RU2477799C1 - Method for hydraulic treatment of coal bed - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: method includes fluid supply through the well into the bed via delivery pump, fluid hydro-pulse impact on the bed, reduction of fluid well-head pressure to atmospheric pressure with its following discharge from the well. Together with fluid hydro-pulse impact on the bed there accumulated is the hydraulic energy of the stream, created by delivery pump, in hydraulic accumulator with the following supply of accumulated fluid into the well and with regular repeating of modes of fluid discharging from the well and its delivery into the bed. When fluid is pumped into the bed, well-head pressure is increased as quickly as possible and it is maintained via accumulated fluid supply for the time necessary for bed cracks formation. Then well-head pressure is decreased as quickly as possible to atmospheric pressure and fluid is discharged from the well. The sizes and configuration of cracks formed are defined by value and duration of applied pressure.

EFFECT: increase of coal bed degassing efficiency, reduction of labour costs.

Description

The present invention relates to the mining industry and can be used for the degassing of coal seams in order to increase the safety of work in mines, as well as for the production of methane for use in industry from coal seams through wells drilled from the surface.

There is a method of developing and cleaning the bottom-hole zone of wells by pulsed drainage (Nosov P.I., Senochkin P.D., Nurislamov N.B. et al. Patent No. 2159326, class E21B 43/25), in which the formation of a pressure drop between the bottom-hole zone of the formation and the cavity of the well is made by pre-pumping fluid into the well, creating periodic pressure pulses in the bottom-hole zone of the formation in the form of a damped standing wave moving along the cavity of the well, and relieving pressure when the fluid moves through the well from the bottom-hole the formation to the day surface with a sharp opening of the well cavity.

However, water hammer has a short exposure time, during which the formation cracks do not have time to fully open and close during the impact. To create formation cracks, deformation of the array is insufficient.

A known method of degassing a coal seam (Puchkov L.A., Slastunov S.V., Faith G.N. Patent No. 2159333, class E21F 7/00), in which a fracture location is selected according to the strength and gas content of the formation, create a zone increased gas permeability in the formation, unloaded from rock pressure, and form a cavity due to the cyclical action of the pressure of the working fluid on the formation.

However, when slowly increasing pressure is applied, a single crack is usually formed, which develops in the zone of least strength. When the pressure is removed, the crack closes, preventing the formation permeability from increasing.

A known method of pulsed hydraulic fracturing (Shipulin A.V. Patent No. 2392425, class E21B 43/25), including the formation of pressure drops between the bottom-hole zone and the cavity of the well by creating periodic pressure pulses in the bottom-hole zone in the form of a wave of movement of a mass of fluid moving along the cavity of the well , for the implementation of which the initial pressure is established in the well at which the formation cracks are closed, then the liquid is sharply supplied to the well under pressure for a time during which the wave of movement of the mass of fluid reaches isoboy zone and acts on the fractures of the reservoir, then stop the injection and drain the fluid to reduce the pressure in the well to the original value.

However, the method provides a sharp opening of cracks and their smooth closure. For intensive crack formation and fracture, rapid deformation of the rock is required both during opening and closing of cracks.

A known method of hydraulic treatment of a coal seam (Puchkov L.A., Slastunov S.V., Karkashadze G.G., Kolikov K.S. Patent No. 2188322, class E21F 7/00), in which they influence the pressure of the working fluid on the reservoir in the mode of hydraulic separation, then create hydraulic shocks with free flow of fluid from the well, cyclically blocking the flow and dumping it into the atmosphere. Water hammer creates an amplitude of water hammer, the value of which is not less than the value of wellhead pressure. The duration of the overlap and discharge of fluid in each cycle is assumed to be the same.

However, the power of the pulses created by interrupting the spout at the wellhead depends on the difference in the borehole and atmospheric pressures and the velocity of the flow, with each pulse the pressure drop decreases, and the discharge velocity and the force of the hydraulic shock decrease accordingly. To create a flow of flowing fluid, sufficient volume of cracks in the formation is necessary. In addition, pressure pulses are transmitted from the wellhead to the formation cracks with attenuation, which reduces the processing efficiency.

A known method of hydraulic processing of a coal seam (Puchkov L.A., Slastunov S.V., Karkashadze G.G., Kolikov K.S. Patent No. 2298650, class E21F 7/00), taken as a prototype, which includes the injection of fluid into the reservoir in the filtration mode, then the creation of hydraulic shocks when the wellhead pressure of the fluid drops to atmospheric pressure, followed by the outflow of fluid from the well and with the simultaneous accumulation of hydraulic energy from the flow generated by the injection pump, for hydraulic disintegration of the formation along the directions of the formed cracks. These processes are repeated until hydroprocessing design areas around the well are formed in the reservoirs.

However, the pressure in the well increases due to the injection of the working fluid and filling of the free space of pores and cracks in the reservoir in the filtration mode, the slow injection of fluid does not contribute to the creation and development of cracks. The power of the pulses created by interrupting the spout at the wellhead depends on the difference in the borehole and atmospheric pressures and the speed of the flow, with a gradual decrease in the pressure drop, the flow rate and the force of the hydraulic shock decrease.

The objective of the invention is the development of a network of fractures of the formation around the well due to its intense deformation.

The problem is solved in that, using the method of hydraulic treatment of a coal seam, which includes supplying fluid through a borehole to a seam by means of a pressure pump, a hydro-pulse action of the liquid on the formation, a discharge of the wellhead pressure of the liquid to atmospheric pressure followed by its outflow from the well, simultaneous with a hydro-pulse treatment of the liquid on the formation accumulation of hydraulic energy of the flow created by the injection pump in the accumulator, followed by the supply of accumulated fluid to the well and with By periodically repeating the regimes of fluid flow from the well and pumping it into the formation, when the fluid is injected into the formation, the pressure at the wellhead is increased as quickly as possible and the pressure is maintained by supplying the accumulated fluid for the time required to form the formation cracks, then the wellhead pressure is rapidly reduced to atmospheric and the well fluid is poured out, the dimensions and configuration of the generated cracks are determined by the magnitude and duration of the pressure application.

This method allows you to create and develop formation cracks by increasing pressure from hydraulic shock generated at the bottom of the well due to the inertia of the mass of the injected fluid, and to provide quick closure of the cracks by periodically creating a vacuum when the fluid spills.

The method is implemented as follows. At the wellhead, valves are installed, the first of which, the spout valve, connects the well to the drain tank, the second, the topping valve - with a hydraulic accumulator connected to the pump unit and under pressure.

The valves have a design that allows them to open and close for a short time period, for example, using a pneumatic actuator.

With the liquid drain valve closed, the topping valve is opened. The supply of fluid accumulated in the accumulator into the well helps maintain high pressure at the wellhead. A rapid increase in pressure at the wellhead sets in motion a mass of the wellbore fluid. The underlying fluid layers are sealed and also set in motion. An increasing in volume, moving with acceleration, the mass of the borehole fluid upon reaching the sump creates a water hammer with increasing pressure in the resulting formation fractures.

High pressure in the formation cracks is formed due to the inertia of the moving mass of the well fluid. To create hydraulic fracturing pressure, there is no need to use a powerful pump unit. The pressure of the hydraulic shock transmitted to the fractures of the reservoir is proportional to the density of the fluid, the flow velocity and the propagation velocity of the shock wave. Formation cracks form from the impact of water hammer and expand by maintaining high fluid pressure. The duration and magnitude of the applied pressure depend on the physical properties of the formation and technological conditions and are selected empirically.

After filling and maximum expansion of the formation cracks in the borehole zone, close the topping valve and open the spout valve. Downhole fluid begins to pour into the drainage tank, the fluid pressure at the wellhead drops to atmospheric pressure, a rarefaction wave forms, which moves from the wellhead to the bottom of the well and forms a depression impulse in the bottomhole zone. Formation cracks close. After the outflow of a portion of the borehole fluid, the operations of pumping the fluid to fill and expand the fractures of the formation and its repeated outflow are repeated.

Periodic reciprocating movement of the mass of fluid through the borehole zone of the formation contributes to its erosion, as well as the creation of new and development of existing fractures, which contributes to an increase in permeability.

Periodic changes in pressure over a wide range contribute to the maximum opening and closing of cracks, therefore, to their development and deformation. Frequent changes in the applied pressure contribute to the creation of a significant number of small cracks diverging from the trunk. Long-term application of pressure increases the length of cracks. During the formation of cracks, the rock is destroyed, crushed and washed out.

The energy of a moving multi-ton mass of fluid affects the formation array. Fluctuations of the infralow frequency have low attenuation, therefore, periodic changes in the bottomhole pressure are transmitted in the form of low frequency waves along the strike of the formations and contribute to the redistribution of stresses in the array, which positively affects the gas recovery.

Preliminary loosening of the coal mass due to the creation of a developed network of cracks during gas extraction contributes to saving labor costs in mining.

Well fluid may contain chemicals for more productive processing. The method can be applied in conjunction with other types of processing: thermal, vibrational, acoustic, etc.

Claims (1)

A method of hydraulically treating a coal seam, including supplying fluid through a borehole to a seam by means of an injection pump, hydroimpulse exposure of a fluid to a formation, discharge of wellhead fluid pressure to atmospheric followed by its outflow from a well, simultaneous with hydroimpulse exposure of a fluid to a formation, accumulation of hydraulic energy of a flow generated by injection pump, in the accumulator, followed by the supply of accumulated fluid into the well and with periodic repetition of modes fluid outflow from the well and its injection into the formation, characterized in that when injecting the liquid into the formation, the pressure at the wellhead is increased as quickly as possible and the pressure is maintained by supplying the accumulated liquid for the time necessary to form the formation cracks, then the wellhead pressure is reduced as quickly as possible to atmospheric and carry out the outflow of the borehole fluid, the size and configuration of the formed cracks is determined by the magnitude and duration of pressure application.