RU2183728C1 - Method of well stage cementing - Google Patents

Abstract

FIELD: drilling of oil and gas wells, particularly, methods of well strong cementing where producing formations are presented by fissured or high-permeability reservoirs. SUBSTANCE: method includes running into well casing string with device for stage cementing installed above producing formation, cementing valve with seat and shoe in lower part; injection of cement mortar of the first stage, removal of excessive amount of cement by direct flushing through said device and letting cement setting injection of cement mortar of the second stage through said device; reduction of pressure after forcing of cement mortar and removal of its excessive amount through tubing string and letting the cement setting. Device for stage cementing is located on hollow plugs which are installed on casing string. Hollow plugs protrude by their bottom part inside it and have weak cross-section. After running of casing string down to designed depth, introduced into its cavity is tubing with blind sealing plunger and perforated branch pipe at end and shearing coupling. Injection of cement mortar of the first stage is performed through tubing with closed interpipe annulus. Then tubing is lowered and hollow plugs are broken by shearing coupling. Sealing plunger is simultaneously landed onto seat above cementing valve. After removal of excessive amount of cement mortar, tubing is raised so that perforated pipe is located somewhat below the device for stage cementing. Cement mortar of the second stage is also injected through tubing with closed interpipe annulus. EFFECT: simplification and reduced cost price of the method. 4 dwg

Description

 The invention relates to the field of drilling oil and gas wells, in particular to methods for stepwise cementing of wells, when the reservoir is represented by 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, a cement valve with a seat and shoe in the lower part, first stage cement mortar injection slightly higher than the device and leaving in the pump compressor tubes (tubing) of a small volume of the solution, removing excess solution by direct washing through the aforementioned device and leaving on burns cement hardening (OZC), injection of a second-stage cement mortar through the aforementioned device, leaving a small volume of the solution in the tubing, reducing the pressure after the solution was forced through, removing its excess through the tubing and leaving it on the OZC (2).

 The method involves the use of cementing separation plugs, which complicates and increases the cost of the process. In addition, 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 to pump cement 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 simple and cheap method that guarantees the operation of step cementing at a high quality level.

 This problem is solved by the proposed method, including the casing run with a device for step cementing installed above the reservoir, a cement valve with a saddle and a shoe in the lower part, pumping cement of the first stage somewhat higher than the mentioned device, removing excess cement mortar by direct washing through the said device and leaving on the OZZ, pumping cement of the second stage through the said device with leaving a small volume of cement solution into the wellbore, the pressure drop after prodavki cement slurry, removing it through tubing over and leaving at WOC.

 New is that the device for step cementing is placed on hollow plugs installed on the casing and protruding the bottom part inside it and having a weakened section; after lowering the casing to the design depth, the tubing is lowered into its cavity with a blank sealing plunger and a perforated pipe at the end and a cutting sleeve; cement mortar of the first stage is pumped through the tubing with the annulus closed, then the tubing is lowered and the hollow plugs are destroyed with a cutting sleeve, and the sealing plunger is simultaneously seated in the seat above the cement valve; after removal of the excess cement mortar, the tubing is raised so that the perforated pipe is slightly lower than the device for step cementing; cement injection of the second stage is also carried out through the tubing with a closed annulus.

 In FIG. 1a shows a flow chart of the implementation of the proposed method at the time of completion of the injection of cement mortar of the first stage.

 In FIG. 1b - the same thing at the time of removal of excess cement mortar by direct washing through a device for step cementing.

 In FIG. 1c - the same at the time of completion of the injection of the cement mortar of the second stage.

 In FIG. 2 - device for step cementing.

 The method is carried out in the following sequence.

 Casing 1 with shoe 2, cementing valve 3 and seat 4 is lowered into the well to the design depth. As a part of the casing string, a device for step cementing is installed on its outer surface, which may consist of one or several units of the same type. Each node consists of a housing 5 (Fig. 2), 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 inside the casing and has a weakened section 11. The number of nodes of the same type depends on the volume of injected cement. The casing is lowered in such a way that the device for step cementing is located above the roof of the productive formation 12 (~ 150-200 m).

 After lowering the casing string into its cavity, the tubing string 13 is lowered with the sealing plunger 14 (Fig. 1a) at the end. There are perforation holes 15 above the plunger in the pipe, and a cutting sleeve 16 is installed slightly higher. The tubing is lowered so that the sealing plunger 14 is located above the seat 4 at a distance of 15-20 m, and the cutting sleeve 16 is at a distance of 7-10 m from devices for step cementing.

 Cement mortar of the first stage is injected through the tubing with closed annulus (Fig. 1a) based on the filling of the annular space 40-50 m above the device for step cementing and leaving 100-150 l of cement mortar in the tubing. Then the tubing is lowered, while the cutting sleeve 16 destroys the hollow plugs 9, and the sealing plunger 14 sits in the seat 4, which provides additional sealing of the bottom of the casing. After this, by direct washing through the tubing and the device for step cementing, the excess cement mortar is removed to the surface (Fig. 1b). Then, the tubing is lifted from the calculation so that the perforations 15 are slightly lower than the device for step cementing and leave the well in the MSC.

 At the end of the OZC, the second stage cement mortar is pumped through the tubing string and the device for step cementing with a closed annulus until the cement slurry appears at the wellhead, leaving excess cement mortar in the tubing in a volume of 100-150 l (Fig. 1c). Then this solution is washed backwash from the well, the tubing string is removed and the well is left in the BSC.

 The proposed method eliminates the use of separation plugs, which simplifies and reduces the cost of the cementing process, and the use of destructible hollow plugs and a spring-loaded valve in the step cementing device in the technological scheme increases reliability and guarantees high quality of the operation for pumping cement of the second stage and cement stone behind the casing .

Information used
1. The analogue. Ramazanov G.S. and other device for combined cementing of casing strings. - M.: Nedra, Oil industry, 1992, 4, p. 19-20, Fig. 1, 2.

 2. The prototype. RF patent 2029066, MKI6 E 21 V 33/13, 1995.

Claims (1)

 A step-wise cementing method for a well, including a casing run with a step-wise cementing device installed above the reservoir, a cementing valve with a seat and shoe in the lower part, pumping the first stage cement slurry slightly higher than the said device, removing excess cement slurry by direct flushing through the said device and leaving to wait for the hardening of cement (OZZ), the injection of cement mortar of the second stage through the specified device with a small volume of cement in the wellbore, pressure reduction after the cement grout is pumped, removing excess of it through tubing and tubing, and leaving it on the OZZ, characterized in that the device for step cementing is placed on hollow plugs installed on the casing and protruding bottom part inside it and having a weakened section; after lowering the casing to the design depth, the tubing is lowered into its cavity with a blank sealing plunger and a perforated pipe at the end and a cutting sleeve; cement mortar of the first stage is pumped through the tubing with the annulus closed, then the tubing is lowered and the hollow plugs are destroyed with a cutting sleeve, and the sealing plunger is simultaneously seated in the seat above the cement valve; after removal of the excess cement mortar, the tubing is raised so that the perforated pipe is slightly lower than the device for step cementing; cement injection of the second stage is also carried out through the tubing with a closed annulus.

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