RU2484234C1 - Well repair method - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention refers to oil and gas industry, and namely to repair methods of wells subject to water circulation behind the string due to disturbance of integrity of cement stone. After preliminary pumping of curable solution of resin to the space behind the string, simultaneous pumping of curable resin solution and cement solution is performed; at that, selection of resin and pumping mode of curable solution of the chosen resin and cement solution shall be made in the ratio of 75:25 vol. %, which provides formation of strong cement-resin stone. In addition, tubing layout includes a packer. Simultaneous pumping of curable resin and cement solution is performed along two concentric tubing columns. As resin, acetone-formaldehyde resin curable with a curing compound with alkali pH is used.

EFFECT: improving the effectiveness of the well repair method owing to preventing formation of weak plugging stone in the mixing zone.

3 cl, 1 dwg

Description

The invention relates to methods for repairing wells exposed to annular circulation of water due to violation of the integrity of cement stone.

There is a method of repairing a well by sequentially injecting a cement mortar and a cured resin solution with an acid hardener, and between the rims of the cement mortar and the cured resin solution with an acid hardener, acid is injected after the cement mortar has cured to increase the injectivity of the treated area and improve the adhesion of the resin [1].

The known method is not effective enough, especially for wells prone to annular circulation, since acid treatment violates the integrity of the cement stone in the zone to be isolated. In addition, during the initial injection of cement mortar, only large cracks in the cement ring are insulated, and microcracks remain subject to the uncontrolled action of acid, as a result of which they can increase even more, and the subsequent injection of a cured resin solution, which allows plugging microcracks, may be ineffective.

The closest in technical essence to the proposed one is a method of repairing a well by successively injecting a cement mortar, a cured resin solution and, again, a cement mortar [2].

During the initial injection of cement mortar, only large cracks in the cement ring are qualitatively insulated. In addition, the injected cement, stopping at the entrance to microcracks, can block access to them for the subsequent rim of the cured resin solution, which will negatively affect the duration of the repair effect, as high-quality insulation of microcracks is possible only if the insulating material penetrates over most of its length.

In addition, during sequential injection according to published data (for example, [3]) in the mixing zone, the concentrations of the curable resin and cement mortar will smoothly change from 1% to 99%, respectively, the properties of the formed stone will change. Laboratory studies of the authors (figure 1) show that with an uncontrolled mixing of resin and cement, as a rule, a cement stone of lower strength is formed in comparison with cement and resin stones. Figure 1 shows the dependences of the compressive strength of cement stone on the ratio of the volumes of the cement mortar (with a water-cement ratio of 0.5) and the cured resin solution (at the following concentrations of hardener in the rejected resin solution:

- acetone-formaldehyde resin ACF-75 (TU 2228-006-48090685-2002 with amendment No. 1): hardener - 10% NaOH solution (the content in the cured resin solution is 40 vol.%);

- resin Sofit (TU 2200-001-17804808-2008): hardener - 32% NaOH solution (the content in the cured resin solution is 10 vol.%);

- Resoil K-1 resin (TU 2221-637-55778270-2004): hardener - KatoRIR H2 (the content in the curable resin solution is 20 vol.%).

It can be seen that for the two investigated resins - Sofit and Rezoyl K-1 - for any ratio of components - a curable resin solution and cement mortar - a cement stone is formed whose strength is lower than the strength of a cement or resin stone.

For ACF-75 resin, there is a certain range of ratios of the curable resin solution and cement mortar, in which the strength of the cement stone is higher than the strength of cement or resin stone. But with most ratios of the curable resin and cement mortar, the strength of the cement is also lower than the strength of the cement or resin.

Also, with a large extent of the mixing zone of the curable resin and cement mortar in the tubing, they may prematurely cure, resulting in an emergency situation. Therefore, the well repair method presented in [2] is not effective enough, and it makes sense to direct efforts to form a mixing zone in the wellbore with a certain ratio of components.

Solved by the claimed technical solution, the problem and the expected technical result are to increase the efficiency of the method of repairing the well by simultaneously injecting a cured resin solution and cement mortar by preventing the formation of unstable cement stone in the mixing zone.

The problem is solved in that after preliminary injection of the curable resin solution into the annulus, the curable resin solution and cement mortar are simultaneously injected, and the choice of resin and the mode of injection of the curable solution of the selected resin and cement mortar are observed so that a durable cement-resin stone is formed.

Additionally, a packer is included in the tubing arrangement.

The simultaneous injection of cured resin and cement mortar is carried out in two concentric tubing columns.

As the resin, an acetone-formaldehyde resin cured with an alkaline pH hardener is used.

The method is carried out by the following sequence of operations.

1. Pre-injection of a curable resin solution into the annulus to isolate microcracks.

2. Simultaneous injection into the insulation interval of the curable resin and cement mortar. To create a durable cement-resin stone, a resin of the acetone-formaldehyde type is chosen when a synergistic effect occurs during the interaction of its cured mortar with the cement mortar according to the strength of the formed cement-resin stone, and the mode of injection of the cement mortar and the cured resin solution is observed, namely, the costs (ratio of volume volumes ) cement mortar and curable resin solution.

3. The rise of tubing. The well is left for the period of waiting for the hardening of the cement stone.

4. After the waiting period for the hardening of the cement stone, a bridge is drilled in the wellbore.

In the case of acetone-formaldehyde resin, a synergistic effect is observed with the interaction of its curable mortar with cement mortar in a volume ratio of "cured resin solution: cement mortar" = 3: 1 (see figure 1). In this case, the strength of the cement stone exceeds the strength of the stone obtained from the components of the mixture separately, which can be used to increase the efficiency of well repair.

In this regard, the repair method is carried out by simultaneous injection of two curable tubing columns (pipe in pipe) of the cured resin solution and cement mortar, the rim volumes and injection mode of which are chosen so that the ratio of the cured resin: cement volume ratio is reached in the mixing zone solution ”= 3: 1 and the formation of a solid cement stone.

At the first stage, using two concentric tubing columns with an open annulus, the cured resin solution and cement mortar are brought to the tubing shoe, which is located 50 m above the upper holes of the perforation interval of the reservoir. In this case, the cured resin solution is supplied, for example, through the outer tubing string, while the cement mortar is supplied through the inner one.

Next, close the inner tubing string and annulus. The cured resin solution begins to be forced through the outer tubing string into the annular circulation region with water or a hydrophobic agent under pressure. The result is a partial penetration of the cured resin solution into the productive and aquifer, as well as the filling of cement stone microcracks in the annular circulation of water.

When the injectivity of the isolation interval is more than 500 m ³ / day (with a pressure at the mouth of 100 atm or less), before injecting the cured resin solution, a preliminary decrease in injectivity with the use of gel-forming or emulsion compositions to about 300 m ³ / day is required.

After that, with the annulus closed, without stopping the flow of the curable resin solution into the annular water circulation region, the inner tubing string is opened and cement grout is started.

The volume of the cured resin solution, after the sale of which it is necessary to begin the sale of cement mortar (V _c1 , m ³ ), is determined by the formula (1):

$${\text{V}}_{\text{c1}}=\text{k}\left[\pi {\text{(R}}_{\text{c}}^{\text{2}}-{\text{R}}_{\text{d}}^{\text{2}}{\text{) h}}_{\text{n}}{\text{m}}_{\text{n}}+\pi {\text{(R}}_{\text{c}}^{\text{2}}-{\text{R}}_{\text{d}}^{\text{2}}{\text{) h}}_{\text{at}}{\text{m}}_{\text{at}}+\text{0}\text{,5}\pi {\text{(R}}_{\text{d}}^{\text{2}}-{\text{R}}_{\text{to}}^{\text{2}}{\text{) (h}}_{\text{n}}+{\text{h}}_{\text{n}}+{\text{h}}_{\text{per}}\text{)}\right]\text{(one)}\text{,}$$

where k is the dilution factor of the curable resin solution with water in the tubing during its injection,

R _{with the} radius of the injection of resin into the oil reservoir, m,

R _d - well radius by bit, m,

R _in - radius of injection of resin into the aquifer, m,

h _n - the thickness of the oil reservoir, m,

m _n - the porosity of the oil reservoir,

h _in - the thickness of the aquifer, m,

m _in - the porosity of the aquifer,

R _{to the} outer radius of the casing, m,

h _per - thickness of the bridge between the productive and aquifers.

The first term in the formula determines the volume of the curable resin solution falling into the reservoir. The second term defines the volume of the cured resin solution that enters the aquifer. The third term defines the volume of the cured resin solution, which is necessary to isolate microcracks in the region of annular circulation of water. At the same time, the radius of resin injection into the oil reservoir cannot exceed the length of the perforations, since this will make it impossible to further develop the reservoir. In the case of using a hydrophobic agent, the coefficient k takes the value 1, when using water - more than 1, and can be calculated, for example, taking into account the formulas presented in [3]. The radii of injection of the cured resin solution into the productive and aquifer can be determined, for example, on the basis of a numerical experiment, as described in [4], or on the basis of the ratio of conductivities (product of permeability to thickness) of the productive and aquifer.

After the cement grout has been started, the flow rate of process fluids is controlled so that in the mixing zone under the tubing shoe the ratio of volumes of “cured resin solution: cement mortar” = 3: 1 is achieved. The cement-resin mortar is not able to penetrate into the porous medium, as a result of which, after filling large cracks, the pressure begins to increase.

The total volume of cement mortar (V _c , m ³ ) and the cured resin solution (V _c , m ³ ) are calculated according to formulas (2) and (3), respectively:

$${\text{V}}_{\text{c}}=[\text{0}\text{,5}\text{A.}\pi {\text{(R}}_{\text{d}}^{\text{2}}-{\text{R}}_{\text{to}}^{\text{2}}{\text{) (h}}_{\text{n}}+{\text{h}}_{\text{at}}+{\text{h}}_{\text{per}}\text{)}+\text{n}\pi {\text{R}}_{\text{P}}^{\text{2}}{\text{one}}_{\text{P}}+\text{A.}\pi {\text{R}}_{\text{0}}^{\text{2}}{\text{(h}}_{\text{n}}+\text{twenty)}+{\text{V}}_{\text{wed}}\text{]}\cdot \text{(one}-\text{W) (2)}\text{,}$$

$${\text{V}}_{\text{c}}={\text{V}}_{\text{c1}}+\text{W [0}\text{,5}\text{A.}\text{A.}\pi {\text{(R}}_{\text{d}}^{\text{2}}-{\text{R}}_{\text{to}}^{\text{2}}{\text{) (h}}_{\text{n}}+{\text{h}}_{\text{at}}+{\text{h}}_{\text{per}}\text{)}+\text{n}\pi {\text{R}}_{\text{P}}^{\text{2}}{\text{one}}_{\text{P}}+\pi {\text{R}}_{\text{0}}^{\text{2}}{\text{(h}}_{\text{n}}+\text{twenty)}+{\text{V}}_{\text{wed}}\text{] (3)}\text{,}$$

where n is the density of perforation, holes / m,

R _{p the} radius of the perforations, m,

l _p - the length of the perforations, m,

R ₀ is the inner radius of the casing, m,

V _cf - the volume of cut cement, m ³ ,

W is the volume fraction of the cured resin solution in the cement-resin solution, at which the maximum strength of the cement-resin stone is achieved.

Upon reaching the test pressure of the production casing, the forcing of the solutions with water or a hydrophobic agent ceases. Then, backwashing and lifting of the tubing is carried out 100-150 m above the interval of perforation of the oil reservoir and the well is left for the waiting period for the hardening of the cement stone.

Example

For example, we have a well in which geophysical studies have established the poor quality of the cement ring and the resulting annular circulation of the fluid. The interval to be isolated (perforation interval) is at a depth of 2500 m; its pick-up is 300 m ³ / day. Let R _d = 0.108 m; R _k = 0.084 m; R _s = 0.3 m; R _in = 0.3 m; h _n = 5 m; m _n = 0.2; h _in = 10 m; m _in = 0.2; h _lane = 10 m; n = 20 holes / m; R _p = 0.01 m; l _p = 0.5 m; R _o = 0.07 m.

We install the shoe of concentric tubing columns 50 m above the upper holes of the perforation interval of the reservoir. When the annulus is open, the cured solution of acetone-formaldehyde resin and cement mortar are brought to the tubing shoe. In this case, a curable solution of acetone-formaldehyde resin will be supplied through the outer tubing string, and cement mortar through the inner one.

We close the inner tubing string and the annulus. Through the outer tubing string, the curable acetone-formaldehyde resin solution will begin to be pressed into the annular circulation region with a hydrophobic agent under pressure. The volume of injection of the curable solution of acetone-formaldehyde resin into the annulus according to the formula (1) is 0.9 m ³ .

Without stopping the sales of the curable solution of acetone-formaldehyde resin to the annular circulation of water, we will open the inner tubing string and begin to sell cement. At the same time, the flow rate of process fluids is regulated in such a way that at the bottom in the mixing zone under the tubing shoe, the ratio of volumes of “cured resin: cement mortar” = 3: 1 is achieved. In this case, 0.6 m ^{3 of the} curable solution of acetone-formaldehyde resin (according to the formula (3)) and 0.2 m ^{3 of} cement solution (according to the formula (2)) will be pumped. The total volume of resin required for the well operation is 1.5 m ³ , cement mortar - 0.2 m ³ .

The cement-resin stone obtained after curing a mixture of a curable solution of acetone-formaldehyde resin and cement mortar will isolate large cracks in the cement ring, perforations and form a bridge in the wellbore. Moreover, its strength exceeds the strength of both cement and resin stones separately, which indicates the desirability of using this method to achieve effective isolation of the annular circulation interval.

Information sources

1. RF patent No. 23233325. The method of isolation of the absorption zone of the formation / Kryuchkov V.I., Ibragimov N.G., Khisamov R.S. and others // Publ. 04/27/2008

2. A.V. Sakhan, A.A. Chegodaeva, and V.V. Gorbunov. Remedial Cementing at High Temperatures (Case Study: Oilfields of Rosneft-StavropoIneftegaz). Paper SPE 135986 presented at the 2010 SPE Russian Oil & Gas Technical conference held in Moscow, Russia, 26-28 Oct. 2010.

3. Blazhevich V. A., Umrikhina E. N., Umetbaev V. G. Repair and insulation work in the operation of oil fields. M .: "Nedra", 1981. - 237 p.

4. Ilyasov A.M. Modeling the process of elimination of annular fluid circulation / A.M. Ilyasov, I.Yu. Lomakina, A.V. Kornilov [et al.] // OAO NPF Geofizika. Collection of articles by graduate students and young professionals. - Ufa: "NPF" Geophysics ", 2009. - Issue 6. - S.80-90.

Claims (3)

1. A method of repairing a well, comprising injecting a resin-cement mortar and a cement mortar into the isolation interval, characterized in that after preliminary injection of a acetone-formaldehyde resin cured resin solution into the annulus with a content of 40% by volume of a 10% NaOH solution as a hardener, simultaneous injection of the specified cured resin and cement mortar, and the range of ratios of the specified cured resin and cement, preferably 75:25 vol.%, at which m plugging stone strength higher than the strength of the cement or resin stone. 2. The method of repairing a well according to claim 1, characterized in that the injection is carried out through the tubing arrangement, which further includes a packer. 3. The method of repairing a well according to claim 1, characterized in that the simultaneous injection of a curable resin solution and cement mortar is carried out in two concentric tubing columns.