RU2322578C2 - Method for dynamic bottomhole zone treatment in high-temperature low-permeable reservoirs - Google Patents

Abstract

FIELD: oil and gas production industry, particularly to develop high-temperature low-permeable reservoirs including aleurolitic- argillaceous and sandy-argillaceous ones in Jurassic formations.

SUBSTANCE: method involves serially injection acid solution and buffer liquids in reservoir; stimulating inflow without well holding to provide reaction. The treatment is carried out in two or more reagent supply and removal cycles. At each next cycle treatment radius increased for 40-70 cm. Acid solution and buffer liquid are injected in hydroimpulsive regime with 2.0-10.0 MPa amplitude of hydraulic impacts applied to reservoir. Inflow is stimulated in cyclic depression regime, which provides maximal reservoir productivity after each treatment cycle. Reservoir is treated in single equipment and tool trip.

EFFECT: increased output of oil-producing and injection wells, prevention of secondary sludge and gel formation along with increased intensity of acid reaction with reservoir rock and with increased completeness of spent solution and reaction products removal from treatment zone.

2 cl, 2 dwg

Description

The invention relates to the oil and gas industry, in particular to the field of increasing the productivity of oil producing and injection wells that have opened high-temperature low-permeability reservoirs, including siltstone and sandy clay reservoirs of Jurassic sediments.

There is a method of processing the bottom-hole zone (BHP) of a reservoir of low permeability reservoirs by sequentially injecting water, an acidic composition and buffer fluids based on aqueous solutions of surfactants, holding the reaction, pumping the alkaline composition and re-holding the reaction (RF patent No. 2106484, 03/10/1998). The disadvantages of the method are the complexity and high duration of its implementation, as well as the low effectiveness of the impact at reservoir temperatures of more than 85-90 ° C on highly clay low-permeability reservoirs. When these reservoirs are exposed to reaction with acid at the indicated temperatures, an intensive process of secondary sedimentation occurs, and the volume of secondary precipitation can be several times greater than the volume of dissolved rock acid. As a result, the treatment of the formation leads to a decrease in its permeability, that is, to a decrease in well productivity.

A known method of SCR of high-temperature low-permeability siltstone clay collectors by sequential injection of buffer fluids, mineral and organic acids into the formation, based on the dynamic mode of exposure without exposure of the well to reactions with injected reagents (RF patent No. 2191260, class. ЕВВ 43/27, publ. 20.10. 2002, Bull. No. 29) - prototype. This method is most effective if the reagents are injected into the formation and pumped out of the treatment zone in the regime of alternate repressions and depressions on the formation using a deep-well pneumatic displacement pump. The disadvantage of this method is that the regime of alternate repressions and depressions on the formation in it can be carried out only at the end of the treatment when not a reactive acid composition is squeezed into the depth of the formation, but a neutral buffer or squeeze liquid, that is, the method eliminates the hydrodynamic injection of acid into the formation. In addition, in the known method, the reagents are injected into the bottom-hole zone along the annulus between the tubing and the production string, and this, firstly, limits the pressure of injection of reagents into the formation to the maximum allowable for crimping the production string (not exceeding 9.0-10.0 MPa), and secondly, it leads to dilution of the injected reagents in the annulus in the annulus.

The objective of the invention is to increase the efficiency of acidic SCR of high-temperature low-permeability siltstone, as well as sand-clay reservoirs by preventing the processes of secondary sedimentation and gelation of reaction products during a more intensive reaction of acid with formation rock and more complete removal of the spent solution and reaction products from the impact zone.

The solution to this problem is provided by the fact that in the SCR method of high-temperature low-permeability reservoirs by successively injecting acid composition and buffer fluids into the formation and causing the inflow without holding the well to the reaction, the treatment is performed in two or more cycles of injection and extraction of reagents, each time increasing the treatment radius by 40 -70 cm, moreover, the injection of acidic compounds and buffer fluids is carried out each time in a hydro-pulse mode with an amplitude of hydroshocks on the formation of 2.0-10.0 MPa, and the inflow is called in iklicheskoy depression, providing maximum productivity reservoir after each treatment cycle; while the impact on the reservoir is carried out in one tripping operation of equipment and tools.

Thus, the fundamental differences between the known and the proposed method, as well as the advantages of the latter are that:

firstly, the treatment is carried out in several cycles of injection and extraction of reagents, each time increasing the radius of action. This reduces the injection pressure each time, since with an increase in the processing radius, the filtration area increases in proportion to its square. In addition, despite the non-stop dynamic injection mode without holding the well for reaction in the process of acid pumping, secondary sedimentation and gelation products nevertheless are formed, which reduce the permeability of the reservoir already during its processing. Timely removal of them from the impact zone during step-by-step processing significantly increases the SCR efficiency, especially in low-permeability clayed collectors;

secondly, the injection into the formation of acid, as well as buffer and other liquids, is carried out in a hydro-pulse mode, and the extraction of the injected reagents is carried out in a cyclic depression mode, which ensures maximum formation productivity after each exposure cycle (stage). Moreover, both operations, i.e. injection and call inflow, produced through tubing. This allows you to increase the injection pressure to 22.0-25.0 MPa and virtually eliminates the dilution of the reagents;

and thirdly, the impact on the formation in several cycles is carried out in one tripping operation of equipment and tools. This significantly reduces the duration and cost of work.

In well conditions, the method is as follows.

The layout of the equipment is lowered into the well to the depth of the perforation interval on the tubing (figure 1), including:

1) accumulator of pulse pressure;

2) packer;

3) circulation valve;

4) jet pump.

Make a landing and, if necessary, crimping the packer (2). Raising the tubing, open the circulation valve (3).

With the circulation valve (3) open, with a pumping unit, for example, CA-320, working reagents — buffer fluid and / or acid — are sequentially pumped into the tubing for circulation into the tubing and brought to the installation depth of the circulation valve (3). The tubing tolerance closes the circulation valve. By pumping a buffer or squeezing fluid into the tubing, the working reagents are pressed into the bottomhole formation zone (PZP) to a depth of 40-70 cm in a hydro-pulse mode with an amplitude of hydroshocks of 2.0-10.0 MPa. Water hammer creates an impulse pressure accumulator (1). Immediately after the injection of working reagents into the PZP, the pump unit is switched to the annular space of the well and the pumping of liquid, for example produced water, with the jet pump (4), pumps the liquid out of the PZP. In this case, the jet pump provides a cyclic depression mode. A well is drilled for inflow in an amount equal to or greater than the volume of working reagents pumped into the bottomhole formation zone. After this, by raising the tubing, the circulation valve (3) is opened and a second cycle of exposure is performed as described above. In the second cycle, the volume of working reagents is increased based on the increase in the radius of their injection into the bottomhole zone 40-70 cm deeper than in the previous case. The number of cycles required for an effective impact is determined by the injectivity of the well, as well as by the volume of fluid flow from the reservoir after each impact cycle.

Upon reaching the desired injectivity or flow rate of the well, the treatment is stopped. Raising the tubing, open the circulation valve, tear off the packer and lift the equipment layout to the surface. Thus, the processing is performed in one round-trip operation of equipment and tools.

As a pulse pressure generator, for example, a device for hydrodynamic impact on the bottomhole zone of wells can be used (P. No. 29333, op. 10.05.2003, bull. No. 13) or any other device of a similar purpose; as a packer - any, for example mechanical, packer, landing and unpacking of which is carried out by rotation of the tubing string; as a circulation valve - a valve of any design that provides the opening and closing of the communicating tubing and the annulus of the hole by raising or allowing the tubing when the packer is planted; as a jet pump, a pump of any design, which provides free pumping of working reagents and squeezing fluid through it when they are pumped through the tubing into the formation and driven by pumping fluid into the annulus of the well.

The cyclicity proposed in the inventive method, as well as the depth of the formation treatment and its growth in each cycle of exposure by 40-70 cm, correspond to the following provisions. It is well known that the bottomhole formation zone is most polluted and clogged during drilling, secondary drilling, killing, flushing and other works in the well in the immediate vicinity of the wellbore at a distance of 5-40 cm, depending on the permeability of the reservoir. Pollution caused by the sedimentation of clay particles, salts, heavy asphalt-resinous and paraffinic oil components in the PZP carried out from the reservoir by the flow of fluid flowing to the well is concentrated in a more remote area from the wellbore up to 70 cm or more, up to several meters - also depending on the permeability of the reservoir. Thus, the most effective depth of treatment, affecting both of these areas, is the impact at a distance of 70 cm or more from the wellbore. It was noted above that in low-permeability reservoirs, timely removal of reaction products from the zone of influence significantly increases the efficiency of the SCR. This implies the rationality of stepwise or cyclic processing: initial cleaning of the PPP at a distance of 40 to 70 cm with the removal of reaction products from this zone and subsequent cleaning cycles of more distant zones up to 1 or more meters with an increase in the radius of action each time by a similar value.

Specified in the inventive method, the amplitude of the hydraulic shock to the formation at the time of injection of working reagents 2.0-10.0 MPa is optimal, which is confirmed by laboratory studies on core material of productive formations. When acidic compositions according to the aforementioned patent (RF No. 2191260 С2, class 7 Е21В 43/27) are pumped into the core columns in static mode, that is, at a constant pressure of 4.0 MPa, their permeability increased by 1.2-1 ,3 times. A short-term sharp increase in pressure by 2.0 MPa, carried out several times during the injection process, increased the permeability by 1.4 times; 6.0 MPa - 1.8 times; and by 10.0 MPA - 2.6 times. In the latter case, after exposure to the core, microcracks formed in it, especially noticeable at the acid inlet into the reservoir model. An increase in the amplitude of pressure jumps to 12.0 MPa led to intense crack formation and practically to the destruction of core rock. Thus, pulsed water hammer with an amplitude of 2.0-10.0 MPa contribute to increasing the effectiveness of acid exposure and are optimal.

The cyclic, that is, time-varying, mode of depression noted in the inventive method at the time of the inflow call and extraction of reaction products from the formation causes a change in the mode, in particular, turbulization of the flow in the bottomhole formation zone. This reduces the likelihood of sedimentation and fixing on the pore walls of the rock of secondary sediments. The magnitude of the depression in this case in each cycle should reach values that ensure maximum inflow, that is, the maximum productivity of the formation achieved by exposure to working reagents. The magnitude of the depression cannot be indicated numerically, since in each well, depending on the permeability of the reservoir and the viscosity of the fluid saturating it, its optimal value changes. At the same time, an insufficient amount of depression will not provide the fluid flow rate required for effective cleaning of the bottomhole formation zone, and too high can lead to a negative effect, for example, narrowing of the pores and closing of cracks when creating pore pressure much lower than the mountain pressure. That is, the magnitude of depression should be optimal, namely, providing maximum flow. The desired depression can be created by injection devices, for example, a jet pump. Theoretically, a jet pump can create an arbitrarily low downhole pressure, that is, an unlimited high depression on the formation. However, in fact, when some maximum depression is reached, above which the reservoir, due to its characteristics can no longer provide a more intensive inflow, the pump feed is automatically cut off, it starts to work “idle” and the depression decreases. Thus, a device such as a jet pump automatically, without specifying the numerical value of the depression, provides the required condition of the proposed method.

The effectiveness of the proposed method is confirmed by experimental work at well No. 2617 of the Nivagal field. A SE ₁ oil-bearing stratum was opened with a borehole temperature of 94.5 ° C, represented in the perforation interval of 2788-2799 m by clay sand and siltstones with an average permeability of 0.0081 μm ² . Before the SCR, the well was operated with a flow rate of 3.8 m ³ / day and a water cut of 7%; the productivity coefficient was 0.07 m ³ / day · atm.

For the SCR, the equipment layout including from bottom to top was lowered to the tubing to a depth of 2795 m:

1) accumulator of pulse pressure;

2) packer;

3) circulation valve;

4) jet pump.

Moreover, the jet pump is equipped with a through eccentric hole with a valve that provides free pumping of working reagents and selling fluid through the pump when they are pumped through the tubing into the formation, and a check valve that puts the pump into operation by pumping fluid into the annulus of the well.

In addition, an autonomous bottomhole pressure recording device was installed at the bottom of the layout. Through the above arrangement, in the sequence described above, two cycles of injection into the PPP and extraction of acid solutions and buffer fluids were carried out. An aqueous solution of 8% hydrochloric and 1% hydrofluoric acids was used as the main acid composition, and an aqueous solution of 5% boric acid was used as a buffer selling solution. In the first cycle, 1 m ^{3 of the} specified working reagents was pumped into the reservoir, and in the second - 6 m ³ . With an average reservoir porosity of 18%, this corresponds to the impact radius in the first cycle of 40 cm, and in the second - 110 cm, i.e. 70 cm deeper.

Figure 2 as an example shows the parameters of the second cycle of injection and extraction of reagents recorded by the device. Point 1 of the bottomhole pressure recording curve corresponds to its stabilization at the reservoir level of 26.5 MPa after the first treatment cycle. Point 2 marks the increase in bottomhole pressure to 28.4 MPa when pumped into the tubing and brought to the bottom with an open circulation valve of the acid solution and buffer fluid. At point 3, by the time the circulation valve closes, the pressure stabilizes at 27.3 MPa, at which the formation practically does not accept. In the interval between points 3 and 8, hydro-pulse injection of reagents into the formation was carried out. Selling of the main acid composition was carried out by water hammer with a maximum pressure in the bottomhole zone at points 4 and 5, respectively, 34.8 and 35.6 MPa, and buffer fluid at points 6 and 7 - 31.6 and 30.2 MPa. At this moment, the diagram shows a series of hydraulic impacts on the formation with amplitudes: from point 3 to point 4 - 7.5 MPa, from 3 to 5 - 8.3 MPa, from 3 to 6 and 7, respectively, 4.3 and 2.9 MPa Thus, the injection of working reagents in the BCP was carried out in a hydro-pulse mode with amplitudes of hydroshocks of 2.9-8.3 MPa. It should be noted that during the injection process, especially at the end from point 5 to point 8, a rather sharp and significant decrease in selling pressure is observed. This is explained by the use of pulsed hydropercussion, the effectiveness of which is much higher in comparison with the usual stable injection mode.

To the right of point 8, the diagram represents a record of the mode of inflow call and well completion after reagent injection. The TsA-320 pump unit was switched to the annulus and immediately, unable to withstand the well for reaction, an inflow call was made. At the initial moment, the bottomhole pressure at point 8 was equal to the reservoir pressure - 26.5 MPa. As the fluid was pumped out by the jet pump, it decreased and reached the level of 18.8 MPa at point 9, that is, the depression on the formation at that moment was 7.7 MPa. On the recording curve between points 8 and 9, there are three peaks in the increase in bottomhole pressure. They are explained by interruptions in the flow of the jet pump at the moments when the corresponding maximum depressions were reached, at which the reservoir could not provide a more intense inflow. When removing the clogging layers and cleaning the formation near the wellbore, the filtration ability of the bottomhole zone increased, the jet pump restored the flow, the bottomhole pressure again decreased and the formation worked with greater productivity. At points 10; 12 and 14, minimums of bottomhole pressures are observed within 19.0-19.4 MPa or maximums of depressions at the level of 7.5-7.1 MPa, at which disruptions of the jet pump feeds also occurred. After the next decolmation cycle of the PZP at points 11; 13 and 15, the pump was resumed, and liquid from the bottom was supplied to the wellhead. The stabilization of the bottomhole pressure corresponding to 20.7 MPa on the right side of the diagram at the level of point 16 indicates the cleaning of the bottomhole zone collector after exposure and stabilization of the inflow from the formation. At this point, the flow rate of the well was 10-11 m ³ / day, and the impact was stopped.

After the SCR described method, the well is operated with a stable flow rate of 12.5 m ³ / day and a water cut of 8%; the coefficient of productivity is 0.37 m ³ / day · atm.

Thus, the proposed method for dynamic processing of the bottom-hole zone of high-temperature low-permeability reservoirs is highly efficient and allows you to multiply the productivity of the wells.

Claims (2)

1. A method for dynamically treating the bottom-hole zone of high-temperature low-permeability reservoirs by sequentially injecting acid composition and buffer fluids into the formation and inducing inflow without holding the well for reaction, characterized in that the treatment is performed in two or more cycles of injection and extraction of reagents, each time increasing the radius of processing 40-70 cm, the injection is carried out in a hydro-pulse mode with an amplitude of hydroshocks on the formation of 2.0-10.0 MPa, and the inflow is called in the cyclic depression mode, which ensures maximum productivity of the formation after each cycle of its processing. 2. The method according to claim 1, characterized in that the processing is carried out in one round trip operation of equipment and tools.

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