RU2361062C1 - Method of elimination of behind-casing flow in wells of small diametre - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention refers to oil industry, particularly to methods of elimination of behind-the-casing flows at repair of wells of small diametre. The method of eliminating behind-the-casing flows in the wells of small diametre consists in forming a cavity in a wall of the well and in plugging behind-the-casing space with cement grout. The cavity is formed by means of solving rock with an acid composition and in pumping it via a flow string into space between a producing well and the wall of the well in an interval of behind-the-casing flows, in pumping for the purpose of driving mineralised water with density equal to density of acid composition, in well shut-down for reacting and in following driving of products of acid composition reaction and rock of neutral buffer fluid into a reservoir, and in the said plugging. Volume of acid composition is not less, than volume of space between the well wall and the producing column with length equal to length of the interval of behind-the-casing overflows.

EFFECT: increased duration of effect from operations of eliminating behind-the-casing overflows due to increased mechanical strength of cement ring.

2 cl, 1 ex

Description

The invention relates to the oil industry, in particular to methods for eliminating annular flows during the repair of small diameter wells.

A known method of eliminating water inflow through a cemented annular space during the operation of oil and gas wells [RF patent No. 2196878, ЕВВ 33/138. Publ. 01/20/2003. Bull. No. 2]. In this method, according to the invention, it is possible to increase the efficiency of isolation of the overflow channels by cutting the casing in the interval below and above the roof of the aquifer, creating a cavity in the indicated interval and filling the cavity with grouting mortar at a pressure equal to the pressure of the hydrostatic column of grouting mortar, which, after solidification, creates impermeable insulation bridge. The disadvantage of this method is that the cavity is created by working out the wellbore after cutting the production string, which requires many complex technological operations associated with a large investment of time and material resources.

The closest technical solution to the proposed one is a method of isolating formation water in a well, including creating a cavity in the wall of the well in the interval between the oil and aquifer and plugging the annulus [a.s. 1546612, ЕВВ 33/13. Publ. 02/28/1990. Bull. No. 8]. In this method, according to the invention, it is possible to increase the efficiency of isolation of formation water by creating caverns and horizontal cracks in the well wall, filling the caverns and cracks with cement mortar, and the cavity is formed during cementing by changing the direction of fluid flow in the required interval of the annulus of the well. The disadvantage of this method is that with the existing hydraulic resistances in the well, it is very difficult to create during cementing conditions for the movement of cement in the annular space between the wall of the well and the production string at a speed that ensures the creation of a cavity of sufficient size in solid rocks, while reducing efficiency insulation work.

An object of the invention is to increase the duration of the effect of the elimination of annular flows by increasing the mechanical strength of the cement ring.

The problem is solved by the method of elimination of annular flows in small diameter wells, including the creation of a cavity in the wall of the well and the plugging of annular space with cement mortar.

What is new is that the cavity is created by dissolving the rocks with an acidic composition and pumping it through tubing into the space between the production string and the borehole wall in the interval of casing flows, injecting it to squeeze mineralized water with a density equal to the density of the acid composition, stop the borehole to the reaction followed by the sale into the formation of the reaction products of the acid composition and rocks with a neutral buffer liquid and the indicated plugging eat.

It is also new that the volume of the acid composition is not less than the amount of space between the wall of the well and the production string with a length equal to the length of the annular flow interval.

One of the main reasons for the hydraulic connection between aquifers and reservoirs in the well is the destruction of the cement ring under the action of alternating loads acting on the production string. It is possible to reduce the probability of fracture of a cement ring by increasing its mechanical strength. The most difficult task is to increase the mechanical strength of the cement ring in wells of reduced diameter, cased with pipes with a nominal diameter of 114 mm or less, due to the small annular gaps between the casing pipes and the borehole wall. So, for the case of a well drilled with a 146 mm drill bit for a production casing with a diameter of 114 mm and a wall thickness of 8 mm, the gap between the wall of the well and the production casing is about 8 mm, and even less in the range of couplings. In such cases, the only effective way to increase the strength of the cement ring is to increase its thickness, which can be achieved by creating a cavity in the borehole wall. The creation of a cavity in the borehole wall in the interval of the overflow channels leads to an increase in the cross-sectional area of the annular gap and provides a cement ring with a larger cross-sectional area and, consequently, higher mechanical strength during plugging. This contributes to a higher resistance of the cement ring to pressure differences existing in the well, and reduces the likelihood of recurring casing flows.

The essence of the invention is to increase the cross-sectional area of the annular gap between the well wall and the production string by creating a cavity by dissolving the rocks with an acid-based composition and plugging the annulus. When carrying out repair work on the well by geophysical methods, the annular flow interval is determined. Using the obtained data on the length of the annular flow interval, the volume of the annular space between the borehole wall and the production string with a length equal to the length of the annular flow interval is determined. Tubing is lowered 3-4 m above the perforation interval into the well. Acid composition and mineralized water are pumped through tubing into the annular flow interval to force the acid composition, then the well is allowed to react. The volume of the acid composition is taken not less than the volume of the annular space between the well wall and the production string with a length equal to the length of the annular flow interval. Hydrochloric acid compositions are used as the acid composition for dissolving carbonate rocks, and hydrochloric and hydrofluoric acid compositions are used in terrigenous rocks. The exact composition and response time are determined based on laboratory test results for core dissolution. In order to exclude the movement of fluids in the well due to the difference in their densities during the reaction of the acid composition, mineralized water with a density equal to the density of the acid composition is used to press the latter. To obtain mineralized water of the required density, for example, formation mineralized water diluted to the required density with fresh water can be used. The interaction of the acid composition with the rocks leads to the creation of a cavity in the borehole wall in the interval of the overflow channels, which allows subsequent cement plugging of the annular space to produce a cement ring of greater thickness, respectively, with greater mechanical strength, which will reduce the likelihood of annular overflows in the future. After the reaction time of the acid composition has expired, in order to prevent a decrease in the quality of the cement stone as a result of mixing the cement solution with the reaction products, the latter are forced into the reservoir by injection of a neutral buffer liquid, for example, water. Following the neutral buffer fluid, the cement slurry is injected to plug the overflow channel, and the well is left for the duration of the curing of the slurry.

Thus, in this proposal, the result is achieved - an increase in the duration of the effect of the elimination of annular flows in small diameter wells by increasing the mechanical strength of the cement ring.

Practical example

In a well drilled to a depth of 1400 m under a production casing with a diameter of 114 mm, drilling was carried out by a downhole screw motor D1-127 with a bit of 146 mm. The perforation interval 1310-1314, in the interval 1310-1350 m, the section of the well is composed of carbonate rocks. According to geophysical research, there are behind-the-casing flows in the range of 1314-1324 m. 0.5 m ³ hydrochloric acid with a concentration of 24% was pumped into the interval of behind-the-casing flows through the perforation interval with a sales of mineralized water with a density of 1120 kg / m ³ . They left the well to respond for 5 hours. Then, plugging the interval of behind-the-casing flows was carried out by pumping the cement slurry, while 1.0 m ^{3 of} fresh water was pumped before the cement slurry as a buffer. The well was left to await the curing of the cement slurry. As a result, by creating caverns in the borehole wall in the interval of flow channels and increasing the thickness of the cement ring, the layers are reliably disconnected and the likelihood of further casing flows in the future is reduced. The well operating time until the recurrent crossflows occur (overhaul period) increases by 1.5 times or more.

Claims (2)

1. A method of eliminating annular flows in small-diameter wells, including creating a cavity in the wall of the well and plugging the annular space with a cement mortar, characterized in that the cavity is created by dissolving the rocks with an acid composition and pumping it through tubing into the space between the production string and the wall of the well in the interval of annular flows, injection for selling mineralized water with a density equal to the density of the acid composition, stops minutes wells to react, followed by the formation prodavkoy acid composition reaction product and rocks neutral buffer liquid and said plugging. 2. The method according to claim 1, characterized in that the volume of the acid composition is not less than the volume of space between the well wall and the production string with a length equal to the length of the annular flow interval.