A method for improving recovery by plugging dominant seepage channels with a through road well

Abstract

The present application relates to the technical field of enhanced recovery in water flooding extra-high water cut stage, and particularly relates to a method for improving recovery by using the advantage of plugging in bypass well, comprising: performing flushing capacity test experiment according to permeability and gel system injection scheme, if the experimental result does not meet the first requirement, adjusting the gel system injection scheme to determine the optimal injection scheme; performing recovery and residual oil saturation test experiment according to the plugging position and the optimal injection scheme, if the experimental result does not meet the second requirement, adjusting the plugging position and / or the gel system injection amount in the optimal injection scheme to determine the final plugging position and / or injection scheme. The present application can realize effective plugging in deep high permeability reservoir, make the injected water divert to displace the remaining oil in low permeability reservoir, and finally realize the improvement of water flooding recovery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of enhanced oil recovery in high water cut stage of water flooding, and particularly relates to a method for enhancing oil recovery by plugging dominant seepage channels with a by-pass well. BACKGROUND

[0002] With the increasingly mature oil and gas resource exploration and development technology in China, many oilfields enter the high water cut stage of water flooding. In this stage, high permeability layers become the focus of attention due to their high water flooding efficiency, while low permeability layers need special treatment to improve the recovery efficiency due to their low water flooding efficiency. Profile control and water plugging technology is designed to plug high permeability layers and make water flow into low permeability layers and drive out the crude oil therein. Profile control and water plugging technology mainly includes chemical water plugging and mechanical water plugging. Chemical water plugging is divided into single liquid method and double liquid method. The single liquid method is to inject a kind of liquid into the oil layer, which forms a plugging material by itself after entering the oil layer, thereby reducing the permeability of the high permeability layer. Commonly used single liquid plugging agents include lime milk, silica sol, gel, sulfuric acid, water-in-thick-oil, etc. The double liquid method involves two working liquids which react to form a plugging material when they meet in the formation. Commonly used double liquid plugging agents include precipitation type, gel type, gel type, and colloidal dispersion type. However, whether profile control is performed through injection wells or water plugging is performed through production wells, the effect of plugging high permeability layers is often not obvious. This is mainly because profile control through injection wells cannot understand the plugging situation in the formation, and due to the limitations of testing instruments and measurement accuracy, a single means cannot accurately give the specific location of the plugging agent in the formation and the plugging situation. Therefore, it is necessary to establish a new method to plug high permeability layers. SUMMARY

[0003] The present application provides a method for enhancing oil recovery by plugging dominant seepage channels with a by-pass well, to solve the problem that the existing profile control and plugging method cannot understand the plugging situation in the formation, the dominant seepage channels exist water channeling, resulting in poor plugging effect and inability to further improve the recovery efficiency.

[0004] According to one aspect of the present application, a method for enhancing oil recovery by plugging dominant seepage channels with a by-pass well is provided, comprising:

[0005] obtaining the reservoir permeability of a target block, the set initial by-pass well plugging position, and the gel system injection scheme;

[0006] performing a scouring capacity test experiment according to the permeability and the gel system injection scheme, obtaining experimental results of the gel system breakthrough pressure gradient, the gelation plugging rate, and the effective plugging radius, and if the experimental results do not meet the first requirement, adjusting the gel system injection scheme to determine the optimal injection scheme corresponding to the case where the experimental results meet the first requirement;

[0007] According to the plugging position and the optimal injection scheme, a recovery and remaining oil saturation test experiment is performed to obtain an oil saturation field distribution experimental result, if the experimental result does not meet the second requirement, the gel system injection amount and concentration in the plugging position and / or the optimal injection scheme are adjusted, and the adjusted plugging position and / or the injection scheme after the injection amount and concentration are adjusted corresponding to the case that the experimental result meets the second requirement are determined as the final plugging position and / or injection scheme.

[0008] Preferably, the method for performing a flushing capacity test experiment according to the permeability and the gel system injection scheme to obtain gel system breakthrough pressure gradient, gelation plugging rate and effective plugging radius experimental results comprises:

[0009] A sandpack model with a predetermined length and a permeability consistent with the permeability of the reservoir in the working area is prepared;

[0010] The sandpack model is vacuumed and saturated with water to determine the pore volume V of the sandpack model, and after being placed in a predetermined temperature constant temperature box for a first predetermined time, water flooding is performed at a predetermined speed to measure the water flooding stage pressure P w ;

[0011] According to the gel system injection scheme, the gel system is injected at a predetermined speed, and the gel is statically gelled;

[0012] The sandpack model is water flooded at a predetermined speed, and the pressure at each pressure measuring point is recorded to determine the maximum injection pressure and the subsequent water flooding stage pressure P w ’;

[0013] According to the maximum injection pressure, the corresponding maximum breakthrough pressure gradient of the gel system is determined;

[0014] According to the water flooding stage pressure P w and the subsequent water flooding stage pressure P w ’, the gelation plugging rate is determined;

[0015] According to the gel system injection scheme, the pore volume of the sandpack model, the maximum breakthrough pressure gradient of the gel system and the length of the sandpack model, the effective plugging radius of the gel system is determined.

[0016] Preferably, the method for determining the gelation plugging rate according to the water flooding stage pressure P w and the subsequent water flooding stage pressure P w ’ comprises:

[0017] The gelation plugging rate is calculated using formula (1);

[0018]

[0019] wherein: η is the plugging rate, %; K w is the permeability of the sandpack model in the water flooding stage, 10 -3 μm 2 ; K' w is the permeability of the sandpack model in the subsequent water flooding stage, 10 -3 μm 2 ; P w is the pressure in the stable section in the water flooding stage, MPa; P w ' is the pressure in the stable section in the subsequent water flooding stage, MPa.

[0020] Preferably, the method for determining the effective plugging radius of the gel system according to the gel system injection scheme, the sandpack model pore volume, the maximum breakthrough pressure gradient of the gel system, and the length of the sandpack model comprises:

[0021] determining the dimensionless design plugging radius of the gel system according to the designed injection volume of the gel system in the gel system injection scheme and the sandpack model pore volume;

[0022] calculating the effective plugging radius of the gel system by using formula (2) according to the dimensionless design plugging radius, the length of the sandpack model, and the length of the sandpack model corresponding to 1 / 2 of the maximum breakthrough pressure gradient of the gel system;

[0023]

[0024] wherein: L' is the effective plugging radius of the gel system, dimensionless; l' is the length of the sandpack model corresponding to 1 / 2 of the maximum breakthrough pressure gradient of the gel system, m; l is the length of the sandpack model, m; L is the dimensionless design plugging radius of the gel system.

[0025] Preferably, the method for determining the dimensionless design plugging radius of the gel system according to the designed injection volume of the gel system in the gel system injection scheme and the sandpack model pore volume comprises:

[0026] calculating the dimensionless design plugging radius of the gel system by using formula (3);

[0027]

[0028] wherein: L is the dimensionless design plugging radius of the gel system, dimensionless; V w is the designed injection volume of the gel system, ml; V is the sandpack model pore volume, ml.

[0029] Preferably, the method for adjusting the gel system injection scheme comprises:

[0030] The polymer concentration in the gel system is increased by a first predetermined value, and / or the injection volume is increased to a second predetermined value, and a flushing capacity test experiment is performed using the gel system injection scheme after the polymer concentration and / or the injection volume is increased until the experimental results obtained meet the first requirement.

[0031] Preferably, the first requirement comprises:

[0032] The gel sealing rate reaches a predetermined sealing rate, and the effective sealing radius is less than a predetermined gel dam radius within a predetermined range, and the breakthrough pressure gradient of the gel system is greater than the measured highest pressure gradient of the target block reservoir;

[0033] And / or,

[0034] The pressure gradient is calculated using formula (4);

[0035]

[0036] In the formula, ΔP is the pressure difference between two adjacent measuring points, and L is the distance between two adjacent measuring points.

[0037] Preferably, the method for obtaining the oil saturation field distribution experimental results according to the sealing position and the optimal injection scheme comprises:

[0038] A microelectrode model is established according to the permeability of the target block reservoir, and a standard curve of resistance and oil saturation is established by testing the model resistance under different proportions of crude oil and water conditions;

[0039] A core model is made according to the permeability of the target block reservoir and the well location;

[0040] The core model is saturated with water and oil;

[0041] The core model is water-flooded at a predetermined displacement speed until the outlet water cut is greater than or equal to a predetermined water cut, and the water-flooded recovery rate is determined;

[0042] The gel system is injected at a predetermined speed according to the gel system injection scheme;

[0043] All injection wells and production wells of the core model are closed, and the gel is allowed to set until static gelation, and then the injection wells and production wells are opened;

[0044] The core model is water-flooded at a predetermined displacement speed until the outlet water cut is greater than or equal to a predetermined water cut, and the water-flooded recovery rate is calculated;

[0045] The resistance values of different test points during the displacement process, water flooding and water flooding after setting are monitored;

[0046] According to the resistance value, an oil saturation value of each test point is determined according to the standard curve, and an oil saturation field distribution result is obtained by using the oil saturation values of the test points.

[0047] Preferably, the method for saturating the core model with water and oil comprises:

[0048] Each pressure test point is vacuumed for a predetermined time from the injection end of the core model;

[0049] The core model is saturated with artificial synthetic brine, and then placed in a target block reservoir temperature incubator for more than a predetermined time;

[0050] Crude oil is injected into the core model from the injection end of the core model, and the displacement is performed until no water is discharged, and the core model is placed in a constant temperature incubator for constant temperature curing for more than a predetermined time.

[0051] Preferably, the second requirement comprises:

[0052] The flow channel permeability resistance of the plugged through well in the core model is increased, the injected water forms a flow around the well after encountering the well dam, the swept area near the production well is expanded, the injection pressure is increased, and the oil washing effect of the water drive swept area is improved.

[0053] The present application has at least the following beneficial effects:

[0054] The present application provides a method for improving recovery by plugging the advantage flow channel of the through well, which plugs the high permeability layer by using the injection gel system of the through well between the injection well and the production well, thereby preventing the advantage flow channel from water channeling, realizing effective plugging of the deep high permeability reservoir, diverting the injected water to displace the remaining oil in the low permeability reservoir, and finally improving the water drive recovery. BRIEF DESCRIPTION OF DRAWINGS

[0055] The accompanying drawings, which are incorporated into and form part of the specification, illustrate embodiments consistent with the present application and, together with the specification, serve to explain the technical solutions of the present application.

[0056] Figure 1 A flow chart of the method for improving recovery by plugging the advantage flow channel of the through well according to an embodiment of the present application is shown;

[0057] Figure 2 A pressure gradient distribution diagram of the target block between the injection well and the production well according to an embodiment of the present application is shown;

[0058] Figure 3 A displacement stage pressure distribution diagram according to an embodiment of the present application is shown;

[0059] Figure 4A schematic diagram showing the gel system flush breakthrough pressure gradient according to an embodiment of the present application;

[0060] Figure 5 A schematic diagram showing a core model according to an embodiment of the present application;

[0061] Figure 6 A plot showing the recovery and water cut variation according to an embodiment of the present application;

[0062] Figure 7 A plot showing the pressure field distribution according to an embodiment of the present application, wherein (a) is the pressure field distribution after water flooding, and (b) is the pressure field distribution after injecting gel;

[0063] Figure 8 A plot showing the oil saturation field distribution according to an embodiment of the present application, wherein (a) is the oil saturation field distribution after model saturation, (b) is the oil saturation field distribution after model water flooding, and (c) is the oil saturation field distribution after model injecting gel, profile control and subsequent water flooding. DETAILED DESCRIPTION

[0064] Various exemplary embodiments, features, and aspects of the present application will be described herein below with reference to the accompanying drawings. The same reference numbers in different drawings represent the same or similar elements. Although various aspects of the embodiments are illustrated in the drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

[0065] The term "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any implementation described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations.

[0066] The term "and / or" used herein only means an association relationship of the associated objects, and means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. In addition, the term "at least one" herein means any one of the plurality or any combination of at least two of the plurality, for example, including at least one of A, B, and C can mean including any one or more elements selected from the set consisting of A, B, and C.

[0067] In addition, in order to better illustrate the present application, numerous specific details are given in the following detailed description. Those skilled in the art should understand that the present application can also be implemented without some specific details. In some examples, methods, means, elements and circuits well known to those skilled in the art are not described in detail in order to highlight the main idea of the present application.

[0068] Figure 1 A flowchart showing a method for improving recovery by plugging the preferential flow channel with a pass-by well according to an embodiment of the present application;Figure 2 A target block injection-production well pressure gradient distribution diagram is shown according to an embodiment of the present application; Figure 3 A displacement stage pressure distribution diagram is shown according to an embodiment of the present application; Figure 4 A gel system flushing breakthrough pressure gradient schematic diagram is shown according to an embodiment of the present application; Figure 5 A core model schematic diagram is shown according to an embodiment of the present application; Figure 6 A recovery factor and water cut change curve is shown according to an embodiment of the present application; Figure 7 A pressure field distribution diagram is shown according to an embodiment of the present application, wherein (a) is a water flooding post pressure field distribution, and (b) is a gel injection post pressure field distribution; Figure 8 An oil saturation field distribution diagram is shown according to an embodiment of the present application, wherein (a) is a model saturated oil post oil saturation field distribution, (b) is a model water flooding post oil saturation field distribution, and (c) is a model gel injection, profile control and subsequent water flooding post oil saturation field distribution. Figures 1-8 As shown in the figure, a method for improving recovery factor by using a passing well to block an advantage seepage channel includes the following steps: S01: obtaining a target block reservoir permeability, a set initial passing well blocking position and a gel system injection scheme; S02: performing a flushing capacity test experiment according to the permeability and the gel system injection scheme, obtaining gel system breakthrough pressure gradient, gel blocking rate and effective blocking radius experimental results, if the experimental results do not meet the first requirement, adjusting the gel system injection scheme, determining that the corresponding gel system injection scheme under the condition that the experimental results meet the first requirement is the optimal injection scheme; S03: performing a recovery factor and remaining oil saturation test experiment according to the blocking position and the optimal injection scheme, obtaining an oil saturation field distribution experimental result, if the experimental result does not meet the second requirement, adjusting the blocking position and / or the gel system injection amount in the optimal injection scheme, determining that the adjusted blocking position and / or the injection amount and concentration after the adjustment are the final blocking position and / or injection scheme under the condition that the experimental result meets the second requirement.

[0069] The method for improving recovery factor by using a passing well to block an advantage seepage channel provided by the embodiment of the present application specifically includes the following steps:

[0070] S01: obtaining a target block reservoir permeability, a set initial passing well blocking position and a gel system injection scheme.

[0071] In the embodiment of the present application, the plugging effect of the gel system in the reservoir has an important influence on improving the recovery rate, and the purpose of the flushing capacity test is to determine the gelation strength and range of the gel system in the reservoir of the target block. In order to determine the gelation strength and gelation distance of the gel system at different positions in the reservoir, a dynamic gelation experiment of the gel system needs to be carried out. When the experiment is carried out, the average permeability of the reservoir to be plugged in the working area needs to be obtained, and a 10m long sand filling pipe (containing 17 pressure measuring points) model is established according to the average permeability. The sand filling pipe model is used to carry out the flushing capacity test experiment by using the initially set gel system injection scheme, the pressure at different pressure measuring points in the process of water drive, gel system injection and water drive after gelation is tested, so as to determine the optimal gel system injection scheme, and the recovery rate and residual oil saturation test experiment is carried out through the initially set plugging position of the through well, so as to determine the final plugging position and the gel system injection scheme. The target block is effectively plugged by using the final plugging position and the gel system injection scheme.

[0072] Step S02: according to the permeability and the gel system injection scheme, carrying out the flushing capacity test experiment, obtaining the gel system breakthrough pressure gradient, gelation plugging rate and effective plugging radius experimental results, if the experimental results do not meet the first requirement, adjusting the gel system injection scheme, determining the corresponding gel system injection scheme as the optimal injection scheme when the experimental results meet the first requirement.

[0073] In the present application, the method for carrying out the flushing capacity test experiment according to the permeability and the gel system injection scheme to obtain the gel system breakthrough pressure gradient, gelation plugging rate and effective plugging radius experimental results comprises: making a sand filling pipe model with a predetermined length and a permeability meeting the permeability of the reservoir in the working area; vacuumizing the sand filling pipe model and saturating water to determine the pore volume V of the sand filling pipe model, and then placing it in a predetermined temperature constant temperature box for a first predetermined hour, then water driving at a predetermined speed to measure the pressure P w of the sand filling pipe model in the stable stage of the water drive stage; according to the gel system injection scheme, injecting the gel system at a predetermined speed, and gelating to static; water driving the sand filling pipe model at a predetermined speed, and recording the pressure of each pressure measuring point to determine the maximum injection pressure and the pressure P w of the sand filling pipe model in the stable stage of the subsequent water drive stage; according to the maximum injection pressure, determining the corresponding maximum breakthrough pressure gradient of the gel system; according to the pressure P w of the sand filling pipe model in the stable stage of the water drive stage and the pressure P w of the sand filling pipe model in the stable stage of the subsequent water drive stage, determining the gelation plugging rate; according to the gel system injection scheme, the pore volume of the sand filling pipe model, the maximum breakthrough pressure gradient of the gel system and the length of the sand filling pipe model, determining the effective plugging radius of the gel system.

[0074] In this embodiment of the invention, the predetermined length is 10 meters. The method for constructing a sand-filled pipe model of predetermined length with a permeability equal to the reservoir permeability of the work area includes: conducting a gel system displacement experiment using a 10-meter-long sand-filled pipe; to prevent sand migration during injection, which could lead to a decrease in local permeability of the sand-filled pipe, the sand is screened, using only two mesh sizes for filling; and the sand is filled by tapping the pipe wall with a hammer to vibrate it. The specific sand-filling steps are as follows:

[0075] 1.1 Screening sand: Use sieves with different mesh sizes to screen sand of 30-50 mesh and 80-90 mesh.

[0076] 1.2. Construct a model based on the permeability of the target block and the filling method of the sand-filled pipe model. If the permeability of the sand-filled model is higher than the permeability K of the target block, increase the proportion of 100-110 mesh sand; conversely, if the permeability of the sand-filled model is lower than the permeability of the target block, increase the proportion of 20-30 mesh sand. Adjust the proportion of different mesh sands until the permeability K of the constructed sand-filled model is reached. w The permeability K of the reservoir in the target block with the dominant seepage channel differs from that of the reservoir in the working area by ±5%, meaning that the model permeability matches the permeability of the reservoir in the working area.

[0077] 1.3. Fill the two straight pipes and one bent pipe together with sand, adding 30ml of sand each time, and tap the pipe wall for 1 minute to ensure that the sand is in stable contact and no longer settles.

[0078] 1.4 Connect the two sets of sand-filling pipes at the top with a bend, and pour sand into the sampling port of the upper bend until the sand no longer settles.

[0079] 1.5 Tighten the plugs at both ends of the connection between the bend and the straight pipe.

[0080] The specific steps of the gel system flushing capacity test include:

[0081] 2.1 After vacuuming the completed sand-filled pipe model and saturating it with water, calculate the pore volume V of the model. Place the model in the target block reservoir temperature constant temperature chamber for the first predetermined hour (24 hours), and then water drive it at a predetermined rate (0.1 ml / min). Measure the steady-state pressure P of the sand-filled pipe model during the water drive stage. w Calculate the water phase permeability K w ;

[0082] 2.2. Inject the gel system into the water-driven sand-filled tube model at a predetermined rate (0.1 ml / min) up to the designed volume V in the injection plan. w Record the pressure at each measurement point; gel the sample into a glass container and allow it to stand statically gel.

[0083] 2.3, water flooding is carried out on the gelled sandpack model at a predetermined speed (0.1 ml / min), and the pressure of each pressure measuring point, the maximum injection pressure, and the subsequent pressure plateau value are recorded.

[0084] The initial gel system injection scheme used in the experiment is shown in Table 1.

[0085] Table 1: Gel system injection scheme

[0086]

[0087] In the embodiment of the present application, the gelling radius is determined by first determining the maximum breakthrough pressure gradient of the gel system in the sandpack model, as shown in the displacement stage pressure distribution diagram of formula (4). Figure 3 As can be seen from the pressure distribution along the sandpack gradually increasing with the increase of the gel injection amount, and the pressure gradient near the inlet drops greatly. According to the measured maximum injection pressure corresponding to the pressure value of the measuring point and the pressure difference ΔP between the adjacent measuring points and the distance L, the maximum breakthrough pressure gradient of the gel system corresponding to the sandpack model is calculated by using formula (4).

[0088] In the present application, the gel sealing rate is determined according to the water flooding stage pressure P w and the subsequent water flooding stage pressure P w '.

[0089]

[0090] In the formula, η is the sealing rate, %; K w is the water flooding stage permeability of the sandpack model (water phase permeability), 10 -3 μm 2 ; K' w is the subsequent water flooding stage permeability of the sandpack model, 10 -3 μm 2 ; P w is the water flooding stage pressure plateau value, MPa; and P' w is the subsequent water flooding stage pressure plateau value, MPa.

[0091] In the embodiment of the present application, the gel system gelling sealing rate η in the reservoir can directly reflect the sealing effect of the gel system after gelling water flooding breakthrough under the dynamic conditions of the injected reservoir, and therefore the gel system gelling sealing rate in the reservoir is taken as a gelling characteristic parameter to evaluate the gelling sealing effect under the dynamic conditions of the injected reservoir. The gelling sealing rate calculation formula is shown in formula (1).

[0092] According to the water flooding and subsequent water flooding pressure of the sandpack model, i.e. the water flooding stage pressure plateau value Pw and the subsequent pressure plateau value P w Substitute the value of P' (the plateau pressure of the subsequent water flooding stage) into formula (1) to calculate the corresponding gelation plugging rate.

[0093] The gelation plugging rate calculated by the embodiment of the present application is shown in Table 2 below.

[0094] Table 2: Gelation plugging rate calculation results of the gel system

[0095]

[0096] In the present application, the method for determining the effective plugging radius of the gel system according to the gel system injection scheme, the pore volume of the sandpack model, the maximum breakthrough pressure gradient of the gel system and the length of the sandpack model comprises: determining the dimensionless design plugging radius of the gel system according to the designed injection amount of the gel system in the gel system injection scheme and the pore volume of the sandpack model; and calculating the effective plugging radius of the gel system by using formula (2) according to the dimensionless design plugging radius, the length of the sandpack model and the length of the sandpack model corresponding to 1 / 2 of the maximum breakthrough pressure gradient of the gel system;

[0097]

[0098] In the formula, L' is the effective plugging radius of the gel system, dimensionless; l' is the length of the sandpack model corresponding to 1 / 2 of the maximum breakthrough pressure gradient of the gel system in the sandpack model, m; l is the length of the sandpack model, m; and L is the dimensionless design plugging radius of the gel system.

[0099] In the present application, the method for determining the dimensionless design plugging radius of the gel system according to the designed injection amount of the gel system in the gel system injection scheme and the pore volume of the sandpack model comprises: calculating the dimensionless design plugging radius of the gel system by using formula (3);

[0100]

[0101] In the formula, L is the dimensionless design plugging radius of the gel system, dimensionless; V w is the designed injection amount of the gel system, ml; and V is the pore volume of the sandpack model, ml.

[0102] In the embodiment of the present application, the effective plugging radius of the gel system in the reservoir can directly reflect the gelation radius under the dynamic conditions after a certain amount of gel system is injected into the reservoir, so the effective plugging radius of the gel system in the reservoir is taken as a gelation characteristic parameter to evaluate the gelation radius under the dynamic conditions after a certain amount of gel system is injected into the reservoir.

[0103] According to the pore volume of the sandpack model and the total designed injection volume of the injection scheme, the corresponding dimensionless plugging radius L of the gel system is calculated by substituting formula (3).

[0104] Table 3: Calculation results of the dimensionless plugging radius of the gel system

[0105]

[0106] As Figure 4 The pressure gradient curve of each test point at each stage of the sandpack model scouring capacity experiment is shown. The length corresponding to the maximum breakthrough pressure gradient 1 / 2 is defined as the effective plugging radius. According to the length of the sandpack model corresponding to the maximum breakthrough pressure gradient 1 / 2, the dimensionless plugging radius and the length of the sandpack model l calculated above, the corresponding effective plugging radius L' of the gel system is calculated by substituting formula (2).

[0107] In the present application, the first requirement includes that the gelation plugging rate reaches a predetermined plugging rate, the effective plugging radius is less than a predetermined range of a predetermined gel dam radius, and the breakthrough pressure gradient of the gel system is greater than the measured maximum pressure gradient of the target block reservoir.

[0108] and / or,

[0109] The pressure gradient is calculated by formula (4);

[0110]

[0111] In the formula, ΔP is the pressure difference between two adjacent pressure measurement points, and L is the distance between two adjacent pressure measurement points.

[0112] In the present application, the method for adjusting the gel system injection scheme includes increasing the polymer concentration in the gel system by a first predetermined value and / or increasing the injection volume to a second predetermined value. The gel system injection scheme after increasing the polymer concentration and / or the injection volume is used for scouring capacity test experiment until the experimental results meet the first requirement.

[0113] In the embodiment of the present application, the predetermined plugging rate is 98%. As shown in Table 2, the plugging rate of the gel system obtained by experiment in the target reservoir can reach 98% or more. The higher the permeability of the target layer, the better the plugging effect of the gel system. If the plugging rate does not reach 98% or more, the viscosity of the gel system is increased by increasing the polymer concentration in the gel system. After increasing the polymer viscosity of the gel system in the injection scheme, the above scouring capacity test experiment is repeated, and the corresponding plugging rate is calculated again by formula (1) according to the experimental results until the plugging rate reaches 98% or more.

[0114] The predetermined range is 50%. If the effective sealing radius of the gel system calculated based on the experimental results is less than 50% of the expected gel radius (predetermined gel dam radius), the amount of gel system injected needs to be increased. After increasing the polymer viscosity of the gel system in the injection scheme, the above-mentioned flushing capacity test experiment is repeated, and the corresponding effective sealing radius is calculated again using formula (2) based on the experimental results until the effective sealing radius is less than 50% of the expected gel radius.

[0115] The highest measured pressure gradient of the target block reservoir is calculated using equation (4) based on the pressure distribution data between the injection wells and production wells in the target block. In this embodiment of the invention, the pressure gradient of the target block is 2.47 MPa / m. The pressure gradients at different locations are obtained by analogy. The resulting pressure gradient distribution map is shown in the attached figure. Figure 2 As shown.

[0116] The erosion resistance of the gel system was evaluated by comparing the calculated breakthrough pressure and gradient of the sand-filled pipe model gel system with the actual injection pressure difference and pressure gradient curves between the injection and production wells in the target block. For example... Figure 4 As shown, the breakthrough pressure gradient of the gel system is much greater than the highest pressure gradient of the gel well in the target block reservoir. The higher the permeability of the target layer, the higher the breakthrough pressure and breakthrough pressure gradient of the gel system.

[0117] When the gel system achieves a plugging rate of over 98% in the target reservoir, the effective plugging radius is less than 50% of the expected gel radius, and the maximum pressure gradient of the gel system is greater than the highest measured pressure gradient in the target block reservoir, the corresponding gel system injection scheme (including the adjusted polymer viscosity and gel system injection volume) is the optimal injection scheme.

[0118] Step S03: Based on the plugging location and the optimal injection scheme, conduct recovery rate and residual oil saturation test experiments to obtain the oil saturation field distribution experimental results. If the experimental results do not meet the second requirement, adjust the injection amount of the gel system in the plugging location and / or the optimal injection scheme to determine the adjusted plugging location and / or the injection scheme after adjusting the injection amount and concentration when the experimental results meet the second requirement. This is the final plugging location and / or injection scheme.

[0119] In the embodiment of the present application, in order to determine the deep reservoir liquid flow diversion capability of the injection gel system of the through road well between injection wells and the development effect after improving the reservoir, the injection well position of the through road well, the injection amount of the gel system and the gel system formula are optimized. By calibrating the resistance and oil saturation, a set of standard curves of resistance and oil saturation suitable for the model used in the present application is established. By monitoring the resistance of the core model with embedded electrodes, the change of oil saturation before and after injecting the gel system of the through road well is calculated, the saturation field distribution cloud map is drawn, and the liquid flow diversion effect and the enhanced oil recovery effect of the injected gel system are evaluated.

[0120] In the present application, the method for obtaining the oil saturation field distribution experimental results by testing the recovery ratio and the remaining oil saturation according to the plugging position and the optimal injection scheme comprises the following steps: establishing a micro-electrode model according to the reservoir permeability of a target block, establishing a standard curve of resistance and oil saturation by testing the model resistance under different proportions of crude oil and water conditions; preparing a core model according to the reservoir permeability and well position of the target block; saturating water and oil in the core model; determining the water drive recovery ratio by water flooding the core model at a predetermined displacement speed until the outlet water cut is higher than a predetermined water cut; injecting the gel system at a predetermined speed according to the gel system injection scheme; closing all injection wells and production wells of the core model, waiting for gelation until static gelation, and then opening the injection wells and production wells; calculating the water drive recovery ratio by water flooding the core model at a predetermined displacement speed until the outlet water cut is higher than a predetermined water cut; monitoring the resistance values of different test points during the displacement process, the water drive and the water drive after waiting for gelation; determining the oil saturation values of each test point according to the standard curve based on the resistance values; and obtaining the oil saturation field distribution results by using the oil saturation values of each test point.

[0121] In the embodiment of the present application, the rock-electricity relationship standard curve is established: a micro-electrode model with a size of 4.5*4.5*4.5 cm is established, the resistance of the micro-electrode model under different proportions of crude oil and water (oil saturation is 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 44%, 48%, 52%, 56%, 60%, 65%, 70%, 75%) is tested, and a standard curve of resistance and oil saturation is established.

[0122] In the present application, the method for saturating water and oil in the core model comprises the following steps: vacuumizing each pressure test point for a predetermined number of hours from the injection end of the core model; saturating the core model with artificial synthetic brine, and then placing it in a target block reservoir temperature incubator for more than a predetermined number of hours; injecting crude oil into the core model from the injection end of the core model until no water is discharged, and then placing the core model in a constant temperature incubator for constant temperature curing for more than a predetermined number of hours.

[0123] In the embodiment of the present application, as shown in Figure 5 The established core model is shown, and the model parameters are: model size 30x30x4.5 cm, permeability 826 mD, rubber dam well position: 1 / 2, interwell communication: 4-way communication, porosity 26.0%, oil saturation: 70.1%. The saturated water and saturated oil process is:

[0124] 3.1, check the air tightness of the core model: put the core with a size of 30x30x4.5 cm into water, pass in gas at a flow rate of 0.5 ml / min, and check whether the model leaks air;

[0125] 3.2, vacuum: vacuum for 6 hours from the injection end of the core model, and vacuum for 1 hour for the remaining 8 pressure test points, for a total of 14 hours;

[0126] 3.3, saturated water: saturated artificial synthetic brine, measure the saturated water volume, calculate the pore volume (pore volume is used for gel injection scheme determination), and then place the core model in the target block reservoir temperature incubator for constant temperature for a predetermined number of hours (72 hours) or more;

[0127] 3.4, model saturated oil: inject crude oil into the four corners of the core from the center point of the core model as the injection end, and displace until no water is discharged; then inject crude oil into the core model from the four injection ends around the center point of the core model, and displace until no water is discharged; finally, inject crude oil into the core model from the outermost 4-point injection end, and displace until the core model does not discharge water. Measure the cumulative water production, calculate the original oil saturation, and again place the core model in the incubator for constant temperature curing for 72 hours or more.

[0128] The process of saturating water and oil for the core model is:

[0129] 3.5, water flooding: water flood the core model at a predetermined displacement rate (1 ml / min) until the outlet water cut is more than 98%, and calculate the water flooding recovery rate;

[0130] 3.6, injection of gel system: inject the gel system at a predetermined speed (1 ml / min) to the designed amount V w ;

[0131] 3.7, waiting for condensation: close all injection wells and production wells of the model, and wait for condensation for 72h until the parallel samples are statically gelled, and then open the water injection wells and production wells;

[0132] 3.8, subsequent water flooding: water flood at a predetermined speed (1 ml / min) until the outlet water cut of the core model is more than 98%, and calculate the subsequent water flooding recovery rate;

[0133] 3.9, Saturation field and pressure field monitoring: the resistance value and pressure value of each monitoring point are monitored once during the displacement process, when the saturated oil, water drive and gel system after the second water drive. As shown in Table 4, the recovery and residual oil saturation test experiment scheme.

[0134] Table 4: Recovery and residual oil saturation test experiment scheme

[0135]

[0136] The recovery and water cut change curve drawn according to the recovery and residual oil saturation test experiment results is shown in Figure 6 , and the pressure field distribution is shown in Figure 7 , wherein (a) is the pressure field distribution after water drive, and (b) is the pressure field distribution after injecting gel. As can be seen from Figure 6 and 7 , the pressure field distribution is uneven, and gradually advances along the injection well to the production well. After injecting gel + waiting for gel + subsequent water drive, the pressure gradient gradually becomes uniform after the gel.

[0137] The resistance of the core model at each test point in different displacement stages is measured by the electrode method, the saturation value of each test point is calculated according to the standard curve between resistance and oil saturation, and the SUFER software is used to form a model oil saturation distribution cloud map, as shown in Figure 8 , wherein (a) is the oil saturation field distribution of the model after saturated oil, (b) is the oil saturation field distribution of the model after water drive, and (c) is the oil saturation field distribution of the model after injecting gel, profile control and subsequent water drive.

[0138] In the present application, the second requirement includes: the seepage resistance of the water flow channel at the plugged through well in the core model is improved, the injected water forms a flow around the gel dam after meeting the through well gel dam, the swept area near the production well is expanded, the injection pressure is increased, and the oil washing effect of the water drive swept area is improved.

[0139] In the embodiment of the present application, according to the final oil saturation field distribution result, it is determined whether the reservoir flow direction in the core model is changed, whether the water injection swept area, injection pressure and oil washing effect are improved compared with before injecting the gel system, to judge whether the final development effect is improved.

[0140] If the test results of the recovery ratio and the remaining oil saturation do not meet the second requirement, the plugging position and / or the injection amount and concentration of the gel system in the optimal injection scheme are adjusted. For example, the gel system cannot change the liquid flow direction, or the swept area near the production well, the injection pressure, and the oil washing effect of the water drive swept area are not changed or reduced, the gel well (passing well) plugging position (including well location, number, and layer position) can be adjusted, and / or the injection amount of the gel system in the optimal injection scheme is increased and the concentration of the gel system component is increased, the passing well position and / or the concentration of the gel system component are adjusted, the above-mentioned recovery ratio and remaining oil saturation test are repeated, and whether the second requirement is met is determined again according to the test results. If the second requirement is met, the adjusted passing well plugging position and the optimal injection scheme of the gel system after the injection amount is adjusted and the concentration of the gel system component is increased are the final determined plugging position and injection scheme. According to the obtained final plugging position and injection scheme, the passing well advantage seepage channel in the target block is plugged to improve the recovery ratio of the block.

[0141] The test results of the remaining oil in the water drive stage show that the injected water forms a water flow advantage channel from the injection well to the production well. The water flow channel at the bottom of the injection well is obviously wider than that at the bottom of the production well, indicating that the sweep in the near-wellbore zone of the injection well is more sufficient, and the sweep degree in the deep part of the reservoir needs to be further improved.

[0142] The test results of the remaining oil in the gel injection + subsequent water drive stage show that the gel well improves the seepage resistance of the water flow channel, and the injected water forms a flow around the gel, expanding the swept area near the production well; and the increase of the injection pressure improves the oil washing effect of the water drive swept area.

[0143] It can be understood that the above-mentioned various method embodiments of the present application can be combined with each other to form combined embodiments without violating the principle logic. Due to the limited space, the present application will not be described again.

[0144] It can be understood by those skilled in the art that in the above-mentioned method of the specific embodiment, the writing order of each step does not mean a strict execution order and does not constitute any limitation on the implementation process, and the specific execution order of each step should be determined by its function and possible internal logic.

[0145] The present application establishes a method for plugging high permeability layers by injecting a gel system into an abandoned through road well between injection and production wells to improve recovery, aiming to better plug high permeability layers to improve recovery and solve the problem of water channeling in dominant seepage channels. As an abandoned through road well between a production well and an injection well, the high permeability layer is plugged by injecting a gel system. Compared with traditional profile control and water plugging methods, the present application has more significant plugging effect on high permeability reservoirs. Traditional profile control and water plugging technology mainly targets the injection well for plugging. However, the present application combines the methods of injection well profile control and gel injection in the through road well, which can more effectively plug high permeability layers and improve recovery. By conducting flushing capacity test experiments and recovery and residual oil saturation test experiments, the injection position and amount of the plugging agent can be more accurately controlled, thereby improving the plugging effect; the actual effective plugging distance is calculated according to the change of interwell pressure gradient, and the plugging rate is determined to evaluate the plugging capacity of the gel system; by comparing the pressure gradient, the production well and injection well gel can be prevented from being broken due to the large pressure gradient between the production well and the injection well, ensuring that the pressure gradient of the through road well between the actual production well and the injection well is less than the maximum breakthrough pressure gradient during the experiment, so that the gel plugging effect is more stable. The gel has the ability to be not easily broken, and the plugging time effect is good, so the recovery is significantly improved. In practical application, by combining the use of injection well profile control and gel injection in the through road well, deep plugging of high permeability reservoirs can be achieved, the injected water can be diverted to displace the remaining oil in low permeability reservoirs, and the water flooding recovery can be improved.

[0146] In summary, the present application plugs high permeability layers by injecting a gel system into an abandoned through road well between injection and production wells, which not only improves the plugging effect, but also significantly improves the recovery, and has a broad application prospect.

[0147] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles, practical applications or technical improvements in the market of the embodiments, or to enable other ordinary skilled persons in the art to understand the embodiments disclosed herein.

Claims

1. A method for enhancing oil recovery by utilizing the advantage of the thief zone blocking of the bypass well, characterized in that, The application relates to a gel system injection scheme optimization method for a target block. The method comprises the following steps: acquiring reservoir permeability of a target block, an initial plugging position of a bypass well and a gel system injection scheme; According to the permeability and the gel system injection scheme, a flushing capacity test experiment is carried out to obtain experimental results of a gel system breakthrough pressure gradient, a gelation plugging rate and an effective plugging radius, if the experimental results do not meet a first requirement, the gel system injection scheme is adjusted, and the gel system injection scheme corresponding to the case that the experimental results meet the first requirement is determined as an optimal injection scheme; The first requirement comprises that the gelation plugging rate reaches a predetermined plugging rate, the effective plugging radius is smaller than a predetermined gel dam radius within a predetermined range, and the gel system breakthrough pressure gradient is greater than a highest measured pressure gradient of a target block reservoir; wherein the predetermined range is 50%, and the pressure gradient is calculated by using formula (4); （4）； In the formula, Delta P is a pressure difference between two adjacent pressure measuring points, and L is a distance between the two adjacent pressure measuring points; The gel system flushing capacity test experiment specifically comprises the following steps: a sand filling pipe model is made, vacuumized, saturated with water, and then the model pore volume V is calculated; after the model is placed in a target block reservoir temperature constant temperature box for a first predetermined time, water is driven at a predetermined speed, the sand filling pipe model water driving stage stable pressure is measured, and the water phase permeability is calculated; the gel system is injected into the water driven sand filling pipe model at a predetermined speed to the designed amount in the injection scheme, and the pressure of each pressure measuring point is recorded; the gel is statically gelled in a glass container; the gelled sand filling pipe model is water driven at a predetermined speed, and the pressure of each pressure measuring point, the maximum injection pressure and the subsequent pressure stable value are recorded; According to the plugging position and the optimal injection scheme, a recovery efficiency and residual oil saturation test experiment is carried out to obtain experimental results of an oil saturation field distribution, if the experimental results do not meet a second requirement, the plugging position and the optimal injection scheme are adjusted, the adjustment comprises adjusting the plugging position of the bypass well, including well position, quantity and layer position, and adjusting the injection amount and concentration of the gel system in the optimal injection scheme by increasing the injection amount of the gel system and increasing the component concentration of the gel system; The adjusted plugging position and the injection scheme after the injection amount and the concentration are adjusted under the condition that the experimental results meet the second requirement are determined as the final plugging position and the injection scheme; the second requirement comprises that the flow channel permeation resistance of the bypass well in the core model is improved, the injected water forms a flow around the gel dam after encountering the bypass well, the swept area near the production well is expanded, the injection pressure is increased, and the oil washing effect of the water driving swept area is improved.

2. The method for enhancing oil recovery by taking advantage of the plugging of the preferential flow channel with the thief zone according to claim 1, characterized in that, The method for carrying out a flushing capacity test experiment according to the permeability and the gel system injection scheme to obtain experimental results of a gel system breakthrough pressure gradient, a gelation plugging rate and an effective plugging radius comprises the following steps: A sand filling pipe model of a predetermined length and permeability consistent with the permeability of the reservoir of the work area is made; if the permeability of the sand filling model is higher than the permeability K of the target block, the proportion of 100-110 mesh sand is increased; otherwise, the proportion of 20-30 mesh sand is increased; the proportion of sand of different mesh is adjusted until the permeability Kw of the sand filling model is within ±5% of the permeability K of the dominant seepage channel reservoir of the target block; The sandpack model is vacuumed and saturated with water to determine the pore volume of the sandpack model V After the sandpack model is placed in a predetermined temperature oven for a first predetermined time, the sandpack model is water flooded at a predetermined rate to determine the pressure at the plateau of the water flood stage of the sandpack model P w ; According to the gel system injection scheme, the gel system is injected at a predetermined speed, and the gel is statically gelled; The sand pack model is water flooded at a predetermined rate and the pressure at each pressure tap is recorded to determine the maximum injection pressure and the plateau pressure during the subsequent water flood stage P w ’ ; According to the maximum injection pressure, the corresponding maximum breakthrough pressure gradient of the gel system is determined; According to the pressure of the stable section of the water drive stage P w , and the pressure of the stable section of the subsequent water drive stage P w ’ , to determine the gel sealing rate; According to the gel system injection scheme, the pore volume of the sand filling pipe model, the maximum breakthrough pressure gradient of the gel system, and the length of the sand filling pipe model, the effective plugging radius of the gel system is determined.

3. The method for improving the recovery ratio by taking advantage of the plugging of the over-road well to block the preferential flow channel according to claim 2, characterized in that, The method for determining the gel sealing rate comprises the following steps: P w The method for determining the gel sealing rate comprises the following steps: P w ’ The method for determining the gel sealing rate comprises the following steps: It comprises: The gel plugging rate is calculated by formula (1); （1）； wherein: is the plugging rate, is the sandpack model permeability during the waterflood stage, 10 -3 μm 2 ; is the sandpack model permeability during the subsequent waterflood stage, 10 -3 μm 2 ; is the plateau pressure during the waterflood stage, MPa. P w ’ is the plateau pressure during the subsequent waterflood stage, MPa.

4. The method for enhancing oil recovery by taking advantage of the plugging effect of the thief zone according to claim 2, characterized in that, The method for determining the effective plugging radius of the gel system according to the gel system injection scheme, the pore volume of the sand filling pipe model, the maximum breakthrough pressure gradient of the gel system, and the length of the sand filling pipe model comprises: According to the gel system design injection amount in the gel system injection scheme and the pore volume of the sand filling pipe model, the dimensionless plugging radius of the gel system is determined; According to the dimensionless plugging radius, the length of the sand filling pipe model, and the corresponding length of the sand filling pipe model at 1 / 2 of the maximum breakthrough pressure gradient of the gel system, the effective plugging radius of the gel system is calculated by formula (2); （2）； In the formula: is the effective plugging radius of the gel system, dimensionless; is the length of the sandpack model corresponding to the maximum breakthrough pressure gradient of the gel system, 1 / 2, m; is the length of the sandpack model, m; L is the dimensionless plugging radius of the gel system design.

5. The method for enhancing oil recovery by taking advantage of the plugging effect of the thief zone according to claim 4, characterized in that, The method for determining the dimensionless plugging radius of the gel system according to the gel system design injection amount in the gel system injection scheme and the pore volume of the sand filling pipe model comprises: The dimensionless plugging radius of the gel system is calculated by formula (3); （3）； In the formula: Dimensionless plugging radius designed for the gel system Injection volume designed for the gel system, ml Sand pack model pore volume, ml 6. The method for enhancing oil recovery by taking advantage of the plugging of the preferential flow channels with the thief zone according to claim 1, wherein, The method for adjusting the gel system injection scheme comprises: The polymer concentration in the gel system is increased by a first predetermined value, and the injection amount is increased to a second predetermined value, and the gel system injection scheme after increasing the polymer concentration and the injection amount is used for the flushing capacity test experiment, until the experimental results meet the first requirement.

7. The method for enhancing oil recovery by taking advantage of the plugging effect of the thief zone according to claim 1, characterized in that, The method for obtaining the oil saturation field distribution experimental results according to the plugging position and the optimal injection scheme comprises: A microelectrode model is established according to the reservoir permeability of the target block, and a standard curve of resistance and oil saturation is established by testing the model resistance under different proportions of crude oil and water conditions; A core model is made according to the reservoir permeability and well location of the target block; The core model is saturated with water and oil; The core model is water-flooded at a predetermined displacement speed until the outlet water cut is above a predetermined water cut, and the water-flooded recovery efficiency is determined; According to the gel system injection scheme, the gel system is injected at a predetermined speed; All injection wells and production wells of the core model are closed, and the gel is statically gelled, and then the injection wells and production wells are opened; The core model is water-flooded at a predetermined displacement speed until the outlet water cut is above a predetermined water cut, and the water-flooded recovery efficiency is calculated; The resistance values of different test points during the displacement process, water flooding, and water flooding after gel setting are monitored; According to the resistance value, an oil saturation value of each test point is determined according to the standard curve, and an oil saturation field distribution result is obtained by using the oil saturation values of the test points.

8. The method for enhancing oil recovery by taking advantage of the plugging effect of the thief zone according to claim 7, characterized in that, The method for saturating the core model with water and oil comprises: Vacuumizing each pressure test point for a predetermined time from the injection end of the core model; Saturating the core model with artificial synthetic brine, and then placing the core model in a target block reservoir temperature incubator for more than a predetermined time; Injecting crude oil into the core model from the injection end of the core model, and displacing until no water is discharged, and then placing the core model in the incubator for more than a predetermined time.

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