An indoor core test and calculation evaluation method for the critical production pressure difference of sand production in a reservoir

Abstract

The present invention belongs to the technical field of oil and gas production engineering in the oil and gas development industry, and particularly relates to an indoor core test and calculation evaluation method for the critical production pressure difference of reservoir sand production. The method comprises the following steps: S1, determining the confining pressure of the experimental core used in the sand production displacement test of the reservoir core; S2, determining the initial flow rate and the stepped flow rate increment of the core displacement used in the sand production displacement test of the reservoir core; S3, determining the critical pressure difference of the reservoir core sand production based on the sand production displacement test of the reservoir core; S4, calculating the critical pressure difference of the actual reservoir sand production according to the critical pressure difference of the reservoir core sand production. The present invention solves the key problem that has long existed in the past, that is, directly and mechanically equating the sand production critical conditions obtained from core tests to the reservoir sand production critical conditions, which leads to unreasonable or even wrong results in the design of reservoir production systems. It has important significance and value for improving the efficient sand production control of sand-prone oil and gas reservoirs and enhancing the exploitation efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas production engineering in the oil and gas development industry, and particularly relates to an indoor core test and calculation evaluation method for the critical production pressure difference of reservoir sand production. Background Art

[0002] At home and abroad, sand-prone reservoirs are widely distributed, and the problem of sand production plagues their normal development. In the optimization of the exploitation policies and systems of such reservoirs, it is necessary to accurately obtain the critical production pressure difference or production rate of the reservoir sand production, that is, the production pressure difference or production rate when obvious sand production phenomena begin to appear in the reservoir during the oil production process, as the critical condition for judging reservoir sand production, an important basis for on-site production control and production system optimization, and a key basis for sand control measure decision-making and anti-sand parameter design optimization.

[0003] At present, the methods for obtaining the critical production pressure difference of reservoir sand production in oilfield sites mainly include numerical simulation prediction methods and core test experimental methods (as shown in the patent document with the publication number CN205135616U). The latter uses reservoir cores to conduct sand production displacement simulation experiments, which has better credibility compared with numerical calculation methods and has become the main technical approach for obtaining the critical production pressure difference of reservoir sand production.

[0004] However, the current technology for obtaining the critical production pressure difference of sand production through reservoir core tests has the following key problems:

[0005] (1) There is a lack of a standardized and effective indoor experimental test method for the critical pressure difference of reservoir core sand production. Existing core experimental test means are difficult to obtain accurate sand production critical conditions. The lack of an effective test method makes it difficult to obtain accurate production pressure difference data. The general experimental method is to conduct a core displacement experiment through the reservoir flow rate under reservoir conditions. The experimental data obtained can judge whether the core produces sand, but the critical pressure difference or critical conditions for core sand production cannot be obtained.

[0006] (2) The critical production pressure difference of sand production obtained from small-scale reservoir core tests is not the critical condition of sand production under actual reservoir production conditions, and there is currently no conversion evaluation method. Directly equating the core sand production critical condition with the reservoir sand production critical condition has a large error or even an error. Since the core scale is extremely different from the actual reservoir, the experimental method uses a unidirectional flow core displacement experiment, and the reservoir fluid flows towards the wellbore in a radial flow manner. Therefore, the critical displacement pressure difference of core sand production obtained from the experiment is not the actual critical pressure difference of reservoir sand production (as shown in (a) and (b) in the appendix, Figure 1 as shown in (a) and (b) below, Figure 1 (a) L in 0Usually more than one hundred meters), there is a lack of a calculation and evaluation method for converting the critical displacement pressure difference of core sand production into the critical production pressure difference of reservoir sand production. Directly equating the critical conditions of core sand production with the critical conditions of reservoir sand production and using them to guide reservoir development production policies and systems have great errors or even mistakes. Summary of the Invention

[0007] Aiming at the key problems of the lack of standardized and effective indoor experimental testing and conversion methods for the critical pressure difference of reservoir core sand production, and the great error in directly equating the critical conditions of core sand production with the critical conditions of reservoir sand production, the present invention provides an indoor core test and calculation evaluation method for the critical production pressure difference of reservoir sand production. One of its purposes is to provide a standardized experimental procedure to obtain accurate critical flow velocity and pressure difference conditions for core sand production, and to solve the problem of the lack of experimental methods to accurately obtain the critical conditions of core sand production; the second purpose is to provide a conversion method to convert the critical displacement pressure difference obtained from core tests into the critical production pressure difference under actual oil reservoir production conditions, and to solve the problem that the current direct equating of the critical conditions of core sand production with the critical conditions of reservoir sand production for guiding reservoir development production policies and systems has great errors or even mistakes.

[0008] Therefore, the indoor core test and calculation evaluation method for the critical production pressure difference of reservoir sand production of the present invention includes the following two major parts:

[0009] The first part: Provide an experimental testing method for the critical displacement pressure difference of reservoir core sand production;

[0010] Based on the core displacement experimental device, this method first proposes a basic method for determining the confining pressure, and then gives a method for determining the initial flow rate of stepped flow displacement and a method for determining the stepped flow rate increment; it proposes two characteristic phenomena of initial slight sand production and obvious sand production and a method for determining the corresponding critical pressure difference conditions. Using the stepped flow method proposed by the present invention, the critical pressure differences corresponding to the initial slight sand production and obvious sand production of reservoir cores can be accurately determined through experiments.

[0011] The second part: Provide a method for calculating and obtaining the critical production pressure difference of actual reservoir sand production based on the critical displacement pressure difference of core sand production;

[0012] This method takes into account the differences in the confining pressure conditions between core experimental tests and actual reservoir confining pressure conditions, the differences in the physical properties of core test fluids and reservoir fluids, and the differences in core scale and the scale of the sand production area near the wellbore, and converts the critical displacement pressure difference obtained from reservoir core tests into the critical displacement pressure difference under actual reservoir conditions.

[0013] Based on this, the specific technical solution of the present invention is as follows:

[0014] An indoor core test and calculation evaluation method for the critical production pressure difference of reservoir sand production, including the following steps:

[0015] S1. Determine the confining pressure of the experimental core used in the sand production displacement test of the reservoir core:

[0016] The present invention provides a method for determining the experimental confining pressure, which refers to the uniaxial compressive strength of the core, aims at finite simulation of reservoir stress conditions, and simultaneously avoids seepage through the core wall surface and crushing of the core due to extrusion.

[0017] S11. Calculate the minimum experimental confining pressure:

[0018] Whether fluid channeling occurs in the gap between the core holder and the core depends on the flow channeling driving pressure and the confining pressure. According to the principle of pressure balance, the critical confining pressure to prevent fluid channeling through the core wall surface can be obtained. To ensure that no wall surface channeling occurs during the entire experiment, the present invention proposes that the minimum confining pressure is 1.25 times the critical channeling confining pressure:

[0019] (Ⅰ)

[0020] In formula (Ⅰ), σ min is the minimum experimental confining pressure, MPa; σ l is the critical confining pressure for fluid channeling through the core wall surface, MPa; μ is the viscosity of the displacement fluid, mPa·s; L is the length of the core, m; Q max is the maximum displacement flow rate in the experiment, m 3 / s; μ c is the friction coefficient, generally taking values of 0.3 - 0.5 according to the rock type and the surface roughness of the core. For dense rocks or cores with relatively smooth surfaces, the value is 0.3; for loose sandstones or cores with relatively rough surfaces, the value is 0.5; b is the height of the gap between the core holder and the core, m; d is the diameter of the core, m;

[0021] S12. Calculate the maximum experimental confining pressure:

[0022] There is an axial support stress in the core holder. To ensure that the core is not crushed during the experiment, the upper limit of the confining pressure is set according to the uniaxial compressive strength of the core σ max :

[0023] (Ⅱ)

[0024] In formula (Ⅱ), σ max is the maximum experimental confining pressure, MPa; αis an empirical coefficient, generally taking a value of 1.5 - 3.0; for weakly cemented unconsolidated sandstone, a recommended value of 3.0 is taken, for moderately consolidated sandstone, a recommended value of about 2.0 is taken, and for strongly consolidated sandstone, a recommended value of about 1.5 is taken; σ c is the uniaxial compressive strength of the core, MPa;

[0025] S13. Determine the confining pressure of the experimental core:

[0026] The confining pressure set in the experiment should be within σ min , σ max . In actual reservoir rocks under in-situ stress environmental conditions, the rocks in any unit of the reservoir are under surrounding rock stress conditions. In order to finitely simulate the formation stress conditions in the core displacement experiment, the present invention proposes to determine the confining pressure of the experimental core used according to the following method:

[0027] (Ⅲ)

[0028] (Ⅳ)

[0029] In formula (Ⅲ), σ ve is the finite formation vertical stress value simulated by the experimental confining pressure, and the recommended value is 20% of the original vertical principal stress of the reservoir, MPa; σ v is the original vertical principal stress of the reservoir; ρ r is the average density of the reservoir rock, kg / m 3 ; g is the acceleration of gravity, with a value of 9.8 N / kg; h is the vertical depth of the reservoir, m;

[0030] In formula (Ⅳ), σ w is the recommended reasonable value of the experimental confining pressure, that is, the confining pressure of the experimental core, MPa.

[0031] S2. Determine the initial flow rate and step flow rate increment of the core displacement for the sand production displacement test of the reservoir core:

[0032] In order to accurately test the critical differential pressure of sand production from the core by gradually increasing the flow rate step by step, it is necessary to determine the initial flow rate of the core displacement and the step flow rate increment used in the displacement experiment. Use Q 0 and Δ Q to represent the initial flow rate of the experimental core displacement and the step flow rate increment respectively, and it is required that Q 0It must be lower than the critical minimum flow rate that causes core sand production (the critical sand production state is truly the target state to be tested in the experiment), and Δ Q should be as small as possible to ensure more accurate testing; however, an overly small Δ Q will increase the testing time and complexity, and a reasonable Δ Q value needs to be selected.

[0033] The present invention proposes a method for calculating the initial displacement flow rate Q 0 and the stepped flow rate increment Δ Q of an experimental core based on the production and sand production conditions of oil and gas wells in the target work area (oil and gas block or reservoir) where the experimental core is sourced, and the calculation is carried out in three cases:

[0034] Case 1: There are no obvious sand production wells (all wells do not produce sand) under the production conditions of the target work area

[0035] For this case Q 0 and Δ Q , the specific calculation steps are as follows:

[0036] S21. Calculate the characteristic volumetric liquid production intensity:

[0037] Sort all the wells in the target work area in descending order of liquid production intensity, and select the top N wells as typical wells ( N select 3 - 5 wells or 1 / 10 of the total number of wells in the target work area). For each typical well, select the daily production report ( n i select 15 - 30 days) under typical production conditions (typical production conditions refer to the key dynamic parameter combinations that commonly exist in reservoir development and affect the sand production risk, such as bottom hole flowing pressure, fluid properties, production regime, etc.). n i From the bottom hole volume production data in the daily production report, divide by the production layer thickness to obtain the liquid production intensity, and then calculate the characteristic volumetric liquid production intensity according to the following formula:

[0038] (Ⅴ)

[0039] (Ⅵ)

[0040] In formula (Ⅴ), is the average characteristic volumetric liquid production intensity of the i th typical well, m 3 / d / m, i takes values of 1, 2.. N ; n i is the number of days of the daily production report of the i th typical well;q ij is the volume liquid production intensity on the i day of the typical well (obtained by dividing the bottom-hole volume production by the thickness of the production layer), m j / d / m, 3 / d / m, j taking values of 1, 2… n i ;

[0041] In formula (Ⅵ), q a is the characteristic volume liquid production intensity of the target work area (in Case 1, the characteristic volume liquid production intensity q a specifically refers to the sand-free characteristic volume liquid production intensity), m 3 / d / m; N is the calculated number of typical wells;

[0042] S22. According to the characteristic volume liquid production intensity q a , calculate the corresponding core displacement flow rate under the same flow velocity condition:

[0043] (Ⅶ)

[0044] In formula (Ⅶ), Q a is the flow velocity equivalent core displacement flow rate (in Case 1, the flow velocity equivalent core displacement flow rate Q a specifically refers to the flow velocity equivalent core displacement flow rate corresponding to the sand-free characteristic volume liquid production intensity), L / min; d is the core diameter, m; d w is N the average wellbore diameter of

[0045] S23. Determine the initial core displacement flow rate and the step flow rate increment of the target work area:

[0046] (Ⅷ)

[0047] (Ⅸ)

[0048] In this case, the initial core displacement flow rate is selected as 0.9 times of the flow velocity equivalent core displacement flow rate Q a , and the step flow rate increment is selected as 0.5 times of Q 0 , that is, x takes the value of 0.9, y takes the value of 0.5.

[0049] Case 2: Some wells in the target working area have sand production or sand production phenomena (while the other wells do not have sand production).

[0050] This case Q 0 and Δ Q The specific calculation steps are as follows:

[0051] S21. Calculate the characteristic volumetric liquid production intensity:

[0052] Sort the non-sand-producing wells in the target working area in descending order of liquid production intensity, and select the top N wells as typical wells ( N Select 3 - 5 wells or 1 / 10 of the total number of non-sand-producing wells in the target working area). For each typical well, select the production daily report under typical production conditions for n i days ( n i Select 15 - 30 days). Divide the bottom-hole volume production data in the production daily report by the production layer thickness to obtain the liquid production intensity, and then calculate the characteristic volumetric liquid production intensity according to formulas (Ⅴ) and (Ⅵ):

[0053] The characteristic volumetric liquid production intensity in Case 2 q a Specifically refers to the non-sand-producing characteristic volumetric liquid production intensity;

[0054] S22. According to the characteristic volumetric liquid production intensity q a calculate the corresponding core displacement flow rate under the same flow rate condition according to formula (Ⅶ):

[0055] The flow rate equivalent core displacement flow rate in Case 2 Q a Specifically refers to the flow rate equivalent core displacement flow rate corresponding to the non-sand-producing characteristic volumetric liquid production intensity;

[0056] S23. Determine the core displacement starting flow rate and step flow rate increment of the target working area according to formulas (Ⅷ) and (Ⅸ):

[0057] In this case, the core displacement starting flow rate Q 0 is selected as 0.75 times of the flow rate equivalent core displacement flow rate Q a , and the step flow rate increment is selected as 0.25 times of Q 0 , that is x Take the value of 0.75, y Take the value of 0.25.

[0058] Case 3: All wells in the target working area have sand production or sand production phenomena

[0059] This situation Q 0 and Δ Q The specific calculation steps are as follows:

[0060] S21. Calculate the characteristic volume liquid production intensity:

[0061] Sort all the wells in the target work area according to the sand production degree from slight to severe, and select the top N wells as typical wells ( N Select 3 - 5 wells or 1 / 10 of the total number of wells in the target work area), and for each typical well, select the daily production report under typical production conditions for n i days ( n i Select 15 - 30 days). Divide the bottom - hole volume production data in the daily production report by the production layer thickness to obtain the liquid production intensity, and then calculate the characteristic volume liquid production intensity according to formulas (Ⅴ) and (Ⅵ):

[0062] The characteristic volume liquid production intensity in Case 3 q a Specifically refers to the characteristic volume liquid production intensity of slight sand production;

[0063] S22. According to the characteristic volume liquid production intensity q a , calculate the corresponding core displacement flow rate under the same flow velocity condition according to formula (Ⅶ):

[0064] The flow - velocity equivalent core displacement flow rate in Case 3 Q a Specifically refers to the flow - velocity equivalent core displacement flow rate corresponding to the characteristic volume liquid production intensity of slight sand production;

[0065] S23. Determine the initial core displacement flow rate and the step - flow rate increment of the target work area according to formulas (Ⅷ) and (Ⅸ):

[0066] In Case 3, the initial core displacement flow rate Q 0 Select according to 0.5 times of the flow - velocity equivalent core displacement flow rate Q a , and select the step - flow rate increment according to Q 0 0.15 times of x Take the value of 0.5, y Take the value of 0.15.

[0067] S3. Use the step - increasing flow rate method to test the critical conditions of slight sand production and obvious sand production of the core

[0068] According to the selected initial core displacement flow rate Q 0and the step - flow increment Δ Q , the sand - production displacement experiment test is carried out by the step - increasing flow method. Two sand - production states and the critical pressure difference under this state are proposed to characterize the sand - production critical pressure difference of the reservoir core:

[0069] Slight sand - production state and its critical pressure - difference condition: The initial slight sand - production state is defined as that the experimental fluid flowing out of the core starts to show obvious turbidity compared with the original inlet fluid, or muddy fine sand grains start to appear on the filter medium (usually filter paper). At this time, it can be judged that the core starts to produce slight sand, and the core displacement pressure difference at this time is the initial slight sand - production critical pressure difference of the core.

[0070] Obvious sand - production state and its critical pressure - difference condition: The obvious sand - production state is defined as the state when obvious sand grains deposition can be observed with the naked eye on the filter medium. At this time, it is judged that the core starts to show obvious sand - production phenomenon, and the core displacement pressure difference at this time is the obvious sand - production critical pressure difference of the core.

[0071] According to the experimental procedure shown in the appendix Figure 3 , the specific experimental test method is as follows:

[0072] a. Set the confining pressure of the core to σ w , and use high - salinity water with the same components as the actual oil reservoir as the experimental fluid.

[0073] b. Take Q 0 as the initial experimental displacement flow rate, and displace at a constant flow rate for 30 min;

[0074] c. On the basis of the previous displacement flow rate, increase the flow rate by Δ Q , and displace at a constant flow rate for 30 min; Observe the state and color of the core produced fluid during the experiment; After each displacement, take out the sand - retaining filter paper and observe the filtration state of the filter paper.

[0075] d. When the slight sand - production state appears, record the slight sand - production critical pressure difference and flow rate at this time, which are respectively recorded as Δ P c1 and Q c1 .

[0076] e. After the slight sand - production state appears, the incremental flow rate for each flow - rate change is reduced to 0.5Δ Q , that is, increase the flow rate by 0.5Δ Q each time, and displace at a constant flow rate for 30 min; Observe the state and color of the core produced fluid during the experiment; After each displacement, take out the sand - retaining filter paper and observe the filtration state of the filter paper.

[0077] f. When the obvious sand - production state appears, record the obvious sand - production critical pressure difference and flow rate at this time, which are respectively recorded as ΔP c2 and Q c2 。Then end the experiment.

[0078] g. If no slight or obvious sand production phenomenon is observed until the maximum flow rate under the displacement condition, it indicates that there is no corresponding sand production phenomenon in the core under the current maximum experimental conditions. A displacement pump with a larger flow rate can be replaced (since the core cannot fully reflect the actual reservoir and there are differences from the actual reservoir, there may be no sand production under the maximum displacement flow rate condition, so a displacement pump with a larger flow rate can be replaced at this time), or the test can be terminated.

[0079] S4. Calculate the sand production critical pressure difference of the actual reservoir according to the sand production critical pressure difference of the reservoir core obtained in step S3, which specifically includes the following steps:

[0080] S41. Calculate the correction coefficient for the difference between the experimental core size and the actual reservoir scale

[0081] To convert the sand production critical pressure difference of the small-scale core to the actual reservoir, the difference between the core size and the actual reservoir size needs to be considered. According to the phenomenon and principle of the pressure drop funnel near the wellbore in the reservoir, the production pressure difference of the oil well (the difference between the reservoir boundary pressure and the bottom-hole flowing pressure, as shown in the appendix Figure 3 ) is mostly consumed within a limited range near the wellbore. The present invention proposes to use the equivalent pressure loss radius R c as an index to characterize the actual reservoir scale, R c The meaning and selection principle of R c are as follows: From the wellbore radius to the P region, the flow pressure drop accounts for 75% of the total production pressure difference Δ Rc is calculated by the following formula:

[0082] (Ⅹ)

[0083] In formula (Ⅹ), R c is the equivalent pressure loss radius characterizing the reservoir scale, m; r w is the wellbore radius, m; r e is the outer boundary radius of the reservoir, m;

[0084] The flow of the experimental core is unidirectional linear flow, and the flow within the equivalent pressure loss radius of the actual reservoir is radial flow. It is proposed to calculate the correction coefficient β 1 for the difference between the experimental core scale and the actual reservoir scale according to the principle of equivalence between the average pressure drop gradient of the radial flow in the reservoir and the pressure drop gradient of the core:

[0085] (Ⅺ)

[0086] In formula (Ⅺ), L is the core length, in m.

[0087] S42. Calculate the correction coefficient for the difference between the physical properties of the core test fluid in the laboratory and those of the actual reservoir fluid

[0088] Propose the definition of the viscosity-density index, which characterizes the product of the fluid density and the z-th power of the viscosity, as shown in the following formula:

[0089] (Ⅻ)

[0090] (XIII)

[0091] In formula (Ⅻ), λ 1 is the viscosity-density index of the laboratory test fluid; is the density of the laboratory test fluid, in kg / m 3 ; is the viscosity of the laboratory test fluid, in Pa·s; z is the empirical index, and it is recommended to take 0.5;

[0092] In formula (XIII), λ 2 is the viscosity-density index of the actual reservoir fluid; is the density of the actual reservoir fluid, in kg / m 3 ; is the viscosity of the actual reservoir fluid, in Pa·s;

[0093] Use the viscosity-density index to characterize the influence of the fluid on the sand production condition and sand carrying in the porous medium. The larger the viscosity-density index (i.e., the larger the fluid viscosity or density), the easier the reservoir is to produce sand, and the smaller the critical production pressure difference for sand production.

[0094] Propose the correction coefficient for the difference between the physical properties of the laboratory test fluid and those of the actual reservoir fluid β 2 is the viscosity-density index of the laboratory test fluid λ 1 and the viscosity-density index of the actual reservoir fluid λ 2 The ratio is shown in the following formula:

[0095] (XIV)

[0096] When calculating the density and viscosity of the oil-water mixture fluid in the reservoir, the respective densities and viscosities of oil and water are used, and the weighted average method with the water cut is used for calculation.

[0097] S43. Calculate the correction coefficient for the difference between the confining pressure (stress) in indoor core tests and the actual reservoir stress conditions

[0098] Propose the correction coefficient for the difference between the confining pressure (stress) in indoor core tests and the actual reservoir stress conditions β 3 It is the ratio of the confining pressure in core experiments to the minimum in-situ principal stress in the actual reservoir, as shown in the following formula:

[0099] (XV)

[0100] In formula (XV) , σ v is the original vertical principal stress of the reservoir, MPa; σ h is the original minimum horizontal principal stress of the reservoir, MPa.

[0101] S44. Calculate the critical differential pressure for sand production in the actual reservoir according to the correction of the critical differential pressure in indoor core tests

[0102] According to the obtained correction coefficient for reservoir scale difference β 1 , the correction coefficient for reservoir fluid physical property difference β 2 and the correction coefficient for reservoir geostress difference β 3 , calculate the corrected critical differential pressure for sand production in the actual reservoir:

[0103] (XVI)

[0104] (XVII)

[0105] In the formula, Δ P 1 is the critical differential pressure for slight sand production in the actual reservoir, MPa; Δ P 2 is the critical differential pressure for obvious sand production in the actual reservoir, MPa. The critical differential pressure for sand production in the actual reservoir is characterized by Δ P 1 , Δ P 2 .

[0106] Compared with the prior art, the beneficial effects of the present invention are:

[0107] (1) The experimental test method for the critical pressure difference of reservoir core sand production provided by the present invention can simply and quickly determine the confining pressure conditions and stepped displacement flow conditions, and perform displacement according to the stepped flow rate increase method to accurately test the critical pressure differences corresponding to initial slight sand production and obvious sand production. This method is simple and convenient, has good operability, and solves the problem that the lack of a standardized experimental method makes it impossible to accurately obtain the critical conditions of core sand production.

[0108] (2) The method for calculating and obtaining the critical production pressure difference of actual reservoir sand production based on the critical pressure difference of reservoir core sand production provided by the present invention fully considers the differences between the core laboratory test conditions and the actual reservoir production conditions (including three main difference conditions: the difference between the confining pressure conditions of core experimental tests and the actual reservoir confining pressure conditions, the difference between the physical properties of the core test fluid and the reservoir fluid, and the difference between the core scale and the scale of the sand production area near the well in the reservoir). It can simply and quickly convert the critical pressure difference obtained from core tests into the critical production pressure difference under the actual oil and gas reservoir production conditions, converting the indoor test results into actual reservoir conditions, and the results are more accurate and reliable.

[0109] (3) The indoor core test and calculation evaluation method for the critical production pressure difference of reservoir sand production provided by the present invention includes both an experimental operation method and a conversion evaluation method for experimental data processing; it is applicable to both oil wells and gas wells, building a bridge between indoor core tests and actual reservoir production conditions and achieving rapid conversion. It solves the key problem that has long existed in the past of directly mechanically equating the critical conditions obtained from core tests with the critical conditions of reservoir sand production (in fact, the two are completely different), which leads to unreasonable or even wrong results when used for reservoir production system design. It has important significance and value for improving the efficient sand production control of easily sand-producing oil and gas reservoirs and increasing the exploitation efficiency. Description of the Drawings

[0110] Figure 1 It is a schematic diagram of the reservoir, where (a) is a schematic diagram of the actual reservoir, and (b) is a schematic diagram of the reservoir rock for experiments;

[0111] Figure 2 It is a schematic diagram of the experimental device for the displacement test of reservoir core sand production;

[0112] Figure 3 It is a schematic diagram of the principle for correcting the core size and the scale of the near-well range of the actual reservoir.

[0113] 1 - Data acquisition system, 2 - Liquid storage tank, 3 - Liquid pump, 4 - Core holder, 5 - Sand collection device. Detailed Embodiments

[0114] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings.

[0115] Taking a certain oilfield block as an example for conversion analysis, sand production occurs in all wells of this reservoir. The depth of the natural core of the main reservoir in this oilfield is 1608 m, and the basic data is shown in Table 1 below.

[0116] Table 1 Basic data of the case

[0117]

[0118] According to step S1, this reservoir is a loose sandstone reservoir, and based on the rock type and core compressive strength, σ c is 19.61 MPa; according to the crossflow drive theory, σ min is 11.13 MPa, and finally the experimental confining pressure is determined to be 15.37 MPa.

[0119] According to step S2, all wells in this reservoir produce sand. According to the average liquid production of the selected wells and the reservoir conditions, the initial flow rate of core displacement is determined to be 0.288 ml / min, and the flow rate gradient is 0.043 ml / min by using the method of case three.

[0120] Among them, N are 3 typical wells, and the n i values are all 20 days, and the q ij of each typical well are all obtained by dividing the bottom-hole production data in its production daily report by the production layer thickness.

[0121] According to step S3, the test is carried out using the experimental device shown in Figure 2 . The experimental device for the sand production displacement test of the reservoir core shown in Figure 2 includes a data acquisition system 1, a liquid storage tank 2, a liquid pump 3, a core holder 4, and a sand collection device 5. Figure 2 The arrow direction in

[0122] Table 2 Core sand production result data table

[0123]

[0124] is the flow direction of the fluid during the experiment, and the data acquisition system 1 is used to collect experimental data. The critical pressure difference results of core testing are shown in Table 2.

[0125]

[0126] Calculate the correction coefficient for the difference in the size of the indoor core and the scale of the near-well range of the actual reservoir:

[0127]

[0128] Calculate the correction coefficient for the difference between the confining pressure (stress) in the indoor core test and the actual reservoir stress conditions:

[0129]

[0130] Calculate the critical production pressure difference Δ for slight sand production in this actual reservoir P 1 :

[0131]

[0132] Calculate the critical production pressure difference Δ for obvious sand production in the actual reservoir P 2 :

[0133]

Claims

1. An indoor core test and calculation evaluation method for critical production pressure difference of reservoir sand production, characterized in that: The steps include: S1. Determine the experimental core confining pressure used in the reservoir core sand displacement test; Based on the critical confining pressure of core wall channeling, the minimum experimental confining pressure is calculated. Based on the uniaxial compressive strength of the core, the maximum experimental confining pressure is calculated. Based on the minimum experimental confining pressure, the maximum experimental confining pressure and the original vertical principal stress of the reservoir, the experimental core confining pressure is determined. σ w ; S2. Determine the core displacement starting flow rate and step flow rate increment used in the reservoir core sand displacement test; Based on the sand production situation of the target reservoir area to be predicted, the characteristic volume production intensity of the target area is calculated, based on the characteristic volume production intensity, the velocity equivalent core displacement flow rate is calculated, and based on the velocity equivalent core displacement flow rate, the core displacement starting flow rate of the target area is determined. Q 0 and step flow increment Δ Q ; S3. Determine the critical pressure difference of reservoir core sanding based on the reservoir core sanding displacement test; The experimental core confining pressure is set to σ w , the core displacement starting flow rate is Q 0, based on Δ Q Set the incremental flow rate and use the step-by-step incremental flow rate method to conduct sand displacement test to determine the critical pressure difference of slight sand production Δ P c1 and critical pressure difference of obvious sand production Δ P c2 ; S4, calculating the actual reservoir sand production critical pressure difference according to the reservoir core sand production critical pressure difference obtained in step S3; (XVI) (XVII) In formula (XVI), Δ P 1 is the critical pressure difference of slight sand production in the actual reservoir, dimensionless; β 1 is the reservoir scale difference correction coefficient, dimensionless; β 2 is the correction coefficient for reservoir fluid property differences, dimensionless; β 3 is the reservoir stress difference correction coefficient, dimensionless; In formula (XVII), ΔP 2 is the critical pressure difference for obvious sand production in the actual reservoir; The actual critical pressure difference of reservoir sand production is Δ P 1. Δ P 2 Characterization.

2. The indoor core testing and calculation evaluation method for critical production pressure difference of reservoir sand production according to claim 1 is characterized in that: Step S1 is specifically as follows: S11. Calculate the minimum experimental confining pressure: (Ⅰ) In formula (I), σ min is the minimum experimental confining pressure, MPa; σ l is the critical confining pressure of core wall flow, MPa; μ is the displacement fluid viscosity, mPa·s; L is the core length, m; Q max is the maximum displacement flow rate of the experiment, m 3 / s; μ c is the friction coefficient, dimensionless; b is the gap height between the core holder and the core, m; d is the core diameter, m; S12. Calculate the maximum experimental confining pressure: (Ⅱ) In formula (II), σ max is the maximum experimental confining pressure, MPa; α is the empirical coefficient, dimensionless; σ c is the uniaxial compressive strength of the core, MPa; S13. Determine the experimental core confining pressure: (Ⅲ) (Ⅳ) In formula (III), σ ve is the vertical stress value of the finite formation simulated by the experimental confining pressure, MPa; σ v is the original vertical principal stress of the reservoir, MPa; ρ r is the average density of reservoir rock, kg / m 3 ; g is the acceleration due to gravity, which is 9.8N / kg; h is the vertical depth of the reservoir, m; In formula (IV), σ w is the experimental core confining pressure, MPa.

3. The indoor core testing and calculation evaluation method for critical production pressure difference of reservoir sand production according to claim 1 is characterized in that: In step S2, the sand production situation of the target work area of ​​the reservoir to be predicted is divided into: situation 1, there is no obvious sand production well under the production conditions of the target work area; situation 2, some wells have produced sand or have sand production under the production conditions of the target work area; situation 3, all wells have produced sand or have sand production under the production conditions of the target work area; Step S2 is specifically as follows: S21. Select the target area of ​​the reservoir to be predicted. N Typical wells, each of which is selected under typical production conditions n i Daily production report for the day, calculate the characteristic volume production intensity: (Ⅴ) (Ⅵ) In formula (V), For the i Average characteristic volumetric fluid production intensity of typical wells, m 3 / d / m, i The value is 1,2.. N ; n i For the i The number of daily production days for a typical well; q ij For the i A typical well j Volumetric liquid production intensity per day, m 3 / d / m, j The value is 1,2… n i In formula (VI), q a is the characteristic volumetric liquid production intensity, m 3 / d / m; Among them, when the sand production situation of the target work area of ​​the reservoir to be predicted is situation one or situation two, a typical well is selected based on the liquid production intensity, and the characteristic volume liquid production intensity obtained by formula (VI) is the characteristic volume liquid production intensity of no sand production; when the sand production situation of the target work area of ​​the reservoir to be predicted is situation three, a typical well is selected based on the degree of sand production, and the characteristic volume liquid production intensity obtained by formula (VI) is the characteristic volume liquid production intensity of slight sand production; S22, calculate the equivalent core displacement flow rate: (Ⅶ) In formula (VII), Q a is the flow rate equivalent to the core displacement flow, L / min; d is the core diameter, m; d w for N Average borehole diameter of typical wells, m; S23. Determine the starting flow rate of core flooding in the target work area and step flow increment Δ Q : (Ⅷ) (Ⅸ) Among them, when the sand production situation of the target reservoir area to be predicted is situation 1, x The value is 0.

9. y The value is 0.5; when the sand production situation of the target area of ​​the reservoir to be predicted is situation 2, x The value is 0.

75. y The value is 0.25; when the sand production situation of the target reservoir area to be predicted is situation 3, x The value is 0.

5. y The value is 0.

15.

4. The indoor core testing and calculation evaluation method for critical production pressure difference of reservoir sand production according to claim 1 is characterized in that: Step S3 is specifically as follows: a. Set the core confining pressure to σ w , the experimental fluid used high-mineralization water with the same composition as the actual reservoir formation sand; b. Q 0 was used as the initial experimental displacement flow rate, and the constant flow was used for 30 min; c. Based on the previous displacement flow, increase the flow rate by Δ each time Q , constant flow displacement for 30 minutes, observe the state and color of the core output fluid during the experiment, take out the sand filter paper after each displacement, and observe the filtering state of the filter paper; d. When slight sanding occurs, record the critical pressure difference Δ for slight sanding at this time. P c1 ; e. After slight sanding occurs, increase the flow rate by 0.5Δ each time Q , constant flow displacement for 30 minutes, observe the state and color of the core output fluid during the experiment, take out the sand filter paper after each displacement, and observe the filtering state of the filter paper; f. When obvious sand production occurs, the critical pressure difference for obvious sand production is recorded as Δ P c2 , and then end the experiment.

5. The indoor core testing and calculation evaluation method for critical production pressure difference of reservoir sand production according to claim 1 is characterized in that: In step S4, the actual reservoir scale difference correction coefficient β The calculation method of 1 is: (Ⅹ) In formula (X), R c is the equivalent pressure loss radius, m; r w is the wellbore radius, m; r e is the radius of the reservoir outer boundary, m; (Ⅺ) In formula (XI), L is the core length, m.

6. The indoor core testing and calculation evaluation method for critical production pressure difference of reservoir sand production according to claim 1 is characterized in that: In step S4, the actual reservoir fluid property difference correction coefficient β 2 is calculated as: (Ⅻ) (XIII) In formula (XII), λ1 is the viscosity index of the fluid in the indoor experiment; is the density of the indoor experimental fluid, kg / m 3 ; is the viscosity of the indoor experimental fluid, Pa·s; z is the experience index; In formula (XIII), λ2 is the actual reservoir fluid viscosity index; is the actual reservoir fluid density, kg / m 3 ; is the actual reservoir fluid viscosity, Pa·s; (XIV)。 7. The indoor core testing and calculation evaluation method for critical production pressure difference of reservoir sand production according to claim 1 is characterized in that: In step S4, the actual reservoir stress condition difference correction coefficient β The calculation method of 3 is: (XV) In formula (XV) , σ v is the original vertical principal stress of the reservoir, MPa; σ h is the original minimum horizontal principal stress of the reservoir, MPa; σ w is the experimental core confining pressure.

8. The indoor core testing and calculation evaluation method for critical production pressure difference of reservoir sand production according to claim 2 is characterized in that: In step S11, μ c The value range is 0.3~0.

5. For dense rocks or cores with relatively smooth surfaces, the value is 0.3; for loose sandstones or cores with relatively rough surfaces, the value is 0.

5.

9. The indoor core testing and calculation evaluation method for critical production pressure difference of reservoir sand production according to claim 2 is characterized in that: In step S12, α The value range is 1.5~3.0; for weakly cemented loose sandstone, the value is 3.0, for moderately consolidated sandstone, the value is 2.0, and for strongly consolidated sandstone, the value is 1.

5.

10. The indoor core testing and calculation evaluation method for critical production pressure difference of reservoir sand production according to claim 6, characterized in that: In step S4, z The value is 0.5.

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