RU2188302C2 - Method of well stage cementing under conditions of abnormally low formation pressures in lost circulation zone - Google Patents

Abstract

FIELD: construction of oil and gas wells. SUBSTANCE: method includes installation of stage cementing collar above roof of lost-circulation formation; injection of spacer fluid, portion of nonaerated cement slurry; forcing of cement slurry by displacing fluid; pumping of low-density fluid to annular space during forcing of cement slurry; mounting of cementing head with lower and upper separating plugs and locking member after installation of stage cementing collar. After injection of spacer fluid, lower part of casing is cemented, above lost circulation zone, by lowering of lower separating plug. Cement slurry is forced by displacing fluid with upper separating plug. After that, locking member is dropped with subsequent washing out of excessive cement slurry. After setting of cement slurry, upper part of casing is cemented through stage cementing collar. Portion of nonaerated cement slurry is injected in amount ensuring filling of annular space in interval from foot of lost circulation formation to stage cementing collar. Subsequent additional portion of cement slurry in amount ensuring filling of annular space from shoe of casing to foot of lost circulation formation is aerated during injection by increasing aeration degree within rage calculated by formulas. Density of aerated cement slurry in well, kg/cu.m is determined by formula. Low-density fluid is used in the form of two-phase foam with aeration degree calculated by formula. Two-phase foam density, kg/cu.m is determined by formula. Consumption of two-phase foam is determined from inequality. Nonaerated cement slurry is used in the form of the following composition, wt.p.p: oil-well portland cement, 100; superplasticizer, 0.9-1.5; polyvinyl alcohol, 0.5-1.0; sulfonol, 0.4-1.0; water, 35. Two-phase foam is used in the form of foaming fluid of the following composition, wt. p. p: aqueous solution of calcium chloride, ρ-1120 kg/cu.m, 100; commercial lignosulfonate, 0.7-1.0. EFFECT: higher efficiency of cementing process. 3 cl

Description

 The invention relates to the field of construction of oil and gas wells.

Analysis of the existing technical level showed the following:
A method of stepwise cementing of a well in the absorption zone is known, according to which the latter is isolated by cementing the lower stage according to traditional technology: a step cementing clutch (MSC) is installed above the absorbing layer, and a non-aerated cement mortar is pumped to the location of the coupling (see A.S. 926240 from 9.06 .80 according to class E 21 B 33/14, published in OB 17, 1982).

The disadvantage of this method is the inefficiency of the cementing process:
- a high probability of absorption of cement mortar below the MSC, leading to disruption of the continuity of the cement ring;
- the appearance of annular gas flows arising during the waiting period for the solidification of the cement slurry (OZZ) with a decrease in the active pressure on the formation with cement slurry;
as a prototype, we took a method of stepwise cementing of a well under conditions of abnormally low formation pressure in the absorption zone, by which MSCs are installed above the roof of the absorbing layer, buffer fluid is pumped, a portion of unaerated cement mortar is pressed through with cement with squeezed fluid, and pumped into the cement mortar annular space low-density fluid - technical water (see. Thesis in the form of a scientific report for the degree of doctor Technical Sciences "Improving the reliability of technological processes and the quality of well completion", applicant: Gnoev AN, 05/15/2000, location - library of NPO Bureniye, Krasnodar, 34 Mira St., p. 44, 45. attached to the application materials).

The disadvantage of this method is the inefficiency of the cementing process:
- create back pressure using technical water, which leads to a sharp increase in the zone of mixing the cement mortar with the latter, increases the likelihood of absorption, does not provide clogging of the absorbing layer and reduces the quality of the formed cement ring;
- receive a shortage of cement mortar to the MSC, which leads to disruption of the continuity of the cement ring and increases the likelihood of intercolumn flows of formation fluids;
- the use of non-aerated cement mortar does not ensure the non-shrinkage of the cement stone, which does not exclude gas and oil flows in the period of water treatment.

The technical result that can be obtained by implementing the invention is reduced to the following:
increases the efficiency of the cementing process due to:
- creating backpressure at the moment the cement slurry enters the annular space with a smaller volume of low density fluid (foam) with simultaneous colmatization of the absorption zones;
- reducing the likelihood of water hammer formation in the well, leading to a gap in the continuity of the cement ring and hydraulic fracturing of the absorbing formation;
- the creation of backpressure to reservoir pressure during the period of the bcc in the lower part of the casing due to the pore pressure of the gas aerated cement mortar;
- ensuring the quality of the cement ring in the interval of placement of the aerated cement mortar due to the lack of its deaeration, and obtaining a non-shrinking cement stone.

где α_{цp min} - минимальная степень аэрации закачиваемого цементного раствора на устье скважины;
α_{цp max} - максимальная степень аэрации закачиваемого цементного раствора на устье скважины;
ρ_цр - плотность неаэрированного цементного раствора, кг/м³;
ρ_o - минимально необходимая плотность аэрированного цементного раствора в скважине, кг/м³, определяемая по формуле

где Р_пл - пластовое давление, МПа;
g - ускорение свободного падения, м/с²;
ρ_p - плотность промывочной жидкости за эксплуатационной обсадной колонной выше муфты ступенчатого цементирования, кг/м³;
Н - глубина установки муфты ступенчатого цементирования, м;
Н_п - уровень подошвы поглощающего пласта, м;
L - глубина спуска цементируемой эксплуатационной обсадной колонны, м;
К - коэффициент растворимости воздуха в жидкости при атмосферном давлении;
P₀ - атмосферное давление, МПа;
Z, Z₀ - коэффициенты сверхсжимаемости газа в интервале от башмака эксплуатационной обсадной колонны до подошвы поглощающего пласта и при атмосферном давлении соответственно;
Т, Т₀ - максимальная температура в интервале от башмака эксплуатационной обсадной колонны до подошвы поглощающего пласта и на устье скважины соответственно, К;
ρ_в - плотность воздуха при атмосферном давлении, кг/м³,
обеспечивая постоянство минимально необходимой плотности, а при продавливании цементного раствора фиксируют момент его выхода в заколонное пространство, причем в качестве флюида пониженной плотности используют двухфазную пену со степенью аэрации, рассчитываемой по формуле

где α_п - степень аэрации двухфазной пены;
ρ_пож - плотность пенообразующей жидкости, кг/м³;
ρ_п - плотность двухфазной пены, кг/м³, определяемая по формуле

где Р_ж - гидростатическое давление сборного столба технологических жидкостей над поглощающим пластом, МПа;
Р_у - устьевое давление, поддерживаемое в процессе продавливания всего объема цементного раствора, МПа,
и расходом, определяемым из неравенства

V_пож - объем пенообразующей жидкости, обеспечивающий после аэрации заполнение заколонного пространства от подошвы поглощающего пласта до устья скважины, м³;
V_пp - объем продавочной жидкости, обеспечивающий заполнение заколонного пространства цементным раствором в интервале от подошвы поглощающего пласта до забоя скважины, м³;
Q_ц - расход цементного раствора, обеспечиваемый суммарной подачей насосов цементировочных агрегатов при продавливании цементного раствора за эксплуатационную обсадную колонну, м³/с.The technical result is achieved by the fact that in the method of stepwise cementing of a well under conditions of abnormally low formation pressure in the absorption zone, including installing a stepwise cementing sleeve over the roof of the absorbing formation, injecting a buffer fluid, a portion of unaerated cement mortar, forcing the cement mortar with a squeezing fluid, and when forcing the cement the solution is pumped into the annulus of low density fluid, after the installation of a step cementing coupling they install a cementing head with lower and upper separation plugs and a locking element, after injecting the buffer liquid, the lower part of the production casing is cemented above the absorption zone by lowering the lower separation plug, the cement mortar is forced through with squeezing liquid with the upper separation plug, and then the locking element is dumped, followed by washing excess cement mortar and after it hardens, cement the upper part of the production string through the step coupling cementing, and a portion of unaerated cement mortar is pumped in a volume that ensures filling the annular space in the interval from the bottom of the absorbing layer to the step cementing sleeve, a subsequent additional portion of cement in the volume that ensures filling the annular space from the shoe of the production casing to the bottom of the absorbing formation is aerated during the injection period, increasing the degree of aeration in the limit calculated by the formulas

where α _{cp min} - the minimum degree of aeration of the injected cement at the wellhead;
α _{cp max} - the maximum degree of aeration of the injected cement at the wellhead;
ρ _cr - the density of non-aerated cement mortar, kg / m ³ ;
ρ _o - the minimum required density of aerated cement in the well, kg / m ³ determined by the formula

where R _PL - reservoir pressure, MPa;
g is the acceleration of gravity, m / s ² ;
ρ _p is the density of the flushing fluid behind the production casing string above the sleeve cementing, kg / m ³ ;
N - installation depth of the coupling of step cementing, m;
N _p - the level of the soles of the absorbing layer, m;
L is the depth of descent of the cemented production casing string, m;
K is the coefficient of solubility of air in a liquid at atmospheric pressure;
P ₀ - atmospheric pressure, MPa;
Z, Z ₀ - gas compressibility coefficients in the interval from the shoe of the production casing to the bottom of the absorbing formation and at atmospheric pressure, respectively;
T, T ₀ - the maximum temperature in the interval from the shoe of the operational casing to the bottom of the absorbing formation and at the wellhead, respectively, K;
ρ _in - the density of air at atmospheric pressure, kg / m ³ ,
ensuring the constancy of the minimum required density, and when pushing the cement mortar, the moment of its exit into the annulus is fixed, moreover, two-phase foam with the degree of aeration calculated by the formula is used as a reduced density fluid

where α _p - the degree of aeration of two-phase foam;
_AMPs ρ - density of the foaming liquid, kg / m ^3;
ρ _p - the density of the two-phase foam, kg / m ³ determined by the formula

where R _f is the hydrostatic pressure of the prefabricated column of process fluids above the absorbing layer, MPa;
P _y - wellhead pressure maintained during the process of forcing the entire volume of cement mortar, MPa,
and expense determined from inequality

_AMPs V - the volume of a foamable liquid, after providing aeration filling casing annulus from the bottom of the absorbent layer to the wellhead, m ^3;
V _pp - the volume of displacement fluid, ensuring filling the annulus with cement mortar in the interval from the bottom of the absorbing layer to the bottom of the well, m ³ ;
Q _c - cement mortar flow rate, provided by the total supply of pumps of cementing aggregates during the forcing of cement mortar for the operational casing string, m ³ / s.

As non-aerated cement mortar use the following composition, parts by weight:
Grouting Portland cement - 100
Superplasticizer brand S-3 - 0.9-1.5
Polyvinyl alcohol - 0.5-1.0
Sulfonol NP-3 - 0.4-1.0
Water - 35
As a two-phase foam using a foaming liquid of the following composition, parts by weight:
Calcium Chloride Aqueous Solution
ρ = 1120kg / m ³ - 100
Technical lignosulfonate LSTP-1 - 0.7-1.0
The inventive volume of non-aerated cement mortar contributes to the weight of aerated cement mortar, preventing its deaeration.

 The inventive volume of aerated cement mortar is selected from the condition of complete filling of the annular space and ensuring the continuity of the cement ring.

 The presence of pore pressure in aerated cement mortar provides a non-shrinking cement stone, as well as high-quality tight contact of cement stone with the walls of the well and production casing.

 The minimum required density of aerated cement mortar is the density that provides a regulated back pressure on the reservoir (within 15-20%).

Changing the degree of aeration within the claimed limits ensures the constancy of the minimum required density in the cementing interval. The choice of the degree of aeration of the aerated cement mortar by the value less _{than the} calculated α _{cp min} will lead to an increase in the density of the aerated cement mortar, which will cause absorption in the reservoir. The choice of the degree of aeration of the aerated cement mortar in a value greater than the calculated α _{cp max} will lead to a decrease in the density of the aerated cement mortar, which will not provide the required back pressure on the reservoir.

 The moment of exit of the cement into the annulus is fixed by the estimated volume of the displacement fluid pumped into the well.

 The need to pump two-phase foam into the annulus at the moment the cement slurry exits the production casing is due to the creation of conditions for the primary entry of foam into the absorption zone, which is achieved by the selected injection mode, i.e. the consumption of two-phase foam and squeezing liquid. At a flow rate equal to or less than the calculated one, the cement mortar will be earlier than the two-phase foam in the absorption zone, which will cause its absorption and under-rise to the MSC.

 Two oncoming flows in the annulus: cement mortar and two-phase foam ensure the forcing of all the liquid that is between them into the absorbing layer. Then, the foam penetrates into the absorbing layer to a shallow depth, filling the pores of the absorbing layer of different sizes, overlaps them due to closed gas-filled shells and elastic air forces. This prevents the further penetration of the foam into the absorbing layer, due to which the absorption pressure in the latter increases several times, which is recorded by the increase in pressure in the annulus at the wellhead when the foam is injected. This is due to the minimum initial volume of injected two-phase foam.

 The presence of pore pressure in the pores of the absorbing layer due to closed foam shells prevents the absorption of cement during its passage through this zone when cementing the lower part of the production casing and allows the cement to be raised behind the column above the absorbing layer to the MSC.

 It should be noted that the degree of aeration of the foam is selected so that the pore pressure of the foam in the absorbing layer for the period of cementing of the bottom of the production casing string is less than the total pressure behind the column of flushing fluid, higher than the MSC and cement mortar located in the interval from the bottom of the absorbing casing formation to the MSC, and also did not exceed the fracture pressure of the absorbing formation. Due to this, the air from the foam located in the absorbing layer will not penetrate through the cement mortar during the period of the SCC, which will prevent channel formation in it.

 The use of aerated cement mortar, as well as two-phase foam, reduces the likelihood of water hammer formation in the well due to the elastic properties of the compositions used, which sharply reduces the relaxation time of the stresses that appeared when pumping these compositions into the annulus, and also ensures the continuity of the cement ring and reduces the likelihood of hydraulic fracturing.

 The formation of backpressure to the formation during the period of the bottom-hole formation in the lower part of the operational casing is ensured by the pore pressure of the gas of the aerated cement mortar, because the hydraulically active pressure of the latter on the reservoir at this time sharply decreases. Otherwise, the appearance of interstratal flows is likely.

 The choice of the composition of non-aerated cement mortar is due to the minimum required water demand and the minimum water yield of the cement mortar under the condition of satisfactory foaming ability.

An analysis of the inventive step showed the following: it is known that to obtain the same density of cement in the initial solution over the entire interval of the depth of the well, it is necessary to introduce a different amount of aerating agent — first less and then more (see Theory and Practice of Well Completion. Ed. A. I. Bulatova, Moscow: Nedra Publishing House OJSC, 1998, v. 4, pp. 95-96); there is a known method of plugging wells by sequentially pumping a non-carbonated and aerated solution into a well (see R. Montman, D. Sutton, Harm with W., Modi B. The Use of Low-Density Foam Solutions - Oil, Gas, and Petrochemicals: Translated Journal of the United States, 1982, 6, pp. 9-19);
There is a known method of plugging wells with foamed solutions with constant density along the depth of the well (see AS 1521859 of November 6, 1987, class E 21 B 33/13, published in OB 42, 1989).

 The choice of foaming fluid is due to the production of stable foam during the cementing period of the lower part of the production casing.

 PCT-II cement grouting is used according to GOST 1581 -96, S-3 superplasticizer according to TU 14-6-55-88, polyvinyl alcohol according to TU 6-05-313-85, sulfonol NP-3 according to TU 6-01-1001- 75, calcium chloride according to TU 6-09-4711-81, technical lignosulfonate LSTP-1 according to TU 54-028-00279580-97.

 Based on the foregoing, we have not identified technical solutions that are based on features that match all the distinguishing features of the claimed technical solution. Thus, the latter does not follow explicitly from the analyzed prior art, i.e. has an inventive step.

 In more detail, the essence of the proposed method is described by the following example.

 Example. Cement well 218 of the North Stavropol area.

Initial data:
Well Depth 800 m
Diameter of a bit П1-215,9С
for production casing, D _d - 215.9 mm
The coefficient of cavity rocks, K _p - 1.15
Depth of descent of 168 mm production casing, L - 800 m
Depth of descent of the 245 mm conductor, l _k - 250 m
The interval of the absorption zone is 350-400 m
Installation depth MSC-16.8R, N - 300 m
Formation pressure, R _pl - 8 MPa
Absorption pressure at the level of the soles of the absorbing layer, R _p - 6 MPa
The density of non-aerated cement mortar, ρ _CR - 1840 kg / m ³
The density of the foaming liquid, ρ _AMPs - 1080 g / m ³
The density of the buffer fluid is 1000 g / m ³
The density of the flushing fluid, ρ _p - 1080 kgm ³
The temperature at the mouth, T ₀ - 273K
The maximum temperature in the interval from the shoe of the production casing to the bottom of the absorbing layer is 315K.

где D_c - диаметр скважины, м,
D_c=К_к•D_д
D_c=1,15-0,2159=0,2483м, тогда

Расчетный объем обеспечивает заполнение заколонного пространства в интервале от подошвы поглощающего пласта до МСЦ.A cementing head of the grade GU Ts 140-168 • 400-2 is installed at the wellhead with the lower and upper dividing plugs and a locking element in the form of a ball. A buffer liquid is pumped, which is industrial water containing 4 wt.% Carboxymethyl cellulose in a volume of 3 m ³ . Carry out the cementing of the lower part of the operational casing string: lower the lower separation plug, pump a portion of non-aerated cement mortar of the following composition, wt.h .:
Grouting Portland cement - 100
Superplasticizer S-3 - 1.5
Polyvinyl alcohol - 0.5
Sulfonol NP-3 - 1.0
Water - 35
in volume, V _CR1 defined by the formula

where D _c is the diameter of the well, m,
D _c = K _to • D _d
D _c = 1.15-0.2159 = 0.2483m, then

The estimated volume provides filling annular space in the interval from the bottom of the absorbing layer to the MSC.

 The subsequent additional portion of unaerated cement mortar is aerated during the pumping period.

2. Для полдержания рассчитанной плотности определяют предел, в котором повышают степень аэрации закачиваемого цементного раствора

3. Рассчитывают объем аэрированного цементного раствора V₀:

где h_с - высота цементного стакана в эксплуатационной обсадной колонне до обратного клапана, равная 15 м;
D_в - внедренный диаметр эксплуатационной обсадной колонны, равный 154 мм.1. Calculate the minimum required density of aerated cement in the well

2. To maintain the calculated density, determine the limit at which the degree of aeration of the injected cement is increased

3. Calculate the volume of aerated cement mortar V ₀ :

where h _{with the} height of the cement in the production casing to the check valve, equal to 15 m;
D _in - embedded diameter of the operational casing string equal to 154 mm

Расчетный объем обеспечивает заполнение заколонного пространства от башмака эксплуатационной обсадной колонны до подошвы поглощающего пласта.

The estimated volume ensures filling the annulus from the shoe of the production casing to the bottom of the absorbing formation.

Так как при атмосферном давлении степень аэрации цементного раствора в рассчитанном пределе изменяется с 25,64 в зоне подошвы поглощающего пласта до 51,36 на забое пропорционально глубине, то закачивают цементный раствор в скважину через аэратор марки УС 20-1.5 по 1,0 м³, добавляя в аэратор соответствующее количество воздуха для получения расчетной степени аэрации. Степень аэрации при атмосферном давлении на каждый м³ неаэрированного цементного раствора повышается на величину 4,51. Расход неаэрированного цементного раствора контролируют при помощи станции контроля за процессом цементирования СКЦ-2М.5. To prepare a given volume of aerated cement mortar, a non-aerated solution in volume is required

Since at atmospheric pressure the degree of aeration of the cement in the calculated limit varies from 25.64 in the zone of the bottom of the absorbing formation to 51.36 at the bottom in proportion to the depth, cement is pumped into the well through an aerator of grade 20-1.5, 1.0 m ³ each by adding the appropriate amount of air to the aerator to obtain a calculated degree of aeration. The degree of aeration at atmospheric pressure for each m ³ unaerated cement mortar increases by 4.51. The flow rate of unaerated cement slurry is controlled using a cementation control station SKTs-2M.

где Н_кл - глубина установки обратного клапана, м;
Н_кл- 785 м,

В качестве продавочной жидкости используют глинистый буровой раствор, на котором проводилось бурение. На момент окончания закачки данной порции продавочной жидкости в скважину сбрасывают шар, предназначенный для перекрытия проходного сечения МСЦ. Фиксируют момент выхода первой порции цементного раствора по объему закачанной продавочной жидкости
V'_пр=V_в-V_цр-V₀,
где V_в - внутренний объем эксплуатационной обсадной колонны, м³;

Следовательно, V'_пр= 14,61-2,62-10,48=1,51 м³, т.е. после закачивания в эксплуатационную обсадную колонну продавочной жидкости в объеме 1,51 м³, что зафиксировано СКЦ-2М, в заколонное пространство начинают подавать двухфазную пену. В момент выхода первой порции цементного раствора в заколонное пространство с устья за обсадную колонну подают двухфазную пену.The upper separation plug is released, on top of which a portion of the squeezing liquid is pumped in volume

where N _CL - the depth of installation of the check valve, m;
N _cl - 785 m

As a squeezing fluid, clay mud is used, on which drilling was carried out. At the time of completion of the injection of this portion of the squeezing fluid into the well, a ball is designed to block the MSC pass-through section. The moment of release of the first portion of cement mortar is recorded by the volume of pumped squeezing fluid
V ' _pr = V _in -V _CR -V ₀ ,
where V _in - the internal volume of the operational casing string, m ³ ;

Therefore, V ' _pr = 14.61-2.62-10.48 = 1.51 m ³ , i.e. after pumping in a production casing string of selling fluid in a volume of 1.51 m ³ , which is recorded by SKTs-2M, two-phase foam is fed into the annulus. At the moment the first portion of the cement slurry enters the annulus from the mouth, a two-phase foam is fed from the casing.

принимают давление на устье в затрубном пространстве, Р_у, равным 2,5 МПа, тогда

2. Рассчитывают степень аэрации двухфазной пены

3. Готовят пенообразующую жидкость следующего состава, маc.ч.:
Водный раствор хлорида кальция, ρ=1120 кг/м³ - 100
Лигносульфонат технический ЛСТП-1 - 1,0
Рассчитывают расход двухфазной пены:
Определяют

где V_зк - объем заколонного пространства от подошвы поглощающего пласта до устья скважины, м³;

где l_k - глубина установки кондуктора, м;
D_вк - внутренний диаметр кондуктора, м;

тогда

Q_n принимают равным 25,6 л/с=0,0256 м³/с, что обеспечивается работой насосов двух цементировочных агрегатов ЗЦА - 400А с диаметром втулок 125 мм на 2-й скорости,

Данный расход способен обеспечить один цементировочный агрегат ЗЦА-400А с диаметром втулок 125 мм на 3-ей скорости подачи. Осуществляют закачивание пены до создания избыточного давления на устье скважины 2,5 МПа и поддерживают его в течение всего продавливания цементного раствора. Резкий рост давления на устье от атмосферного до указанной величины свидетельствуют о создании двухфазной пеной кольматирующего барьера в зоне поглощения. Изменение давления на устье скважины фиксируют манометром.1. To determine foam density is calculated biphasic P _w

take the pressure on the mouth in the annulus, P _y equal to 2.5 MPa, then

2. Calculate the degree of aeration of two-phase foam

3. Prepare a foaming liquid of the following composition, wt.h .:
An aqueous solution of calcium chloride, ρ = 1120 kg / m ³ - 100
Technical lignosulfonate LSTP-1 - 1.0
Calculate the consumption of two-phase foam:
Determine

where V _ZK - the annular space from the bottom of the absorbing layer to the wellhead, m ³ ;

where l _k - the installation depth of the conductor, m;
D _VK - the inner diameter of the conductor, m;

then

Q _{n is} taken equal to 25.6 l / s = 0.0256 m ³ / s, which is ensured by the operation of the pumps of two cementing units ZCA - 400A with a sleeve diameter of 125 mm at the 2nd speed,

This flow rate can be provided by one cementing unit ZCA-400A with a sleeve diameter of 125 mm at the 3rd feed rate. Foam is pumped to create an excess pressure at the wellhead of 2.5 MPa and is maintained during the entire cement slurry. A sharp increase in pressure at the mouth from atmospheric to the indicated value indicates the creation of a collating barrier in the absorption zone by two-phase foam. The change in pressure at the wellhead is fixed with a manometer.

 When the upper separation plug reaches the lower, the pumping fluid is temporarily suspended until the ball passes through the MSC cross-section. At the same time, the supply of two-phase foam to the annular space is stopped. Excess pressure is created to open the MSC washing windows, through which excess cement slurry is washed.

 The well is left for 24 hours.

 Carry out the cementing of the upper part of the production casing in a direct manner through the MSC.

где h_цс - высота цементного стакана в эксплуатационной обсадной колонне на момент окончания цементирования верхней части эксплуатационной обсадной колонны М, тогда

Расчетный объем цементного раствора продавливают за эксплуатационную обсадную колонну продавочной жидкостью. Объем продавочной жидкости пределяют следующим образом:

После чего скважину оставляют на 24 часа ОЗЦ.Complete cement slurry of normal density in volume

where h _cs is the height of the cement cup in the production casing at the time of cementing the upper part of the production casing M, then

The estimated volume of the cement slurry is pushed through the production casing with squeezing fluid. The volume of the squeezing liquid is limited as follows:

After that, the well is left for 24 hours with an OZZ.

 The data of geophysical studies showed the absence of discontinuities in the cement ring, and during subsequent operation no intercolumn gas flows were detected, which indicates the effectiveness of the claimed technology.

Claims (2)

1. A method of stepwise cementing of a well under conditions of abnormally low formation pressure in the absorption zone, including installing a step cementing sleeve over the roof of the absorbing layer, injecting a buffer fluid, a portion of unaerated cement mortar, forcing the cement mortar with a squeezing fluid, and pumping it into the annulus low density fluid, characterized in that after the installation of the stepped cementing clutch is mounted cement After the buffer fluid is injected, the lower part of the production casing string is cemented above the absorption zone by lowering the lower separation plug, the cement mortar is pressed with squeezing fluid with the upper separation plug, and then the locking element is discarded, followed by washing out the excess cement mortar and after its hardening cement the upper part of the production string through the coupling step cementing, p why a portion of unaerated cement mortar is pumped in a volume that ensures filling the annular space in the interval from the bottom of the absorbing layer to the step cementing sleeve, the next additional portion of cement in the volume that ensures filling the annular space from the shoe of the production casing to the bottom of the absorbing formation is aerated during the injection period increasing the degree of aeration in the limit calculated by the formulas

where α _{cp min} - the minimum degree of aeration of the injected cement at the wellhead;
α _{cp max} - the maximum degree of aeration of the injected cement at the wellhead;
ρ _cr - the density of non-aerated cement mortar, kg / m ³ ;
ρ ₀ - the minimum required density of aerated cement in the well, kg / m ³ determined by the formula

where R _PL - reservoir pressure, MPa;
g is the acceleration of gravity, m / s ² ;
ρ _p is the density of the flushing fluid behind the production casing string above the sleeve cementing, kg / m ³ ;
N - installation depth of the coupling of step cementing, m;
N _p - the level of the soles of the absorbing layer, m;
L is the depth of descent of the cemented production casing string, m;
K is the coefficient of solubility of air in a liquid at atmospheric pressure;
P ₀ - atmospheric pressure, MPa;
Z, Z ₀ - gas compressibility coefficients in the interval from the shoe of the production casing to the bottom of the absorbing formation and at atmospheric pressure, respectively;
T, T ₀ - the maximum temperature in the interval from the shoe of the operational casing to the bottom of the absorbing formation and at the wellhead, respectively. TO;
ρ _in - the density of air at atmospheric pressure, kg / m ³ ,
ensuring the constancy of the minimum required density, and when pushing the cement mortar, the moment of its exit into the annulus is fixed, moreover, two-phase foam with the degree of aeration calculated by the formula is used as a reduced density fluid

where α _p - the degree of aeration of two-phase foam;
_AMPs ρ - density of the foaming liquid, kg / m ^3;
ρ _p - the density of the two-phase foam, kg / m ³ determined by the formula

where R _f is the hydrostatic pressure of the prefabricated column of process fluids above the absorbing layer, MPa;
P _y - wellhead pressure maintained during the process of forcing the entire volume of cement mortar, MPa,
and expense determined from inequality

where Q _n is the flow rate of two-phase foam, m ³ / s;
_AMPs V - the volume of a foamable liquid, after providing aeration filling casing annulus from the bottom of the absorbent layer to the wellhead, m ^3;
V _np is the volume of the displacement fluid, ensuring filling the annulus with cement mortar in the interval from the bottom of the absorbing layer to the bottom of the well, m ³ ;
Q _c - cement mortar flow rate, provided by the total supply of pumps of cementing aggregates during the forcing of cement mortar for the operational casing string, m ³ / s. 2. The method according to claim 1, characterized in that as the non-aerated cement mortar use the following composition, wt.h .:
Grouting Portland cement - 100
Superplasticizer S-3 - 0.9-1.5
Polyvinyl alcohol - 0.5-1.0
Sulfonol NP-3 - 0.4-1.0
Water - 35
3. The method according to claim 1, characterized in that as a two-phase foam using a foaming liquid of the following composition, wt.h .:
An aqueous solution of calcium chloride, ρ = 1120 kg / m ³ - 100
Technical lignosulfonate LSTP-1 - 0.7-1.0e