above devices, and leaving it on the BCP, the second stage cement slurry through the above-mentioned devices, leaving a small volume of the solution in the wellbore, reducing the pressure after pumping the solution and removing this solution through the tubing and leaving it on the OZZ (2).

 When pumping cement mortar through the casing, it is possible to dilute it with water under a squeeze plug, which can lead to poor cementing. In addition, rings of cement remain in the coupling zone between the pipe ends, which harden over time, and subsequently, when the equipment is lowered into the well, the cement stone collapses, crumbles and leads to equipment jamming and other complications (clogging of the formation, face). To avoid this, in practice, hydrotreating of pipe joints has recently been carried out, which is associated with the cost of considerable time, additional equipment and material resources. It should also be noted that the control of the elastic ball in the device for step cementing is difficult to control, and therefore the efficiency and reliability of the operation of pumping the cement mortar of the second stage and ensuring the proper quality of the cement stone are very problematic.

 The objective of the invention is to provide a two-stage cementing method that provides the necessary quality of cement stone behind the casing and allows you to save significant material resources.

 This problem is solved by the proposed method, including casing runoff with step cementing devices installed above the reservoir, landing sub, cementing valve and shoe in the lower part, first stage cement mortar injection slightly higher than step cementing devices using squeeze plug, removal of cement mortar, located above the above devices, and leaving on the OZZ, injection of cement mortar of the second stage through the above devices with leaving a small volume of the solution in the wellbore, reducing the pressure after pumping the solution, removing this solution through the tubing and leaving it on the OZZ.

 New is that devices for step cementing are placed on hollow plugs installed on the casing and protruding the bottom part inside it and having a weakened section; after the casing is lowered to the design depth, the tubing is lowered into its cavity with a sealing nipple at the end and a cutting sleeve and the hollow plugs are destroyed, and then the sealing nipple is put into the landing sub; cement of the first stage is pumped through the tubing until the cork plug enters the landing sub; before removing the cement mortar, located above the devices for step cementing, the sealing nipple is removed from the landing sub and sealing the annulus, and after removal of the solution, the tubing is raised to the position of the sealing nipple opposite the mentioned devices, and after the first stage OZC, the cement mortar of the second stage is also injected through tubing with a closed annulus.

 In FIG. 1 shows a diagram of the implementation of the proposed method at the time of entry into the casing string with a sealing nipple and a shear sleeve.

 In FIG. 2 - at the time after the destruction of the pole of the plugs and the installation of the sealing nipple in the landing sub after the injection of cement mortar of the first stage.

 Figure 3 - at the time of removal of cement, located above the devices for step cementing by direct flushing.

 Figure 4 - at the time of injection of the cement mortar of the second stage.

 Figure 5 - device for step cementing.

 The method is carried out in the following sequence.

 The casing 1 (figure 1) with a shoe 2, a cementing valve 3 and a landing sub 4 is lowered into the well to the design depth. As a part of the casing string, devices for step cementing are installed on its outer surface. Each of them consists of a housing 5 (figure 5), a ball valve 6, a spring 7 and a grill 8. The housing 5 is connected to the hollow plug 9 and communicates with it through the channel 10. The bottom plug is passed into the inside of the casing and has a weakened section 11. The casing is lowered so that the devices for step cementing are higher than the reservoir 12 (figure 1).

 After lowering the casing string into its cavity, the tubing string 13 with a sealing nipple 14 (Fig. 1) at the end and a cutting sleeve 15 is lowered. The latter destroys the hollow plugs 9 as the tubing is lowered, and the nipple 14, having reached the sub 4, enters the cylindrical bore 16 to the stop 17. The equipment is ready for cementing.

 On the string tubing 13 (figure 2) pumped cement mortar of the first stage, forcing it through a plug 18. After planting it in the sub 4, the cessation is stopped. The tubing is lifted onto one pipe, the annulus is sealed at the mouth and the cement mortar located above the step cementing devices is removed by direct washing (Fig. 3). After that, the tubing is raised to the position of the sealing nipple 14 opposite the mentioned devices. At the end of the period of time, the second stage cement slurry is pumped through the tubing string and step cementing device with closed annulus until the cement slurry appears at the wellhead, leaving a small volume of cement slurry in the tubing and casing (Fig. 4). Pressure is relieved, check valves 6 are closed. Then this solution is washed backwash, tubing is removed and the well is left on the bcc.

 Since the injection and sale of cement mortar according to the proposed method is carried out on a tubing string, dilution of the solution with water under the squeeze plug is minimized or eliminated altogether. Completely excluded the ingress of cement into the joints of the casing and the associated negative consequences. The use in the technological scheme of destructible hollow plugs and a spring-loaded metal check valve in step cementing devices together with the above-mentioned factors increases reliability and guarantees high quality of the operation for pumping cement of the second stage and cement stone behind the casing. The method allows to save significant material resources due to the fact that there is no need to carry out after cementing work on cleaning casing pipes, flushing, etc.

Information used
1. The analogue. Ramazanov G.S. and other device for combined cementing of casing strings. M .: Nedra, Oil industry, 4, 1992, p. 19-20, fig. 12.

 2. The prototype. RF patent 2029066, MKI 6 E 21 V 33/13, 1995.

Claims (1)

 A two-stage cementing method for a well, including lowering a casing with stage cementing devices installed above the reservoir, a landing sub, cementing valve and shoe in the lower part, injecting cement of the first stage slightly higher than cementing devices using a squeeze plug, removing cement located above the above devices, and leaving to wait for the cement to solidify - OZZ, injection of cement mortar the second stage through the aforementioned devices with leaving a small volume of the solution in the wellbore, reducing the pressure after pumping the solution, removing this solution through tubing - tubing and leaving on the OZZ, characterized in that the devices for step cementing are placed on hollow plugs installed on casing string and protruding bottom inward and having a weakened section; after the casing is lowered to the design depth, the tubing is lowered into its cavity with a sealing nipple at the end and a cutting sleeve and the hollow plugs are destroyed, and then the sealing nipple is put into the landing sub; cement of the first stage is pumped through the tubing until the cork plug enters the landing sub; before removing the cement mortar, located above the devices for step cementing, the sealing nipple is removed from the landing sub and sealing the annulus, and after removal of the solution, the tubing is raised to the position of the sealing nipple opposite the mentioned devices, and after the first stage OZC, the cement mortar of the second stage is also injected through tubing with a closed annulus.

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