Method for determining dolomitization mechanism of carbonate rock and evaluating reservoir effect

Abstract

The application discloses a method for determining a dolomitization mechanism of a carbonate rock and evaluating a reservoir-forming effect. The steps for determining the dolomitization mechanism are as follows: a piston-shaped dolomite sample is prepared; a reaction solution is prepared; the sample is immersed in the reaction solution, and a sample dissolution simulation experiment under high temperature and high pressure is carried out; Ca 2+ concentration and Mg g2+ concentration in the reaction solution under different temperature and pressure points are determined respectively; and the dolomitization mechanism of a deep or super-deep carbonate rock is determined according to the ratio change of the Ca 2+ concentration and Mg 2+ concentration, thereby breaking the controversy existing in the dolomitization mechanism of a deep or super-deep reservoir. In the method for evaluating the reservoir-forming effect, the dolomitization mechanism is associated with the reservoir-forming effect, thereby providing scientific guidance for deep or super-deep oil and gas reservoir potential prediction and development.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration technology, and in particular to a method for determining the dolomiteification mechanism of carbonate rocks and evaluating reservoir formation effects. Background Technology

[0002] Dolomite reservoirs possess enormous exploration potential in oil and gas exploration. The dolomitization mechanism, the formation and maintenance of dolomite porosity, and the reservoir-forming benefits of dolomite have long been research hotspots for many scholars, but a consensus on the genesis of dolomite remains elusive. Currently, the mainstream dolomitization models mainly include: permeation-recirculation dolomitization, capillary concentration dolomitization, evaporation-pump dolomitization, mixed-water dolomitization, adjustment-compacting dolomitization, burial-compacting dolomitization, seawater thermal convection dolomitization, and tectonic hydrothermal dolomitization. Dolomitization mainly occurs in two stages: the syn- or quasi-syn-genetic stage and the burial stage. Dolomitization in the burial stage is generally considered to be caused by Mg in the magnesium-rich diagenetic medium. 2+ Ca in metasomatism 2+ , making Ca 2+ / Mg 2+ The dolomitization process gradually increases and approaches a value of 1, achieving a transformation from limestone to proto-dolomite, then to low-order dolomite, and finally to high-order dolomite. Grains gradually coarsen, and the crystal form changes from anhedral to euhedral. In recent years, as deep-to-ultra-deep carbonate rocks (internationally defined as those exceeding 4500 meters in burial depth) have become an important successor area for oil and gas exploration and development, there is an urgent need to reveal the dolomitization mechanism of deep-to-ultra-deep carbonate rocks, as well as to identify and evaluate the corresponding reservoir-forming effects. Summary of the Invention

[0003] In view of the above problems, the purpose of this invention is to provide a method for determining the dolomite formation mechanism of carbonate rocks and evaluating the reservoir formation effect.

[0004] In a first aspect, embodiments of the present invention provide a method for determining the dolomitization mechanism of carbonate rocks, comprising the following steps:

[0005] Prepare a plunger-shaped dolomite sample; prepare a reaction solution; immerse the sample in the reaction solution and conduct a sample dissolution simulation experiment under high temperature and high pressure;

[0006] Determine the Ca content in the reaction solution at different temperature and pressure points. 2+ Concentration and Mg 2+ concentration;

[0007] According to the Ca 2+ Concentration and the Mg 2+ The change in concentration ratio was used to determine the dolomitization mechanism of deep and ultradeep carbonate rocks.

[0008] In one embodiment, the sample selected is calcareous dolomite.

[0009] In one embodiment, the initial porosity of the calcareous dolomite is 10% to 20%;

[0010] The initial permeability of the calcareous dolomite is 5–15 md.

[0011] In one embodiment, the dissolution simulation experiment employs a flow-based open system;

[0012] The flow rate of the reaction solution is 1.0 ml / min.

[0013] In one embodiment, the prepared reaction solution is a saturated carbon dioxide solution.

[0014] In one embodiment, the Ca in the reaction solution 2+ Concentration and Mg 2+ Concentration is determined in real time.

[0015] In one embodiment, the temperature range is 130–250°C and the pressure range is 80–150 MPa.

[0016] In one embodiment, the method further includes: conducting a sample dissolution simulation experiment under low temperature and low pressure.

[0017] In one embodiment, in the low-temperature and low-pressure corrosion simulation experiment, the temperature is less than 130°C and the pressure is less than 80 MPa.

[0018] In a second aspect, embodiments of the present invention provide a method for evaluating reservoir formation effect based on the dolomitization mechanism of carbonate rocks, wherein the dolomitization mechanism of carbonate rocks is determined according to the method in the first aspect embodiment described above.

[0019] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following:

[0020] The method for determining the dolomitization mechanism of carbonate rocks provided by this invention addresses the insufficient applicability of traditional dolomitization models in deep to ultra-deep reservoirs. This invention conducts dolomite dissolution simulation experiments under high temperature and high pressure conditions, and determines the Ca content in the reaction solution... 2+ Concentration and Mg 2+ The concentration changes clarified the Ca concentration in the dolomite sample under high temperature and high pressure environment and the action of the reaction solution. 2+ Concentration and Mg 2+ The dynamic law of the ratio of content was studied, which revealed the dolomitization mechanism of deep-ultra-deep carbonate rocks and provided key experimental evidence for breaking through the controversy of the dolomitization mechanism of deep-ultra-deep reservoirs.

[0021] Furthermore, Ca was measured in real time during the dissolution simulation experiment. 2 By analyzing the changes in the concentrations of Mg²⁺ and Mg²⁺, combined with the ratio of their concentrations at different temperature and pressure points, the Ca²⁺ content in calcareous dolomite during dolomitization can be dynamically tracked. 2 The changes in the content of Mg2+ and Mg2+ provide a scientific basis for determining the dolomite petrification mechanism.

[0022] Furthermore, by conducting comparative experiments on calcareous dolomite under low temperature and low pressure and high temperature and high pressure, the dolomitization process of shallow and deep to ultra-deep carbonate rocks during a certain historical period can be realistically reproduced.

[0023] Furthermore, by clarifying key parameters such as the initial porosity, initial permeability, and flow rate of the reaction liquid in the experimental samples, direct data support is provided for revealing the dolomitization mechanism of calcareous dolomite.

[0024] The method for evaluating reservoir formation effect based on the dolomitization mechanism of carbonate rocks provided in this invention links the revealed dolomitization mechanism with the reservoir formation effect, providing scientific guidance for the prediction and development of deep-ultra-deep oil and gas reservoir potential, reducing exploration risks, and improving resource development efficiency.

[0025] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0026] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0027] Figure 1 This is a flowchart illustrating the method for determining the dolomitization mechanism of carbonate rocks in an embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram of the simulation experiment results of calcareous dolomite dissolution in an embodiment of the present invention. Detailed Implementation

[0029] This embodiment provides a method for determining the dolomiteification mechanism of carbonate rocks and evaluating reservoir-forming effects. Although exemplary embodiments of this disclosure are shown in the accompanying drawings, it should be understood that this disclosure can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of this disclosure and to fully convey the scope of this disclosure to those skilled in the art.

[0030] This invention provides a method for determining the dolomitization mechanism of carbonate rocks, referring to... Figure 1 As shown, the method includes the following steps:

[0031] S11. Prepare a plunger-shaped dolomite sample; prepare a reaction solution; immerse the sample in the reaction solution and conduct a sample dissolution simulation experiment under high temperature and high pressure;

[0032] S12. Determine the Ca content in the reaction solution at different temperature and pressure points. 2+ Concentration and Mg 2+ concentration;

[0033] S13, according to the Ca 2+ Concentration and the Mg 2+ The change in concentration ratio was used to determine the dolomitization mechanism of deep and ultradeep carbonate rocks.

[0034] This invention simulates the dissolution of dolomite under high temperature and high pressure, and determines the Ca content in the reaction solution. 2+ Concentration and Mg 2+ The concentration changes clarified the effects of high temperature and high pressure environment and the reaction solution on the Ca concentration in the dolomite sample. 2+ Concentration and Mg 2+ The dynamic law of the ratio of content was studied, thereby revealing the dolomitization mechanism of deep-ultra-deep carbonate rocks.

[0035] In one embodiment, the sample selected in step S11 above is calcareous dolomite.

[0036] In one embodiment, in step S11 above, the initial porosity of the calcareous dolomite is 10% to 20%; the initial permeability of the calcareous dolomite is 5 to 15 md.

[0037] In one embodiment, in step S11 above, the dissolution simulation experiment adopts a flow-open system; the flow rate of the reaction solution is 1.0 ml / min.

[0038] In one embodiment, the reaction solution prepared in step S11 is a saturated carbon dioxide solution.

[0039] In one embodiment, in step S11 above, the temperature range is 130–250°C and the pressure range is 80–150 MPa at different temperature and pressure points.

[0040] In one embodiment, step S11 above further includes conducting a sample dissolution simulation experiment under low temperature and low pressure.

[0041] In one embodiment, the corrosion simulation experiment under low temperature and low pressure is conducted at a temperature of less than 130°C and a pressure of less than 80 MPa.

[0042] In one embodiment, in step S11 above, a calcareous oolitic dolomite plunger sample is selected, with an initial porosity of 16.7% and an initial permeability of 9.3 md.2+ / Mg 2+ = 1.3:0.7. The dissolution experiment under high temperature and high pressure conditions used a saturated carbon dioxide acidic solution in an open flow system with a reaction fluid flow rate of 1.0 ml / min. Four temperature and pressure values ​​were set for the high temperature and high pressure environment: (150℃, 90 MPa), (180℃, 108 MPa), (210℃, 126 MPa), and (240℃, 144 MPa). In addition, four temperature and pressure values ​​were set for a low temperature and low pressure environment: (30℃, 18 MPa), (60℃, 36 MPa), (90℃, 54 MPa), and (120℃, 72 MPa), to compare with the dissolution results of carbonate rocks in shallow and medium-depth reservoirs. In addition, considering the temperature at which hydrocarbons mature into organic acids and the instability (pyrolysis) of acetic acid (organic acid) under high temperature and high pressure, as well as the dominant role of deep and ultra-deep saturated carbon dioxide solution (inorganic acid), a dissolution simulation experiment with an acetic acid solution at a concentration of 2.0 ml / l was added to the simulation experiment of carbonate rock dissolution in shallow reservoirs.

[0043] In one embodiment, in step S12 above, based on the Ca determined after the reaction... 2+ Concentration and Mg 2+ Concentration, to obtain Ca 2 + Concentration and Mg 2+ The relationship curves between concentration and temperature / baric point are referenced. Figure 2 Specifically, from Figure 2 As can be seen, for the dissolution results of shallow and medium-depth dolomite under low temperature and low pressure conditions, regardless of whether the reaction solution is acetic acid solution or saturated carbon dioxide solution, as the temperature and pressure increase, the Ca... 2+ Concentration and Mg 2+ The concentrations all showed a gradually increasing trend, and Ca... 2+ Concentration greater than Mg 2+ Concentration, Ca 2+ It seems to be better than Mg 2+ It is more easily dissolved and expelled. Regarding the dissolution results of deep and ultra-deep dolomite under high temperature and pressure conditions, in a reaction solution saturated with carbon dioxide, Mg increases with increasing temperature and pressure. 2+ The concentration increase slows down until a dynamic equilibrium is reached, while Ca... 2+ The concentration then showed a rapid decreasing trend, followed by a decrease in Mg. 2+ The concentrations tend to converge, reaching a dynamic equilibrium. After the reaction reaches dynamic equilibrium, a sample is taken from the reaction solution, and the Ca content is measured. 2+ / Mg 2+The ratio ≈1:1 indicates that the sample met the chemical composition requirements after dolomite formation under high temperature and pressure. However, its degree of order was still low (<0.3), suggesting that the order of the dolomite lattice is not only affected by Ca... 2+ / Mg 2+ Control still requires sufficient time to complete Ca 2+ With Mg 2+ Adjustments within the crystal lattice further enhance the degree of order. The dissolution rate of the calcareous oolitic dolomite sample is an inherent property of the mineral lattice. Under low-temperature and low-pressure conditions, the Ca in the reaction solution... 2+ Concentration greater than Mg 2+ This concentration phenomenon is not caused by the dissolution rate, but rather by the concentration of Ca in the early mineral lattice. 2+ Content > Mg 2+ Content-related (initial sample conditions: Ca) 2+ / Mg 2+ =1.3:0.7). Under high temperature and high pressure conditions, as the Ca in the mineral lattice... 2+ The large amount of Ca precipitated 2+ The content decreased rapidly, Ca 2+ With Mg 2+ The content difference gradually narrows, thus leading to a decrease in Ca in the reaction solution. 2+ The content of also decreased rapidly, and with Mg 2+ Once the content of Ca in the mineral lattice tends to be uniform and chemical equilibrium is reached, the Ca content will decrease. 2+ / Mg 2+ ≈1:1.

[0044] In one embodiment, in step S13 above, the inventors proposed a novel dolomitization mechanism for deep and ultra-deep carbonate rocks. This mechanism is specifically for calcium-rich dolomite, i.e., mineral lattices rich in Ca. 2+ In the process of dissolution by acidic fluids, the Ca in the mineral lattice of dolomite... 2+ The precipitation rate is greater than that of Mg 2+ The precipitation rate increases the amount of Mg in the mineral lattice. 2+ / Ca 2+ The traditional dolomite formation mechanism involves Mg in the diagenetic fluids. 2+ Replacement of Ca in mineral lattices 2+ A suitable explanation for the dolomitization mechanism in the transformation of pure limestone into dolomite, based on the premise of Mg enrichment in the diagenetic medium, often requires that the diagenetic medium be rich in Mg. 2+ The dolomitization mechanism proposed in this invention, along with the traditional dolomitization mechanism, can both lead to a chemical composition reaching Ca. 2+ / Mg 2+ The formation of dolomite with a ratio of approximately 1:1. However, the dolomite formed by the dolomitization mechanism proposed in this embodiment of the invention may not have a high degree of order, and sufficient time is still needed to complete the Ca...2+ With Mg 2+ Adjustments within the crystal lattice further enhance the degree of order. In summary, the vast majority of dolomite is likely the result of the combined effects of these two burial dolomitization mechanisms.

[0045] This invention provides a method for evaluating reservoir formation effects based on the dolomitization mechanism of carbonate rocks. The dolomitization mechanism of carbonate rocks is determined using the method described in this invention. Correlating the revealed dolomitization mechanism with reservoir formation effects provides scientific guidance for predicting and developing the potential of deep and ultra-deep oil and gas reservoirs, reducing exploration risks, and improving resource development efficiency.

[0046] In one embodiment, the ion-precipitation dolomite formation mechanism proposed in this invention is based on Ca in the mineral lattice. 2+ The precipitation of Mg 2+ / Ca 2+ This process is completed when the mineral lattice exhibits a significant mass defect. Traditional ion-replacement dolomite formation mechanisms are based on the presence of Mg in the mineral lattice. 2+ Explain Ca 2+ The mineral lattice mass defect is not significant. Clearly, the reservoir effect identified using the dolomitization mechanism proposed in this invention is significantly better than the reservoir-forming effect evaluated by the traditional theoretical dolomitization mechanism. This well explains why some deep and ultra-deep dolomites formed by dolomitization are dense dolomites while others are porous dolomites. Calcareous dolomites that underwent weak to moderate dolomitization in the early stages, undergoing a second ion precipitation-type dolomitization process under deep and ultra-deep conditions, exhibit a better dolomitization reservoir-forming effect. Conversely, limestone under deep and ultra-deep conditions undergoing an ion replacement-type dolomitization process results in a poorer dolomitization reservoir-forming effect.

[0047] The method for determining the dolomitization mechanism of carbonate rocks provided by this invention addresses the insufficient applicability of traditional dolomitization models in deep to ultra-deep reservoirs. This invention conducts dolomite dissolution simulation experiments under high temperature and high pressure conditions, and determines the Ca content in the reaction solution... 2+ Concentration and Mg 2+ The concentration changes clarified the Ca concentration in the dolomite sample under high temperature and high pressure environment and the action of the reaction solution. 2+ Concentration and Mg 2+ The dynamic law of the ratio of content was studied, which revealed the dolomitization mechanism of deep-ultra-deep carbonate rocks and provided key experimental evidence for breaking through the controversy of the dolomitization mechanism of deep-ultra-deep reservoirs.

[0048] Furthermore, Ca was measured in real time during the dissolution simulation experiment. 2By analyzing the changes in the concentrations of Mg²⁺ and Mg²⁺, combined with the ratio of their concentrations at different temperature and pressure points, the Ca²⁺ content in calcareous dolomite during dolomitization can be dynamically tracked. 2 The changes in the content of Mg2+ and Mg2+ provide a scientific basis for determining the dolomite petrification mechanism.

[0049] Furthermore, by conducting comparative experiments on calcareous dolomite under low temperature and low pressure and high temperature and high pressure, the dolomitization process of shallow and deep to ultra-deep carbonate rocks during a certain historical period can be realistically reproduced.

[0050] Furthermore, by clarifying key parameters such as the initial porosity, initial permeability, and flow rate of the reaction liquid in the experimental samples, direct data support is provided for revealing the dolomitization mechanism of calcareous dolomite.

[0051] The method for evaluating reservoir formation effect based on the dolomitization mechanism of carbonate rocks provided by this invention correlates the revealed dolomitization mechanism with the reservoir formation effect, providing scientific guidance for the prediction and development of deep and ultra-deep oil and gas reservoir potential, reducing exploration risks and improving resource development efficiency.

[0052] Obviously, those skilled in the art can make various modifications to this invention without departing from its spirit and scope. Therefore, if these modifications fall within the scope of the claims and their equivalents, this invention is also intended to include these modifications.

Claims

1. A method for determining the dolomitization mechanism of carbonate rocks, characterized in that, include: Preparation of plunger-shaped dolomite samples; Prepare the reaction solution; The sample was immersed in the reaction solution, and a sample dissolution simulation experiment was carried out under high temperature and high pressure. Determine the Ca content in the reaction solution at different temperature and pressure points. 2+ Concentration and Mg 2+ concentration; According to the Ca 2+ Concentration and the Mg 2+ The change in concentration ratio was used to determine the dolomitization mechanism of deep and ultradeep carbonate rocks.

2. The method as described in claim 1, characterized in that, The selected sample was calcareous dolomite.

3. The method as described in claim 2, characterized in that, The initial porosity of the calcareous dolomite is 10% to 20%; The initial permeability of the calcareous dolomite is 5–15 md.

4. The method as described in claim 1, characterized in that, The dissolution simulation experiment adopted a flow-oriented open system; The flow rate of the reaction solution is 1.0 ml / min.

5. The method as described in claim 4, characterized in that, The prepared reaction solution is a saturated carbon dioxide solution.

6. The method as described in claim 5, characterized in that, Ca in the reaction solution 2+ Concentration and Mg 2+ Concentration is determined in real time.

7. The method as described in claim 1, characterized in that, The different temperature and pressure points have a temperature range of 130–250℃ and a pressure range of 80–150MPa.

8. The method as described in claim 7, characterized in that, Also includes: A simulation experiment of sample dissolution was conducted under low temperature and low pressure.

9. The method as described in claim 8, characterized in that, In the low-temperature and low-pressure corrosion simulation experiment, the temperature is less than 130℃ and the pressure is less than 80MPa.

10. A method for evaluating reservoir formation effect based on dolomiteification mechanism of carbonate rocks, characterized in that, The dolomitization mechanism of the carbonate rocks is determined by the method according to any one of claims 1-9.

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