RU2121569C1 - Method for shutoff of water inflow of bottom water in gas wells under conditions of abnormally low formation pressures - Google Patents

Abstract

FIELD: methods of bottom water shutoff in gas wells. SUBSTANCE: method includes filling of well with displacement fluid whose structural velocity factor is lower than that of formation water. Tubing shoe is installed at the level of foot of gas-bearing horizon. Blocking-off agent is injected by intervals through annular space. Tubing is lowered down to the level of foot of water-bearing horizon and blocking-off agent is injected. Difference of pressures of agents displacement is determined by formula. EFFECT: reliable shutoff of bottom water inflow and preserved reservoir properties of formation.

Description

 The invention relates to the mining industry, in particular, to methods for isolating and restricting water inflows in gas wells.

 An analysis of the existing state of the art showed the following: there is a known method of isolating the bottom water inflow by lowering the tubing to the boundary of the oil-water contact, sequentially injecting unfiltered fluid, an insulating agent and squeezing fluid into the tubing with further lifting of the unfiltered fluid into the annulus against the interval of oil and gas saturated formations and the sale of an insulating agent in the lower flooded layer (see AS No. 688603 of July 5, 2017, class E 21 B 33/13, publ. AB N 36.79 g.).

 The disadvantage of this method is the poor isolation of the bottom water inflow in the absence of a clear separation of the aquifer and productive horizons. The isolation agent circulates at the upper boundary of the aquifer, which in turn prevents the isolation agent from penetrating into the aquifer throughout the interval. If the injection pressure of the insulating agent is equal to the selling pressure of the blocking agent, as a result, the insulating agent will penetrate into the productive and aquifers, and at those intervals, the reservoir of which is filled with non-filtering liquids that have minimal resistance. Non-filtering fluid having a low structural viscosity compared with the structural viscosity of formation water, is displaced deep into the reservoir. Water from uninsulated intervals will flow into the well, and the reservoir will be contaminated with an insulating agent. The method cannot be used in conditions of abnormally low pressures (ANPD) in the intervals of the layers represented by fractured highly permeable rocks; as a prototype, a method was taken to isolate the bottom water inflow in gas wells by installing a packer above the water-producing interlayer and sequential air injection for a steady state filtration and plugging composition in the air stream in the mode of aerosol formation in the water-showing interlayer through the tubing and simultaneously pumping crude oil or stable gas condensate into the gas-saturated part of the formation through the annulus (see AS N 1804549 dated 04.16.91 according to class E 21 B 33/138, publ. OB N 11.93). The injection pressure of the air and the plugging composition exceeds the injection pressure of crude oil or stable gas condensate by 1.5-2.0 times, and the injection pressure of oil or gas condensate does not exceed the pressure of the test casing.

 The disadvantage of this method is the inability to isolate the inflow of plantar water under the conditions of the AAP in the intervals of the layers represented by fractured highly permeable rocks. Accurate separation of reservoirs into aquifers and gas-bearing horizons using a borehole packer seems unlikely, because the gas-bearing and water-bearing formations have the same reservoir properties and, in addition, the separation by the packer takes place inside the casing and does not extend to the annulus. This will lead to the simultaneous penetration of oil or gas condensate into the gas-bearing and water-bearing strata over the entire interval through the perforation channels available in the production casing. In turn, the walls of the well along the cracks and pores of the formation form stable repressive flows in all directions, which will lead to the penetration of oil or gas condensate, formation water and an insulating agent into aquifers and gas-bearing formations in the same state and their subsequent mixing. The increase in pressure in the tubing when selling an insulating agent to a value that is, as stated, 1.5-2.0 times higher than the injection pressure of oil or gas condensate, will push the previously pumped fluids and air deeper into the reservoir. This process occurs due to the fact that initially liquids having a low structural viscosity penetrate into the formation and they penetrate into the intervals of the formation that provide minimal resistance, which in turn depends on the structural viscosity of the fluids filling the reservoir of productive and aquifers. The process continues until the reservoir is saturated with injected fluids and blocking of the reservoir occurs. As a result, the principle of targeted injection of blocking and insulating agents is violated. The insulating agent is carried by local air currents into the depth of the productive and aquifer, creating an insulating screen over the entire interval, reducing the reservoir properties of the reservoir and impairing the isolation of the flow of suspended formation water.

 The technical result that can be obtained by carrying out the present invention is as follows: the quality of isolation of the bottom water inflow is improved under the conditions of AIP, when the layers are fractured highly permeable rocks, by preventing the insulating agent from entering the gas-saturated part and preserving the reservoir properties of the productive formation.

где
ΔP - разница давлений продавки блокирующего и изолирующего агентов, МРП;
η - коэффициент структурной вязкости блокирующего агента, МПа•с;
Q - объемный расход блокирующего агента, м³/с;
k - коэффициент проницаемости породы пласта, м²;
h_г - толщина газоносного пласта, м;
R_к - контур питания газоносного пласта, м;
r_c - радиус скважины, м.The technical result is achieved using the known method, which consists in the interval pumping of the blocking agent through the annulus, the insulating agent through the tubing and ensuring the pressure differences of the agents through which the well is first filled with a buffer fluid whose structural viscosity coefficient satisfies the condition
η _buffer <η _PL ,
Where
η _buffer is the coefficient of structural viscosity of the buffer fluid, MPa • s;
η _PL - the coefficient of structural viscosity of produced water, MPa • s,
additionally select the composition of the blocking agent, the coefficient of structural viscosity of which satisfies the condition
η _b > η _pl ,
Where
η _b is the coefficient of structural viscosity of the blocking agent, MPa • s,
for its injection, the shoe of the tubing is installed at the level of the sole of the gas-bearing horizon, and for pumping of an insulating agent, the tubing is lowered to the level of the bottom of the aquifer, and the pressure difference between the agents is determined by the formula

Where
ΔP is the pressure difference of the selling of blocking and insulating agents, MCI;
η is the coefficient of structural viscosity of the blocking agent, MPa • s;
Q is the volumetric flow rate of the blocking agent, m ³ / s;
k is the permeability coefficient of the formation rock, m ² ;
h _g is the thickness of the gas-bearing formation, m;
R _{to the} gas supply circuit of the gas-bearing formation, m;
r _c - well radius, m

 The present invention has an inventive step, because the set of essential features of the distinguishing part of the claims used to obtain the claimed result, taking into account the conditions for choosing the structural viscosity of the buffer fluid and the blocking agent in relation to the structural viscosity of the produced water and the mathematically determined difference in the selling pressures of the blocking and insulating agents, is not revealed by us from available sources of fame (patent documentation and scientific and technical literature).

First, a buffer liquid (for example, diesel fuel) is pumped into the well, which is necessary to force the gas in the well into the formation. In this case, the reservoir of the reservoir is filled with a liquid with a structural viscosity lower than the structural viscosity of the formation water. In this case, the overpressure at the wellhead is reduced to zero. Next, the tubing shoe is installed at the level of the sole of the gas-bearing formation and a blocking agent with a certain structural viscosity is pumped into the annulus, which will allow creating a blocking zone only in the gas-bearing formation, since circulation will occur above the interval. Displacing the buffer fluid, the blocking agent penetrates the reservoir, because has a structural viscosity greater than the structural viscosity of the buffer fluid. The penetration of the blocking agent into the aquifer does not occur, because this will require the injection of a buffer fluid and blocking agents in a large volume, which could increase the resistance of the gas-bearing formation to the value of the resistance of the aquifer. This process does not occur, because the amount of blocking agent pumped through the annulus is calculated, and the immediate blocking of the formation is determined by the quality of the blocking agent used. The selling pressure of the blocking agent (P _b ) is chosen so that it meets the condition
P _PL <P _b <0.9P _Opp .
Where
P _PL - reservoir pressure;
P _ODA - pressure testing of the production casing.

где
l - глубина проникновения блокирующего агента, м;
γ - градиент давления сдвига, МПа/м.P _b is determined by the formula

Where
l is the penetration depth of the blocking agent, m;
γ is the shear pressure gradient, MPa / m.

The amount of blocking agent (Q) is selected depending on the thickness of the gas-bearing formation (h _g ). For calculations, the height of the liquid column is taken as 2h _g .

After the blocking agent is pushed into the reservoir, the tubing is lowered to the level of the bottom of the aquifer, i.e. before the bottom of the well, and an insulating agent (grouting mortar) is pumped, forcing it into the aquifer. The selling pressure of the insulating agent (P _and ) is chosen so that it meets the condition.

Проникновение изолирующей жидкости в продуктивный горизонт не происходит, т.к. соблюдено условие P_и < P_б и блокирующая зона не разрушается.P _PL <P _and <P _b ,
P _and determined by the formula
P _and = P _PL + l _γ ,
then the difference in selling pressures of blocking and insulating agents (ΔP) is determined by the formula

Penetration of the insulating liquid into the productive horizon does not occur, because the condition P _and <P _{b are} met and the blocking zone is not destroyed.

 The insulating agent displaces only produced water from the bottomhole zone into the depth of the aquifer, since the structural viscosity of formation water is less than the structural viscosity of a blocking agent, and penetrates the aquifer throughout the interval.

 The presence of certain conditions in the selection of values of the structural viscosities of the buffer fluid, blocking agent and formation water, as well as the claimed pressure difference between the agents, contributes to the fact that the gas-bearing layer is blocked by a blocking agent, and the aquifer is isolated by cement slurry, while the reservoir properties of the gas-bearing formation are preserved and ensured reliable isolation of the bottom water inflow in the conditions of the ANPD.

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

 Example.

 The bottom water inflow is isolated at the well of the Vyngapurovskoye field.

Соблюдено условие
η_буф < η_пл = 0,09•10^-8МПа•c < 0,12•10^-8МПа•c
Далее рассчитывают давление продавки изолирующего агента
P_и = P_пл + lγ = 3,4 + 1•2,0 = 5,4 МПа,
определяют по формуле

рассчитывают давление продавки блокирующего агента
P_б = P_и + ΔP = 5,4 + 3,5 = 8,9 МПа
Устанавливают башмак НКТ на уровне подошвы газоносного горизонта - 1030 м и закачивают в затрубное пространство блокирующий агент, представляющий собой незамерзающую пенообразующую жидкость следующего состава, об.%:
КССБ - 3
Хлористый кальций - 25
Газовый конденсат - 21
Вода - Остальное
обработанную торфощелочным реагентом из расчета 7% к объему пенообразующей жидкости. Соблюдено условие
η_б > η_пл = 10,0•10^-8МПа•c > 0,12•10^-8МПа•c.
Объем закачиваемого блокирующего агента рассчитывают по формуле

После чего спускают НКТ до уровня подошвы водоносного горизонта - 1081 м и закачивают по трубному пространству изолирующий агент, представленный тиксотропным тамопнажным раствором на основе портландцемента с добавкой гипана в количестве 0,5% от массы цемента и карбоната натрия в количестве 0,8% от массы цемента.Well depth, N - 1081 m
The interval of the reservoir - 1030 - 1006 m
Perforation interval - 1081 - 1006 m
The thickness of the gas-bearing formation, h _g - 1030 - 1006 = 24 m
The thickness of the aquifer, h _in - 51 m
Formation pressure, P _pl - 3.4 MPa
The diameter of the tubing, D _tubing - 0,073 m
Inner tubing diameter, D in _tubing - _0,065 m
The depth of descent of the tubing, H _tubing - 1038 m
The diameter of the production casing, D _e - 0,168 m
Pressure testing the production casing, P _ODA - 20.5 MPa
The inner diameter of the production casing, D _ve - 0,132 m
The penetration depth of the blocking fluid, l - 1 m
The permeability coefficient of the formation rock, k - 1.0 • 10 ^-12 m ²
Shear pressure gradient γ - 2.0 MPa / m
The volumetric flow rate of the blocking agent, Q - 5 • 10 ^-3 m ³ / s
Well radius, r _s - 0.1 m
Gas supply circuit, R _k - 1.1 m
Coefficient of structural viscosity of a blocking agent, η _b - 10.0 • 10 ^-8 MPa • s
Coefficient of structural viscosity of the buffer fluid, η _buffer - 0.09 • 10 ^-8 MPa • s
The coefficient of structural viscosity of produced water, η _PL - 0.12 • 10 ^-8 MPa • s
The coefficient of structural viscosity of the insulating agent, η _and - 2.5 • 10 ^-8 MPa • s
After tying the equipment to the wellhead, buffer fluid - diesel fuel is pumped into the tubing space in the volume calculated according to the following formula:

Condition met
η _buffer <η _PL = 0.09 • 10 ^-8 MPa • c <0.12 • 10 ^-8 MPa • s
Next, calculate the selling pressure of the insulating agent
P _and = P _PL + lγ = 3.4 + 1 • 2.0 = 5.4 MPa,
determined by the formula

calculate the selling pressure of the blocking agent
P _b = P _and + ΔP = 5.4 + 3.5 = 8.9 MPa
The tubing shoe is installed at the level of the sole of the gas-bearing horizon - 1030 m and a blocking agent is pumped into the annulus, which is an anti-freezing foam-forming fluid of the following composition, vol.%:
KSSB - 3
Calcium Chloride - 25
Gas condensate - 21
Water - Else
treated with peat alkaline reagent at the rate of 7% by volume of foaming liquid. Condition met
η _b > η _pl = 10.0 • 10 ^-8 MPa • c> 0.12 • 10 ^-8 MPa • s.
The volume of injected blocking agent is calculated by the formula

After that, the tubing is lowered to the level of the bottom of the aquifer - 1081 m and the insulating agent, which is a thixotropic mud slurry based on Portland cement with hypane in the amount of 0.5% by weight of cement and sodium carbonate in the amount of 0.8% by weight, is pumped through the pipe space cement.

Продавливают изолирующий агент в водоносный горизонт с помощью технической воды, P_и = 5,4 МПа. Далее поднимают НКТ до безопасной величины - 1000 м и скважину оставляют на ОЗЦ.The volume of injected insulating agent is calculated by the formula

Push the insulating agent into the aquifer using industrial water, P _and = 5.4 MPa. Next, the tubing is raised to a safe value of 1000 m and the well is left on the baffle.

 The inventive method provides reliable isolation of the influx of bottom water in gas wells and preserves the reservoir properties of the gas-bearing formation in the conditions of the ANPD.

Claims (1)

Method for isolating bottom water inflow in gas wells under conditions of abnormally low reservoir pressure by interval pumping of a blocking agent through the annulus, an insulating agent through tubing and providing pressure differences in the delivery of agents, characterized in that the well is first filled with buffer fluid, coefficient structural viscosity which satisfies the condition
η _buffer <η _PL ,
where η _buffer is the coefficient of structural viscosity of the buffer fluid, MPa • s;
η _PL - the coefficient of structural viscosity of produced water, MPa • s,
additionally select the composition of the blocking agent, the coefficient of structural viscosity of which satisfies the following condition:
η _b > η _pl ,
where η _b is the coefficient of structural viscosity of the blocking agent, MPa • s,
for its injection, the shoe of the tubing is installed at the level of the sole of the gas-bearing horizon, and for pumping of an insulating agent, the tubing is lowered to the level of the bottom of the aquifer, and the pressure difference between the agents is determined by the formula

where ΔP is the pressure difference of the selling blocking and insulating agents, MPa;
η is the coefficient of structural viscosity of the blocking agent, MPa • s;
Q is the volumetric flow rate of the blocking agent, m ³ / s;
k is the permeability coefficient of the formation rock, m ² ;
h _g is the thickness of the gas-bearing formation, m;
R _{to the} gas supply circuit of the gas-bearing formation, m;
r _s - well radius, m