A method for correcting porosity in nuclear magnetic resonance logging
By constructing a characteristic factor of pollution intrusion and multiple regression models, the porosity of NMR logs is corrected, and the problem of low porosity in high-temperature and high-pressure environments is solved, the logging accuracy is improved, the accuracy of reserve parameters is ensured, and oilfield development is supported.
Patent Information
- Application Number
- CN202411247870.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-06
- Publication Date
- 2024-12-24
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
The porosity obtained by nuclear magnetic resonance logging in high temperature and high pressure environments is relatively low, resulting in low calculation results of oil and gas reservoir reserves, which is not conducive to the development of oil and gas reservoirs.
By obtaining core samples of different physical properties, saturated formation water treatment and high specific gravity water-based mud pollution simulation experiments were carried out, pollution invasion characteristic factors were constructed, and a multivariate regression model of the ratio of nuclear magnetic resonance porosity to the porosity after pollution was established to perform porosity, and porosity was carried out. degree correction.
The accuracy of nuclear magnetic resonance logging porosity has been improved, the accuracy of reserve parameters has been ensured, the implementation plan for oil field development has been guided, and the purpose of increasing oilfield reserves and production has been achieved.
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Figure CN118837960B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of oil and gas exploration, and in particular to a nuclear magnetic resonance logging porosity correction method. Background Art
[0002] Under the compaction and diagenesis of high-temperature and high-pressure reservoirs in the sea, the reservoirs are mostly characterized by low porosity and low permeability. In order to ensure the safety of offshore oil and gas exploration and development work in such reservoirs, a high-density water-based mud system is often used in the drilling process. This type of mud system adds barite and manganese ore powder as weighting materials, and the particle size is from micrometer to nanometer.
[0003] During drilling, the mud column pressure is generally greater than the formation pressure, which creates a positive pressure difference between the wellbore and the formation. The reservoir is very susceptible to invasion, mainly including mud filtrate and weighting material particles. After the weighting material particles invade the formation, they will be deposited in some large pore spaces, resulting in a decrease in reservoir porosity.
[0004] During oil and gas drilling, drilling in high-temperature and high-pressure formation environments has high requirements for well control. In addition, neutron density logging requires radioactive source operations. Therefore, in many cases, neutron and density logging data are not measured while drilling during the drilling process, and nuclear magnetic resonance logging is often used instead. Nuclear magnetic resonance logging generally uses cable measurement, which has a great impact on drilling fluid invasion. Due to the contamination of weighting material particles in high-density drilling fluid, the porosity obtained by nuclear magnetic resonance logging is smaller than the porosity calculated by neutron, density and sound waves, resulting in a low porosity result. The porosity parameter is the core parameter of oil and gas reservoir reserve evaluation. A small porosity parameter will inevitably lead to a low reserve calculation result, which is not conducive to the development of oil and gas reservoirs. Summary of the invention
[0005] The purpose of the present invention is to provide a nuclear magnetic resonance logging porosity correction method to solve the problem that the porosity obtained by the existing nuclear magnetic resonance logging is too low, which is not conducive to the development of oil and gas reservoirs.
[0006] The technical solution of the present invention to solve the above technical problems is as follows:
[0007] A nuclear magnetic resonance logging porosity correction method comprises the following steps:
[0008] S1: Obtain multiple core samples with different physical properties;
[0009] S2: All core samples are treated with saturated formation water, and the NMR porosity of all core samples treated with saturated formation water before contamination is obtained;
[0010] S3: Conduct high-density water-based mud contamination simulation experiments under different invasion times and different invasion pressure differences on all core samples, and obtain the nuclear magnetic resonance porosity of all core samples after contamination;
[0011] S4: Construct the pollution invasion characteristic factor according to the invasion time and invasion pressure difference of the core sample;
[0012] S5: The least square method is used to establish a multivariate regression model between the ratio of the NMR porosity before pollution and the NMR porosity after pollution and the pollution invasion characteristic factors;
[0013] S6: Obtain the relationship between the ratio of the NMR porosity before pollution and the NMR porosity after pollution and the pollution invasion characteristic factor through fitting analysis;
[0014] S7: Obtain the nuclear magnetic resonance porosity of the target reservoir section before contamination through the relationship between the ratio of the nuclear magnetic resonance porosity before contamination to the nuclear magnetic resonance porosity after contamination and the contamination invasion characteristic factor, and complete the correction of the nuclear magnetic resonance porosity;
[0015] S8: Result output.
[0016] Furthermore, in the above step S1, the obtained core samples are sequentially subjected to oil washing, drying and vacuuming operations.
[0017] Furthermore, in the above step S2, the water saturation of the core sample after being treated with saturated formation water is 100%.
[0018] Furthermore, in the above step S3, the composition of the high-density water-based mud is consistent with the composition of the high-density water-based mud used in the actual drilling process.
[0019] Furthermore, in the above step S4, the calculation formula of the pollution intrusion characteristic factor WR is:
[0020] WR=a*P+b*H;
[0021] Where P is the intrusion pressure difference, H is the intrusion time, and a and b are dimensionless coefficients.
[0022] Furthermore, in the above step S5, the coefficients a and b are dynamically adjusted so that the correlation coefficient R of the multivariate regression model is not less than 0.999, and the specific values of the coefficients a and b are determined, and the calculation formula of the pollution intrusion characteristic factor is updated.
[0023] Furthermore, in the above step S6, the relationship between the ratio of the NMR porosity before contamination to the NMR porosity after contamination and the contamination intrusion characteristic factor is:
[0024] PORF / PORO=l*WR^2+m*WR+n;
[0025] Wherein, PORF is the NMR porosity before contamination, PORO is the NMR porosity after contamination, l, m and n are all dimensionless coefficients.
[0026] Furthermore, in the above step S7, the nuclear magnetic resonance porosity of the target reservoir section after contamination is measured by a cable nuclear magnetic resonance logging instrument, and the invasion pressure difference and invasion time parameters during the drilling process are obtained. The nuclear magnetic resonance porosity of the target storage section before contamination is obtained through the relationship between the ratio of the nuclear magnetic resonance porosity before contamination to the nuclear magnetic resonance porosity after contamination and the pollution invasion characteristic factor.
[0027] The present invention has the following beneficial effects:
[0028] The present invention is based on the core sample test and analysis data, constructs the pollution invasion characteristic factor, and establishes a multivariate regression model between the ratio of the nuclear magnetic resonance porosity before pollution and the nuclear magnetic resonance porosity after pollution and the pollution invasion characteristic factor, thereby obtaining the relationship between the ratio of the nuclear magnetic resonance porosity before pollution and the nuclear magnetic resonance porosity after pollution and the pollution invasion characteristic factor, and then correcting the nuclear magnetic resonance porosity of the high-temperature and high-pressure reservoir before pollution. Compared with the prior art, the nuclear magnetic resonance logging porosity correction method provided by the present invention has higher result accuracy, simpler technical process, and is more suitable for on-site promotion and application. The high precision of porosity can ensure accurate evaluation of reserve parameters, guide the formulation of oil field development implementation plans, and achieve the purpose of increasing oil field reserves and production. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Figure 1 Schematic diagram of the process of the nuclear magnetic resonance logging porosity correction method of Example 1;
[0030] Figure 2 The saturated water T2 spectrum measurement results of the 1# core sample of Example 2 before and after contamination;
[0031] Figure 3 It is a multiple regression model between the ratio of the nuclear magnetic resonance porosity before contamination and the nuclear magnetic resonance porosity after contamination in Example 2 and the contamination intrusion characteristic factor. DETAILED DESCRIPTION
[0032] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.
[0033] Embodiment 1:
[0034] Please refer to Figure 1 This embodiment provides a nuclear magnetic resonance logging porosity correction method, comprising the following steps:
[0035] S1: Obtain multiple core samples with different physical properties, and wash, dry and vacuum the core samples in turn. In this embodiment, the number of core samples is not less than 5. Obviously, in order to ensure the accuracy of the data, the number of core samples should be as large as possible. The porosity and permeability of rocks under formation conditions have a wide range of distribution. Only by selecting cores with different physical properties can they be representative of the real formation.
[0036] S2: All core samples are treated with saturated formation water. Specifically, all core samples are immersed in formation water in a vacuum environment for at least 24 hours to ensure that the water saturation of all core samples is 100%. All core samples are measured using a magnetic resonance T2 spectrum measuring instrument to obtain T2 spectrum data of all core samples. The T2 spectrum is processed to obtain the nuclear magnetic resonance porosity of all core samples before contamination.
[0037] S3: A high-density water-based mud contamination simulation experiment is carried out on all core samples under different invasion times and different invasion pressure differences. The invasion time and invasion pressure difference are taken as actual drilling parameters, and the nuclear magnetic resonance porosity of all core samples after contamination is obtained by a magnetic resonance T2 spectrum measuring instrument. The acquisition process is consistent with step S2; wherein, the composition of the high-density water-based mud is consistent with the composition of the high-density water-based mud used in the actual drilling process.
[0038] S4: Construct the pollution invasion characteristic factor according to the invasion time and invasion pressure difference of the core sample; the calculation formula of the pollution invasion characteristic factor WR is:
[0039] WR=a*P+b*H;
[0040] Where P is the intrusion pressure difference, H is the intrusion time, and a and b are dimensionless coefficients.
[0041] S5: The least squares method is used to establish a multivariate regression model between the ratio of the nuclear magnetic resonance porosity before pollution and the nuclear magnetic resonance porosity after pollution and the pollution intrusion characteristic factor. In the multivariate regression model, coefficients a and b are variables. The coefficients a and b are dynamically adjusted so that the correlation coefficient R of the multivariate regression model is not less than 0.999, and the specific values of coefficients a and b are determined, and the calculation formula of the pollution intrusion characteristic factor is updated.
[0042] S6: The relationship between the ratio of the NMR porosity before contamination to the NMR porosity after contamination and the contamination intrusion characteristic factor is obtained through fitting analysis:
[0043] PORF / PORO=l*WR^2+m*WR+n;
[0044] Wherein, PORF is the NMR porosity before contamination, PORO is the NMR porosity after contamination, l, m and n are all dimensionless coefficients.
[0045] S7: The NMR porosity of the target reservoir section after contamination is obtained by measuring with a cable NMR logging instrument, and the invasion pressure difference and invasion time parameters during the drilling process (obtained based on drilling data) are obtained. The NMR porosity of the target storage section before contamination is obtained through the relationship between the ratio of the NMR porosity before contamination to the NMR porosity after contamination and the contamination invasion characteristic factor, and the correction of the NMR porosity is completed.
[0046] S8: Result output.
[0047] The present invention constructs pollution invasion characteristic factors based on core sample test and analysis data, and provides a fast and reliable nuclear magnetic resonance logging porosity correction method for high-temperature and high-pressure reservoirs in the sea. Compared with the existing technology, the nuclear magnetic resonance logging porosity correction method provided by the present invention has higher result accuracy, simpler technical process, and is more suitable for on-site promotion and application. The high precision of porosity can ensure accurate evaluation of reserve parameters, guide the formulation of oil field development implementation plans, and achieve the purpose of increasing oil field reserves and production.
[0048] Embodiment 2:
[0049] This embodiment illustrates the porosity correction method of nuclear magnetic resonance logging of the present invention by an example. This embodiment provides a porosity correction method of nuclear magnetic resonance logging, comprising the following steps:
[0050] S1: Obtain 12 core samples with different physical properties, and perform oil washing, drying and vacuuming operations on the obtained core samples in turn.
[0051] S2: All core samples were treated with saturated formation water. Specifically, all core samples were immersed in formation water in a vacuum environment for at least 24 hours to ensure that the water saturation of all core samples was 100%. All core samples were measured using a magnetic resonance T2 spectrum measuring instrument to obtain the saturated water T2 spectrum data of all core samples before contamination. The T2 spectrum was processed to obtain the nuclear magnetic resonance porosity of all core samples before contamination, as shown in Table 1.
[0052] S3: A high-density water-based mud contamination simulation experiment was carried out on all core samples under different invasion times and different invasion pressure difference conditions, and the nuclear magnetic resonance porosity of all core samples after contamination was obtained by a magnetic resonance T2 spectrum measuring instrument. The acquisition process was consistent with step S2, as shown in Table 1; wherein, the composition of the high-density water-based mud was consistent with that of the high-density water-based mud used in the actual drilling process, and the composition of the high-density water-based mud included water, bentonite, barite, manganese ore powder, etc.
[0053] Table 1 Comparison of NMR porosity of 12 core samples before and after contamination
[0054]
[0055]
[0056] Taking the 1# core sample as an example, the saturated water T2 spectrum measurement results of the 1# core sample before and after contamination are as follows: Figure 2 As shown in the figure, it can be seen that the NMR porosity of the 1# core sample after contamination is significantly smaller than the NMR porosity before contamination.
[0057] S4: Construct the pollution invasion characteristic factor according to the invasion time and invasion pressure difference of the core sample; the calculation formula of the pollution invasion characteristic factor WR is:
[0058] WR=a*P+b*H;
[0059] Where P is the intrusion pressure difference, H is the intrusion time, and a and b are dimensionless coefficients.
[0060] S5: The least square method is used to establish a multivariate regression model between the ratio of the NMR porosity before contamination to the NMR porosity after contamination and the contamination invasion characteristic factor. Please refer to Figure 3 In this multiple regression model, coefficients a and b are variables. Coefficients a and b are adjusted dynamically to make the correlation coefficient R of the multiple regression model 2 is 0.9992, the coefficient a is 0.7, b is 0.3, and the calculation formula of the updated pollution intrusion characteristic factor is:
[0061] WR=0.7*P+0.3*H.
[0062] S6: The relationship between the ratio of the NMR porosity before contamination to the NMR porosity after contamination and the contamination intrusion characteristic factor is obtained through fitting analysis:
[0063] PORF / PORO=0.0145*WR^2-0.0461*WR+1.0498;
[0064] Among them, PORF is the NMR porosity before contamination, and PORO is the NMR porosity after contamination.
[0065] S7: The NMR porosity of the target reservoir section after contamination is obtained by measuring with a cable NMR logging instrument, and the invasion pressure difference and invasion time parameters during the drilling process (obtained based on drilling data) are obtained. The NMR porosity of the target storage section before contamination is obtained through the relationship between the ratio of the NMR porosity before contamination to the NMR porosity after contamination and the contamination invasion characteristic factor, and the correction of the NMR porosity is completed.
[0066] S8: Result output.
[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims
1. A method for correcting porosity in nuclear magnetic resonance logging, characterized in that: The following steps are involved: S1: Obtain multiple core samples with different physical properties; S2: All core samples are treated with saturated formation water, and the NMR porosity of all core samples treated with saturated formation water before contamination is obtained; S3: Conduct high-density water-based mud contamination simulation experiments under different invasion times and different invasion pressure differences on all core samples, and obtain the nuclear magnetic resonance porosity of all core samples after contamination; S4: Construct the pollution invasion characteristic factor according to the invasion time and invasion pressure difference of the core sample; S5: The least square method is used to establish a multivariate regression model between the ratio of the NMR porosity before pollution and the NMR porosity after pollution and the pollution invasion characteristic factors; S6: Obtain the relationship between the ratio of the NMR porosity before pollution and the NMR porosity after pollution and the pollution invasion characteristic factor through fitting analysis; S7: Obtain the nuclear magnetic resonance porosity of the target reservoir section before contamination through the relationship between the ratio of the nuclear magnetic resonance porosity before contamination to the nuclear magnetic resonance porosity after contamination and the contamination invasion characteristic factor, and complete the correction of the nuclear magnetic resonance porosity; S8: Result output.
2. The NMR logging porosity correction method according to claim 1, characterized in that: In step S1, the obtained core sample is subjected to oil washing, drying and vacuuming operations in sequence.
3. The nuclear magnetic resonance logging porosity correction method according to claim 1, characterized in that: In step S2, the water saturation of the core sample after being treated with saturated formation water is 100%.
4. The nuclear magnetic resonance logging porosity correction method according to claim 1, characterized in that: In step S3, the composition of the high-density water-based mud is consistent with the composition of the high-density water-based mud used in the actual drilling process.
5. The nuclear magnetic resonance logging porosity correction method according to claim 1, characterized in that: In step S4, the calculation formula of the pollution intrusion characteristic factor WR is: WR=a*P+b*H; Where P is the intrusion pressure difference, H is the intrusion time, and a and b are dimensionless coefficients.
6. The NMR logging porosity correction method according to claim 5, characterized in that: In step S5, the coefficients a and b are dynamically adjusted so that the correlation coefficient R of the multivariate regression model is not less than 0.999, and the specific values of the coefficients a and b are determined, and the calculation formula of the pollution intrusion characteristic factor is updated.
7. The NMR logging porosity correction method according to claim 6, characterized in that: In step S6, the relationship between the ratio of the nuclear magnetic resonance porosity before contamination to the nuclear magnetic resonance porosity after contamination and the contamination intrusion characteristic factor is: PORF / PORO=l*WR^2+m*WR+n; Wherein, PORF is the NMR porosity before contamination, PORO is the NMR porosity after contamination, l, m and n are all dimensionless coefficients.
8. The nuclear magnetic resonance logging porosity correction method according to claim 1, characterized in that: In step S7, the nuclear magnetic resonance porosity of the target reservoir section after contamination is measured by a cable nuclear magnetic resonance logging instrument, and the invasion pressure difference and invasion time parameters during the drilling process are obtained. The nuclear magnetic resonance porosity of the target storage section before contamination is obtained through the relationship between the ratio of the nuclear magnetic resonance porosity before contamination to the nuclear magnetic resonance porosity after contamination and the pollution invasion characteristic factor.