Method for determining movable closed porosity of low-clay-content shale reservoirs

Abstract

The application provides a method for determining movable closed porosity of shale reservoirs with low clay content, and relates to the technical field of shale exploration and development, and the method comprises the following steps: obtaining the actual temperature of the stratum corresponding to the shale sample to be measured; applying a stepwise temperature rise to the saturated shale sample, synchronously determining the connected porosity under each temperature gradient, and determining the temperature corresponding to the stable connected porosity as the highest safe drying temperature of the shale sample; determining the first connected porosity at the actual temperature; determining the second connected porosity at the highest safe drying temperature; and obtaining the movable closed porosity based on the first connected porosity and the second connected porosity. The application establishes a test and calculation method suitable for calculating the closed porosity proportion of shale with low clay content under different stratum temperature conditions, and further determining the degree to which the closed porosity can be converted into connected porosity, which is of great significance for shale oil and gas reservoir evaluation.

Description

Technical Field

[0001] This invention relates to the field of shale exploration and development technology, and in particular to a method for determining the available closed porosity of shale reservoirs with low clay content. Background Technology

[0002] The porosity characteristics of continental shale reservoirs are a core parameter for evaluating the potential and feasibility of shale oil and gas resources. Total porosity reflects the total volume of all pore spaces in the rock, including connected and closed pores; effective porosity refers only to those interconnected pore spaces that can be effectively occupied and flowed by fluids; closed porosity refers to pores that are completely isolated from the outside environment. The magnitude of closed porosity directly reflects the complexity and connectivity of the pore structure of the shale reservoir. In shale gas exploration and development, high closed porosity means that there are a large number of pore spaces in the reservoir that cannot be effectively utilized, which not only affects the recoverable gas reserves but also increases the difficulty of extraction. Therefore, accurately determining the closed porosity of shale reservoirs is of great significance for shale gas resource evaluation, reservoir stimulation scheme design, and development strategy formulation.

[0003] Existing methods for calculating closed porosity generally employ image-based methods (such as Fib-SEM electron microscopy) and X-ray methods (CT, NMR) to measure the total porosity of shale reservoirs, and then use fluid intrusion methods (helium gas intrusion method, mercury porosimetry) to test the interconnected porosity of the shale. The closed porosity is then obtained by subtracting the two methods. However, existing methods have the following problems: (1) The results obtained by the existing methods are static. However, due to the different effects of formation fluid properties on reservoir pore sealing under formation conditions, connected pores and closed pores are dynamically transformed into each other. The existing methods cannot reflect the changes in closed pores under dynamic formation conditions, nor can they reflect under what conditions "closed pores" under laboratory conditions can become connected pores.

[0004] (2) To prevent the degradation of bound water in shale clay minerals at high temperatures, existing methods for testing interconnected porosity use a drying temperature of 60°C for samples with formation temperatures below 60°C and 105°C for samples with formation temperatures above 60°C. This temperature setting is too coarse and cannot accurately test the porosity of samples under formation temperature conditions. At a drying temperature of 60°C, the liquid water in the pore throats of the shale reservoir cannot evaporate completely, and the pores sealed by the small pore throats containing liquid water are not transformed into interconnected pores. Under formation conditions, the pores sealed by the small pore throats containing liquid water still contain a large amount of free and adsorbed shale gas. At a drying temperature of 105°C, the sample is over-dried, and the tested interconnected porosity is far higher than the actual situation in the formation.

[0005] (3) Existing methods for calculating closed porosity generally require testing connected porosity and total porosity, and then calculating the results. However, the testing principles for connected porosity and total porosity are different, and the types of pores tested are different, making it difficult to directly compare the test results. The closed porosity calculated by different methods is also different.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] One of the objectives of this invention is to provide a method for determining the available closed porosity of shale reservoirs with low clay content, so as to at least solve one of the technical problems existing in the prior art.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a method for determining the movable closed porosity of shale reservoirs with low clay content, comprising the following steps: (a) Obtain the actual temperature of the formation corresponding to the shale sample to be tested; (b) Apply a stepped heating to the saturated shale sample, simultaneously measure the interconnected porosity at each temperature gradient, and determine the temperature at which the interconnected porosity tends to stabilize as the maximum safe drying temperature of the shale sample. (c) After maintaining the saturated shale sample at the actual temperature, the first interconnected porosity is measured. (d) After maintaining the shale sample at the highest safe drying temperature, the second interconnected porosity is measured; (e) Based on the first connected porosity and the second connected porosity, obtain the movable closed porosity.

[0009] Furthermore, the actual temperature is obtained through any of the following methods: The calculation formula is as follows: T 1= H × G + T 0; where, T 1 represents the formation temperature. H The depth of the strata. G The unit is geothermal gradient, and the unit is °C / km. T 0 represents the Earth's surface temperature.

[0010] Furthermore, the actual temperature is based on the measured well temperature data at the corresponding drilling depth.

[0011] Furthermore, the temperature gradient interval of the stepped heating is 10℃ to 30℃, and the constant temperature holding time under each temperature gradient is 12 hours to 48 hours.

[0012] Furthermore, the saturation treatment in step (b) uses a potassium chloride aqueous solution with a concentration of 10wt% to 20wt% and is saturated for more than 48 hours at a pressure of 15MPa to 25MPa.

[0013] Furthermore, the saturation treatment in step (c) uses a potassium chloride aqueous solution with a concentration of 10wt% to 20wt% and is saturated for more than 48 hours at a pressure of 15MPa to 25MPa.

[0014] Furthermore, the first interconnected porosity, the second interconnected porosity, and the interconnected porosity at each temperature gradient in step (b) were all measured using the helium method, and the calculation formulas are as follows: φ= V 连通孔隙体积 / V 总体积 ×100%=(V 总体积 -V 骨架体积 ) / V 总体积 ×100%; in, f V represents porosity. 总体积 V represents the total volume of the sample. 骨架体积 This represents the sample skeleton volume.

[0015] Furthermore, with f 可动用封闭 The formula for calculating the movable closed porosity is as follows: f 可动用封闭 =φ 2- f 1; in, f 1 represents the first level of interconnected porosity, expressed as % f 2 represents the second connectivity porosity, in percentages.

[0016] Furthermore, the second interconnected porosity is greater than the first interconnected porosity.

[0017] Furthermore, the trend towards stability is defined as follows: the absolute value of the difference between the interconnected porosity measured under the current temperature gradient and the interconnected porosity measured under the previous temperature gradient is not greater than 0.10%, and the difference is reduced by 50% or more compared to the change in interconnected porosity between the previous adjacent temperature gradients; the maximum safe drying temperature is the minimum temperature gradient that satisfies the trend towards stability.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for determining the usable closed porosity of low-clay shale reservoirs. This method measures the interconnected porosity at both the actual formation temperature and the maximum safe drying temperature, and derives the first and second closed porosities under corresponding conditions based on these measurements. The difference between these two values ​​is then used to define the usable closed porosity, thus overcoming the limitation of existing technologies that can only obtain static closed porosity. This invention can accurately quantify the proportion of usable closed porosity in low-clay shale reservoirs at formation temperature, compensating for the deficiencies of existing static testing methods and providing reliable technical support for shale oil and gas resource evaluation, reservoir stimulation scheme design, and development strategy formulation. Detailed Implementation

[0019] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a method for determining the movable closed porosity of shale reservoirs with low clay content, comprising the following steps: (a) Obtain the actual temperature of the formation corresponding to the shale sample to be tested; (b) Apply a stepped heating to the saturated shale sample, simultaneously measure the interconnected porosity at each temperature gradient, and determine the temperature at which the interconnected porosity tends to stabilize as the maximum safe drying temperature of the shale sample. (c) After maintaining the saturated shale sample at the actual temperature, the first interconnected porosity is measured. (d) After maintaining the shale sample at the highest safe drying temperature, the second interconnected porosity is measured; (e) Based on the first connected porosity and the second connected porosity, obtain the movable closed porosity.

[0022] This invention aims to solve the technical problems of existing shale closed porosity testing methods, which cannot reflect the dynamic transformation characteristics of pores under formation temperature, cannot completely remove bound water from pore throats at conventional drying temperatures, and cannot accurately measure the available closed porosity. This invention modifies the method for testing connected porosity at shale drying temperature (60℃), further clarifying the connected porosity under formation temperature conditions, the connected porosity after appropriate technical modification (under the highest drying temperature conditions), and the available closed porosity after modification.

[0023] This method first obtains the formation temperature T1 corresponding to the shale sample, and then determines the highest drying temperature T2 of the low-clay-content shale sample without damaging the pore structure through a gradual heating drying test. The interconnected porosity under T1 and T2 conditions is then tested separately, and the difference between the two is used to calculate the usable closed porosity of the sample. This invention establishes a testing and calculation method applicable to low-clay-content shale under different formation temperature conditions for calculating the proportion of closed pores, and thus determining the degree to which closed pores can be converted into interconnected pores. This method is of great significance for the evaluation of shale oil and gas reservoirs.

[0024] The principle behind this invention is as follows: Under formation conditions, the pores of shale gas reservoirs are filled with a two-phase fluid of gas and water. During the generation of methane (gas) from shale organic matter, the increased gas volume displaces more of the pore space originally occupied by liquid water, gradually driving the liquid water out of the reservoir. However, due to limitations imposed by capillary forces, intermolecular forces, etc., a large amount of liquid water bound by tiny pore throats at formation temperatures cannot be expelled by the gas, thus forming modifiable closed pores.

[0025] This invention obtains the usable closed porosity by testing the interconnected porosity under formation temperature conditions and the interconnected porosity under laboratory conditions (completely dry).

[0026] In a preferred embodiment of the present invention, the method for determining the usable closed porosity of the low-clay-content shale reservoir includes the following steps: (1) Obtaining the formation temperature data T1 of the sample Before this experiment, it is necessary to obtain the formation temperature data at the depth of the sample collection layer. This data can be obtained by calculating it based on the local geothermal gradient, using the following formula: T 1= H × G + T 0; in, T 1 represents the formation temperature, in °C; H The depth is measured in km. G The geothermal gradient is expressed in °C / km. T 0 represents the Earth's surface temperature, in °C.

[0027] If well temperature data is available, drilling temperature data at the corresponding depth of the sample can also be used as the formation temperature.

[0028] (2) Obtain the highest drying temperature T2 of the sample in this region. For shale with high clay content, excessively high drying temperatures may alter the bound water of clay minerals, leading to damage to the pore structure. However, for Cambrian high-siliceous shale and Sinian high-dolomitic shale in western Hubei, which have low clay mineral content and stable structures that are not easily damaged, the drying temperature can be appropriately increased. Specifically: Samples saturated with 10wt%–20wt% potassium chloride solution (preferably 15wt%) were dried using a gradual temperature drying method, starting from the formation temperature and gradually increasing the temperature (in stages of 10–30°C, preferably 10°C or 20°C), maintaining each temperature gradient for 12–48 hours (preferably 24 hours) to ensure complete desorption of the bound fluid at that temperature. This avoids sudden temperature increases that could damage the sample's pore structure or result in incomplete fluid desorption. After each temperature gradient was completed, the sample was removed, cooled to room temperature, and its interconnected porosity was tested using the helium method. If continued heating did not result in a significant change in interconnected porosity, it meant that both free and adsorbed water in the pore throats had been expelled. Further heating caused the pore structure to be disrupted due to the reaction of mineral-bound water, and the interconnected porosity changed again (it may increase or decrease depending on the mineral composition). The temperature at which no significant change in interconnected porosity occurred was taken as the highest drying temperature for the sample in this region.

[0029] (3) Test the interconnected porosity of the sample under formation temperature conditions Shale reservoir samples were prepared into standard 1-inch plunger samples and pretreated according to "GB / T 29172-2012 Core Analysis Methods" including cleaning and drying. The treated shale reservoir samples were then placed in a pressure saturator and evacuated for 12 hours (vacuum degree 1×10⁻⁶). 4 After vacuuming, the sample is pressurized and saturated with a 10wt%–20wt% potassium chloride solution (preferably 15wt%) at a pressure of 15MPa–25MPa, preferably 20MPa, for more than 48 hours to ensure that the pores are completely filled with potassium chloride solution. The role of the potassium chloride solution is to prevent shale clay from deforming and altering the pore structure. The saturated sample is then placed in an oven and dried at the formation temperature T1 for 12–48 hours, preferably 24 hours. After cooling, the porosity of the sample is tested using the helium method.

[0030] The total volume of the plunger sample was determined using vernier calipers; the skeletal volume of the sample was determined using Boyle's two-chamber method with helium as the medium, and the result was obtained using the formula: φ= V 连通孔隙体积 / V总体积 ×100%=(V 总体积 -V 骨架体积 ) / V 总体积 ×100%; in, f V represents porosity. 总体积 V represents the total volume of the sample. 骨架体积 This represents the sample skeleton volume.

[0031] The above formula yields the interconnected porosity of shale under formation temperature conditions. f 1 (i.e., first connected porosity).

[0032] It should be noted that the interconnected porosity measured under each temperature gradient in step (2) is also calculated using the same formula mentioned above.

[0033] (4) Test the interconnected porosity at the highest drying temperature. The sample is heated to the highest drying temperature T2 and dried for 12 to 48 hours, preferably 24 hours. The interconnected porosity of the sample is then tested again using the helium method to obtain the interconnected porosity under these conditions. f 2. Because the drying temperature is higher, more moisture trapped within the tiny pores is evaporated, therefore... f 2> f 1.

[0034] (5) Calculation of available closed porosity Under formation temperature conditions, the first connected porosity is: f 1, then the first closed porosity under this condition f 封闭1 = f 总 - f 1; in, f 总 Total porosity of the sample, expressed as a percentage. f 1 represents the first level of interconnected porosity (i.e., the interconnected porosity of shale under formation temperature conditions), in units of %.

[0035] Under the highest drying temperature condition, the second interconnected porosity is: f 2, then the second closed porosity under this condition f 封闭2 = f 总 - f 2; in, f 总 Total porosity of the sample, expressed as a percentage. f 2 represents the second interconnected porosity (i.e., the interconnected porosity of shale under the highest drying temperature condition), in units of %.

[0036] The interconnected porosity is determined by f 1 rise to f During process 2, some pores are transformed from closed pores into interconnected pores. f 封闭2 < f 封闭1 .

[0037] Available closed porosity: f 可动用封闭= f 封闭1 -f 封闭2= (f) 总 - f 1 )-(φ 总 - f 2 )=φ 2- f 1; f 1: Shale connectivity porosity under formation temperature conditions, % f 2: Shale connectivity porosity under the highest drying temperature condition, %.

[0038] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0039] Example 1 This embodiment provides a method for determining the usable closed porosity of shale reservoirs with low clay content. Taking the Cambrian Niutitang Formation black siliceous shale and the Sinian Doushantuo Formation dolomitic mudstone in western Hubei as examples, the testing instruments used are a high-temperature vacuum drying oven and a He porosity analyzer. The test environment temperature is 26.0℃ inside the constant temperature chamber, with a temperature variation of ±0.2℃ during repeated tests, and the environmental pressure is basically stable at sea level pressure. The method specifically includes the following steps: (1) Obtaining the formation temperature data T1 of the sample Before this experiment, it is necessary to obtain the formation temperature data at the depth of the sample collection layer. This data is generally obtained by calculating it based on the local geothermal gradient. The calculation formula is as follows: T 1= H × G + T 0; in, T 1 represents the formation temperature, in °C; H The depth is measured in km. GThe geothermal gradient in this region is 20℃ / km. T 0 represents the surface temperature, and the surface temperature in this region is 15℃.

[0040] Table 1. Calculation table of the temperature of the stratum where the sample is located.

[0041] According to the calculation results, the average formation temperature of the Niutitang shale samples is 75.6℃, and the actual formation temperature measured by drilling is 71℃. For the convenience of temperature control in the drying oven, an approximate value of 70℃ is adopted. The average formation temperature of the Doushantuo Formation shale samples is 82.7℃. For the convenience of temperature control in the drying oven, an approximate value of 80℃ is adopted.

[0042] (2) Gradual temperature drying For Cambrian high-siliceous shale and Sinian high-dolomitic shale in western Hubei, which have low clay mineral content and stable structure that is not easily damaged, the drying temperature can be appropriately increased. The specific method is as follows: Shale reservoir samples were prepared into standard 1-inch plunger samples and pretreated according to "GB / T 29172-2012 Core Analysis Methods" including cleaning and drying. The treated shale reservoir samples were then placed in a pressure saturator and evacuated for 12 hours (vacuum degree 1×10⁻⁶). 4 After vacuuming, the solution is pressurized to saturate with 15wt% potassium chloride solution at a pressure of 20MPa for 96 hours.

[0043] Samples saturated with 15% potassium chloride solution were dried using a gradual temperature increase mode, starting from the formation temperature and gradually increasing the temperature (mainly in 20℃ increments). The drying temperatures for Cambrian Niutitang Formation shale samples were 70℃, 80℃, 100℃, 120℃, and 140℃, while those for Sinian Doushantuo Formation shale samples were 80℃, 100℃, 120℃, and 140℃. Each temperature gradient was dried at a constant temperature for 24 hours. After each temperature gradient was completed, the samples were removed, cooled to room temperature, and their interconnected porosity was tested using the helium method. The results are shown in Table 2. To demonstrate the improved effect of this calculation method, a standard drying temperature of 60℃ was added for comparison, with a drying time of 24 hours.

[0044] For the Niutitang Formation, after determining the first interconnected porosity at the actual temperature, the actual temperature was used as a baseline for an initial temperature increase of 10°C, followed by a stepped temperature increase at fixed intervals of 20°C. After each step, the interconnected porosity was measured after maintaining a constant temperature. This was because vacuum drying and pressure saturation were performed in batches in actual operation. For ease of operation, a batch of samples used the same temperature, except for the Cambrian Niutitang Formation, which had an additional starting temperature of 70°C, reducing workload without affecting the results. The interconnected porosity of two samples from the Cambrian Niutitang Formation after drying at the formation temperature (70°C) was... f The values ​​were 4.17% and 3.84%, respectively. After heating, the interconnected porosity remained basically stable at 100℃. This determined that the maximum drying temperature for the Cambrian Niutitang Formation was 100℃. The interconnected porosity of the shale under the highest drying temperature condition was... f The values ​​for 2 were 4.49% and 4.10%. The interconnected porosity of the two samples from the Doushantuo Formation of the Sinian System after drying at formation temperature (80℃) was... f The values ​​were 1.30% and 1.01%. After heating, the interconnected porosity remained basically stable at 120℃. This determined that the maximum drying temperature of the Doushantuo Formation of the Sinian System was 120℃, corresponding to the interconnected porosity. f 2 represents 1.34% and 1.07%.

[0045] Table 2. Connected porosity of shale samples at different drying temperatures

[0046] (3) Calculation of available closed porosity According to the formula for calculating the usable closed porosity: f 可动用封闭= f 封闭1 -f 封闭2= (f) 总 - f 1 )-(φ 总 - f 2 ）= f 2- f 1; among which, f 1 represents the interconnected porosity of shale under formation temperature conditions, in percentages. f 2 represents the interconnected porosity of shale under the highest drying temperature condition, in percentages.

[0047] The movable closed porosity of the two Cambrian Niutitang Formation shale samples was 0.32% and 0.19%, respectively; compared with the porosity under formation temperature conditions, the proportion of movable closed pores to total connected porosity was 7.67% and 4.95%, respectively. The movable closed porosity of the two Sinian Doushantuo Formation shale samples was 0.04% and 0.06%, respectively; compared with the porosity under formation temperature conditions, the proportion of movable closed pores to total connected porosity was 3.08% and 5.94%, respectively.

[0048] This shows that when the reservoir temperature is above 60℃, a considerable proportion (average 5%) of the closed pores in the Niutitang Formation and Doushantuo Formation can be transformed into connected pores, allowing the shale gas trapped in the pores to be released.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the usable closed porosity of shale reservoirs with low clay content, characterized in that, Includes the following steps: (a) Obtain the actual temperature of the formation corresponding to the shale sample to be tested; (b) Apply a stepped heating to the saturated shale sample, simultaneously measure the interconnected porosity at each temperature gradient, and determine the temperature at which the interconnected porosity tends to stabilize as the maximum safe drying temperature of the shale sample. (c) After maintaining the saturated shale sample at the actual temperature, the first interconnected porosity is measured. (d) After maintaining the shale sample at the highest safe drying temperature, the second interconnected porosity is measured; (e) Based on the first connected porosity and the second connected porosity, obtain the movable closed porosity.

2. The method for determining the usable closed porosity of low-clay-content shale reservoirs according to claim 1, characterized in that, The actual temperature is obtained through any of the following methods: The calculation formula is as follows: T 1= H × G + T 0; where, T 1 represents the formation temperature. H The depth of the strata. G The unit is geothermal gradient, and the unit is °C / km. T 0 represents the Earth's surface temperature.

3. The method for determining the usable closed porosity of low-clay-content shale reservoirs according to claim 1, characterized in that, The actual temperature is based on the measured well temperature data at the corresponding drilling depth.

4. The method for determining the usable closed porosity of low-clay-content shale reservoirs according to claim 1, characterized in that, The temperature gradient interval for the stepped heating is 10℃ to 30℃, and the constant temperature holding time under each temperature gradient is 12 hours to 48 hours.

5. The method for determining the usable closed porosity of low-clay-content shale reservoirs according to claim 1, characterized in that, The saturation treatment in step (b) uses a potassium chloride aqueous solution with a concentration of 10wt% to 20wt% and is saturated for more than 48 hours at a pressure of 15MPa to 25MPa.

6. The method for determining the usable closed porosity of low-clay-content shale reservoirs according to claim 1, characterized in that, The saturation treatment in step (c) uses a potassium chloride aqueous solution with a concentration of 10wt% to 20wt% and is saturated for more than 48 hours at a pressure of 15MPa to 25MPa.

7. The method for determining the usable closed porosity of low-clay-content shale reservoirs according to claim 1, characterized in that, The first connectivity porosity, the second connectivity porosity, and the connectivity porosity at each temperature gradient in step (b) were all measured using the helium method, and the calculation formulas are as follows: φ= V 连通孔隙体积 / V 总体积 ×100%=(V 总体积 -V 骨架体积 ) / V 总体积 ×100%; in, φ V represents porosity. 总体积 V represents the total volume of the sample. 骨架体积 This represents the sample skeleton volume.

8. The method for determining the usable closed porosity of low-clay-content shale reservoirs according to claim 1, characterized in that, by φ 可动用封闭 The formula for calculating the movable closed porosity is as follows: φ 可动用封闭 =φ 2- φ 1； in, φ 1 represents the first level of interconnected porosity, expressed as % φ 2 represents the second connectivity porosity, in percentages.

9. The method for determining the movable closed porosity of low-clay-content shale reservoirs according to claim 8, characterized in that, The second connectivity porosity is greater than the first connectivity porosity.

10. The method for determining the usable closed porosity of low-clay-content shale reservoirs according to claim 1, characterized in that, The condition of reaching stability is defined as follows: the absolute value of the difference between the interconnected porosity measured under the current temperature gradient and the interconnected porosity measured under the previous temperature gradient is not greater than 0.10%, and the difference is reduced by 50% or more compared with the change in interconnected porosity between the previous adjacent temperature gradients; the maximum safe drying temperature is the minimum temperature gradient that satisfies the condition of reaching stability.

Images