CN109507241B - Method and equipment for measuring rock wettability by resistance method - Google Patents
Method and equipment for measuring rock wettability by resistance method Download PDFInfo
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- CN109507241B CN109507241B CN201710824893.5A CN201710824893A CN109507241B CN 109507241 B CN109507241 B CN 109507241B CN 201710824893 A CN201710824893 A CN 201710824893A CN 109507241 B CN109507241 B CN 109507241B
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Abstract
The invention provides a new method and equipment for measuring rock wettability by a resistance method, belonging to the field of earth (rock) physics. The invention provides consistent and stable measurement conditions; monitoring the resistance change of the rock sample in the whole measuring process; replacing the fluid in the sample inlet (lower) pipeline with an injection fluid (crude oil), and keeping an oil interface between the sample and the electrode to form a self-priming condition; monitoring the change of rock resistance and the change of liquid level in the metering tube in the self-priming process, wherein the change of the liquid level can be regarded as the liquid level in the Amott method; and establishing corresponding resistivity wetting index and wetting judgment standard. The rock wettability is represented by monitoring the change of the rock resistivity in the self-absorption and discharge process in real time, the problem that the influence of sample size and measurement conditions on the rock wettability is not considered in the prior art is solved, the reliability and the measurement precision of the rock wettability are improved, and an experimental basis is provided for reservoir evaluation and modification.
Description
1. Field of the invention
The invention relates to a new method and equipment for measuring the wettability index of a rock sample, belonging to the field of earth (rock) physics.
2. Background of the invention
Under the action of capillary force, the phenomenon that wetting fluid enters pores by self-suction and non-wetting fluid in the pores is driven by the rock side by side occurs. The method for measuring the wettability of the rock comprises the following steps: self-priming method (Amott method), centrifugal method, contact angle method. For a long time, the "self-priming method" proposed by Earl Amott in 1959 has been commonly used. In 2007, after some processes are improved, a petroleum industry standard 'SY/T5153-2007 reservoir rock wettability determination method' is formed.
A large number of experiments show that the low-pore low-permeability rock is difficult to measure the discharged liquid in the self-priming process by using the Amott method, and the volume change of oil and water caused by wettability is too small. The Amott method is limited by equipment and technology in the whole process from oil drive (aging), self-water-absorption oil discharge, water drive, self-oil-absorption water discharge to secondary oil drive, and measurement under different conditions (repeated heating and pressurization) is required.
Oil and water in rock are very different in electricity. Even when the rock water saturation is not changed, the rock resistance changes if the oil-water existence state (shape) changes. The change in rock wettability causes oil and water to be redistributed, resulting in a significant change in rock resistance. And a proper sample size and an electrode system are selected, so that the resistance change of the sample caused by wettability can be accurately and quickly measured. The change of the wettability of different stages is described by using the change of the resistance instead of the change of the liquid level by using the Amott method, so that a corresponding resistivity wetting index and a wettability criterion are constructed, and the principle is used for measuring the wettability of the rock by using the resistance method. The invention can complete the whole experimental process from oil driving, water aging at constant temperature, self-water-sucking and oil discharging, water driving, self-oil sucking and water discharging to secondary oil driving under the condition of the same temperature and shaft confining pressure, monitors whether each process is reasonable or not, and determines whether the corresponding steps are finished or not by using quantitative indexes.
3. Summary of the invention
A method and experimental equipment for measuring rock wettability by using a resistivity method.
The invention mainly aims to provide a measuring method and a measuring device for indicating rock wettability. The method solves the problems that errors are caused by the change of the measurement conditions of the Amott method and the wettability of the low-porosity and low-permeability rock cannot be measured.
In order to achieve the above object, according to an aspect of an embodiment of the present invention, there is provided a method for measuring wettability of rock by a resistivity method. The method comprises the following steps: providing consistent, stable measurement conditions for each step; monitoring the resistance change of the rock sample in real time in the whole measuring process; the holder adopts horizontal displacement and vertical self-absorption. In the state that oil drives water to be bound with water, adopting horizontal displacement, and determining whether the aging process is finished or not according to the resistance variation; in the process of self-water-absorption and oil-discharge, the holder is converted into a vertical type, the fluid in a pipeline at the inlet end (lower end) of the sample is replaced by formation water, a water interface is kept on the lower end surface of the sample to form a self-absorption condition, and the resistance of the sample is reduced under the action of wettability until the resistance of the sample tends to be stable; in the process of oil displacement by water, the holder is replaced by a horizontal holder, and the resistance of the sample is continuously reduced until the resistance of the sample tends to be stable; in the self-priming oil drainage process, the clamp is turned into a vertical type again, the fluid in the pipeline at the inlet end (lower end) of the sample is replaced by crude oil, an oil interface is kept between the sample and the electrode to form a self-priming condition, at the moment, the resistance begins to rise, and tends to be stable when reaching a certain value, and the self-priming oil drainage process is considered to be finished; the holder is adjusted to be horizontal, secondary oil is used for driving water, the resistance of the sample rises, and when the resistance tends to be stable, movable oil in the sample is considered to be replaced by formation water. The change in resistance was monitored during each run while the change in level in the metering tube was measured. Establishing corresponding resistance wetting index and wettability judgment standards according to the relative variation of the resistivity of the samples at different stages; the liquid level change of the metering tube is similar to the volume discharged by Amott self-suction, and corresponding volume wetting index and wettability judgment standards can be established.
In order to achieve the above object, according to another aspect of the embodiments of the present invention, there is provided a rock wettability measuring apparatus. The device includes: the position-adjustable core holder is used for applying overburden pressure, stratum lateral pressure and pore pressure to a rock sample and measuring the resistance and the temperature of two ends of the rock sample; the insulation short section and the pressure sensor ensure the insulation of the resistance measurement system and indicate the pore pressure of the inlet and outlet ends; the piston type intermediate container ensures that injected oil gas is isolated from a displacement pressure system and provides stable displacement pressure; the axial pressure and confining pressure control system is used for providing stable overburden formation pressure and formation lateral pressure for the rock core holder; the back pressure control system is used for keeping the pore pressure of the rock sample stable; the displacement pressure control system provides stable and controllable pressure for the piston type intermediate container; the RLC resistance measurement system measures the resistance at two ends of the rock sample by a four-stage method; the computer acquisition control system is used for monitoring various pressures in real time and automatically recording the temperature, various pressures and resistance parameters in a time-sharing manner; the constant temperature box simulates the formation temperature in a hot air circulation mode; a metering tube to display the volume of liquid discharged during self-priming. The thin lines in the figure are signal control lines and the thick black lines are fluid lines.
According to the embodiment of the invention, the rock wettability is represented by monitoring the change of the rock resistivity in the self-priming discharge process in real time, the influence of sample size and measurement conditions on the rock wettability is not considered in the prior art, the reliability and the measurement precision of the rock wettability are improved, and an experimental basis is provided for reservoir evaluation and modification.
4. Description of the drawings
Fig. 1 is a schematic diagram of measuring core wettability using resistivity.
FIG. 2 is a schematic diagram of an apparatus for measuring rock wettability by a resistivity method. In the figure: firstly, a rock core holder; a porous plate; ③ the six-way valve; fourthly, a pressure sensor; emptying the valve; sixthly, stratum water container; seventhly, a crude oil container; eighthly, communicating a metering pipe with a valve; ninthly, a U-shaped metering pipe, ninthly-1 is an upper metering pipe, and ninthly-2 is a lower metering pipe; an RLC bridge at the R and a computer acquisition control system; (11) a shaft pressure and confining pressure control system; pumping a high-pressure advection pump; the incubator is selected in a selection mode. The dashed boxes in the figure represent the devices placed in the incubator, the thin wires being the signal control lines and the thick black wires being the fluid lines.
Due to the adoption of the technical scheme, the invention has the following advantages:
1) the invention utilizes the Amott method that the volume content, occurrence state and distribution form of oil and water in the rock are changed when the wettability of the rock is changed, which leads the resistance of the rock to be obviously changed, the wettability change is determined by measuring the resistivity of the rock, and the detection precision is far higher than the measured discharge volume.
2) The measurement conditions are controllable, the measurement conditions of each stage (S103 to S108) are consistent, and the result is visual and reliable.
3) According to the rock resistance variable quantity in unit time, the aging process and the self-suction discharge process are expressed quantitatively for the first time. The method for determining the aging time and the displacement saturation by experience in an industry standard SY/T5153-2007 is avoided.
4) Compared with the Amott method, the method is simpler and more reliable to operate.
5) The wettability index of the resistance method is provided, and simultaneously, the wettability index of the resistance method is provided like the Amott method.
5. Detailed description of the preferred embodiments
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The invention is explained in detail below with reference to the embodiments and with reference to the figures. It is to be understood that the embodiments described are only some embodiments of the invention and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example one
The embodiment of the invention provides a method for measuring rock wettability by a resistivity method, as shown in fig. 1, the method comprises the following steps:
in step S101, the sample for measuring rock wettability is also a plunger sample, but the sample diameter is required to be larger than the sample length, and a sample with a diameter of 3.81 cm is generally taken. And determining the axial pressure, confining pressure and temperature for the experiment according to the burial depth of the sample.
Step S102, sample preparation comprises sample processing, oil washing, salt washing, solution preparation, sample saturation and the like, and is a necessary condition for ensuring the accuracy of measurement data. Formation water is typically used as a saturated solution.
And S103, horizontally mounting the core holder, and measuring the water resistivity R0 of the rock sample under the condition of simulating the stratum. In order to eliminate the change of water saturation caused by the sample in the processes of installation, heating and pressurization, formation water with 2-3 times of pore volume needs to be injected from the inlet end to ensure that no air bubbles are discharged from the sample. The resistivity of the sample R0 was measured by a four-level method at a frequency of 1 KHz.
And S104, in order to achieve higher oil saturation, slowly injecting crude oil at constant pressure, discharging water in a sample from the outlet end of a holder, determining the volume of the discharged water by using a metering tube, calculating the oil saturation in the sample, when the increment of the resistivity of the sample in 1 hour is less than 1 omega, considering that a bound water state is achieved, closing an inlet end valve, redistributing oil and water, waiting for resistance balance, considering that the sample is completely aged if the resistivity variation in 8 hours is less than 1 omega, recording the resistivity Rt of the sample, and calculating the bound water saturation. The sample now had the conditions for self-priming oil drainage.
And step S105, adjusting the clamp holder from the horizontal type to the vertical type, and starting self-water-absorption oil-discharge. The crude oil at the lower end of the holder was replaced with formation water, maintaining an oil interface between the sample and the perforated plate. The method comprises the specific steps of cleaning crude oil in a pipeline at the lower end by using an organic solvent by using a double-pipe structure on a probe, then discharging cleaning liquid in the pipeline by using formation water, and closing a valve. And adjusting the heights of the water column and the oil column in the U-shaped pipe to ensure that the oil-water interface is consistent with the lower end face of the sample in height. And opening a corresponding valve, adjusting the height of a water column in the U-shaped pipe to enable the water column to be slightly higher than the lower end face of the sample by 1-2mm, only moving an oil-water interface into the sample from the contact surface of the probe and the sample in the process, rapidly descending a resistance curve along with the water entering of an injection end, recording the resistivity Rt1 at the moment, keeping the measurement condition unchanged, observing the self-water-absorption oil-discharge process of the sample under the action of wettability, normally descending the liquid level of water, ascending the oil level and descending the resistance of the sample. If the resistance curve changes less than 1 Ω in 8 hours, the self-priming oil drainage process is deemed to be complete, the sample resistivity Rt2 is recorded, the change in resistivity Δ Ro1 is determined as Rt1-Rt2, and the amount of oil drained at the oil end of the U-tube is read off as Vo 1.
Step S106, the water flooding is to determine the volume of movable oil and enable the sample to have the conditions of self-oil-absorption and water-drainage. Using formation water to displace crude oil in the sample at constant flow at the lower end of the holder, displacing the crude oil into 5% of the pore volume each time, and driving 5% of water after the resistance is balanced; or observing the liquid level change at the end, stopping driving when the liquid level starts to rise, driving again after the equal resistance is stabilized until the resistivity is stabilized at the same value Rt3 after the two water drives, considering that the sample reaches the residual oil state, and recording the change amount delta Ro2 of the resistivity of the sample as ABS (Rt2-Rt 3); the volume of oil discharged, Vo2, was metered and the remaining oil saturation was calculated.
Step S107, closing the upper end valve, opening the lower end injection valve and the lower end emptying valve, replacing the formation water in the pipeline and the porous plate with crude oil, if only 'oil does not flow out' in the lower return pipe, the resistivity of the sample is almost unchanged or slightly increased, considering that the water at the bottom end of the sample is completely replaced by the oil, the crude oil is in the inlet (lower) end pipeline, the water is in the outlet (upper) end pipeline, adjusting the oil-water interface position in the U-shaped metering pipe to be consistent with the lower end surface of the sample, and recording the resistivity Rt4 at the moment. Observing the change of the resistivity and the water level at the outlet end, if the resistance of the sample rises and the water level at the outlet end rises, indicating that the sample is undergoing self-priming drainage, waiting until the resistivity of the sample is stable, and the change amount in 8 hours is less than 1 omega, considering that the self-priming drainage process is finished, recording the resistivity of the sample Rt5 and the volume Vw1 of the drainage water in the metering pipe, and calculating the resistivity change amount delta Rw1 which is equal to (Rt4-Rt 5).
And S108, determining the volume of movable water in the secondary oil drive, replacing water in a pipeline at the upper end of the holder with crude oil, displacing and injecting the crude oil into a sample containing residual oil until the water is bound, monitoring the resistivity change of the sample at different oil drive speeds, increasing the resistance at the beginning of the oil drive, slowly increasing the resistance, reducing the resistance after stopping the oil drive, repeating the steps for multiple times, and if the resistivities after stopping the oil drive for multiple times are close to each other, indicating that the sample reaches the water bound state. The sample resistivity Rt6 was recorded, as well as the driven water volume Vw2 in the metering tube, and the change in resistivity Δ Rw2 was calculated (Rt5-Rt 6).
Step S109, calculating and distinguishing the wettability index, the invention provides two groups of indexes reflecting the rock wettability: a resistance method wettability index and a self-priming method wettability index.
Resistance method water-wet index: iw ═ Δ Ro1/(Δ Ro1+ Δ Ro 2);
resistance method oil wet index: io ═ Δ Rw1/(Δ Rw1+ Δ Rw 2);
relative wetting index of resistance method: ir ═ Iw-Io.
Reference table for evaluating wettability of reservoir rock by resistance method relative wetting index
The water wet index was calculated (similar to the Amott method) from the self-priming discharge level change: ww Vo1/(Vo1+ Vo 2);
self-priming oil wet index: wo ═ Vw1/(Vw1+ Vw 2).
Self-priming relative wetting index (Amott index): ia is Ww-Wo.
Self-priming method relative wetting index evaluation reservoir rock wettability reference table
Example two
The embodiment of the invention also provides an experimental device for measuring the rock wettability by a resistance method. As shown in fig. 2, the apparatus may include:
firstly, a rock core holder; the pressure environment of rock sample under stratum condition can be simulated, and the parameters of resistance, temp. and pressure can be measured, and said equipment is formed from high-pressure kettle, pressure-applying cylinder, probe, temp. sensor, electrode system, rubber sleeve and valve. Two power supply electrodes and two measuring electrodes are arranged in the core holder, the probe can accurately measure the resistance change of two ends of a sample, the probe is vertically installed when measuring wettability, a lower probe is a fixed probe relative to an axial pressure force application probe, a resistor and a temperature sensor are installed in the fixed probe, and the position of the lower end face of the sample can be indicated on the holder shell. The clamper can rotate within 90 degrees, and is adjusted from a horizontal type to a vertical type, or vice versa.
Porous plate: the conductive porous metal plate, usually installed between the sample and the lower probe, facilitates the exchange and removal of the self-priming fluid, resulting in a larger self-priming exchange area for the sample.
③ six-way valve: the system uses at least 3 six-way valves. A first control shaft confining pressure system; the second controls the operations of fluid injection, self-suction, replacement, cleaning, balance and the like at the lower end of the clamp; and the third controls the operations of fluid injection, discharge, replacement, cleaning, balancing and the like at the upper end of the clamp holder.
Fourthly, the pressure sensor: the system uses at least 4 pressure sensors. The device comprises a shaft pressure sensor, a confining pressure sensor, a sample upper end pressure sensor and a sample lower end pressure sensor. The pressure sensors at the upper end and the lower end of the sample are high-precision monocrystalline silicon sensors with temperature compensation.
Evacuation valve: the system uses 2 emptying valves, an upper end emptying valve and a lower end emptying valve, so that the fluid at the upper end and the lower end of the holder can be conveniently replaced, cleaned and balanced, and meanwhile, an oil-water interface in the U-shaped metering pipe is adjusted to keep the oil-water interface at the same position with the lower end surface of the sample.
Sixthly, stratum water container: a piston-type intermediate container, which is pressure resistant, provides a saturated fluid, typically formation water, to the sample.
Seventh, crude oil container: a piston-type intermediate container, which is resistant to a certain pressure, provides a displacement fluid, typically crude oil, to the sample.
Eigh, the metering pipe communicating valve: and a valve connected between the upper metering pipe and the lower metering pipe in the U-shaped metering pipe is convenient for adjusting the position of the oil-water interface to be consistent with the position of the lower end surface of the sample.
Ninthly U-shaped metering pipe, which is a U-shaped pipe with a valve, wherein ninthly-1 is an upper metering pipe, and ninthly-2 is a lower metering pipe. The upper and lower metering tubes are filled with different types of fluids in different self-priming and displacement stages. Because of the different densities of oil and water, the liquid columns that produce the same pressure are different in height. The oil-water interface in the metering tube must be adjusted to be consistent with the position of the lower end of the sample on the clamp.
The R RLC bridge and the computer acquisition control system: the system comprises an RLC bridge, a computer, a sensor compensation circuit, a multi-way switch and measurement and control software. All parameters relevant to the experiment were recorded and displayed, and analyzed and prompted in real time.
Claims (4)
1. A method for measuring rock wettability by a resistance method is characterized by providing consistent and stable measuring conditions; monitoring the resistance change of the rock sample in the whole measuring process; replacing the fluid in the sample inlet pipeline with injection fluid, and keeping the interface of the injection fluid between the sample and the electrode to form a self-priming condition; monitoring rock resistance change and U-shaped metering tube liquid level change in the self-priming process, establishing corresponding resistance wetting index and wettability judging standards according to the relative change of the sample resistivity in different stages, wherein the U-shaped metering tube liquid level change represents the volume discharged by the Amott self-priming, and establishing corresponding volume wetting index and wettability judging standards;
the measuring device adopted by the method comprises a rotatable core holder, a porous plate, a first six-way valve, a second six-way valve, a third six-way valve, a first pressure sensor, a second pressure sensor, a third pressure sensor, a fourth pressure sensor, a first emptying valve, a second emptying valve, a formation water container, a crude oil container, a metering pipe communicating valve, a U-shaped metering pipe, an RLC electric bridge, a computer acquisition control system, an axial pressure confining pressure control system, a high-pressure advection pump and a thermostat; the core holder comprises an autoclave, a pressurizing cylinder, a probe, a temperature sensor, an electrode system, a rubber sleeve and a valve, wherein the probe is of a double-tube structure, two power supply electrodes and two measuring electrodes are arranged in the core holder, the probe can accurately measure resistance changes at two ends of a sample, the vertical installation is adopted when the wettability is measured, the lower probe is a fixed probe relative to the axial pressure pressurizing probe, the resistance and the temperature sensor are arranged in the fixed probe, the position of the lower end face of the sample can be indicated on the shell of the core holder, the core holder can rotate within a 90-degree range, and the horizontal adjustment is vertical;
the first port of the first six-way valve is connected with the second pressure sensor through a pipeline, the second port of the first six-way valve is connected with the core holder through a pipeline, the third port of the first six-way valve is connected with the first pressure sensor through a pipeline, the fifth port of the first six-way valve is connected with the shaft pressure confining pressure control system through a pipeline, and the first six-way valve is used for controlling the shaft confining pressure control system;
a first port of a second six-way valve is connected with a third pressure sensor through a pipeline, a second port of the second six-way valve is connected with a metering pipe communicating valve through a pipeline, a third port of the second six-way valve is connected with the core holder through a pipeline, a fourth port of the second six-way valve is connected with a crude oil container through a pipeline, and the second six-way valve is used for controlling the injection, discharge, replacement, cleaning and balance operation of fluid at the upper end of the core holder;
a first port of a third six-way valve is connected with the crude oil container through a pipeline, a second port of the third six-way valve is connected with the formation water container through a pipeline, a third port of the third six-way valve is connected with a fourth pressure sensor through a pipeline, a fifth port of the third six-way valve is connected with a metering pipe communicating valve through a pipeline, a sixth port of the third six-way valve is connected with the core holder through a pipeline, and the third six-way valve is used for controlling the injection, self-absorption, replacement, cleaning and balance operation of fluid at the lower end of the core holder;
the first emptying valve is connected to the upper end of the core holder through a pipeline, so that fluid at the upper end of the core holder can be replaced, cleaned and balanced conveniently;
the second emptying valve is connected to the lower end of the core holder through a pipeline, so that the fluid at the lower end of the core holder can be replaced, cleaned and balanced conveniently;
the metering pipe communicating valve is connected with an upper metering pipe and a lower metering pipe in the U-shaped metering pipe and is connected with the second six-way valve and the third six-way valve through pipelines;
the high-pressure constant-flow pump is connected with the crude oil container and the formation water container through pipelines to provide constant flow and stable pressure;
the RLC bridge and the computer acquisition control system are connected with each pressure sensor and the rock core holder through signal control lines, record and display all parameters related to the experiment, and perform real-time analysis and prompt;
the constant temperature box is customized according to the size and the placement mode of the core holder, and the core holder, the second six-way valve, the third six-way valve, the formation water container and the crude oil container are all arranged inside the constant temperature box;
the crude oil container is a piston type intermediate container which can resist certain pressure and provides displacement fluid for a sample, and the displacement fluid is crude oil;
the formation water container is a piston type middle container which can resist certain pressure and provides saturated fluid for the sample, and the saturated fluid is formation water
The method specifically comprises the following steps:
step S101, a sample for measuring rock wettability is a plunger sample, the diameter of the sample is required to be larger than the length of the sample, the sample with the diameter of 3.81 centimeters is taken, and the axial pressure, the confining pressure and the temperature for experiments are determined according to the buried depth of the sample;
step S102, sample preparation comprises sample processing, oil washing, salt washing, solution preparation and sample saturation, and formation water is used as a saturated solution;
step S103, horizontally installing a core holder, wherein the upper end of the core holder is an outlet end and is provided with an upper end valve, the lower end of the core holder is an inlet end and is provided with a lower end valve, the upper end of the core holder is connected to a third six-way valve and an upper end emptying valve through pipelines, the lower end of the core holder is connected to a first six-way valve, a second six-way valve and a lower end emptying valve through pipelines, and measuring the water-containing resistivity R0 of a rock sample under the condition of simulating a stratum; injecting formation water with 2-3 times of pore volume from the inlet end to ensure that no bubbles are discharged from the sample, and measuring the resistivity R0 of the sample by a four-electrode method, wherein the measuring frequency is 1 KHz;
s104, slowly injecting crude oil at constant pressure, discharging water in a sample through the outlet end of a core holder, determining the volume of the discharged water by using an upper metering pipe of a U-shaped metering pipe, calculating the oil saturation degree of the sample, when the increment of the resistivity of the sample in 1 hour is less than 1 omega, considering that the bound water state is achieved, closing a lower end valve, redistributing oil and water, waiting for resistance balance, considering that the sample is completely aged if the resistivity variation in 8 hours is less than 1 omega, recording the resistivity of the sample Rt, and calculating the saturation degree of the bound water;
s105, adjusting the core holder from horizontal to vertical, placing a sample in the core holder, installing a porous plate between the sample and a lower probe of the core holder, starting self-water-absorption and oil-discharge, replacing crude oil at the lower end of the core holder with formation water, and keeping an oil interface between the sample and the porous plate, wherein a double-pipe structure on the probe is utilized, the crude oil in a pipeline at the lower end is cleaned by an organic solvent, then the cleaning liquid in the pipeline is discharged by the formation water, a valve is closed, the heights of a water column and an oil column in a U-shaped metering tube are adjusted, so that the oil-water interface is consistent with the lower end surface of the sample in height, the corresponding valve is opened, the height of the water column in the U-shaped metering tube is adjusted to be 1-2mm higher than the lower end surface of the sample, the process is only that the oil-water interface is moved into the sample from the contact surface of the lower probe and the sample, and a resistance curve is quickly lowered along with the entering of water at an injection end, recording the resistivity Rt1 at the moment, keeping the measuring condition unchanged, observing the self-water-sucking and oil-discharging process of the sample under the action of wettability, wherein the water liquid level is reduced, the oil liquid level is increased, the resistance of the sample is reduced, if the variation of a resistance curve in 8 hours is less than 1 omega, the self-water-sucking and oil-discharging process is considered to be finished, recording the resistivity Rt2 of the sample, determining the variation delta Ro1 of the resistivity to be Rt1-Rt2, and reading the discharged oil volume Vo1 at the oil end of the U-shaped measuring tube;
step S106, water flooding is to determine the volume of movable oil, so that a sample has the conditions of self-oil-absorption and water-drainage, crude oil in the sample is displaced by formation water at the lower end of the rock core holder in a constant flow mode, the crude oil is displaced into 5% of the pore volume each time, and 5% of water is displaced after resistance is balanced; or observing the liquid level change at the end, stopping driving when the liquid level starts to rise, driving again after the equal resistance is stabilized until the resistivity is stabilized at the same value Rt3 after the two water drives, considering that the sample reaches the residual oil state, and recording the change amount delta Ro2 of the resistivity of the sample as ABS (Rt2-Rt 3); measuring the volume Vo2 of the discharged oil, and calculating the saturation degree of the residual oil;
step S107, closing the upper end valve, opening the lower end valve, replacing the stratum water in the pipeline and the porous plate with crude oil, if "oil only and no water out" is in the lower metering tube, the resistivity of the sample hardly changes or slightly rises, it is considered that the water at the bottom end of the sample has been completely replaced by oil, then crude oil is in the inlet pipeline, water is in the outlet pipeline, the oil-water interface position in the U-shaped metering pipe is adjusted to be consistent with the lower end face of the sample, the resistivity Rt4 at the moment is recorded, the resistivity of the sample and the change of the outlet water level are observed, if the resistance of the sample rises and the water level at the outlet end rises, the sample is subjected to self-oil-absorption drainage until the resistivity of the sample tends to be stable, the amount of change in 8 hours is less than 1 Ω, the self-priming drainage process is considered to be complete, the sample resistivity Rt5 and the drainage water volume Vw1 in the U-shaped metering tube are recorded, and the sample resistivity change Δ Rw1 ═ is calculated (Rt4-Rt 5);
step S108, determining the volume of movable water in the secondary oil drive, replacing water in a pipeline at the upper end of the core holder with crude oil, injecting the crude oil into a sample containing residual oil from the upper end until the water is bound, monitoring the resistivity change of the sample at different oil drive speeds, increasing the resistance at the beginning of the oil drive, slowly increasing the resistance, reducing the resistance after stopping the oil drive, repeating the steps for multiple times, and if the resistivities after stopping the oil drive for multiple times are close to each other, indicating that the sample reaches the water bound state;
step S109, establishing corresponding calculation and judgment of the resistivity wetting index and the wettability, and providing two groups of indexes reflecting the rock wettability: a wettability index by a resistance method and a wettability index by a self-priming method,
the method specifically comprises the following steps:
and calculating the resistivity method wettability index of the rock by the following formula:
step A, calculating by the following formula to generate the resistance method water-wet index of the rock:
Iw＝ΔRo1/(ΔRo1+ΔRo2)，
in the formula, Iw is a resistance method water-moisture index, delta Ro1 is the resistivity variation in the process of self-water absorption and oil drainage, and delta Ro2 is the resistivity variation in the process of water displacement to residual oil;
and step B, calculating by the following formula to generate the oil-moisture index of the rock by a resistance method:
Io＝ΔRw1/(ΔRw1+ΔRw2)，
in the formula, Io is an oil-wet index of a resistance method, delta Rw1 is the resistivity variation in the self-oil-absorption and water-drainage process, and delta Rw2 is the resistivity variation in the secondary oil-displacement process;
obtaining a calculation formula of a relative wetting index of a resistance method:
Ir＝Iw-Io，
calculating the self-priming wettability index of the rock by the following formula:
step C, calculating by the following formula to generate the self-priming water-wet index of the rock:
Ww＝Vo1/(Vo1+Vo2)，
in the formula, Ww is a self-priming water-wet index, Vo1 is the volume of oil discharged in the process of self-priming oil discharge, and Vo2 is the volume of oil discharged in the process of oil displacement from water to residual oil;
and D, calculating by the following formula to generate the self-priming oil wet index of the rock:
Wo＝Vw1/(Vw1+Vw2)，
in the formula, Wo is the oil humidity index of the self-priming method, Vw1 is the volume of water discharged in the self-priming oil drainage process, and Vw2 is the volume of water discharged in the secondary oil flooding process;
obtaining a calculation formula of the relative wetting index of the self-priming method:
Ia＝Ww-Wo。
2. the method for measuring the rock wettability by the electrical resistance method according to claim 1, wherein a horizontal displacement and vertical self-absorption mode of a core holder is adopted.
3. The method of claim 1, wherein the porous plate is a conductive porous metal plate, and is installed between the sample and the lower probe to facilitate the exchange and removal of the self-priming fluid, thereby providing the sample with a larger self-priming exchange area.
4. The method for measuring rock wettability by using a resistivity method according to claim 1, wherein the RLC bridge and the computer acquisition control system comprise the RLC bridge, a computer, a sensor compensation circuit, a multi-way switch and measurement and control software, and all parameters related to the experiment are recorded and displayed, and are analyzed and prompted in real time.
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