RU2345212C1 - Casting method of cementing - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: casting method of cementing consists in gasified cement injection in casing pipe, two-stage squeezing into hole clearance considering gasified cement degassing while it is activated in borehole cavity, as well as considering gasified cement compressibility in thermobaric borehole environment. Improved gasified cement-bond in borehole is ensured by defect breakdown at the first stage of structure formation (activation) of gasified cement suspension owing to staged squeezing of gasified cement considering its stability.

EFFECT: improved gasified cement-bond in borehole.

3 dwg

Description

The invention relates to the construction of oil, gas and exploratory wells, in particular, to methods for cementing them with carbonated grouting mortars.

A known method of cementing casing strings [and.with. 1723308 SU, IPC ⁵ Е21В 33/14, publ. 03/30/92], which consists in increasing the reliability of the process by providing stepwise removal of the hydrostatic pressure of the liquid column behind the casing. In the waiting period for cement hardening, hydraulic communication is maintained through the bottom of the annular and pipe spaces with each other, and the column height of the next part of the grout is limited by the permissible external pressure on the casing.

A known method of cementing casing strings [and.with. 1454953 SU, IPC ⁴ Е21В 33/14, publ. 01/30/89], which consists in the fact that in order to reduce the intensity of absorption of the cement mortar by the absorbing formations, the injection of the buffer fluid and the cement slurry is carried out with a back pressure at the wellhead that is not less than the formation absorption pressure, but less than the hydraulic fracturing pressure, and during cement grouting counterpressure at the mouth is discharged in accordance with the rate of growth of the bursting pressure.

A known method of cementing casing strings [and.with. 1707185 SU, IPC ⁵ Е21В 33/14, publ. 01/23/92], which consists in the fact that in order to improve the quality of cementing by preventing degassing and ensuring that the carbonated cement slurry rises to the wellhead, a pressure of at least 2 MPa is created in the process of forcing and setting carbonated cement slurry at the wellhead.

The reasons that impede the achievement of the claimed technical result of these known analogues are the creation in the annular space of excessive pressure, causing absorption in horizons with abnormally low reservoir pressures. In the process of creating a back pressure at the wellhead of at least 2 MPa and more in the initial period of forcing a carbonated solution, there are complications associated with the low compressibility of the foam (carbonated composition), which can lead to hydraulic fracturing, under-rise to the design height of the cement slurry.

The problem to which the invention is directed is the development of a method for cementing a well with aerated cement slurries.

In the implementation of the invention, the task is solved by achieving a technical result, which consists in improving the quality of cementing by destroying a defective structure in the first stage of structure formation (activation) of aerated grouting slurry by stagewise forcing aerated grouting mortar taking into account its stability.

The specified technical result is achieved in two stages. At the first stage, buffer fluid, aerated cement slurry are pumped and pressed to the design height. At the second stage, the process is stopped at the time of the first phase of structure formation of aerated cement slurry, and the end of the process of bursting, taking into account the degassing of aerated cement slurry during the time of the first phase of structure formation.

According to I.G. Grankovsky, there are 4 stages of structure formation. At the first stage, colloidal particles coagulate, forming a spatial framework of the coagulation structure, with clinker particles covered with hydrated neoplasms. The contracture reaches its maximum value, as a result, the structure is weak, which with development leads to a loss of strength. At this point, it is advisable to apply mechanical action.

In turn, aerated cement slurry is characterized by stability, that is, the lifetime ("life") of a certain volume of it. Based on this, the volume of aerated cement slurry V injected into the well should be calculated taking into account its stability:

where V ^I is the volume of aerated cement slurry at the end of the first injection phase, m ³ ;

φ is the stability of aerated cement slurry,%.

The stability of aerated grouting mixture is determined from the following expression (Tikhomirov V.K. Pena. Theory and practice of production and destruction. M: Chemistry. 1983):

where V ^I and V ^II are the volumes of the carbonated suspension at the time of the end of the first injection stage T ₁ (min) and the beginning of the second injection stage T ₂ (min), corresponding to the end of the first stage of structure formation of the carbonated grouting mixture.

The beginning of the second stage of injection of T ₂ , corresponding to the end of the first stage of structure formation of carbonated grouting mixture. The stability of the carbonated suspension φ for this time is determined in laboratory conditions, taking into account the thermobaric conditions at the bottom of the well.

Example.

It is required to calculate the volume V required for cementing a well with a volume of cemented space V ^I = 160 m ^{3 with} aerated cement slurry with a stability of φ = 98%.

As a result of calculations by expression (1), the volume V of aerated cement slurry for cementing a well will be 163.2 m ³ .

The essence of the invention lies in the fact that in the process of forcing a carbonated grouting mortar in a volume greater than necessary by an amount inverse to the stability of aerated grouting slurry, the process of forcing for a while is stopped:

where T ₁ is the end time of the first stage, min;

T ₂ - time of the first stage of structure formation of aerated cement slurry taking into account thermobaric (well) conditions, min

That is, the process of forcing a carbonated cement slurry is accompanied by its activation directly in the cemented well.

The method includes a number of technological operations associated with the activation and lifting of aerated cement slurry to the design level (punching) after activation (the first stage of structure formation).

The method is illustrated by drawings, where figure 1 shows the distribution of process fluids at the end of the first stage T _{1 of} the cementing process of the well with aerated cement slurry. The numbers indicate: 1 - casing string, 2 - cementing plug, 3 - “stop ring”, 4 - casing shoe, 5 - carbonated grouting fluid, 6 - squeezing fluid, 7 - design elevation height of carbonated grouting grout.

Figure 2 presents a diagram of the distribution of levels of carbonated grout, squeezing and buffer fluids in the casing and annulus for a period of time corresponding to T ₂ . The numbers indicate: 1 - casing string, 2 - cementing plug, 3 - “stop ring”, 4 - casing shoe, 5 - carbonated grouting fluid, 6 - squeezing fluid, 7 - design height of carbonated grouting mortar, 8 - level carbonated cement slurry at time T ₂ .

Figure 3 presents the process of forcing aerated cement slurry before the cementing plug is placed on the "stop ring". The numbers indicate: 1 - casing string, 2 - cementing plug, 3 - “stop ring”, 4 - casing shoe, 5 - carbonated grout, 6 - squeeze fluid, 7 - design elevation height of carbonated grout.

The method of cementing wells is as follows. The first stage: Initially, buffer fluid, carbonated grouting mortar 5, squeezing fluid 6 are pumped into the casing 1 and pressed into the annulus to the design height 7 (FIG. 1). The volume of carbonated grouting mortar 5 is determined by the expression (1). The volume of carbonated grouting mortar 5, located between the cementing plug 2 and the “stop ring” 3, is determined from the condition of multiplicity, compressibility with stability φ, which depends on the type of surfactant used, as well as degassing (foam destruction) for time T ₂ . In the process of forcing, the cement plug 2 is at a certain distance from the “stop ring” 3.

The second stage: It includes stopping the forcing process for a time T and resuming forcing after a given time interval T. The time interval T is determined by expression (3) for each individual well, taking into account the influence of thermobaric factors and the brand of grouting Portland cement, for example, either experimentally or in laboratory conditions or experimentally.

The application of the proposed method improves the quality of cementing a well with aerated cement slurry due to the activation of aerated cement slurry in the well, which increases the strength obtained by hardening the stone, and compensates for the effect of the sedimentation of foam in the upper intervals.

Claims (1)

A method of cementing a well, including pumping a buffer fluid, aerated cement slurry into the casing, forcing a carbonated grout into the annulus, characterized in that the volume of aerated cement slurry V injected into the well, taking into account its stability, is determined from the expression:

where V ^I is the volume of aerated cement slurry at the end of the first injection phase, m ³ ;
φ is the stability of aerated cement slurry,%,
and the process of punching is carried out taking into account the degassing of aerated cement slurry during its activation in the well and with a temporary stop
T = T ₂ -T ₁ ,
where T ₁ is the end time of the first stage, min;
T ₂ - time of the first stage of structure formation of aerated cement slurry taking into account thermobaric (well) conditions, min

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