A comprehensive evaluation method for determining crossflow channel types in offshore unconsolidated sandstone reservoirs

Abstract

The present invention provides a comprehensive evaluation method for determining the type of crossflow channel in an offshore unconsolidated sandstone reservoir, comprising the following steps: collecting static data from production wells and injection wells and production dynamic data over a period of time; calculating the control volume and interwell conductivity based on the static data and production dynamic data; calculating the permeability, injection-to-volume ratio, water injection efficiency, and water cut increase rate based on the interwell conductivity, control volume, and liquid separation volume in each injection-production direction; performing weighted averaging and normalization on the permeability, injection-to-volume ratio, water injection efficiency, and water cut increase rate to obtain a comprehensive evaluation index; and characterizing the crossflow channel according to the comprehensive evaluation index. The present invention is used to accurately classify the types of crossflow channels, thereby providing a basis for subsequent targeted adjustments and control measures for different levels of crossflow channels. The model is simple to construct, has low operational difficulty, and low testing costs.

Description

Technical Field

[0001] The present invention relates to the technical field of oil development, and in particular to a comprehensive evaluation method for determining the type of crossflow channels in offshore loose sandstone oil reservoirs. Background Art

[0002] Unconsolidated sandstone reservoirs account for a significant proportion of the Bohai heavy oil fields. The Minghuazhen, Guantao, and Dongying Formations, as well as portions of the Shahejie reservoirs, are all unconsolidated sandstones characterized by strong reservoir heterogeneity, high crude oil viscosity, early injection timing, and multi-layer commingled injection and production. After years of waterflooding development, these oil fields are poised to enter, or have already entered, a period of "high water cut" or even "extra-high water cut." Under the long-term impact of fluid flushing, reservoir formation parameters such as porosity and permeability have significantly changed compared to their initial stages. This has led to the formation of crossflow channels between production wells and injection wells, allowing injected water to easily advance along high-permeability zones or strata, resulting in uneven sweep. This makes it difficult to effectively mobilize the remaining oil in low-permeability zones, reduces sweep coefficients and flooding efficiency, and ultimately impacts recovery.

[0003] Currently, the main methods for identifying crossflow channels include injection well logging data inversion, observation well coring data identification, interwell tracer monitoring, and well test analysis. However, these methods all have limitations such as long construction period, little output information, and high construction cost. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies in the above-mentioned prior art and provide a comprehensive evaluation method for determining the types of crossflow channels in offshore loose sandstone reservoirs, so as to accurately classify the types of crossflow channels and provide a basis for subsequent targeted adjustments and treatment measures for crossflow channels of different levels. The model is simple to construct, has low operation difficulty and low testing cost.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A comprehensive evaluation method for determining the type of crossflow channel in an offshore unconsolidated sandstone reservoir comprises the following steps:

[0007] Collect static data of all production wells and injection wells in the target block and dynamic production data over a period of time;

[0008] Calculate the interwell conductivity T based on the static data and the production dynamic data ij and the control volume V ij ;

[0009] According to the interwell conductivity T ij , control volume V ij Calculate the permeability K ij , injection ratio RI ij , water injection efficiency EW ijand the water content increasing rate VW ij ;

[0010] The permeability K ij , the injection ratio RI ij , the water injection efficiency EW ij and the water content increasing rate VW ij Perform weighted averaging and normalization to obtain the comprehensive evaluation index M ij ;

[0011] According to the comprehensive evaluation index M ij The crossflow channels were characterized by graded characterization.

[0012] Preferably, the static data include well location, bottom hole pressure, porosity, initial permeability, water saturation and perforation information, and the production dynamic data include daily fluid production, daily oil production, water cut and daily injection total polymer.

[0013] Preferably, the interwell conductivity T ij Calculated by the following formula:

[0014]

[0015] Where: α is the unit conversion coefficient; is the average reservoir permeability between well i and well j; V ii is the control volume between well i and well j; is the average porosity of the reservoir between well i and well j; μ0 is the oil phase viscosity; L ij is the distance between well i and well j.

[0016] Preferably, the control volume V ij Calculated by the following formula:

[0017]

[0018] Where: L ij 、h ij and are the distance between well i and well j, the average reservoir thickness, and the average reservoir porosity, respectively; N w is the total number of water injection wells and oil production wells in the oil field; V F is the total pore volume of the reservoir.

[0019] Preferably, the permeability K ij Calculated by the following formula:

[0020]

[0021] Where: μ is the actual oil phase viscosity in the oil field; T ijis the interwell conductivity between injection well i and production well j; The porosity of the perforation section selected for the injection well; ij is the distance between injection well i and production well j; V ij is the control volume between injection well i and production well j.

[0022] Preferably, the injection ratio RI ij Calculated by the following formula:

[0023]

[0024] Where: q inj is the water injection volume under one injection-production unit; V ij is the control volume between injection well i and production well j.

[0025] Preferably, the water injection efficiency EW ii Calculated by the following formula:

[0026]

[0027] Where: q0 is the oil displacement; q inj The water injection volume for one injection-production unit.

[0028] Preferably, the water content increasing rate VW ij Calculated by the following formula:

[0029]

[0030] Where: fwwct ij.t is the moisture content at time t; is the moisture content at time t0.

[0031] Preferably, the comprehensive evaluation index M ij Calculated by the following formula:

[0032] M ij =K ij ·W1+RI ij W2+EW ij W3+VW ij W4

[0033] Where W1, W2, W3 and W4 are weight coefficients.

[0034] Preferably, the comprehensive evaluation index M ij In the classification characterization of crossflow channels, the comprehensive evaluation index M ij When <0.55, the corresponding crossflow channel type is not obviously developed. The comprehensive evaluation index M ijWhen it is 0.55-0.65, the corresponding crossflow channel type is a dominant channel, and the comprehensive evaluation index M ij When it is 0.65-0.75, the corresponding crossflow channel type is a large channel, and the comprehensive evaluation index M ij When it is 0.75-0.85, the corresponding crossflow channel type is medium-large channel, and the comprehensive evaluation index M ij When ≥0.85, the corresponding crossflow channel type is an extra-large channel.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention can realize the classification of crossflow channels in offshore loose sandstone reservoirs. The comprehensive evaluation method is not only simple and feasible to operate, but also significantly reduces the cost and is easy to promote and apply.

[0037] (2) The present invention directly uses static data such as permeability and dynamic data such as injection efficiency and water cut rise rate to classify crossflow channels. This is simple, convenient, and easy to implement. The calculation results provide support for the subsequent adjustment and treatment measures for large channels of different levels, thereby achieving the purpose of expanding the swept volume and increasing production.

[0038] (3) The present invention does not require additional on-site operations and testing, which reduces construction costs and shortens operation cycles, thereby achieving the goal of reducing costs and increasing efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the specific embodiments of the present invention, the following briefly introduces the drawings required for use in the specific embodiments. It should be noted that in all the drawings, the various elements or parts are not necessarily drawn according to the actual scale.

[0040] Figure 1 Schematic diagram of a flow chart of a comprehensive evaluation method for determining the type of crossflow channel in an offshore unconsolidated sandstone reservoir according to an embodiment of the present invention;

[0041] Figure 2 Schematic diagram of the connection unit body in an embodiment of the present invention. DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0043] In the description of the present invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the systems or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the use of terms such as "first" and "second" to define components is solely for the purpose of distinguishing those components. Unless otherwise stated, these terms have no special meanings and should not be construed as indicating or implying relative importance.

[0044] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0045] After years of water flooding development, the oil field is about to enter or has entered the "high water cut" or even "ultra-high water cut" period. Under the long-term scouring effect of the fluid, the formation parameters such as porosity and permeability of the oil reservoir have undergone significant changes compared with the initial stage, forming a crossflow channel between the production well and the water injection well. The injected water easily advances along the high permeability zone or layer, resulting in an uneven sweep degree, making it difficult to effectively mobilize the remaining oil in the low permeability zone and reducing the sweep coefficient and oil displacement efficiency, ultimately affecting the recovery rate. At present, the main methods for identifying crossflow channels include injection well logging data inversion, observation well coring data identification, interwell tracer monitoring, well test analysis, etc. However, the above methods all have limitations such as long construction period, little output information, and high construction cost when applied. Therefore, the present invention provides a comprehensive evaluation method for determining the type of crossflow channel in offshore loose sandstone oil reservoirs, which is used to accurately classify the type of crossflow channel and provide a basis for subsequent targeted adjustment and control measures for crossflow channels of different levels. The model is simple to construct, has low operation difficulty and low testing cost.

[0046] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0047] like Figure 1As shown, an embodiment of the present invention provides a comprehensive evaluation method for determining the type of crossflow channel in an offshore loose sandstone reservoir, comprising the following steps:

[0048] Step 1: Collect static data of all production wells and injection wells in the target block and dynamic production data over a period of time.

[0049] Among them, static data includes well location, bottom hole pressure, porosity, initial permeability, water saturation and perforation information, and production dynamic data includes daily liquid production, daily oil production, water cut and daily injection total (water injection plus injection).

[0050] Step 2: Calculate the control volume V based on the collected static data and the production dynamic data ij and interwell conductivity T ij .

[0051] Specifically, the control volume V ij and interwell conductivity T ij The calculation method is as follows:

[0052] Based on the characteristics of reservoir fluids and rock properties, the reservoir is considered to be composed of connected units between wells. These units are characterized by interwell conductivity and control volume. Interwell conductivity reflects the seepage strength of the fluid in the connected unit, while control volume represents the effective pore volume of the connected unit, providing a direct reflection of the amount of fluid.

[0053] The schematic diagram of the connected unit body is as follows Figure 2 As shown, the control volume V of the connected unit body ij Expressed as:

[0054]

[0055] Where: i, j refers to the well mark; L ij 、h ij and are the distance between well i and well j, the average reservoir thickness, and the average reservoir porosity, respectively.

[0056] Therefore, the control volume V of the connected unit cell ij The calculation expression is:

[0057]

[0058] Where: N w is the total number of water injection wells and oil production wells in the oil field; V F is the total pore volume of the reservoir.

[0059] From the connotation of conductivity, we can know that the interwell conductivity T ij The calculation expression is:

[0060]

[0061] Where: α = 0.0864, is the unit conversion coefficient; is the average reservoir permeability between well i and well j; A ij is the average cross-sectional area of the reservoir between well i and well j; is the average porosity of the reservoir between well i and well j; μ0 is the oil phase viscosity; h ij is the average reservoir thickness between well i and well j.

[0062] From the above, we can see that the approximate expression of the control volume is:

[0063]

[0064] The conductivity can be calculated by the following formula:

[0065]

[0066] The above calculations of conductivity and connected unit volume only use static reservoir data. In actual calculations, dynamic production data can be combined for analysis to improve accuracy. In practical applications, actual production data analysis can be used to categorize well connections. Based on these categorizations, the initial conductivity value, which reflects the reservoir fluid flow capacity, can be corrected. The specific calculation formula for this correction is as follows:

[0067] T″T ij =Level ij ×T ij

[0068] Where: Level ii Refers to the level of well-to-well connection relationship analyzed by actual production data analysis method. For the connection unit with better inter-well connection relationship, Level ij The value can be between three and five. For the connection unit with poor inter-well connection relationship, Level ij The value is around 1, which makes the conductivity assignment more reasonable.

[0069] Step 3: According to the interwell conductivity T ij , control volume V ij Calculate the permeability K ij、 Injection ratio RI ij、 Water injection efficiency EW ij and the water content increasing rate VW ij .

[0070] Specifically, each injection well and its corresponding production well are defined as an injection-production unit. The permeability K of each injection-production unit isij The calculation formula is as follows:

[0071]

[0072] Where: μ is the actual oil phase viscosity in the oil field; T ij is the interwell conductivity between injection well i and production well j; The porosity of the perforation section selected for the injection well; ij is the distance between injection well i and production well j; V ij is the control volume between injection well i and production well j.

[0073] Injection ratio RI ij Indicates the water injection volume and control volume V under one injection and production unit ij The specific calculation formula is as follows:

[0074]

[0075] Where: q inj is the water injection volume under one injection-production unit; V ij is the control volume between injection well i and production well j.

[0076] Water injection efficiency EW ij The calculation formula is as follows:

[0077]

[0078] Where: q0 is the oil displacement; q inj The water injection volume for one injection-production unit.

[0079] Water content rising rate VW ij The calculation formula is as follows:

[0080]

[0081] Where: fwwct ij.t is the moisture content at time t; is the moisture content at time t0.

[0082] Step 3: The permeability K ij、 The injection ratio RI ij , the water injection efficiency EW ij and the water content increasing rate VW ij Perform weighted averaging and normalization to obtain the comprehensive evaluation index M ij .

[0083] Among them, M ij The calculation formula is as follows:

[0084] M ij=K ij ·W1+RI ij W2+EW ij W3+VW ij W4

[0085] Where W1, W2, W3 and W4 are weight coefficients.

[0086] Preferably, W1:W2:W3:W4=1:3:5:5.

[0087] Step 4: Based on the comprehensive evaluation index M ij The crossflow channels were characterized by graded characterization.

[0088] Among them, the comprehensive evaluation index M ij When it is less than 0.55, the corresponding crossflow channel type is not obviously developed, and the comprehensive evaluation index M ij When it is 0.55-0.65, the corresponding crossflow channel type is the dominant channel, and the comprehensive evaluation index M ij When it is 0.65-0.75, the corresponding crossflow channel type is large channel, and the comprehensive evaluation index M ij When it is 0.75-0.85, the corresponding crossflow channel type is medium-large channel, and the comprehensive evaluation index M ij When ≥0.85, the corresponding crossflow channel type is an extra-large channel.

[0089] It is understandable that the results of the graded characterization in step 4 can be used as a basis for carrying out adjustments and treatment measures for large pores of different levels, so that targeted adjustments and treatment measures can be carried out for the different levels of crossflow channels in the future.

[0090] The comprehensive evaluation method for determining the type of crossflow channel in an offshore loose sandstone reservoir provided by the embodiment of the present invention has the following beneficial effects:

[0091] (1) The embodiments of the present invention can realize the classification of crossflow channels in offshore loose sandstone reservoirs. The comprehensive evaluation method is not only simple and feasible to operate, but also significantly reduces costs and is easy to promote and apply.

[0092] (2) The embodiment of the present invention directly uses static data such as permeability and dynamic data such as injection efficiency and water cut rise rate to classify crossflow channels. This is simple, convenient, and easy to implement. The calculation results provide support for the subsequent adjustment and treatment measures for large channels of different levels, thereby achieving the purpose of expanding the swept volume and increasing production.

[0093] (3) The embodiments of the present invention do not require additional on-site operations and testing, which reduces construction costs and shortens operation cycles, thereby achieving the goal of reducing costs and increasing efficiency.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A comprehensive evaluation method for determining the type of crossflow channel in an offshore loose sandstone reservoir, characterized in that: The following steps are involved: Collect static data of all production wells and injection wells in the target block and dynamic production data over a period of time; Calculate the control volume based on the static data and the production dynamic data and interwell conductivity ; According to the interwell conductivity , control volume Calculate the permeability separately , injection ratio , water injection efficiency and the rate of increase of water content ; The permeability The injection ratio , the water injection efficiency and the water content rising rate Perform weighted averaging and normalization to obtain comprehensive evaluation indicators ; According to the comprehensive evaluation index Conduct hierarchical characterization of crossflow channels; The interwell conductivity Calculated by the following formula: Where: α is the unit conversion coefficient; is the average reservoir permeability between well i and well j; is the control volume between well i and well j; is the average porosity value of the reservoir between well i and well j; is the oil phase viscosity; is the distance between well i and well j; The control volume Calculated by the following formula: Where: 、 and are the distance between well i and well j, the average reservoir thickness, and the average reservoir porosity, respectively; is the total number of water injection wells and oil production wells in the oil field; is the total pore volume of the reservoir; The permeability Calculated by the following formula: Where: μ is the actual oil phase viscosity in the oil field; is the interwell conductivity between injection well i and production well j; the porosity of the perforated section selected for the injection well; is the distance between injection well i and production well j; is the control volume between injection well i and production well j; The injection ratio Calculated by the following formula: Where: is the water injection volume under one injection-production unit; is the control volume between injection well i and production well j; The water injection efficiency Calculated by the following formula: Where: is the oil displacement volume; is the water injection volume under one injection-production unit; The water content increasing rate Calculated by the following formula: Where: is the moisture content at time t; for Moisture content at the time; According to the comprehensive evaluation index In the classification characterization of crossflow channels, the comprehensive evaluation index When <0.55, the corresponding crossflow channel type is not obviously developed. When it is 0.55-0.65, the corresponding crossflow channel type is a dominant channel, and the comprehensive evaluation index When it is 0.65-0.75, the corresponding crossflow channel type is large channel, and the comprehensive evaluation index When it is 0.75-0.85, the corresponding crossflow channel type is medium-large channel, and the comprehensive evaluation index When ≥0.85, the corresponding crossflow channel type is an extra-large channel.

2. The comprehensive evaluation method for determining the crossflow channel type in an offshore loose sandstone reservoir according to claim 1, characterized in that: The static data includes well location, bottom hole pressure, porosity, initial permeability, water saturation and perforation information, and the production dynamic data includes daily fluid production, daily oil production, water cut and daily injection total polymer.

3. The comprehensive evaluation method for determining the crossflow channel type in an offshore loose sandstone reservoir according to claim 1, characterized in that: The comprehensive evaluation index Calculated by the following formula: In the formula 、 、 and is the weight coefficient.

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