A method for calculating element content through casing in complex reservoirs

Abstract

The present invention discloses a method for calculating the through-casing element content in complex reservoirs, belonging to the field of nuclear well logging technology. Specifically, the method comprises the following steps: performing through-casing measurement on the formation to be measured to obtain a true energy spectrum, decomposing the spectrum and applying a weighted least squares method to obtain the initial yield of each element contained in the energy spectrum; obtaining constraints on each element contained in the energy spectrum by the through-casing measurement, including sequential yield correction, dry weight correction, element reaction cross-section influence correction and through-casing / cement sheath correction, calculating the yield limit value of each element, and then calculating the final yield of each element by using a constrained weighted least squares method; the present invention improves the accuracy of gamma spectrum analysis through multiple corrections, and is particularly suitable for complex lithology identification in buried hill reservoirs.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear well logging, and in particular relates to a method for calculating through-casing element content in complex reservoirs. Background Art

[0002] In recent years, global oil demand has grown rapidly, and conventional reservoirs have been unable to meet this growing demand. Consequently, concealed reservoirs, such as buried-hill reservoirs, have become a key focus of oil and gas exploration. As a key concealed oil and gas resource, buried-hill reservoirs are crucial to my country's energy security and economic development.

[0003] Buried-hill reservoirs are influenced by complex geological structures, with their reservoirs primarily composed of fractures, dissolution pores, and microstructural fractures. These characteristics determine the reservoir's distribution, permeability, and oil saturation, directly impacting oil and gas reserves and development outcomes. Lithology identification plays a key role in understanding and evaluating buried-hill reservoirs. Accurate lithology identification can determine the reservoir's physical and chemical properties, helping to elucidate its genesis and evolutionary history, and providing crucial geological evidence and technical support for subsequent oil and gas exploration and development.

[0004] Currently, the main methods for lithologic identification include core observation, standard mineralogy calculations, gravity and magnetic techniques, seismic technology, and remote sensing. However, in complex lithologies such as bedrock buried-hill reservoirs, pulsed neutron elemental logging technology demonstrates significant advantages. First, it can acquire a wealth of geological information in real time, including lithologic type and elemental composition, providing data support for subsequent work. Second, its high vertical resolution enables identification of subtle variations and distinct strata, helping to reveal complex reservoir structures. Furthermore, it is unaffected by porosity and is applicable to a wide range of rock types, making it particularly valuable for bedrock buried-hill reservoirs.

[0005] The inversion process for pulsed neutron logging consists of two parts: element content inversion and mineral content inversion. Element content inversion uses weighted least squares to process inelastic gamma ray spectrum and capture gamma ray spectrum data to obtain the inelastic gamma ray spectrum yield and capture gamma ray spectrum yield of the element. Mineral content inversion uses various models to convert the inelastic gamma ray spectrum yield and capture gamma ray spectrum yield of the element into inelastic dry weight and capture dry weight, ultimately obtaining the mineral dry weight.

[0006] In the actual process of gamma-ray spectrum interpretation, when the elements in the formation being interpreted are complex, using weighted least squares methods to interpret gamma-ray spectra often produces unrealistic solutions. The main minerals in buried-hill reservoirs can be divided into three categories: quartz, feldspar, and dark minerals. Quartz is primarily composed of SiO2, feldspar is a mixture of KAlSi3O8, NaAlSi3O8, and CaAl2Si2O8 in certain proportions, and dark minerals are primarily Fe and Mg. Therefore, when using gamma-ray spectrum data for elemental analysis in complex buried-hill reservoir lithology identification, conventional inversion algorithms may fall into local optima, resulting in deviated calculated elemental contents. This deviation can affect the accuracy of mineral identification, and consequently, impact reservoir evaluation and development decisions.

[0007] Therefore, designing an element measurement algorithm for complex reservoirs through casing has positive significance for solving the lithologic identification of buried hill reservoirs. Summary of the Invention

[0008] To address the problem of element content deviating from reality during the identification of complex lithology in buried hill reservoirs due to conventional inversion algorithms falling into local optimality, the present invention provides a method for calculating the through-casing element content in complex reservoirs, which helps to improve the accuracy of gamma ray spectrum analysis and is particularly suitable for the identification of complex lithology in buried hill reservoirs.

[0009] In order to achieve the above purpose, the technical methods adopted by the present invention are as follows:

[0010] A method for calculating the through-casing element content in complex reservoirs includes the following steps:

[0011] Step 1: A cement sheath and casing are sequentially installed in the well of the formation to be measured to reinforce the well. The formation element logging instrument is used to measure the casing of the formation to be measured to obtain a true energy spectrum. After the spectrum is decomposed by the standard spectrum of the casing elements, the initial yield of each element included in the energy spectrum is calculated using the weighted least squares method;

[0012] Step 2: Obtain the constraints on each element included in the energy spectrum from the through-casing measurement, including:

[0013] Step 2.1: Use the yield correction method to correct the yield of each element, specifically:

[0014] Step 2.1.1: Assuming that the mineral M in the formation to be tested contains element E and element E1, a formation element logging numerical simulation calculation model is established with mineral M as the formation through Monte Carlo simulation. After the standard spectrum of casing elements is decomposed, the first analytical yield of element E is obtained, and then the initial yield is obtained by fitting. and the first output correction value COR1 M,E wherein the first yield correction value COR1 M,Eis the yield correction value of mineral M for element E, specifically the difference between the actual yield of element E and the first analytical yield;

[0015] For all minerals containing element E in the measured stratum, the first yield correction value COR1 corresponding to each mineral is calculated. M,E The sum is the total first yield correction value COR1 of element E E ;

[0016] Step 2.1.2: Based on the chemical formula of all minerals containing element E in the formation to be tested, take the maximum dry weight of element E in different minerals as the first limit value of dry weight of element E WF1 E , and then determine the first limit value Y1 of the yield of element E E ;

[0017] Step 2.1.3: Based on the total first output correction value COR1 E , the first limit value Y1 for the yield of element E E Correction is made to obtain the second limit value Y2 of the yield of element E E ;

[0018] Step 2.1.4: Based on steps 2.1.1 to 2.1.3, obtain the second limit value of the yield of each element included in the energy spectrum;

[0019] Step 2.2: Use the dry weight correction method to correct the yield of each element, specifically:

[0020] Step 2.2.1: Assume that the mineral N in the stratum to be tested contains element E and element E2. According to step 2.1.4, obtain the second limit value of the yield of element E2. Then we get the second limit value of dry weight of element E2 Through Monte Carlo simulation, a numerical simulation calculation model of formation element logging with mineral N as the formation was established. After the standard spectrum of casing elements was decomposed, the second analytical yield of element E was obtained, and then the second limit value of dry weight was obtained by fitting. and the second output correction value COR2 N,E wherein the second yield correction value COR2 N,E is the correction value of the yield of mineral N to element E, specifically the difference between the actual yield of element E and the second analytical yield;

[0021] For all minerals containing element E in the measured stratum, the second yield correction value COR2 corresponding to each mineral is calculated. N,E The sum is the total second yield correction value COR2 of element E E ;

[0022] Step 2.2.2: Based on the total second output correction value COR2 E, the second limit value Y2 for the yield of element E E Correction is made to obtain the third limit value Y3 of the yield of element E E ;

[0023] Step 2.2.3: Based on steps 2.2.1 and 2.2.2, obtain the third limit value of the yield of each element included in the energy spectrum;

[0024] Step 2.3: Use the influence of element reaction cross section to modify the yield of each element, specifically:

[0025] Step 2.3.1: Assume that the stratum to be measured contains element E and L elements that affect the dry weight of element E due to the reaction cross section. According to step 2.2.3, the third limit value of the yield of L elements is obtained. The third limit value of the yield of the lth element, where l = 1, 2, ..., L, is Y3 l ,l=1,2,…,L;

[0026] Step 2.3.2: Through Monte Carlo simulation, a numerical simulation calculation model of formation element logging is established with element E and the first element as the formation. After the standard spectrum of casing elements is decomposed, the first analytical dry weight of element E corresponding to the first element is obtained, and then the third limit value of yield is obtained by fitting as Y3 l Corrected value with first dry weight The relationship between them is:

[0027]

[0028] Where, CCS E,l is the influence factor of the reaction cross section of the lth element on the dry weight of element E; is the reaction cross section correction value of the lth element to the dry weight of element E, specifically the difference between the true dry weight of element E and the first analytical dry weight of element E corresponding to the lth element;

[0029] Sum the first dry weight correction values ​​of L elements to obtain the dry weight correction value

[0030]

[0031] Step 2.3.3: According to the third limit value of output Y3 E , obtain the third limit value of dry weight of element E WF3 E ;

[0032] Step 2.3.4: Corrected value based on dry weight The third limit value of dry weight of element E WF3 E Correction is made to obtain the fourth limit value WF4 of the dry weight of element E E, and then the fourth limit value Y4 of the yield of element E is obtained E ;

[0033] Step 2.3.5: Based on steps 2.3.1 to 2.3.4, obtain the fourth limit value of the yield of each element included in the energy spectrum;

[0034] Step 2.4: Determine whether each element exists in both the formation to be tested and the cement sheath, or in both the formation to be tested and the casing. If so, proceed to step 2.5; otherwise, use the fourth yield limit value of the element as its yield constraint and proceed to step 3.

[0035] Step 2.5: Correct the yield of each element by casing / cement sheath, specifically:

[0036] Step 2.5.1. Through Monte Carlo simulation, a numerical simulation calculation model of formation element logging is established with element E as the formation. After the standard spectrum of casing elements is decomposed, the third analytical yield of element E is obtained, and then the thickness of casing / cement sheath and the third yield correction value COR3 of element E are obtained by fitting. E wherein the third yield correction value COR3 E is the difference between the true yield of element E and the third analytical yield;

[0037] Step 2.5.2: Based on the actual thickness of the cement sheath and casing set in step 1, obtain the third yield correction value COR3 corresponding to the cement sheath. E1 , and the third yield correction value COR3 corresponding to the casing E2 , and the sum is the total third yield correction value COR3 of element E E , and then the fourth limit value Y4 of the yield of element E E Correction is made to obtain the fifth limit value Y5 of the yield of element E E , as the yield constraint of element E;

[0038] Step 2.5.3: Based on steps 2.5.1 and 2.5.2, obtain the yield constraints for each element included in the energy spectrum;

[0039] Step 3: Based on the yield constraints of each element, a constrained weighted least squares method is used to obtain the final yield of each element included in the energy spectrum.

[0040] Furthermore, in step 2.1.2, for the mineral M contained in the formation to be measured, the dry weight WF of the element E is calculated according to the chemical formula of the mineral M. E The specific formula is:

[0041]

[0042] Where Matom is the total relative atomic mass of element E in mineral M; M molecule is the relative molecular mass of mineral M.

[0043] Furthermore, in step 2.1.2, the first limit value Y1 of the yield of element E is determined. E The specific formula is:

[0044]

[0045] Where S is the relative sensitivity factor of element E obtained by simulation or measurement; XY is the oxide index.

[0046] Furthermore, the second limit value Y2 of the yield of element E in step 2.1.3 is E The calculation formula is:

[0047] Y2 E =Y1 E -COR1 E

[0048] Furthermore, the formation element logging instrument is a pulsed neutron instrument, which is green and safe.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The present invention proposes a method for calculating the through-casing element content in complex reservoirs. By sequentially performing yield correction, dry weight correction, element reaction cross-section influence correction, and through-casing / cement sheath correction, the yield limit value of each element is calculated, and then the final yield of each element is calculated using the constrained weighted least squares method. The present invention improves the accuracy of gamma ray spectrum analysis through multiple corrections and is particularly suitable for complex lithology identification in buried hill reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0052] Figure 1 This is a flow chart of the method for calculating the through-casing element content in a complex reservoir proposed in Example 1;

[0053] Figure 2 1. This is a schematic diagram of a numerical simulation calculation model for logging while drilling formation elements after setting a cement sheath and casing in the formation to be measured in Example 1;

[0054] Figure 3 This is a comparison curve between the inverted energy spectrum obtained by the through-casing element content calculation method for complex reservoirs in Example 1 and the initial inverted energy spectrum. DETAILED DESCRIPTION

[0055] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than for limiting the claims of the invention.

[0056] Example 1

[0057] This embodiment proposes a method for calculating the through-casing element content in a complex reservoir, specifically a buried hill reservoir. The fractured reservoir of the buried hill oil reservoir contains minerals such as quartz, feldspar, and dark minerals. The process is as follows: Figure 1 As shown, the following steps are included:

[0058] Step 1: Figure 2 As shown in FIG, a cement sheath and a casing are sequentially set in a well of the test formation to reinforce the well. A formation element logging instrument (specifically a pulsed neutron instrument) is used to perform casing measurement on the test formation to obtain a true energy spectrum. After the standard spectrum of the casing elements is decomposed, the initial yield of each element included in the energy spectrum is obtained by the weighted least squares method. The specific process is as follows:

[0059] The true energy spectrum can be regarded as a linear combination of the standard spectra of the corresponding through-the-casing elements, and the equation group is expressed as:

[0060]

[0061] Where, d i ,i=1,2,…,n is the normalized counting rate of the ith channel in the real energy spectrum; s ij ,i=1,2,…,n,j=1,2,…,m is the normalized count rate of the jth element in the standard spectrum of the element at the i-th channel; y j ,j=1,2,…,m is the relative yield of the jth element;

[0062] The system of equations can be expressed in matrix form as follows:

[0063]

[0064] Where, ε i ,i=1,2,…,n is the counting error of the i-th address;

[0065] Then, the matrix form is recorded as:

[0066] d=s·y+ε

[0067] The initial yield of each element contained in the energy spectrum is obtained by weighted least squares method, that is, the optimal solution of element yield is found by minimizing the error. Since the statistical errors of the counting of each channel address in the real energy spectrum are not equal, the minimization problem of fitting error should be considered as the weighted sum of the square of the error, that is,

[0068] R=ε T Wε=(ds·y) T W(ds·y)

[0069] Where W is the diagonal weight matrix, which can be expressed as:

[0070]

[0071] Step 2: Obtain the constraints on each element included in the energy spectrum from the through-casing measurement, including:

[0072] Step 2.1: Use the yield correction method to correct the yield of each element, specifically:

[0073] Step 2.1.1. Assume that the mineral M in the stratum to be tested contains element E and element E1. For example, Mg and Ca exist simultaneously in dolomite. Dolomite is mineral M, Mg is element E1, and Ca is element E.

[0074] Through Monte Carlo simulation, a numerical simulation calculation model of formation element logging was established with mineral M as the formation. After the standard spectrum of casing elements was decomposed, the first analytical yield of element E was obtained, and then the initial yield was obtained by fitting. and the first output correction value COR1 M,E The relationship between them is:

[0075]

[0076] Among them, the first output correction value COR1 M,E is the yield correction value of mineral M for element E, specifically the difference between the actual yield of element E and the first analytical yield; a1, b1 and c1 are all COR1 M,E The fitting coefficient of

[0077] For all minerals containing element E in the measured stratum, the first yield correction value COR1 corresponding to each mineral is calculated. M,E The sum is the total first yield correction value COR1 of element E E ;

[0078] Step 2.1.2: Based on the chemical formula of all minerals containing element E in the formation to be tested, take the maximum dry weight of element E in different minerals as the first limit value of dry weight of element E WF1 E ;

[0079] Taking mineral M as an example, the dry weight of element E is calculated based on the chemical formula of mineral M. The specific formula is:

[0080]

[0081] Where M atom is the total relative atomic mass of element E in mineral M; M molecule is the relative molecular mass of mineral M;

[0082] For example, the main component of potassium feldspar is KAlSi3O8. If the mineral M is pure potassium feldspar, the dry weight of Si is 0.2161. By comparing and taking the maximum value, the first limit value of the dry weight of element E in the buried hill reservoir can be obtained.

[0083] Then determine the first limit value Y1 of the yield of element E E , the specific formula is:

[0084]

[0085] Where S is the relative sensitivity factor of element E obtained by simulation or measurement, specifically:

[0086]

[0087] Where N A is Avogadro's constant, σ C is the thermal neutron absorption cross section of element E, M is the gamma ray transmission and detection probability, A is the atomic weight of element E, for example, the relative sensitivity factor of element Ca is 1.847; XY is the oxide index, specifically the conversion relationship between element E and its corresponding oxide, which can be obtained through the chemical formula. For example, the oxide corresponding to Ca is CaO, so its oxide index O XY is 1.399;

[0088] Step 2.1.3: Based on the total first output correction value COR1 E , the first limit value Y1 for the yield of element E E Correction is made to obtain the second limit value Y2 of the yield of element E E ,Right now:

[0089] Y2 E =Y1 E -COR1 E

[0090] Step 2.1.4: Based on steps 2.1.1 to 2.1.3, obtain the second limit value of the yield of each element included in the energy spectrum;

[0091] Step 2.2: Use the dry weight correction method to correct the yield of each element, specifically:

[0092] Step 2.2.1. Assume that the mineral N in the stratum to be tested contains element E and element E2, and Al and Ca exist simultaneously in anorthite. Anorthite is considered as mineral N, Al as element E2, and Ca as element E.

[0093] According to step 2.1.4, the second limit value of the yield of element E2 is obtained Then we get the second limit value of dry weight of element E2 Right now:

[0094]

[0095] Through Monte Carlo simulation, a numerical simulation calculation model of formation element logging with mineral N as the formation was established. After the standard spectrum of casing elements was decomposed, the second analytical yield of element E was obtained, and then the second limit value of dry weight was obtained by fitting. and the second output correction value COR2 N,E The relationship between them is:

[0096]

[0097] Among them, the second output correction value COR2 N,E is the yield correction value of mineral N to element E, specifically the difference between the actual yield of element E and the second analytical yield; a2, b2, c2 and d2 are all COR2 N,E The fitting coefficient of

[0098] For all minerals containing element E in the measured stratum, the second yield correction value COR2 corresponding to each mineral is calculated. N,E The sum is the total second yield correction value COR2 of element E E ;

[0099] Step 2.2.2: Based on the total second output correction value COR2 E , the second limit value Y2 for the yield of element E E Correction is made to obtain the third limit value Y3 of the yield of element E E ,Right now:

[0100] Y3 E =Y2 E -COR2 E

[0101] Step 2.2.3: Based on steps 2.2.1 and 2.2.2, obtain the third limit value of the yield of each element included in the energy spectrum;

[0102] Step 2.3: Use the influence of element reaction cross section to modify the yield of each element, specifically:

[0103] Step 2.3.1: Assume that the stratum to be measured contains element E and L elements that affect the dry weight of element E due to the reaction cross section. According to step 2.2.3, obtain the third limit value of the yield of L elements. The third limit value of the yield of element l, l = 1, 2 is Y3 l ,l=1,2;

[0104] In this embodiment, Ca is the element E, K and Fe are the elements that affect the dry weight of the element E due to the reaction cross section, that is, the first element is K and the second element is Fe;

[0105] Step 2.3.2: Through Monte Carlo simulation, a numerical simulation calculation model of formation element logging is established with element E and the first element as the formation. After the standard spectrum of casing elements is decomposed, the first analytical dry weight of element E corresponding to the first element is obtained, and then the third limit value of yield is obtained by fitting as Y3 l Corrected value with first dry weight The relationship between them is:

[0106]

[0107] Where, CCS E,l is the influence factor of the reaction cross section of the lth element on the dry weight of element E; is the reaction cross section correction value of the lth element to the dry weight of element E, specifically the difference between the true dry weight of element E and the first analytical dry weight of element E corresponding to the lth element;

[0108] Sum the first dry weight correction values ​​of L elements to obtain the dry weight correction value

[0109]

[0110] In this embodiment, CCS E,1 and CCS E,2 They are 0.574326428 and 0.574326428 respectively;

[0111] Step 2.3.3: According to the third limit value of output Y3 E , obtain the third limit value of dry weight of element E WF3 E ,Right now:

[0112]

[0113] Step 2.3.4: Corrected value based on dry weight The third limit value of dry weight of element E WF3E Correction is made to obtain the fourth limit value WF4 of the dry weight of element E E ,Right now:

[0114]

[0115] Then we get the fourth limit value Y4 of the yield of element E E ,Right now:

[0116]

[0117] Step 2.3.5: Based on steps 2.3.1 to 2.3.4, obtain the fourth limit value of the yield of each element included in the energy spectrum;

[0118] Step 2.4: Determine whether each element exists in both the formation to be tested and the cement sheath, or in both the formation to be tested and the casing. If so, proceed to step 2.5; otherwise, use the fourth yield limit value of the element as its yield constraint and proceed to step 3.

[0119] Step 2.5: Correct the yield of each element by casing / cement sheath, specifically:

[0120] Step 2.5.1. Through Monte Carlo simulation, a numerical simulation calculation model of formation element logging is established with element E as the formation. After the standard spectrum of casing elements is decomposed, the third analytical yield of element E is obtained, and then the thickness of casing / cement sheath and the third yield correction value COR3 of element E are obtained by fitting. E wherein the third yield correction value COR3 E is the difference between the true yield of element E and the third analytical yield;

[0121] Step 2.5.2: Based on the actual thickness of the cement sheath and casing set in step 1, obtain the third yield correction value COR3 corresponding to the cement sheath. E1 , and the third yield correction value COR3 corresponding to the casing E2 , and the sum is the total third yield correction value COR3 of element E E , and then the fourth limit value Y4 of the yield of element E E Correction is made to obtain the fifth limit value Y5 of the yield of element E E , as the yield constraint of element E, that is:

[0122] Y5 E =Y4 E -COR3 E

[0123] Step 2.5.3: Based on steps 2.5.1 and 2.5.2, obtain the yield constraints for each element included in the energy spectrum;

[0124] Step 3: Based on the yield constraints of each element, a constrained weighted least squares method is used to obtain the final yield of each element included in the energy spectrum.

[0125] Figure 3 is a comparison curve of the inverted energy spectrum (recorded as after using this method) and the initial inverted energy spectrum (before using this method) obtained by the through-casing element content calculation method for complex reservoirs in this embodiment, wherein the initial inverted energy spectrum is obtained based on the initial yield of each element obtained in step 1, and the inverted energy spectrum obtained by the through-casing element content calculation method for complex reservoirs is obtained based on the final yield of each element obtained in step 3; according to Figure 3 It can be seen that the inverted energy spectrum after using this method is closer to the real energy spectrum, indicating that the through-casing element content calculation method for complex reservoirs proposed in this embodiment helps to improve the accuracy of gamma spectrum analysis, and is particularly suitable for complex lithology identification of buried hill reservoirs.

[0126] The above embodiments are intended to provide a better understanding of the present invention, and are not intended to limit the optimal implementation scheme described herein, nor to limit the content and scope of protection of the present invention. Any product identical or similar to the present invention that is derived by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

Claims

1. A method for calculating the element content through casing in complex reservoirs, characterized in that: The following steps are involved: Step 1: A cement sheath and casing are sequentially set in the well of the formation to be measured, and a formation element logging instrument is used to perform casing measurement on the formation to be measured to obtain a true energy spectrum. After the spectrum is decomposed by the standard spectrum of the casing elements, the initial yield of each element included in the energy spectrum is calculated using the weighted least squares method; Step 2: Obtain the constraints on each element included in the energy spectrum from the through-casing measurement, including: Step 2.1, using the yield correction method to correct the yield of each element, and obtain the second limit value of the yield of each element included in the energy spectrum; Step 2.2, using the dry weight correction method to correct the yield of each element, specifically based on the second limit value of the yield, to obtain the third limit value of the yield of each element included in the energy spectrum; Step 2.3: Using the influence of the element reaction cross section, correct the yield of each element. Specifically, based on the third limit value of the yield, obtain the fourth limit value of the yield of each element included in the energy spectrum; Step 2.4: Determine whether each element exists in both the formation to be tested and the cement sheath, or in both the formation to be tested and the casing. If so, proceed to step 2.

5. Otherwise, use the fourth yield limit value of the element as its yield constraint and proceed to step 3. Step 2.5: Perform casing / cement sheath correction on the yield of each element to obtain the yield constraint of each element included in the energy spectrum; Step 3: Based on the yield constraints of each element, a constrained weighted least squares method is used to obtain the final yield of each element included in the energy spectrum.

2. The method for calculating element content through casing in complex reservoirs according to claim 1, characterized in that: The specific process of step 2.1 is: Step 2.1.1: Assuming that the mineral M in the formation to be tested contains element E and element E1, a formation element logging numerical simulation calculation model is established with mineral M as the formation through Monte Carlo simulation. After the standard spectrum of casing elements is decomposed, the first analytical yield of element E is obtained, and then the initial yield is obtained by fitting. and the first output correction value COR1 M,E wherein the first yield correction value COR1 M,E is the yield correction value of mineral M for element E, specifically the difference between the actual yield of element E and the first analytical yield; For all minerals containing element E in the measured stratum, the first yield correction value COR1 corresponding to each mineral is calculated. M,E The sum is the total first yield correction value COR1 of element E E ; Step 2.1.2: Based on the chemical formula of all minerals containing element E in the formation to be tested, take the maximum dry weight of element E in different minerals as the first limit value of dry weight of element E WF1 E , and then determine the first limit value Y1 of the yield of element E E ; Step 2.1.3: Based on the total first output correction value COR1 E , the first limit value Y1 for the yield of element E E Correction is made to obtain the second limit value Y2 of the yield of element E E ; Step 2.1.4: Based on steps 2.1.1 to 2.1.3, obtain the second limit value of the yield of each element included in the energy spectrum.

3. The method for calculating element content through casing in complex reservoirs according to claim 2, characterized in that: The specific process of step 2.2 is: Step 2.2.1: Assume that the mineral N in the stratum to be tested contains element E and element E2. According to step 2.1.4, obtain the second limit value of the yield of element E2. Then we get the second limit value of dry weight of element E2 Through Monte Carlo simulation, a numerical simulation calculation model of formation element logging with mineral N as the formation was established. After the standard spectrum of casing elements was decomposed, the second analytical yield of element E was obtained, and then the second limit value of dry weight was obtained by fitting. and the second output correction value COR2 N,E wherein the second yield correction value COR2 N,E is the correction value of the yield of mineral N to element E, specifically the difference between the actual yield of element E and the second analytical yield; For all minerals containing element E in the measured stratum, the second yield correction value COR2 corresponding to each mineral is calculated. N,E The sum is the total second yield correction value COR2 of element E E ; Step 2.2.2: Based on the total second output correction value COR2 E , the second limit value Y2 for the yield of element E E Correction is made to obtain the third limit value Y3 of the yield of element E E ; Step 2.2.3: Based on steps 2.2.1 and 2.2.2, obtain the third limit value of the yield of each element included in the energy spectrum.

4. The method for calculating element content through casing in complex reservoirs according to claim 3, characterized in that: The specific process of step 2.3 is: Step 2.3.1: Assume that the stratum to be measured contains element E and L elements that affect the dry weight of element E due to the reaction cross section. According to step 2.2.3, the third limit value of the yield of L elements is obtained. The third limit value of the yield of the lth element, where l = 1, 2, ..., L, is Y3 l ,l=1,2,…,L; Step 2.3.2: Through Monte Carlo simulation, a numerical simulation calculation model of formation element logging is established with element E and the first element as the formation. After the standard spectrum of casing elements is decomposed, the first analytical dry weight of element E corresponding to the first element is obtained, and then the third limit value of yield is obtained by fitting as Y3 l Corrected value with first dry weight The relationship between them is: Where, CCS E,l is the influence factor of the reaction cross section of the lth element on the dry weight of element E; is the reaction cross section correction value of the lth element to the dry weight of element E, specifically the difference between the true dry weight of element E and the first analytical dry weight of element E corresponding to the lth element; Sum the first dry weight correction values ​​of L elements to obtain the dry weight correction value Step 2.3.3: According to the third limit value of output Y3 E , obtain the third limit value of dry weight of element E WF3 E ; Step 2.3.4: Corrected value based on dry weight The third limit value of dry weight of element E WF3 E Correction is made to obtain the fourth limit value WF4 of the dry weight of element E E , and then the fourth limit value Y4 of the yield of element E is obtained E ; Step 2.3.5: Based on steps 2.3.1 to 2.3.4, obtain the fourth limit value of the yield of each element included in the energy spectrum.

5. The method for calculating element content through casing in complex reservoirs according to claim 4, characterized in that: The specific process of step 2.5 is as follows: Step 2.5.

1. Through Monte Carlo simulation, a numerical simulation calculation model of formation element logging is established with element E as the formation. After the standard spectrum of casing elements is decomposed, the third analytical yield of element E is obtained, and then the thickness of casing / cement sheath and the third yield correction value COR3 of element E are obtained by fitting. E wherein the third yield correction value COR3 E is the difference between the true yield of element E and the third analytical yield; Step 2.5.2: Based on the actual thickness of the cement sheath and casing set in step 1, obtain the third yield correction value COR3 corresponding to the cement sheath. E1 , and the third yield correction value COR3 corresponding to the casing E2 , and the sum is the total third yield correction value COR3 of element E E , and then the fourth limit value Y4 of the yield of element E E Correction is made to obtain the fifth limit value Y5 of the yield of element E E , as the yield constraint of element E; Step 2.5.3: Based on steps 2.5.1 and 2.5.2, obtain the yield constraints of each element included in the energy spectrum.

6. The method for calculating element content through casing in complex reservoirs according to claim 5, characterized in that: Furthermore, in step 2.1.2, for the mineral M contained in the formation to be measured, the dry weight WF of the element E is calculated according to the chemical formula of the mineral M. E The specific formula is: Where M atom is the total relative atomic mass of element E in mineral M; M molecule is the relative molecular mass of mineral M.

7. The method for calculating element content through casing in complex reservoirs according to claim 5, characterized in that: Determine the first limit value Y1 of the yield of element E in step 2.1.2 E The specific formula is: Where S is the relative sensitivity factor of element E obtained by simulation or measurement; XY is the oxide index.

8. The method for calculating element content through casing in complex reservoirs according to claim 5, characterized in that: The second limit value Y2 of the yield of element E in step 2.1.3 E The calculation formula is: Y2 E =Y1 E -COR1 E 。

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