CN115032337A - Maximized CO 2 Brine pre-pumping amount and reinjection amount calculation method for sealing efficiency and site test verification method - Google Patents
Maximized CO 2 Brine pre-pumping amount and reinjection amount calculation method for sealing efficiency and site test verification method Download PDFInfo
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Abstract
The invention belongs to CO 2 The field of geological sequestration, and relates to maximized CO 2 A method for calculating the pre-pumping amount and the reinjection amount of the brine with the sealing efficiency and a site test verification method, and provides a method for improving CO 2 The pre-pumping-reinjection method of the sealing efficiency respectively takes the calculated pre-pumping amount and reinjection amount of the saline water as CO 2 Controlling conditions of actual saline extraction and reinjection in the sealing process, and simultaneously establishingStand for CO 2 Relation between injection speed and saline extraction speed, saline reinjection speed and CO 2 Injection velocity relationship. Maximized CO designed by the invention 2 The field test verification method and device for the sealing efficiency verify that the precision of the calculation method exceeds 95% compared with a field test; the brine pre-pumping and reinjection strategies are implemented by calculating the brine pre-pumping amount and the reinjection amount, and compared with a conventional sealing test, the sealing capacity is improved by 25%, and the sealing safety is improved by 20%.
Description
Technical Field
The invention belongs to CO 2 The field of geological sequestration, and relates to a maximized CO 2 A method for calculating the pre-pumping amount and the reinjection amount of the brine with the sealing efficiency and a site test verification method.
Background
CO 2 Geological sequestration has become the focus of current research, particularly maximizing CO 2 Geological sequestration efficiency has become an important factor. CO 2 2 The sealing efficiency is closely related to the sealing capability and the sealing safety. To increase CO 2 Sequestration capacity, can be in CO 2 Pre-extraction of brine to increase CO prior to injection into brine layers 2 And (4) storing space. However, pre-pumping brine will reduce formation pore pressure and very easily induce formation collapse. In addition, in CO 2 After injection, the formation pore pressure rises rapidly from low pressure (due to brine pre-pumping) to high pressure, which in turn causes the formation to swell and even fracture. To address the formation fracture issue, the extracted brine may be reinjected into the upper adjacent brine layer, mitigating formation swelling deformation caused by the lower formation pore pressure rise. Meanwhile, the re-injection of the pre-pumped saline water can also save a complex saline water treatment process and save high saline water treatment cost. In summary, brine pre-pumping and re-injection can increase CO 2 Geological sequestration capacity and containment safety, however, implementation of this strategy requires calculation of saline pre-pump and re-fill volumes. The amount of brine pre-pumping is controlled by formation collapse conditions and the amount of brine re-injection is controlled by formation fracture conditions. In view of this, it is desirable to maximize CO 2 The method for calculating the pre-pumping amount and the reinjection amount of the brine with the sealing efficiency is used, and the reliability of the calculation method in practical application is verified through a field test.
Currently, a few experimental devices for simulating CO are developed by scholars 2 Geological sequestration, e.g. CO simulation by an experiment 2 System for feasibility of geological sequestration (CN202010239445.0), a CO 2 Formation sealStorage system (CN202020387776.4), a CO 2 Methods and systems for formation sequestration (CN 202010215234.3). However, the above experimental setup mainly simulates CO 2 The migration rule in the saline water layer is difficult to evaluate the CO pre-pumping and reinjection of the saline water 2 The effect of sequestration efficiency is less likely to determine the specific saline pre-draw and saline refill volumes. In view of this, a method for maximizing CO is proposed 2 The calculation method of the saline water pre-pumping amount and the reinjection amount of the sealing efficiency and the field test verification are imperative.
Disclosure of Invention
The invention provides a method for maximizing CO 2 The method for calculating the pre-pumping amount and the reinjection amount of the brine with the sealing efficiency and the site test verification method calculate the pre-pumping amount and the reinjection amount of the brine under the conditions of stratum collapse and stratum rupture.
To achieve the above objects, an aspect of the present invention provides a method for maximizing CO 2 The method for calculating the pre-pumping amount and the reinjection amount of the brine with the sealing efficiency comprises the following calculation steps:
(1) calculating the pre-pumping volume V of the brine of the bottom brine layer Pre-pumping device
The amount of saline pre-pumped is indicated in CO 2 Saline extraction amount before injection; CO 2 2 After the injection, the saline water extraction still lasts for a period of time, but the amount of the saline water extraction in the period of time is not counted in the saline water pre-extraction amount;
determining allowable collapse pressure value of bottom salt water layer
In the formula, P w c 、
The critical value and the allowable value of the collapse pressure of the bottom brine layer are MPa; sigma H 、σ h Maximum and minimum horizontal principal stresses, respectively, obtained from the applied horizontal confining pressure,MPa；P p obtaining the initial formation pore pressure of the brine layer from the applied formation pore pressure, MPa;
the internal friction angle is obtained through Moire envelope curves of a plurality of groups of triaxial compression experiments; c is cohesion, and is obtained by Mohr envelope curve of a plurality of groups of triaxial compression experiments, and is MPa; alpha is a Biao coefficient, generally 0.85; n is 1 Setting in combination with engineering experience for safety factor and dimensionless;
② determining the pore pressure reduction Delta P of the bottom brine layer caused by brine pre-pumping p pre-pumping At the reduced pore pressure value P p -ΔP p pre-pumping Not lower than allowable collapse pressure
Calculating the saline water pre-suction volume V for the critical conditions Pre-pumping device ；
In the formula,. DELTA.P p pre-pumping The pore pressure change of a bottom brine layer caused by brine pre-pumping is MPa; h Pre-pumping device M is the water level height change caused by the pre-pumping of the saline water; gamma ray Salt water Heavy saline water, KN m -3 ；V Pre-pumping device 、V Oozing the mixture Respectively the amount of the pre-pumped saline water and the amount of the supplement of the underground fluid from infinity to the pre-pumped well seepage caused by the pre-pumped saline water under the actual condition, m 3 (ii) a S is the horizontal area of the bottom brine layer, m 2 ；φ Lower part Is the porosity of the bottom brine layer, and is dimensionless;
(2) calculating the brine refilling volume V of the top brine layer Reinjection
Determining allowable rupture pressure value of top saline layer
In the formula, P w f 、
The critical value and the allowable value of the rupture pressure of the saline layer are MPa; sigma t The tensile strength of the saline layer is obtained by the Brazilian split test, and is MPa; n is a radical of an alkyl radical 2 Setting in combination with engineering experience for safety factor and dimensionless;
② determining the pore pressure increase Δ P of the top brine layer caused by brine reinjection Reinjection of p To the increased value of the pore pressure P p +ΔP Reinjection of p Not higher than the allowable rupture pressure
Calculating brine recharge V for critical conditions Reinjection ；
In the formula,. DELTA.P Reinjection of p The pore pressure change of a top brine layer caused by brine reinjection is MPa; h Reinjection M is the water level height change caused by brine reinjection; v Reinjection 、V′ Oozing out The amount of brine reinjection and the overflow amount of seepage of underground fluid from a reinjection well to infinity, m, caused by brine reinjection under actual conditions 3 (ii) a S' is the horizontal area of the top brine layer, m 2 ；φ On the upper part Is the porosity of the top brine layer, dimensionless;
(3) bottom brine layer CO 2 Fill and brine extractionWhen synchronization occurs, CO is established 2 Velocity v of injection Note that With the speed v of withdrawal of brine Extraction of The relationship of (1):
in the formula,. DELTA.P P notes Is CO 2 Injection induced pore pressure changes in bottom brine layer
MPa； v Note that Is CO 2 Injection velocity, m 3 ·s -1 ；v Extraction of As the saline water pumping speed, m 3 ·s -1 ；v″ Oozing out -v Oozing out The rate of replenishment of subsurface flow from the bottom brine reservoir to the pre-pump and injection wells at infinity under practical conditions, m 3 ·s -1 ；
(4) Bottom brine layer CO 2 CO build-up when injection occurs in synchrony with top brine layer brine reinjection 2 Velocity v of injection Note that Velocity v of reinjection with saline Reinjection The relationship of (c):
in the formula, v Reinjection The saline reinjection speed, m 3 ·s -1 ；v Note that Is CO 2 Injection velocity, m 3 ·s -1 。
In another aspect of the invention, an enhanced CO is provided 2 The pre-pumping-reinjection method for the sealing efficiency adopts the calculation method and specifically comprises the following steps:
firstly, carrying out brine pre-pumping on a bottom brine layer; when the pre-pumping quantity of the saline reaches the pre-pumping quantity V of the saline obtained by the calculation Pre-pumping device At the beginning of CO injection into the bottom brine layer 2 While CO is established by the above 2 CO control by relationship between injection rate and saline extraction rate 2 The injection speed; when CO is present 2 Detection of CO by the detector 2 Stopping the saline water extraction; when the pore pressure of the bottom brine layer is restored to the initial pore pressure, brine reinjection into the top brine layer is started, and the established brine reinjection speed and CO are used for simultaneously reinjecting brine into the top brine layer 2 Controlling the saline water reinjection speed according to the injection speed relation; when the brine refilling amount reaches the calculated brine refilling amount V Reinjection Stopping saline reinjection; stopping CO when pore pressure of bottom brine layer reaches allowable rupture pressure 2 And (5) injecting.
The invention also provides a method for maximizing CO 2 A site test verification method for sealing efficiency and a calculation method for verifying the pre-pumping quantity and the reinjection quantity of saline water comprise the following operation steps:
step 1: layout field test
Laying CO 2 A field test device for sealing;
step 2: develop field test
(1) Applying pressure
Applying three-way confining pressure to a saline water layer through a hydraulic support and a balancing weight, and applying initial formation pore pressure to the saline water layer through a liquid supercharger and a pressure-bearing steel pipe;
(2) pre-pumping salt water
In CO 2 Before injection, extracting brine from a bottom brine layer through a pre-pumping well and temporarily storing the brine in a storage tank; in CO 2 After injection, when the salt water is pumped into the well bottom CO 2 Detection of CO by the detector 2 Stopping the saline water extraction;
(3) CO injection 2
When the pore pressure of the bottom brine layer monitored by the fluid pressure sensor reaches the collapse pressure allowable value, the CO injection into the bottom brine layer through the injection well is started 2 (ii) a When the pore pressure of the bottom brine layer monitored by the fluid pressure sensor reaches the allowable rupture pressure value, CO is stopped 2 Injecting;
(4) reinjection of saline
When the pore pressure value of the bottom brine layer monitored by the fluid pressure sensor is restored to the initial pore pressure, starting to reinject the brine extracted from the bottom brine layer into the top brine layer through the reinjection well; stopping brine reinjection when the pore pressure of the top brine layer monitored by the fluid pressure sensor reaches the allowable top brine layer fracture pressure value;
(5) end of the test
Stopping CO 2 Injecting and finishing the test; recording CO 2 The injection amount, the swelling deformation value of the bottom brine layer, the actual saline extraction amount when the pore pressure monitoring value of the bottom brine layer reaches the allowable collapse pressure value, and the actual saline reinjection amount when the pore pressure monitoring value of the top brine layer reaches the allowable rupture pressure value;
and step 3: verification calculation method
(1) Salt water pre-pumping amount verification
Obtaining the actual extraction quantity of the saline water when the pore pressure monitoring value of the bottom saline water layer reaches the collapse pressure allowable value, comparing the equivalent volume of the actual extraction quantity of the saline water with the theoretical value of the pre-extraction quantity of the saline water, and if the error is within 5%, indicating that the computing method of the pre-extraction quantity of the saline water can meet the requirements of field engineering;
(2) brine refill verification
Acquiring the actual reinjection amount of the brine when the pore pressure monitoring value of the top brine layer reaches the allowable rupture pressure value, comparing the equivalent volume of the actual reinjection amount of the brine with the theoretical value of the reinjection amount of the brine, and if the error is within 5%, indicating that the calculation method of the reinjection amount of the brine can meet the requirements of site engineering;
and 4, step 4: contrast sealing efficiency
(1) Maximizing CO by (1), (2), (3) and (4) in step 2 2 Performing field test on the sealing efficiency, namely obtaining CO through the step (5) in the step 2 2 Injection amount and maximum uplift deformation of the bottom brine layer;
(2) conventional CO development by (1) and (3) in step 2 2 Sealing site test, obtaining CO through (5) in step 2 2 Injection amount and maximum uplift deformation of the bottom brine layer;
(3) comparison of CO in (1) and (2) above 2 Injection amount, confirmation of maximized CO 2 The field test of the sealing efficiency has the advantage of sealing capability; maximum swelling deformation of the bottom brine layer in comparison of (1) and (2) confirmed to maximize CO 2 The field test of the sealing efficiency has the advantage of sealing safety.
In the present invention, CO 2 A cover layer (the cover layer is CO) is arranged in the sealed field test device 2 Necessary conditions for sequestration of site selection), the brine layer above the cap layer is referred to herein as the top brine layer, and the brine layer below the cap layer is referred to herein as the bottom brine layer.
Further, in the present invention, the CO is 2 The field test device comprises a foundation pit, a bottom salt water layer, a cover layer, a top salt water layer, a displacement sensor, a fluid pressure sensor, an anti-seepage box body, a 'return' -shaped foundation pit, a hydraulic support, a balancing weight, a liquid supercharger, a pressure-bearing steel pipe, a pre-pumping well, a storage box, CO 2 Detector, constant pressure pump, constant pressure water tank and supercritical CO 2 Gas tanks, injection wells, reinjection wells; the bottom brine layer, the cover layer and the top brine layer form a brine layer, the brine layer is wrapped by an anti-seepage box body, the brine layer and the anti-seepage box body are both arranged in the foundation pit, and soil is backfilled between the anti-seepage box body and the wall surface of the foundation pit tightly; arranging a displacement sensor on the upper surface of the brine layer at the bottom, and monitoring the deformation of the brine layer; excavating a 'back' shaped foundation pit around the foundation pit, placing a hydraulic support in the 'back' shaped foundation pit, and applying horizontal confining pressure; arranging a balancing weight at the top of the brine layer, and applying vertical confining pressure; the liquid booster is connected with a pressure-bearing steel pipe in the brine layer and is responsible for injecting pressurized brine into the brine layer to realize the application of initial formation pore pressure; the pre-pumping well is arranged in the brine layer and is used for pumping brine from the bottom brine layer and temporarily storing the brine in the storage tank; CO 2 2 The detector is arranged at the bottom of the pre-pumping well and used for judging CO 2 Whether the bottom of the pre-pumping well is reached or not; an injection well is disposed at the center of the brine layer and connected to the supercritical CO 2 Gas tank for injecting CO into bottom brine layer 2 (ii) a The reinjection well is arranged on the top saline layer and is responsible for reinjecting the saline stored in the storage tank to the top saline layer; the constant pressure pump and the constant pressure water tank are communicated with the brine layer through the pressure-bearing steel pipe, the constant pressure in the constant pressure water tank is maintained by the constant pressure pump and is equal to the initial formation pore pressure, and the pre-pumping of brine and CO is simulated 2 Underground fluid seepage under actual conditions caused by saline injection and reinjectionFlow processes (i.e., self-regulating function of pore pressure within an infinite stratum); and arranging fluid pressure sensors at the bottom hole positions of the pre-pumping well, the injection well and the reinjection well, and monitoring the pore pressure of the saline stratum.
In the present invention, maximizing CO is calculated under conditions of formation collapse and fracture 2 The pre-pumping amount and the reinjection amount of the saline water with the sealing efficiency are calculated to obtain the pre-pumping amount V of the saline water Pre-pumping device Preventing the bottom brine layer from causing formation collapse during pre-pumping brine for the control conditions during actual brine pumping; to calculate the obtained reinjection quantity V Reinjection Preventing the top brine layer from causing formation fracture during brine reinjection for controlling conditions during actual brine reinjection; at the same time build up CO 2 Relationship between injection rate and saline extraction rate, saline reinjection rate and CO 2 Injection velocity relationship. In addition, the invention designs a maximized CO 2 The field test verification method and device for the sealing efficiency have the advantages of compact and reasonable structure, reliable principle and high feasibility.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention provides a method for maximizing CO 2 The method for calculating the saline water pre-pumping amount and the brine refilling amount of the sealing efficiency calculates the saline water pre-pumping amount and the brine refilling amount under the condition of stratum collapse and fracture, and the calculation precision is more than 95 percent through comparison verification with a field test;
2. the invention designs a maximized CO 2 The field test verification method and device for the sealing efficiency implement the brine pre-pumping and reinjection strategies by calculating the brine pre-pumping amount and the reinjection amount, and compared with the conventional sealing test, the sealing capacity is improved by 25%, and the sealing safety is improved by 20%.
Drawings
FIG. 1 is a CO of the present invention 2 The structure schematic diagram of the sealed field test device;
FIG. 2 is a CO of the present invention 2 A top view of the sealed field test device;
FIG. 3 is a flow chart of the brine pre-extraction calculation of the present invention;
FIG. 4 is a flow chart of brine refill calculation according to the present invention;
FIG. 5 is a comparison graph of the verification of the calculation method of the present invention;
FIG. 6 is a graph comparing the results of example 1 of the present invention;
in the figure: 1. a foundation pit; 2. a bottom brine layer; 3. a cap layer; 4. a top brine layer; 5. a displacement sensor; 6. a fluid pressure sensor; 7. an anti-seepage box body; 8. a foundation pit shaped like a Chinese character 'hui'; 9. a hydraulic support; 10. A balancing weight; 11. a liquid pressure booster; 12. a pressure-bearing steel pipe; 13. pre-pumping a well; 14. a storage tank; 15. CO 2 2 A detector; 16. a constant pressure pump; 17. a constant pressure water tank; 18. supercritical CO 2 A gas tank; 19. an injection well; 20. And (4) reinjecting the oil into the well.
Detailed Description
The details of the present invention can be more clearly understood in conjunction with the accompanying drawings and the description of the embodiments of the present invention. However, the specific embodiments of the present invention described herein are for the purpose of illustration only and are not to be construed as limiting the invention in any way. Any possible variations based on the present invention may be conceived by the skilled person in the light of the teachings of the present invention, and these should be considered to fall within the scope of the present invention.
In one aspect, the present embodiments provide a method for maximizing CO 2 The method for calculating the pre-pumping amount and the reinjection amount of the brine with the sealing efficiency comprises the following calculation steps:
(1) calculating the pre-pumping quantity V of the brine of the bottom brine layer 2 Pre-pumping device
The pre-pumping amount of brine is indicated in CO 2 Saline extraction amount before injection; CO 2 2 After the injection, the saline water extraction still lasts for a period of time, but the amount of the saline water extraction in the period of time is not counted in the saline water pre-extraction amount;
determining the stress distribution of the wall surrounding rock of the pre-pumped well 13 of the bottom saline water layer 2 according to the elasticity mechanics (see formula (1)), and determining the radial effective stress sigma' r Hoop effective stress σ' θ And (3) substituting the Mohr-Coulomb criterion to determine the collapse pressure critical value of the bottom brine layer 2, see formula (2):
considering safety requirements, the collapse pressure critical value in practical engineering is usually replaced by allowable value, see formula (3):
in the formula, P w The pressure of a well 13 of a pre-pumping well for a bottom saline layer 2 is MPa; p w c 、
The critical value and the allowable value of the collapse pressure of the bottom brine layer 2 are MPa; sigma H 、σ h Maximum and minimum horizontal principal stresses, respectively, obtained from the applied horizontal confining pressure, MPa; p p Obtaining the initial formation pore pressure of the brine layer from the applied formation pore pressure, MPa;
the internal friction angle is obtained through Moire envelope curves of a plurality of groups of triaxial compression experiments; c is cohesion, and is obtained by Mohr envelope curve of a plurality of groups of triaxial compression experiments, and is MPa; alpha is a Biao coefficient, generally 0.85; n is 1 The safety coefficient is set in combination with engineering experience without dimension;
② the pressure of the bottom brine layer 2 pore space is reduced by delta P caused by pre-pumping brine p pre-pumping The decreased pore pressure value is not lower than the allowable collapse pressure value, i.e.
The pre-pumping quantity V of the brine is calculated by taking the pre-pumping quantity V as a control condition Pre-pumping device ；
According to the calculation formula of the water head pressure, the pore pressure of the bottom brine layer 2 is reduced by delta P p pre-pumping Represented by formula (4):
substituting formula (4) into
The pre-pumping quantity V of the saline water can be calculated Pre-pumping device See formula (5):
in the formula,. DELTA.P p pre-pumping The pore pressure change, MPa, of the bottom brine layer 2 caused by brine pre-pumping; h Pre-pumping device M is the water level height change caused by the pre-pumping of the saline water; gamma ray Salt water Heavy saline water, KN m -3 ；V Pre-pumping device 、V Oozing out The replenishment quantity m is respectively the salt water pre-pumping quantity and the seepage quantity of the underground fluid from infinity to the pre-pumping well 13 caused by the salt water pre-pumping under the actual condition 3 (ii) a S is the horizontal area of the bottom brine layer 2, m 2 ；φ Lower part The porosity of the bottom brine layer 2 is dimensionless;
with V Pre-pumping device Preventing the bottom brine layer 2 from causing formation collapse during pre-brine extraction for the control conditions during actual brine extraction;
(2) calculating the salt water refilling amount V of the top salt water layer 4 Reinjection
Phi ' effective radial stress sigma ' in formula (1) ' r Hoop effective stress σ' θ Substituting the maximum tensile stress criterion to determine the formation fracture pressure, see formula (6) below:
P w f ＝3σ h -σ H -αP p +σ t (6)
considering safety requirements, the critical value of rupture pressure in practical engineering is usually replaced by an allowable value, see formula (7):
in the formula, P w f 、
The critical value and the allowable value of the rupture pressure of the saline layer are MPa; sigma t The tensile strength of the saline layer is obtained by the Brazilian split test, and is MPa; n is 2 The safety coefficient is set in combination with engineering experience without dimension;
② the brine reinjection causes the pore pressure of the top brine layer 4 to increase by Delta P Reinjection of p The increased value of the pore pressure is not higher than the allowable value of the fracture pressure, i.e.
The salt water refilling amount V is calculated by taking the calculated amount as the control condition Reinjection ；
According to the calculation formula of the head pressure, the pore pressure of the top brine layer 4 is increased by delta P Reinjection of p Represented by formula (8):
substituting formula (8) into
Then the salt water refilling amount V can be calculated Reinjection See formula (9):
in the formula,. DELTA.P Reinjection of p The pore pressure change, MPa, of the top brine layer 4 caused by brine reinjection; h Reinjection M is the water level height change caused by brine reinjection; v Reinjection 、V′ Oozing the mixture The amount of brine recharge, the amount of seepage of the subsurface fluid from the recharge well 20 to infinity, m, caused by brine recharge under actual conditions, respectively 3 (ii) a S' is the horizontal area of the top brine layer 4, m 2 ；φ Upper part of Porosity of the top brine layer 4, no amountA line;
at V Reinjection Preventing the top brine layer 4 from causing formation fracturing during the brine reinjection for controlling conditions during the actual brine reinjection;
(3) establishment of CO 2 Injection rate vs. saline extraction rate
After extracting brine and injecting CO 2 When synchronized, the pore pressure drop in the bottom brine layer 2 caused by brine draw equals CO 2 The increase in pore pressure of the bottom brine layer 2 caused by the injection is a control condition, and CO is established 2 The relationship between the injection rate and the saline extraction rate is shown in the following formula (10):
in the formula,. DELTA.P P notes Is CO 2 The injection causing a change in the pore pressure of the bottom brine layer 2
MPa；v Note that Is CO 2 Injection velocity, m 3 ·s -1 ；v Extraction of As the saline water pumping speed, m 3 ·s -1 ；v″ Oozing out -v Oozing out The replenishment rate of the subsurface fluid of the bottom brine layer 2 from infinity to the pre-pumping well 13 and the injection well 19 under actual conditions is determined by the pressure difference between the formation pore pressure and the constant pressure water tank 17 and Darcy's law, and is expressed by the following formula (11):
wherein k is the formation permeability coefficient and is obtained by permeability experiment, m.s -1 (ii) a A is the cross-sectional area of the stratum perpendicular to the seepage direction, m 2 (ii) a L is the length of the seepage path, m;
(4) establishing brine reinjection velocity and CO 2 Injection velocity relationship
In the injection of CO 2 CO when occurring in synchronism with the brine reinjection 2 The pore pressure increase of the bottom brine layer 2 caused by the injection is equal to the pore pressure increase of the top brine layer 4 caused by the brine reinjection under the control condition that the brine reinjection speed and the CO are established 2 The injection rate relationship is given by the following equation (12):
in the formula, v Reinjection The saline reinjection speed, m 3 ·s -1 ；v Note that Is CO 2 Injection velocity, m 3 ·s -1 ；v′ Oozing out The overflow velocity of the subsurface fluid from the return well 20 to infinity under practical conditions, m 3 ·s -1 ；v″ Oozing the mixture The overflow rate of the subsurface fluid from the injection well 19 to infinity, m 3 ·s -1 ；
In particular, from "CO 2 The condition that the pore pressure of the bottom brine layer 2 increases by the injection and the pore pressure of the top brine layer 4 increases by the brine reinjection "can determine that the pressure differences between the bottom brine layer 2, the top brine layer 4 and the surge tank 17 are equal, and further determine v ' by combining Darcy's law ' Oozing out ＝v″ Oozing out For this reason, formula (12) is further simplified to formula (13):
another aspect of the invention provides a method for maximizing CO 2 The field test of the sealing efficiency verifies the calculation method of the saline water pre-pumping quantity and the reinjection quantity, and the operation steps are as follows:
step 1: layout field test
As shown in fig. 1-2, one such method maximizes CO 2 The site test device for the sealing efficiency comprises a foundation pit 1, a bottom saline layer 2, a cover layer 3, a top saline layer 4, a displacement sensor 5, a fluid pressure sensor 6, an anti-seepage box body 7, a 'Hui' shaped foundation pit 8, a hydraulic support 9, a balancing weight 10, a liquid supercharger 11, a pressure-bearing steel pipe 12, a pre-pumping unitWell 13, storage tank 14, CO 2 Detector 15, constant pressure pump 16, constant pressure water tank 17 and supercritical CO 2 Gas tank 18, injection well 19, return well 20;
excavating a foundation pit 1, wherein the size of the foundation pit 1 is 3km multiplied by the width of the foundation pit 1 multiplied by the depth of the foundation pit 1, and a bottom saline layer 2, a cover layer 3 and a top saline layer 4 with the heights of 50m, 10m and 40m are sequentially filled in the foundation pit 1 from bottom to top to jointly form a saline layer; the mortar mass ratio of the bottom salt water layer 2 to the top salt water layer 4 is cement: sand: water equal to 1: 0.33: 0.42, the mass ratio of the cover layer 3 mortar is cement: sand: water equal to 1: 0.11: 0.42; an anti-seepage box body 6 (made of a thin steel plate) wraps the outside of the brine layer, so that the brine is prevented from seeping out of the brine layer under a high-pressure condition, and soil is backfilled between the anti-seepage box body 6 and the wall surface of the foundation pit 1 to be compact; transversely and longitudinally arranging displacement sensors 5 on the upper surface of the bottom brine layer 2 at intervals of 600m, and monitoring the deformation of the brine layer;
excavating a 'back' shaped foundation pit 8 with the width of 2m and the height of 100m at intervals of 50m around the foundation pit 1, placing a hydraulic support 9 in the 'back' shaped foundation pit 8, fixing the bottom of the hydraulic support 9 on the outer wall surface of the 'back' shaped foundation pit 8 (namely the wall surface far away from the foundation pit 1), fixing the top of the hydraulic support 9 on the inner wall surface of the 'back' shaped foundation pit 8 (namely the wall surface close to the foundation pit 1), and applying horizontal confining pressure; arranging balancing weights 10 transversely and longitudinally at intervals of 300m at the top of the brine layer, and applying vertical confining pressure; the liquid supercharger 11 is connected with a pressure-bearing steel pipe 12 in the brine layer and is responsible for injecting pressurized brine into the brine layer to realize the application of initial formation pore pressure;
one end of the injection well 19 is connected with supercritical CO 2 The other end of the gas tank 18 extends vertically from the top center of the brine layer into the bottom brine layer 2 by 20m to inject CO into the bottom brine layer 2 2 (ii) a The pre-pumping wells 13 are arranged at the left side and the right side of the injection well 19 at 1km respectively and extend into the bottom brine layer 2 for 20m, and are used for pumping the brine from the bottom brine layer 2 and temporarily storing the brine in the storage tank 14; CO 2 2 A detector 15 is arranged at the bottom of the pre-pumping well 13 for determining CO 2 Whether the bottom of the pre-pumping well 13 is reached; the reinjection wells 20 are arranged at the left and right sides of the center of the top brine layer 4 by 1km and extend into the top brine layer 4 by 15m, and are responsible for reinjecting the brine stored in the storage tank 14 into the top brine layer 4; constant pressureThe pump 16 and the constant pressure water tank 17 are communicated with a brine layer through the pressure bearing steel pipe 12, the constant pressure pump 16 maintains the pressure in the constant pressure water tank 17 to be constant and equal to the initial formation pore pressure, and the constant pressure water tank is used for simulating pre-pumping brine and CO 2 The actual conditions caused by the saline water injection and reinjection are the subsurface fluid seepage process (i.e. the self-regulation function of the pore pressure in the infinite stratum); arranging fluid pressure sensors 6 at the bottom positions of the pre-pumping well 13, the injection well 19 and the reinjection well 20 to monitor the pore pressure of the saline stratum;
step 2: develop field test
(1) Applying pressure
Applying three-way confining pressure to a brine layer through a hydraulic support 9 and a balancing weight 10; pressurizing the saline water through a liquid pressurizer 11, and then injecting the pressurized saline water into a saline water layer through a pressure-bearing steel pipe 12 to realize the application of initial formation pore pressure;
(2) pre-pumping salt water
The brine is extracted from the bottom brine layer through the pre-pumping well 13 and temporarily stored in the storage tank 14, and the brine extraction speed v is set according to engineering experience Extraction of (ii) a Meanwhile, the constant pressure water tank 17 and the pressure-bearing steel pipe 12 simulate the replenishment process of the seepage of underground fluid of the bottom brine layer caused by pre-pumped brine from infinity to the pre-pumped well under the actual condition;
(3) CO injection 2
When the pore pressure of the bottom brine layer 2 detected by the fluid pressure sensor 6 at the bottom hole position of the pre-pumping well 13 reaches the collapse pressure allowable value, the injection of CO into the bottom brine layer 2 through the injection well 19 is started 2 While calculating CO according to the formula (10) 2 Injection velocity v Note that ；
(4) Stopping saline extraction
CO arranged at the bottom of the saline water pre-pumping well 13 2 The detector 15 detects CO 2 Stopping the saline water extraction;
(5) reinjection of brine
When the pore pressure of the bottom brine layer 2 monitored by the fluid pressure sensor 6 at the bottom hole position of the injection well 19 is restored to the original formation pore pressure, the brine extracted from the bottom brine layer 2 is started to be returned through the return well 20Into the top brine layer 4, while calculating the brine reinjection velocity v according to equation (13) Reinjection ；
(6) Stopping saline reinjection
Stopping the brine reinjection when the pore pressure of the top brine layer 4, as monitored by the fluid pressure sensor 6 (at the bottom hole location of the reinjection well 20), reaches the cracking pressure allowable value;
(7) stopping CO 2 Injection of
When the pore pressure of the bottom brine layer 2 monitored by the fluid pressure sensor 6 (at the bottom hole position of the injection well 19) reaches the allowable burst pressure value, CO is stopped 2 Injecting;
(8) end of the test
Stopping CO 2 Injecting and finishing the test; recording CO 2 The actual saline extraction volume V when the injection volume, the swelling deformation value of the bottom saline layer 2 and the pore pressure monitoring value of the bottom saline layer 2 reach the allowable collapse pressure value Pre-draw-test When the pore pressure monitoring value of the top brine layer 4 reaches the rupture pressure allowable value, the actual refilling volume V of the brine Reinjection-test ；
And 3, step 3: verification calculation method
In particular, the initial pore pressure of the brine layer in the field test is realized by pressurizing the brine by the liquid pressurizer 11, but not the initial pore pressure of the brine which is achieved by the gravity of the brine under the actual condition, so the volume of the brine injected into the brine layer in the field test (marked as the brine pressurizing volume V) Brine-pressurized Directly obtained from field testing) is much smaller than the volume of brine (noted as the original volume of brine, expressed as brine original volume) that would produce the same pore pressure under practical conditions
Or
) (ii) a In view of the above, the pressurization volume of the brine in the field test and the original volume of the brine under the actual condition should be equivalently converted so as to be compared with the brine pre-pumping quantity and the brine refilling quantity obtained by the theoretical calculation method;
(1) brine pre-pumping amount verification
Obtaining the actual extraction quantity V of the brine when the pore pressure monitoring value of the bottom brine layer 2 reaches the allowable collapse pressure value Pre-pump test After equivalence to obtain
And is mixed with the theoretical value V of the saline water pre-pumping quantity Theory of pre-pumping Comparing, if the error is within 5%, indicating that the calculation method of the pre-extraction amount of the saline water can meet the requirements of field engineering;
(2) brine refill amount verification
Obtaining the actual refilling volume V of the brine when the pore pressure monitoring value of the top brine layer 4 reaches the allowable rupture pressure value Reinjection-test After equivalence to obtain
And is reinjected with the saline water to obtain the theoretical value V Theory of reinjection Comparing, if the error is within 5%, indicating that the calculation method of the saline water reinjection amount can meet the requirements of field engineering;
and 4, step 4: contrast sealing efficiency
(1) Maximizing CO by (1) - (7) development in step 2 2 Performing field test on the sealing efficiency, namely obtaining CO through the step (8) in the step 2 2 Injection quantity V 1 And maximum uplift deformation u of the bottom brine layer 2 1 ；
(2) Conventional CO development by (1), (3) and (7) in step 2 2 Sealing site test, obtaining CO through (8) in step 2 2 Injection quantity V 2 And maximum uplift deformation u of the bottom brine layer 2 2 ；
(3) Comparison of CO in (1) and (2) above 2 Injection quantity V 1 、V 2 Confirmation of maximized CO 2 The field test of the sealing efficiency has the advantage of sealing capability; maximum swelling deformation u of the bottom brine layer 2 in comparison (1) and (2) 1 、u 2 Confirmation of maximized CO 2 The field test of the sealing efficiency has the advantage of sealing safety.
Example 1:
laying a field test according to the step 1; by rock strengthThe tensile strength sigma of the bottom brine layer 2 and the top brine layer 4 is obtained through testing t 4MPa, cohesion c of 9MPa, internal friction angle
Is 40 degrees; the permeability k of the bottom brine layer 2 and the top brine layer 4 is 1 multiplied by 10 which is obtained by permeability experiment -10 m/s, porosity phi is 0.15; setting the maximum horizontal pressure, the minimum horizontal pressure and the vertical confining pressure of 20MPa, 16MPa and 10MPa according to the step (1) in the step 2, and setting the initial formation pore pressure of 12 MPa; setting a safety factor n according to engineering experience 1 、n 2 1.25 and 1.35 respectively, and the allowable collapse pressure value and the allowable rupture pressure value are respectively 10.9MPa and 14.8MPa according to the formulas (3) and (7); obtaining saline water and supercritical CO by data 2 The gravity is respectively 9.8KN m -3 、4.48KN·m -3 (ii) a Developing maximum CO according to (2) - (7) in step 2 2 In the field test of the storage efficiency, the salt water extraction speed is set to be 0.5kg/s, and CO is calculated according to the formula (10) and the formula (11) 2 The injection rate was 1.13kg/s, and then the saline reinjection rate was 0.52kg/s, calculated according to equation (13); conventional CO development according to (3) and (7) in step 2 2 Sealing and storing site test; obtaining maximum CO according to (1) and (2) in step 3 respectively 2 Saline water pre-pumping quantity (equivalent volume) under field test of sealing efficiency
And respectively pre-pumping with salt water to obtain a theoretical value V Theory of pre-pumping Saline water reinjection amount theoretical value V Theory of reinjection In contrast, as shown in FIG. 5; obtaining maximum CO according to (1) and (2) in step 4 2 Sealing efficiency field test, conventional CO 2 CO under seal site test 2 Injection quantity V 1 、V 2 Maximum swelling deformation u of the bottom brine layer 2 1 、u 2 (ii) a Comparison of CO under two conditions according to (3) in step 4 2 Injection quantity V 1 、V 2 Maximum swelling deformation u of the bottom brine layer 2 1 、u 2 As shown in fig. 6.
As can be seen from FIG. 5, the present invention maximizes CO 2 The difference between the theoretical values of the pre-pumping quantity and the reinjection quantity of the brine of the sequestration efficiency and the actual pumping quantity and the actual reinjection quantity of a field test is only 3.1 percent and 4.3 percent, which shows that the CO is maximized 2 The method for calculating the pre-pumping amount and the reinjection amount of the brine with the sealing efficiency can meet the requirements of field engineering.
As can be seen from FIG. 6, the present invention maximizes CO 2 Sealing efficiency field test is more conventional CO 2 The sealing field test has the advantage of sealing capability, CO 2 The injection amount is improved by 25%; maximizing CO 2 Sealing efficiency field test is more conventional CO 2 The sealing site test has the advantage of safety sealing, and the maximum swelling deformation of the bottom brine layer 2 is reduced by 20%.
Claims (5)
1. Maximized CO 2 The method for calculating the pre-pumping amount and the reinjection amount of the brine with the sealing efficiency is characterized by comprising the following specific calculation steps:
(1) calculating the pre-pumping volume V of the brine of the bottom brine layer Pre-pumping device
The amount of saline pre-pumped is indicated in CO 2 Saline extraction amount before injection; CO 2 2 After the injection, the saline water extraction still continues for a period of time, but the amount of the saline water extraction in the period of time does not account for the amount of the saline water pre-extraction;
determining allowable collapse pressure value of bottom brine layer
In the formula, P w c 、
The critical value and the allowable value of the collapse pressure of the bottom brine layer are MPa; sigma H 、σ h Maximum and minimum horizontal principal stresses, respectively, obtained from the applied horizontal confining pressure, MPa; p p Pore formation initiation for saline aquifersPressure, obtained from the applied formation pore pressure, MPa;
the internal friction angle is obtained through Moire envelope lines of a plurality of groups of triaxial compression experiments; c is cohesion, and is obtained by Mohr envelope curve of a plurality of groups of triaxial compression experiments, and is MPa; alpha is a Biao coefficient, generally 0.85; n is 1 The safety coefficient is set in combination with engineering experience without dimension;
② determining the pore pressure decrease Delta P of the bottom brine layer caused by brine pre-pumping p pre-pumping At the reduced pore pressure value P p -ΔP p pre-pumping Not lower than allowable collapse pressure
Calculating the saline water pre-suction volume V for the critical conditions Pre-pumping device ；
In the formula,. DELTA.P p pre-pumping The pore pressure change of a bottom brine layer caused by brine pre-pumping is MPa; h Pre-pumping device M is the water level height change caused by the pre-pumping of the saline water; gamma ray Salt water Is the severity of salt water, KN m -3 ；V Pre-pumping device 、V Oozing out Respectively the amount of the pre-pumped saline water and the amount of the supplement of the underground fluid from infinity to the pre-pumped well seepage caused by the pre-pumped saline water under the actual condition, m 3 (ii) a S is the horizontal area of the bottom brine layer, m 2 ；φ Lower part Is the porosity of the bottom brine layer, and is dimensionless;
(2) calculating the brine refilling amount V of the top brine layer Reinjection
Determining allowable rupture pressure value of top saline layer
In the formula, P w f 、
The critical value and the allowable value of the fracture pressure of the brine layer are MPa; sigma t Tensile strength for saline aquifers, obtained by brazilian split test, MPa; n is a radical of an alkyl radical 2 The safety coefficient is set in combination with engineering experience without dimension;
② determination of pore pressure increase Δ P of top brine layer caused by brine reinjection Reinjection of p To the increased value of the pore pressure P p +ΔP Reinjection of p Not higher than the allowable rupture pressure
Calculating brine recharge V for critical conditions Reinjection ；
In the formula,. DELTA.P Reinjection of p The pore pressure change of a top brine layer caused by brine reinjection is MPa; h Reinjection M is the water level height change caused by brine reinjection; v Reinjection 、V′ Oozing the mixture The amount of brine reinjection and the overflow amount of seepage of underground fluid from a reinjection well to infinity, m, caused by brine reinjection under actual conditions 3 (ii) a S' is the horizontal area of the top brine layer, m 2 ；φ Upper part of Is the porosity of the top brine layer, dimensionless;
(3) bottom brine layer CO 2 CO build-up when injection and brine extraction occur simultaneously 2 Injection velocity v Injection bottle With the speed v of withdrawal of brine Extraction of The relationship of (1):
in the formula,. DELTA.P P notes Is CO 2 Injection induced pore pressure changes in bottom brine layer
MPa；v Note that Is CO 2 Injection velocity, m 3 ·s -1 ；v Extraction of As the saline extraction speed, m 3 ·s -1 ；v″ Oozing the mixture -v Oozing out The rate of replenishment of subsurface flow from the bottom brine reservoir to the pre-pump and injection wells at infinity under practical conditions, m 3 ·s -1 ；
(4) Bottom brine layer CO 2 CO build-up when injection occurs in synchrony with top brine layer brine reinjection 2 Injection velocity v Note that Velocity v of reinjection with saline Reinjection The relationship of (c):
in the formula, v Reinjection The saline reinjection speed, m 3 ·s -1 ；v Note that Is CO 2 Injection velocity, m 3 ·s -1 。
2. Improve CO 2 The pre-pumping-reinjection method for the sealing efficiency is characterized by comprising the following steps:
firstly, carrying out brine pre-pumping on a bottom brine layer; when the pre-suction volume of brine reaches the pre-suction volume V of brine calculated in claim 1 Pre-pumping device At the beginning of CO injection into the bottom brine layer 2 CO simultaneously established in claim 1 2 CO control based on relationship between injection rate and saline extraction rate 2 The injection speed; when CO is present 2 CO detection by detector 2 Stopping the saline water extraction; when the pore pressure of the bottom brine layer returns to the initial pore pressure, the brine reinjection into the top brine layer is initiated, with the brine reinjection rate and CO established in claim 1 2 Controlling the saline water reinjection speed according to the injection speed relation; the amount of brine return V calculated in claim 1 when the amount of brine return reaches the amount of brine return V Reinjection Stopping saline reinjection; stopping CO when pore pressure of bottom brine layer reaches allowable rupture pressure 2 And (4) injecting.
3. Maximized CO 2 Method for verifying field test of sequestration efficiency by verifying maximized CO as claimed in claim 1 2 The method for calculating the pre-pumping amount and the reinjection amount of the brine with the sealing efficiency is characterized by comprising the following specific operation steps:
step 1: layout field test
Laying CO 2 A field test device for sealing;
step 2: develop field test
(1) Applying pressure
Applying three-way confining pressure to a saline water layer through a hydraulic support and a balancing weight, and applying initial formation pore pressure to the saline water layer through a liquid supercharger and a pressure-bearing steel pipe;
(2) pre-pumping salt water
In CO 2 Before injection, extracting brine from the bottom brine layer through a pre-pumping well and temporarily storing the brine in a storage tank; in CO 2 After injection, when the salt water is pumped into the well bottom CO 2 CO detection by detector 2 Stopping the saline water extraction;
(3) CO injection 2
When the pore pressure of the bottom brine layer monitored by the fluid pressure sensor reaches the collapse pressure allowable value, CO injection into the bottom brine layer through the injection well is started 2 (ii) a When the pore pressure of the bottom brine layer monitored by the fluid pressure sensor reaches the allowable rupture pressure value, stoppingCO 2 Injecting;
(4) reinjection of brine
When the pore pressure value of the bottom brine layer monitored by the fluid pressure sensor is restored to the initial pore pressure, starting to reinject the brine extracted from the bottom brine layer into the top brine layer through a reinjection well; stopping brine reinjection when the pore pressure of the top brine layer monitored by the fluid pressure sensor reaches the allowable top brine layer fracture pressure value;
(5) end of the test
Stopping CO 2 Injecting and finishing the test; recording CO 2 The injection amount, the swelling deformation value of the bottom brine layer, the actual saline extraction amount when the pore pressure monitoring value of the bottom brine layer reaches the allowable collapse pressure value, and the actual saline reinjection amount when the pore pressure monitoring value of the top brine layer reaches the allowable rupture pressure value;
and 3, step 3: verification calculation method
(1) Brine pre-pumping amount verification
Obtaining the actual extraction quantity of the saline water when the pore pressure monitoring value of the bottom saline water layer reaches the collapse pressure allowable value, comparing the equivalent volume of the actual extraction quantity of the saline water with the theoretical value of the pre-extraction quantity of the saline water, and if the error is within 5%, indicating that the computing method of the pre-extraction quantity of the saline water can meet the requirements of field engineering;
(2) brine refill amount verification
Obtaining the actual reinjection amount of the brine when the pore pressure monitoring value of the top brine layer reaches the allowable rupture pressure value, comparing the equivalent volume of the actual reinjection amount of the brine with the theoretical value of the reinjection amount of the brine, and if the error is within 5%, indicating that the calculation method of the reinjection amount of the brine can meet the requirements of field engineering;
and 4, step 4: contrast sealing efficiency
(1) Maximizing CO by (1), (2), (3) and (4) in step 2 2 Sealing efficiency field test, obtaining CO through (5) in step 2 2 Injection amount and maximum uplift deformation of a bottom saline layer;
(2) conventional CO development by (1) and (3) in step 2 2 Sealing site test, obtaining CO through (5) in step 2 2 Maximum change in injection volume and bottom brine layerShaping;
(3) comparison of CO in (1) and (2) above 2 Injection amount, confirmation of maximized CO 2 The field test of the sealing efficiency has the advantage of sealing capability; maximum swelling deformation of the bottom brine layer in comparison of (1) and (2) confirmed to maximize CO 2 The field test of the sealing efficiency has the advantage of sealing safety.
4. Maximum CO according to claim 3 2 The field test verification method of the sequestration efficiency is characterized in that the CO is 2 The field test device for sealing comprises a foundation pit, a bottom brine layer, a cover layer, a top brine layer, a displacement sensor, a fluid pressure sensor, an anti-seepage box body, a 'Hui' shaped foundation pit, a hydraulic support, a balancing weight, a liquid supercharger, a pressure-bearing steel pipe, a pre-pumping well, a storage box and CO 2 Detector, constant pressure pump, constant pressure water tank and supercritical CO 2 Gas tank, injection well, reinjection well.
5. Maximizing CO, according to claim 4 2 The field test verification method for the sealing efficiency is characterized in that a brine layer is formed by a bottom brine layer, a cover layer and a top brine layer, an anti-seepage box body wraps the outside of the brine layer, the brine layer and the anti-seepage box body are both arranged in the foundation pit, and soil is backfilled between the anti-seepage box body and the wall surface of the foundation pit to be compact; arranging a displacement sensor on the upper surface of the bottom brine layer to monitor the deformation of the brine layer; excavating a 'back' shaped foundation pit around the foundation pit, placing a hydraulic support in the 'back' shaped foundation pit, and applying horizontal confining pressure; arranging a balancing weight at the top of the brine layer, and applying vertical confining pressure; the liquid pressurizer is connected with the pressure-bearing steel pipe in the saline water layer and is responsible for injecting pressurized saline water into the saline water layer to realize application of initial formation pore pressure; one end of the injection well is connected with supercritical CO 2 The other end of the gas tank vertically extends into the bottom brine layer from the top center of the brine layer to realize the injection of CO into the bottom brine layer 2 (ii) a The pre-pumping well is arranged in the brine layer and is used for pumping the brine from the bottom brine layer and temporarily storing the brine in the storage tank; CO 2 2 The detector is arranged at the bottom of the pre-pumping well and used for judging CO 2 Whether or not to reachPre-pumping the bottom of the well; the reinjection well is arranged on the top brine layer and is responsible for reinjecting the brine stored in the storage tank to the top brine layer; the constant pressure pump and the constant pressure water tank are communicated with the brine layer through the pressure-bearing steel pipe, the constant pressure in the constant pressure water tank is maintained by the constant pressure pump and is equal to the initial formation pore pressure, and the pre-pumping of brine and CO is simulated 2 The seepage process of underground fluid under the actual conditions caused by injecting and reinjecting saline water, namely the self-regulation function of pore pressure in an infinite stratum; and arranging fluid pressure sensors at the bottom hole positions of the pre-pumping well, the injection well and the reinjection well, and monitoring the pore pressure of the saline stratum.
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