RU2194850C2 - Method of fluid pulse injection into formation - Google Patents

Abstract

FIELD: oil producing industry; applicable in increase of fluid injection efficiency into injection wells. SUBSTANCE: method includes excitation of low-frequency fluctuations of hydrodynamic pressure in injection wells during fluid injection through tubing string to under-packer zone separated from other part of well by packer. Included into lower part of tubing string are pipes with diameter smaller than that in remaining parts of tubing string. Parameters of tubing string and under-packer zone are selected on bases of conditions determined by mathematical expression. Included into upper part of tubing string are pipes of large diameter and total length equaling one fourth of length of excited wave. Parameters of tubing string and well depth are matched in certain manner. Distance from wellhead to upper end of small diameter pipes is selected multiple to length of half-wave excited in fluid inside tubing string. EFFECT: higher injectivity of injection wells and equalized injectivity profile. 3 cl, 1 dwg

Description

 The invention relates to the oil industry and can be used to increase the efficiency of injection wells.

 Pulsations of the hydrodynamic pressure in the fluid flow into the reservoir contribute to additional crack formation in the bottomhole zone of the well, cleaning of the pore and fracture spaces from impurities polluting it, unloading the rock mass from excess stresses, etc., which helps to increase the injectivity of the well and alignment of the injectivity profile due to connection to the process of pumping liquid low permeability layers.

 Known methods of exciting fluctuations in hydrodynamic pressure in a fluid stream using hydrodynamic wave emitters that convert part of the energy of a moving fluid into the energy of elastic flow oscillations (/ 1, 2 /, A.S. USSR 507368, 1011276, 1131554, 1151328, 1489847, 1034790, 1227260 , 1227261, 479498, 664698). In hydrodynamic emitters of various types (liquid whistles, vortex emitters, etc.), the fluid flow interacts with cavities of various shapes and sizes, which leads to resonant excitation of oscillations with a frequency and amplitude determined by the parameters of the cavity and the flow velocity. Such emitters as generators of pressure waves are inserted into the string of tubing, lowered into the well, and the injection of fluid through this arrangement occurs in a pulsating mode.

 The closest is the method implemented in the technology of pumping water into the injection well / 2, pp. 44-57 /, in which a hydrodynamic emitter is placed in the lower part of the tubing string, lowered into the well to the level of the reservoir, and the injection zone is separated from the reservoir the rest of the well with a packer installed on the tubing string above the reservoir. The injection of water into the reservoir in such a pulsating mode can continue for a long time, which contributes to both an increase in the intensity of oil recovery and an increase in oil recovery.

 The disadvantage of this method is that the frequency of the excited oscillations is in the kilohertz range, while field experiments have established that the optimal range is the range of the first few hertz / 2 /. In addition, the amplitude of the oscillations when using such pressure generators depends on the fluid flow rate or, in other words, on the volume of water injected into the well per unit time, which should be large enough for the intensity of pressure fluctuations to be significant. In injection wells with low injectivity, it is often impossible to provide the necessary rate of water injection for this.

 The problem solved by the invention is to increase the efficiency of the process of pulsed injection of fluid into the reservoir by generating pressure waves with a low frequency in the range of several first hertz and the possibility of increasing the amplitude of the pulsations.

 The technical result that can be obtained by implementing the method is to increase the injectivity of injection wells and alignment of the injectivity profile.

,
откуда следует, что при значениях параметров L, 1, D, d, приемлемых для проведения оценок для нагнетательных скважин
L, l ~20-40 м, D ~130-150 мм, d ~20-40 мм
и скорости звука в жидкости c≈500 м/с, частота генерируемых колебаний будет находиться в диапазоне в несколько герц, то есть будет соответствовать частотам из оптимального для волнового воздействия диапазона.To solve this problem, the method uses the following mechanism for exciting low-frequency oscillations in a fluid stream pumped into the formation through a tubing string into a sub-packer space separated by the packer from the rest of the well. Pipes with a diameter smaller than the diameter of the remaining pipes in the string are included in the lower part of the tubing string, while the resulting hydrodynamic system, composed of sub-packer space and small-diameter pipes, will be a device similar in principle to the Helmholtz resonator / 3 /, amplifying hydrodynamic waves a certain frequency. Such a resonator, which is a cavity, the entrance to which is through a thin tube, is characterized by the compactness property, that is, by the fact that the wavelength excited by the resonator far exceeds its own dimensions. For a resonator composed of a pipe of length L of large diameter D and a pipe of small diameter d of length l, a formula that is sufficiently accurate for practical calculations that determines the length λ of the excited wave will be:

,
whence it follows that with the values of the parameters L, 1, D, d acceptable for conducting assessments for injection wells
L, l ~ 20-40 m, D ~ 130-150 mm, d ~ 20-40 mm
and the speed of sound in a liquid c≈500 m / s, the frequency of the generated oscillations will be in the range of several hertz, that is, it will correspond to the frequencies from the optimal range for the wave action.

,
из которых с учетом формулы (1) следует результирующее необходимое условие, связывающее длину L подпакерной зоны скважины, внутренний диаметр обсадных труб D, общую длину l и внутренний диаметр d труб малого диаметра в нижней части НКT:

.Theoretical calculations show that the compactness condition necessary for the effective operation of the resonator has the form of restrictions imposed on the resonator parameters,

,
of which, taking into account formula (1), the resulting necessary condition follows, relating the length L of the sub-packer zone of the well, the inner diameter of the casing pipes D, the total length l and the inner diameter d of the pipes of small diameter in the lower part of the NKT:

.

 If this condition is violated, the resonance properties of the arrangement will be practically insignificant.

 In the drawing are indicated: 1 - tubing string, 2 - casing of the injection well, 3 - packer, 4 - pipes of small diameter, 5 - sub-packer zone, 6 - reservoir into which the fluid is injected.

 It should be noted that the sub-packer zone is an imperfect cavity for the resonator due to the fact that its tightness is violated by hydrodynamic coupling with the reservoir. At the same time, the calculations show that at well injectivity of the order of 100 cubic meters of fluid per day at a pressure drop of 10 MPa, the resonance amplification coefficient at the above characteristic values of the parameters L, 1, D, d will be quite large and approximately equal to 20-30, and for wells with lower injectivity, the gain will exceed these values.

 Analysis of the results of calculations of the parameters of the generated waves allows us to formulate the following additions to the proposed method, increasing its effectiveness.

 The resonance properties of the arrangement will increase if the depth of the well, or rather, the distance from the wellhead to the upper end of the pipes of small diameter, is a multiple of half the wavelength excited in the fluid in the tubing, that is, additional matching of the parameters L, l, D, d with depth wells increases the efficiency of the method.

 The calculations also show that the efficiency of the method will increase if the upper part of the tubing string with a length of a quarter of the excited wave has a diameter larger than the diameter of the rest of the pipes.

 Thus, the use of the proposed method of injecting fluid into the reservoir allows one or two orders of magnitude to enhance the low-frequency components of the natural pressure fluctuations in the flow of fluid injected into the reservoir. This method will have the greatest efficiency in case of pumping liquid using piston pumping units, for example, when using cementing aggregates characterized by a high level of initial pressure fluctuations in the liquid reaching several atmospheres. In this case, the pressure fluctuations in the sub-packer zone will have an amplitude of several tens of atmospheres.

 To increase the reliability of the packing equipment in the tubing arrangement, it is advisable to use an anchor, which takes up the bulk of the developing dynamic loads.

 The practical implementation of the method is obvious, since it differs from the usual practice of pumping fluid into the reservoir by preliminary calculation of the layout parameters that achieve resonance effects, and the composition of the pipes in accordance with this calculation. The remaining steps for equipping the well for pumping the liquid and putting the well into operation are standard, therefore, their description is not given here. If necessary, the resonance properties of the arrangement can be eliminated without raising the equipment by installing any pressure compensator at the wellhead.

 Variations of the method are possible in which the cavity of the cavity will be the interpacker space formed by two packers, for example, when liquid is pumped into a separate layer or interlayers that are isolated from other layers or interlayers by these packers. The method is also applicable for exciting vibrations in a fluid stream in a producing well, if the production technology allows the formation of a cavity, for example, also using packers necessary for exciting pressure fluctuations in accordance with this method.

 The most successfully claimed method can be applied in the oil industry, and the method can be used in combination with other methods of influencing the bottom-hole zones of wells, such as, for example, thermal or physicochemical methods.

SOURCES OF INFORMATION
1. Agranat B.A., Dubrovin M.N., Khavsky N.N., Eskin G.I. Fundamentals of physics and technology of ultrasound. - M.: Higher School, 1987, 352 p.

 2. Nevolin V.G., Pozdeev O.V. Acoustic impact in technological processes during oil production. - Perm: PermNIPIneft, 1991, 81 p.

 3. Yavorsky B.M., Deglaf A.A. Handbook of Physics. For engineers and university students. - M .: Nauka, 1968, 940 p.

Claims (3)

1. The method of pulsed injection of fluid into the reservoir, including the excitation of pressure fluctuations when injecting fluid into the reservoir through a lowered string of tubing with a packer installed on it, separating the zone of fluid injection into the reservoir from the rest of the well, characterized in that the lower part of the tubing string is composed of pipes of a smaller diameter than in the rest of the string, while the total length of the pipes of a smaller diameter is selected based on the following condition:

where l is the total length of the pipes of smaller diameter, m;
d is the inner diameter of the pipes of smaller diameter, mm;
L is the length of the sub-packer zone of the well, m;
D is the inner diameter of the well casing in the under-packer zone, mm.  2. The method according to p. 1, characterized in that the upper part of the tubing string with a length equal to a quarter of the wavelength excited in the fluid inside the tubing is made up of pipes with a diameter larger than the rest of the string.  3. The method according to p. 1, characterized in that the distance from the wellhead to the upper end of the pipes of smaller diameter is selected as a multiple of the half-wave length excited in the fluid inside the tubing.