SU1257167A1 - Method of cementing holes with abnormally high formation pressures - Google Patents

Description

The invention relates to the drilling of wells, in particular, to methods for cementing wells with abnormally high formation pressures.

The aim of the invention is to increase the efficiency of cementing wells by decreasing the collation of the productive layers by the cement slurry filtrate, as well as improving the reliability of preventing the absorption of cement slurry and fluids from the wells.

The method is carried out as follows.

The cement slurry is prepared using conventional technology and pumped into the well. A sample of the solution is placed in a laboratory mixer and stirred during the entire process of cementing the well. At the moment of its termination, the solution from the mixer is poured into the device for measuring the static shear stress (SNA) of the solution and the change of this characteristic with time is observed. Since the decrease in the hydrostatic dip of the cement slurry occurs due to the growth of its SNS, then at the moment when the SNS reaches a certain value of 0, at which the clogging of the productive pressure is fixed, the gradient of the reservoir and pore pressure of the basal solution in the well is not equal and possible inflow of formation fluid in the annular space of the ScBA; “the inlet at the mouth begins to create pressure using cementing units.

In this case, 0, calculated by the formula

, 25g (d, - dj) {rso5f p, Kd), (1)

where d. n r1,

P and External and inner diameter of the annular space, m; density of cement slurry and its liquid phase kg / m Cf - the angle of inclination of the axis of the well to the vertical, degrees

Kd is the reservoir pressure anomaly coefficient {

g 9,81 M / S ,. The rate of increase of daEjfCHHH in the annulus is set in proportion to the growth rate of the SNS solution in accordance with the for.

reservoir by filtrate of grouting bed. Otherwise (if the pressure is created from the moment hydrastatics of the cement slurry is reduced 35, the filtrate of the cement slurry will not be avoided to enter the reservoir, since the pressure generated will correspond to the initial hydrostatics of the cement slurry 40, which in turn is assumed to be prevented above the reservoir by the registered value. I

If the threshold pressure of the cement slurry is equal to the pressure pressure, the danger of the pressure problem is eliminated due to the occurrence of this moment of shear stresses at the contacts of the wellbore and the column, which is (1 time with the threshold pressure imeM of the cement slurry).

An example (implementation of the proposed method)

During drilling, the formation with anomalously high reservoir pressure was opened at depths (K4 1 bore diameter d, 0.216 n, dia

45

50

5s

V ai

(2)

and a

s

0

five

where V is the optimum rate of pressure increase in the annulus. Pa / min; growth rate of SNS suspension, Pa / Min;

coefficient of proportionality, calculated by the formula-e-1; 9T- 1 where L is the distance from the wellhead to the roof of the high-pressure formation, m;

9.- SNS tampon solution, in which the entire solid phase of it freezes on the walls of the well and the process of reducing the pore pressure is stopped, Pa; & J calculated by the formula

, 25g. (D (- dgXpcoscf-p,) (4) When the SNS of the solution reaches the value of 2, the pressure increase in the annulus stops.

After the RPT time, the pressure in the annulus is relieved.

With such a set of operations (optimal time to create pressure in the annulus), the clogging of the productive

reservoir filtrate cement slurry. Otherwise (if the pressure is created from the moment of hydration of the cement slurry), the filtrate of the cement slurry will inevitably flow into the reservoir, since the pressure created will correspond to the initial hydrostatics of the cement slurry, which, in turn, is assumed to prevent formation of regulated value. I

If the threshold pressure of the cement slurry is equal to the reservoir pressure, the danger of fluid pressure is eliminated due to the appearance at this point of the pressure of the cement slurry at its contacts with the wellbore machines and the column, which is (I, 1, is measured with the threshold pressure imeM of the cement slurry.

Example (implementation of the proposed method)

During drilling, fermentation at depths in m was opened by a formation with abnormally high formation pressure (K4 1.65), borehole diameter d, 0.216 n, diameter

the casing lowered into it, 168 m. The angle of deviation of the well from the vertical cf 0. The well is cemented to the mouth with a cement slurry with a density of 2100 kg / m, which is shut on a brine with density r, 1180 kg / m. The values of b, and b for these data, calculated by formulas (1) and (4), are 18 and 108 Pa, respectively. The coefficient of proportionality is co-linear (3), 710.

after reaching a value of 8f, in the first 30 minutes at a speed of 0.7, therefore, the rate of pressure in the annulus was set equal to

V, 1 ,,, 2-10 Pa / min, In the future, the SNS increased at a speed of 1.6 Pa / min. The corresponding speed is optimal.

Order 4888/24. Circulation 548 Subscription

VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

Production and printing company, Uzhgorod, Projecto st., 4

pressure at the mouth is equal to

V ,, 1,, 7. 10 Pa / min. The duration of the pressure increase at such a rate, c (90-0.7.30) / 1,, 5 min,

and the final pressure set in the annular space for the period of FPZH is equal to

, 210 30 + 2.7-10 42.5

14.1 MPa.

The combination of features of the proposed invention allows, on the one hand, to avoid a premature and excessive increase in pressure on

reservoir and, thus, eliminate the risk of its fracturing, and on the other - reliably prevent the inflow of formation fluid into the well in hardening cement slurry, exclude

the formation of vertical channels in it through which inter-layer flows occur.

Compiled by V. Grishanon

Tehred M. Khodanich Proofreader A.Obruchar

Claims (1)

METHOD FOR CEMENTING WELLS WITH ABNORMALLY HIGH LAYER PRESSURES, including filing cement slurry into the annulus, creating excess pressure at the wellhead in the annulus before embracing the grouting fluid and increasing the excess pressure at a design speed, characterized in that, in order to increase cementing efficiency by reducing the mudding of productive formations by the filtrate of the cement slurry, as well as increasing the reliability of preventing the absorption of t mponazhnogo solution and flyuidoproyavleny from wells positive pressure in annular space creates a moment equality between the threshold pressure gradient of cement slurry in the borehole and formation pressure gradient, and the velocity V of increasing overpressure at the wellhead is determined from the following expression: V = lpgu Kj_ _z j. θα-β, where L is the distance from the wellhead to the formation roof with an abnormally high formation pressure, m; 0 - the density of the liquid phase there ¹ I 3 ponazhnogo mortar, kg / m To _d - coefficient of anomalous reservoir pressure; U is the growth rate of the static shear stress of the cement slurry, Pa / min; Θ, is the static shear stress of the cement slurry, at which the equality of the gradient of the pore pressure of the cement slurry in the well to the formation pressure, Pa; . - the static shear stress of the cement slurry, at which its entire solid phase hangs on the walls of the well, Pa; g is the acceleration of gravity (g = 9.81 m / s ² ). S. SU 1257167 — A f