SU1745883A1 - Method for isolation of lost-circulation zones - Google Patents

Description

R

Qo Kn p Rizb, GK

where Kn is the initial injectivity coefficient of the formation (before carrying out the isolation works). m3 / h-MPa;

PH is the pressing pressure of the entire formation before the insulation works during the injection of fluid into the formation with the flow rate Oz m3 / h;

Рк is the planned final pressing pressure of the entire formation at the final stage of injection of the mixture into the formation with the flow rate Oz, m3 / h.

Rieb excess pressure that occurs in the roof of the reservoir due to the additional resistance, MPa.

In addition, a separation plug is used as an additional resistance in the method of isolating the mud absorption zones. The preliminarily created additional resistance K is the final value of the coefficient of injectivity of the formation, at which the reliability of the insulation is ensured.

Interconnection of initial hydrodynamics-. the reservoir characteristic, the injectivity coefficient K (before the insulation works) and its final value (Kk) after isolation, is determined from the expression:

v - ° s

Knr

03 Kn Ph.

(3)

where PH is the pressing pressure of the entire formation before the insulation works during the injection of fluid into the formation with the flow rate Oz:

Solving equation (2) with respect to Oz and equating the corresponding parts (2) and (3), we get:

W

Put in (1) the value of PK from (2) and replacements of QC from (4), we obtain:

Rieb - gg y

GN KN

(five)

Pk

From- (2), (3) it can be seen that the ratio -k- to

 H

Formula (5) and KN are constant values with respect to a particular formation at various flow rates of fluid injection into the formation.

Hence, relation (5) is a function of two variables Q and Rizb, where Rhizb is determined mainly by the principle of operation and the design features of the movable separation plug, which are predetermined and determined by the conditions in the well and the of the work. An independent variable, a variation of which the proposed method can be implemented, is the consumption of the cement mix Qo, under which condition (1) is fulfilled.

Hence, relation (5) is written in the following form:

Salt plug installed in the roof of the absorbing reservoir. Designs of mobile dividing traffic jams can be various. Consider, for example, a variant of the proposed method using a self-sealing pop-up separating plug. In this case, an overpressure (Rhizb) is created due to lifting (archimedean) force. To create a Rizb, it is necessary that the average density of the entire plug is less than the density of the fluid that fills the well.

For a popup plug, we define a Reese:

Р r Gapx-Gn Yn (yR-Yn) ieb SCKB 0.785-DcW

0.785 -dn -InCyp-yn) 0.785 DCKB

taking dn DCKB we get:

 ur -up), (7)

PH-R "P7

(6)

where Rizb is the overpressure arising in the roof of the formation due to the additional resistance.

Thus, the fulfillment of relation (6) makes it possible to set such a mode of injection of the mixture into the reservoir, at which the near-bottom part of the reservoir is filled to a certain depth, at which reliable insulation is achieved.

Similar technical solutions were not found by the authors. Therefore, this solution has significant differences.

The method is carried out as follows.

After opening the absorbing formation, hydrodynamic studies are carried out to determine its characteristics, i.e. the initial value of the coefficient of injectivity, K, as well as determining the type of cement mixture (depending on K) for the upcoming insulation works, and depending on the properties of the mixture, the values of Pk and Oz are determined (pressure testing mode). After that, a device 2 is lowered into the well on the drill pipe 1 to seal the annular space, for example, a hydro mechanical packer and a separation plug 3 (FIG. 1). Separately Gapx - the mass of a liquid, is equal to the volume of the plug;

dn. In, Vn, ynpn - diameter, length, volume, density and mass of the tube, respectively;

ur is the density of the fluid in the well;

SCKB, DCKB are, respectively, the cross-sectional area of the well and the diameter. Substituting the RIZb value from (7) to (6), the flow rate Qo.c is calculated with which the injected mixture is injected into the reservoir:

  | Ј Chick-up), (8)

After the descent and installation of the plug in the roof of the reservoir (Fig. 2), the unpacking of the hydromechanical packer 2 is performed and the preparation and injection of the grouting mixture into the pipe string is started. Upon reaching the lower boundary of the mixture of the movable separation plug 3 located in the roof of the reservoir, the consumption of the grouting mixture O0 is set in accordance with (8). At the same time, the plug 3 is lowered, opening the upper permeable part of the reservoir into which the mixture begins to flow. As the open part of the reservoir is filled with the mixture, the injection pressure increases with clogging of the permeable rock and increasing the resistance to movement of the mixture through the reservoir. When the injection pressure of the mixture into the reservoir reaches the Rhizb value in accordance with (1), the pop-up plug drops even lower, opening the next, uninsulated part of the reservoir, into which the mixture begins to flow.

In this way, the entire formation is insulated from the top to the bottom. Moreover, the reservoir is filled in each part with a cementing substance to obtain the required technological pressure Pk, i.e. to a predetermined depth, which ensures reliable isolation of the reservoir. This eliminates the preferential filling of the plantar part.

The moment of termination of the injection of the mixture into the reservoir is controlled by increasing the pressure of the injection of the mixture into the reservoir by 5-10% compared with Pk, as well as by the calculated (planned) volume of the mixture.

At the end of the run, the tubing string with the packer is lifted out of the well, the RFQ is maintained (waiting for cement to harden), then the cement bridge formed in the well is drilled and the formation is tested for injectivity to assess the reliability of the insulation.

An example implementation of the method.

When drilling a well with a diameter of 215.9 mm in the Namursky deposits in the range of 850-870 m, a complete absorption zone was encountered. According to the results of hydrodynamic studies, the injectivity coefficient of the formation was m3 / h MPa.

A cork made of lightweight material with a density of 500 kg / m and a length of 10 m and a diameter of 205 mm can be used as a separation plug. In the upper part of the cork there are rubber sealing cuffs with an outer diameter of 216 mm.

A grouting mixture based on 10 tons of cement with additives of up to 5% of large-sized fillers and 10% of bentonite was prepared to eliminate absorption. For this type of mixture and the initial injectivity of the formation, m3 / h. MPa), the MPa at m3 / h satisfies the insulation reliability criterion. According to research data at m3 / h, 1 MPa.

According to formula (8), we determine the flow rate of the plug-in mixture Q0 when it is injected into the reservoir, which should be at least 0.5 me / h.

  ()

0.1

 10 150 - 10 (1500 - 500) 0.5 MJ / M

where 10 is the conversion factor that takes into account the dimensions of the quantities in the formula (8). The density of the fluid (ur). in which there is a plug, in the calculation it was assumed to be equal to the density of the drilling fluid, which filled the well.

The technological process is carried out as follows.

A separation plug is lowered into the well and delivered to the top of the reservoir.

by pushing a drill pipe along the well, on the end of which a hydromechanical packer is installed.

After that, the column of pipes with a packer lifts and packs the packer on

a depth of 800 m. Then proceed to the preparation and injection of the cement mixture into the pipes. As the mixture is injected, the displaced drilling fluid in the pipe string and sub-packer zone is absorbed by the upper part of the reservoir to be isolated. At the same time, the traffic jam was just below the roof, i.e. This process is carried out at a pressure less than Pk. After approaching the cement mixture to the roof of the reservoir, the mode of its injection, i.e., the flow rate, was established in accordance with the calculation, i.e. at the level of 4 m / h. which satisfies the calculation condition. After pumping out the estimated volume of the squeezing fluid, the injection pressure rises to 3.5 MPa, which serves as a signal for the end of the isolation process. A string of drill pipe with a packer is lifted out of the well and, after a time delay, RFQ is drilled out a cement bridge in

an interval of 820-880 m. Absorption is liquidated.

The technical and economic advantages of the described method of isolating the mud absorption zones in comparison with the known method are in reducing the consumption of cement materials and the time of the insulation work. These advantages are achieved by successively filling the absorbing layer from the roof to the sole with a cement material and eliminating the need for additional insulation work.

Claims (1)

Invention Formula The method of isolating the mud absorption zones, including the lowering of the casting pipes and the injection of the cement mix into the reservoir, characterized in that, in order to increase the efficiency of the insulation work by sequentially filling the 4 absorbing reservoir with a cement mix, starting from its roof to the foot, additional resistance is created of the injected cement mix by placing the absorbing reservoir in the roof , while the flow rate of the injected mixture is determined by the ratio: Qo Kn Rieb. . GK G. T 0 where Кn is the initial injectivity coefficient of the formation (before carrying out the isolation works), m3 / h-MPa; PH is the pressing pressure (MPa) of the entire formation before the insulation works during the injection of fluid into the formation with the flow rate Oz m3 / h; Рк - the planned final pressing pressure (MPa) of the entire formation at the final stage of injection of the mixture into the formation with the flow rate Oz m3 / h; Hub-overpressure that occurs in the roof of the reservoir due to excessive resistance, MPa.