GB2376031A

GB2376031A - Pulse treatment method to stimulate formation production

Info

Publication number: GB2376031A
Application number: GB0212871A
Authority: GB
Inventors: Vladimir Alekseevich Gubar; Sergei Aleksandrov Karaoglanov; Said Al Nabouda Ahmed
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-06-01
Filing date: 2001-11-27
Publication date: 2002-12-04
Anticipated expiration: 2021-11-27
Also published as: WO2002097238A1; RU2196887C1; GB0212871D0; GB2376031B

Abstract

A method of stimulating a formation involves charging a down-hole pressure pulse generator with a fire-safe and explosion-proof gas and lowering the pulse generator into a borehole. A survey is initially carried out to determine the formation pressure and the pulse generator is then used near a formation of interest to generate a series of pressure pulses at least three times the formation pressure. The process can then be used to stimulate a number of formations by lowering the pulse generator further into the borehole. A reflector screen may be placed above the pulse generator to focus the pulses.

Description

PULSE TREATMENT METHOD TO STIMULATE BOTTOMHOLE FORMATION ZONE IN A WELL This invention pertains to the operation of oil, gas, water-intake and other wells. The invention is particularly though not exclusively designed to improve the permeability of the rock in which the well is sunk, and the ability of the well to produce.

The petroleum industry is well acquainted with the technique of well stimulation whereby the pressure required to induce residual cracks in the surrounding rock formations is produced by the energy of gases generated by powder charge combustion (see Popov A. A."Shock Methods of Bottomhole Formation Zone Stimulation", Moscow,"Nedra" Publishers, 1990, pages 38-45). This technique utilizes pressure accumulators or propellant pressure generators suspended in the field by a load-carrying logging cable.

Ignition occurs by detonating a powder charge, using a spiral filament or by activating a pyrocartridge with an electric pulse originating from an external current source.

This technique has certain limitations, and specifically it makes use of explosives and thereby implies a significant increase of temperature during propellant deflagration which can bring about mud cooking in the bottomhole formation zone. Other limitations are that this technique fails to provide an easy control over the process parameters.

A further method of well stimulation is described in Russian Patent No. 2105874 which describes a bottomhole formation zone treatment technique. This method involves the delivery of a downhole high-pressure pulse generator into the wellbore. The pressure pulse generator is lowered to a depth corresponding to the location of the maximum oil/gas saturation value and inflow, whereupon it begins to apply 250-400 kilojoule pressure pulses. Then

after a complete dumping or attenuation of the shock wave oscillation, the tool starts producing 6-8 kilojoule/10-15 hertz pulses.

We have appreciated that the drawback of this technique is that the level of treatment energy applied is set without due regard for reservoir pressure, a basic geological parameter characterizing a well. Although a maximum effect can be achieved by applying a pressure pulse far greater than the reservoir pressure, that is, far overbalancing the reservoir pressure, the positioning of the generator at local intervals showing maximum inflow rate does not necessarily ensure maximum hydrocarbon production. This is because the fluid increase produced can be caused by an enhanced delivery of water, which is injected to maintain reservoir pressure, and which flows into the wellbore through the flooded-out reservoir zones near the perforated interval.

Another undesirable feature of this technique is the bottom-upwards treatment of the perforation zone intervals, which we have appreciated prevents a more effective stimulation of the pay zone. That is, the shock wave distribution in the treatment zone occurs in a manner that channels it largely upwards, thus decreasing the effect of the treatment on the bottomhole formation zone in the perforated interval or layer of the wellbore.

Other prior proposals are described in Russian Patents 2,026, 969 and 2,143, 554; United States Patent 4,558, 737; and International Patent Application W001/12947.

Summary of the Invention The invention is defined in the independent claims below to which reference may now be made. Advantageous features are set forth in the appendant claims.

A preferred embodiment of the invention is described below by way of example. Briefly, this preferred embodiment is applicable to the operation of oil, gas,

water-intake and other wells and is comprises a treatment applied for the pulse stimulation of the bottomhole formation zone to improve the formation rock permeability and increase deliverability of the well. A high-pressure pulse generator is inserted in the wellbore perforation zone, positioned in the upper interval which can potentially produce a maximum volume of hydrocarbon, and pulses are applied. The applied pressure of the pulses has a peak value at least three times greater than the reservoir pressure in the treatment zone.

As described more fully below, the gas-pulse technique stimulates the bottomhole formation zone. In this technique a down-hole pressure pulse generator, charged with a fire-safe and explosion-proof gas or gas mixture, is inserted in the wellbore. Pulse stimulation of the perforation zone is progressively performed by halting the downward transition of the tool in the wellbore.

In accordance with this invention the treatment is preceded by a well geophysical survey to identify local perforation intervals containing pay zone non-producing interlayers and to record local intervals showing maximum hydrocarbon reserves. A measurement is made of the reservoir pressure in each identified local interval. The required intervals are then treated with a high pressure gas mixture pulse with the treatment pressure being at least three times greater than the reservoir pressure in the treatment zone.

The whole perforation zone is treated by progressively moving the generator downwards from the upper perforation zone section.

In the preferred gas-pulse technique to stimulate bottomhole formation zone, the pulse treatment of a well is performed by halting the generator in the perforation zone interval against local intervals showing maximum hydrocarbon reserves, while the pressure wave is focussed in the treatment zone of the wellbore by wellhead-tobottomhole screening.

Detailed Description of the Preferred Embodiment The method for carrying out the preferred embodiment of the invention will now be described in more detail by way of example.

The following description assumes a knowledge of the technical field including the prior documents referred to in the introduction.

Stimulation of the bottom zone to produce an increase in fluid production occurs in a multistage process. The first stage is the carrying out of a geophysical survey on the well to identify the layers (perforation zone local intervals) of underlying rock which are not able or less able to produce the desired fluid compared with other more fertile layers, and to register local intervals which can potentially yield a maximum volume of hydrocarbon reserves. A measurement is made of the depth of the upper and lower bounds of these non-producing layers, and a measurement is additionally taken of the reservoir pressure in each of the layers thus found. This then gives the user an indication of which underground layers are producing most fluid, and which ones are producing significantly less. The user will wish for maximum production from the well and therefore wishes to stimulate these areas or layers of lower production rates.

A pressure pulse generator is then delivered to a cased well and positioned in the perforation zone which has been previously surveyed with the objective of identifying perforation zone local intervals which can potentially yield a maximum volume of hydrocarbons. The down-hole pressure pulse generator is charged or primed with a fire-safe and explosion-proof gas mixture and is inserted in the wellbore.

The generator is lowered into the wellbore and progressively moved from the upper perforation zone section downwards. The downward movement of the tool in the wellbore is periodically halted and the perforation zone is progressively stimulated by positioning the pulse

generator for a wellbore treatment operation. To enhance the treatment effect in a swift manner, the pulse treatment is performed by suspending the down-hole generator in a perforation zone interval against local sections showing maximum hydrocarbon content. In each treatment operation the layers receive treatment with a high pressure gas mixture pulse to stimulate the perforation zone. The peak treatment pressure is at least three times greater than the reservoir pressure in the treatment zone.

Once the generator has been positioned at a specified location in the perforation zone, a command from the surface sets the tool in action. It applies a short-term pressure pulse lasting 0.05 to 1.00 second, the peak pressure being at least three times greater than the reservoir pressure in the treatment zone, as noted above.

The high pressure pulse induces a net of micro cracks in the rock formation near the bottomhole formation zone and cleans up the pore space.

The generator is now rapidly moved further down to the next perforation zone interval below the one which has been treated and a similar treatment process takes place.

Due to the high speed of the fluid moving down the wellbore, a short-term pressure drawdown effect occurs in the already treated intervals, which helps clean up the bottomhole formation zone and improve its permeability.

The operation is performed over and over again until the well perforation zone has been completely treated.

The creation of a peak pulse pressure which is at least three times greater than the reservoir pressure in a given treatment zone, allows the perforation zone pore space to be cleaned or a network of additional microcracks to be induced with allowance for the geological characteristics of the formation. The confined treatment impact permits residual reserves to be recovered by tapping hitherto non-producing pay bed interlayers.

During the treatment of each subsequent section, a

progressive top-downwards stimulation of individual intervals in the perforation zone creates a short term pressure drawdown in already treated intervals, which facilitates removal of mechanical admixtures and other plugging substances from the bottomhole formation zone into the wellbore.

Placing a wave screen/reflector in the wellbore above the generator helps to make the best of the high-energy impact on the bottomhole formation zone. The focussing of the shock wave in the treatment zone is further enhanced by the wellbore from-wellhead-to-bottomhole screening.

The screening is achieved by selecting the well killing fluid and various packers. The screen makes it possible to make the best use of the energy impact on the bottomhole formation zone.

The system thus provides a selective treatment method for the wellbore perforation section by high energy gases.

The technique described can improve the performance of oil wells giving a three-fold rate increase and an after-treatment effect lasting over ten months. The technique increases the deliverability of oil wells, taps hitherto non-producing interlayers in the pay zone, and brings about a short-term pressure drawdown.

Many modifications and improvements can be made to the method described by way of example within the scope of the appended claims.

Claims

CLAIMS 1. A method of stimulating a bottomhole formation zone in a well, comprising the steps of: charging a down-hole pressure pulse generator with a fire-safe and explosion-proof gas or gas mixture ; inserting and lowering the charged pressure pulse generator in the wellbore ; halting the downward transition of the charged pressure pulse generator in the wellborei and stimulating the perforation zone by effecting a, treatment operation by operating the charged pressure pulse generator ; characterised in that: the treatment operation is preceded by a well geophysical survey to identify local perforation intervals containing pay zone non-producing interlayers and/or to record local intervals showing maximum hydrocarbon reserves, and to measure the reservoir pressure in each identified local interval ; and such intervals are treated with a high pressure gas pulse with the peak treatment pressure being at least three times greater than the reservoir pressure in the treatment zone.
2. A method according to claim 1, in which the perforation zone is treated by progressively moving the generator downwards from the upper perforation zone section, periodically halting the generator at a plurality of desired layers showing maximum hydrocarbon reserves, and effecting a treatment operation at each such layer.

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3. A method according to claim 1 or 2, in which the pressure wave is focussed in the treatment zone by wellhead-to-bottomhole screening in the wellbore.
4. A method according to claim 1,2 or 3, in which a reflector screen is placed in the wellbore above the generator.
5. A method according to any of claims 1 to 4, in which the pressure pulse lasts 0.05 to 1.00 seconds.
6. A method of stimulating a bottomhole formation zone in a well substantially as in the preferred embodiment of the invention herein described.