Thermal reservoir classification method based on sandstone recharge capacity evaluation

Abstract

The present invention provides a heat reservoir type classification method based on sandstone reinjection capacity evaluation, comprising: step 1, using a hydrodynamic reinjection amount calculation formula to determine a sandstone reinjection capacity evaluation factor; step 2, according to a reservoir classification method and a water injection well reinjection pressure change law, determining the division boundary of the sandstone heat reservoir reinjection capacity evaluation factor; step 3, using logging, well logging and physical property analysis data to statistically calculate the heat reservoir permeability, and determining the heat reservoir permeability type according to a reservoir permeability classification standard; step 4, statistically calculating the heat reservoir single-layer sandstone thickness, and determining the heat reservoir reinjection difficulty level type according to a single-layer sandstone thickness classification standard; step 5, comprehensively using the heat reservoir permeability and single-layer sandstone thickness, these sandstone reinjection capacity evaluation factors, to classify the heat reservoir type. The heat reservoir type classification method based on sandstone reinjection capacity evaluation has strong operability, and at the same time provides a more scientific and effective basis for the next step of determining the heat reservoir reinjection amount and reinjection pressure, and designing a production and injection well network.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield development, and in particular to a thermal reservoir type classification method based on sandstone reinjection capacity evaluation. Background Art

[0002] At present, Shengli Oilfield is vigorously promoting the development and utilization of geothermal resources in the production and injection mode. However, in the process of utilization, there have been low reinjection rates, gradually reduced reinjection volumes, and increasing reinjection pressures. The main reason for these problems is that the reinjection capacity evaluation has not been carried out, resulting in unreasonable production and injection plans. Specifically, it is because the differences in the reinjection capacity of thermal storage sandstones have not been clarified, and the impact of different sandstone reinjection capacities on thermal storage production and injection plans has not been considered.

[0003] Previous researchers have classified heat reservoir types from different perspectives, such as distribution characteristics, storage space, and medium type. However, the current heat reservoir type classification scheme cannot fully reflect the strength of the heat reservoir re-injection capacity, thus restricting the green and sustainable development and utilization of sandstone heat reservoir geothermal resources based on the extraction and injection mode.

[0004] In the Chinese patent application with application number: CN201510823903.4, a method for classifying sedimentary basin geothermal resources is involved, which includes: step 1, using drilling, logging, mud logging, and seismic data to divide the sedimentary basin tectonic belt; step 2, determining the lithology combination and thickness of the strata for different tectonic belts; step 3, clarifying the thermal conductivity of different lithology strata in each tectonic belt through core sampling tests; step 4, obtaining the wellbore temperature measurement data of the tectonic belt, and determining the geothermal gradient distribution using the wellbore temperature measurement data; step 5, comprehensively utilizing the thermal conductivity of different lithologies and geothermal gradients to calculate the geothermal heat flow value through geothermal formulas, and clarifying the planar distribution law of the geothermal heat flow value; and step 6, classifying the sedimentary basin geothermal resource types according to the planar geothermal heat flow value distribution. The sedimentary basin geothermal resource type of this patent is a classification scheme based on the temperature recovery capacity of the heat reservoir. The classification is based on the temperature recovery rate of the low-temperature reinjection tail water reinjected into the heat reservoir, but it does not take into account the reinjection difficulty of the clastic rock heat reservoir, that is, the reinjection capacity. The evaluation of the reinjection capacity is an important link that restricts whether the sedimentary basin type clastic rock heat reservoir can achieve green and sustainable development and utilization in the mining and injection mode. For this reason, we have invented a new method for classifying heat reservoir types based on the evaluation of sandstone reinjection capacity, which solves the above technical problems. Summary of the invention

[0005] The object of the present invention is to provide a method for classifying heat reservoir types by utilizing the thickness of a single layer of sandstone and the permeability of the heat reservoir.

[0006] The object of the present invention can be achieved through the following technical measures: a method for classifying heat reservoir types based on sandstone reinjection capacity evaluation, the method for classifying heat reservoir types based on sandstone reinjection capacity evaluation comprising: step 1, using a hydrodynamic reinjection volume calculation formula, combined with geothermal development practice, to determine the sandstone reinjection capacity evaluation factor; step 2, according to the reservoir division method and the law of reinjection pressure change of injection wells, determining the division boundary of the sandstone heat reservoir reinjection capacity evaluation factor; step 3, using logging, well logging and physical property analysis data, statistically analyzing the heat reservoir permeability, and determining the heat reservoir permeability type according to the reservoir permeability classification standard; step 4, statistically analyzing the thickness of a single-layer sandstone of the heat reservoir, and determining the reinjection difficulty level type of the heat reservoir according to the single-layer sandstone thickness classification standard; step 5, comprehensively utilizing the heat reservoir permeability and single-layer sandstone thickness, these sandstone reinjection capacity evaluation factors, to classify the heat reservoir types.

[0007] The purpose of the present invention can also be achieved by the following technical measures:

[0008] In step 1, according to the calculation formula of hydrodynamic reinjection volume and practical experience in geothermal development and utilization, the evaluation factors of sandstone thermal reservoir reinjection capacity are permeability coefficient, thermal reservoir utilization thickness and reinjection pressure, among which the thermal reservoir utilization thickness is controlled by the heat demand, the permeability coefficient represents the strength of the original seepage capacity of the thermal reservoir, and the reinjection pressure parameter represents the difficulty of thermal reservoir reinjection; thus, the evaluation factors of thermal reservoir reinjection capacity are thermal reservoir permeability and reinjection pressure; the smaller the thermal reservoir permeability, the greater the reinjection pressure, indicating that the sandstone reinjection capacity is worse.

[0009] In step 1, the hydrodynamic recharge volume is calculated as:

[0010] Q = 2.73KMH / lg(R / r) (Formula 1)

[0011] Where, Q is the amount of water injected into a single well, m 3 / d;

[0012] K-permeability coefficient, m / d;

[0013] M-sandstone thickness, m;

[0014] H-reinjection pressure, head height, m;

[0015] r-well diameter, m, take 0.065m;

[0016] R-influence radius, m.

[0017] In step 2, according to the oil and gas reservoir evaluation method, the thermal reservoir is divided into three types according to the permeability: ultra-high permeability, i.e., the permeability coefficient K ≥ 2000md, high permeability, i.e., the permeability coefficient K ranges from 500md≤K<2000md, and medium permeability, i.e., the permeability coefficient K ranges from 50md≤K<500md.

[0018] In step 2, the concept of unit reinjection pressure is introduced to analyze the changing law of reinjection pressure of injection wells. Unit reinjection pressure is the reinjection pressure of unit volume of water. The correlation between unit reinjection pressure and original parameters of thermal reservoirs such as total thickness of sandstone, thickness of single-layer sandstone, and lithology of thermal reservoir is analyzed. It is clear that the thickness of single-layer sandstone and unit reinjection pressure are inversely proportional, that is, the greater the thickness of single layer, the smaller the unit reinjection pressure. According to the change of single-layer thickness with unit reinjection pressure, thermal reservoirs are divided into three types: thick layer > 20 meters, medium-thick layer 8-20 meters, and thin layer < 8 meters.

[0019] In step 2, the unit reinjection pressure is calculated as:

[0020] p=P / V (Formula 2)

[0021] Where, p is the unit reinjection pressure (10-3MPa / m 3 ); P—reinjection pressure (10-3MPa); V—reinjection water volume (m 3 ).

[0022] In step 3, the classification standard of thermal reservoir permeability is based on the oil and gas reservoir evaluation method. The permeability of thermal reservoir is statistically analyzed using the logging, well logging and physical property analysis data. The permeability type of thermal reservoir is determined according to the following criteria: ultra-high permeability, i.e., permeability coefficient K ≥ 2000md; ​​high permeability, i.e., permeability coefficient K ranges from 500md ≤ K < 2000md; ​​and medium permeability, i.e., permeability coefficient K ranges from 50md ≤ K < 500md.

[0023] In step 4, the thickness of single-layer sandstone in the thermal reservoir is counted, and the single-layer thickness type of the thermal reservoir is determined according to the classification standard of single-layer sandstone thickness of thick layer > 20 meters, medium-thick layer 8-20 meters, and thin layer < 8 meters.

[0024] In step 5, according to the permeability of the heat reservoir and the thickness of the single-layer sandstone, the heat reservoir type of the sandstone heat reservoir based on the recharge capacity evaluation is determined according to the classification standards of good recharge capacity, i.e. thick layer with extra-high permeability, medium-thick layer with extra-high permeability, and thick layer with high permeability; medium recharge capacity, i.e. thin layer with extra-high permeability, medium-thick layer with high permeability, and thick layer with medium permeability; and poor recharge capacity, i.e. thin layer with high permeability, medium-thick layer with medium permeability, and thin layer with medium permeability.

[0025] The heat reservoir type classification method based on the evaluation of sandstone reinjection capacity of the present invention is applicable on the premise that there are certain exploration and development well data and the geothermal development and utilization block has been clarified, and the reinjection capacity evaluation can be carried out. The new heat reservoir type classification method based on the evaluation of sandstone reinjection capacity solves the problem of evaluating the difficulty of sandstone heat reservoir reinjection, and provides an evaluation method for determining parameters such as reinjection volume and reinjection pressure, avoiding problems such as incomplete reinjection or reduced heat reservoir pressure and reduced water extraction temperature due to inaccurate determination of reinjection parameters. The whole method is highly operable, and the heat reservoir type classification based on the evaluation of sandstone reinjection capacity is realized, providing technical support and theoretical support for improving the recycling efficiency of geothermal resources. The new heat reservoir type classification method based on the evaluation of sandstone reinjection capacity of the present invention realizes the pre-drilling prediction of sandstone heat reservoir reinjection capacity, and its process and method are highly operable; the established reinjection capacity evaluation factors and their division boundaries and standards can all be tested by similar geothermal fields, and the proposed evaluation factors and their division boundaries, as well as the heat reservoir type classification method are obtained by comparison based on a large number of experimental studies and geothermal numerical simulations, and have practical significance for guiding geothermal development and utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a flow chart of a specific embodiment of the method for classifying heat reservoir types based on sandstone reinjection capacity evaluation of the present invention;

[0027] Figure 2 It is a thermal storage single layer thickness division boundary analysis diagram in a specific embodiment of the present invention;

[0028] Figure 3 It is a schematic diagram of the classification of heat storage types in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings.

[0030] like Figure 1 As shown, Figure 1 The present invention is a flow chart of a new method for classifying thermal reservoir types based on sandstone reinjection capacity evaluation.

[0031] In step 101, according to the hydrodynamic recharge calculation formula (Formula 1), the evaluation factors of the sandstone thermal reservoir recharge capacity are the permeability coefficient, the thermal reservoir utilization thickness and the recharge pressure, wherein the thermal reservoir utilization thickness is controlled by the heat demand (when the total thickness of the thermal reservoir is small, the number of water wells can be increased), the permeability coefficient represents the strength of the original seepage capacity of the thermal reservoir, and the recharge pressure parameter represents the difficulty of the thermal reservoir recharge; thus, the evaluation factors of the thermal reservoir recharge capacity are the thermal reservoir permeability and the recharge pressure. The smaller the thermal reservoir permeability, the greater the recharge pressure, indicating that the sandstone recharge capacity is worse.

[0032] Q = 2.73KMH / lg(R / r) (Formula 1)

[0033] Where, Q is the amount of water injected into a single well (m 3 / d);

[0034] K-permeability coefficient (m / d);

[0035] M-sandstone thickness (m);

[0036] H-reinjection pressure (water head height, m);

[0037] r-well diameter (m, take 0.065m);

[0038] R-influence radius (m)

[0039] In step 102, according to the oil and gas reservoir evaluation method, the thermal reservoir is divided into three types according to permeability: extra-high permeability (K≥2000md), high permeability (500md≤K<2000md), and medium permeability (50md≤K<500md); the concept of unit reinjection pressure is introduced to analyze the variation law of reinjection pressure of injection wells. The unit reinjection pressure is the reinjection pressure of a unit volume of water (Formula 2). Through analysis, the unit reinjection pressure is inversely proportional to the thickness of a single layer of sandstone, that is, the greater the thickness of the single layer, the smaller the unit reinjection pressure. According to the variation of the single layer thickness with the unit reinjection pressure, the thermal reservoir is divided into three types: thick layer (>20 meters), medium-thick layer (8-20 meters), and thin layer (<8 meters).

[0040] p=P / V (Formula 2)

[0041] Where, p is the unit reinjection pressure (10-3MPa / m 3 )

[0042] P—Reinjection pressure (10-3MPa)

[0043] V—Reinjection water volume (m 3 )

[0044] In step 103, the thermal reservoir permeability classification standard is based on the oil and gas reservoir evaluation method, and the thermal reservoir permeability is statistically analyzed using the logging, well logging and physical property analysis data, and the permeability type of the thermal reservoir is determined according to the ultra-high permeability (K≥2000md), high permeability (500md≤K<2000md), and medium permeability (50md≤K<500md).

[0045] In step 104, the thickness of the single-layer sandstone of the thermal reservoir is counted, and the single-layer thickness type of the thermal reservoir is determined according to the classification standard of single-layer sandstone thickness thick layer (>20 meters), medium-thick layer (8-20 meters), and thin layer (<8 meters).

[0046] In step 105, according to the permeability of the thermal reservoir and the thickness of the single-layer sandstone, the thermal reservoir type of the sandstone thermal reservoir based on the recharge capacity evaluation is determined according to the classification standards of good recharge capacity (thick layer extra-high permeability, medium-thick layer extra-high permeability, thick layer high permeability), medium recharge capacity (thin layer extra-high permeability, medium-thick layer high permeability, thick layer medium permeability), and poor recharge capacity (thin layer high permeability, medium-thick layer medium permeability, thin layer medium permeability).

[0047] In a specific embodiment of the present invention, the following steps are included:

[0048] Step 1: According to the calculation formula of hydrodynamic reinjection volume (Formula 1), the evaluation factors of sandstone thermal reservoir reinjection capacity are permeability coefficient, thermal reservoir utilization thickness and reinjection pressure, where thermal reservoir utilization thickness is controlled by heat demand (when the total thickness of thermal reservoir is small, the number of water wells can be increased), permeability coefficient represents the strength of the original seepage capacity of thermal reservoir, and reinjection pressure parameter represents the difficulty of thermal reservoir reinjection; thus, the evaluation factors of thermal reservoir reinjection capacity are thermal reservoir permeability and reinjection pressure. The smaller the thermal reservoir permeability, the greater the reinjection pressure, indicating that the sandstone reinjection capacity is worse.

[0049] Step 2: According to the oil and gas reservoir evaluation method, the thermal reservoir is divided into three types according to permeability: extra-high permeability (K ≥ 2000md), high permeability (500md ≤ K < 2000md), and medium permeability (50md ≤ K < 500md); the concept of unit reinjection pressure is introduced to analyze the variation law of reinjection pressure of water injection wells. The unit reinjection pressure is the reinjection pressure of unit volume of water (Formula 2). The unit reinjection pressure is calculated for the oil field development water injection block with relatively stable reinjection status. By compiling relevant maps such as unit reinjection pressure-sandstone thickness and unit reinjection pressure-single-layer sandstone thickness, the unit reinjection pressure is analyzed. The correlation between unit reinjection pressure and sandstone thickness is not obvious, but it is inversely proportional to the thickness of single-layer sandstone, that is, the larger the single-layer thickness, the smaller the unit reinjection pressure ( Figure 2 ), and there are two obvious inflection points on the inverse proportional relationship curve. According to the distribution of inflection points on the curve of single layer thickness changing with unit reinjection pressure, the heat reservoir can be divided into three types: thick layer (>20 meters), medium-thick layer (8-20 meters), and thin layer (<8 meters).

[0050] p=P / V (Formula 2)

[0051] Where, p is the unit reinjection pressure (10-3MPa / m 3 ); P—reinjection pressure (10-3MPa); V—reinjection water volume (m 3 )

[0052] Step 3: The classification standard of thermal reservoir permeability is based on the oil and gas reservoir evaluation method. The permeability of thermal reservoir is statistically analyzed using the logging, well logging and physical property analysis data. The permeability type of thermal reservoir is determined according to the extremely high permeability (K≥2000md), high permeability (500md≤K<2000md) and medium permeability (50md≤K<500md).

[0053] Step 4, count the thickness of single-layer sandstone in the thermal reservoir, and determine the single-layer thickness type of the thermal reservoir according to the classification standards of single-layer sandstone thickness: thick layer (>20 meters), medium-thick layer (8-20 meters), and thin layer (<8 meters).

[0054] Step 5: According to the permeability of the thermal reservoir and the thickness of the single-layer sandstone, the thermal reservoir type of the sandstone thermal reservoir based on the evaluation of the recharge capacity is determined according to the classification standards of good recharge capacity (thick layer extra-high permeability, medium-thick layer extra-high permeability, thick layer high permeability), medium recharge capacity (thin layer extra-high permeability, medium-thick layer high permeability, thick layer medium permeability), and poor recharge capacity (thin layer high permeability, medium-thick layer medium permeability, thin layer medium permeability). For example, the single-layer thickness of the sandstone thermal reservoir in the depth range of 1450m-1520m in Well Fan 7 is less than 8m, and the permeability is 400md-800md, which belongs to the thin layer high permeability or thin layer medium permeability thermal reservoir with poor recharge capacity ( Figure 3 ), the single-layer thickness of sandstone thermal reservoirs in the depth range of 1080m-1340m in Che59 well is mainly greater than 20m, with a permeability of 1000md-3000md, which belongs to thick-layer ultra-high permeability or thick-layer high permeability thermal reservoirs with good recharge capacity ( Figure 3 ).

[0055] The heat reservoir type classification method based on sandstone reinjection capacity evaluation of the present invention has strong operability and provides a more scientific and effective basis for determining the heat reservoir reinjection volume and reinjection pressure and designing the production and injection well network in the next step.

[0056] The above description is only an ideal model implementation of the present invention and is not intended to limit the patent scope of the present invention. Other equivalent changes that apply the patent spirit of the present invention should all fall within the patent scope of the present invention.

Claims

1. A method for classifying heat reservoir types based on sandstone recharge capacity evaluation, characterized in that: The thermal reservoir classification method based on sandstone recharge capacity evaluation includes: Step 1, using the hydrodynamic recharge calculation formula to determine the sandstone recharge capacity evaluation factor; Step 2: Determine the division boundary of the sandstone thermal reservoir reinjection capacity evaluation factor according to the reservoir division method and the reinjection pressure variation law of the water injection well; Step 3, using the logging, well logging and physical property analysis data, statistically analyzing the thermal reservoir permeability, and determining the thermal reservoir permeability type according to the reservoir permeability classification standard; Step 4, counting the thickness of a single-layer sandstone of the thermal reservoir, and determining the difficulty level of reinjection of the thermal reservoir according to the classification standard of the single-layer sandstone thickness; Step 5, comprehensively utilizing the heat reservoir permeability and single-layer sandstone thickness, which are sandstone recharge capacity evaluation factors, to classify the heat reservoir types; In step 1, according to the calculation formula of hydrodynamic reinjection volume, the evaluation factors of sandstone thermal reservoir reinjection capacity are permeability coefficient, thermal reservoir utilization thickness and reinjection pressure, among which the thermal reservoir utilization thickness is controlled by the heat demand, the permeability coefficient represents the strength of the original seepage capacity of the thermal reservoir, and the reinjection pressure parameter represents the difficulty of thermal reservoir reinjection; thus, the evaluation factors of thermal reservoir reinjection capacity are thermal reservoir permeability and reinjection pressure; the smaller the thermal reservoir permeability and the greater the reinjection pressure, the worse the sandstone reinjection capacity; The calculation formula of hydrodynamic recharge volume is: Q = 2.73KMH / lg (R / r) (Formula 1) Where, Q is the amount of water injected into a single well, m 3 / d; K-permeability coefficient, m / d; M-sandstone thickness, m; H-reinjection pressure, head height, m; r-well diameter, m; R-influence radius, m.

2. The method for classifying heat reservoir types based on sandstone reinjection capacity evaluation according to claim 1 is characterized in that: In step 2, according to the oil and gas reservoir evaluation method, the thermal reservoir is divided into three types according to the permeability: ultra-high permeability, i.e., the permeability coefficient K ≥ 2000m / d, high permeability, i.e., the permeability coefficient K ranges from 500m / d≤K<2000m / d, and medium permeability, i.e., the permeability coefficient K ranges from 50m / d≤K<500m / d.

3. The method for classifying heat reservoir types based on sandstone reinjection capacity evaluation according to claim 2 is characterized in that: In step 2, the concept of unit reinjection pressure is introduced to analyze the changing law of reinjection pressure of injection wells. Unit reinjection pressure is the reinjection pressure of unit volume of water. The correlation between unit reinjection pressure and original parameters of thermal reservoirs such as total thickness of sandstone, thickness of single-layer sandstone, and lithology of thermal reservoir is analyzed. It is clear that the thickness of single-layer sandstone and unit reinjection pressure are inversely proportional, that is, the greater the thickness of single layer, the smaller the unit reinjection pressure. According to the change of single-layer thickness with unit reinjection pressure, thermal reservoirs are divided into three types: thick layer > 20 meters, medium-thick layer 8-20 meters, and thin layer < 8 meters.

4. The method for classifying heat reservoir types based on sandstone reinjection capacity evaluation according to claim 3 is characterized in that: In step 2, the unit reinjection pressure is calculated as: p=P / V (Formula 2) Where, p is the unit reinjection pressure, MPa / m 3 ; P—reinjection pressure, MPa; V—reinjection water volume, m 3 .

5. The method for classifying heat reservoir types based on sandstone reinjection capacity evaluation according to claim 1 is characterized in that: In step 3, the classification standard of thermal reservoir permeability is based on the oil and gas reservoir evaluation method. The permeability of thermal reservoir is statistically analyzed using the logging, well logging and physical property analysis data. The permeability type of thermal reservoir is determined according to the following criteria: ultra-high permeability, i.e., permeability coefficient K ≥ 2000m / d; high permeability, i.e., permeability coefficient K ranges from 500m / d≤K<2000m / d; medium permeability, i.e., permeability coefficient K ranges from 50m / d≤K<500m / d.

6. The method for classifying heat reservoir types based on sandstone reinjection capacity evaluation according to claim 1 is characterized in that: In step 4, the thickness of single-layer sandstone in the thermal reservoir is counted, and the single-layer thickness type of the thermal reservoir is determined according to the classification standard of single-layer sandstone thickness of thick layer > 20 meters, medium-thick layer 8-20 meters, and thin layer < 8 meters.

7. The method for classifying heat reservoir types based on sandstone reinjection capacity evaluation according to claim 1 is characterized in that: In step 5, according to the permeability of the heat reservoir and the thickness of the single-layer sandstone, the heat reservoir type of the sandstone heat reservoir based on the recharge capacity evaluation is determined according to the classification standards of good recharge capacity, i.e. thick layer with extra-high permeability, medium-thick layer with extra-high permeability, and thick layer with high permeability; medium recharge capacity, i.e. thin layer with extra-high permeability, medium-thick layer with high permeability, and thick layer with medium permeability; and poor recharge capacity, i.e. thin layer with high permeability, medium-thick layer with medium permeability, and thin layer with medium permeability.

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