Carbon dioxide energy increasing and pressure supplementing method for low-pressure tight gas reservoir

Abstract

The invention discloses a low-pressure tight gas reservoir carbon dioxide energy increasing and pressure supplementing method which comprises the following steps: establishing a gas pressurization basic model according to original formation pressure, the method comprises the following steps: dividing reservoirs into low-pressure I-type gas reservoirs, low-pressure II-type gas reservoirs, normal-pressure gas reservoirs, low-porosity gas reservoirs, ultra-low-porosity gas reservoirs, gas saturation A-type gas reservoirs and gas saturation B-type gas reservoirs according to a gas pressurization basis, and predicting CO2 injection amounts required for different types of reservoir stratum pressure coefficients to reach a set value; liquid CO2 / base fluid pre-mixed injection is carried out on a low-pressure I-type gas reservoir, a low-pressure II-type gas reservoir and a normal-pressure gas reservoir; cO2 / guanidine gum fracturing fluid sand-carrying mixed injection and normal-pressure gas reservoir guanidine gum fluid sand-carrying injection are carried out on a low-pressure I-type gas reservoir and a low-pressure II-type gas reservoir; and carrying out base fluid displacement on the low-pressure I-type gas reservoir, the low-pressure II-type gas reservoir and the normal-pressure gas reservoir. The method is easy to operate, energy increasing and a large amount of sand carrying are both considered, the liquid drainage period can be shortened, the flow-back capacity is improved, and the overall gas reservoir transformation effect is improved.

Description

Technical Field

[0001] The invention relates to a method for increasing the energy and compensating the pressure of carbon dioxide in a low-pressure tight gas reservoir, and belongs to the technical field of hydraulic fracturing in the development of oil and gas fields. Background Art

[0002] CO2 volume fracturing technology uses the advantages of supercritical seepage and rock breaking, and has clear technical pertinence for low-pressure and dense reservoirs. However, the liquid CO2 in conventional CO2 energy-enhanced fracturing has high friction and low viscosity, and is generally only used for pre-energy enhancement, and cannot take into account both reservoir energy enhancement and sand carrying performance at the same time.

[0003] When determining the amount of liquid CO2 on site, the development experience of conventional reservoirs is usually used, but there is a lack of theoretical basis, and the relationship between the amount of CO2 and the key geological parameters of the reservoir is not clearly understood. At present, CO2 volume fracturing technology in Changqing Oilfield is becoming more and more common, but the effects after fracturing are uneven.

[0004] In the article "Research on CO2 Rock Breaking Mechanism and Fracturing Technology", Ding Yong established a gas pressurization basic model to calculate the amount of liquid CO2 injected when the formation pressure coefficient is increased to a certain value. However, the model is limited to standard atmospheric pressure and standard ground temperature conditions, while the ground temperature during on-site construction is generally between 10°C and 40°C. Therefore, the model has great limitations on the ground temperature. The calculated amount of liquid CO2 injected cannot reflect the real-time temperature conditions on site and is difficult to apply on site. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for carbon dioxide energy enhancement and pressure replenishment in low-pressure tight gas reservoirs, which has high construction efficiency and can increase the gas well production.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for increasing the energy and pressure of carbon dioxide in a low-pressure tight gas reservoir comprises the following steps:

[0008] (1) Calculate the original formation pressure based on different formation pressure coefficients and hydrostatic column pressure, or measure the formation pressure of each reservoir using an electronic pressure gauge and obtain the original formation pressure through production performance curve analysis;

[0009] (2) Based on the original formation pressure, a gas pressurization basic model considering the effect of ground temperature on the volume conversion of CO2 gas and liquid is established. According to the comprehensive fracturing fluid volume sweep coefficient of the gas pressurization basic model, the reservoirs are divided into low-pressure type I gas reservoirs, low-pressure type II gas reservoirs, normal pressure gas reservoirs, low-porosity gas reservoirs, ultra-low-porosity gas reservoirs, gas saturation type A gas reservoirs and gas saturation type B gas reservoirs. The CO2 injection volume required when the formation pressure coefficient of different types of reservoirs reaches 1.0 is predicted respectively;

[0010] (3) Pre-injection of liquid CO2 / base fluid into low-pressure Class I gas reservoirs, low-pressure Class II gas reservoirs, and normal-pressure gas reservoirs;

[0011] (4) CO2 / Guan gel fracturing fluid mixed injection with sand is carried out in low-pressure Class I gas reservoirs and low-pressure Class II gas reservoirs, and guanidine gel fluid mixed injection with sand is carried out in normal-pressure gas reservoirs;

[0012] (5) Carry out base fluid displacement in low-pressure Class I gas reservoirs, low-pressure Class II gas reservoirs, and normal-pressure gas reservoirs.

[0013] Further, the value is set to 1.0.

[0014] Furthermore, the basic model of gas pressurization considering the effect of the actual ground temperature on the volume conversion of CO2 gas and liquid is shown in formulas (1)-(4);

[0015]

[0016]

[0017] β=nRT sc / P sc ,T sc ∈(283K,313K) (3)

[0018] V=ψ(G'-G) / β (4)

[0019] Where G is the original gas reservoir geological reserves; G' is the gas reservoir geological reserves when the formation pressure coefficient reaches 1.0, β is the gas expansion coefficient, V is the injection volume of liquid CO2, A is the gas-bearing area; h is the average effective thickness; S wi is the initial water saturation; Z i is the gas deviation coefficient; ψ is the fracturing fluid volume sweep coefficient; is the pressure coefficient; n is the amount of gas substance; R is the molar gas constant; P w is the hydrostatic column pressure; H is the hydrostatic column height; ρ w is the static liquid column density; g is the gravitational acceleration; P sc is the surface pressure; T is the air temperature; P i is the original formation pressure; P i ' is the energy storage formation pressure; T sc is the ground temperature.

[0020] Furthermore, the ground temperature T sc ∈ (283K, 293K), β = 499;

[0021] Ground temperature T sc ∈ (293K, 303K), β = 517;

[0022] Ground temperature T sc ∈ (303K, 313K), β = 534.

[0023] Furthermore, the low-pressure Class I gas reservoir refers to a gas reservoir with a formation pressure coefficient of 0.7 to 0.8;

[0024] The low-pressure type II gas reservoirs mentioned above refer to gas reservoirs with a formation pressure coefficient of 0.8 to 0.9;

[0025] The normal pressure gas reservoir refers to a gas reservoir with a formation pressure coefficient of 0.9 to 1.0;

[0026] The ultra-low porosity gas reservoirs are gas reservoirs with a porosity of 1% to 5.5%;

[0027] The low-porosity gas reservoir refers to a gas reservoir with a porosity of 5.5% to 10%;

[0028] The gas saturation Class A gas reservoir refers to a gas reservoir with a gas saturation of 60% to 80%;

[0029] The gas saturation Class B gas reservoir refers to a gas reservoir with a gas saturation of 40% to 60%.

[0030] Furthermore, in step (3), low pressure type I gas reservoir, low pressure type II gas reservoir and normal pressure gas reservoir adopt 4m 3 / min displacement base fluid and mixed injection of liquid CO2.

[0031] Furthermore, in step (3):

[0032] (1) For low-pressure Class I low-porosity Class A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the volume ratio of CO2 / guar gum fracturing fluid system is 3:10; the liquid CO2 injection volume is 58% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min;

[0033] (2) For low-pressure Class I extra-low-porosity Class A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 6:10; the liquid CO2 injection volume is 58% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min;

[0034] (3) For low-pressure Class II low-porosity A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 2:10; the liquid CO2 injection volume is 55% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min;

[0035] (4) For low-pressure Class II extra-low-porosity A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 4:10; the liquid CO2 injection volume is 57% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min;

[0036] (5) For normal pressure low porosity A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 1:10; the liquid CO2 injection volume is 100% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min;

[0037] (6) For normal pressure and ultra-low porosity A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 2:10; the liquid CO2 injection volume is 100% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 30% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min.

[0038] Furthermore, in step (4), the low-pressure type I gas reservoir and the low-pressure type II gas reservoir adopt 6m 3 / min displacement of guar gum fracturing fluid, mixed injection of liquid CO2 to carry sand to support fractures, low-pressure Class I gas reservoir injection displacement is stepped, from 1.5m 3 / min down to 0.8m 3 / min; normal pressure gas reservoirs use 6m 3 / min displacement of guar gum fracturing fluid, low-pressure type I gas reservoir, low-pressure type II gas reservoir and normal pressure gas reservoir all carry 70-140 mesh ceramsite proppant to fully fill the support seams.

[0039] Furthermore, in step (4):

[0040] (1) For low-pressure Class I low-porosity Class A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the volume ratio of CO2 / guar gum fracturing fluid system is 3:10; the liquid CO2 injection volume is 42% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 0.8-2m 3 / min, the injection volume of guar cross-linking fluid is 60% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min;

[0041] (2) For low-pressure Class I and extra-low-porosity Class A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 6:10; the liquid CO2 injection volume is 42% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 0.8-2m 3 / min, the injection volume of guar cross-linking fluid is 61% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min;

[0042] (3) For low-pressure Class II low-porosity A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 2:10; the liquid CO2 injection volume is 45% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 0.8-2m 3 / min, the injection volume of guar cross-linking fluid is 60% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min;

[0043] (4) For low-pressure Class II extra-low-porosity A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 4:10; the liquid CO2 injection volume is 43% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 0.8-2m 3 / min, the injection volume of guar cross-linking fluid is 60% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min;

[0044] (5) For normal pressure low porosity A and B gas reservoirs: the injection volume of guar crosslinking fluid is 61% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min;

[0045] (6) For normal pressure and ultra-low porosity A and B gas reservoirs: the injection volume of guar crosslinking fluid is 60% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min.

[0046] Furthermore, in step (5), the low-pressure type I gas reservoir, the low-pressure type II gas reservoir, and the normal-pressure gas reservoir use 6m3 / min displacement of base fluid to displace the wellbore, and the fracturing operation is completed after the displacement is completed.

[0047] Furthermore, in step (5):

[0048] (1) For low-pressure Class I and low-porosity Class A and B gas reservoirs: the base fluid injection volume is 9% of the total guar gum fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min;

[0049] (2) For low-pressure Class I extra-low-porosity Class A and B gas reservoirs: the base fluid injection volume is 9% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min;

[0050] (3) For low-pressure Class II low-porosity Class A and B gas reservoirs: the base fluid injection volume is 9% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min;

[0051] (4) For low-pressure Class II extra-low-porosity A and B gas reservoirs: the base fluid injection volume is 9% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min;

[0052] (5) For normal pressure low porosity A and B gas reservoirs: the base fluid injection volume is 8% of the total guar gel fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min;

[0053] (6) For normal pressure and ultra-low porosity A and B gas reservoirs: the base fluid injection volume is 10% of the total guar gel fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min.

[0054] Compared with the prior art, the beneficial technical effects of the present invention are:

[0055] The present invention adopts the mixed injection of CO2 / guar gum fracturing fluid system, with low construction friction, stable displacement during the construction process, guaranteed crack opening degree, high construction efficiency, and the combined proppant realizes efficient support for the main cracks and branch cracks, effectively improving the fracture conductivity and increasing the gas well production. The CO2 energy enhancement and pressure replenishment method for low-pressure and low-porosity gas reservoirs provided by the present invention meets the on-site needs of the oil field, is simple to operate, takes into account both energy enhancement and large-scale sand carrying, can shorten the drainage cycle, improve the return flow capacity, and improve the overall effect of gas reservoir transformation. It can be widely used in various low-pressure, low-porosity, low-permeability, strong water-sensitive and water-locked gas reservoir fracturing transformations; this method can produce greater economic and social benefits, and has a greater impact on the field of strategic and advanced reserve technology.

[0056] Furthermore, the present invention optimizes the single-stage CO2 injection amount, base liquid injection amount, injection displacement, and injection method for different types of gas reservoirs, thereby improving the CO2 energy enhancement effect, greatly increasing the reservoir transformation volume, and improving the post-compression flowback effect.

[0057] Furthermore, CO2 volume fracturing and conventional water-based fracturing are rationally combined to form a uniform mixed phase system containing part of the guar fracturing fluid system in liquid CO2. According to the SY / T6168-2009 gas reservoir classification standard, combined with the sensitivity factors of the gas boosting basic model, the reservoirs are divided into 12 categories. The gas reservoirs with a pressure coefficient of 0.7 to 1.0 are divided into low-pressure type I, low-pressure type II and normal pressure type; the gas reservoirs with a porosity of 1%-10% are divided into low porosity and ultra-low porosity; the gas reservoirs with a gas saturation of 40%-80% are divided into type A and type B. The liquid CO2 injection volume of different types of reservoirs when the formation pressure coefficient is increased to 1.0 is predicted, and the volume ratio of the CO2 / guar fracturing fluid system and the mixed injection method of the pre-fluid and sand-carrying fluid stage are determined according to the gas reservoir type. Six CO2 / guar fracturing fluid system mixed injection energy-enhancing and pressure-replenishing methods are provided, so as to maximize the gas well production on the basis of making the production well blow through once. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 Schematic diagram of the method for mixing and injecting energy and pressure boosting of the pre-fluid and sand-carrying fluid of the low-pressure Class I low-porosity Class A and B gas reservoir CO2 / guar gum fracturing fluid system in Example 1 of the present invention;

[0059] Figure 2 Schematic diagram of the method for mixing and injecting energy and pressure boosting of the pre-fluid and sand-carrying fluid of the low-pressure Class II low-porosity Class A and B gas reservoir CO2 / guar gum fracturing fluid system in Example 2 of the present invention;

[0060] Figure 3 Schematic diagram of the method for mixing and injecting energy and pressure boosting of the pre-fluid and sand-carrying fluid of the low-pressure Class I extra-low-porosity Class A and Class B gas reservoir CO2 / guar gum fracturing fluid system in Example 3 of the present invention;

[0061] Figure 4 Schematic diagram of the method for mixing and injecting energy and pressure boosting of the pre-fluid and sand-carrying fluid of the low-pressure Class II extra-low-porosity Class A and Class B gas reservoir CO2 / guar gum fracturing fluid system in Example 4 of the present invention;

[0062] Figure 5 Schematic diagram of the mixed injection energy-enhancing and pressure-replenishing method of the pre-fluid stage of the CO2 / guar gum fracturing fluid system for normal-pressure low-porosity A and B gas reservoirs in Example 5 of the present invention;

[0063] Figure 6 It is a schematic diagram of the mixed injection energy-enhancing and pressure-replenishing method for the pre-fluid stage of the CO2 / guar gum fracturing fluid system for normal-pressure and extra-low-porosity A and B gas reservoirs in Example 6 of the present invention. DETAILED DESCRIPTION

[0064] The present invention is described in detail below with reference to the accompanying drawings.

[0065] In the formula of the present invention, "." means multiplication.

[0066] The present invention provides a method for boosting and compressing carbon dioxide in low-pressure tight gas reservoirs, which reasonably combines CO2 volume fracturing and conventional water-based fracturing to form a uniform mixed phase system containing a part of the guar fracturing fluid system in liquid CO2. According to the SY / T6168-2009 gas reservoir classification standard, the reservoirs are divided into 12 categories in combination with the sensitive factors of the gas boosting basic model. Gas reservoirs with a pressure coefficient of 0.7 to 1.0 are divided into low-pressure category I, low-pressure category II and normal pressure category; gas reservoirs with a porosity of 1% to 10% are divided into low porosity and ultra-low porosity; gas reservoirs with a gas saturation of 40% to 80% are divided into category A and category B. It also predicts the amount of liquid CO2 injected when the formation pressure coefficient is increased to 1.0 for different types of reservoirs, determines the volume ratio of the CO2 / guar gum fracturing fluid system and the mixed injection method of the pre-fluid and sand-carrying fluid stages according to the gas reservoir type, and provides 6 CO2 / guar gum fracturing fluid system mixed injection energy-enhancing and pressure-replenishing methods, thereby maximizing the gas well production on the basis of making the production well blow through once.

[0067] The low-pressure Class I gas reservoir refers to a gas reservoir with a formation pressure coefficient of 0.7 to 0.8.

[0068] The low-pressure Class II gas reservoir refers to a gas reservoir with a formation pressure coefficient of 0.8 to 0.9.

[0069] The normal pressure gas reservoir refers to a gas reservoir with a formation pressure coefficient of 0.9 to 1.0.

[0070] The ultra-low porosity gas reservoir refers to a gas reservoir with a porosity of 1% to 5.5%.

[0071] The low-porosity gas reservoir refers to a gas reservoir with a porosity of 5.5% to 10%.

[0072] The gas saturation Class A gas reservoir refers to a gas reservoir with a gas saturation of 60% to 80%.

[0073] The gas saturation Class B gas reservoir refers to a gas reservoir with a gas saturation of 40% to 60%.

[0074] The volume ratio of the CO2 / guar fracturing fluid system is determined according to the gas reservoir type, which means that the volume ratio of the CO2 / guar fracturing fluid system for low-pressure type I low-porosity A and B gas reservoirs is 3:10, the volume ratio of the CO2 / guar fracturing fluid system for low-pressure type I extra-low-porosity A and B gas reservoirs is 6:10, the volume ratio of the CO2 / guar fracturing fluid system for low-pressure type II low-porosity A and B gas reservoirs is 2:10, the volume ratio of the CO2 / guar fracturing fluid system for low-pressure type II extra-low-porosity A and B gas reservoirs is 4:10, the volume ratio of the CO2 / guar fracturing fluid system for normal-pressure low-porosity A and B gas reservoirs is 1:10, and the volume ratio of the CO2 / guar fracturing fluid system for normal-pressure extra-low-porosity A and B gas reservoirs is 2:10.

[0075] The mixed injection method of the pre-fluid and sand-carrying fluid stages is determined based on the gas reservoir type. For low-pressure Class I low-porosity gas reservoirs, low-pressure Class I extra-low-porosity gas reservoirs, low-pressure Class II low-porosity gas reservoirs, and low-pressure Class II extra-low-porosity gas reservoirs, due to low formation energy, CO2 pre-fluid and sand-carrying fluid are mixed in two stages; while for normal-pressure low-porosity gas reservoirs and normal-pressure extra-low-porosity gas reservoirs, CO2 pre-fluid mixed injection is used as the injection method due to normal reservoir pressure.

[0076] The six CO2 / Guar gum fracturing fluid system mixed injection energy enhancement and pressure replenishment methods are:

[0077] (1) Low-pressure Class I low-porosity Class A and B gas reservoirs: CO2 and guar gum fracturing fluid system are mixed and injected during the pre-fluid and sand-carrying fluid stages, where the volume ratio of CO2 / guar gum fracturing fluid system is 3:10. ① For the pre-fluid stage, the liquid CO2 injection volume is 58% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min; ② For the sand-carrying liquid stage, the liquid CO2 injection volume is 42% of the total liquid CO2 injection volume, and the liquid CO2 pump injection displacement is 0.8~2m 3 / min, the injection volume of guar cross-linking fluid is 60% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min; ③ For the displacement fluid stage, the base fluid injection volume is 9% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min;

[0078] (2) Low-pressure Class I extra-low-porosity Class A and B gas reservoirs: CO2 and guar gum fracturing fluid system are mixed and injected during the pre-fluid and sand-carrying fluid stages, where the ratio of CO2 / guar gum fracturing fluid system is 6:10. ① For the pre-fluid stage, the liquid CO2 injection volume is 58% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min; ② For the sand-carrying liquid stage, the liquid CO2 injection volume is 42% of the total liquid CO2 injection volume, and the liquid CO2 pump injection displacement is 0.8~2m 3 / min, the injection volume of guar cross-linking fluid is 61% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min; ③ For the displacement fluid stage, the base fluid injection volume is 9% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min;

[0079] (3) Low-pressure Class II low-porosity A and B gas reservoirs: Mix CO2 and guar gum fracturing fluid system in the pre-fluid and sand-carrying fluid stages, where the ratio of CO2 / guar gum fracturing fluid system is 2:10. ① For the pre-fluid stage, the liquid CO2 injection volume is 55% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min; ② For the sand-carrying liquid stage, the liquid CO2 injection volume is 45% of the total liquid CO2 injection volume, and the liquid CO2 pump injection displacement is 0.8~2m 3 / min, the injection volume of guar cross-linking fluid is 60% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min; ③ For the displacement fluid stage, the base fluid injection volume is 9% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min;

[0080] (4) Low-pressure Class II extra-low-porosity Class A and B gas reservoirs: Mix CO2 and guar gum fracturing fluid system in the pre-fluid and sand-carrying fluid stages, where the ratio of CO2 / guar gum fracturing fluid system is 4:10. ① For the pre-fluid stage, the liquid CO2 injection volume is 57% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min; ② For the sand-carrying liquid stage, the liquid CO2 injection volume is 43% of the total liquid CO2 injection volume, and the liquid CO2 pump injection displacement is 0.8~2m 3 / min, the injection volume of guar cross-linking fluid is 60% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min; ③ For the displacement fluid stage, the base fluid injection volume is 9% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min;

[0081] (5) Normal pressure low porosity A and B gas reservoirs: CO2 and guar gum fracturing fluid system are mixed and injected only in the pre-fluid stage, where the ratio of CO2 / guar gum fracturing fluid system is 1:10. ① For the pre-fluid stage, the liquid CO2 injection volume is 100% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min; ② For the sand-carrying fluid stage, the injection volume of guar cross-linking fluid is 61% of the total injection volume of the guar fracturing fluid system, and the guar fracturing fluid pumping volume is 6m 3 / min; ③ For the displacement fluid stage, the base fluid injection volume is 8% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min;

[0082] (6) Normal pressure type extra-low porosity A and B gas reservoirs: CO2 and guar gum fracturing fluid system are mixed and injected only in the pre-fluid stage, where the ratio of CO2 / guar gum fracturing fluid system is 2:10. ① For the pre-fluid stage, the liquid CO2 injection volume is 100% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 30% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min; ② For the sand-carrying fluid stage, the injection volume of guar cross-linking fluid is 60% of the total injection volume of guar fracturing fluid system, and the guar fracturing fluid pumping volume is 6m 3 / min; ③ For the displacement fluid stage, the base fluid injection volume is 10% of the total guar gum fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min;

[0083] Among them, the percentage of the total liquid CO2 injection amount and the percentage of the total guar gum fracturing fluid system injection amount in the above 6 CO2 / guar gum fracturing fluid system mixed injection energy enhancement and pressure replenishment methods (1) to (6) can be appropriately ±3% based on the actual pumping conditions on site.

[0084] The guar fracturing fluid system is composed of a base fluid, a guar cross-linking fluid and a breaker (ammonium persulfate);

[0085] The base liquid is prepared by mixing water, a clay stabilizer and a high-efficiency drainage aid (sodium dodecyl sulfate), wherein the concentration of the clay stabilizer is 0.1%wt and the concentration of the high-efficiency drainage aid is 0.1%wt;

[0086] The guar gum cross-linking liquid is prepared from water, hydroxypropyl guar gum, a bactericide (tetrakis hydroxymethyl sulfate), a high-efficiency drainage aid (sodium dodecyl sulfonate), a clay stabilizer (hexadecyl trimethyl ammonium salt), a regulator (organic boron), and a cross-linking agent. The concentration of hydroxypropyl guar gum is 0.45%wt, the concentration of the bactericide is 0.1%wt, the concentration of the high-efficiency drainage aid is 0.3%wt, the concentration of the clay stabilizer is 0.3%wt, the concentration of the regulator is 0.2%, and the concentration of the cross-linking agent is The viscosity of the guar gum cross-linking liquid is ≥1000 mpa·s, see the table below for details.

[0087]

[0088]

[0089] The method for increasing the energy and pressure of carbon dioxide in a low-pressure tight gas reservoir comprises the following steps:

[0090] (1) The original formation pressure can be converted based on different formation pressure coefficients and hydrostatic column pressure, or the original formation pressure of each reservoir can be obtained by measuring the formation pressure of each reservoir with an electronic pressure gauge and analyzing the production performance curve;

[0091] (2) Based on the original formation pressure, a basic gas pressurization model considering the effect of ground temperature on the volume conversion of CO2 gas and liquid is established. Based on the comprehensive fracturing fluid volume sweep coefficient of the basic gas pressurization model, 12 types of reservoirs are distinguished, including low-pressure type I, low-pressure type II and normal pressure, low porosity and ultra-low porosity, type A gas-saturated and type B gas-saturated, and the required CO2 injection volume when the formation pressure coefficient of different types of reservoirs reaches 1.0 is predicted. The basic gas pressurization model considering the effect of the actual ground temperature on the volume conversion of CO2 gas and liquid is shown in formulas (1)-(4).

[0092]

[0093]

[0094] β=nRT sc / P sc ,T sc ∈(283K,313K) (3)

[0095] V=ψ(G'-G) / β (4)

[0096] in:

[0097] ① Ground temperature T sc ∈ (283K, 293K), β = 499;

[0098] ② Ground temperature T sc∈ (293K, 303K), β = 517;

[0099] ③ Ground temperature T sc ∈ (303K, 313K), β = 534.

[0100] Where G is the original gas reservoir geological reserves; G' is the gas reservoir geological reserves when the formation pressure coefficient reaches 1.0, β is the gas expansion coefficient, V is the injection volume of liquid CO2, A is the gas-bearing area; h is the average effective thickness; S wi is the initial water saturation; Z i is the gas deviation coefficient; ψ is the fracturing fluid volume sweep coefficient; is the pressure coefficient; n is the amount of gas substance; R is the molar gas constant; P w is the hydrostatic column pressure; H is the hydrostatic column height; ρ w is the static liquid column density; g is the gravitational acceleration; P sc is the surface pressure; T is the air temperature; P i is the original formation pressure; P i ' is the energy storage formation pressure; T sc is the ground temperature, T sc ∈(283K, 313K);

[0101] (3) For low-pressure type I, low-pressure type II and normal-pressure gas reservoirs, select the corresponding method from the above six CO2 / guar gum fracturing fluid system mixed injection energy enhancement and pressure replenishment methods to perform liquid CO2 / base fluid pre-injection. Among them, low-pressure type I, low-pressure type II and normal-pressure gas reservoirs use 4m 3 / min large displacement base fluid (45mpa·s) and mixed injection of liquid CO2 (1-3m 3 / min), using high viscosity and large displacement to form fractures of a certain scale, connecting the middle end of the fracture and the far well gas reservoir, providing enough space for subsequent proppant.

[0102] (4) For low-pressure type I and type II gas reservoirs, select the corresponding method from the above six CO2 / guar gum fracturing fluid system mixed injection energy enhancement and pressure replenishment methods to carry out CO2 / guar gum fracturing fluid mixed injection with sand, and for normal pressure gas reservoirs, guar gum liquid with sand injection. Among them, low-pressure type I and low-pressure type II gas reservoirs use 6m 3 / min large displacement guar fracturing fluid (45mpa·s), mixed injection of liquid CO2 (1.5-2m 3 / min) sand-carrying fractures, the injection displacement of low-pressure Class I gas reservoirs is stepped, from 1.5m 3 / min down to 0.8m 3 / min; normal pressure gas reservoirs use 6m 3 / min large displacement guar gum fracturing fluid (45mpa·s), all kinds of gas reservoirs carry 70-140 mesh ceramsite proppant to fully fill the branch fractures, and carry 40-70 mesh ceramsite to effectively support the main fractures.

[0103] (5) For low-pressure type I, low-pressure type II and normal-pressure gas reservoirs, select the corresponding method from the above six CO2 / guar gum fracturing fluid system mixed injection energy-enhancing and pressure-replenishing methods to replace the base fluid. Among them, 6m 3 / min large displacement of base fluid (45mpa·s) to displace the wellbore, and the fracturing operation is completed after the displacement is completed.

[0104] Table 1 The dosage ratio of single-stage liquid CO2 and guar gum fracturing fluid system at different ground temperatures of the present invention

[0105]

[0106]

[0107] Table 2 In Examples 1-6 of the present invention, the ground temperature T sc ∈(293K, 303K) Single-stage liquid CO2 dosage, guar gum fracturing fluid system dosage

[0108]

[0109] Example 1

[0110] A CO2 energy boost and pressure supplement design was carried out for a low-pressure Class I low-porosity gas well. During the on-site construction, the ground temperature T sc ∈(293K, 303K), according to the CO2 energy enhancement and pressure replenishment method for low-pressure tight gas reservoirs:

[0111] like Figure 1 As shown, the method for mixing and injecting energy and pressure in the pre-fluid and sand-carrying fluid stages of the CO2 / guar gum fracturing fluid system for low-pressure Class I low-porosity Class A and Class B gas reservoirs specifically includes the following steps:

[0112] ① The original formation pressure can be converted based on different formation pressure coefficients and hydrostatic column pressure, or the original formation pressure of the reservoir can be obtained by measuring the reservoir formation pressure with an electronic pressure gauge in the early stage and analyzing the production performance curve;

[0113] ②Based on the original formation pressure, a basic gas pressurization model considering the effect of ground temperature on the volume conversion of CO2 gas and liquid was established. The volume sweep coefficient of the fracturing fluid was considered to identify the reservoir as a low-pressure Class I low-porosity Class A and B gas reservoir, and the required CO2 injection volume was predicted when the reservoir formation pressure coefficient reached 1.0 (Table 2).

[0114] ③Pre-injection of liquid CO2 / base fluid into low-pressure Class I low-porosity Class A and B gas reservoirs, using large-volume base fluid (4m 3 / min), mixed injection of liquid CO2 (2m 3 / min). For Class A gas reservoirs, the amount of liquid CO2 used is 100m 3 , the base liquid dosage is 180m 3 For Class B gas reservoirs, the amount of liquid CO2 is 90m 3 , the base liquid dosage is 190m 3 . Use high-viscosity fluid with large displacement to form fractures of a certain scale, connect the middle end of the fractures and the gas reservoir far from the well, and provide sufficient space for subsequent proppant.

[0115] The base liquid is prepared from water and guar gum, with a mass concentration of 0.15%;

[0116] ④ Liquid CO2 / Guan gel crosslinking liquid was mixed with sand for low-pressure Class I low-porosity Class A and B gas reservoirs. A large displacement of guar gel crosslinking liquid (6m 3 / min), mixed injection of liquid CO2 (by 1.5m 3 / min down to 0.8m 3 / min) to carry sand and support fractures. For Class A gas reservoirs, the amount of liquid CO2 used is 75m 3 , the amount of guar gum cross-linking liquid is 350m 3 For Class B gas reservoirs, the amount of liquid CO2 is 65m 3 , the amount of guar gum cross-linking liquid is 370m 3 Carry 70-140 mesh ceramsite proppant to fill branch fractures, and carry 40-70 mesh ceramsite to effectively support main fractures.

[0117] The guar gum cross-linking liquid is prepared from a base liquid and a cross-linking agent, and the mass concentration of the cross-linking agent is 0.9%;

[0118] ⑤ For low-pressure Class I low-porosity A and B gas reservoirs, base liquid (6m 3 / min) displacement, among which, for Class A gas reservoirs, the base fluid dosage is 50m 3 For Class B gas reservoirs, the base fluid dosage is 55m 3 After the displacement is completed, the fracturing operation is ended.

[0119] The base liquid is prepared from water and guar gum, and the mass concentration is 0.2%.

[0120] Example 2

[0121] A CO2 energy boost and pressure supplement design was carried out for a low-pressure Class II low-porosity gas well. During the on-site construction, the ground temperature T sc∈(293K, 303K), according to a method of CO2 energy enhancement and pressure supplementation in low-pressure tight gas reservoirs:

[0122] like Figure 2 As shown, the method for mixing and injecting energy and pressure in the pre-fluid and sand-carrying fluid stages of the CO2 / guar gum fracturing fluid system for low-pressure Class II low-porosity Class A and Class B gas reservoirs specifically includes the following steps:

[0123] ① The original formation pressure can be converted based on different formation pressure coefficients and hydrostatic column pressure, or the original formation pressure of the reservoir can be obtained by measuring the reservoir formation pressure with an electronic pressure gauge in the early stage and analyzing the production performance curve;

[0124] ②Based on the original formation pressure, a basic gas pressurization model considering the effect of ground temperature on the volume conversion of CO2 gas and liquid was established. The volume sweep coefficient of the fracturing fluid was considered to identify the reservoir as a low-pressure Class II low-porosity Class A and B gas reservoir, and the required CO2 injection volume was predicted when the reservoir formation pressure coefficient reached 1.0 (Table 2).

[0125] ③Pre-injection of liquid CO2 / base fluid into low-pressure Class II low-porosity A and B gas reservoirs, using large displacement of base fluid (4m 3 / min), mixed injection of liquid CO2 (2m 3 / min). For Class A gas reservoirs, the amount of liquid CO2 is 70m 3 , the base liquid dosage is 180m 3 For Class B gas reservoirs, the amount of liquid CO2 is 50m 3 , the base liquid dosage is 185m 3 . Use high-viscosity fluid with large displacement to form fractures of a certain scale, connect the middle end of the fractures and the gas reservoir far from the well, and provide sufficient space for subsequent proppant.

[0126] The base liquid is prepared from water and guar gum, with a mass concentration of 0.2%;

[0127] ④ Liquid CO2 / Guan gel crosslinking liquid was mixed with sand for low-pressure Class II low-porosity A and B gas reservoirs. A large displacement of guar gel crosslinking liquid (6m 3 / min), mixed injection of liquid CO2 (by 1.5m 3 / min down to 0.8m 3 / min) to carry sand and prop up fractures. For Class A gas reservoirs, the amount of liquid CO2 used is 55m 3 , the amount of guar gum cross-linking liquid is 350m 3 For Class B gas reservoirs, the amount of liquid CO2 is 45m 3 , the amount of guar gum cross-linking liquid is 360m 3 Carry 70-140 mesh ceramsite proppant to fill branch fractures, and carry 40-70 mesh ceramsite to effectively support main fractures.

[0128] The guar gum cross-linking liquid is prepared from a base liquid and a cross-linking agent, and the mass concentration of the cross-linking agent is 0.8%;

[0129] ⑤ For low-pressure Class II low-porosity A and B gas reservoirs, base liquid (6m 3 / min) displacement, among which, for Class A gas reservoirs, the base fluid dosage is 50m 3 For Class B gas reservoirs, the base fluid dosage is 50m 3 After the displacement is completed, the fracturing operation is ended.

[0130] The base liquid is prepared from water and guar gum, and the mass concentration is 0.17%.

[0131] Example 3

[0132] A CO2 energy boost and pressure supplement design was carried out for a low-pressure Class I extra-low-porosity gas well. During the on-site construction, the ground temperature T sc ∈(293K, 303K), according to a method of CO2 energy enhancement and pressure supplementation in low-pressure tight gas reservoirs:

[0133] like Figure 3 As shown, the method for mixing and injecting energy and pressure in the pre-fluid and sand-carrying fluid stages of the CO2 / guar gum fracturing fluid system for low-pressure Class I extra-low-porosity Class A and Class B gas reservoirs specifically includes the following steps:

[0134] ① The original formation pressure can be converted based on different formation pressure coefficients and hydrostatic column pressure, or the original formation pressure of the reservoir can be obtained by measuring the reservoir formation pressure with an electronic pressure gauge in the early stage and analyzing the production performance curve;

[0135] ②Based on the original formation pressure, a basic gas pressurization model considering the effect of ground temperature on the volume conversion of CO2 gas and liquid was established. The volume sweep coefficient of the fracturing fluid was comprehensively considered to identify the reservoir as a low-pressure Class I extra-low-porosity Class A and B gas reservoir, and the required CO2 injection volume was predicted when the reservoir formation pressure coefficient reached 1.0 (Table 2).

[0136] ③Pre-injection of liquid CO2 / base fluid into low-pressure Class I extra-low-porosity Class A and B gas reservoirs, using large-volume base fluid (4m 3 / min), mixed injection of liquid CO2 (3m 3 / min). For Class A gas reservoirs, the amount of liquid CO2 used is 185m 3 , the base liquid dosage is 155m 3 For Class B gas reservoirs, the amount of liquid CO2 used is 150m 3 , the base liquid dosage is 175m 3 . Use high-viscosity fluid with large displacement to form fractures of a certain scale, connect the middle end of the fractures and the gas reservoir far from the well, and provide sufficient space for subsequent proppant.

[0137] The base liquid is prepared from water and guar gum, with a mass concentration of 0.17%;

[0138] ④ Liquid CO2 / Guan gel crosslinking liquid was mixed with sand for low-pressure Class I extra-low-porosity Class A and Class B gas reservoirs. A large-volume guar gel crosslinking liquid (6m 3 / min), mixed injection of liquid CO2 (2m 3 / min) to carry sand and prop up fractures. For Class A gas reservoirs, the amount of liquid CO2 used is 135m 3 , the amount of guar gum cross-linking liquid is 300m 3 For Class B gas reservoirs, the amount of liquid CO2 used is 110m 3 , the amount of guar gum cross-linking liquid is 345m 3 Carry 70-140 mesh ceramsite proppant to fill branch fractures, and carry 40-70 mesh ceramsite to effectively support main fractures.

[0139] The guar gum cross-linking liquid is prepared from a base liquid and a cross-linking agent, and the mass concentration of the cross-linking agent is 1.1%;

[0140] ⑤ For low-pressure Class I extra-low-porosity A and B gas reservoirs, base liquid (6m 3 / min) displacement, among which, for Class A gas reservoirs, the base fluid dosage is 45m 3 For Class B gas reservoirs, the base fluid dosage is 50m 3 After the displacement is completed, the fracturing operation is ended.

[0141] The base liquid is prepared from water and guar gum, and the mass concentration is 0.17%.

[0142] Example 4

[0143] A CO2 energy boost and pressure supplement design was carried out for a low-pressure Class II ultra-low-porosity gas well. During the on-site construction, the ground temperature T sc ∈(293K, 303K), according to a method of CO2 energy enhancement and pressure supplementation in low-pressure tight gas reservoirs:

[0144] like Figure 4 As shown, the method for mixing and injecting energy and pressure in the pre-fluid and sand-carrying fluid stages of the CO2 / guar gum fracturing fluid system for low-pressure Class II extra-low-porosity Class A and Class B gas reservoirs specifically includes the following steps:

[0145] ① The original formation pressure can be converted based on different formation pressure coefficients and hydrostatic column pressure, or the original formation pressure of the reservoir can be obtained by measuring the reservoir formation pressure with an electronic pressure gauge in the early stage and analyzing the production performance curve;

[0146] ②Based on the original formation pressure, a basic gas pressurization model considering the effect of ground temperature on the volume conversion of CO2 gas and liquid was established. The volume sweep coefficient of the fracturing fluid was considered to identify the reservoir as a low-pressure Class II extra-low-porosity Class A and B gas reservoir, and the required CO2 injection volume was predicted when the reservoir formation pressure coefficient reached 1.0 (Table 2).

[0147] ③Pre-injection of liquid CO2 / base fluid into low-pressure Class II extra-low-porosity A and B gas reservoirs, using large-volume base fluid (4m 3 / min), mixed injection of liquid CO2 (3m 3 / min). For Class A gas reservoirs, the amount of liquid CO2 is 135m 3 , the base liquid dosage is 185m 3 For Class B gas reservoirs, the amount of liquid CO2 is 90m 3 , the base liquid dosage is 200m 3 . Use high-viscosity fluid with large displacement to form fractures of a certain scale, connect the middle end of the fractures and the gas reservoir far from the well, and provide sufficient space for subsequent proppant.

[0148] The base liquid is prepared from water and guar gum, with a mass concentration of 18%;

[0149] ④ Liquid CO2 / Guan gel crosslinking liquid was mixed with sand for low-pressure Class II extra-low-porosity A and B gas reservoirs. A large-volume guar gel crosslinking liquid (6m 3 / min), mixed injection of liquid CO2 (2m 3 / min) to carry sand and support fractures. For Class A gas reservoirs, the amount of liquid CO2 used is 100m 3 , the amount of guar gum cross-linking liquid is 360m 3 For Class B gas reservoirs, the amount of liquid CO2 is 70m 3 , the amount of guar gum cross-linking liquid is 385m 3 Carry 70-140 mesh ceramsite proppant to fill branch fractures, and carry 40-70 mesh ceramsite to effectively support main fractures.

[0150] The guar gum cross-linking liquid is prepared from a base liquid and a cross-linking agent, and the mass concentration of the cross-linking agent is 1%;

[0151] ⑤ For low-pressure Class II extra-low-porosity A and B gas reservoirs, base liquid (6m 3 / min) displacement, among which, for Class A gas reservoirs, the base fluid dosage is 50m 3 For Class B gas reservoirs, the base fluid dosage is 55m 3 After the displacement is completed, the fracturing operation is ended.

[0152] The base liquid is prepared from water and guar gum, and the mass concentration is 0.16%.

[0153] Example 5

[0154] A CO2 energy boost and pressure supplement design was carried out for a normal-pressure low-porosity gas well. During the on-site construction, the ground temperature T sc ∈(293K, 303K), according to a method of CO2 energy enhancement and pressure supplementation in low-pressure tight gas reservoirs:

[0155] like Figure 5 As shown, the method for increasing energy and pressure by mixing the pre-fluid and sand-carrying fluid of the CO2 / guar gum fracturing fluid system in the normal pressure low-porosity A and B gas reservoirs specifically includes the following steps:

[0156] ① The original formation pressure can be converted based on different formation pressure coefficients and hydrostatic column pressure, or the original formation pressure of the reservoir can be obtained by measuring the reservoir formation pressure with an electronic pressure gauge in the early stage and analyzing the production performance curve;

[0157] ②Based on the original formation pressure, a basic gas pressurization model was established that took into account the effect of ground temperature on the volume conversion of CO2 gas and liquid. The volume sweep coefficient of the fracturing fluid was considered to identify the reservoir as a normal pressure low-porosity A and B gas reservoir, and the required CO2 injection volume was predicted when the reservoir formation pressure coefficient reached 1.0 (Table 2).

[0158] ③Pre-injection of liquid CO2 / base fluid into normal pressure low-porosity A and B gas reservoirs, using large displacement of base fluid (4m 3 / min), mixed injection of liquid CO2 (1m 3 / min). For Class A gas reservoirs, the amount of liquid CO2 is 50m 3 , the base liquid dosage is 195m 3 For Class B gas reservoirs, the amount of liquid CO2 is 40m 3 , the base liquid dosage is 200m 3 . Use high-viscosity fluid with large displacement to form fractures of a certain scale, connect the middle end of the fractures and the gas reservoir far from the well, and provide sufficient space for subsequent proppant.

[0159] The base liquid is prepared from water and guar gum, with a mass concentration of 0.19%;

[0160] ④ For normal pressure low porosity A and B gas reservoirs, guar gum crosslinking liquid sand injection was carried out, and a large displacement of guar gum crosslinking liquid (6m 3 / min) sand-carrying fractures. For Class A gas reservoirs, the amount of guar gum cross-linking liquid used is 385m 3 For type B gas reservoirs, the amount of guar gum cross-linking fluid used is 390m 3 Carry 70-140 mesh ceramsite proppant to fill branch fractures, and carry 40-70 mesh ceramsite to effectively support main fractures.

[0161] The guar gum cross-linking liquid is prepared from a base liquid and a cross-linking agent, and the mass concentration of the cross-linking agent is 1%;

[0162] ⑤ Base fluid (6m 3 / min) displacement, among which, for Class A gas reservoirs, the base fluid dosage is 50m 3 For Class B gas reservoirs, the base fluid dosage is 45m 3 After the displacement is completed, the fracturing operation is ended.

[0163] The base liquid is prepared from water and guar gum, and the mass concentration is 0.15%.

[0164] Example 6

[0165] A CO2 energy boost and pressure supplement design was carried out for a normal-pressure ultra-low-porosity gas well. During the on-site construction, the ground temperature T sc ∈(293K, 303K), according to a method of CO2 energy enhancement and pressure supplementation in low-pressure tight gas reservoirs:

[0166] like Figure 6 As shown, the method for increasing energy and pressure by mixing and injecting pre-fluid and sand-carrying fluid in the CO2 / guar gum fracturing fluid system for normal pressure extra-low porosity A and B gas reservoirs specifically includes the following steps:

[0167] ① The original formation pressure can be converted based on different formation pressure coefficients and hydrostatic column pressure, or the original formation pressure of the reservoir can be obtained by measuring the reservoir formation pressure with an electronic pressure gauge in the early stage and analyzing the production performance curve;

[0168] ②Based on the original formation pressure, a basic gas pressurization model considering the effect of ground temperature on the volume conversion of CO2 gas and liquid was established. The volume sweep coefficient of the fracturing fluid was considered to identify the reservoir as a normal pressure extra-low porosity A and B gas reservoir, and the required CO2 injection volume was predicted when the reservoir formation pressure coefficient reached 1.0 (Table 2).

[0169] ③Pre-injection of liquid CO2 / base fluid into atmospheric pressure and ultra-low porosity A and B gas reservoirs, using large displacement of base fluid (4m 3 / min), mixed injection of liquid CO2 (2m 3 / min). For Class A gas reservoirs, the amount of liquid CO2 used is 100m 3 , the base liquid dosage is 200m 3 For Class B gas reservoirs, the amount of liquid CO2 is 80m 3 , the base liquid dosage is 205m 3 . Use high-viscosity fluid with large displacement to form fractures of a certain scale, connect the middle end of the fractures and the gas reservoir far from the well, and provide sufficient space for subsequent proppant.

[0170] The base liquid is prepared from water and guar gum, with a mass concentration of 0.15%;

[0171] ④ For normal pressure and ultra-low porosity A and B gas reservoirs, guar gum crosslinking liquid is injected with sand, and a large displacement of guar gum crosslinking liquid (6m 3 / min) sand-carrying fractures. For Class A gas reservoirs, the amount of guar gum cross-linking liquid used is 390m 3 For type B gas reservoirs, the amount of guar gum cross-linking fluid used is 400m 3 Carry 70-140 mesh ceramsite proppant to fill branch fractures, and carry 40-70 mesh ceramsite to effectively support main fractures.

[0172] The guar gum cross-linking liquid is prepared from a base liquid and a cross-linking agent, and the mass concentration of the cross-linking agent is 0.8%;

[0173] ⑤ For normal pressure type extra low porosity A and B type gas reservoirs, base liquid (6m 3 / min) displacement, among which, for Class A gas reservoirs, the base fluid dosage is 60m 3 For Class B gas reservoirs, the base fluid consumption is 70m 3 After the displacement is completed, the fracturing operation is ended.

[0174] The base liquid is prepared from water and guar gum, and the mass concentration is 0.2%.

[0175] In the present invention, a basic model of gas pressurization is established, the CO2 consumption under different geological parameters is calculated, and the influence of ground temperature on the volume conversion of CO2 gas and liquid is considered. At the same time, a differentiated liquid CO2 / guar gum fracturing fluid system mixed injection mode is designed, which has the performance of energy enhancement, fracture creation and sand carrying, thereby increasing oil and gas production.

[0176] The CO2 energy enhancement and pressure replenishing method for low-pressure and low-porosity gas reservoirs provided by the present invention meets the on-site needs of Changqing Oilfield, is simple to operate, takes into account both energy enhancement and large-scale sand carrying, can shorten the drainage cycle, improve the return flow capacity, and enhance the overall effect of gas reservoir transformation, and can be widely used in various low-pressure, low-porosity, low-permeability, strong water-sensitive and water-locked gas reservoir fracturing transformations; the method can produce greater economic and social benefits, and has a greater impact on the field of strategic and advanced reserve technology.

[0177] The above description is only for the best embodiment of the present invention, but it should not be understood as limiting the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to be changed. However, all changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

[0178] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

Claims

1. A method for increasing the energy and pressure of carbon dioxide in a low-pressure tight gas reservoir, characterized in that: The following steps are involved: (1) Calculate the original formation pressure based on different formation pressure coefficients and hydrostatic column pressure, or measure the formation pressure of each reservoir using an electronic pressure gauge and obtain the original formation pressure through production performance curve analysis; (2) Based on the original formation pressure, a gas pressurization basic model considering the effect of ground temperature on the volume conversion of CO2 gas and liquid is established. According to the comprehensive fracturing fluid volume sweep coefficient of the gas pressurization basic model, the reservoirs are divided into low-pressure type I gas reservoirs, low-pressure type II gas reservoirs, normal pressure gas reservoirs, low-porosity gas reservoirs, ultra-low-porosity gas reservoirs, gas saturation type A gas reservoirs and gas saturation type B gas reservoirs, and the CO2 injection volume required when the formation pressure coefficient of different types of reservoirs reaches the set value is predicted respectively; (3) Pre-injection of liquid CO2 / base fluid into low-pressure Class I gas reservoirs, low-pressure Class II gas reservoirs, and normal-pressure gas reservoirs; (4) CO2 / Guan gel fracturing fluid mixed injection with sand is carried out in low-pressure Class I gas reservoirs and low-pressure Class II gas reservoirs, and guanidine gel fluid mixed injection with sand is carried out in normal-pressure gas reservoirs; (5) Carry out base fluid displacement in low-pressure Class I gas reservoirs, low-pressure Class II gas reservoirs, and normal-pressure gas reservoirs.

2. The method for increasing the energy and pressure of carbon dioxide in low-pressure tight gas reservoirs according to claim 1, characterized in that: The basic model of gas pressurization considering the effect of actual ground temperature on the volume conversion of CO2 gas and liquid is shown in formulas (1)-(4); β=nRT sc / P sc ,T sc ∈(283K,313K) (3) V=ψ(G'-G) / β (4) Where G is the original gas reservoir geological reserves; G' is the gas reservoir geological reserves when the formation pressure coefficient reaches 1.0, β is the gas expansion coefficient, V is the injection volume of liquid CO2, A is the gas-bearing area; h is the average effective thickness; S wi is the initial water saturation; Z i is the gas deviation coefficient; ψ is the fracturing fluid volume sweep coefficient; is the pressure coefficient; n is the amount of gas substance; R is the molar gas constant; P w is the hydrostatic column pressure; H is the hydrostatic column height; ρ w is the density of the static liquid column; g is the acceleration due to gravity; P sc is the ground pressure; T is the air temperature; P i is the original formation pressure; P i ' is the energy storage formation pressure; T sc is the ground temperature.

3. The method for increasing the energy and pressure of carbon dioxide in low-pressure tight gas reservoirs according to claim 2, characterized in that: Ground temperature T sc ∈ (283K, 293K), β = 499; Ground temperature T sc ∈ (293K, 303K), β = 517; Ground temperature T sc ∈ (303K, 313K), β = 534.

4. The method for increasing the energy and pressure of carbon dioxide in low-pressure tight gas reservoirs according to claim 1, characterized in that: The low-pressure Class I gas reservoirs are gas reservoirs with a formation pressure coefficient of 0.7 to 0.8; The low-pressure type II gas reservoirs mentioned above refer to gas reservoirs with a formation pressure coefficient of 0.8 to 0.9; The normal pressure gas reservoir refers to a gas reservoir with a formation pressure coefficient of 0.9 to 1.0; The ultra-low porosity gas reservoirs are gas reservoirs with a porosity of 1% to 5.5%; The low-porosity gas reservoir refers to a gas reservoir with a porosity of 5.5% to 10%; The gas saturation Class A gas reservoir refers to a gas reservoir with a gas saturation of 60% to 80%; The gas saturation Class B gas reservoir refers to a gas reservoir with a gas saturation of 40% to 60%.

5. The method for increasing the energy and pressure of carbon dioxide in low-pressure tight gas reservoirs according to claim 4, characterized in that: In step (3), low pressure type I gas reservoir, low pressure type II gas reservoir and normal pressure gas reservoir adopt 4m 3 / min displacement base fluid and mixed injection of liquid CO2.

6. The method for increasing the energy and pressure of carbon dioxide in low-pressure tight gas reservoirs according to claim 4, characterized in that: In step (3): (1) For low-pressure Class I low-porosity Class A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the volume ratio of CO2 / guar gum fracturing fluid system is 3:10; the liquid CO2 injection volume is 58% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min; (2) For low-pressure Class I extra-low-porosity Class A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 6:10; the liquid CO2 injection volume is 58% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min; (3) For low-pressure Class II low-porosity A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 2:10; the liquid CO2 injection volume is 55% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min; (4) For low-pressure Class II extra-low-porosity A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 4:10; the liquid CO2 injection volume is 57% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min; (5) For normal pressure low porosity A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 1:10; the liquid CO2 injection volume is 100% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 31% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min; (6) For normal pressure and ultra-low porosity A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 2:10; the liquid CO2 injection volume is 100% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 1-3m 3 / min, the base fluid injection volume is 30% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 4m 3 / min.

7. The method for increasing the energy and pressure of carbon dioxide in low-pressure tight gas reservoirs according to claim 4, characterized in that: In step (4), low-pressure type I gas reservoirs and low-pressure type II gas reservoirs use 6m 3 / min displacement of guar gum fracturing fluid, mixed injection of liquid CO2 to carry sand to support fractures, low-pressure Class I gas reservoir injection displacement is stepped, from 1.5m 3 / min down to 0.8m 3 / min; normal pressure gas reservoirs use 6m 3 / min displacement of guar gum fracturing fluid, low-pressure type I gas reservoir, low-pressure type II gas reservoir and normal pressure gas reservoir all carry 70-140 mesh ceramsite proppant to fully fill the support seams.

8. The method for increasing the energy and pressure of carbon dioxide in low-pressure tight gas reservoirs according to claim 4, characterized in that: In step (4): (1) For low-pressure Class I low-porosity Class A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the volume ratio of CO2 / guar gum fracturing fluid system is 3:10; the liquid CO2 injection volume is 42% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 0.8-2m 3 / min, the injection volume of guar cross-linking fluid is 60% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min; (2) For low-pressure Class I and extra-low-porosity Class A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 6:10; the liquid CO2 injection volume is 42% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 0.8-2m 3 / min, the injection volume of guar cross-linking fluid is 61% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min; (3) For low-pressure Class II low-porosity A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 2:10; the liquid CO2 injection volume is 45% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 0.8-2m 3 / min, the injection volume of guar cross-linking fluid is 60% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min; (4) For low-pressure Class II extra-low-porosity A and B gas reservoirs: mixed injection of CO2 and guar gum fracturing fluid system, where the ratio of CO2 / guar gum fracturing fluid system is 4:10; the liquid CO2 injection volume is 43% of the total liquid CO2 injection volume, and the liquid CO2 pumping displacement is 0.8-2m 3 / min, the injection volume of guar cross-linking fluid is 60% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min; (5) For normal pressure low porosity A and B gas reservoirs: the injection volume of guar crosslinking fluid is 61% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min; (6) For normal pressure and ultra-low porosity A and B gas reservoirs: the injection volume of guar crosslinking fluid is 60% of the total injection volume of guar fracturing fluid system, and the pumping volume of guar fracturing fluid is 6m 3 / min.

9. The method for increasing the energy and pressure of carbon dioxide in low-pressure tight gas reservoirs according to claim 4, characterized in that: In step (5), low pressure type I gas reservoir, low pressure type II gas reservoir and normal pressure gas reservoir adopt 6m 3 / min displacement of base fluid to displace the wellbore, and the fracturing operation is completed after the displacement is completed.

10. The method for increasing the energy and pressure of carbon dioxide in low-pressure tight gas reservoirs according to claim 4, characterized in that: In step (5): (1) For low-pressure Class I and low-porosity Class A and B gas reservoirs: the base fluid injection volume is 9% of the total guar gum fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min; (2) For low-pressure Class I extra-low-porosity Class A and B gas reservoirs: the base fluid injection volume is 9% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min; (3) For low-pressure Class II low-porosity Class A and B gas reservoirs: the base fluid injection volume is 9% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min; (4) For low-pressure Class II extra-low-porosity A and B gas reservoirs: the base fluid injection volume is 9% of the total guar fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min; (5) For normal pressure low porosity A and B gas reservoirs: the base fluid injection volume is 8% of the total guar gel fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min; (6) For normal pressure and ultra-low porosity A and B gas reservoirs: the base fluid injection volume is 10% of the total guar gel fracturing fluid system injection volume, and the base fluid pumping displacement is 6m 3 / min.

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