RU2010949C1 - Method of cementing wells - Google Patents

Abstract

FIELD: well operation. SUBSTANCE: oil-well slurry is pumped into well. Then a binary system in the form of fluid-and-gas mixture is pumped into well. After pumping fluid and gas into well, oil-well slurry is squeezed into formation. Then gas is bled off at wellhead with a prerequisite that well pressure obtained not exceed formation pressure. Then squeezing/bleeding-off cycle is repeated, the number of cycles n being chosen from relationship 2≅ n≅ 5. EFFECT: efficiency of well cementing increased due to improved completeness of filling lost-circulation formation pore channels.

Description

 The invention relates to the field of drilling deep wells, in particular to methods for cementing them.

 A known method of cementing wells using casting pipes, the implementation of which provides the condition of pressure equilibrium in the well-formation system.

 The disadvantage of this method is the inevitability of imbalance in the pressure in the well-formation system when flushing pipes before they rise (increase pressure in the well) and rise (decrease). Moreover, the process of imbalance is uncontrollable.

 The closest technical solution is a method of cementing wells, including the injection and sale of plugging mixture into the absorbing layer with a two-component system - liquid and gas.

 The disadvantage of this method is the use of reverse circulation, and a two-component system is used to prevent cement from entering the absorbing layer.

 The aim of the invention is to increase the efficiency of the cementing method by increasing the completeness of filling the pore channels of the absorbing layers.

The goal is achieved by the fact that in the known method of cementing wells, which includes injecting a plugging mixture and a two-component system in the form of a liquid and gas, after injecting the liquid and gas into the well, the plugging mixture is pushed into the formation, the gas is vented to the wellhead from the condition of obtaining pressure in the well has no more than reservoir pressure, after which the squeeze-bleed cycle is repeated, and the number of cycles (n) is taken from the condition:
2 ≅ n ≅ 5
For successful isolation of the absorbing layer, it is necessary that two conditions are met: 1) P _c = P _p ; 2) ρ _t gh = ρ _p gh = ρ _t = ρ _p where P _s is the pressure in the well against the absorbing formation; R _p - pressure in the absorbing layer (decide on the roof or on the bottom of the formation); ρ _t - the density of the cement slurry, which is used to fill the absorption zone; ρ _p - the density of the reservoir fluid in the occurrence of the absorbing reservoir; g is the acceleration of gravity; h is the thickness of the reservoir.

The second condition must be observed to prevent the negative impact of gravitational forces on the distribution of cement slurry over the thickness of the absorbing layer. In the above-described method for eliminating absorption, this is not taken into account and, as a rule, ρ _t > ρ _p .

Selling the calculated portion of the plugging mixture into the absorption zone is carried out by the main column of fluids having different densities. The density of the fluids is selected so that at the end of the sale of the plugging mixture into the absorption zone, the condition P _c = P _p or
P _c = ρ ₁ ˙gh ₁ + ρ _Z g (Hh ₁ ), P _p =
= ρ _n g (Hh _c ) and ρ ₁ gh ₁ +
+ ρ _Z g (Hh ₁ ) = ρ _п g (Hh _c ) (3) where ρ _{1 and} h ₁ are the density and height of the column of one fluid; ρ _z is the density of another fluid; N is the depth of the absorbing layer; ρ _p is the density of the reservoir fluid; h _c is the static fluid level of the absorbing formation.

Condition (3) can be written in the following form:
P _y + ρ ₁ gh ₁ + ρ _z g (Hh ₁ ) =
= ρ _n g (Hh _c ), (4)
where P _y is the pressure at the wellhead.

 The amount of fluids for sale can be taken and more, for example, if you include a buffer fluid, etc.

The fulfillment of condition (2) allows isolating karst voids. In karst voids and in permeable formations, there is a directed movement of fluids, which can lead to the movement of cement slurry in the direction of the moving flow from the bottomhole (near-well) zone of the well of the absorbing formation. In order to avoid this, it is proposed that the back-and-forth movement of the grouting mixture be carried out in the bottom-hole zone of the absorbing formation, i.e., the formation should be isolated at Р _с ≥ Р _p (4) and Р _с ≅ Р _п (5). The reciprocating movement of the plugging mixture will provide a more complete filling of the pore channels of the absorbing layer.

 The number of cycles N of the reciprocating motion 2 <N <5 is chosen from the physicochemical properties of the plugging mixture and the filling conditions of the pore channels. The lower limit is from the condition of filling the pore channels, the upper limit is from the physicochemical properties of the mixture and the time of the absorption elimination process (process technology). An increase in the viscosity of the cement slurry and a reduction in the time of its setting also lead to a decrease in the quality of insulation of the absorbing layer.

Filling of the absorption zone can be carried out both through a drilling tool, and directly into the wellbore without a drilling tool, both with and without a packer. It is possible to fill in the annular space between the drill pipes and the walls of the borehole. In cases where the absorption zone is poured without a drilling tool and into the annular space, the pressure in the well P _s will be less than when pouring through drill pipes with an open end by the amount of hydrodynamic pressure that occurs when the fluid system moves along the barrel or annular space, which must be taken into account in the calculations then for a two-component column P _c = ρ ₁ dh ₁ + ρ ₂ d (Hh ₁ ) -ΔP _d + P _d where ΔP _d is the hydrodynamic pressure during fluid movement.

With known R _p and P _y it is easy to fulfill conditions (4) and (5) to ensure reciprocating motion of the plugging mixture.

PRI me R. Initial conditions: complete flushing fluid withdrawal, static level h _c = 100 m, flushing fluid - industrial water, ρ ₁ = 1000 kgm ^-3 , the roof of the absorbing layer is 1100 m, the sole is 1106 m, the bottom is 1115 m.

1. Determine the reservoir pressure along the roof of the absorbing layer ρ _p = 1000 kgm ^-3 .

P _p = ρ _p ˙g˙ (Hh _c ) =
= 1000 x 9.8 (1100 - 100) =
= 9.8 x 10 ⁶ Pa = 9.8 MPa.

2. Determine the volume of cement mixture to isolate the absorption zone
V = V ₁ + V ₂ = 0.785 ˙ D ² ˙ h +
+ 0.785 ˙ D ₁ ² ˙ h _p ˙ m =
= 0.785 x 0.22 ² x 10.0 +
+0.785 x 1.0 ² x 6.0 x 0.5 = 2.73 m ³ , where V ₁ is the volume to fill the well; V ₂ - volume to fill the pore space; D is the diameter of the well; h - fill height in the well; D ₁ - the diameter of the filled borehole space in the absorbing formation; h _p - the thickness of the absorbing layer; m is its porosity.

Take V = 3.0 m ³ .

3. Determine the height of the column of the cement mixture in the well during pumping
h ₁ = V ˙ (0.785˙ D ² ) ^-1 =
= 3.0 x (0.785 x 0.22 ² ) ^-1 = 78.4 m.

Take the density of the cement mixture ρ _cm = 1800 kgm ^-3 .

4. Then, after injection of the mixture, the static level in the well will be established
h _c3 = h _c + h ₁ ˙ (ρ _cm -ρ _n ) x 10 ^-3 =
= 100 + 78.4 (1800 - 1000) x 10 ^-3 = 162.8 m.

5. Determine the volume of air for selling the mixture P˙V = P ₁ ˙V ₁ ; V = P _{1 1} ˙V ˙P ^-1 (ideal gas), where PV - the pressure and volume of gas at normal conditions, P = 0.1 MPa; P ₁ x V ₁ - pressure and volume of gas during the sale; P ₁ = 9.8 MPa, V ₁ = 0.785 x D ² x 1020 + Δ V = = 0.785 x 0.22 ² x 1020 + 0.5 = 41.92 42 m ³ , Δ V is the volume of gas in the piping line .

For the operation, the compressor UPK-80 is chosen, the working pressure is maximum 8 MPa, productivity 6.0 nm ³ min ^-1 .

According to the characteristic, the selected compressor cannot provide the set pressure. Then casting technique carried out as follows: the mixture was injected plugging in the desired amount, then it is forced by the compressor to a pressure of 8.0 MPa, then pumped at constant pressure calculated amount of process water, which is determined by V _in = D ² 0.785 x ˙ h _2, where h ₂ = (P _p - P _k ) (ρg) ^-1 = (9.8 -8.0) x (1000 x 9.8) ^-1 x 10 ⁶ = 176.4 m; V _in = = 0.785 x 0.22 ² x 176.4 = 6.7 m ³ .

Having pumped 6.7 m ^{3 of} water, proceed to the reciprocating movement of the grouting mixture.

Upon reaching the time t = T _n (the beginning of setting the grouting mixture), replacing the air with water, bring P _y = 0 ⁺ . Thus, it is possible to eliminate the absorption zone without the use of a drill string and the use of a compressor having a maximum working pressure less than the reservoir pressure of the absorbing formation.

 The proposed method can eliminate any absorption by choosing the right plugging solution (viscosity, density, dispersion, setting time) and the technology of pouring in any pore medium. The same method can be used to install cement bridges during well abandonment.

 A method for eliminating the absorption zones and installing cement bridges with the sale of plugging mortar with a multicomponent fluid with the reciprocating movement of the cement slurry in the near-well zone of the absorbing layer is proposed.

Claims (1)

 METHOD FOR CEMENTING WELLS, which includes injecting a plugging mixture and a two-component system in the form of a liquid and gas into the well, characterized in that, in order to increase the efficiency of the method by increasing the completeness of the pore channels of the absorbing layers, the plugging mixture is forced into the well after pumping the liquid and gas into the formation, then the gas is vented at the wellhead from the condition of obtaining pressure in the well of not more than the reservoir pressure, after which the cycle of squeezing and bleeding is repeated, while t he n cycles is received from the condition 2 ≅ n ≅ 5.