RU2142555C1 - Method of drilling-in in cased well - Google Patents

Abstract

FIELD: mining industry, drilling-in in cased oil and gas wells. SUBSTANCE: method includes injection into well of fluid; building up of differential pressure and perforation. Fluid is injected into well to attain height of fluid column determined from relation H=(P₁-P₂)/ρ₁θ, where H is height of column of weighted fluid in well, m; P₁ is formation pressure, MPa; P₂ is differential pressure exerted on formation, Pa; ρ₁ is density of injected weighted fluid in well, kg/cu.m; q=9.81 m/s is free fall acceleration. Density of injected fluid is determined with the help of relation given in the invention description. EFFECT: simplified technology of drilling-in.

Description

 The invention relates to the mining industry and is intended for the opening of layers of cased oil or gas wells.

 A known method of opening a cased well formation, including filling the well with liquid, lowering the perforator in the interval of the opening formation, sealing the wellhead and perforating when depressed on the formation (1).

 The closest analogue of the invention is a method of opening a cased well formation, including pumping fluid into the well, creating depression and perforation (2).

 The technical result of the invention is the elimination of these disadvantages.

The necessary technical result is achieved by the fact that by the method of opening the cased hole, the fluid is injected into the well, depression and perforation are created, according to the invention, the fluid is injected into the well to the height of the liquid column, determined from the ratio
H = (P ₁ -P ₂ ) / ρ ₁ q,
where H is the height of the column of weighted fluid in the well, m;
P ₁ - reservoir pressure, Pa;
P ₂ - depression on the reservoir, Pa;
ρ ₁ is the density of the injected weighted fluid in the well, kg / m ³ ;
q = 9.81 m / s ² - acceleration of gravity,
the density of the injected fluid is determined from the following ratio:
ρ ₁ ≥ ρ ₂ (P ₁ -P ₂ )) / (Lρ ₂ qP ₂ -P ₃ ),
where ρ ₂ is the density of the reservoir fluid, kg / m ³ ;
P ₃ - regulatory repression, Pa;
L - well depth, m

 Thanks to these features, the secondary opening of the reservoir can be carried out without complications, without equipping the wellhead with sealing devices, as well as packers separating the annulus, which facilitates the descent into the well of a perforator, which in turn, depending on the thickness of the opening, requires multiple descent for space. At the same time, in the event of a fluid influx from the formation, the risk of liquid spillage or gushing is eliminated, since self-silencing of the well is ensured due to the presence of a heavier fluid in it, with a density determined from the mathematical expression noted above.

 The method is carried out in the following sequence.

By conducting research with depth instruments, a formation pressure P ₁ , a formation fluid density ρ ₂ , and a well depth are first established. The regulatory repression of P ₃ onto the formation for safe work is also determined in accordance with clause 2.10 of the Safety Rules in the Oil and Gas Industry. M., Gosgortekhnadzor of Russia, 1993, then set the value of P ₂ depression per layer. Based on these data, the density ρ _{1 of the} weighted fluid is calculated and then the drilling mud in the well is replaced with this fluid, which guarantees self-silencing of the well when fluid enters the formation after perforating work.

The balance of reservoir pressure and hydrostatic pressure of a column of fluids in the well after lumbago occurs under the condition
P ₁ = ρ ₁ qH ₁ + ρ ₂ q (H ₂ -H ₁ ), (1)
Depression P ₂ created on the formation is determined from the expression:
P ₂ = P ₁ -ρ ₁ qH ₁ (2)
where H ₁ - the height of the liquid column above the reservoir before perforation.

Вертикальная глубина скважины с учетом статического уровня жидкости H₃ жидкости после самоглушения соответствует:

Из (3) и (4) совместным решением определяют расчетную плотность закачиваемой в скважину утяжеленной жидкости, которой заменяют скважинную жидкость и которая обеспечивает производство работ по вскрытию пласта при депрессиях и спуско-подъемные работы без герметизации устья скважины:

При этой плотности утяжеленной жидкости ее высота в скважине перед перфорацией должна быть:

После перфорации уровень жидкости в скважине поднимается и высота ее над пластом составит:

Статический уровень (высота опорожненного ствола) составит

Проверочно H₃ = L - H₂.The height of the liquid column H ₂ during self-suppression is determined by the joint solution (1) and (2)

The vertical depth of the well, taking into account the static level of the liquid H ₃ fluid after self-suppression, corresponds to:

From (3) and (4), a joint solution determines the estimated density of the weighted fluid pumped into the well, which replaces the well fluid and which provides for opening the formation during depressions and tripping without sealing the wellhead:

At this density of the weighted fluid, its height in the well before perforation should be:

After perforation, the liquid level in the well rises and its height above the reservoir will be:

The static level (height of the empty trunk) will be

Testing H ₃ = L - H ₂ .

 As the injected fluid into the well, formation water with the addition of calcium chloride weighting agent can be used.

 Then, after lowering the underground equipment into the well, the well is washed with oil and put into operation.

 An example of a specific implementation of the method.

The method was tested on well N 156, its parameters are as follows:
L = 1600 m - well depth,
P ₁ = 16 • 10 ⁶ , Pa - reservoir pressure.

ρ ₂ = 890 kg / m ³ is the density of the reservoir fluid.

The oil reservoir is opened using one of the known methods using a perforator for depression on the reservoir P ₂ = 1 • 10 ⁶ Pa.

Таким образом, перед созданием депрессии на пласт скважинную жидкость заменяют на пластовую воду, утяжеленную хлористым кальцием, до ρ₁ = 1214 кг/м³ согласно расчету.According to the formula (5), the density of the weighted liquid is chosen:

Thus, before creating a depression on the formation, the borehole fluid is replaced with produced water heavier with calcium chloride, up to ρ ₁ = 1214 kg / m ³ according to the calculation.

После перфорации ожидалось, что жидкость в скважине поднимается и высота ее соатавит:

После чего произойдет самоглушение скважины, т. к. гидростатическое давление столба жидкости будет равно пластовому и статический уровень жидкости будет равен пластовому, и статический уровень жидкости в скважине установится: 1600 - 1375 = 225 м.Depression before perforation is created by the compressor, lowering the tubing into the well. The height of the liquid column above the reservoir is calculated:

After perforation, it was expected that the fluid in the well rises and its height will add:

After which the well will self-suppress, since the hydrostatic pressure of the liquid column will be equal to the reservoir and the static liquid level will be equal to the reservoir, and the static liquid level in the well will be established: 1600 - 1375 = 225 m.

This is equivalent to a pressure safety reservoir:
890 • 9.81 • 225 = 2 • 10 ⁶ Pa,
that meets the requirements of the safety rules.

 In fact, after 26 hours, the liquid level in the well after self-suppression was established at a depth of 236 m, which is explained by the error of technological processes and the arrival of heavier fluid from the formation.

 After perforation, a tubing with a diameter of 75 mm was lowered into the well, washed with oil and the well was put into operation with a deep pump.

 Technical and economic indicators are as follows.

 The use of the method will simplify the technology of opening the formation in the depression without the use of sealing devices of the wellhead, therefore, facilitating the descent of the perforator along the open hole, increases labor safety, eliminates spillage during tripping and after the perforation operation.

Sources of information
1.SU 1520917 A1, 11/27/96.

 2. SU 1572084 A1, 11/20/96.

Claims (1)

A method of opening a cased well formation, including injecting fluid into the well, creating depression and perforation, characterized in that the fluid is injected into the well to a height of the liquid column, determined from the ratio
H (P ₁ -P ₂ ) / ρ ₁ g,
where N is the height of the column of weighted fluid in the well, m;
P ₁ - reservoir pressure, Pa;
P ₂ - depression on the reservoir, Pa;
ρ ₁ is the density of the injected weighted fluid in the well, kg / m ³ ;
g = 9.81 m / s ² - acceleration of gravity,
the density of the injected fluid is determined from the following relation: ρ ₁ ≥ (ρ ₂ (P ₁ -P ₂ )) / (Lρ ₂ qP ₂ -P ₃ ),
where ρ ₂ is the density of the reservoir fluid, kg / m ³ ;
P ₃ - regulatory repression, Pa;
L - well depth, m