Dynamic adjustment method for water injection of multi-layer heterogeneous sandstone reservoir

Abstract

The invention relates to the technical field of oil exploration and development, in particular to a multi-layer heterogeneous sandstone reservoir water injection dynamic adjustment method which comprises the steps that a separated layer water injection indication curve and water absorption profile data of a work area target well are obtained; determining an injection-production ratio, and determining a water injection rate according to the injection-production ratio; dividing each layer section of the target well into a limiting layer or a reinforcing layer; determining the maximum water injection pressure and the minimum water injection pressure; and according to the water injection rate, the maximum water injection pressure and the minimum water injection pressure, water injection is conducted on each layer section of the target well, during water injection, plugging or profile control or single-clamping injection stopping adjustment is conducted on all the limiting layers through the separated layer water injection indication curve and water absorption profile data, and pressure increasing or fracturing or acidification adjustment is conducted on all the reinforcing layers. The invention aims to solve the problem that the final development effect is affected due to the fact that the influence of formation pressure and water content is not fully considered and an adjustment scheme is designed depending on the experience of technicians when the oilfield water injection scale and layered water injection are optimized and adjusted previously, and the deviation from the actual condition of the formation is large.

Description

Technical Field

[0001] The present invention relates to the technical field of oil exploration and development, and particularly to a method for dynamically adjusting water injection in a multi-layer heterogeneous sandstone reservoir. Background Art

[0002] Water injection is the most mature, lowest-cost, and most economically beneficial way to improve oil recovery in oilfield development. Water injection is an important condition for ensuring formation energy supply and effectively exploiting oil layers. With the continuous deepening of oilfield development, fine layered water injection has gradually developed and matured. However, in the actual water injection process, many problems often occur, such as the inconsistency between static and dynamic conditions, and the inconsistency between the water absorption profile and the test card, which affect the understanding of the injection status of the oil layer. What should be strengthened is restricted, and what should be restricted is strengthened, resulting in a poor accuracy of the plan and affecting the improvement of the oil layer utilization status and development effect. Therefore, it is necessary to regularly optimize and adjust the layered water injection, which mainly includes two aspects: one is to determine the water injection scale of the reservoir at different water cut stages and different formation pressures; the other is to perform corresponding dynamic optimization and adjustment on different water injection intervals during the exploitation process. In determining the water injection scale of the reservoir, currently, models such as Logistic, Gompertz, and Usher are often used for prediction. Although this method is relatively simple, it does not consider the influence of formation pressure and water cut stage; in terms of optimizing and adjusting the water injection scale of the water injection interval, it is usually determined by the experience and knowledge of technicians, which is greatly affected by human factors and subjectivity; there is also a method of calculation and determination based on reservoir engineering theory, but this method is relatively cumbersome and has a large deviation from the actual field situation. Therefore, it is necessary to establish a method for optimizing and adjusting water injection in a multi-layer heterogeneous reservoir that combines the properties of underground reservoirs with development dynamics (combining static and dynamic). Summary of the Invention

[0003] The present invention proposes a method for dynamically adjusting water injection in a multi-layer heterogeneous sandstone reservoir to solve the problems that in the past, when optimizing and adjusting the water injection scale and layered water injection in oilfields, the influence of formation pressure and water cut was not fully considered, and the adjustment plan was designed relying on the experience of technicians, resulting in a large deviation from the actual formation situation and affecting the final development effect.

[0004] According to one aspect of the present invention, there is provided a method for dynamically adjusting water injection in a multi-layer heterogeneous sandstone reservoir, including:

[0005] Obtaining the layered water injection indication curve and water absorption profile data of the target well in the work area;

[0006] Determining the injection-production ratio of the target well at a certain pressure recovery rate, and determining the water injection volume of the target well according to the injection-production ratio;

[0007] Dividing each interval of the target well into a restricted layer or a strengthened layer;

[0008] Determining the maximum injection pressure and minimum injection pressure of the target well interval;

[0009] Water injection is carried out for each interval of the target well according to the water injection volume, the maximum water injection pressure and the minimum water injection pressure. If there is an initiation pressure gradient in the target well, during water injection, plugging, profile control or single - card shut - off adjustment is carried out for all the restricted intervals by using the layered water injection indication curve and the water absorption profile data, and pressure increase, fracturing or acidification adjustment is carried out for all the enhanced intervals.

[0010] Preferably, the method for determining the injection - production ratio of the target well at a certain pressure recovery rate includes:

[0011] Using formula (1), determine the injection - production ratio of the target well at a certain pressure recovery rate;

[0012]

[0013] In the formula: IPR is the injection - production ratio, dimensionless; N is the geological reserve, 10 4 t; C e is the comprehensive compressibility, f; B oi is the original oil volume factor, f; d(ΔP) is the differential pressure, MPa; dt is the differential time; q L is the liquid production rate, m 3 / d; f w is the water cut, decimal; B o is the volume factor of formation oil, f; B w is the volume factor of formation water, f.

[0014] Preferably, the method for determining the water injection volume of the target well according to the injection - production ratio includes:

[0015] Using formula (2), determine the water injection volume of the target well;

[0016] Qi = IPR * Q L = IPR * (Q o / (1 - f w ))(2);

[0017] In the formula: Q i is the water injection volume, 10 4 t; IPR is the injection - production ratio, dimensionless; Q L is the liquid production rate, 10 4 t; Q o is the oil production rate, 10 4 t; f w is the water cut.

[0018] Preferably, the method for dividing each interval of the target well into restricted intervals or enhanced intervals includes:

[0019] If the effective thickness h of the interval > 1.0 m and the permeability k > 0.05 μm 2 or the relative water absorption q of a single layer in the interval ir > 50% or the water saturation S w > 60%, then this layer is a restricted layer;

[0020] If the effective thickness h of the interval < 0.5 m and the permeability k < 0.01 μm 2 or the relative water absorption q of a single layer in the interval ir < 10% or the water saturation S w < 40%, then this layer is an enhanced layer.

[0021] Preferably, the method for determining the maximum injection pressure and the minimum injection pressure of the target well interval includes:

[0022] According to the water absorption profile data, determine the injection pressures corresponding to the predetermined maximum utilization degree and the predetermined minimum utilization degree of the interval respectively;

[0023] Among them, the injection pressure corresponding to the predetermined maximum utilization degree is the maximum injection pressure, and the injection pressure corresponding to the predetermined minimum utilization degree is the minimum injection pressure;

[0024] Among them, the maximum injection pressure is not greater than the formation fracture pressure.

[0025] Preferably, the method for determining the maximum injection pressure of the target well interval includes:

[0026] Use formula (3) to determine the maximum injection pressure of the target well interval;

[0027] P iwmax = γ0 × H0 - 0.5 - ρ L × g × H0 × 10 -5 + P a (3);

[0028] In the formula: P iwmax is the maximum pressure at the wellhead of the injection well, MPa; r o is the formation fracture pressure gradient, MPa / m; H o is the depth of the top of the oil layer, m; ρ L is the density of water, 10 3 kg / m 3 ; g is the acceleration of gravity, with a value of 9.8, m / s 2 ; P a is the additional pressure, MPa.

[0029] Preferably, the method for plugging or profile control adjustment of all the restricted layers by using the stratified injection indication curve and the water absorption profile data during the water injection process includes:

[0030] Judging whether the utilization degree of the restricted layer is greater than a predetermined degree and whether it is a high water absorption layer according to the water absorption profile data and the stratified water injection indication curve. If so, determining the corresponding pressure under the condition of retaining the lowest utilization degree of the restricted layer according to the stratified water injection indication curve, and plugging or single card stopping water injection for the restricted layer according to the pressure corresponding to the lowest utilization degree condition;

[0031] Judging whether the utilization degree of the restricted layer is less than a predetermined degree and whether it is a high water absorption layer according to the water absorption profile data and the stratified water injection indication curve. If so, performing profile control on the restricted layer;

[0032] The method for performing pressure increase, fracturing or acidification adjustment on all enhanced layers by using the stratified water injection indication curve and the water absorption profile data during water injection includes:

[0033] Performing pressure increase on the enhanced layer. During the pressure increase process, judging whether the utilization degree of the enhanced layer reaches the predetermined degree under the condition that the overlying rock pressure permits according to the water absorption profile data and the stratified water injection indication curve;

[0034] If not, judging whether the enhanced layer is a low permeability layer. If so, fracturing the enhanced layer. If not, acidifying the enhanced layer.

[0035] Preferably, if there is no starting pressure gradient in the target well, the water injection pressure after layer section adjustment is determined according to formula (4);

[0036] p i =q i / j i (4);

[0037] In the formula: p i is the water injection pressure of the i-th layer section, MPa; q i is the water injection volume of the i-th layer section, m 3 / d; j i is the water absorption index of the i-th layer section, m 3 / (d·MPa).

[0038] Preferably, if there is no stratified water injection indication curve, the method for dividing each layer section of the target well into a restricted layer or an enhanced layer is:

[0039] Judging according to the water absorption profile data whether the relative water absorption ratio of the layer section is less than 10% or the utilization degree is less than 80%. If so, it is an enhanced layer. Judging whether the relative water absorption ratio of the layer section is greater than 50%. If so, it is a restricted layer.

[0040] Preferably, if there is no stratified water injection indication curve, then during water injection, all the restricted layers and enhanced layers are adjusted according to the water injection coefficient. The method includes:

[0041] Respectively determine the water injection coefficients corresponding to the restricted layer and the enhanced layer by using formula (5);

[0042] According to the water injection coefficients, respectively determine the theoretical water injection volumes corresponding to the restricted layer and the enhanced layer by using formula (6);

[0043] If the actual water injection volume of the enhanced layer is less than the corresponding theoretical water injection volume, then increase the injection pressure of the enhanced layer for additional injection. If the actual water injection volume of the restricted layer is greater than the corresponding theoretical water injection volume, then plug the restricted layer or stop the injection of a single layer;

[0044]

[0045] q di =∑q i =∑a i q d (6);

[0046] In the formula: a i is the water injection coefficient, dimensionless; k i is the permeability of the i-th layer, um 2 ; h i is the effective thickness of the i-th layer, m; q i is the water injection volume of the i-th layer, m 3 / d; q di is the water injection volume of the i-th section, m 3 / d; q d is the water injection volume of a single well, m 3 / d.

[0047] The present invention has at least the following beneficial effects:

[0048] The present invention proposes a method for dynamic adjustment of water injection in a multi-layer heterogeneous sandstone reservoir. By applying the stratified water injection indication curve for dynamic optimization adjustment of water injection intervals, it avoids the deficiencies of the original method relying on artificial experience. The method is simple and easy to implement, suitable for dynamic optimization adjustment during fine water injection in a multi-layer heterogeneous sandstone reservoir, making the optimized water injection plan more reasonable, and thus can further improve the oilfield development effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The drawings here are incorporated into the specification and form a part of this specification. These drawings show embodiments consistent with the present invention and are used together with the specification to explain the technical solutions of the present invention.

[0050] Figure 1A flowchart showing a method for dynamically adjusting water injection in a multi-layer heterogeneous sandstone reservoir according to an embodiment of the present invention;

[0051] Figure 2 A scatter plot showing the water injection pressure and the degree of utilization according to an embodiment of the present invention;

[0052] Figure 3 A scatter plot showing the regression of the injection-production ratio in the NC block according to an embodiment of the present invention. Detailed implementation manners

[0053] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below with reference to the accompanying drawings. The same reference numerals in the drawings denote elements having the same or similar functions. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise specified.

[0054] The term "exemplary" used herein means "serving as an example, embodiment, or illustration". Any embodiment described herein as "exemplary" is not necessarily to be construed as superior or better than other embodiments.

[0055] The term "and / or" herein merely describes an association relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the term "at least one" herein means any one of a plurality or any combination of at least two of a plurality. For example, including at least one of A, B, and C may represent including any one or more elements selected from the set composed of A, B, and C.

[0056] In addition, for a better description of the present invention, numerous specific details are given in the following detailed implementation manners. Those skilled in the art should understand that the present invention can be implemented without some specific details. In some instances, methods, means, elements, and circuits well-known to those skilled in the art are not described in detail so as to highlight the gist of the present invention.

[0057] Figure 1 A flowchart showing a method for dynamically adjusting water injection in a multi-layer heterogeneous sandstone reservoir according to an embodiment of the present invention; Figure 2 A scatter plot showing the water injection pressure and the degree of utilization according to an embodiment of the present invention; Figure 3 A scatter plot showing the regression of the injection-production ratio in the NC block according to an embodiment of the present invention. As Figures 1 - 3As shown in the figure, a method for dynamically adjusting water injection in a multi-layer heterogeneous sandstone reservoir includes: Step S01: Obtain the stratified water injection indication curve and water absorption profile data of the target well in the work area; Step S02: Determine the injection-production ratio of the target well at a certain pressure recovery rate, and determine the water injection volume of the target well according to the injection-production ratio; Step S03: Divide each layer section of the target well into restricted layers or enhanced layers; Step S04: Determine the maximum water injection pressure and minimum water injection pressure of the target well layer section; Step S05: Inject water into each layer section of the target well according to the water injection volume, the maximum water injection pressure and the minimum water injection pressure. If there is an initial pressure gradient in the target well, during water injection, use the stratified water injection indication curve and the water absorption profile data to carry out plugging or profile control or single-card shut-off adjustment on all the restricted layers, and carry out pressure increase or fracturing or acidification adjustment on all the enhanced layers.

[0058] A method for dynamically adjusting water injection in a multi-layer heterogeneous sandstone reservoir provided by an embodiment of the present invention specifically includes the following steps:

[0059] Step S01: Obtain the stratified water injection indication curve and water absorption profile data of the target well in the work area.

[0060] In the embodiment of the present invention, based on the stratified water injection indication curve, three understandings can be obtained: First, clarify the initial pressure of different water injection layer sections; second, grasp the change characteristics of the water absorption capacity of the same layer section under different water injection pressures; third, understand the change characteristics of the water absorption capacity of different layer sections under the same pressure conditions. Grasping the initial pressure and the change characteristics of the water absorption capacity of different water injection layer sections lays a foundation for formulating dynamic optimization adjustment countermeasures for water injection layer sections.

[0061] Step S02: Determine the injection-production ratio of the target well at a certain pressure recovery rate, and determine the water injection volume of the target well according to the injection-production ratio.

[0062] In the present invention, the method for determining the injection-production ratio of the target well at a certain pressure recovery rate includes: using formula (1) to determine the injection-production ratio of the target well at a certain pressure recovery rate;

[0063]

[0064] In the formula: IPR is the injection-production ratio, dimensionless; N is the geological reserve, 10 4 t; C e is the comprehensive compressibility, f; B oi is the original oil volume factor, f; d(ΔP) is the differential pressure, MPa; dt is the time differential; q L is the liquid production rate, m 3 / d; f w is the water cut, decimal; B o is the volume factor of formation oil, f; B wis the formation water volume factor, f.

[0065] In the embodiments of the present invention, oilfield development centers around completing the annual crude oil production task. On the premise of meeting the annual production and injection allocation requirements, after clarifying the planned annual oil production and water cut targets, through the material balance principle, fully considering the influence of different water cut stages and different formation pressures, the reasonable injection-production ratio is determined by regression based on past data, so as to obtain the reasonable water injection scale of the reservoir, that is, the water injection volume.

[0066] The formation pressure level mainly depends on the cumulative oil production, cumulative water production, cumulative water injection, and the physical properties (compressibility coefficient, volume coefficient) of oil, water, and rock. According to the material balance equation (Equation 1-1), it can be known that:

[0067] W i B w -N p B o -W p B w = NC e B oi ΔP(1-1);

[0068] In the formula: N p is the cumulative oil production, 104t; W p is the cumulative water production, 10 4 t; W i is the cumulative water injection, 10 4 t; B o is the formation oil volume factor, f; B oi is the original crude oil volume factor, f; B w is the formation water volume factor, f; N is the geological reserve, 10 4 t; C e is the comprehensive compressibility coefficient, f; ΔP is the pressure difference, MPa.

[0069] Taking the derivative of both sides of the above formula (1-1) with respect to time and ignoring the derivative of the volume coefficient with respect to time, we have:

[0070] q i B w -q o B o -q w B w = NC e B oi d(ΔP) / dt (1-2);

[0071] In the formula: q o is the oil production, t / d; q w is the water production, t / d; q i is the water injection volume, t / d.

[0072] It can be obtained from the above formula (1-2):

[0073]

[0074] Since the injection-production ratio can be expressed as:

[0075]

[0076] In the formula: IPR is the injection-production ratio, dimensionless.

[0077] The water cut can be expressed as:

[0078]

[0079] In the formula: f w is the water cut, in decimals.

[0080] After substituting the expressions of the injection-production ratio and the water cut into formula (1-3) respectively, we get:

[0081]

[0082] After further arrangement, the injection-production ratio under different pressure change rates can be obtained, that is, formula (1). Obviously, it can be seen that the pressure change rate increases with the increase of the injection-production ratio.

[0083] Formula (1) is the relational formula between the injection-production ratio and the liquid production volume, water cut, volume coefficient of water, volume coefficient of oil, geological reserves, rock compressibility, and formation pressure recovery rate.

[0084] Let NC in the above formula (1) e B oi =K. Taking the IPR of each year in the work area as the ordinate as the abscissa, draw a curve, then the slope of the curve is the K value. Substitute the obtained K value into formula (1) to calculate the injection-production ratio IPR under a certain pressure recovery rate.

[0085] In the present invention, the method for determining the water injection volume of the target well according to the injection-production ratio includes: using formula (2) to determine the water injection volume of the target well;

[0086] Qi = IPR * Q L = IPR * (Q o / (1 - f w )) (2);

[0087] In the formula, Q i is the water injection volume, 10 4 t; IPR is the injection-production ratio, dimensionless; Q L is the liquid production volume, 10 4 t; Q ois the oil production, 10 4 t; f w is the water cut rate.

[0088] In the embodiment of the present invention, the oil production and the predicted water cut rate are determined according to the oilfield production allocation, the liquid production is obtained, and then the injection-production ratio calculated according to Equation (1) is substituted into Equation (2) to determine the injection volume of the target well.

[0089] By determining the injection volume through the above method, both the static parameters such as the physical properties of the reservoir and the exploitation dynamics are considered, which is an effective method for determining the reasonable water injection scale of the reservoir by combining static and dynamic factors.

[0090] Step S03: Divide each layer section of the target well into a restricted layer or an enhanced layer.

[0091] In the present invention, the method for dividing each layer section of the target well into a restricted layer or an enhanced layer includes: if the effective thickness h of the layer section > 1.0 m and the permeability k > 0.05 um 2 or the relative water absorption q of a single layer in the layer section ir > 50% or the water saturation S w > 60%, then this layer is a restricted layer; if the effective thickness h of the layer section < 0.5 m and the permeability k < 0.01 um 2 or the relative water absorption q of a single layer in the layer section ir < 10% or the water saturation S w < 40%, then this layer is an enhanced layer.

[0092] In the embodiment of the present invention, according to the development conditions such as the effective thickness and permeability of different water injection layer sections, as well as the changes in the relative water absorption and water saturation of the layer sections, it is determined whether to restrict water injection, balance water injection or enhance water injection, that is, restricted layer, balanced layer, enhanced layer. The specific determination conditions are shown in Table 1 below. Usually, field dynamic personnel make a comprehensive determination by considering one main index or multiple indexes according to the actual water injection change characteristics of the oil layer.

[0093] Table 1: Main index boundary table for determining the adjustment nature of water injection layer sections

[0094] Effective thickness h / Permeability k <![CDATA[Relative water absorption capacity q of a single layer in a layer section ir > <![CDATA[Water saturation S w > Classification result <![CDATA[h > 1.0 m and k > 0.05 µm 2 > <![CDATA[q ir >50%]]> <![CDATA[S w >60%]]> Restriction layer <![CDATA[h > 0.5 m and k > 0.01 µm 2 > <![CDATA[q ir [10% to 50%]]]> <![CDATA[S w [40%-60%]]]> Balanced layer <![CDATA[h < 0.5 m and k < 0.01 um2]]> <![CDATA[q ir <10%]]> <![CDATA[S w <40%]]> Reinforcement layer

[0095] During the optimization and adjustment of water injection, the adjustment is mainly carried out for the restricted layer and the enhanced layer, and the original water injection plan for the balanced layer remains unchanged.

[0096] Step S04: Determine the maximum injection pressure and the minimum injection pressure of the layer section of the target well;

[0097] In the present invention, the method for determining the maximum injection pressure and the minimum injection pressure of the target well section includes: respectively determining the injection pressures corresponding to the predetermined maximum utilization degree and the predetermined minimum utilization degree of the section according to the water absorption profile data; wherein, the injection pressure corresponding to the predetermined maximum utilization degree is the maximum injection pressure, and the injection pressure corresponding to the predetermined minimum utilization degree is the minimum injection pressure; wherein, the maximum injection pressure is not greater than the formation fracture pressure.

[0098] In an embodiment of the present invention, the minimum injection pressure and the maximum injection pressure are determined according to the minimum utilization degree and the maximum utilization degree of the oil formation. According to the water absorption profile data, the utilization degree of the oil formation under different injection pressures is determined, and the injection pressure corresponding to the predetermined minimum utilization degree is determined, and this injection pressure is the minimum injection pressure; the injection pressure corresponding to the predetermined maximum utilization degree is determined, and this injection pressure is the maximum injection pressure. As Figure 2 shown, it is a diagram of the relationship between the injection pressure and the utilization degree in the water absorption profile data. In Figure 2 , if the predetermined minimum utilization degree is 80%, then the minimum injection pressure of the corresponding target well is 12 MPa.

[0099] During the actual determination of the adjustment direction of the reservoir injection pressure in the oil field, mainly based on 4 principles: one is to consider the recovery and utilization of formation energy; the second is that the upper limit is not greater than the formation fracture pressure; the third is that the lower limit is to ensure that the vast majority of oil layers can absorb water (the minimum utilization degree); the fourth is to consider the safety of the injection well casing.

[0100] Therefore, the minimum injection pressure should not be lower than the lower limit value determined according to the predetermined minimum utilization degree, and the maximum injection pressure should not be higher than the upper limit value determined according to the overlying rock pressure (formation fracture pressure), and it can be specifically determined according to the oil field dynamics or the production allocation requirements.

[0101] In the present invention, the method for determining the maximum injection pressure of the target well section includes: using formula (3) to determine the maximum injection pressure of the target well section;

[0102] P iwmax =γ0×H0 - 0.5 - ρ L ×g×H0×10 -5 +P a (3);

[0103] In the formula, P iwmax is the maximum pressure at the wellhead of the injection well, MPa; r o is the formation fracture pressure gradient, MPa / m; H o is the depth of the top of the oil formation, m; ρ L is the density of water, 10 3 kg / m 3 ; g is the acceleration of gravity, generally taken as 9.8, m / s2 ; P a is the additional pressure, including the wellbore and borehole friction pressures, etc., in MPa.

[0104] In the embodiments of the present invention, there are two methods for determining the maximum injection pressure. One is determined through the water absorption profile data as described above, and the other is to determine the maximum injection pressure through the overburden rock pressure method. To avoid formation fracture caused by excessive pressure, the maximum injection pressure is calculated according to the formation fracture pressure gradient. At the same time, to avoid casing damage caused by formation fracture, it is generally about 0.5 MPa lower than the fracture pressure, as shown in Equation (3). The P calculated according to Equation (3) iwmax is the maximum injection pressure of the interval.

[0105] Step S05: Inject water into each interval of the target well according to the injection volume, the maximum injection pressure, and the minimum injection pressure. If there is a startup pressure gradient in the target well, then during water injection, use the stratified water injection indicator curve and the water absorption profile data to plug, profile control, or single - card shut - off adjustment for all the restricted layers, and perform pressure increase, fracturing, or acidification adjustment for all the enhanced layers.

[0106] In the present invention, the method of using the stratified water injection indicator curve and the water absorption profile data to perform plugging or profile control adjustment on all the restricted layers during the water injection process includes: judging whether the utilization degree of the restricted layer is greater than a predetermined degree and whether it is a high - water - absorption layer according to the water absorption profile data and the stratified water injection indicator curve. If so, determine the corresponding pressure under the condition of retaining the lowest utilization degree of the restricted layer according to the stratified water injection indicator curve, and perform plugging or single - card shut - off injection on the restricted layer according to the pressure corresponding to the lowest utilization degree; judging whether the utilization degree of the restricted layer is less than a predetermined degree and whether it is a high - water - absorption layer according to the water absorption profile data and the stratified water injection indicator curve. If so, perform profile control on the restricted layer; the method of using the stratified water injection indicator curve and the water absorption profile data to perform pressure increase, fracturing, or acidification adjustment on all the enhanced layers during the water injection process includes: increasing the pressure of the enhanced layer. During the pressure - increasing process, judge whether the utilization degree of the enhanced layer reaches the predetermined degree under the condition allowed by the overburden rock pressure according to the water absorption profile data and the stratified water injection indicator curve; if not, judge whether the enhanced layer is a low - permeability layer. If so, perform fracturing on the enhanced layer, and if not, perform acidification on the enhanced layer.

[0107] In the embodiments of the present invention, the underground oil reservoirs vary greatly and are highly heterogeneous, making it difficult to accurately understand the properties of oil layers thousands of meters underground. Moreover, oil layer pollution widely exists during the actual water injection development process, which can lead to the inability to inject water into some intervals (there is a starting pressure gradient). These non-water-absorbing layers are generally low-permeability oil layers or medium-high permeability oil layers with reduced permeability due to pollution and thus cannot inject water. Therefore, it is necessary to restrict water injection by measures such as plugging and profile control of highly water-absorbing layers, and to strengthen water injection for low or non-water-absorbing layers by measures such as pressure increase and fracturing, so as to control highly water-absorbing layers, start low or non-water-absorbing layers, and achieve the purpose of improving the development effect of water injection oil reservoirs.

[0108] The water absorption profile data can only determine the current water absorption volume and the degree of utilization; the layer-by-layer injection index curve can not only determine the current water absorption volume and the degree of utilization, but also determine the water absorption volume and the degree of utilization under different pressure conditions, and the results obtained are more and more accurate. On the basis of determining the reasonable water injection scale of the oil reservoir, according to the layer-by-layer injection index curve of the injection well, dynamic optimization adjustment can be further carried out based on the layer-by-layer test results. The layer-by-layer injection index curve of the injection well is the curve of the relationship between the injection volume and the injection pressure of each interval of the injection well measured by a stable well test. According to the layer-by-layer water injection index curve, the starting pressure of each interval can be grasped, and the difference in water absorption capacity between each interval can be judged.

[0109] Among them, the method for judging whether the restricted layer and the enhanced layer are highly water-absorbing layers or low water-absorbing layers includes: judging whether the relative water absorption volume of a single layer in the restricted layer or the enhanced layer is greater than 50%. If so, it is a highly water-absorbing layer; judging whether the relative water absorption volume of a single layer in the restricted layer or the enhanced layer is less than 10%. If so, it is a low water-absorbing layer. Among them, the predetermined degree is 80%.

[0110] The measures for the dynamic adjustment of injection wells mainly have two aspects and six types. The first aspect is the injection control adjustment of the restricted layer, and the injection volume is reduced by three means: plugging, profile control, and single-string injection shutoff; the second aspect is the injection increase adjustment of the enhanced layer, and the injection volume is increased by three means: pressure increase, fracturing, and acidification.

[0111] (1) For the restricted layer, judged according to the water absorption profile data and the layer-by-layer water injection index curve. When the relative water absorption volume of a single layer in the restricted layer > 50%, it is a highly water-absorbing layer, and when the degree of reservoir utilization is greater than 80%, plugging and pressure reduction for injection control can be selected. If the lowest degree of utilization is 80%, the specific method is: determine the injection pressure corresponding to the degree of utilization of 80% according to the layer-by-layer injection index curve, and lower the real-time injection pressure of the restricted layer to the injection pressure corresponding to this lowest degree of utilization, reaching not less than the lower limit value according to the degree of utilization of 80%; judge according to the layer-by-layer water injection index curve that if the degree of utilization of the restricted layer still cannot be reduced to the lowest degree of utilization after plugging, the single-string injection shutoff measure can be taken.

[0112] (2) For the restricted layer, based on the water absorption profile data and the sectional water injection indicator curve, when the relative water absorption of a single layer > 50%, it is a high water absorption layer, and when the degree of reservoir utilization is less than 80%, profile control and injection control can be selected. The specific method is as follows: Determine the optimal water injection pressure range according to the sectional water injection indicator curve of the initial injection test. This optimal water injection pressure range should be less than the upper limit allowed by the overlying rock pressure, and meet the lower limit values of the minimum degree of utilization > 80% and the relative water absorption < 50%.

[0113] (3) For the enhanced layer, based on the water absorption profile data and the sectional water injection indicator curve, when the degree of utilization of the enhanced layer is less than the minimum degree of utilization, that is, the degree of utilization < 80%, and the relative water absorption < 10%, it is a low water absorption layer. First, increase the injection pressure according to the sectional water injection indicator curve. If during the process of increasing the pressure, the real-time water injection pressure meets the requirements that the degree of reservoir utilization reaches 80% and the relative water absorption of a single layer < 50% within the range allowed by the overlying rock pressure, then this water injection pressure is a reasonable value. If either requirement is not met, and the enhanced layer is a low permeability layer, then the enhanced layer needs to be fractured. Determine the reasonable water injection pressure (degree of utilization 80% and relative water absorption < 50%) according to the sectional water injection indicator curve.

[0114] (4) For the enhanced layer, if the enhanced layer is a medium-high permeability layer and the permeability decreases after the reservoir is contaminated, resulting in the situation that the degree of utilization or water absorption cannot meet the requirements of the degree of utilization 80% and the relative water absorption < 50%, then the enhanced layer needs to be acidified.

[0115] Among them, the high permeability layer refers to the reservoir with a permeability greater than 0.05um 2 and the low permeability layer refers to the reservoir with a permeability less than 0.001um 2 and the rest are medium permeability layers.

[0116] On the basis of a comprehensive understanding of the water absorption capacity of each water injection interval, fully apply the static and dynamic data of different intervals of the injection well, that is, the water absorption profile data and the sectional water injection indicator curve, to guide the play of reservoir measures such as plugging, single packer shut-off injection, profile control, pressure increase, fracturing, and acidification, so as to achieve the purpose of continuously improving the water injection development effect.

[0117] Taking profile control as an example, for high-permeability and high-water-absorbing intervals with large interlayer differences, simply relying on controlling the injection volume cannot alleviate the interlayer contradiction. Therefore, profile control technology is applied to control high-water-absorbing intervals. In the past, the selection of intervals for profile control wells was mainly determined based on water absorption profile data, mainly by empirical analysis. Water absorption profile data is generally obtained through annulus or isotope data testing, but it can only obtain the water absorption status of different horizons under current conditions and cannot determine the variation characteristics of the reservoir coefficient capacity under different injection pressures. Therefore, by adding the application of the stratified injection indicator curve results on the basis of water absorption profile data, a more comprehensive and realistic understanding of the water absorption capacity of each injection interval can be obtained, the high-water-absorbing intervals can be more accurately determined, and the well and interval selection principles have a more scientific basis, ensuring better profile control and plugging effects for high-water-absorbing intervals.

[0118] Similarly, for low-permeability oil reservoirs or contaminated medium-high permeability oil reservoirs, low-water-absorbing or non-water-absorbing intervals, by increasing the injection pressure, some low-permeability layers can be started for injection, but there are still some thin and poor intervals that cannot be started for injection. Therefore, measures such as fracturing must be used to improve the production status of thin and poor oil layers. Using the stratified injection indicator curve can effectively determine non-water-absorbing or poor-water-absorbing intervals, and based on this, comprehensive measures can be taken to transform such intervals to ensure obvious improvement in the development effect after implementation.

[0119] In the present invention, if there is no starting pressure gradient in the target well, then according to formula (4), the injection pressure after interval adjustment is determined;

[0120] p i =q i / j i (4);

[0121] In the formula: p i is the injection pressure of the i-th interval, MPa; q i is the injection volume of the i-th interval, m 3 / d; j i is the water absorption index of the i-th interval, m 3 / (d·MPa).

[0122] In the embodiment of the present invention, when the current injection pressure is less than the pressure condition allowed by the overlying rock pressure, each interval can be started for injection, indicating that there is room for increasing the injection pressure, and the injection pressure can be appropriately adjusted. The injection volume of the interval can be determined using formula (2) according to the interval properties and considering the production allocation requirements, and then the reasonable injection pressure can be determined according to formula (4). Among them, the water absorption index of the interval can be obtained from field dynamic test data or split according to experience.

[0123] In the present invention, in the absence of the stratified water injection indication curve, the method for dividing each layer section of the target well into a restricted layer or an enhanced layer is as follows: according to the water absorption profile data, determine whether the relative water absorption ratio of the layer section is less than 10% or the degree of utilization is less than 80%. If so, it is an enhanced layer. Determine whether the relative water absorption ratio of the layer section is greater than 50%. If so, it is a restricted layer.

[0124] In the present invention, in the absence of the stratified water injection indication curve, during water injection, all the restricted layers and enhanced layers are adjusted according to the water injection coefficient. The method includes: respectively determining the water injection coefficients corresponding to the restricted layer and the enhanced layer by using formula (5); according to the water injection coefficients, respectively determining the theoretical water injection volumes corresponding to the restricted layer and the enhanced layer by using formula (6); if the actual water injection volume of the enhanced layer is less than the corresponding theoretical water injection volume, then increase the injection pressure of the enhanced layer for water injection augmentation. If the actual water injection volume of the restricted layer is greater than the corresponding theoretical water injection volume, then plug the restricted layer or stop water injection for a single layer by single card.

[0125]

[0126] q di =∑q i =∑a i q d (6);

[0127] In the formula, a i is the water injection coefficient, dimensionless; k i is the permeability of the i-th layer, um 2 ; h i is the effective thickness of the i-th layer, m; q i is the water injection volume of the i-th layer, m 3 / d; q di is the water injection volume of the i-th layer section, m 3 / d; q d is the water injection volume of a single well, m 3 / d.

[0128] In an embodiment of the present invention, on the basis of determining the reasonable water injection scale of the oil reservoir, in the absence of the stratified water injection indication curve, the dynamic adjustment of layer section water injection can be carried out according to the actual field dynamics. Field applications and statistics show that generally the water injection coefficient method is mainly used for the dynamic adjustment of water injection.

[0129] For wells without a layered water injection indicator curve, the method for dividing the restricted layer, balanced layer, and enhanced layer is as follows: Determine according to the water absorption profile data. If the relative water absorption ratio of a single layer is less than 10% or the degree of utilization is less than 80%, then it is an enhanced layer and enhanced water injection is required; if the relative water absorption ratio is between 10% - 50% or the degree of utilization is not more than 80%, then it is a balanced layer, that is, keep the current state without optimization and adjustment; if the relative water absorption ratio is greater than 50%, then it is a restricted layer and restricted water injection is required.

[0130] Calculate the single-layer separate water injection coefficient in the layer section according to formula (5), and calculate the theoretical water injection volume of a single layer according to the separate water injection coefficient and formula (6). Among them, the theoretical water injection volume of the i-th layer: q i = a i q d .

[0131] Finally, compare the calculated theoretical water injection volume with the actual water injection volume, and formulate optimization and adjustment countermeasures according to the following situations:

[0132] (1) For the enhanced layer, if the actual water injection volume value of the i-th layer (enhanced layer) is less than the theoretical water injection volume value, then increase the pressure or take measures to increase water injection, otherwise, keep the current water injection state;

[0133] (2) For the restricted layer, if the actual water injection volume value of the i-th layer (restricted layer) is less than the theoretical water injection volume value, then keep the current state, otherwise, conduct plugging control injection or single packer shut-off injection according to it.

[0134] In the embodiment of the present invention, in addition to the enhanced layer and the restricted layer that need to be adjusted according to the above process, there are also some special layer sections, including: 1. Layer sections prone to casing damage; 2. Layer sections with casing damage; 3. Plugging layer sections for chemical polymer flooding. For the above three situations, when making adjustments, if it is a layer section prone to casing damage, then controlled injection water injection adjustment is required; if it is a layer section with casing damage, then fine subdivision single packer shut-off injection adjustment is required; if it is a plugging layer section for chemical polymer flooding, then single packer shut-off injection adjustment is conducted.

[0135] In the embodiment of the present invention, taking a typical block NC in the Daqing La-Sa-Xing Oilfield as an example, the Sa, Putaohua, and Gaoyou oil layer groups in the NC block belong to fluvial-delta deposition. According to the sedimentary characteristics of the oil layers and the development status of sand bodies, the Sa, Putaohua, and Gaoyou oil layer groups are subdivided into 110 sedimentary units and can be divided into more than 10 sedimentary types. The NC block started development in 1966, using a line drive pattern to exploit the Sa and Putaohua oil layers. In 1982, the first infill was carried out, in 1996, the second infill was carried out, and in 2008, the third infill was carried out. Currently, there are 4 sets of well patterns in the block.

[0136] Obtain the layered water injection indicator curve and water absorption profile data of the NC block.

[0137] Obtain the injection-production ratio IPR data of the NC block from 2010 to 2020, and plot the relationship curve of the regression scatter plot of IPR and as shown in Figure 3 Perform regression on the curve to obtain the expression:

[0138]

[0139] That is, the value of the slope k is 197.34, and the required pressure build-up rate per year is 0.1 MPa. Substitute the planned liquid production and water cut in 2021 into the above formula to obtain the predicted injection-production ratio in 2021: IPR = 1.057.

[0140] According to the field practice, the general annual pressure build-up rate is 0.1 MPa. The planned oil production in the block in 2021 is 251,800 tons, and the water cut of the block is 92.71%. According to formula (2), the water injection scale of the block is obtained as 3.7664 million cubic meters.

[0141] For injection wells with stratified water injection indication curves, take the stratified water injection indication curves as the standard and the water absorption profile data as the supplement for dynamic adjustment; for injection wells without stratified indication curves, based on the water absorption profile data, perform dynamic adjustment through the sub-injection coefficient method.

[0142] Divide the restricted layers and enhanced layers of the target wells in the NC block. Among them, the effective oil-bearing thickness in the water injection interval is greater than 1.0 m and the permeability is greater than 0.05 μm 2 Well-developed oil layers, or the relative water absorption of a single layer section is greater than 50%, need to restrict water injection, which are restricted layers; the effective oil-bearing thickness in the water injection interval is between 0.5 - 1.0 m, and the permeability is between 0.01 - 0.05 μm 2 Medium-developed oil layers, or the relative water absorption of a single layer section is between 10 - 50%, maintain the current water injection scale, which are balanced layers; the effective oil-bearing thickness in the water injection interval is less than 0.5 m and the permeability is less than 0.01 μm 2 , or the relative water absorption of a single layer section is less than 10%, which are poor and extra-table oil layers and need to strengthen water injection, which are enhanced layers.

[0143] According to the statistical results of the water absorption profile data, the degree of oil layer utilization needs to reach 80%. The minimum water injection pressure of the NC block is 12.8 MPa; according to the overlying rock pressure method, that is, formula (3), the maximum water injection pressure is determined to be 14.5 MPa.

[0144] Compare the adjustment plan determined by the enhanced layers and restricted layers divided by the method in step S03 above with the original water injection adjustment plan to optimize and adjust the original water injection plan.

[0145] If it conforms to the original plan, optimize and adjust according to the original plan design. For example, in a water injection well A1, the whole well is divided into 7 sections for water injection. The on-site measured stratified indicator curve results show that under the pressure conditions allowed by the overlying rock pressure, each section can start water injection. Compared with the original plan, for the restricted sections A1-1 and A1-2, the indicator curve shows high water absorption layers, which are the sections that should be restricted; for the enhanced sections A3-4, A5, and A6-7, the indicator curve shows low water absorption layers, which are the sections that should be enhanced. The original plan conforms to the measured results. Therefore, the original plan conforms to the measured results, and effective water injection is implemented according to the original plan.

[0146] After adjusting the stratified water nozzles and checking and matching the water volume according to the stratified water injection indicator curve, raise the water injection pressure to the overlying rock pressure. The water injection pressure is increased from 13.6 MPa to 14.1 MPa, increase the throttling pressure difference of the high water absorption layer, strictly control the injection volume of the high water absorption layer, and improve the water absorption capacity of the low water absorption layer to meet the injection allocation requirements of the low water absorption oil layer to the greatest extent. The adjustment effect of Well A is obvious. The proportion of sandstone water absorption thickness increases from 24.4% to 59.8%. The daily oil production of the 4 connected production wells increases by 3.2 t, and the water cut decreases by 1.8 percentage points. The production effect of the well group is significantly improved.

[0147] If it does not conform to the original plan, re-adjust the section properties and perform dynamic adjustment. For example, in a water injection well A2, the whole well is divided into 7 sections for water injection. The originally planned water injection restricted section A1-3 shows a low water absorption layer in the stratified indicator curve, which is the section that should be enhanced; the originally planned enhanced section A4-7 shows a high water absorption layer in the stratified indicator curve, which is the section that should be restricted. The original plan does not conform to the measured results. Therefore, it is necessary to re-define according to the stratified water injection indicator curve and adjust the section properties.

[0148] By re-defining according to the stratified indicator curve and adjusting the adjustment method of the section allocation plan, the adjustment effect of Well A2 is obvious, and the water absorption profile structure is significantly improved. After stopping the water injection of the high water absorption layer, the water absorption condition of the low water absorption layer is significantly improved. The proportion of sandstone water absorption thickness increases from 35.9% to 61.8%. The daily oil production of the 3 connected production wells increases by 2.1 t, and the water cut decreases by 1.3 percentage points. The production effect of the well group is significantly improved.

[0149] Take water injection well A3 as an example. The whole well is divided into 7 sections for water injection. Comparing with the original plan according to the division results of the enhanced layer and restricted layer in step S03, there are two prominent contradictions. One is inconsistent with the original plan. The enhanced layer section A1-4 in the original plan shows a high water absorption layer in the water injection indication curve of separate layers, which should be the restricted layer. The other is that the enhanced layer sections A5-7 in the original plan do not absorb water due to the restriction of the overlying rock pressure and should be the enhanced layer. Therefore, the water injection plan is adjusted. Plugging and stopping water injection are carried out for the 4 water absorption layer sections of A1-4, and water injection is only carried out for the 3 lower layer sections. At this time, the top boundary of the oil layer changes, and the overlying rock pressure increases from 14.3 MPa to 15.4 MPa, and the water injection pressure can be increased to carry out single-section water injection. The separate injection condition of the A5-7 layer section is significantly improved. The water injection volume of the layer section with a water injection pressure of 14.2 MPa is 3 m 3 , and the water injection volume of the layer section with a water injection pressure of 14.5 MPa increases to 16 m 3 . After the low-permeability layer starts water injection, its water absorption capacity gradually increases. The adjustment effect of Well A3 is obvious, and the water absorption profile structure is significantly improved. After the high water absorption layer stops water injection, the water absorption condition of the low water absorption layer is significantly improved. In particular, the thin and poor oil layers that have not been used for a long time at the bottom start to absorb water. The proportion of the sandstone water absorption thickness increases from 22.6% to 48.3%. The daily oil production of the 4 connected production wells increases by 1.4 t, and the water cut decreases by 1.9 percentage points, and the production effect of the well group is significantly improved.

[0150] Take water injection well A4 as an example. If only judged according to the water absorption profile data, the profile control target layer section should be the A1-2 layer section, and the water absorption volume accounts for 31.9% of the whole well. However, the separate layer indication curve shows that the water absorption capacities of the A1-2 and A4 sections are strong, and the water absorption volume accounts for 66.4% of the whole well. It is initially determined that these two sections can be used as the profile control layer sections. After the profile control is implemented in this well, the effect is very remarkable, and the water absorption profile is significantly improved. The relative water absorption volume of the profile control target layer decreases from 66% to 10%. Due to the control of the high water absorption layer, the interlayer interference is reduced, the water absorption structure is improved, the water absorption capacity of the low-permeability layer is enhanced, and the proportion of the sandstone water absorption thickness of the whole well increases from 41.7% to 56%. The two connected production wells are significantly effective. The daily liquid production decreases by 0.8 t, the daily oil production increases by 0.5 t, and the water cut decreases by 1.8 percentage points, improving the production effect of the well group.

[0151] Take water injection well A5 as an example. It is divided into four sections for water injection, and the overlying rock pressure is 14.6 MPa. The top oil layer has poor water absorption. Even by using methods such as plugging for the restricted layer, the poor oil layer still cannot be started. The separate layer indication curve shows that under the condition of a water injection pressure of 14.6 MPa, the top layer sections A1-2 do not absorb water. This well must implement water injection enhancement measures to improve the water absorption condition of the enhanced layer. Fracturing is carried out on the non-water-absorbing layer sections A1-2, and the daily water injection increases by 20 m 3, the water absorption capacity is improved, and according to further subdivision adjustments, 3 injection layers are strengthened, 1 injection layer is restricted from injection, and 2 layers are balanced. After the measures, the proportion of water-absorbing layers increases from 30% to 56%, and the proportion of water-absorbing thickness in sandstone increases from 37% to 68%. The daily oil production of the 3 connected oil production wells increases by 1.3 t, and the water cut decreases by 1.7 percentage points.

[0152] For the wells in the NC block that have not undergone stratified water absorption tests, that is, the wells without stratified injection indication curves, relative water absorption ratio standards are formulated to determine the nature of the injection layers. Layers with a relative water absorption ratio lower than 10% need to be strengthened in injection, layers with a relative water absorption ratio between 10% and 50% need to be balanced in injection, and layers with a relative water absorption ratio greater than 50% need to be restricted in injection.

[0153] First, according to the liquid production demand and injection-production ratio, that is, the water injection volume can be determined by Equation (2) (similar to the method for determining the water injection volume in the block); second, the injection coefficient is calculated according to Equation (5); finally, the layer injection volume is determined according to Equation (6).

[0154] The calculation results are shown in Table 2 below. The injection volume of the strengthened layer is above 34.0 m 3 / d, the injection volume of the balanced layer is 14.0 - 34 m 3 / d, and the injection volume of the restricted layer is less than 14.0 m 3 / d.

[0155] Table 2: Dynamic Optimization and Adjustment Table for Injection Layers in NC Block

[0156]

[0157]

[0158] For example, for Layer 1 of Well A5, its utilization degree is 60%, and the daily injection volume is 34 m 3 / d. It is determined as a strengthened layer. According to the water absorption profile data, the original injection volumes (actual values) of its 7 sub-layers are measured, and the theoretical injection volume q di (theoretical value) is calculated according to the injection coefficient, that is, Equations (5) and (6). By comparing the two, it can be shown that Sub-layers 2, 3, and 4 of this layer need to be pressurized or measures need to be taken to increase injection, as shown in Table 3 below.

[0159] Table 3: Adjustment Table for Layer 1 of Well A5 (Strengthened Layer)

[0160] Sub - layer number k h kh ai Theoretical value Actual value Actual - Theoretical Remarks 1 2.01 0.40 0.81 0.11 3.78 5.09 1.32 2 2.20 0.55 1.22 0.17 5.68 4.69 -0.99 Pressure increase or measure for enhanced injection 3 3.06 0.49 1.51 0.21 7.06 4.45 -2.62 Pressure increase or measure for enhanced injection 4 2.85 0.48 1.38 0.19 6.43 5.28 -1.15 Pressure increase or measure for enhanced injection 5 1.89 0.44 0.84 0.12 3.93 4.99 1.06 6 1.84 0.42 0.78 0.11 3.62 5.29 1.67 7 1.60 0.50 0.80 0.11 3.73 4.21 0.48 Total / Average 15.44 0.47 7.28 1.00 34 34 0

[0161] For Layer 2 of Well A5, its utilization degree is 83%, and the daily injection volume is 66 m 3 / d, but the water absorption of this interval accounts for more than 50% of the total well water absorption, so it is determined as a restricted interval. According to the water absorption profile data, the original injection volume (actual value) of its 7 sub-layers is measured, and according to the injection allocation coefficient, that is, formulas (5) and (6), its theoretical injection volume (theoretical value) is calculated. By comparing the two, it can be shown that sub-layers 1, 3, and 5 of this interval are the intervals that need to be adjusted by plugging and controlling injection or single string shut-in injection, as shown in Table 4 below.

[0162] Table 4: Adjustment Table for Interval 2 (Restricted Interval) of Well A5

[0163] Sub - layer number k h kh ai Theoretical value Actual value Actual - Theoretical Remarks 1 0.08 0.30 0.02 0.02 1.13 11.19 10.06 Plugging and injection control or single - card shut - in injection 2 0.73 0.31 0.22 0.16 10.62 12.33 1.72 3 0.33 0.24 0.08 0.06 3.84 15.24 11.40 Plugging and injection control or single - card shut - in injection 4 0.63 0.23 0.14 0.10 6.84 5.72 -1.12 5 0.47 0.17 0.08 0.06 3.79 8.99 5.20 Plugging and injection control or single - card shut - in injection 6 0.57 0.33 0.19 0.13 8.82 3.83 -4.98 7 1.72 0.38 0.65 0.47 30.97 8.69 -22.27 Total / Average 4.53 0.28 1.39 1.00 66 66 0

[0164] According to field practice and statistics, for the special intervals in the NC Block, Interval A2 is the interval where casing damage has occurred. The daily injection volume at the initial stage of casing damage is 78 m 3 / d. Interval A3 is the interval prone to casing damage, and Interval A4 needs to carry out chemical polymer flooding. Therefore, for Interval A2 where casing damage has occurred, it is subdivided and single string shut-in injection is carried out; for Interval A3 prone to casing damage, the daily injection volume is controlled within 78 m 3 / d; for the plugging interval of Interval A4 for chemical polymer flooding, single string shut-in injection is carried out.

[0165] It can be understood that for the above-mentioned various method embodiments mentioned in the present invention, without violating the principle logic, they can be combined with each other to form a combined embodiment. Due to space limitations, the present invention will not elaborate further.

[0166] Those skilled in the art can understand that in the above method of the specific implementation manner, the writing order of each step does not mean a strict execution order that constitutes any limitation to the implementation process. The specific execution order of each step should be determined according to its function and possible internal logic.

[0167] The present invention establishes a method for optimizing and adjusting water injection in a multi-layer heterogeneous oil reservoir by combining the properties of the underground oil reservoir and the development dynamics (combining static and dynamic). By applying the material balance method, considering different water cut stages and different formation pressures, a method for determining the reasonable water injection scale based on a reasonable injection-production ratio is established; on this basis, the water injection intervals are dynamically optimized and adjusted by applying the stratified water injection indicator curve; secondly, in the absence of stratified test data, the injection allocation coefficient method is used for stratified dynamic optimization and adjustment. This method can achieve the purpose of "less investment, more output, and continuously improving the development effect", can make full use of the existing test data and field dynamics of the oilfield, fully consider the organic combination of static and dynamic parameters of the oil reservoir, and can formulate corresponding adjustment countermeasures according to the dynamic characteristics of different water injection intervals, avoiding both the deficiencies of the original method relying on artificial experience and the complexity of the theoretical calculation method of reservoir engineering, and is very suitable for dynamic optimization and adjustment during fine water injection in multi-layer heterogeneous sandstone oil reservoirs.

[0168] The embodiments of the present invention have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art in the technical field without departing from the scope and spirit of the described embodiments. The choice of terms used herein is intended to best explain the principles of the embodiments, the practical application, or the improvement of the technology in the market, or to enable other ordinary technical personnel in the technical field to understand the embodiments disclosed herein.

Claims

1. A method for dynamically adjusting water injection in a multi-layer heterogeneous sandstone oil reservoir, characterized in that, Including: Obtaining the layer-by-layer water injection indication curve and water absorption profile data of the target well in the work area; Determining the injection-production ratio of the target well at a certain pressure recovery rate, and determining the water injection volume of the target well according to the injection-production ratio; Dividing each layer section of the target well into restricted layers or enhanced layers; Determining the maximum water injection pressure and minimum water injection pressure of the target well layer section; Injecting water into each layer section of the target well according to the water injection volume, the maximum water injection pressure and the minimum water injection pressure. If there is a starting pressure gradient in the target well, during water injection, use the layer-by-layer water injection indication curve and the water absorption profile data to plug, profile control or single-card shut off injection adjustment for all the restricted layers, and perform pressure increase, fracturing or acidification adjustment for all the enhanced layers.

2. The water injection dynamic adjustment method for a multi-layer heterogeneous sandstone reservoir according to claim 1, wherein The method for determining the injection-production ratio of the target well at a certain pressure recovery rate includes: Using formula (1) to determine the injection-production ratio of the target well at a certain pressure recovery rate; Where: IPR is the injection-production ratio, dimensionless; N is the geological reserve, 10 4 t; C e is the comprehensive compressibility, f; B oi is the original oil volume factor, f; d(ΔP) is the differential pressure differential, MPa; dt is the time differential; q L is the liquid production rate, m 3 / d; f w is the water cut, decimal; B o is the volume factor of formation oil, f; B w is the volume factor of formation water, f.

3. The water injection dynamic adjustment method for a multi-layer heterogeneous sandstone oil reservoir according to claim 1, wherein The method for determining the water injection volume of the target well according to the injection-production ratio includes: Using formula (2) to determine the water injection volume of the target well; Qi = IPR * Q L = IPR * (Q o / (1 - f w )) (2); Where: Q i is the water injection volume, 10 4 t; IPR is the injection-production ratio, dimensionless; Q L is the liquid production volume, 10 4 t; Q o is the oil production volume, 10 4 t; f w is the water cut.

4. The water injection dynamic adjustment method for a multi-layer heterogeneous sandstone reservoir according to claim 1, characterized in that The method for dividing each layer section of the target well into restricted layers or enhanced layers includes: If the effective thickness h of the layer interval > 1.0 m and the permeability k > 0.05 μm 2 or the relative water absorption q of a single layer in the layer interval ir > 50% or the water saturation S w > 60%, then this layer is a restricted layer; If the effective thickness h of the layer section is < 0.5 m and the permeability k is < 0.01 μm 2 or the relative water absorption q of a single layer in the layer section ir < 10% or the water saturation S w < 40%, then this layer is a strengthened layer.

5. The water injection dynamic adjustment method for a multi-layer heterogeneous sandstone oil reservoir according to claim 1, characterized in that, The method for determining the maximum water injection pressure and minimum water injection pressure of the target well layer section includes: According to the water absorption profile data, respectively determine the water injection pressures corresponding to the predetermined maximum utilization degree and the predetermined minimum utilization degree of the layer section; Wherein, the water injection pressure corresponding to the predetermined maximum utilization degree is the maximum water injection pressure, and the water injection pressure corresponding to the predetermined minimum utilization degree is the minimum water injection pressure; Wherein, the maximum water injection pressure is not greater than the formation fracture pressure.

6. The water injection dynamic adjustment method for a multi-layer heterogeneous sandstone oil reservoir according to claim 1, characterized in that, The method for determining the maximum water injection pressure of the target well layer section includes: Using formula (3) to determine the maximum water injection pressure of the target well layer section; P iwmax = γ0 × H0 - 0.5 - ρ L × g × H0 × 10 -5 + P a (3); Where: P iwmax is the maximum pressure at the wellhead of the water injection well, MPa; r o is the formation fracture pressure gradient, MPa / m; H o is the depth at the top of the oil reservoir, m; ρ L is the density of water, 10 3 kg / m 3 ; g is the acceleration due to gravity, with a value of 9.8, m / s 2 ; P a is the additional pressure, MPa.

7. The method for dynamically adjusting water injection in a multi-layer heterogeneous sandstone oil reservoir according to claim 1, wherein The method for plugging, profile control or single-card shut off injection adjustment for all the restricted layers by using the layer-by-layer water injection indication curve and the water absorption profile data during water injection includes: According to the water absorption profile data and the layer-by-layer water injection indication curve, judge whether the utilization degree of the restricted layer is greater than the predetermined degree and whether it is a high water absorption layer. If so, determine the corresponding pressure under the condition of retaining the minimum utilization degree of the restricted layer according to the layer-by-layer water injection indication curve, and perform plugging or single-card shut off injection on the restricted layer according to the corresponding pressure under the condition of the minimum utilization degree; According to the water absorption profile data and the layer-by-layer water injection indication curve, judge whether the utilization degree of the restricted layer is less than the predetermined degree and whether it is a high water absorption layer. If so, perform profile control on the restricted layer; The method for pressure increase, fracturing or acidification adjustment for all the enhanced layers by using the layer-by-layer water injection indication curve and the water absorption profile data during water injection includes: Performing pressure increase on the enhanced layer. During the pressure increase process, according to the water absorption profile data and the layer-by-layer water injection indication curve, judge whether the utilization degree of the enhanced layer reaches the predetermined degree under the condition that the overlying rock pressure permits; If not, judge whether the enhanced layer is a low permeability layer. If so, perform fracturing on the enhanced layer. If not, perform acidification on the enhanced layer.

8. The method for dynamic adjustment of water injection in a multi-layer heterogeneous sandstone oil reservoir according to claim 1, characterized in that: If there is no startup pressure gradient in the target well, the water injection pressure after interval adjustment is determined according to formula (4). p i = q i / j i (4); Where: p i is the water injection pressure of the i-th interval, MPa; q i is the water injection volume of the i-th interval, m 3 / d; j i is the water absorption index of the i-th interval, m 3 / (d·MPa).

9. The water injection dynamic adjustment method for a multi-layer heterogeneous sandstone oil reservoir according to claim 1, characterized in that, If there is no separate layer water injection indicator curve, the method for dividing each interval of the target well into a restricted layer or an enhanced layer is as follows: Based on the water absorption profile data, judge whether the relative water absorption ratio of the interval is less than 10% or the degree of utilization is less than 80%. If so, it is an enhanced layer. Judge whether the relative water absorption ratio of the interval is greater than 50%. If so, it is a restricted layer.

10. The water injection dynamic adjustment method for a multi-layer heterogeneous sandstone reservoir according to any one of claims 1-9, characterized in that, If there is no separate layer water injection indicator curve, during water injection, all the restricted layers and enhanced layers are adjusted according to the separate injection coefficient. The method includes: Respectively determine the separate injection coefficients corresponding to the restricted layer and the enhanced layer using formula (5); According to the separate injection coefficients, respectively determine the theoretical water injection volumes corresponding to the restricted layer and the enhanced layer using formula (6); If the actual water injection volume of the enhanced layer is less than the corresponding theoretical water injection volume, increase the injection pressure for the enhanced layer. If the actual water injection volume of the restricted layer is greater than the corresponding theoretical water injection volume, plug the restricted layer or stop the injection of a single packer. q di = ∑q i = ∑a i q d (6); Where: a i is the injection coefficient, dimensionless; k i is the permeability of the i-th layer, um 2 ; h i is the effective thickness of the i-th layer, m; q i is the injection volume of the i-th layer, m 3 / d; q di is the injection volume of the i-th section, m 3 / d; q d is the injection volume of a single well, m 3 / d.

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