Tidal effect monitoring experiment system and method based on distributed optical fiber strain sensing

Abstract

The invention belongs to the technical field of oil exploitation, and particularly relates to a tidal effect monitoring experiment system and experiment method based on distributed optical fiber strain sensing, and the tidal effect monitoring experiment system based on distributed optical fiber strain sensing can reproduce the tidal effect and reservoir characteristics. And the response process of each layer section in the well under the tidal action is really simulated. According to the tidal effect monitoring experiment system based on distributed optical fiber strain sensing, strain change of each layer section in a well caused by reservoir strain change in different tidal effect processes can be simulated more truly, response characteristics and response rules of different reservoirs are obtained, and theoretical and method support is provided for analyzing field well testing data.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil exploitation, and particularly relates to a tidal effect monitoring experiment system and experiment method based on distributed optical fiber strain sensing. BACKGROUND

[0002] The influence of tidal effect on well bottom pressure is often non-negligible in offshore oil and gas field testing, especially in shallow sea area testing. Tides are a natural phenomenon occurring in coastal areas, which is the periodic rising and falling of sea level caused by the gravity of celestial bodies (mainly the moon and the sun) and the rotation of the earth. The phenomenon of tides is mainly affected by the relative motion between the moon and the earth, and the distance between the moon and the earth. The place directly opposite the moon is affected by the gravity, and the seawater expands outward. Tidal types can be divided into semi-diurnal, diurnal and mixed types according to the period. The semi-diurnal type refers to two high tides and two low tides in a solar day, and the tidal range of the first high tide and low tide is approximately the same as that of the second high tide and low tide, and the time of the rising tide process and the falling tide process is also almost equal. The diurnal type refers to only one high tide and one low tide in a solar day, such as Shantou in the South China Sea, Qinhuangdao in the Bohai Sea and the Beibu Gulf in the South China Sea, which are typical diurnal tide areas in the world. The mixed type refers to some time in a month appearing two high tides and two low tides, but the tidal range of the two high tides and low tides is quite different, and the time of the rising tide process and the falling tide process is also not equal; while at other times, there is only one high tide and one low tide.

[0003] When the formation of an offshore oil and gas well is tested, the seabed pressure is transmitted to the reservoir through the overlying rock, causing the reservoir pressure to be unstable, and thus causing abnormal fluctuations in the pressure test data. Especially in shallow high-permeability reservoirs, the amplitude of pressure fluctuation may reach several psia. In addition, the degree of influence of well bottom pressure by tidal effect is also related to the reservoir properties, rock properties and fluid parameters.

[0004] Tidal compression of the reservoir pore causes the reservoir fluid to enter the well. Combining the change of well fluid level with the change of tide with other geological information can be used to estimate the reservoir compressibility and permeability. The volume strain of the reservoir skeleton affects the pore pressure response, and thus affects the well fluid level response. The change of fluid level driven by tides is particularly useful for characterizing the permeability of reservoir fractures. From the well fluid level change data, information about the geomechanical properties and fracture direction can be inferred. However, in actual production, a well may penetrate multiple intervals, and the traditional well fluid level change or well bottom pressure change measurement is the integrated result of multiple intervals, and it is difficult to distinguish the true response of each interval. In addition, the traditional measurement technology is usually single-point measurement, and can only measure the interval determined in advance by other logging techniques. Therefore, a new means is needed to realize the tidal effect measurement of multiple intervals, and to provide support for accurately understanding the reservoir characteristics. SUMMARY

[0005] The application aims to provide a tidal effect monitoring experimental system and experimental method based on distributed optical fiber strain sensing, which utilizes a piston rod, a driving connecting rod and a rotating disc to form a connecting rod mechanism to drive a plunger to move up and down in a reaction container to simulate tidal effects, and the tidal effects act on the surface of a core through sieve holes, and a steel armored optical cable is used to measure the strain change in a through hole in the core under the influence of the tidal effects.

[0006] The technical problem to be solved by the application is solved by the following technical scheme: a tidal effect monitoring experimental system based on distributed optical fiber strain sensing, comprising a reaction container, a reservoir simulation system, a tidal simulation system and a strain measurement system. The reservoir simulation system is arranged in the reaction container and comprises a sieve core barrel and a core, the core is arranged vertically in the sieve core barrel, the top and bottom of the core are arranged in close contact with the top cover and bottom cover of the sieve core barrel, the top cover and bottom cover of the sieve core barrel are made of impermeable material, the side wall of the sieve core barrel is provided with sieve holes, and a through hole is arranged in the core along the axial direction. The tidal simulation system comprises a sliding rail, a plunger, a piston rod, a driving connecting rod, a rotating disc and a variable frequency driving motor, the sliding rail is arranged vertically in the reaction container, the plunger is arranged to be slidable up and down on the sliding rail, the piston rod is arranged vertically on the upper end of the plunger, the piston rod is arranged to be slidable up and down on the top end of the reaction container, and the two ends of the driving connecting rod are respectively hingedly connected to the plunger and the rotating disc. The variable frequency driving motor is used to drive the rotating disc to rotate around the center, and the driving connecting rod is arranged to be detachable on the side of the rotating disc away from the center. The strain measurement system comprises a steel armored optical cable and a distributed optical fiber strain sensing demodulator, the steel armored optical cable is arranged vertically in the through hole in the core and is connected to the distributed optical fiber strain sensing demodulator through the reaction container. A gap is arranged between the outer wall of the sieve core barrel and the inner wall of the reaction container, a liquid working medium is arranged in the reaction container, and the liquid level of the liquid working medium is higher than the sieve core barrel and the sliding rail.

[0007] Preferably, the core is a man-made cylindrical core, and the liquid working medium is water or hydraulic oil.

[0008] Preferably, the core is a single-layer core with homogeneous, heterogeneous, fractured or faulted single attribute or a multi-layer core with homogeneous, heterogeneous, fractured or faulted multiple attributes.

[0009] Preferably, the slide rail is vertically fixed on the top of the screen core barrel. The slide rail is arranged on the top of the screen core barrel, and the plunger is used to exert the tidal effect on the liquid working medium above the screen core barrel, so as to simulate the influence of the tidal effect on the reservoir pressure.

[0010] Preferably, the slide rail is two parallel rails, and the plunger is provided with a groove matched with the two rails. The plunger is arranged between the two parallel rails, and the rails provide a guide for the up-down reciprocating movement of the plunger, effectively maintaining the stability of the plunger during the up-down movement.

[0011] Preferably, the side wall of the core is gap-fitted or in contact with the side wall of the screen core barrel.

[0012] Preferably, the rotating disc is provided with a plurality of fixed holes at different distances from the center in the radial direction, and the end of the driving link is hinged with a connecting lock block which is detachably arranged in the fixed hole on the rotating disc. By adjusting the position of the connecting lock block on the rotating disc, a sinusoidal motion with different amplitudes can be simulated.

[0013] The application further discloses a tidal effect monitoring experiment method based on a distributed optical fiber strain sensing, which utilizes the above-mentioned tidal effect monitoring experiment system based on a distributed optical fiber strain sensing and comprises the following steps. S1, a core model is made, the tidal effect monitoring experiment system based on a distributed optical fiber strain sensing is assembled, and a liquid working medium higher than the screen core barrel is injected into the reaction container; S2, the variable frequency driving motor is started and adjusted to a predetermined frequency, the plunger is driven to make up-down reciprocating movement on the slide rail, the liquid working medium in the reaction container is driven to simulate the tidal effect, the tidal effect of the liquid working medium acts on the core through the screen holes around the screen core barrel, and the distributed optical fiber strain sensing demodulator collects strain distribution values along the height direction of the core in the through hole in real time through the steel armored optical cable; S3, after the experiment is completed, the strain data collected by the distributed optical fiber strain sensing demodulator are exported, and the strain distribution and frequency distribution along the height direction of the core are drawn; S4, the distance between the driving link and the center of the rotating disc is changed, and the step S2 is repeated to obtain strain amplitudes and frequency distributions under different tidal amplitudes; S5, change the frequency of the variable frequency drive motor, repeat step S2, get the strain amplitude and frequency distribution under different tidal amplitude and different tidal frequency.

[0014] The application preferably changes the type of core in step S1 to obtain the response characteristics and response rules of different reservoirs.

[0015] The application preferably, after assembling in step S1, starts the distributed optical fiber strain sensing demodulator, and measures the positioning point by knocking the steel armor optical cable at the outlet of the reaction container.

[0016] During the experiment, the variable frequency drive motor drives the rotating disc to rotate around its center, which in turn drives the drive connecting rod to make a sinusoidal motion and transmits the sinusoidal motion to the piston rod, thereby driving the plunger to move up and down along the slide rail in a straight line. The up and down reciprocating linear motion of the plunger drives the tidal effect of the liquid working medium in the reaction container, which is transmitted to the core through the screen holes around the screen core barrel. The steel armor optical cable embedded in the core through the inner hole senses the tidal effect and collects the strain signal in real time through the distributed optical fiber strain sensing demodulator.

[0017] The variable frequency drive motor can simulate multiple tidal frequencies, and only one tidal frequency can be simulated at a time when the variable frequency drive motor is working.

[0018] Compared with the prior art, the application has the following advantages: (1) The tidal effect monitoring experimental system based on distributed optical fiber strain sensing constructed by the application can reproduce the tidal effect and reservoir characteristics, and truly simulate the response process of each layer in the well under the action of the tide.

[0019] (2) The application uses distributed optical fiber strain sensing technology to realize the monitoring of tidal effects in the well, providing a new monitoring method for studying the influence of tides in the well.

[0020] (3) The tidal effect monitoring experimental system based on distributed optical fiber strain sensing can more realistically simulate the strain changes of each layer in the well caused by the strain changes of the reservoir in different tidal effect processes, obtain the response characteristics and response rules of different reservoirs, and provide theoretical and methodological support for analyzing field testing data. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The application provides a schematic diagram of the tidal effect monitoring experimental system based on distributed optical fiber strain sensing; Figure 2 The connection structure of the rotating disc, the drive connecting rod and the piston rod is shown in the connection structure schematic diagram of the track and the plunger. Figure 3 The connection structure of the rotating disc, the drive connecting rod and the piston rod is shown in the connection structure schematic diagram of the track and the plunger. Figure 4 A schematic diagram of strain in each section of the wellbore obtained by distributed fiber optic strain sensing. Figure 5 A schematic diagram of the frequencies of each section of the wellbore obtained by distributed fiber optic strain sensing; In the figure, reaction vessel 1, perforated core cylinder 2, core 3, core through-hole 31, slide rail 4, plunger 5, piston rod 6, drive connecting rod 7, rotating disk 8, variable frequency drive motor 9, steel armored optical cable 10, and distributed fiber optic strain sensor demodulator 11. Track 41, groove 51, fixing hole 81, connecting lock block 71. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0023] Example 1 like Figures 1-3 As shown, an experimental system for monitoring tidal effects based on distributed optical fiber strain sensing includes a reaction vessel 1, a reservoir simulation system, a tidal simulation system, and a strain measurement system.

[0024] The reservoir simulation system is housed within the reaction vessel 1 and includes a perforated core cylinder 2 and a core 3. The core 3 is vertically positioned within the perforated core cylinder 2, with its top and bottom fitting snugly against the top and bottom covers of the perforated core cylinder 2. The top and bottom covers of the perforated core cylinder 2 are made of impermeable material. The sidewalls of the perforated core cylinder 2 are provided with perforations that are evenly distributed. A core-penetrating inner hole 31 is axially located at the center of the core 3. The core-penetrating inner hole 31 is located at the center of the core 3 and extends axially through the entire core, providing a deployment channel for the steel-armored optical cable 10. During operation, the liquid working medium permeates through the core 3 and fills the core-penetrating inner hole 31.

[0025] The liquid working medium directly contacts the perimeter of core 3 through the sieve holes, so that the tidal effect is uniformly applied to core 3.

[0026] The tidal simulation system includes a slide rail 4, a plunger 5, a piston rod 6, a drive connecting rod 7, a rotating disk 8, and a variable frequency drive motor 9. The slide rail 4 is vertically arranged inside the reaction vessel 1. The plunger 5 is slidably mounted on the slide rail 4. The piston rod 6 is vertically arranged above the plunger 5 and slidably mounted at the top of the reaction vessel 1. The two ends of the drive connecting rod 7 are hinged to the plunger 5 and the rotating disk 8, respectively. The piston rod 6 drives the plunger 5 to reciprocate up and down along the slide rail 4 inside the reaction vessel 1, applying a tidal effect to the core 3 in the reservoir simulation system.

[0027] The variable frequency drive motor 9 is used to drive the rotating disk 8 to rotate around the center. The drive linkage 7 is detachably installed on the side of the rotating disk 8 off-center. In this embodiment, the rotating disk 8 is rotatably mounted on the bracket via a rotating shaft. The variable frequency drive motor 9 drives the rotating shaft to rotate, thereby realizing the rotation of the rotating disk 8.

[0028] The strain measurement system includes a steel-armored optical cable 10 and a distributed optical fiber strain sensor demodulator 11. The steel-armored optical cable 10 is vertically installed inside the core penetration hole 31 and passes through the reaction container 1 to connect with the distributed optical fiber strain sensor demodulator 11. It is used to measure the strain changes in the core penetration hole 31 under the influence of tidal effects.

[0029] A gap is provided between the outer wall of the perforated core cylinder 2 and the inner wall of the reaction container 1. The reaction container 1 is filled with a liquid working medium, and the liquid level of the liquid working medium is higher than that of the perforated core cylinder 2 and the slide rail 4.

[0030] The core 3 is an artificial cylindrical core, and the liquid working medium is water or hydraulic oil.

[0031] The core sample 3 is a single-layer core with a single attribute (homogeneous, heterogeneous, fractured, or fault-containing), or a multi-layer core with multiple attributes (homogeneous, heterogeneous, fractured, or fault-containing, with any combination of these attributes). The core preparation method is existing technology and will not be described in detail here.

[0032] The slide rail 4 is vertically fixed at the top of the sieve core cylinder 2.

[0033] like Figure 3 As shown, the slide rail 4 consists of two parallel tracks 41, and the plunger 5 has grooves 51 that match the tracks on both sides. In this embodiment, the plunger 5 is cylindrical.

[0034] The sidewall of the core 3 is either in clearance fit or in contact with the sidewall of the sieve core cylinder 2.

[0035] like Figure 2 As shown, the rotating disk 8 is provided with a plurality of fixing holes 81 at different distances from the center along the radial direction, and the end of the drive connecting rod 7 is hinged with a connecting locking block 71. The connecting locking block 71 is detachably set in the fixing holes 81 on the rotating disk 8 by bolts, screws or pins.

[0036] An experimental method for monitoring tidal effects based on distributed optical fiber strain sensing, utilizing the tidal effect monitoring experimental system based on distributed optical fiber strain sensing described in this embodiment, includes the following steps: S1. Fabricate core model 3. In this embodiment, core model 3 is a single frequency, heterogeneous, two-stage reservoir. Assemble the tidal effect monitoring experimental system based on distributed optical fiber strain sensing and inject liquid working medium higher than the sieve core tube 2 into reaction vessel 1.

[0037] Specifically, firstly, the top cover of the perforated core cylinder 2 is opened, and the core model 3 is placed inside the perforated core cylinder 2; secondly, the steel-armored optical cable 10 is vertically arranged inside the core penetration hole 31 and led out from the top cover of the perforated core cylinder 2; thirdly, liquid working medium is injected into the core penetration hole 31, and the top and bottom covers of the perforated core cylinder 2 are tightened with bolts to press the top and bottom ends of the core 3, and then the penetration hole of the steel-armored optical cable 10 through the top cover of the perforated core cylinder 2 is sealed with a rubber cap; fourthly, the assembled reservoir... The simulation system is placed inside the reaction vessel 1 and fixed to the bottom of the reaction vessel 1; fifth, connect the plunger 5 and the piston rod 6, align the grooves 51 on both sides of the plunger 5 with the track 41 and slide it down to the bottom of the track 41; sixth, lead the armored optical cable 10 out of the reaction vessel 1 and connect it to the distributed fiber optic strain sensor demodulator 11; seventh, inject liquid working medium into the reaction vessel 1 and keep the liquid level above the top of the track 41; eighth, connect the piston rod 6 in sequence to the drive connecting rod 7, the rotating disk 8 and the frequency conversion drive motor 9.

[0038] Step S1: After assembly is completed, start the distributed fiber optic strain sensor demodulator 11 and locate the measurement point by tapping the steel armored optical cable 10 at the outlet of the reaction vessel 1.

[0039] S2. Start the variable frequency drive motor 9, adjust it to the predetermined frequency, and drive the plunger 5 to move up and down on the slide rail 4. This drives the liquid working medium in the reaction vessel 1 to simulate the tidal effect. The tidal effect of the liquid working medium acts on the core 3 through the sieve holes around the core cylinder 2. The distributed fiber optic strain sensor demodulator 11 collects the strain distribution values ​​along the height direction of the core 3 in real time through the steel armored optical cable 10 through the core through the inner hole 31.

[0040] S3. After completing the experiment, export the strain data collected by the distributed fiber optic strain sensor demodulator 11, and plot the strain distribution and frequency distribution along the height direction of core 3. For example... Figure 4 and Figure 5 As shown, the strain amplitude and frequency distribution of the two segments are obtained. Figure 4 It is a plot of the distribution of strain amplitude with location obtained by using a distributed fiber optic strain sensor demodulator. Figure 5 It is a plot of the distribution of strain frequency with location obtained by using a distributed fiber optic strain sensor demodulator.

[0041] S4. Change the distance from the drive link 7 to the center of the rotating disk 8, and repeat step S2 to obtain the strain amplitude and frequency distribution under different tidal amplitudes.

[0042] S5. Change the frequency of the variable frequency drive motor 9 and repeat step S2 to obtain the strain amplitude and frequency distribution under different tidal amplitudes and frequencies.

[0043] This embodiment allows us to study the variation patterns of strain amplitude and frequency under different tidal amplitudes and frequencies.

[0044] Example 2 Due to differences in reservoir properties, even when the same frequency and amplitude of tidal effects are applied, the resulting strain amplitude and strain frequency will differ. This embodiment differs from Embodiment 1 in that the type of core 3 in step S1 is changed to obtain the response characteristics and patterns of different reservoirs.

[0045] When studying homogeneous reservoirs with a single frequency, it is necessary to create a homogeneous core model.

[0046] When studying single-frequency, fractured reservoirs, it is necessary to create a core model with fractures.

[0047] When studying single-frequency, faulted reservoirs, it is necessary to create a core model with faults.

Claims

1. A tidal effect monitoring experimental system based on distributed fiber optic strain sensing, characterized in that: It comprises a reaction container (1), a reservoir simulation system, a tidal simulation system and a strain measurement system. The reservoir simulation system is arranged in the reaction container (1) and comprises a screen core barrel (2) and a core (3), the core (3) is arranged vertically in the screen core barrel (2), the top and bottom of the core (3) are arranged in close contact with the top cover and bottom cover of the screen core barrel (2), the top cover and bottom cover of the screen core barrel (2) are made of impermeable material, the side wall of the screen core barrel (2) is provided with a screen hole, and the center of the core (3) is provided with a core through inner hole (31) in the axial direction. The tidal simulation system comprises a slide rail (4), a plunger (5), a piston rod (6), a driving connecting rod (7), a rotating disc (8) and a variable frequency drive motor (9), the slide rail (4) is arranged vertically in the reaction container (1), the plunger (5) is arranged vertically on the slide rail (4), the piston rod (6) is arranged vertically on the upper end of the plunger (5), the piston rod (6) is arranged vertically on the top end of the reaction container (1), and the two ends of the driving connecting rod (7) are respectively hinged to the plunger (5) and the rotating disc (8). The variable frequency drive motor (9) is used for driving the rotating disc (8) to rotate around the center, and the driving connecting rod (7) is detachably arranged on the side of the rotating disc (8) deviating from the center. The strain measurement system comprises a steel armored optical cable (10) and a distributed optical fiber strain sensing demodulator (11), the steel armored optical cable (10) is arranged vertically in the core through inner hole (31) and connected to the distributed optical fiber strain sensing demodulator (11) through the reaction container (1). A gap is arranged between the outer wall of the screen core barrel (2) and the inner wall of the reaction container (1), a liquid working medium is arranged in the reaction container (1), and the liquid level of the liquid working medium is higher than that of the screen core barrel (2) and the slide rail (4).

2. The experimental system for monitoring tidal effects based on distributed fiber optic strain sensing according to claim 1, characterized in that: The core (3) is a man-made cylindrical core, and the liquid working medium is water or hydraulic oil. 3.The experimental system for monitoring tidal effect based on distributed optical fiber strain sensing according to claim 1, characterized in that: The core (3) is a single-layer core with homogeneous, heterogeneous, cracked or faulted single attribute or a multi-layer core with homogeneous, heterogeneous, cracked or faulted multiple attributes.

4. The experimental system for monitoring tidal effects based on distributed optical fiber strain sensing according to claim 1, characterized in that: The slide rail (4) is vertically fixed on the top of the screen core barrel (2).

5. The experimental system for monitoring tidal effects based on distributed optical fiber strain sensing according to claim 4, characterized in that: The slide rail (4) is composed of two parallel tracks (41), and the plunger (5) is provided with grooves (51) matched with the two tracks. 6.The experimental system for monitoring tidal effect based on distributed optical fiber strain sensing according to claim 1, characterized in that: The side wall of the core (3) is gap-fitted or in contact with the side wall of the screen core barrel (2).

7. The experimental system for monitoring tidal effects based on distributed optical fiber strain sensing according to claim 1, characterized in that: The rotating disc (8) is provided with a plurality of fixed holes (81) at different distances from the center in the radial direction, and the end of the driving connecting rod (7) is hinged with a connecting lock block (71), which is detachably arranged in the fixed hole (81) on the rotating disc (8).

8. A tidal effect monitoring experiment method based on distributed fiber optic strain sensing, characterized in that, The tidal effect monitoring experimental system based on the distributed optical fiber strain sensing according to any one of claims 1-10 comprises the following steps: S1, make core (3) model, assemble the tidal effect monitoring experimental system based on distributed optical fiber strain sensing, inject liquid working medium higher than the screen core barrel (2) into the reaction container (1); S2, start the variable frequency drive motor (9), adjust to the predetermined frequency, drive the plunger (5) to make up and down reciprocating motion in the slide rail (4), drive the liquid working medium in the reaction container (1) to simulate the tidal effect, the tidal effect of the liquid working medium acts on the core (3) through the screen hole around the screen core barrel (2), the distributed optical fiber strain sensing demodulator (11) collects the strain distribution value along the height direction of the core (3) in the core through hole (31) through the steel armored cable (10); S3, after completing the experiment, export the strain data collected by the distributed optical fiber strain sensing demodulator (11), draw the strain distribution and frequency distribution along the height direction of the core (3); S4, change the distance from the driving connecting rod (7) to the center of the rotating disc (8), repeat step S2 to get the strain amplitude and frequency distribution under different tidal amplitude; S5, change the frequency of the variable frequency drive motor (9), repeat step S2 to get the strain amplitude and frequency distribution under different tidal amplitude and different tidal frequency.

9. The experimental method for monitoring the tidal effect based on the distributed optical fiber strain sensing according to claim 8, characterized in that: Change the type of core (3) in step S1 to get the response characteristics and response rules of different reservoirs.

10. The experimental method for monitoring tidal effects based on distributed optical fiber strain sensing according to claim 8, characterized in that: Step S1, after completing the assembly, start the distributed optical fiber strain sensing demodulator (11), knock the steel armored cable (10) at the outlet of the reaction container (1) to locate the measurement point.

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