GB2571338A

GB2571338A - Extraction of hydrocarbons

Info

Publication number: GB2571338A
Application number: GB1803067.6A
Authority: GB
Inventors: Llewellyn Williams Gerwyn
Original assignee: Technoleg Ltd
Current assignee: Technoleg Ltd
Priority date: 2018-02-26
Filing date: 2018-02-26
Publication date: 2019-08-28
Anticipated expiration: 2038-02-26
Also published as: GB201803067D0; GB2571338B

Abstract

Hydrocarbon recovery of using pellets (50, fig 3) formed by creating a solid frozen shell (51, fig 3) of carbonated water around a reagent (52, fig 3), such as sodium bicarbonate, which produces carbon dioxide gas when mixed with water to increase fluid pressure. The temperature of the stimulating fluid in the well bore 53 rises, thereby causing the shell to melt and release the carbon dioxide gas that is dissolved therein in the form of bubbles. The sodium bicarbonate reagent 52 is also released into the water, thereby producing carbon dioxide bubbles to cause micro-fissures in the rock strata 56. A laser 57 may also be used to energise the formed bubbles 59 to increase fracturing pressure. The stimulating liquid may comprises liquified nitrogen, which is then allowed to change from its liquid phase to a gas and cause fracturing

Description

EXTRACTION OF HYDROCARBONS

This invention relates to the extraction of unconventional hydrocarbons from shale, coal and other strata in a manner which requires stimulation of the strata to allow the liquid or gas hydrocarbons to flow into a well bore.

Hydraulic fracking or so-called fracking is commonly used to stimulate rock strata to allow the liquid or gas hydrocarbons trapped therein to flow into a well bore. Hydraulic fracking is a mixture of water and chemicals that are pumped under high pressure into shale rock to split the layers of rock and allow gas or oil flow to escape. This method has attracted a lot of media attention and opposition in recent years.

Generally, the fracking process involves drilling a borehole well into the earth to a depth of over 1,000m, whereupon a series of steel casings are cemented into place within the borehole prior to any hydraulic fracking activity to provide an impermeable protective barrier between the borehole walls and any underground water sources. The casing is installed past the pre-identified depths of any groundwater sources. The casing is tested before and after installation to ensure its integrity. A highpressure fluid mixture of water and sand is then injected into the rock under controlled conditions. This creates millimetre sized fractures in the rock which allows the gas to flow out to the head of the well. The sand grains contained in the fluid hold the fractures open encouraging optimum recovery. A small percentage of the fracking fluid may include additives which reduce friction, remove bacteria and act as a tracer. By reducing the friction between the water and the wall of the borehole, the pressure required during the hydraulic fracking process can also be reduced. The composition of the fracking fluid improves the performance and efficiency of the hydraulic fracking operations. However, the contents of the fracking fluid must be approved by a relevant environmental authority before any hydraulic fracking can take place: the contents are also disclosed on the authorities’ website. The type and extremely low quantities of the additives often result in the fracking fluid being classed as nonhazardous and many are registered as being safe for drinking water, with some often used to treat water to a drinking water standard.

Approximately 40% of the fracking fluid returns to the surface as returned water within the initial few weeks of operations. Much of the remainder returns over the lifecycle of the well. The returned water comprises both the fracking fluid and any underground water which may egress from the shale rock. The returned water is tested and often classed as non-hazardous by the relevant environmental authorities before either being recycled back into the borehole or disposed of at an approved waste water treatment plant.

The fracking process can be carried out vertically or, more commonly, by steering a drill horizontally to the rock layer to create new fracture pathways or extend existing channels. The horizontal pathway is pre-identified by experienced geologists and engineers. Continued advances in knowledge and technology lead to increased efficiency of operations.

The step of hydraulic fracking is usually performed at the start of the life of a well. Several further steps, of no more than one to two hours each, are usually required and this process can be carried out over successive weeks whilst data is taken and assessed. Once hydraulic fracking is completed, a well can go on to produce hydrocarbons for 30-50 years without the need for further treatments. At present, approximately 60% of onshore natural gas production is from hydraulically fractured wells.

Several concerns have been raised regarding the negative effects that hydraulic fracking and its associated operations may have on people and the environment, and the present invention attempts to solve some of these issues and to simplify the hydraulic process.

In accordance with the present invention, as seen from a first aspect, there is provided a method of stimulation of rock strata to allow liquid or gas hydrocarbons trapped therein to flow into a well bore, the method comprising admitting a stimulating fluid into at least a portion of the well bore that extends through the rock strata to be stimulated, the fluid comprising solid particles contained in a liquid medium, the method further comprising allowing the solid particles to release a gas to cause an increase in the fluid pressure in the portion of the well bore.

The method of the present invention is considerably less complex than conventional hydraulic fracking, since there is no need to use pumps to increase the fluid pressure and this helps to reduce the environmental impact of the method. The released gas manifests as bubbles in the liquid medium which build up pressure and cavitate to cause micro-fissures in the strata.

The solid particles may be allowed to release the gas by subjecting the fluid in said well bore portion to an increased temperature compared with that at a proximal end of the well bore.

The fluid may be chilled to a temperature which is less than the determined or expected geo-thermal temperature at said well bore portion. As the liquid reaches the well bore portion, the temperature of the fluid rises, and the gas is naturally released and applied to the surrounding strata where it finds the weakest points in the strata to create the micro-fissures. Hydrocarbons, particularly in coal, may start to flow back to the well bore at this stage, however, for denser and harder rock further steps may need to be applied.

The solid particles may be subjected to a phase change from a solid to a liquid in said well bore portion.

The solid particles may be allowed to release the gas by subjecting the liquid to a phase change to said gas in said well bore portion.

Alternatively, or additionally, the solid particles may be formed by freezing a liquid in which the gas has been dissolved under pressure, the solid particles being allowed to release the gas by subjecting the frozen liquid to a phase change from a solid to a liquid, thereby releasing the gas. The liquid may be carbonated water comprising water in which carbon dioxide has been dissolved under pressure.

Alternatively, or additionally, the solid particles may be formed by freezing a liquid in which a reagent is suspended, the solid particles being allowed to release the gas by subjecting the frozen liquid to a phase change from a solid to a liquid, thereby releasing the reagent to produce the gas.

Alternatively, or additionally, the solid particles may be formed by freezing a liquid to form a shell in which a reagent is contained, the solid particles being allowed to release the gas by subjecting the frozen liquid to a phase change from a solid to a liquid, thereby releasing the reagent from inside the shell to produce the gas.

The reagent may comprise sodium bicarbonate which creates carbon dioxide gas when mixed with water. Alternatively, the reagent chlorine or another reagent having a low boiling point of less than 60°C, so as to produce the gas by vaporisation of the liquid.

The reagent causes a chemical reaction which causes a massive increase in pressure over and above that already existing in the well bore portion. This increased causes micro-fissures to form in the strata and causes the walls of the fissures to become coated with the released reagent to form a film between the strata layers. The film will have a different natural resonant frequency than the surrounding strata.

The proximal and/or distal ends of said well bore portion may be at least partially sealed by a plug or so-called packer, so as to at least partially confine the increased pressure caused by the gas in said well bore portion.

The method may comprise at least partially sealing one end of said well bore portion with a plug having a reflective surface directed axially of the well bore towards the opposite end of said well bore portion, and at least partially sealing said opposite end of said well bore portion with a plug having a laser directed axially of the well bore towards the reflective surface. The method then comprises activating the laser to irradiate the gas bubbles, thereby causing cavitation and a series of explosions, which release very large amounts of energy thereby amplifying the previously formed micro-fissures in the strata and helping to release hydrocarbons from the strata. Bubbles of gas can be one of the most destructive forces in nature. Use of a laser to excite the bubbles in the liquid medium causes the bubbles to collide and burst, whereupon a substantial sound wave is created that helps to rupture the strata.

In accordance with the present invention, as seen from a second aspect, there is provided a method of stimulation of rock strata to allow liquid or gas hydrocarbons trapped therein to flow into a well bore, the method comprising admitting a stimulating fluid into at least a portion of the well bore that extends through the rock strata to be stimulated, the fluid comprising a liquid, the method further comprising subjecting the liquid to a phase change into a gas to cause an increase in the fluid pressure in the portion of the well bore.

The liquid may be a liquified gas such as nitrogen which is injected into the well bore in liquid form whereupon it penetrates the strata.

A series of high amplitude sonic pulses are applied to the nitrogen or other gas in the portion of the well bore and these are transmitted to the strata causing micro fissures to form to act as a conduit for the hydrocarbons to flow back to the well bore. The pulses may comprise positive and/or negative pressure waves and may be varied in frequency to find the resonant frequency of the strata.

The nitrogen or other selected liquified gas is harmless and the method avoids the need for a very high-pressure fracking shock which could induce earth tremors. Hence the invention avoids controversial concerns relating to conventional hydraulic fracking.

The application of the correct frequency causes cavitation i.e. the bubbles of nitrogen or other gas in the strata and creates fissures creating a flow of hydrocarbon back to the well bore.

Once the flow of hydrocarbon starts to diminish, a sonic generator is installed at or adjacent said well bore portion whereupon high amplitude sonic pressure waves are generated to attune to the natural resonance properties of the surrounding strata and/or the film coating in the micro fissures of the strata.

At this stage hydrocarbon output of the well is controllable by variation of the or each applied frequency. Resonance is a driven harmonic oscillation and will be tuned to those two layers of natural frequency of the rock and the film layer. Direction of the sound waves applied is important.

In coal there is no need for the coating, as a difference in resonant frequencies will be achieved between the resonant frequency of solid coal and the resonant frequency of natural cieating in the coal, which will be unidirectional in nature thereby directing the applied sound waves in the correct direction to split the coal microscopically causing hydrocarbon gas flow.

Embodiments of the present invention will now be described by way examples only and with reference to the accompanying drawings, in which:

Figure 1 is a flow diagram of a method in accordance with the first aspect of the invention for the stimulation of rock strata to allow liquid or gas hydrocarbons trapped therein to flow into a well bore;

Figure 2 is a schematic diagram of a well bore formed in accordance with the method of Figure 1; and

Figure 3 is a sectional view through a pellet of stimulating fluid admitted into a portion of the well bore of Figure 2.

Referring to Figures 1 to 3 of the drawings, at step 10, pellets 50 are formed by creating a solid shell 51 of carbonated water around a reagent 51, such as sodium bicarbonate, which produces carbon dioxide gas when mixed with water. The frozen pellets are then stored ready for use, although it is envisaged that they could be produced at the point of use.

At step 11, a well bore 53 is then drilled into the earth to a depth of over 1000 metres, whereupon the well bore 53 can be driven horizontally along the rock strata from which gasses or other hydrocarbons are to be obtained. Any water in the well bore 53 is then pumped out at step 12, whereupon a distal packer 54 in the horizontal well section is closed at step 13. The previously-formed ice pellets 50 are then mixed with chilled water at step 14 to form a stimulating fluid which is then introduced to the well bore 53. A proximal packer 55 is then closed at step 15 to cause the stimulating fluid to be trapped between the distal and proximal packers 54, 55 in a portion of the well bore 53 which extends through a portion 56 of the earth’s strata from which hydrocarbons are to be obtained.

The temperature of the earth at depths of over 1000 metres is considerably greater than that at the earth’s surface. Hence, the temperature of the stimulating fluid in the well bore 53 rises, thereby causing the frozen shell 51 of the pellets 50 to melt and release the carbon dioxide gas that is dissolved therein in the form of bubbles. The melting of the shells 51 also releases the sodium bicarbonate reagent 52 into the water, thereby producing further bubbles of carbon dioxide gas. The pressure of the gas is allowed to increase at step 16 and it will be appreciated that the packers 54, 55 ensure that the pressure is contained in the portion 56 of the strata to be treated. The increase in pressure causes the layered rock strata to split and part, thereby allowing trapped hydrocarbon gasses to escape. In order to recover the gasses, the packer 55 is removed or deflated at step 17 and the well bore 53 is pumped out at step 18, whereupon the hydrocarbon gas can be recovered at the proximal end of the well bore 53.

Depending on the geological conditions, the splitting and parting of the strata by the increased gas pressure may not be sufficient to release the trapped hydrocarbon gas. In this event, a laser 57 in the approximal packer 55 is energised to direct laser light axially along the well bore 53 towards the distal packer 54. The distal packer 54 is provided with a reflective surface 58, which reflects the laser light back along the well bore 53. The laser light impacts the formed bubbles 59 of gas causing them to collide and burst at step 21, thereby producing substantial forces which help to sufficiently split and part the strata portion 56. The hydrocarbon gas is then recovered by performing steps 17 to 19 described above.

Over time, the hydrocarbon volume of gas recovered from the strata portion 56 will diminish. In order to maximise the life of the well bore 53, a sonic generator (not shown) can be inserted into the well bore 53 adjacent the strata portion 56 at step 20. The frequency of the sonic generator is then tuned at step 21 to allow the continued recovery of hydrocarbon gas at the desired flow rate. The flow rate of the hydrocarbon gas is dependent on the sonic frequency applied, with a greater volume of gas being emitted when the sonic frequency is at or near the resonant frequency of the strata portion 56. Hence the desired flow rate is continuously monitored at step 22 and the frequency is continuously adjusted at step 21 to produce the desired gas-flow characteristics as the age of the well increases. In some cases, the fissures in the strata portion 56 may have become coated by the reagent 52 released from the pellets 50. This coating will have a different resonant frequency than the surrounding rock strata and thus the sonic generator may also be configured to operate at this frequency.

In an alternative embodiment, the step 10 of forming the pellets is omitted and the step 14 of introducing the stimulating liquid comprises introducing liquified nitrogen, which is then allowed to change from its liquid phase to a gas: this gas then causes splitting and parting of the strata portion 56 in the same manner as hereinbefore described.

It will be appreciated that the methods in accordance with the present invention are relatively simple, yet have significant environmental benefits compared with conventional hydraulic fracturing methods.

Claims

1. A method of stimulation of rock strata to allow liquid or gas hydrocarbons trapped therein to flow into a well bore, the method comprising admitting a stimulating fluid into at least a portion of the well bore that extends through the rock strata to be stimulated, the fluid comprising solid particles contained in a liquid medium, the method further comprising allowing the solid particles to release a gas to cause an increase in the fluid pressure in the portion of the well bore.

2. The method of claim 1, comprising allowing the solid particles to release the gas by subjecting the fluid in said well bore portion to an increased temperature compared with that at a proximal end of the well bore.

3. The method of claim 2, comprising chilling the fluid prior to admitting it into said well bore.

4. The method of any preceding claim, comprising subjecting the particles to a phase change from a solid to a liquid in said well bore portion.

5. The method of claim 4, comprising subjecting the liquid to a phase change to said gas in said well bore portion.

6. The method of claim 4 or claim 5, comprising forming the solid particles by freezing a liquid in which the gas has been dissolved under pressure, the solid particles being allowed to release the gas by subjecting the frozen liquid to a phase change from a solid to a liquid, thereby releasing the gas.

7. The method of claim 6, comprising forming the solid particles by freezing water in which carbon dioxide gas has been dissolved under pressure, the solid particles being allowed to release the carbon dioxide gas by subjecting the frozen water to a phase change from a solid to a liquid, thereby releasing the gas.

8. The method of any of claims 4 to 7, comprising forming the solid particles by freezing a liquid in which a reagent is suspended, the solid particles being allowed to release the gas by subjecting the frozen liquid to a phase change from a solid to a liquid, thereby releasing the reagent to produce the gas.

9. The method of any of claims 4 to 8, comprising forming the solid particles by freezing a liquid to form a shell in which a reagent is contained, the solid particles being allowed to release the gas by subjecting the frozen liquid to a phase change from a solid to a liquid, thereby releasing the reagent from inside the shell to produce the gas.

10. The method of claim 9, comprising forming the shell around sodium bicarbonate.

11. The method of claim 9, comprising forming the shell around a reagent having a low boiling point of less than 60°C, and producing the gas by vaporisation of the liquid.

12. The method of any preceding claim, comprising at least partially sealing the proximal and/or distal ends of the well bore portion using a plug or so-called packer, so as to at least partially confine the increased pressure caused by the gas in said well bore portion.

13. The method of any preceding claim, comprising at least partially sealing one end of said well bore portion with a plug having a reflective surface directed axially of the well bore towards the opposite end of said well bore portion, and at least partially sealing said opposite end of said well bore portion with a plug having a laser directed axially of the well bore towards the reflective surface, and activating the laser to irradiate bubbles of the gas.

14. The method of any preceding claim, comprising installing a sonic generator at or adjacent said well bore portion and applying high amplitude sonic pressure waves to the surrounding strata.

15. The method of claim 14, comprising adjusting the frequency of the waves to control the flow-rate of hydrocarbons into the well bore.

16. A method of stimulation of rock strata to allow liquid or gas hydrocarbons trapped therein to flow into a well bore, the method comprising admitting a stimulating fluid into at least a portion of the well bore that extends through the rock strata to be stimulated, the fluid comprising a liquid, the method further comprising subjecting the liquid to a phase change into a gas to cause an increase in the fluid pressure in the portion of the well bore.

17. The method of claim 16, comprising admitting a liquified gas into the well bore.

18. The method of claim 16 or 17, comprising applying a series of high amplitude sonic pulses are applied to the gas in the portion of the well bore.

19. The method of claim 18, comprising adjusting the frequency of the pulses to cause cavitation of gas bubbles in the well bore.

20. The method of any of claims 16 to 19, comprising installing a sonic generator at or adjacent said well bore portion and applying high amplitude sonic pressure waves to the surrounding strata.

21. The method of claim 20, comprising adjusting the frequency of the waves to control the flow-rate of hydrocarbons into the well bore.