A method for quantifying the influencing factors of the change in the width of hydraulic fracturing fractures in saline reservoirs

Abstract

The present invention discloses a method for quantifying the influencing factors of the change in the width of hydraulic fracturing fractures in a salt-bearing reservoir. The present invention includes conducting a triaxial compression creep experiment using a high-temperature and high-pressure creep instrument to calculate the creep rate of salt rock in the salt-bearing reservoir, measuring the embedment depth of proppants and the total height change of fractures and rock slabs using a long-term flow conductivity testing device, calculating the karst rate of salt rock in the salt-bearing reservoir through the mass change of the rock slab before and after, the dissolution time, and the reaction area, and subtracting the numerical values of the effects of three actions, namely salt rock creep, salt rock karstification, and proppant embedment, on the fracture width from the total width change of fractures and rock slabs. The present invention can quantitatively measure the width of proppant fractures in a salt-bearing reservoir and quantify three main actions affecting the fracture width in a salt-bearing reservoir: the karstification action of the salt-bearing reservoir, the creep action of the salt-bearing reservoir, and the embedment action of proppants. This method is highly comprehensive, simple to operate, and easy to quantify, and can provide reliable data support for the development of salt-bearing reservoirs.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas field exploration and development, and specifically relates to a method for quantifying the influencing factors of the change in the width of hydraulic fracturing fractures in a salt-bearing reservoir. Background Art

[0002] High-salt reservoirs have characteristics such as strong plasticity and strong creep ability, and contain rich oil and gas resources. Their effective development plays an increasingly prominent role in ensuring domestic energy. At present, there is certain research on the fracturing technology and theory for salt-bearing reservoirs, but the transformation effect is not ideal. The key factors to improve the transformation effect are mainly to maintain an effective hydraulic fracture width and enhance the reservoir conductivity. Compared with conventional reservoirs, the factors affecting the fracture width of salt-bearing reservoirs are more complex, mainly including factors such as the creep, dissolution of salt rock, and proppant embedment. How to quantitatively analyze the influencing factors of the width of hydraulic fracturing fractures in salt-bearing reservoirs and adopt an optimized process to maintain an effective fracture width for the dominant factors is a difficult problem in the hydraulic fracturing of such reservoirs.

[0003] Calculating the change in fracture width through numerical simulation is a commonly used method. However, due to the special lithology of the reservoir, the actual change in fracture width is affected by various factors, and it is difficult to accurately consider these factors in numerical simulation, resulting in a large error in fracture width prediction.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for quantifying the influencing factors of the change in the width of hydraulic fracturing fractures in a salt-bearing reservoir, solving the problems proposed in the above background art.

[0006] To solve the above technical problems, the basic concept of the technical solution adopted by the present invention is as follows:

[0007] A method for quantifying the influencing factors of the change in the width of hydraulic fracturing fractures in a salt-bearing reservoir, comprising the following steps:

[0008] S1: Performing a triaxial compression creep experiment using a high-temperature and high-pressure creep instrument to calculate the creep rate of salt rock in the salt-bearing reservoir;

[0009] S2: Measuring the proppant embedment depth and the total height change of the fracture and the rock plate using a long-term conductivity test device;

[0010] S3: Calculating the karst rate of salt rock in the salt-bearing reservoir through the mass change before and after the rock plate, the dissolution time, and the reaction area;

[0011] S4: Subtracting the numerical values of the effects of salt rock creep, salt rock dissolution, and proppant embedment on the fracture width from the total change in the width of the fracture and the rock plate, and the change in the salt rock fracture width can be obtained.

[0012] Optionally, the steps for calculating the salt rock creep rate of the salt-bearing reservoir in step S1 are as follows:

[0013] Install the rock sample and the upper and lower pads on the same axis, put on a heat-shrinkable plastic sheath and heat-shrink it until the specimen and the end blocks are in close contact;

[0014] Put the rock sample into the pressure chamber of the high-temperature and high-pressure creep tester, fill the pressure chamber with oil using an oil pump, heat the temperature of the triaxial chamber to the formation temperature at a rate of 1 °C / min and maintain it for 2 - 3 hours to form a uniform temperature field;

[0015] Apply confining pressure to the required pressure and maintain a predetermined value, apply axial pressure to the required pressure and maintain a predetermined value;

[0016] Determine that the specimen enters steady-state creep through the strain-time curve graph, record the total creep rate within 12 hours, and after maintaining it steadily for a period of time, transfer to the next-level experiment with a greater axial stress;

[0017] After the experiment is completed, stop heating, unload the axial pressure and the confining pressure, take out the rock sample, and draw an axial strain-time relationship graph through the axial strain experimental data.

[0018] Optionally, in step S1, through the formula Calculate the creep rate, where v1 is the creep rate in the creep stage, Δε is the corresponding strain in the creep stage, and Δt is the creep stage time.

[0019] Optionally, the long-term diversion capacity test device in step S2 includes a diversion chamber, a displacement sensor, a differential pressure sensor, a hydraulic system, a backpressure device, a constant-speed and constant-pressure pump. The internal structure of the diversion chamber includes a diversion chamber upper piston, an upper rock plate, proppant, a lower rock plate, and a diversion chamber lower piston. The proppant and the rock plates are loaded into the diversion chamber in this order, and the displacement sensor is installed between the upper and lower pistons.

[0020] Optionally, the steps for calculating the proppant embedment depth and the total height change of the fracture and the rock plate in step S2 are as follows:

[0021] Prepare the proppant diversion capacity evaluation device and experimental materials, including upper and lower rock plates made of reservoir rock or two standard upper and lower rock plates with the same properties, proppant, and fracturing fluid, and measure the laying thickness of the proppant in the diversion chamber when adding the proppant;

[0022] Put the lower rock plate, the proppant, and the upper rock plate into the diversion chamber in sequence, install the displacement sensing device for the upper and lower pistons of the diversion chamber, and adjust the backpressure of the diversion chamber to the formation flowing pressure;

[0023] Fill the liquid into the liquid pumping container, set the liquid flow rate of the constant-speed and constant-pressure pump, and heat the diversion chamber and the liquid to the formation temperature;

[0024] Pump the liquid into the diversion chamber to allow the liquid to flow through the gaps between the upper and lower rock plates and the proppants. After the system stabilizes, increase the closing pressure of the overlying rock plate by adjusting the hydraulic system, and record the displacement changes of the displacement sensor.

[0025] Record the displacement value until the change stops, then disassemble the rock plate, dry it and weigh it, and scan the fracture surface.

[0026] Optionally, the steps for calculating the karst rate of the salt plate in the salt-bearing reservoir in step S3 are as follows:

[0027] Calculate the dissolution rate through the mass change of the rock plate before and after step S2, the dissolution time, and the reaction area. The formula is: where v is the dissolution rate; Δm is the mass dissolved during the corresponding time interval t, B is the dissolution area, and t is the time interval.

[0028] Optionally, the steps for obtaining the change in the width of the salt rock fracture by subtracting the influence values of salt rock creep, salt rock karst, and proppant embedment on the fracture width from the total width change of the fracture and the rock plate in step S4 are as follows:

[0029] Use the salt rock creep rate result in step S1 and the formula l1 = P * h to calculate the creep amount values of the upper and lower rock plates under each closing pressure in step S2, which are the fracture width values affected by the creep effect. In the formula, l1 is the creep amount of the rock plate, in mm; P is the creep rate, and h is the total thickness of the upper and lower rock plates, in mm;

[0030] Use the salt rock karst rate result in S3, the fluid passing time, and the formula to calculate the change in the fracture width caused by the karst of the rock plate. In the formula, l2 is the karst height of the rock plate, in mm; h is the total thickness of the upper and lower rock plates of the rock plate, A is the contact area between the rock plate and the fluid; t is the time; m0 is the total weight of the upper and lower rock plates;

[0031] The embedding depths l 3上 and l 3下 of the proppant in the upper and lower rock plates can be obtained from the scanning result of the rock plate after the experiment;

[0032] The total thickness of the proppant in the diversion chamber measured in step S2 is l, which is the initial fracture width wf o , then the total displacement change is calculated through the formula l = l1 - l2 + l 3上 + l 3下 and the fracture width change is calculated using the formula w fo - w f = l 3上 + l 3下 - l2. Calculate the fracture width of the hydraulic fracturing proppant in the salt-bearing reservoir under a single closing pressure, and analyze the dominant factors affecting the fracture width change.

[0033] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art. Of course, any product implementing the present invention does not necessarily need to achieve all the advantages described below at the same time:

[0034] The present invention can quantitatively measure the width of the proppant fracture in the salt-bearing reservoir and quantify the three main effects affecting the fracture width in the salt-bearing reservoir: the dissolution effect of the salt-bearing reservoir, the creep effect of the salt-bearing reservoir, and the embedding effect of the proppant. This method is comprehensive, simple to operate and easy to quantify, and can provide reliable data support for the development of salt-bearing reservoirs, ensuring the effective width of the fracture during the exploitation process, thereby improving the recovery rate and economic benefits of oil and gas resources. By comprehensively analyzing and quantifying these influencing factors, this method can not only optimize the fracturing construction parameters, but also provide a scientific basis for reservoir stimulation, contribute to improving the stimulation effect of salt-bearing reservoirs, reducing the production decline rate, extending the stable production period, and further enhancing the development potential of the reservoir.

[0035] The following further describes in detail the specific embodiments of the present invention with reference to the accompanying drawings. Description of the Drawings

[0036] The drawings in the following description are only some embodiments. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts. In the attached

[0037] In the figures:

[0038] Figure 1 is the technical principle diagram adopted by the present invention;

[0039] Figure 2 is the internal structure diagram of the diversion chamber used by the present invention;

[0040] Figure 3 is the experimental curve graph of salt rock creep;

[0041] Figure 4 is the piston displacement curve graph in the diversion experiment.

[0042] In the drawings, the list of components represented by each reference numeral is as follows:

[0043] 1. Upper piston of the diversion chamber; 2. Upper rock plate; 3. Proppant; 4. Lower rock plate; 5. Lower piston of the diversion chamber.

[0044] It should be noted that these drawings and the textual descriptions are not intended to limit the scope of the concept of the present invention in any way, but to illustrate the concept of the present invention to those skilled in the art by referring to specific embodiments. Specific Embodiments

[0045] Now, the present invention will be further described in detail with reference to the accompanying drawings.

[0046] Please refer to Figures 1-4 As shown, in this embodiment, a method for quantifying the influencing factors of the change in the width of hydraulic fracturing fractures in a saline reservoir is provided, including the following steps:

[0047] S1: Conduct a triaxial compression creep experiment using a high-temperature and high-pressure creep instrument to calculate the creep rate of the salt rock in the saline reservoir;

[0048] S2: Measure the embedment depth of the proppant and the total height change of the fracture and the rock slab using a long-term conductivity test device;

[0049] S3: Calculate the karst rate of the salt rock in the saline reservoir through the mass change before and after the rock slab, the dissolution time, and the reaction area;

[0050] S4: Subtract the numerical values of the effects of salt rock creep, salt rock dissolution, and proppant embedment on the fracture width from the total change in the width of the fracture and the rock slab to obtain the change in the width of the salt rock fracture.

[0051] In this embodiment, the steps for calculating the creep rate of the salt rock in the saline reservoir in step S1 are as follows:

[0052] Install the rock sample and the upper and lower pads on the same axis, put on a heat-shrinkable plastic sheath and heat-shrink it until the specimen and the end block are closely attached;

[0053] Put the rock sample into the pressure chamber of the high-temperature and high-pressure creep instrument, fill the pressure chamber with oil using an oil pump, heat the temperature of the triaxial chamber to the formation temperature at a rate of 1°C / min and keep it for about 3 hours to form a uniform temperature field;

[0054] Apply confining pressure to the formation confining pressure of 40 MPa and keep the preset value, apply axial pressure to 70 MPa to simulate the closure pressure and keep the preset value;

[0055] Determine that the specimen enters steady-state creep through the strain-time curve graph, record the total creep rate within 12 hours, and transfer to the next-level experiment with a greater axial stress after maintaining it steadily for a period of time;

[0056] After the experiment, stop heating, unload the axial pressure and the confining pressure, take out the rock sample, and draw an axial strain-time relationship graph through the axial strain experimental data.

[0057] Δε

[0058] The creep rate is calculated by the formula v1 = Δε / Δt, where v1 is the creep rate in the creep stage, Δε is the corresponding strain in the creep stage, and Δt is the time in the creep stage. According to the experimental results, it can be known that under a constant load, after the salt rock quickly completes elastic deformation, it enters a period of transient creep and then a relatively long period of steady-state creep. Therefore, only the total creep rate within 12 h needs to be known, and the calculated total creep rate is 7.23%.

[0059] In this embodiment, the long-term diversion capacity test device in step S2 includes a diversion chamber, a displacement sensor, a differential pressure sensor, a hydraulic system, a backpressure device, and a constant-speed and constant-pressure pump. The internal structure of the diversion chamber includes a diversion chamber upper piston 1, an upper rock plate 2, proppant 3, a lower rock plate 4, and a diversion chamber lower piston 5. The proppant 3 and the rock plates are loaded into the diversion chamber in this order, and the displacement sensor is installed between the upper and lower pistons. Since the upper and lower pistons of the diversion chamber have very high stiffness and basically do not deform under high pressure, the overall height change of the upper and lower rock plates 4 and the proppant 3 can be reflected according to the height difference between the upper and lower pistons.

[0060] In this embodiment, the steps for calculating the proppant embedment depth and the total height change of the fracture and the rock plate in step S2 are as follows:

[0061] Prepare the proppant diversion capacity evaluation device and experimental materials, including upper and lower rock plates made of reservoir rocks or two standard upper and lower rock plates of the same nature, proppant, and fracturing fluid. Measure the laying thickness of the proppant in the diversion chamber when adding the proppant. In this embodiment, the proppant is 30 / 50-mesh ceramsite, and the proppant sand concentration is 5 kg / m2. The fracturing fluid is clear water. Measure the laying thickness of the proppant in the diversion chamber when adding the proppant, and the thickness is 2.56 mm, which is the initial width wf of the salt rock fracture under no closure pressure. o 。

[0062] Place the lower rock plate, proppant, and upper rock plate into the diversion chamber in sequence, install the displacement sensing device for the upper and lower pistons of the diversion chamber, and adjust the backpressure of the diversion chamber to the formation flowing pressure of 6 MPa;

[0063] Fill the liquid into the pump liquid container, set the liquid flow rate of the constant-speed and constant-pressure pump to 10 ml / min, and heat the diversion chamber and the liquid to the formation temperature of 100 °C;

[0064] Pump the liquid into the diversion chamber, that is, the liquid flows through the gaps between the upper and lower rock slabs and the proppants. After the system stabilizes, quickly increase the overburden closing pressure of the rock slab by adjusting the hydraulic system, and record the displacement changes of the displacement sensor, which are the displacement changes of the upper and lower rock slabs. The recording time depends on the properties of the reservoir rock slab and can be ended when the recorded displacement values basically no longer change. After recording the displacement sensor values under a set of closing pressures, if it is necessary to know the displacement changes under other closing pressures, then disassemble the rock slab, replace it with a new pair of rock slabs of the same properties, change the closing pressure, and repeat the above steps until the displacement values under all target closing pressures are recorded.

[0065] After recording the displacement sensor values under a set of closing pressures, if it is necessary to know the displacement changes under other closing pressures, then disassemble the rock slab, replace it with a new pair of rock slabs of the same properties, change the closing pressure, and repeat the above steps until the displacement values under all target closing pressures are recorded.

[0066] Table 1 shows the change of the displacement sensor values over time

[0067] Time (h) 1 2 3 4 5 6 Displacement change (mm) 3.44 3.80 4.13 4.38 4.44 4.51 Time (h) 7 8 9 10 11 12 Displacement change (mm) 4.62 4.67 4.72 4.76 4.81 4.85

[0068] After the experiment, take out the rock slab, dry it, weigh it, and scan the crack surface of the rock slab.

[0069] In this embodiment, the steps of calculating the karst rate of the salt slab in the salt-bearing reservoir in step S3 are as follows:

[0070] Calculate the dissolution rate through the mass change of the rock slab before and after step S2, the dissolution time, and the reaction area. The formula is: Among them, v is the dissolution rate; Δm is the mass dissolved within the corresponding time interval t, B is the dissolution area, and t is the time interval. According to the above technology, it is known that the rock slab has dissolved 6.69 g, and the calculated dissolution rate is 7.2×10−5 g / (cm2·min)

[0071] In this embodiment, the steps of obtaining the change in the salt rock crack width by subtracting the influence values of the three effects of salt rock creep, salt rock karst, and proppant embedding on the crack width from the total width change of the crack and the rock slab in step S4 are as follows:

[0072] Use the salt rock creep rate result in step S1 to calculate the creep amount value of the upper and lower rock slabs at 70 MPa closing pressure for 12 hours in step S2, which is the crack width value l1 affected by the creep effect, where l1 is the creep amount of the rock slab, mm; P is the creep rate, and h is the total thickness of the upper and lower rock slabs, mm. The measured creep rate is 7.23%, and the total thickness h of the upper and lower rock slabs = 40 mm. Calculate the total creep value of the upper and lower rock slabs to be 2.89 mm.

[0073] Using the salt rock karst rate results and fluid passing time in S3, calculate the change in fracture width caused by slab dissolution. In the formula, l2 is the height of slab dissolution, in mm; h is the total thickness of the upper and lower slabs, A is the contact area between the slab and the fluid; t is the time; m0 is the total weight of the upper and lower slabs; according to the calculation, the total thickness of the upper and lower slabs is 40 mm, and the slab dissolution rate v = 7.2×10 -5 g / (cm 2 ·min), the contact area between the slab and the fluid A = 64.5 mm 2 ; the time t is 720 min; the total weight of the upper and lower slabs m0 = 461.37 g. The calculated height of slab dissolution l2 is 0.58 mm.

[0074] Using the scanning results of the slab after the experiment, the embedding depths l 3上 and l 3下 of the proppant in the upper and lower slabs can be obtained. The scanning result shows that the embedding depth l 3上 of the upper slab is 0.68 mm, and the embedding depth l 3下 of the lower slab is 0.69 mm;

[0075] The total thickness of the proppant in the diversion chamber measured in step S2 is l, which is the initial fracture width wf o , then the total displacement change: l = l1 - l2 + l 3上 + l 3下 , the fracture width change is: w fo - w f = l 3上 + l 3下 - l2. The total displacement change measured using the above formula is l = 4.85 mm. It is calculated that the fracture width of the proppant in the salt-bearing reservoir hydraulic fracturing under a closure pressure of 70 MPa is reduced by 0.79 mm, among which the embedding effect is reduced by 1.37 mm, and the dissolution effect is increased by 0.58 mm, indicating that the embedding effect dominates the influence on the fracture width.

[0076] The present invention is not limited to the above embodiments. Anyone should know that structural changes made under the inspiration of the present invention, as long as they have the same or similar technical solutions as the present invention, fall within the protection scope of the present invention. The technologies, shapes, and structures not detailedly described in the present invention are all well-known technologies.

Claims

1. A method for quantifying factors affecting crack width variation in saline reservoir hydraulic fracturing, characterized in that: The following steps are involved: S1: Triaxial compression creep test was carried out using a high temperature and high pressure creep instrument to calculate the creep rate of salt rock in salt-bearing reservoirs; S2: Using a long-term conductivity test device to measure the proppant embedment depth and the total height change of the fracture and rock plate; S3: Calculate the karst rate of salt rock in salt-bearing reservoirs through the mass change of the rock slab before and after, the dissolution time and the reaction area; S4: The change in the width of the salt rock crack is obtained by subtracting the influence of the three effects of salt rock creep, salt rock dissolution and proppant embedding on the crack width from the total width change of the crack and the rock plate; Step S4 uses the total width change of the crack and the rock plate to subtract the influence of the three effects of salt rock creep, salt rock dissolution and proppant embedding on the crack width, that is, the steps of obtaining the change of the salt rock crack width are: Using the salt rock creep rate results and formula in step S1 Calculate the creep value of the upper and lower rock plates under each closing pressure in step S1, which is the crack width value affected by creep. In the formula, is the creep amount of rock plate, mm; is the creep rate, is the total thickness of the upper and lower rock plates, mm; Using the salt rock karst rate results and fluid passage time in S3 and the formula Calculate the change in crack width caused by rock slab dissolution, where: is the dissolution height of the rock slab, mm; is the total thickness of the rock slab from top to bottom, is the contact area between the rock plate and the fluid; For time; is the total weight of the upper and lower rock plates; The rock plate scanning results after the experiment can be used to obtain the embedding depth of the upper and lower rock plates of the proppant. and ; The total thickness of the proppant in the diversion chamber measured in step S2 is l, which is the initial crack width , then the total displacement change is expressed by the formula Calculate and use the formula The crack width change is calculated. The crack width of the proppant in the saline reservoir hydraulic fracturing under a single closure pressure is calculated by the above formula, and the dominant factors affecting the crack width change are analyzed.

2. A method for quantifying factors affecting the change of crack width in saline reservoir hydraulic fracturing according to claim 1, characterized in that: Step S1: The steps for calculating the creep rate of salt rock in the salt-bearing reservoir are: Install the rock sample and the upper and lower pads on the same axis, cover them with heat shrinkable plastic sheaths and heat shrink until the sample and the end blocks are in close contact; Place the rock sample into the pressure chamber of the high-temperature and high-pressure creep instrument, fill the pressure chamber with oil using an oil pump, heat the triaxial chamber to the formation temperature at a rate of 1°C / min and maintain it for 2-3 hours to form a uniform temperature field; Add the confining pressure to the required pressure and maintain it at the predetermined value, and add the axial pressure to the required pressure and maintain it at the predetermined value; The specimen enters steady-state creep through the strain-time curve, and the total creep rate within 12 hours is recorded. After it remains stable for a period of time, it is transferred to the next level of experiment with greater axial stress. After the experiment, the heating was stopped, the axial pressure and confining pressure were unloaded, the rock sample was taken out, and the axial strain-time relationship diagram was drawn based on the axial strain experimental data.

3. A method for quantifying factors affecting the change of crack width in saline reservoir hydraulic fracturing according to claim 1, characterized in that: In step S1, the formula Calculate the creep rate, where is the creep rate in the creep stage, is the corresponding strain in the creep stage, is the creep stage time.

4. A method for quantifying factors affecting the change of crack width in saline reservoir hydraulic fracturing according to claim 1, characterized in that: The long-term flow conductivity testing device in step S2 comprises a flow diversion chamber, a displacement sensor, a pressure difference sensor, a hydraulic system, a back pressure device, and a constant speed and pressure pump. The internal structure of the flow diversion chamber comprises an upper piston (1) of the flow diversion chamber, an upper rock plate (2), a proppant (3), a lower rock plate (4) and a lower piston (5) of the flow diversion chamber. The proppant (3) and the rock plate are loaded into the flow diversion chamber in this order, and the displacement sensor is installed between the upper and lower pistons.

5. The method for quantifying the factors affecting the change of crack width of hydraulic fracturing in saline reservoirs according to claim 1, characterized in that: Step S2: The steps for calculating the embedding depth of the proppant and the total height change of the fracture and the rock plate are: Prepare a proppant conductivity evaluation device and experimental materials, including upper and lower rock plates made of reservoir rock or two standard upper and lower rock plates of the same nature, proppant and fracturing fluid, and measure the laying thickness of the proppant in the diversion chamber when adding the proppant; Place the lower rock plate, proppant and upper rock plate into the diversion chamber in sequence, install the upper and lower piston displacement sensors of the diversion chamber, and adjust the back pressure of the diversion chamber to the formation flow pressure; Put the liquid into the pump liquid container, set the liquid flow rate of the constant speed and constant pressure pump, and heat the diversion chamber and the liquid to the formation temperature; Pump the liquid into the diversion chamber to make the liquid flow through the gaps between the upper and lower rock plates. After the system is stable, increase the closing pressure of the overburden rock plate by adjusting the hydraulic system and record the displacement change of the displacement sensor. The displacement value was recorded until the change stopped, then the rock slab was disassembled, dried and weighed, and the crack surface was scanned.

6. A method for quantifying factors affecting crack width changes in saline reservoir hydraulic fracturing according to claim 3, characterized in that: Step S3: The steps for calculating the karst rate of the salt plate of the saline reservoir are: The dissolution rate is calculated by the change in rock mass before and after step S2, the dissolution time and the reaction area. The formula is: in, is the dissolution rate; is the mass dissolved in the corresponding time interval t, is the dissolution area, is the time interval.

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