CN115032337B - Calculation method of brine pre-pumping quantity and reinjection quantity and field test verification method - Google Patents
Calculation method of brine pre-pumping quantity and reinjection quantity and field test verification method Download PDFInfo
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Abstract
The invention belongs to CO 2 The field of geological sequestration, which relates to a method for maximizing CO 2 Brine pre-pumping amount and reinjection amount calculation method for sealing efficiency and field test verification method, and provides a method for improving CO 2 The pre-pumping and reinjection method of the sealing efficiency respectively takes the calculated brine pre-pumping amount and reinjection amount as CO 2 Control conditions for actual brine extraction and reinjection in the sealing process are established at the same time 2 Relationship between injection rate and brine extraction rate, brine reinjection rate and CO 2 Injection velocity relationship. Maximizing CO by the design of the invention 2 The field test verification method and device of the sealing efficiency are compared with the field test to verify that the accuracy of the calculation method is more than 95%; and the brine pre-pumping and reinjection strategy is implemented by calculating the brine pre-pumping amount and the reinjection amount, so that 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, which relates to a method for maximizing CO 2 The brine pre-pumping amount and reinjection amount calculation method of the sealing efficiency and the field test verification method.
Background
CO 2 Geological sequestration has become a current research hotspot, in particular maximizing CO 2 The efficiency of geological sequestration has become a major concern. CO 2 The sealing efficiency is closely related to sealing capacity and sealing safety. To increase CO 2 The sealing capacity can be realized by CO 2 Pre-extraction of brine before brine layer injection to increase CO 2 A storage space. However, pre-pumping brine will reduce formation pore pressure, and is extremely prone to induce formation collapse. In addition, anotherIn addition to CO 2 After injection, the formation pore pressure rapidly rises from a low pressure (caused by brine pre-pumping) to a high pressure state, which in turn will cause the formation to expand or even fracture. To address formation fracture problems, the extracted brine may be reinjected into the upper adjacent brine layer, relieving formation swelling deformation caused by lower formation pore pressure lifting. Meanwhile, the re-injection of the pre-pumped brine can save a complex brine treatment process and high brine treatment cost. In summary, brine pre-pumping and reinjection can improve CO 2 Geological sequestration capacity and sequestration safety, however, implementing this strategy requires calculation of brine pre-pump and reinjection. Brine pre-pump is controlled by formation collapse conditions, while brine reinjection is controlled by formation fracture conditions. In view of this, there is an urgent need to propose a process for maximizing CO 2 The brine pre-pumping amount and the reinjection amount of the sealing efficiency are calculated, and the reliability of the calculation method in practical application is verified through field tests.
At present, a few experimental devices for simulating CO have been developed by students 2 Geological sequestration, e.g. an experimental simulation of CO 2 Geological sequestration feasibility System (CN 202010239445.0), a CO 2 Stratum sealing system (CN 202020387776.4), CO 2 Formation sequestration methods and systems (CN 202010215234.3). However, the above experimental setup was mainly simulating CO 2 Migration rules in a saline water layer are difficult to evaluate the CO of saline water pre-pumping and saline water reinjection 2 The influence of the sealing efficiency can not determine the specific brine pre-pumping quantity and brine reinjection quantity. In view of this, a method of maximizing CO is proposed 2 The brine pre-pumping amount and reinjection amount calculation method with sealing efficiency and field test verification are imperative.
Disclosure of Invention
The invention provides a method for maximizing CO 2 The brine pre-pumping amount and the brine reinjection amount of the sealing efficiency are calculated on the condition of formation collapse and formation fracture.
To achieve the above object, one aspect of the present invention provides a method for maximizing CO 2 Brine pre-pumping amount and reinjection amount calculating method with sealing efficiency, and calculating stepsThe method comprises the following steps:
(1) Calculating the brine pre-pumping quantity V of the brine layer at the bottom Pre-suction
Brine pre-pumping refers to the CO 2 Saline extraction prior to injection; CO 2 After injection, the brine extraction still lasts for a period of time, but the brine extraction amount in the period of time is not counted in the brine pre-extraction amount;
(1) determination of bottom brine layer collapse pressure permit
Wherein P is w c 、
The bottom saline layer collapse pressure critical value and allowable value are MPa; sigma (sigma) H 、σ h The maximum and minimum horizontal main stresses are respectively obtained by the applied horizontal confining pressure and are MPa; p (P) p Initial formation pore pressure for the brine layer, derived 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 cohesive force, and is obtained through Moire envelope curves of a plurality of groups of triaxial compression experiments, and MPa; alpha is the specific austenite coefficient, typically 0.85; n is n 1 Is set for the safety coefficient without dimension by combining engineering experience;
(2) determination of bottom brine layer pore pressure drop ΔP caused by brine pre-pump p pre-pumping With a reduced pore pressure value P p -ΔP p pre-pumping Not lower than the allowable value of collapse pressure
Calculating the brine pre-pumping quantity V for critical conditions Pre-suction ；
Wherein DeltaP p pre-pumping The pore pressure of a bottom saline layer is changed due to the pre-pumping of saline water, and the pressure is MPa; h Pre-suction The water level height change, m, caused by brine pre-pumping; gamma ray Brine Is severe in salt water, KN.m -3 ；V Pre-suction 、V Infiltration process Respectively the pre-pumping amount of the brine and the supply amount of the seepage flow of the underground fluid from infinity to the pre-pumping well caused by the pre-pumping of the brine under the actual condition, m 3 The method comprises the steps of carrying out a first treatment on the surface of the S is the horizontal area of the bottom saline layer, m 2 ；φ Lower part(s) The porosity of the bottom brine layer is dimensionless;
(2) Calculate the top brine layer brine reinjection amount V Reinjection
(1) Determination of top brine layer fracture pressure allowable value
Wherein P is w f 、
The critical value and the allowable value of the fracture pressure of the brine layer are MPa; sigma (sigma) t The tensile strength of the salt water layer is obtained by Brazilian split test and is MPa; n is n 2 Is set for the safety coefficient without dimension by combining engineering experience;
(2) determination of the top saline layer pore pressure increase ΔP caused by saline reinjection p reinjection To an increased pore pressure value P p +ΔP p reinjection Not higher than the allowable value of fracture pressure [ P ] w f ]Calculating the brine reinjection amount V for critical conditions Reinjection ；
Wherein DeltaP p reinjection The pore pressure of the top saline layer is changed due to the reinjection of saline water, and the pressure is MPa; h Reinjection The water level height change, m, caused by the reinjection of the brine; v (V) Reinjection 、V′ Infiltration process Respectively the brine reinjection amount and the overflow amount of underground fluid seepage from the reinjection well to infinity caused by brine reinjection under actual conditions, m 3 The method comprises the steps of carrying out a first treatment on the surface of the S' is the horizontal area of the top brine layer, m 2 ；φ Upper part Is the top salt water layer porosity, dimensionless;
(3) Bottom brine layer CO 2 CO is established when injection and brine extraction occur simultaneously 2 Injection velocity v Pouring And brine extraction rate v Extraction of Is the relation of:
wherein DeltaP P-injection Is CO 2 Injection causes bottom brine layer pore pressure changes
MPa；v Pouring Is CO 2 Injection speed, m 3 ·s -1 ；v Extraction of For the brine extraction speed, m 3 ·s -1 ；v″ Infiltration process -v Infiltration process To the supply speed of the seepage of the bottom saline layer underground fluid from infinity to the pre-pumping well and the injection well under the actual condition, m 3 ·s -1 ；
(4) Bottom brine layer CO 2 CO is established when injection and top brine layer brine reinjection occur simultaneously 2 Injection velocity v Pouring With saline reinjection rate v Reinjection Is the relation of:
in the formula, v Reinjection For the saline reinjection rate, m 3 ·s -1 ；v Pouring Is CO 2 Injection speed, m 3 ·s -1 。
Another aspect of the invention provides an enhanced CO 2 The pre-pumping-reinjection method for the sealing efficiency adopts the calculation method and specifically comprises the following steps:
firstly, pre-pumping brine from a brine layer at the bottom; when the brine pre-pumping quantity reaches the brine pre-pumping quantity V obtained by the calculation Pre-suction At the beginning of the CO injection into the bottom brine layer 2 At the same time by the CO established above 2 Control of CO in injection rate versus brine extraction rate 2 Injection rate; when CO 2 The detector detects CO 2 Stopping the brine extraction when the water is in the water; when the bottom brine layer pore pressure returns to the initial pore pressure, brine is initially reinjected into the top brine layer, with the brine reinjection rate and CO established as described above 2 The injection speed relationship controls the saline reinjection speed; when the brine reinjection amount reaches the brine reinjection amount V obtained by the calculation Reinjection Stopping saline reinjection when the saline is filled; stopping CO when the pore pressure of the bottom saline layer reaches the allowable value of the fracture pressure 2 And (5) injection.
The invention also provides a method for maximizing CO 2 The field test verification method for the sealing efficiency verifies that the brine pre-pumping amount and the reinjection amount are calculated by the method, and the method comprises the following operation steps:
step 1: layout field test
Laying out CO 2 The field test device is used for sealing;
step 2: develop field test
(1) Applying pressure
Applying three-way confining pressure to the saline water layer through the hydraulic support and the balancing weight, and applying initial stratum pore pressure to the saline water layer through the liquid booster and the pressure-bearing steel pipe;
(2) Pre-pumping brine
In CO 2 Before injection, extracting brine from a brine layer at the bottom through a pre-pumping well and temporarily storing the brine in a storage tank; in CO 2 Injection into a cavityAfter that, when brine is pre-pumped into the well bottom, CO is extracted 2 The detector detects CO 2 Stopping the brine extraction when the water is in the water;
(3) CO injection 2
When the pore pressure of the bottom brine layer monitored by the fluid pressure sensor reaches the allowable value of collapse pressure, CO is injected into the bottom brine layer through the injection well 2 The method comprises the steps of carrying out a first treatment on the surface of the Stopping CO when the pore pressure of the bottom brine layer monitored by the fluid pressure sensor reaches the allowable value of the fracture pressure 2 Injecting;
(4) Reinjection brine
When the bottom brine layer pore pressure value monitored by the fluid pressure sensor is restored to the initial pore pressure, starting to reinject 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 an allowable value of the rupture pressure of the top brine layer;
(5) Ending the test
Stopping CO 2 Injecting, and ending the test; recording CO 2 The injection amount, the bottom brine layer bulge deformation value, the brine actual extraction amount when the bottom brine layer pore pressure monitoring value reaches the collapse pressure allowable value, and the brine actual reinjection amount when the top brine layer pore pressure monitoring value reaches the fracture pressure allowable value;
step 3: verification calculation method
(1) Brine pre-pumping verification
Obtaining the actual extraction amount of the brine when the pore pressure monitoring value of the brine layer at the bottom reaches the collapse pressure allowable value, comparing the equivalent volume of the actual extraction amount of the brine with the theoretical value of the brine pre-extraction amount, and if the error is within 5%, indicating that the brine pre-extraction amount calculating method can meet the field engineering;
(2) Brine reinjection amount verification
Obtaining the actual reinjection amount of the brine when the pore pressure monitoring value of the top brine layer reaches the allowable value of the fracture pressure, and comparing the equivalent volume of the actual reinjection amount of the brine with the theoretical value of the reinjection amount of the brine, wherein if the error is within 5%, the method for calculating the reinjection amount of the brine can meet the requirements of field engineering;
step 4: contrast sealing efficiency
(1) maximizing CO by the steps (1), (2), (3) and (4) in step 2 2 A sequestration efficiency site test, wherein the CO is obtained through the step (5) in the step (2) 2 Injection volume and maximum swelling deformation of the bottom brine layer;
(2) Conventional CO is carried out by (1) and (3) in the step 2 2 A sealing and storing field test, wherein the CO is obtained through the step (5) in the step (2) 2 Injection volume and maximum swelling deformation of the bottom brine layer;
(3) Comparison of the COs in (1) and (2) above 2 The injection amount confirmed to maximize CO 2 The sealing efficiency field test has the advantage of sealing capability; comparing the maximum swelling deformation of the bottom brine layer in (1) and (2), confirming the maximization of CO 2 The sealing efficiency field test has the advantage of sealing safety.
In the present invention, CO 2 The sealed field test device is provided with a cover layer (the cover layer is CO 2 The requisite for seal addressing), 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 2 The sealed site test device comprises a foundation pit, a bottom saline layer, a cover layer, a top saline layer, a displacement sensor, a fluid pressure sensor, an anti-seepage box body, a 'back' shaped foundation pit, a hydraulic support, a balancing weight, a liquid booster, 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 A gas tank, an injection well, and a reinjection well; the bottom saline layer, the cover layer and the top saline layer form a saline layer, the outside of the saline layer is wrapped with an anti-seepage box body, the saline layer and the anti-seepage box body are arranged in the foundation pit, and the space between the anti-seepage box body and the wall surface of the foundation pit is backfilled and compacted by soil; a displacement sensor is arranged on the upper surface of the bottom saline layer, and deformation of the saline layer is monitored; digging a reverse-U-shaped foundation pit around the foundation pit, placing a hydraulic support in the reverse-U-shaped foundation pit, and applying horizontal confining pressure; arranging a balancing weight on the top of the saline water layer, and applying vertical confining pressure; the liquid booster is connected with the pressure-bearing steel pipe in the saline water layer,the pressurized brine is injected into a brine layer to realize the application of the pore pressure of the initial stratum; the pre-pumping well is arranged in the saline water layer and is used for pumping saline water from the saline water layer at the bottom and temporarily storing the saline water in the storage box; CO 2 A detector arranged at the bottom of the pre-pumping well for judging CO 2 Whether the bottom of the pre-pumping well is reached or not; the injection well is arranged at the center of the saline water layer and is connected with the supercritical CO 2 Gas tank for injecting CO into bottom saline water layer 2 The method comprises the steps of carrying out a first treatment on the surface of the The reinjection well is arranged at 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 pressure-bearing steel pipes, the constant pressure pump maintains the constant pressure in the constant pressure water tank and is equal to the pore pressure of the initial stratum, and the pre-pumping of brine and CO is simulated 2 The subsurface fluid seepage process (namely self-regulating function of pore pressure in infinite stratum) under the actual condition caused by the injection and reinjection of saline water; and arranging fluid pressure sensors at the bottom positions of the pre-pumping well, the injection well and the reinjection well, and monitoring the pore pressure of the saline layer stratum.
In the invention, the maximization of CO is calculated on the condition of formation collapse and fracture 2 The brine pre-pumping quantity and the reinjection quantity with the sealing efficiency are calculated to obtain the brine pre-pumping quantity V Pre-suction The control conditions in the actual brine extraction process are used for preventing the bottom brine layer from causing formation collapse in the brine pre-extraction process; with calculated reinjection quantity V Reinjection The control condition in the actual brine reinjection process is used for preventing the top brine layer from causing formation fracture in the brine reinjection process; at the same time establish CO 2 Relationship between injection rate and brine extraction rate, brine reinjection rate and CO 2 Injection velocity relationship. Furthermore, the invention designs a method for maximizing CO 2 The field test verification method and device for the sealing efficiency are compact and reasonable in structure, reliable in principle and high in feasibility.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention provides a method for maximizing CO 2 Brine pre-pumping amount and reinjection amount calculation method with sealing efficiency, and calculating brine pre-pumping amount and reinjection amount under the condition of formation collapse and fracture, and comparing with field testThe accuracy of the certificate calculation exceeds 95%;
2. the invention designs a method for maximizing CO 2 The site test verification method and device for the sealing efficiency are used for implementing the brine pre-pumping and reinjection strategy by calculating the brine pre-pumping and 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 schematic diagram of CO according to the present invention 2 A structural schematic diagram of the sealed field test device;
FIG. 2 is a schematic diagram of CO according to the present invention 2 A top view of the stored field test device;
FIG. 3 is a flow chart of the brine pre-pump calculation of the present invention;
FIG. 4 is a flow chart of the saline refill amount calculation of the present invention;
FIG. 5 is a graph of a comparison of the calculation method of the present invention;
FIG. 6 is a graph showing comparison of results of example 1 of the present invention;
in the figure: 1. a foundation pit; 2. a bottom brine layer; 3. a cover layer; 4. a top brine layer; 5. a displacement sensor; 6. a fluid pressure sensor; 7. an impermeable box body; 8. the foundation pit is shaped like a Chinese character 'hui'; 9. a hydraulic support; 10. balancing weight; 11. a liquid pressurizer; 12. a pressure-bearing steel pipe; 13. pre-pumping the well; 14. a storage tank; 15. CO 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 (5) reinjecting the well.
Detailed Description
The details of the invention will be more clearly understood in conjunction with the accompanying drawings and description of specific embodiments of the invention. However, the specific embodiments of the invention described herein are for the purpose of illustration only and are not to be construed as limiting the invention in any way. Given the teachings of the present invention, one of ordinary skill in the related art will contemplate any possible modification based on the present invention, and such should be considered to be within the scope of the present invention.
In one aspect, the present embodiment provides a method of maximizing CO 2 The brine pre-pumping amount and reinjection amount calculating method of the sealing efficiency comprises the following calculating steps:
(1) Calculate the brine pre-pumping amount V of the bottom brine layer 2 Pre-suction
Brine pre-pumping refers to the CO 2 Saline extraction prior to injection; CO 2 After injection, the brine extraction still lasts for a period of time, but the brine extraction amount in the period of time is not counted in the brine pre-extraction amount;
(1) determining stress distribution of 13 well walls surrounding rock of the pre-pumped well of the bottom saline layer 2 (see (1)) according to elastic mechanics, and determining radial effective stress sigma' r Effective stress sigma 'in circumferential direction' θ Substituting the Mohr-Coulomb criterion to determine the bottom brine layer 2 collapse pressure threshold, see formula (2):
considering safety requirements, the collapse pressure threshold in actual engineering is usually replaced by an allowable value, see formula (3):
wherein P is w Pre-pumping well 13 borehole pressure for bottom brine layer 2, MPa; p (P) w c 、
The collapse pressure critical value and the allowable value of the bottom saline layer 2 are MPa; sigma (sigma) H 、σ h The maximum and minimum horizontal main stresses are respectively obtained by the applied horizontal confining pressure and are MPa; p (P) p Initial formation pore pressure for the brine layer, derived 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 cohesive force, and Moire envelope curve obtained through a plurality of groups of triaxial compression experimentsObtaining MPa; alpha is the specific austenite coefficient, typically 0.85; n is n 1 Is set for the safety coefficient without dimension by combining engineering experience;
(2) pre-pumping brine causes a decrease in pore pressure ΔP in the bottom brine layer 2 p pre-pumping The value of the pore pressure after the drop is not lower than the allowable value of collapse pressure, namely
Taking the pre-pumping quantity V of the brine as a control condition to calculate Pre-suction ；
The pore pressure of the bottom saline layer 2 is reduced by delta P according to the water head pressure calculation formula p pre-pumping Represented by formula (4):
substituting formula (4)
The pre-pumping quantity V of the brine can be calculated Pre-suction See formula (5):
wherein DeltaP p pre-pumping The pore pressure of the bottom saline layer 2 is changed due to the pre-pumping of the saline water, and the pressure is MPa; h Pre-suction The water level height change, m, caused by brine pre-pumping; gamma ray Brine Is severe in salt water, KN.m -3 ；V Pre-suction 、V Infiltration process Respectively, the pre-pumping amount of the brine and the supply amount of the seepage of the underground fluid from infinity to the pre-pumping well 13 caused by the pre-pumping of the brine under the actual condition, m 3 The method comprises the steps of carrying out a first treatment on the surface of the S is the horizontal area of the bottom saline layer 2, m 2 ；φ Lower part(s) The porosity of the bottom saline layer 2 is dimensionless;
in V form Pre-suction The control conditions in the actual brine extraction process are used for preventing the bottom brine layer 2 from causing formation collapse in the brine pre-extraction process;
(2) Calculate the top brine layer 4 brine reinjection amount V Reinjection
(1) Will be described in(1) In (2) radial effective stress sigma' r Effective stress sigma 'in circumferential direction' θ Substituting the maximum tensile stress criterion to determine the formation fracture pressure, the following formula (6):
P w f ＝3σ h -σ H -αP p +σ t (6)
in view of safety requirements, the burst pressure threshold in actual engineering is generally replaced by an allowable value, see formula (7):
wherein P is w f 、
The critical value and the allowable value of the fracture pressure of the brine layer are MPa; sigma (sigma) t The tensile strength of the salt water layer is obtained by Brazilian split test and is MPa; n is n 2 Is set for the safety coefficient without dimension by combining engineering experience;
(2) reinjection of brine causes the top brine layer 4 pore pressure to increase by ΔP p reinjection The increased pore pressure value is not higher than the allowable value of fracture pressure, i.e
Calculating the saline reinjection amount V by taking the water quality as a control condition Reinjection ；/>
The pore pressure of the top saline layer 4 is increased by delta P according to the water head pressure calculation formula p reinjection Represented by formula (8):
substituting formula (8)
The reinjection amount V of the brine can be calculated Reinjection See formula (9):
wherein DeltaP p reinjection The pore pressure of the top saline layer 4 is changed due to the reinjection of the saline water, and the pressure is MPa; h Reinjection The water level height change, m, caused by the reinjection of the brine; v (V) Reinjection 、V′ Infiltration process The overflow amount of the underground fluid flowing from the reinjection well 20 to infinity caused by the reinjection of the saline water and the reinjection of the saline water under the actual conditions are respectively, m 3 The method comprises the steps of carrying out a first treatment on the surface of the S' is the horizontal area of the top saline layer 4, m 2 ；φ Upper part 4 porosities of a top saline layer and is dimensionless;
in V form Reinjection For the control condition in the actual brine reinjection process, the top brine layer 4 is prevented from causing formation fracture in the brine reinjection process;
(3) Establishing CO 2 Relationship between injection rate and brine extraction rate
After extracting brine and injecting CO 2 When the synchronous happens, the pore pressure drop of the bottom saline layer 2 caused by the extraction of the saline water is equal to CO 2 The pore pressure increase of the bottom saline layer 2 caused by injection is taken as a control condition to build up CO 2 The relationship between the injection rate and the saline withdrawal rate is shown in the following formula (10):
wherein DeltaP P-injection Is CO 2 Injection causes a change in pore pressure in the bottom brine layer 2
MPa；v Pouring Is CO 2 Injection speed, m 3 ·s -1 ；v Extraction of For the brine extraction speed, m 3 ·s -1 ；v″ Infiltration process -v Infiltration process The supply speed of the subsurface fluid of the bottom saline layer 2 from infinity to the pre-pumping well 13 and the injection well 19 is obtained by the pressure difference between the formation pore pressure and the constant pressure water tank 17 and darcy law, and the following formula (11):
wherein k is the stratum permeability coefficient, and m.s is obtained through permeability experiments -1 The method comprises the steps of carrying out a first treatment on the surface of the A is the cross-sectional area of the stratum perpendicular to the seepage direction, m 2 The method comprises the steps of carrying out a first treatment on the surface of the L is the seepage length, m;
(4) Establishing saline reinjection rate and CO 2 Injection velocity relationship
At the time of CO injection 2 In synchronization with reinjection of brine, in CO 2 The increase of the pore pressure of the bottom saline layer 2 caused by injection is equal to the increase of the pore pressure of the top saline layer 4 caused by saline reinjection, which is taken as a control condition, and the saline reinjection speed and the CO are established 2 Injection velocity relationship, formula (12) below:
in the formula, v Reinjection For the saline reinjection rate, m 3 ·s -1 ；v Pouring Is CO 2 Injection speed, m 3 ·s -1 ；v′ Infiltration process To the overflow rate of the subsurface fluid from the reinjection well 20 to infinity under practical conditions, m 3 ·s -1 ；v″ Infiltration process To the overflow rate of the seepage of the underground fluid from the injection well 19 to infinity under practical conditions, m 3 ·s -1 ；
In particular, by "CO 2 The condition that the pore pressure increase of the bottom brine layer 2 caused by injection is equal to the pore pressure increase of the top brine layer 4 caused by brine reinjection can determine that the pressure differences among the bottom brine layer 2, the top brine layer 4 and the constant pressure water tank 17 are equal, and further the Darcy law is combined to obtain v' Infiltration process ＝v″ Infiltration process For this purpose, formula (12) is further simplified to formula (13):
another aspect of the invention provides a method of maximizing CO 2 Site test of sealing efficiency, verifying pre-pumping quantity and pre-pumping quantity of brineThe reinjection amount calculating method comprises the following operation steps:
step 1: layout field test
As shown in fig. 1-2, the one maximizes CO 2 The field 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 7, a 'reverse' type foundation pit 8, a hydraulic support 9, a balancing weight 10, a liquid booster 11, a pressure-bearing steel pipe 12, a pre-pumping well 13, a storage box 14 and CO 2 Detector 15, constant pressure pump 16, constant pressure water tank 17, supercritical CO 2 A gas tank 18, an injection well 19, and a reinjection well 20;
excavating a foundation pit 1, wherein the volume is 3km long, 3km wide and 100m deep, 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 form a saline layer together; the mortar mass ratio of the bottom saline layer 2 and the top saline layer 4 is cement: sand: water is equal to 1:0.33:0.42, the mass ratio of the mortar of the cover layer 3 is cement: sand: water is equal to 1:0.11:0.42; the outside of the brine layer is wrapped with an anti-seepage box body 7 (manufactured by a thin steel plate), so that the brine is prevented from seeping out of the brine layer under the high-pressure condition, and the anti-seepage box body 7 and the wall surface of the foundation pit 1 are backfilled with soil to be compact; a displacement sensor 5 is arranged on the upper surface of the bottom saline layer 2 transversely and longitudinally every 600m, and deformation of the saline layer is monitored;
digging a square 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 square foundation pit 8, fixing the bottom of the hydraulic support 9 on the outer wall surface of the square 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 square foundation pit 8 (namely the wall surface near the foundation pit 1), and applying horizontal confining pressure; balancing weights 10 are arranged at the top of the saline water layer transversely and longitudinally at intervals of 300m, and vertical confining pressure is applied; the liquid pressurizer 11 is connected with a pressure-bearing steel pipe 12 in the saline water layer and is responsible for injecting pressurized saline water into the saline water layer to realize the application of initial stratum pore pressure;
one end of the injection well 19 is connected with supercritical CO 2 A gas tank 18, the other end of which vertically penetrates into the bottom saline layer 2 from the center of the top of the saline layer for 20m, so as to realize CO injection into the bottom saline layer 2 2 The method comprises the steps of carrying out a first treatment on the surface of the The pre-pumping well 13 is arranged at 1km on the left and right sides of the injection well 19 and penetrates into the bottom saline layer 2 for 20m, and is used for pumping saline water from the bottom saline layer 2 and temporarily storing the saline water in the storage tank 14; CO 2 A detector 15 is arranged at the bottom of the pre-pump well 13 for determining CO 2 Whether the bottom of the pre-pumping well 13 is reached; the reinjection well 20 is arranged at 1km on the left and right sides of the center of the top brine layer 4 and goes deep into the top brine layer 4 for 15m and is responsible for reinjection of the brine stored in the storage tank 14 into the top brine layer 4; the constant pressure pump 16 and the constant pressure water tank 17 are communicated with the brine layer through the pressure-bearing steel pipe 12, and the constant pressure of the constant pressure water tank 17 is maintained constant and equal to the initial stratum pore pressure by the constant pressure pump 16, so as to simulate pre-pumping brine and CO 2 The subsurface fluid seepage process (namely self-regulating function of pore pressure in infinite stratum) under the actual condition caused by the injection and reinjection of saline water; arranging fluid pressure sensors 6 at the bottom positions of the pre-pumping well 13, the injection well 19 and the reinjection well 20, and monitoring the stratum pore pressure of the saline water layer;
step 2: develop field test
(1) Applying pressure
Applying three-way confining pressure to the saline water layer through a hydraulic support 9 and a balancing weight 10; pressurizing the brine by the liquid pressurizer 11, and then injecting the pressurized brine into a brine layer by the pressure-bearing steel pipe 12 to realize the application of the initial formation pore pressure;
(2) Pre-pumping brine
Brine is extracted from the bottom brine layer through the pre-pumping well 13 and is temporarily stored in the storage tank 14, and the brine extraction speed v is set according to engineering experience Extraction of The method comprises the steps of carrying out a first treatment on the surface of the Meanwhile, the replenishing process of underground fluid from infinity to pre-pumping well seepage caused by pre-pumping brine in the bottom brine layer under actual conditions is simulated through the constant pressure water tank 17 and the pressure-bearing steel pipe 12;
(3) CO injection 2
When the pore pressure of the bottom brine layer 2 monitored by the fluid pressure sensor 6 at the bottom position of the pre-pumping well 13 reaches the allowable value of collapse pressure, CO injection into the bottom brine layer 2 through the injection well 19 is started 2 Simultaneously calculate CO according to formula (10) 2 Injection velocity v Pouring ；
(4) Stopping brine extraction
CO arranged at the bottom of the brine pre-pumping well 13 2 The detector 15 detects CO 2 Stopping the brine extraction when the water is in the water;
(5) Reinjection brine
When the bottom brine layer 2 pore pressure monitored by the fluid pressure sensor 6 at the bottom hole position of the injection well 19 is restored to the initial formation pore pressure, the brine extracted from the bottom brine layer 2 is started to be refilled into the top brine layer 4 through the refill well 20 while the brine refill speed v is calculated according to formula (13) Reinjection ；
(6) Stopping saline reinjection
Stopping brine reinjection when the pore pressure of the top brine layer 4 monitored by the fluid pressure sensor 6 (at the bottom position of the reinjection well 20) reaches a fracture pressure allowable value;
(7) Stopping CO 2 Injection into a cavity
Stopping CO when the pore pressure of the bottom brine layer 2 monitored by the fluid pressure sensor 6 (at the bottom of the injection well 19) reaches the allowable value of the fracture pressure 2 Injecting;
(8) Ending the test
Stopping CO 2 Injecting, and ending the test; recording CO 2 Injection amount, bottom brine layer 2 bulge deformation value, brine actual extraction amount V when bottom brine layer 2 pore pressure monitoring value reaches collapse pressure allowable value Pre-pump test Brine actual reinjection quantity V when top brine layer 4 pore pressure monitoring value reaches fracture pressure allowable value Reinjection-test ；
Step 3: verification calculation method
In particular, the initial pore pressure of the brine layer in the field test is achieved by pressurizing the brine by the liquid pressurizer 11, rather than the initial pore pressure achieved by the brine under actual conditions by gravity itself, so that the brine volume injected into the brine layer in the field test (denoted as brine pressurizing volume V Brine-boost Obtained directly from field trials) is much smaller than the brine volume (noted as the brine raw volume, expressed as
Or->
) The method comprises the steps of carrying out a first treatment on the surface of the In view of the above, the equivalent conversion is carried out on the pressurized volume of the brine in the field test and the original volume of the brine under the actual condition so as to be compared with the brine pre-pumping amount and the brine reinjection amount obtained by a theoretical calculation method;
(1) Brine pre-pumping verification
Obtaining the actual extraction quantity V of brine when the pore pressure monitoring value of the bottom brine layer 2 reaches the collapse pressure allowable value Pre-pump test Equivalent to obtain
And is matched with the theoretical value V of the pre-pumping quantity of the brine Pre-pump theory Comparing, if the error is within 5%, the method for calculating the pre-pumping amount of the brine can meet the field engineering;
(2) Brine reinjection amount verification
Obtaining the actual reinjection quantity V of the brine when the pore pressure monitoring value of the top brine layer 4 reaches the allowable value of the fracture pressure Reinjection-test Equivalent to obtain
And is matched with the theoretical value V of the reinjection quantity of the saline Reinjection theory Comparing, if the error is within 5%, the method for calculating the saline reinjection amount can meet the field engineering;
step 4: contrast sealing efficiency
(1) Maximizing CO by performing steps (1) - (7) in step 2 2 A sequestration efficiency site test, wherein the CO is obtained through the step (8) in the step 2 2 Injection quantity V 1 And maximum bulging deformation u of bottom brine layer 2 1 ；
(2) Conventional CO is carried out by (1), (3) and (7) in step 2 2 A sealing and storing field test, wherein the CO is obtained through the step (8) in the step 2 2 Injection quantity V 2 And maximum bulging deformation u of bottom brine layer 2 2 ；
(3) Comparison of the COs in (1) and (2) above 2 Injection quantity V 1 、V 2 And (3) determiningMaximizing CO 2 The sealing efficiency field test has the advantage of sealing capability; comparison of bottom brine layer 2 maximum swelling deformation u in (1) and (2) 1 、u 2 Confirm the maximization of CO 2 The sealing efficiency field test has the advantage of sealing safety.
Example 1:
laying out a field test according to the step 1; obtaining the tensile strength sigma of the bottom saline layer 2 and the top saline layer 4 through rock strength experiments t 4MPa, cohesion c of 9MPa, internal friction angle
40 °; obtaining the permeability k of the bottom saline layer 2 and the top saline layer 4 to be 1 multiplied by 10 through a permeability experiment -10 m/s, porosity phi of 0.15; setting the maximum level, the minimum level and the vertical confining pressure to 20MPa, 16MPa and 10MPa according to the step (1) in the step (2), and setting the initial stratum pore pressure to 12MPa; setting a safety coefficient n according to engineering experience 1 、n 2 1.25 and 1.35 respectively, and the collapse pressure allowable value and the fracture pressure allowable value are respectively 10.9MPa and 14.8MPa according to the formulas (3) and (7); brine and supercritical CO acquisition by data 2 The weight of the materials is 9.8 KN.m respectively -3 、4.48KN·m -3 The method comprises the steps of carrying out a first treatment on the surface of the Maximizing CO according to steps (2) - (7) in step 2 2 In the field test of sealing efficiency, the brine extraction speed was set to 0.5kg/s, and CO was calculated according to the formulas (10) and (11) 2 The injection rate was 1.13kg/s, and then the brine reinjection rate was calculated to be 0.52kg/s according to formula (13); developing conventional CO according to (3), (7) in step 2 2 Testing a sealing and storing site; the maximized CO is obtained according to the steps (1) and (2) in the step 3 2 Brine pre-pumping amount (equivalent volume) under storage efficiency field test>
And respectively match with the theoretical value V of the pre-pumping quantity of the brine Pre-pump theory Theoretical value of saline reinjection amount V Reinjection theory In contrast, as shown in fig. 5; the maximized CO is obtained according to the steps (1) and (2) in the step 4 2 Site test of sequestration efficiency and conventional CO 2 CO under the test of the sealing and storing field 2 Injection quantity V 1 、V 2 Maximum bulging deformation u of bottom brine layer 2 1 、u 2 The method comprises the steps of carrying out a first treatment on the surface of the Comparing the two conditions of CO according to (3) in step 4 2 Injection quantity V 1 、V 2 Maximum bulging deformation u of bottom brine layer 2 1 、u 2 As shown in fig. 6.
As can be seen from FIG. 5, the maximizing CO according to the present invention 2 The difference between the theoretical value of the brine pre-pumping quantity and the reinjection quantity of the sealing efficiency and the actual pumping quantity and the actual reinjection quantity of the field test is only 3.1 percent and 4.3 percent, which shows that the method maximizes CO 2 The brine pre-pumping quantity and reinjection quantity calculation method with the sealing efficiency can meet the field engineering requirements.
From FIG. 6, it can be seen that the present invention maximizes CO 2 Compared with the conventional CO, the sequestration efficiency field test is carried out 2 The sequestration site test has the advantage of sequestration capacity, CO 2 The injection quantity is improved by 25%; maximizing CO 2 Compared with the conventional CO, the sequestration efficiency field test is carried out 2 The sealing field test has the sealing safety advantage, and the maximum uplift deformation of the bottom saline layer 2 is reduced by 20%.
Claims (5)
1. Maximizing CO 2 The brine pre-pumping amount and reinjection amount calculating method for the sealing efficiency is characterized by comprising the following specific calculating steps of:
(1) Calculating the brine pre-pumping quantity V of the brine layer at the bottom Pre-suction
Brine pre-pumping refers to the CO 2 Saline extraction prior to injection; CO 2 After injection, the brine extraction still lasts for a period of time, but the brine extraction amount in the period of time is not counted in the brine pre-extraction amount;
(1) determination of bottom brine layer collapse pressure permit
Wherein P is w c 、
The bottom saline layer collapse pressure critical value and allowable value are MPa; sigma (sigma) H 、σ h The maximum and minimum horizontal main stresses are respectively obtained by the applied horizontal confining pressure and are MPa; p (P) p Initial formation pore pressure for the brine layer, derived 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 cohesive force, and is obtained through Moire envelope curves of a plurality of groups of triaxial compression experiments, and MPa; alpha is the specific austenite coefficient, typically 0.85; n is n 1 Is set for the safety coefficient without dimension by combining engineering experience;
(2) determination of bottom brine layer pore pressure drop ΔP caused by brine pre-pump p pre-pumping With a reduced pore pressure value P p -ΔP p pre-pumping Not lower than the allowable value of collapse pressure [ P ] w c ]Calculating the brine pre-pumping quantity V for critical conditions Pre-suction ；
Wherein DeltaP p pre-pumping The pore pressure of a bottom saline layer is changed due to the pre-pumping of saline water, and the pressure is MPa; h Pre-suction The water level height change, m, caused by brine pre-pumping; gamma ray Brine Is severe in salt water, KN.m -3 ；V Pre-suction 、V Infiltration process Respectively the pre-pumping amount of the brine and the supply amount of the seepage flow of the underground fluid from infinity to the pre-pumping well caused by the pre-pumping of the brine under the actual condition, m 3 The method comprises the steps of carrying out a first treatment on the surface of the S is the horizontal area of the bottom saline layer, m 2 ；φ Lower part(s) As a bottom brine layerPorosity, dimensionless;
(2) Calculate the top brine layer brine reinjection amount V Reinjection
(1) Determination of top brine layer fracture pressure allowable value
Wherein P is w f 、
The critical value and the allowable value of the fracture pressure of the brine layer are MPa; sigma (sigma) t The tensile strength of the salt water layer is obtained by Brazilian split test and is MPa; n is n 2 Is set for the safety coefficient without dimension by combining engineering experience;
(2) determination of the top saline layer pore pressure increase ΔP caused by saline reinjection p reinjection To an increased pore pressure value P p +ΔP p reinjection Not higher than the allowable value of fracture pressure
Calculating the brine reinjection amount V for critical conditions Reinjection ；
Wherein DeltaP p reinjection The pore pressure of the top saline layer is changed due to the reinjection of saline water, and the pressure is MPa; h Reinjection The water level height change, m, caused by the reinjection of the brine; v (V) Reinjection 、V′ Infiltration process Respectively brineReinjection amount, overflow amount of underground fluid from reinjection well to infinite seepage caused by brine reinjection under actual condition, m 3 The method comprises the steps of carrying out a first treatment on the surface of the S' is the horizontal area of the top brine layer, m 2 ；φ Upper part Is the top salt water layer porosity, dimensionless;
(3) Bottom brine layer CO 2 CO is established when injection and brine extraction occur simultaneously 2 Injection velocity v Pouring And brine extraction rate v Extraction of Is the relation of:
wherein DeltaP P-injection Is CO 2 Injection causes bottom brine layer pore pressure changes
MPa；v Pouring Is CO 2 Injection speed, m 3 ·s -1 ；v Extraction of For the brine extraction speed, m 3 ·s -1 ；v″ Infiltration process -v Infiltration process To the supply speed of the seepage of the bottom saline layer underground fluid from infinity to the pre-pumping well and the injection well under the actual condition, m 3 ·s -1 ；
(4) Bottom brine layer CO 2 CO is established when injection and top brine layer brine reinjection occur simultaneously 2 Injection velocity v Pouring With saline reinjection rate v Reinjection Is the relation of:
in the formula, v Reinjection For the saline reinjection rate, m 3 ·s -1 ；v Pouring Is CO 2 Injection speed, m 3 ·s -1 。
2. Improving CO 2 The pre-pumping and reinjection method for the sealing efficiency is characterized by comprising the following steps ofThe method comprises the following steps:
firstly, pre-pumping brine from a brine layer at the bottom; when the brine pre-pumping amount reaches the brine pre-pumping amount V calculated in the claim 1 Pre-suction At the beginning of the CO injection into the bottom brine layer 2 At the same time by the CO established in claim 1 2 Control of CO in injection rate versus brine extraction rate 2 Injection rate; when CO 2 The detector detects CO 2 Stopping the brine extraction when the water is in the water; when the bottom brine layer pore pressure returns to the initial pore pressure, brine is started to be refilled into the top brine layer, while the brine refill speed and CO established in claim 1 2 The injection speed relationship controls the saline reinjection speed; when the brine reinjection amount reaches the brine reinjection amount V calculated in claim 1 Reinjection Stopping saline reinjection when the saline is filled; stopping CO when the pore pressure of the bottom saline layer reaches the allowable value of the fracture pressure 2 And (5) injection.
3. Maximizing CO 2 Site test verification method of sequestration efficiency, verifying maximized CO as recited in claim 1 2 The brine pre-pumping amount and reinjection amount calculating method for the sealing efficiency is characterized by comprising the following specific operation steps of:
step 1: layout field test
Laying out CO 2 The field test device is used for sealing;
step 2: develop field test
(1) Applying pressure
Applying three-way confining pressure to the saline water layer through the hydraulic support and the balancing weight, and applying initial stratum pore pressure to the saline water layer through the liquid booster and the pressure-bearing steel pipe;
(2) Pre-pumping brine
In CO 2 Before injection, extracting brine from a brine layer at the bottom through a pre-pumping well and temporarily storing the brine in a storage tank; in CO 2 After injection, when brine is pre-pumped into the well bottom, CO 2 The detector detects CO 2 Stopping the brine extraction when the water is in the water;
(3) CO injection 2
When the fluid pressure sensor monitorsWhen the pore pressure of the bottom brine layer reaches the allowable value of collapse pressure, CO is injected into the bottom brine layer through the injection well 2 The method comprises the steps of carrying out a first treatment on the surface of the Stopping CO when the pore pressure of the bottom brine layer monitored by the fluid pressure sensor reaches the allowable value of the fracture pressure 2 Injecting;
(4) Reinjection brine
When the bottom brine layer pore pressure value monitored by the fluid pressure sensor is restored to the initial pore pressure, starting to reinject 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 an allowable value of the rupture pressure of the top brine layer;
(5) Ending the test
Stopping CO 2 Injecting, and ending the test; recording CO 2 The injection amount, the bottom brine layer bulge deformation value, the brine actual extraction amount when the bottom brine layer pore pressure monitoring value reaches the collapse pressure allowable value, and the brine actual reinjection amount when the top brine layer pore pressure monitoring value reaches the fracture pressure allowable value;
step 3: verification calculation method
(1) Brine pre-pumping verification
Obtaining the actual extraction amount of the brine when the pore pressure monitoring value of the brine layer at the bottom reaches the collapse pressure allowable value, comparing the equivalent volume of the actual extraction amount of the brine with the theoretical value of the brine pre-extraction amount, and if the error is within 5%, indicating that the brine pre-extraction amount calculating method can meet the field engineering; the brine pre-pumping theoretical value refers to the brine pre-pumping V of the bottom brine layer in the step (1) of the claim 1 Pre-suction ；
(2) Brine reinjection amount verification
Obtaining the actual reinjection amount of the brine when the pore pressure monitoring value of the top brine layer reaches the allowable value of the fracture pressure, and comparing the equivalent volume of the actual reinjection amount of the brine with the theoretical value of the reinjection amount of the brine, wherein if the error is within 5%, the method for calculating the reinjection amount of the brine can meet the requirements of field engineering; the brine reinjection amount theoretical value refers to the brine reinjection amount V of the top brine layer in the step (2) of the claim 1 Reinjection ；
Step 4: contrast sealing efficiency
(1) maximizing CO by the steps (1), (2), (3) and (4) in step 2 2 A sequestration efficiency site test, wherein the CO is obtained through the step (5) in the step (2) 2 Injection volume and maximum swelling deformation of the bottom brine layer;
(2) Conventional CO is carried out by (1) and (3) in the step 2 2 A sealing and storing field test, wherein the CO is obtained through the step (5) in the step (2) 2 Injection volume and maximum swelling deformation of the bottom brine layer;
(3) Comparison of the COs in (1) and (2) above 2 The injection amount confirmed to maximize CO 2 The sealing efficiency field test has the advantage of sealing capability; comparing the maximum swelling deformation of the bottom brine layer in (1) and (2), confirming the maximization of CO 2 The sealing efficiency field test has the advantage of sealing safety.
4. A maximized CO according to claim 3 2 The site test verification method of the sealing efficiency is characterized in that the CO 2 The sealed site test device comprises a foundation pit, a bottom saline layer, a cover layer, a top saline layer, a displacement sensor, a fluid pressure sensor, an anti-seepage box body, a 'back' shaped foundation pit, a hydraulic support, a balancing weight, a liquid booster, 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. A maximized CO according to claim 4 2 The field test verification method of the sealing efficiency is characterized in that a saline layer is formed by a bottom saline layer, a cover layer and a top saline layer, an anti-seepage box body is wrapped outside the saline layer, the saline layer and the anti-seepage box body are arranged in a foundation pit, and soil is used for backfilling between the anti-seepage box body and the wall surface of the foundation pit to be compact; a displacement sensor is arranged on the upper surface of the bottom saline layer, and deformation of the saline layer is monitored; digging a reverse-U-shaped foundation pit around the foundation pit, placing a hydraulic support in the reverse-U-shaped foundation pit, and applying horizontal confining pressure; arranging a balancing weight on the top of the saline water layer, and applying vertical confining pressure; liquid boosterThe pressurized brine is injected into the brine layer to realize the application of the pore pressure of the initial stratum; one end of the injection well is connected with supercritical CO 2 The other end of the air tank vertically penetrates into the bottom saline water layer from the center of the top of the saline water layer, so that CO is injected into the bottom saline water layer 2 The method comprises the steps of carrying out a first treatment on the surface of the The pre-pumping well is arranged in the saline water layer and is used for pumping saline water from the saline water layer at the bottom and temporarily storing the saline water in the storage box; CO 2 A detector arranged at the bottom of the pre-pumping well for judging CO 2 Whether the bottom of the pre-pumping well is reached or not; the reinjection well is arranged at 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 pressure-bearing steel pipes, the constant pressure pump maintains the constant pressure in the constant pressure water tank and is equal to the pore pressure of the initial stratum, and the pre-pumping of brine and CO is simulated 2 The seepage process of the underground fluid under the actual condition caused by the injection and reinjection of the saline water, namely the self-regulating function of the pore pressure in the infinite stratum; and arranging fluid pressure sensors at the bottom positions of the pre-pumping well, the injection well and the reinjection well, and monitoring the pore pressure of the saline layer stratum.
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