RU2244815C1 - Method for hydraulic fracturing of bed - Google Patents

Abstract

FIELD: oil and gas extractive industry.

SUBSTANCE: method includes lowering and mounting tubing string with packer in a well. Fracturing liquid is pumped into tubing string with certain speed and pressure, and hydro-impacts are formed. Before fracturing liquid a deep secondary opening of high-productive bed portion is performed. Column of tubing pipes with tail piece and cone in lower part is performed. Resilient-viscous compound is pumped into well and pushed to position of formed cracks. Fracturing liquid is forced into tubing pipe, while at starting period - at increased speed. Hydraulic impacts are formed by stopping fracturing liquid flow from the surface, and through same well bed products are extracted.

EFFECT: higher oil yield.

1 ex, 4 dwg

Description

The proposal relates to the oil and gas industry, in particular to methods of hydraulic fracturing, and can be used to increase oil and gas recovery from fields (deposits) at various stages of development.

A known method of processing the bottom-hole zone of the formation by creating in the bottom-hole zone of the secondary fracture by lowering and restoring the reservoir pressure in the zone of the depression funnel. The formation of secondary fracturing throughout the entire bottom-hole zone of the formation is carried out at depressions of 0.4-0.6 from the initial reservoir pressure [A.S. No. 1609978, 11/30/90, Bull. No. 44].

The disadvantage of this method is that lowering and restoring the reservoir pressure of the reservoir is a long process (years) and requires significant costs. In addition, the process is uncontrolled.

A known method of hydraulic fracturing, including the descent into the well to a predetermined depth of a sandblasting puncher with a rotator, cutting slits in the horizontal plane, raising the punch with a rotator, lowering the tubing string with the packer into the well and installing it, sequential injection into the tubing string pipes of a fracturing fluid, a suspension of a carrier fluid with a fixing material and a squeezing fluid with an injection rate providing a bottom pressure higher than the fracture pressure, technological exposure and putting the well into operation [RF Patent No. 2055172].

The advantage of this method is that hydraulic fracturing is carried out purposefully.

The disadvantage of this method is that cracks are created in a narrow localized zone and the method is applicable for the initial stage of development of an operational facility. According to the known method, the fracturing fluid reveals only the local most hydroconducting (mainly in the horizontal direction along the reservoir) zone. The oil recovery effect has a short-term (peak) character. The process is expensive and at the late stage of development when breaking thin layers, it does not pay off with additional oil production. When a low-permeability oil-saturated formation is co-occurring with a highly-permeable water-flooded formation, some wells have to be rejected when selecting fracturing facilities.

Closest to the proposed method is a hydraulic fracturing method, including isolating the production interval, filling the tubing with liquid and creating hydraulic shocks by pumping and depressurizing the fluid in the tubing, pumping the fluid out of the well with a hydraulic pump, and then isolating the fracturing interval below the dynamic level in well, but above the production interval, close the valve and pump the overpressure in the tubing with a hydraulic pump, relieving it into the under-packer zone when a predetermined value is achieved by means of a valve [RF Patent No. 2203412, publ. 04/27/2003 - prototype].

The disadvantage of this method is that the volume of fluid under high pressure created in a closed cavity of tubing has a constant value and is insufficient for fracturing powerful formations. In addition, when exposed to the formation due to the larger amplitude of the repression half-wave, the particles of the formation and adsorption deposits will be torn off the pores of the formation and mainly “pushed” deep into the bottomhole zone. The latter is undesirable because the pores of the formation will be clogged in more remote zones of the bottom-hole zone, and it is more difficult to clean them.

The technical problem is to increase oil recovery by eliminating these disadvantages.

The solution to the problem is achieved by a method that includes the descent and installation of a tubing string with a packer in the well, pumping a fracturing fluid into the tubing string at a certain rate, pressure, and creating hydraulic shocks.

What is new is that before the injection of the fracturing fluid, an in-depth secondary opening of the highly productive part of the formation is carried out, tubing with a liner and a funnel in the lower part are installed, the rim of the viscoelastic composition is pumped and pushed to the location of the created cracks, then pumped into the pump compressor pipes fluid fracture, and in the initial period with an increased rate, the creation of water hammer is produced by stopping the flow of fluid fracture from the surface, through the same well produced formation products removed.

Figure 1 presents a vertical projection, partially in the context of the reservoir, when the tubing, the liner and deepened perforation of a highly productive formation are lowered into the well.

In Fig.2 - the same as in Fig.1, the injection operation of the rims of viscoelastic composition.

In Fig.3 - the same as in Fig.1, the hydraulic fracturing operation.

In Fig.4 - the same as in Fig.1, the operation of the removal of formation products.

The method is carried out in the following sequence.

Before the implementation of the method, a reservoir study is carried out, the oil and water saturated thickness of the formation is determined, its capacitive and filtration parameters, water intake intervals, and well production samples are taken. Geophysical methods determine the injectivity of reservoirs depending on the discharge pressure. Update the latest information on the mode of operation of the well and its design: initial injection pressure, throttle response (for an injection well), flow rate, water cut (for producing wells), diameters of the casing string and tubing string, marks of artificial bottom hole, perforation intervals, the area of perforations is calculated, reservoir pressure, potential characteristics of the bottom-hole zone in terms of productivity (according to data from previously performed treatments), the maximum allowable pressure value of the fluid injection into the well.

Based on the information received, it was found that the total area of the perforations is smaller than the cross-sectional area of the tubing string. Therefore, cutting slits against a highly productive formation with a total cross-sectional area of not less than the cross-sectional area of the tubing (figure 1). During the initial opening (after drilling) of the formation, deep perforation can be omitted. A casing of tubing 2 with a liner 4 is lowered into the well 1 so that the funnel is located in the upper part of the processed perforation interval, and the whole system is fixed by the packer 3. Then, the fringes of the viscoelastic composition are pumped and pushed to the estimated distance from the bottomhole zone of the well (figure 2). The estimated distance is determined from the condition of the required location of the created cracks. After holding the injected rim of the viscoelastic composition 6, the fracture fluid is injected (FIG. 3), and the injection is carried out at the maximum speed from the very beginning. The injection of the fracturing fluid at maximum speed allows you to create a water hammer in the reservoir, leading to the creation of cracks 7 in the reservoir. The pressure that is created in the reservoir consists of the following components: pressure at the wellhead generated by the pump; the weight of the liquid column in the tubing; pressure pulse of the transition of the kinetic energy of the moving fluid of a fracture upon impact on a viscoelastic composition.

In the well with the closed position of the ground breaker 5 from the pump unit, the fracture fluid is pumped to a certain pressure value. Upon reaching the set pressure value determined by the pressure gauge, the pump unit is switched off. After shutting down the unit, the circuit breaker opens and rupture fluid begins to pour into the groove tank along the flow line. When reaching the highest spout speed, determined by the pressure of the spilled liquid, the interrupter is abruptly closed. When the breaker is closed in the cavity of the tubing due to the reactive force, a standing elastic wave is created, which first cyclically moves down to the bottomhole zone and the formation itself. Then, reflected from them, it returns to the wellhead and so on, repeating the cycles of repression and depression of hydraulic impacts on the bottomhole formation zone and formation. The speed of wave propagation is close to the value of 1000-1400 m / s. The amplitude of the oscillations increases with increasing initial value of wellhead pressure (Rust) and reaches 1.5 (Rust) at a maximum and a minimum of 0.3 (Rust) in the period of the first oscillation of a standing wave. In subsequent periods, the oscillation amplitudes decrease (up to 6-20 times) and reach a zero value. The number of fluctuations is the less, the stronger the well is caked. Subsequently, when the formation is cleaned of frac products and contaminants, the number of vibrations increases by 2 or more times.

The energy of a standing wave is spent not only on depression and repression strikes on the bottom-hole zone of the formation and sump, but also on friction against the walls of tubing when moving along the cavity. It was experimentally established that in the tubing with decreasing diameter, the number of oscillations is significantly reduced. Therefore, in wells with less injectivity, the diameter of the tubing used should be larger than in highly productive ones. A standing wave has practically no significant effect on the casing 9 located in the well above the funnel, because, firstly, the amplitude of the oscillations of the standing wave when it leaves the tubing in the casing will be less in the annulus space, due to an increase in the cross-sectional area of the casing in comparison with the area of the tubing; secondly, it will be further reduced due to significant losses in the small gap between the funnel and the casing. The amplitude of the impact on the bottom-hole zone of the formation will be greatest at the lower cut of the funnel and slightly lower, namely, in the transition zone of transformation of large values of the amplitudes of pressure fluctuations when the standing wave leaves the cavity of the tubing to their small values - at the entrance to the cavity of the casing string . In this regard, to increase the success of the formation treatment and for the selective processing of individual sections of the perforation interval, a funnel must be installed opposite the desired section of the perforation interval. To enhance the selectivity of processing on a separate perforation interval on the bottom of the column in front of the funnel an additional shank of a smaller diameter is installed than that of the tubing. In the liner, the amplitude of the oscillations (pressure) will be larger compared to the rest of the column, therefore, the impact on the bottomhole zone will increase. Using a shank allows you to adjust the number and amplitude of vibrations. Water hammer is produced in a highly productive formation, which is associated with unproductive. Using a highly productive formation as a waveguide and a conductor allows you to create cracks in 3-dimensional space and connect non-drainable reserves to the development. In case of repressive-depressive action on the formation due to the greater amplitude of the repression half-wave as compared to the depression, the products of the formation can “push” deep into the bottomhole zone. To eliminate the undesirable effect, a standing wave is interrupted in the first period of oscillations, namely, at the time of the largest amplitude of the depressed half-wave. To this end, the interrupter is re-opened at the minimum of the pressure gauge mounted on the valve, and for some time the fluid is poured from the well into the groove tank (Fig. 4). At this moment, the depression amplitude of the standing wave oscillations is added to the depression pressure of the formation and the products from the formation 8 together with the formation fluid move to the well and enter the cavity of the tubing. Then, backwashing is carried out so that during gravity settling the products do not fall into the casing 9 below the funnel, and then into the sump of the well.

The processing process is completed in the absence of samples of mechanical impurities, asphalt-resinous substances. The final control is carried out according to the level of productivity values before and after processing.

Example.

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Carbonate Manifold

Production well depth 1200 m

Production casing diameter 146 m

Perforation Interval:

Unproductive reservoir 1180-1184 m

Highly productive layer 1184-1190 m

The diameter of the tubing is 83 mm

Depth of descent of the pump brand NGN-2-56 800 m

Depth of descent of the tubing shoe 1100 m

Formation Permeability:

unproductive 50 microns ²

highly productive 300 microns ²

Burst Pressure (at the bottom):

unproductive 26 MPa

highly productive 23 MPa

Viscosity of reservoir oil 15 MPa · s

Wellhead pressure at the beginning of fluid injection

rupture 12 MPa

The pressure of the column of fluid break 18 MPa

Kinetic energy pressure

driving fluid fracture 5 MPa

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The density of the fluid break 1500 kg / m ³

The volume of viscoelastic solution (crosslinked polymer system) 6 m ³

Volume of squeezing liquid 10 m ³

Volume of fracture fluid injection (hydrochloric acid emulsion

in oil) 20 m ³

Oil production rate before operations 0.1 t / day

Oil production rate after operations 10 tons / day

Water cut of wells before operations 95%

Water cut after operations 33%

The technical and economic advantage of the proposal is as follows. An integrated approach to hydraulic fracturing allows you to extend profitable oil production and take an additional 9,400 tons of oil in three years, increase oil recovery in the well area by 12.5% and reduce the water cut of produced products. The costs of events taking into account the costs of lifting, transport and oil preparation amount to 800 thousand rubles. The value of additionally extracted oil is 9.4 thousand tons • 3 thousand rubles / t = 28.2 million rubles. The profit from operations to connect the oil-saturated part of the reservoir in development is 27.4 million rubles.

Claims (1)

A method of hydraulic fracturing, including the descent and installation of a tubing string with a packer in a well, pumping a fracturing fluid into a string of tubing with a certain pace, pressure, and creating hydraulic shocks, characterized in that a deep secondary opening is performed before the fracturing fluid is injected with a highly productive parts of the reservoir, install tubing with a liner and a funnel in the lower part, pump the rim of the viscoelastic composition and push it to the location created cracks, then fracture fluid is pumped into the tubing, and in the initial period with an increased pace, the creation of hydraulic shock is produced by stopping the flow of fracture fluid from the surface, formation products are removed through the same well.

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