RU2175059C2 - Solid-fuel gas generator with controllable pressure pulse for stimulation of wells - Google Patents

Abstract

FIELD: oil and gas production, mining industry. SUBSTANCE: invention is intended for fracture and thermal gas-chemical treatment of face zone of pool by gaseous products of burning of solid rocket fuel to intensify recovery of mineral resources such as oil and gas from coal formations and of metals mined by method of underground leaching. Solid-fuel gas generator provides for rise of rate of growth of pressure of powder gases with time and for efficient action on formation thanks to employment of armored and non-armored charges of different configuration taken in certain proportion, thanks to increase of their total number and thanks to use powerful high-speed igniters. Solid- fuel gas generator includes powder tubular armored charges, ignition charge placed under them and load-bearing geophysical cable with members for attachment of structure. Non-armored tubular charges are positioned between ignition charge and armored charges. Their number with reference to number of armored charges is determined by formulas. EFFECT: increased functional efficiency of solid-fuel gas generator. 4 cl, 4 dwg

Description

 The invention relates to the oil and gas and mining industries, and in particular to devices designed for fracturing and thermogaschemical treatment of the bottomhole formation zone with powder gases in wells for various purposes: during intensification of oil and gas production, during dehydration, degassing and methane production in coal seams, in metal mining underground leaching method.

 The invention relates to devices using the combustion mode of solid energy, in this case, solid rocket fuel. The effectiveness of the impact of such devices on the formation in order to improve its filtration characteristics in the near-wellbore zone depends on many factors, first of all, on the amplitude and dynamics of the increase of the pressure pulse created in the combustion zone and the total duration of the impact, which determine the number and extent of the created cracks.

 Numerous analogs of the device are known - solid fuel gas generators that are lowered into the well on a cable and are distinguished by their design and the possibilities of stimulating the formation.

 US Pat. No. 3,174,545 [1] proposes a device containing sealed charges of gunpowder, plates, and the like. with a burning arch thickness of up to 1 mm. Devices with the same type of charges but operating in pulsation mode or with packer systems are described in US Pat. No. 3,422,760 [2] and [3], as well as in US Pat. No. 3,090,436 [4] and [5]. The devices of this group are characterized by the presence of a metal or polyvinyl chloride case. The pressure pulse created by them is relatively small in time (up to several milliseconds), the pressure pulse is adjusted by the ratio of the number of powder particles of various sizes and shapes and the choice of the optimal charge mass.

 In US patent N 4530396 [6] proposed a device consisting of two charges. The upper charge, enclosed in an airtight shell, is made from granular powder, and the space between the grains of powder is filled with oil. The second charge is located below and made of ballistic gunpowder. Ignition is carried out in the central channel of charges by an electric igniter, or in combination with a fast-burning linear igniter of various lengths. The first charge creates an initial pressure impulse with a duration of the first tens of milliseconds and a value sufficient to break the formation. This is followed by a lengthy stretch of relatively low pressure, but sufficient to increase the size of the cracks formed by the initial pressure pulse. Like the above devices, its drawbacks are the difficulty of manufacturing sealed charges from granular gunpowder, as well as the possibility of impacting the formation with a pulse only with a high-speed front of pressure increase and short duration.

 US Pat. Nos. 4,684,943 [7] and 5,005,641 [8] describe devices using solid rocket propellant charges and fast-burning powerful linear ignitors. In the first device, the charges have a protective outer coating. With appropriate assembly, they can work in a cyclic mode, as well as with a cumulative hammer drill. In the second device, charges are placed in a perforated metal case. Both devices differ from the above in that the pressure pulse is adjusted only by selecting the charge mass, they create a lower slew rate, but a longer duration of the effective pressure pulse, up to 100 ms. (Effective pressure is a pressure value of approximately 0.8 rock pressure sufficient to form artificial cracks).

The operation of all of these gas generators is characterized by a high rate of increase in the load on the formation exceeding 10 ⁴ MPa / s, which, according to the materials of American researchers [9, 10], leads to the formation of numerous cracks.

A known design of a gas generator with charges of solid rocket fuel, in which to increase the rate of increase in pressure and the formation of many cracks using the ignition system of the detonation action located in the central channels of charges along their entire length [11]. A powerful ignition pulse from the detonation products of the cord creates a developed system of new combustion surfaces in the charges. As a result, the load rise rate reaches 10 ⁵ - 10 ⁶ MPa / s, which leads to the formation of 4-10 cracks in the formation. The diameter, number of charges and energy of the ignition system vary and can be optimized to obtain the best results in a particular well. The total duration of an effective pressure pulse is from several to 100-200 ms. Typically, the descent of charges into the well is carried out in a steel perforated casing. However, due to the limited possibilities for adjusting the duration of the formation pressure, the length of the generated cracks does not exceed 5-7 m. An increase in the number of charges in the gas generator assembly leads to a sharp increase in the maximum pressure of the powder gases and, as a result, to possible damage to the well structure.

 Known downhole pressure accumulators ADS [12], where a significant mass and length of the gas generator assembly of unarmored charges is ignited from above and below simultaneously by an electric spiral mounted in the ends of the ignition charges.

Газогенераторы подобного типа применяют в основном для воздействия на прискважинную зону пласта с целью очистки от кольматантов.The insufficient power of the heat pulse of ignition of charges and the long propagation time of the gas front of ignition from the bottom up up the well cause a low gas generation rate and the generation of a long-time pressure pulse with a load rise rate

Gas generators of this type are mainly used to influence the borehole zone of the reservoir in order to clean from the mud.

до величины 10⁴ МПа/с. Однако, продолжительность эффективного импульса давления и, следовательно, протяженность создаваемых трещин при применении этих конструкций остаются недостаточными.Significantly greater possibilities for adjusting the rate of rise of the load are obtained through the use of unarmored charges with a high initial combustion surface and a small thickness of the burning arch. For example, charges with gaps in the fuel mass [13] or multi-tube block products increase

up to 10 ⁴ MPa / s. However, the duration of the effective pressure pulse and, consequently, the length of the created cracks when using these structures remain insufficient.

 RF patent N 2018508 [14] proposes a gas generator with a detonation ignition system for tubular charges consisting of mixed solid fuel. Each charge has armor plating on the side surface and a thin-walled metal tube in the central channel, in which a detonating cord is connected along the entire length of the generator assembly, connected to a sealed explosive cartridge. This quick-burning gas generator allows you to develop a sufficiently high pressure and produce a multi-crack rupture in a short period of time.

 The possibility of adjusting the duration of a pressure pulse based on such a gas generator is proposed in RF patent N 2047744 [15], in which there are similar ignition charges, in the form of one or more groups, above them or between them are charges with a thick-walled metal tube in the central channel and their ignition carried out by hot gases of igniter charges. The duration of an effective pressure pulse can be adjusted from units to several hundred milliseconds.

 The disadvantages of this gas generator are: clogging of the well with the remnants of metal tubes of igniter charges, which are broken by a detonating cord into tapes with torn edges and can create conditions of passage for downhole tools in subsequent studies; high metal consumption and the need for expensive mixed fuels.

 In the patent of the Russian Federation N 933959 [16] a powder pressure generator PGDBK-100M is described. This device processed more than 10 thousand wells in various regions of the Russian Federation and CIS countries. It is taken as a prototype of the proposed device. The generator consists of tubular powder charges, armored on the outer surface. One of the central charges in the generator assembly is igniter, in its channel there is a sealed metal tube with an electric fuse and pieces of pyrotechnic composition. In the channels of the remaining charges, powder bombs are inserted, which serve to increase the combustion surface and have a central channel under the carrier cable.

 The number of tubular powder charges depends on the conditions in the well, type of reservoir, its mechanical and reservoir properties and is determined by calculation (computer simulation) or based on nomograms and graphs [17].

 The main disadvantage of the used pressure generator is the low rate of pressure buildup over time and the inability to regulate it, as well as the limitation of the number of charges according to the conditions of the structural strength of the well.

, что приводит к образованию в пласте единичной пары трещин.Another disadvantage of the prototype is the use of a sealed metal-intensive igniter device. Insignificant penetration of moisture into the device leads to failure of ignition of absorbent pieces from the pyrotechnic composition. In addition, an igniter of this type provides a “soft” mode of ignition of the igniter charge due to the local thermal heating of the metal tube to a high temperature. Ultimately, a gas generator with a “soft” ignition mode produces a pulse with a low rate of pressure rise of the order of

, which leads to the formation of a single pair of cracks in the reservoir.

 Summing up the review of existing designs of solid fuel gas generators capable of developing high pressures sufficient for fracturing, the following can be noted.

 The development of gas generators in the United States with the use of grain powders and rocket fuels is aimed at creating hull apparatuses that create high-speed short-pulse power loads, which lead to the formation of many small cracks in the rock.

 The development of gas generators in the Russian Federation was aimed at creating open-frame apparatuses using tubular charges from rocket fuels, after the combustion of which basically only a load-carrying cable is removed to the surface. Gas generators with fast and slowly burning charges are known, capable of correspondingly forming a plurality of short cracks or single long cracks.

 The objective of the invention is the development of the design of a solid fuel gas generator with an adjustable pressure pulse to stimulate wells, which allows to increase the rate of increase in pressure in the well.

The problem is solved in that between the igniter charge located at the bottom of the gas generator assembly and the known number of armored charges of height H _br there is a certain amount of unarmored tubular powder charges of height H (Fig. 1), or charges with a large initial combustion surface. We define the dependence of H on H _br .

где φ - коэффициент, учитывающий тепловые потери;
f - сила пороха;
ρ_П плотность пороха;
m - масса порохового заряда;
S_с - площадь сечения скважины;
ν и x - скорость границы раздела между продуктами горения и скважинной жидкостью и расстояние, проходимое этой границей раздела,

V_Т - объем образуемых трещин в пласте, (dV_Т/dt ≈ ΔР),
V_ψ - объем, занимаемый сгоревшим пороховым зарядом.According to [17], the rate of increase of pressure of powder gases during the burning of armored charges is determined by the ratio

where φ is the coefficient taking into account heat losses;
f is the power of gunpowder;
ρ _{P the} density of the powder;
m is the mass of the powder charge;
S _with - the cross-sectional area of the well;
ν and x are the speed of the interface between the combustion products and the well fluid and the distance traveled by this interface,

V _T - the volume of formed cracks in the reservoir, (dV _T / dt ≈ ΔР),
V _ψ is the volume occupied by the burnt powder charge.

где U - текущая скорость горения;
U₁ - скорость горения при P=P₁;
S(t) - текущая поверхность горения.The change in mass of a burning tubular powder charge with time is

where U is the current burning rate;
U ₁ - burning rate at P = P ₁ ;
S (t) is the current combustion surface.

при

где K₁ и K₂ - коэффициенты пропорциональности, определяемые из уравнений (1) и (2);
S₀ и S_τ - поверхности горения при t=0 и t=τ ), когда достигается ΔP_max.From equations (1) and (2) it follows that

at

where K ₁ and K ₂ are the proportionality coefficients determined from equations (1) and (2);
S ₀ and S _τ are the combustion surfaces at t = 0 and t = τ), when ΔP _max .

где D₀ и d₀ - внешний и внутренний диаметры трубчатого заряда.From equation (4) it follows that in order to maintain the required pressure drop ΔP _max after combustion of unarmored charges of the proposed generator with a height (H + H _br ) it is necessary to provide the condition

where D ₀ and d ₀ are the external and internal diameters of the tubular charge.

где α₀ = 0,8-0,9;
К ≈ (0,9-1,2)•10^-3;
D - диаметр скважины.On the right in equation (5), the value of the final surface of the known pressure generator [17] is recorded, for which, with a degree of accuracy sufficient for practical purposes, the length of the powder charge, which provides an increase in pressure in the well to the required value, is determined by the formula

where α ₀ = 0.8-0.9;
K ≈ (0.9-1.2) • 10 ^-3 ;
D is the diameter of the well.

что при D₀ >> d₀ составляет 0,5.From here

that for D ₀ >> d ₀ is 0.5.

На фиг. 2 представлены зависимости P(t), полученные расчетным путем на компьютере, при горении известного порохового заряда высотою H_бр = 2 м (кривая 1) и предлагаемого заряда высотою H + H_бр = 1 м + 2 м = 3 м (кривая 2) в 5'' скважине при гидростатическом давлении P₀ = 30 МПа.After combustion of all unarmored charges, the pressure decreases somewhat, and then again reaches the same differential ΔP _max due to the progressive nature of the burning of armored charges. Moreover, in accordance with relation (3), the rate of increase in pressure increases n times

In FIG. Figure 2 shows the dependences P (t) obtained by calculation on a computer when burning a known powder charge with a height of H _br = 2 m (curve 1) and the proposed charge with a height of H + H _br = 1 m + 2 m = 3 m (curve 2) in a 5 '' well with hydrostatic pressure P ₀ = 30 MPa.

где m - масса заряда;
e - толщина горящего свода заряда.If, as unarmored charges, charges with a large combustion surface, for example, gap or multi-tube ones, are used, then equation (5) takes the form

where m is the mass of the charge;
e is the thickness of the burning vault of charge.

Таким образом, использование в заявляемой конструкции газогенератора комбинации из бронированных и небронированных зарядов, взятых в определенном соотношении, позволяет увеличить скорость нарастания давления в несколько раз. Если одновременно в предлагаемой конструкции заменить герметичное воспламенительное устройство на негерметичное с дополнительным зажигательным зарядом (фиг. 1), дающее прямой форс огня на ракетное топливо одного-двух воспламенительных зарядов газогенератора с развитой начальной поверхностью горения (см. фиг. 3), то скорость нарастания давления повышается на порядок.From here:

Thus, the use in the claimed design of the gas generator of a combination of armored and unarmored charges taken in a certain ratio allows you to increase the rate of increase in pressure several times. If, at the same time, in the proposed design, the sealed igniter is replaced by an unsealed one with an additional incendiary charge (Fig. 1), which gives a direct force of fire to rocket fuel of one or two igniter charges of a gas generator with a developed initial combustion surface (see Fig. 3), then the slew rate pressure rises by an order of magnitude.

(см. кривую 3 на фиг.2), необходимой для многотрещинного разрыва.An even greater increase in the pressure rise rate is achieved by using an ignition device of the detonation action (Fig. 4) with an explosive cartridge, detonating cord and an additional incendiary charge of mixed fuel placed in a perforated housing. When such a device is triggered, a network of radial and concentric cracks is formed in the fuel of the combustible charge, and an additional incendiary charge, initiated by the detonation products of the cord, gives a large amount of ignition gases at high pressure. In combination with charges with a highly developed initial combustion surface (Fig. 3), the pressure rise rate reaches a value

(see curve 3 in figure 2), necessary for a multi-crack gap.

 Computer simulation of the charge burning process for various downhole conditions shows that the proposed gas generator exceeds the known analogues by 20-30% in terms of the duration of the impact on the formation and, accordingly, the ability to form more extended cracks.

 The proposed gas generator is shown in FIG. 1-4.

 FIG. 1. Scheme of a gas generator, consisting of a certain number of armored 1 and unarmored 2 and 3 charges and an ignition device, in which inside the perforated tube 4 there is an ignition cartridge 5, a detonating cord 6 and an additional charge of mixed fuel 7.

 FIG. 2. The dependences P (t) obtained by calculation for the following conditions: 1 - burning of a known armored charge 2 m high with a fire type ignition device; 2 - burning of the proposed unarmored charge 1 m high and an armored charge 2 m high with an ignition device of the same type; 3 - combustion of an unarmored charge with a developed combustion surface according to FIG. 3 and the armored charge in the detonation type ignition device according to FIG. 4.

 FIG. 3. Scheme of the lower part of the gas generator, similar to FIG. 1, in which a slotted or multi-tube charge 8 is used as an igniter charge 3, and an igniter cartridge 5 is used as an ignition device.

 FIG. 4. Scheme of the lower part of the gas generator, similar to FIG. 1, in which a detonation type ignition device is implemented, consisting of an explosive cartridge 9, a detonating cord 6 and an additional charge of the mixed fuel 7.

 In FIG. 1 shows the main embodiment of the proposed gas generator according to this invention. The gas generator consists of armored 1 and unarmored 2 tube charges, a lower ignition charge 3, in the channel of which there is an unsealed ignition device consisting of a perforated tube 4, a cable fastening head 10, an ignition cartridge 5, a detonating cord 6 and an additional charge of mixed fuel 7. Gas generator mounted on the spit 11 of the geophysical cable, charges are pulled together by the tip-fairing 12 and 13.

 The armor plating of 14 charges is made of a non-combustible, but easily destructible material that does not clog the well. The ends of unarmored charges have protective belts for safe descent of the gas generator into the well.

 In FIG. 3 shows a second embodiment of a gas generator circuit in which a tubular igniter charge 3 is replaced by a slot or multi-tube charge 8 having a large combustion surface. At the same time, a device for its ignition from the igniter cartridge 5 is shown, which is fixed on a special unit and is tightly pressed to the surface of the internal charge channel.

 In FIG. 4 shows a third embodiment of a gas generator circuit in which a detonation type ignition device is used, consisting of a perforated tube 4, an explosive cartridge 9 provided with a rubber cover to protect the tube 4 from completely breaking, a detonating cord 6 and an additional charge 7 made of mixed fuel. The design of such an ignition device makes it possible to use both mixed and ballistic fuel in ignition charges 3 without the danger of initiating its detonation.

 It should be noted that the downhole gas generators operate in the downhole fluid at high hydrostatic pressure. Our direct experiments with inert models of borehole charges when detonating cords with a weight of up to 40-50 g per linear meter were blown in their channel under conditions of limited transverse dimensions of the borehole showed that the charges are not fragmented into individual fragments, but only discontinuities in the form of radial and concentric cracks.

 The gas generator operates as follows.

 It is collected directly at the wellhead and lowered to a predetermined interval on a geophysical cable. An electric impulse is supplied from the blasting machine through the cable to the ignition cartridge 5 (Figs. 1 and 3) or the explosive cartridge 9 (Fig. 4). When the cartridge 5 is activated, the detonating cord 6 and the additional charge 7 are ignited and burned; from their combustion products ignite charge 3 on the inner and outer surfaces. When the explosive cartridge 9 detonates, detonate the cord 6; from the products of their detonation, an additional charge 7 lights up, from which an igniter charge 3 lights up.

 The products of combustion of charge 3 ignite unarmored charges 2 located above. Then, with some delay, the burning of armored charges 1 located in the upper part of the gas generator begins. The combustion of charges 2 occurs along the inner channel and the outer surface at the same time. In this case, the main front of the fire propagates in parallel layers from the central channel and side surfaces into the charge. The burning of charges 1 begins almost simultaneously over the entire surface of the central channels, while the main front of the fire propagates in parallel layers from the central channel to the side of the side surface.

 When the energy of combustion of charges generated per unit time exceeds the energy loss for heating the environment, for raising the wellbore fluid and crushing it and the combustion products into the formation, the pressure in the well increases. With certain ratios of borehole, reservoir and rock pressures, conditions are created for the opening of natural or the formation of artificial cracks, which subsequently do not completely close.

 According to our estimates, cracks, as well as the thermal and physicochemical effects of powder gases on the formation propagate in a radius of 15 m or more.

 As seen in FIG. 2, the combustion of charges is accompanied by pressure pulsations, which also contribute to an increase in the processing efficiency due to the destruction of the walls of cracks and colmatants with alternating loads.

 The proposed device expands the possibilities of stimulating the formation by selecting (planning) the loading rate of the rocks, based on their physical properties, as well as by increasing the duration of the force impact, which, based on the actual linear speeds of fuel combustion and geotechnical conditions of the wells, with a central system ignition can reach 1-1.5 s.

Sources of information
1. US patent N 3174545. Method of stimulating well production by explosive induced hydraulic fracturing of productive formation. Henry H. Mohaupt (USA) .- N 708481; Claim 01/13/58; Publ. 03/23/65; NKI 166/36.

 2. US patent N 3422760. MKI E 21 B 43/26. Gas - generating device for stimulating the flow of well fluids. Henry H. Mohaupt (USA). - N 584563; Claim 05.10.66; Publ. 01/21/69; NKI 102-21.6.

 3. Shrnidf R.A., Warpinski N.R., Cooper P.W. Jn Situ Evaluation of Several Tailored - Pulse Well Shooting Concepts // Paper SPE 8934 presented at the SPE / DOE Symposium on Unconventional Gas Recovery. Pittsburgh. 1980, May.

 4. US patent N 3090436. Wire line hydraulic fracturing tool. Geerge K. Briggs, Halliburton Co (USA) .- N 844, 670; Claim 10/10/59; Publ. 05.21.63; NKI 166/63.

 5. Guderman J.F., Nothrop D.A. A Propellant - Based Technology for Multiple Fracturing Wellbores to Enchance Gas Recovery: Aplication and Results in Devonian Shale // Unconventional Gas recovery Symposium. Pittsburgh, P.A. May 1984.

6. US patent N 4530396, MKI ³ E 21 B 29/02, E 21 B 43/25. Device for stimulating a subterranean formation. Henry H. Mohaupt (USA). - N 483251; Claim 04/08/83; Publ. 07/23/85; NKI 166/63.

7. US patent N 4683943, MKI ³ E 21 B 21/02. Well Treating system for stimulating recovery of fluids. Gilrnan A. Hill, Richard S. Passmaneck, Kevell J. Tonrym; Mt. Moriaach Trust (USA). - N 890077; Claim 07.24.86; Publ. 08/04/87; NKI 166/63.

8. US patent N 5005641, MKI ³ E 21 B 43/263; F 42V 3/10. Gas generator with improved ignition assembly. Henry H. Mohaupt (USA). - N 546, 898; Claim 08/02/90; Publ. 04/09/91; NKI 166/63.

 9. Pionering new concepts in wireline conveyed stimulation and serveillance. Hi Tech Natural Resources, Jnc, 1991.

 10. Swift R.P., Kusubov A.S. Multiple Fracturing of Boreholes By Using Tailored - Pulse Loading. SPE Journal, 1982, N 12, pp. 923 - 932.

 11. Haney B., Cuthill D. Technical review of the high energy gas stimulation technique. Computalog Ltd, 1996.

 12. Chazov G.A., Azamatov V.I. et al. Thermochemical effect on low-production and complicated wells. M .: Nedra, 1986.

 13. Copyright certificate of the USSR N 1704513 A1, 5 cl. E 21 B 43/263. A device for impacting a formation by pressure of solid fuel combustion products. Sukhorukov G.I., Belyaev B.M. et al. 05/03/1988, Registered on 09/08/1991.

 14. RF patent N 2018508, C1, 5 С 06 С 5/00. Solid fuel well gas generator. Kroshchenko V.D., Kolyasov S.M. et al. 01/02/90; Publ. 08/30/94, Bull. N 16.

 15. RF patent N 2047744, C1, 6 E 21 B 43/11, 43/26. Device for stimulating the formation. Gaivoronsky I.N., Kroshchenko V.D. et al. 03/23/92; Publ. 11/10/95; Bull. N 31.

16. RF patent N 933959, M.cl ³ E 21 B 43/26, (prototype). Powder pressure generator for the well. Belyaev B.M., Sliozberg R.A. et al. 11/06/1980; Publ. 06/07/1982; Registered August 24, 1995.

 17. Instructions for the use of powder generators pressure PGD.BK in wells. Belyaev B.M., Gribanov N.I. et al., M., VIEMS, 1989.0

Claims (4)

1. A solid fuel gas generator with an adjustable pressure pulse for stimulating wells, including powder tubular armored charges, an igniter charge placed under them, and a load-bearing geophysical cable with structural fastening elements, characterized in that unarmored tubular charges are placed between the igniter charge and armored charges on the outer surface charges, while their number (λ) relative to armored is

where D ₀ , d ₀ - external and internal diameters of the armored and unarmored tubular charge.  2. The gas generator according to claim 1, characterized in that the igniter charge has a device for igniting it, consisting of an igniter or explosive cartridge in the protective shell, a perforated tube and a mixed fuel charge, in the channel of which a detonating cord is placed. 3. A solid fuel gas generator with an adjustable pressure pulse for stimulating wells, including powder tubular armored charges, an igniter charge placed under them and a load-bearing geophysical cable with structural fastening elements, characterized in that unarmored tubular charges are placed between the igniter charge and the armored charges on the outer surface charges with a large initial combustion surface, while their number (λ) relative to armored is

where D ₀ , d ₀ - external and internal diameters of the tubular armored and unarmored charge;
e is the thickness of the burning vault of charge.  4. The gas generator according to claim 3, characterized in that the igniter charge has a device for igniting it, consisting of an igniter or explosive cartridge in the protective shell, a perforated tube and a mixed fuel charge, in the channel of which a detonating cord is placed.

Images