Comprehensive calculation method for formation water salinity and oil saturation based on lithology scanning

Abstract

The application discloses a kind of stratum water salinity and oil saturation comprehensive calculation method based on lithology scanning.The original measurement energy spectrum and time spectrum of stratum are measured using measurement system, after obtaining the inelastic yield and capture yield of stratum by analyzing original measurement energy spectrum based on stratum element standard spectrum, element yield is converted into atomic number ratio, the inelastic atomic number ratio of carbon element, oxygen element and magnesium element and the capture atomic number ratio of remaining elements in stratum are used to construct stratum element atomic number ratio dataset, the mass fraction of each element in stratum is determined, the macroscopic capture cross section of stratum is obtained by processing time spectrum, combined with the mass fraction of chlorine element, the porosity and density of stratum, stratum water salinity and oil saturation comprehensive calculation model is established to calculate stratum water salinity and oil saturation.The application solves the influence of poor chlorine element content calculation accuracy on stratum water salinity and oil saturation monitoring accuracy, and widens the application range of element logging.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of mine geophysical logging, and particularly relates to a stratum water salinity and oil saturation comprehensive calculation method based on lithology scanning. BACKGROUND

[0002] As an important parameter in the process of oil and gas exploration, quantitative monitoring of oil saturation has become one of the targets of post-casing pulse neutron logging. In nuclear logging, fast neutrons released by a D-T neutron source interact with atomic nuclei of stratum elements, and secondary gamma ray information is detected to reflect the properties of stratum fluid, which is of great significance for stratum oil and gas evaluation and guidance of reservoir development.

[0003] At present, the evaluation method of reservoir oil saturation based on pulse neutron logging mainly includes C / O spectral logging and neutron lifetime logging. The neutron lifetime logging is affected by the uncertainty of stratum water salinity, and it is difficult to accurately obtain the Sigma parameter of fluid, resulting in great calculation error of stratum oil saturation. Therefore, how to accurately obtain the Cl element content is a prerequisite for accurate evaluation of reservoir oil saturation.

[0004] The Cl element yield in element logging can be used to calculate the stratum water salinity, but the element yield as a relative value has great error in the calculation of stratum water salinity under the condition that the stratum minerals are relatively complex, and it is difficult to meet the demand of determining the fluid macroscopic capture cross section in neutron lifetime logging, and has certain limitations.

[0005] Therefore, it is urgent to propose a stratum water salinity and oil saturation comprehensive calculation method based on lithology scanning, which can broaden the application range of element logging and eliminate the negative influence of stratum water salinity uncertainty on quantitative monitoring of oil saturation. SUMMARY

[0006] In view of the above problems, the original measurement spectrum and time spectrum information collected by stratum element logging are used to propose a stratum water salinity and oil saturation comprehensive calculation method based on lithology scanning, which solves the negative influence of the calculation accuracy of the content of chlorine element in the stratum on the monitoring of stratum water salinity and oil saturation, and realizes accurate acquisition of the double parameters of the stratum.

[0007] The application specifically adopts the following technical solutions:

[0008] The stratum water salinity and oil saturation comprehensive calculation method based on lithology scanning is measured in the well by using a measurement system provided with a D-T neutron source and at least one gamma detector, and specifically includes the following steps:

[0009] Step 1, measuring the original measurement spectrum of the formation by using the measurement system, analyzing the original measurement spectrum to obtain the formation element yield based on the standard spectrum of the formation element, and determining the non-elastic yield and capture yield of each element in the formation;

[0010] Step 2, based on the sum of the atomic number proportions of each element in the formation being 1, converting the non-elastic yield of each element in the formation into the non-elastic atomic number proportion, converting the capture yield of each element in the formation into the capture atomic number proportion, constructing the non-elastic atomic number proportion data set and the capture atomic number proportion data set of the formation element, extracting the non-elastic atomic number proportions of carbon element, oxygen element and magnesium element from the non-elastic atomic number proportion data set of the formation element, combining the capture atomic number proportions of the elements other than carbon element, oxygen element and magnesium element in the capture atomic number proportion data set of the formation element, constructing the atomic number proportion data set of the formation element, determining the mass fraction of each element in the formation, and constructing the formation element mass fraction set;

[0011] Step 3, processing the time spectrum measured by the measurement system by selecting a time window, and calculating the macroscopic capture cross section of the formation;

[0012] Step 4, extracting the mass fraction of chlorine element from the formation element mass fraction set, combining the macroscopic capture cross section of the formation, the formation porosity and the formation density obtained from the open hole data, establishing a comprehensive calculation model of formation water salinity and oil saturation, and calculating the formation water salinity and oil saturation by using the comprehensive calculation model of formation water salinity and oil saturation.

[0013] Preferably, in the step 1, the original measurement spectrum includes non-elastic gamma spectrum and capture gamma spectrum, and the formation element yield includes the non-elastic yield and capture yield of each element in the formation;

[0014] First, the non-elastic gamma spectrum is analyzed by using the weighted least squares method to determine the non-elastic yield of each element in the formation, and then the capture gamma spectrum is analyzed by using the weighted least squares method to determine the capture yield of each element in the formation;

[0015] The formation element yield calculation formula is:

[0016] x=(A T WA) -1 A T Wb (1)

[0017] Wherein,

[0018]

[0019] In the formula, x is the formation element yield; A is the formation element standard spectrum matrix, each column vector in the formation element standard spectrum matrix corresponds to the standard spectrum of different elements in the formation; T is the transpose matrix, and W is the weight matrix;N b is the weight of the Nth channel count in the original measurement spectrum N b is the weight of the Nth channel count in the original measurement spectrum

[0020] When calculating the non-elastic yield of the formation element, b substituted in the formation element yield calculation formula is the non-elastic gamma spectrum, w substituted in the weight matrix W is N b is the weight of the Nth channel count in the non-elastic gamma spectrum N b is the weight of the Nth channel count in the non-elastic gamma spectrum

[0021] When calculating the capture yield of the formation element, b substituted in the formation element yield calculation formula is the capture gamma spectrum, w substituted in the weight matrix W is N b is the weight of the Nth channel count in the capture gamma spectrum N b is the weight of the Nth channel count in the capture gamma spectrum

[0022] Preferably, in step 2, the following steps are specifically included:

[0023] Step 2.1, obtaining the atomic number sensitivity of each element in the formation based on the formation element yield;

[0024] First, the non-elastic atomic number sensitivity factor of each element in the formation is calculated according to the non-elastic yield of each element in the formation, and then the capture atomic number sensitivity factor of each element in the formation is calculated according to the capture yield of each element in the formation, to obtain the non-elastic atomic number sensitivity factor and the capture atomic number sensitivity factor of each element in the formation;

[0025] Step 2.2, determining the formation atomic normalization coefficient based on the atomic number normalization closure model and combining the atomic number sensitivity factor of each element in the formation;

[0026] First, the formation atomic non-elastic normalization coefficient is calculated according to the non-elastic atomic number sensitivity factor and the non-elastic yield of each element in the formation, and then the formation atomic capture normalization coefficient is calculated according to the capture atomic number sensitivity factor and the capture yield of each element in the formation, to determine the formation atomic non-elastic normalization coefficient and the formation atomic capture normalization coefficient;

[0027] Step 2.3, determining the atomic number proportion of each element in the formation based on the formation atomic normalization coefficient, and establishing the non-elastic atomic number proportion data set and the capture atomic number proportion data set of the formation elements;

[0028] The non-elastic element atom number proportion of each element in the formation is calculated according to the non-elastic yield of each element in the formation and the non-elastic normalization coefficient of the formation atoms, and the capture element atom number proportion of each element in the formation is calculated according to the capture yield of each element in the formation and the capture normalization coefficient of the formation atoms, the non-elastic element atom number proportion and the capture element atom number proportion of each element in the formation are determined, the formation element non-elastic atom number proportion dataset is established according to the non-elastic atom number proportion of each element in the formation, and the formation element capture atom number proportion dataset is established according to the capture atom number proportion of each element in the formation;

[0029] Step 2.4, the non-elastic atom number proportion of carbon element, oxygen element and magnesium element is extracted from the formation element non-elastic atom number proportion dataset, and then combined with the capture atom number proportion of elements other than carbon element, oxygen element and magnesium element extracted from the formation element capture atom number proportion dataset, to construct the formation element atom number proportion dataset;

[0030] Step 2.5, according to the formation element atom number proportion dataset, the element mass fraction of each element in the formation is calculated to construct the formation element mass fraction set.

[0031] Preferably, in the step 2.1, based on the sum of the atom number proportions of each element in the formation being 1, the atom number sensitivity factor of oxygen element is set to 1, the atom number sensitivity factor of each element in the formation is calculated, and the atom number sensitivity factor calculation formula is:

[0032]

[0033] In the formula, j is the serial number of the formation element, j is a positive integer and 1≤j≤m, m is the number of types of formation elements; S j is the atom number sensitivity factor of element j, j is the serial number of the formation element, y j is the yield of element j, n j is the atom number of element j; y o is the yield of oxygen element, n o is the atom number of oxygen element;

[0034] When calculating the non-elastic atom number sensitivity factor of each element in the formation, the yield y j is the non-elastic yield of element j, the yield y o is the non-elastic yield of oxygen element, and the calculated atom number sensitivity factor S j is the non-elastic atom number sensitivity factor of element j;

[0035] When calculating the capture atom number sensitivity factor of each element in the formation, the yield y j is the capture yield of element j, and the yield yo The calculated atomic sensitivity factor S for the capture yield of element j j The calculated atomic sensitivity factor S for the capture yield of element j.

[0036] Preferably, in the step 2.2, the formation atomic inelastic normalization factor and the formation atomic capture normalization factor are respectively calculated by using the atomic number normalization closure model, which is shown in the formula (4):

[0037]

[0038] In the formula, F is the formation atomic normalization factor;

[0039] When the formation atomic inelastic normalization factor is calculated, the yield y j The calculated atomic sensitivity factor S for the inelastic yield of element j j The calculated atomic sensitivity factor S for the inelastic yield of element j, the calculated formation atomic normalization factor F is the formation atomic inelastic normalization factor;

[0040] When the formation atomic capture normalization factor is calculated, the yield y j The calculated atomic sensitivity factor S for the capture yield of element j j The calculated atomic sensitivity factor S for the capture yield of element j, the calculated formation atomic normalization factor F is the formation atomic capture normalization factor.

[0041] Preferably, in the step 2.3, the formula for calculating the atomic number proportion of the formation element is:

[0042]

[0043] In the formula, n′ j The calculated atomic sensitivity factor S for the inelastic yield of element j

[0044] When the yield y j The calculated atomic sensitivity factor S for the inelastic yield of element j j The calculated atomic sensitivity factor S for the inelastic yield of element j, the calculated formation atomic normalization factor F is the formation atomic inelastic normalization factor, and the calculated atomic number proportion n′ j The calculated atomic sensitivity factor S for the inelastic yield of element j

[0045] When the yield y j The calculated atomic sensitivity factor S for the capture yield of element j jis the number of captured atoms of element j, F is the stratum atom normalization coefficient, and n′ is the calculated atomic number proportion of element j in the stratum j is the number of captured atoms of element j in the stratum.

[0046] Preferably, in step 2.5, the mass fraction of the stratum element is calculated according to the following formula:

[0047]

[0048] where i is the sequence number of an element in the atomic number proportion data set of the stratum element, i is a positive integer and 1≤i≤m; w i is the mass fraction of element i in the atomic number proportion data set of the stratum element, n i ′ is the atomic number proportion of element j in the atomic number proportion data set of the stratum element, M i is the mass number of element j in the atomic number proportion data set of the stratum element.

[0049] Preferably, in step 3, a first time window and a second time window are selected in the time spectrum, and the macroscopic capture cross section of the stratum is calculated using the gamma counts in the first time window and the second time window, as shown in formula (7):

[0050]

[0051] where Σ is the macroscopic capture cross section of the stratum, N1 is the gamma count in the first time window, N2 is the gamma count in the second time window, and ΔT is the interval between the first time window and the second time window.

[0052] Preferably, in step 4, the mass proportion of fresh water in the stratum is expressed according to the relationship between the stratum porosity, the stratum density, and the oil saturation of the stratum as:

[0053]

[0054] where is the mass proportion of fresh water, is the density of fresh water, is the volume of fresh water, ρ is the density of the stratum, V f is the volume of the stratum pore, φ is the porosity of the stratum, S O is the oil saturation of the stratum.

[0055] The salinity of the stratum water is expressed as:

[0056]

[0057] where C w is the salinity of the stratum water, w Nacl is the mass proportion of salt water, wCl is the mass fraction of the chlorine element;

[0058] An oil saturation volume model based on a formation macroscopic capture cross section is established, as shown in formula (10):

[0059]

[0060] wherein,

[0061]

[0062] In the formula, Σ is a formation macroscopic capture cross section, Σ ma is a capture cross section of a formation skeleton, is a capture cross section of salt water in a formation, Σ oil is a capture cross section of oil in a formation, is a capture cross section of fresh water in a formation;

[0063] By combining formulae (9)-(11), a comprehensive calculation model of formation water salinity and oil saturation is obtained, as shown in formula (12):

[0064]

[0065] The beneficial technical effects brought by the present application are:

[0066] The present application uses the original energy spectrum information collected by element logging measurement, establishes a Cl element content determination method based on the sum of the atomic number proportions of each element in the formation being 1, combines the formation macroscopic capture cross section Σ obtained from the time spectrum measured by element logging measurement and the formation porosity and formation density obtained from the open hole data, establishes a comprehensive calculation model of formation water salinity and oil saturation, simultaneously determines the optimal solution of the formation water salinity and oil saturation in the formation by using the comprehensive calculation model of formation water salinity and oil saturation, realizes real-time calculation of the formation water salinity and oil saturation, solves the influence of inaccurate Cl element content calculation on the monitoring accuracy of the formation water salinity and oil saturation, improves the accuracy of real-time monitoring of the formation water salinity and oil saturation, widens the application range of element logging, and has important significance for formation oil and gas bearing property evaluation and guidance of reservoir development. BRIEF DESCRIPTION OF DRAWINGS

[0067] Figure 1 Fig. 1 is a structural schematic diagram of a single-probe element logging instrument according to the present application.

[0068] Figure 2 Fig. 2 is a flowchart of a formation element mass fraction calculation method based on atomic number proportions according to the present application.

[0069] Figure 3The comparison chart of the element mass fraction calculation method of the present application and the Cl element content calculated by the conventional oxygen closure method.

[0070] Figure 4 The comparison chart of the formation water salinity calculated value of the present application and the formation water salinity simulated value.

[0071] Figure 5 The comparison chart of the oil saturation calculated value of the present application and the oil saturation simulated value.

[0072] In the figure: 1 is a D-T neutron source, 2 is a tungsten-nickel-iron shielding body, 3 is a gamma detector, 4 is an instrument shell, 5 is a borehole, 6 is a formation. DETAILED DESCRIPTION

[0073] The present application will be described in detail below in combination with the drawings and specific embodiments:

[0074] The present application proposes a lithology scanning-based comprehensive calculation method of formation water salinity and oil saturation, which is applicable to all formation element measuring instruments. The present embodiment takes a single-detector element logging instrument as an example. The structure of the single-detector element logging instrument is shown in the figure. Figure 1 A D-T neutron source 1 and a gamma detector 3 are arranged in the instrument shell 4. A tungsten-nickel-iron shielding body 2 is arranged between the D-T neutron source 1 and the gamma detector 3. The instrument measures the original measurement energy spectrum and time spectrum of the formation 6 in the borehole 5 wall. The lithology scanning-based comprehensive calculation method of formation water salinity and oil saturation proposed by the present application is further described in detail, which specifically includes the following steps:

[0075] Step 1: The original measurement energy spectrum is measured by the single-detector element logging instrument, including non-elastic gamma spectrum and capture gamma spectrum. The original measurement energy spectrum is analyzed based on the formation element standard spectrum to obtain the formation element yield, including the non-elastic yield and the capture yield of each element in the formation.

[0076] In the present embodiment, the non-elastic gamma spectrum measured by the single-detector element logging instrument is first analyzed by using the weighted least squares method to determine the non-elastic yield of each element in the formation. Then, the capture gamma spectrum measured by the single-detector element logging instrument is analyzed by using the weighted least squares method to determine the capture yield of each element in the formation.

[0077] The non-elastic yield and the capture yield of each element in the formation are calculated by using the formation element yield calculation formula, which is:

[0078] x=(A T WA) -1 A T Wb (1)

[0079] wherein,

[0080]

[0081] wherein x is the formation element yield; A is a formation element standard spectrum matrix, each column vector of the formation element standard spectrum matrix corresponding to a standard spectrum of a different element in the formation; T is a transpose matrix; and W is a weight matrix; w N is the weight of the Nth channel count in the original measured spectrum; b N is the count of the Nth channel in the original measured spectrum.

[0082] When calculating the inelastic yield of the formation element, b substituted in formula (1) is the inelastic gamma spectrum, w N substituted in the weight matrix W is the weight of the Nth channel count in the inelastic gamma spectrum, b N substituted is the count of the Nth channel in the inelastic gamma spectrum, and the calculated formation element yield x is the inelastic yield.

[0083] When calculating the capture yield of the formation element, b substituted in formula (1) is the capture gamma spectrum, w N substituted in the weight matrix W is the weight of the Nth channel count in the capture gamma spectrum, b N substituted is the count of the Nth channel in the capture gamma spectrum, and the calculated formation element yield x is the capture yield.

[0084] Step 2, based on the sum of the atomic number fractions of each element in the formation being 1, by converting the inelastic yield of each element in the formation into an inelastic atomic number fraction and converting the capture yield of each element in the formation into a capture atomic number fraction, an inelastic atomic number fraction data set and a capture atomic number fraction data set of the formation element are constructed, and the inelastic atomic number fractions of carbon, oxygen and magnesium are extracted from the inelastic atomic number fraction data set of the formation element, and the capture atomic number fractions of elements other than carbon, oxygen and magnesium are extracted from the capture atomic number fraction data set of the formation element, to construct a formation element atomic number fraction data set, determine the mass fraction of each element in the formation, and construct a formation element mass fraction set, as shown in Figure 2 and specifically comprising the following steps:

[0085] Step 2.1, obtaining the atomic number sensitivity of each element in the formation based on the formation element yield.

[0086] In this embodiment, the inelastic atomic number sensitivity factor of each element in the formation is first calculated according to the inelastic yield of each element in the formation, and then the capture atomic number sensitivity factor of each element in the formation is calculated according to the capture yield of each element in the formation, to obtain the inelastic atomic number sensitivity factor and the capture atomic number sensitivity factor of each element in the formation.

[0087] Based on the sum of the atomic number proportion of each element in the stratum being 1, the atomic number sensitivity factor of oxygen element in the stratum is set to 1, the non-elastic atomic number sensitivity factor and the capture atomic number sensitivity factor of each element in the stratum are respectively calculated by using the atomic number sensitivity factor calculation formula, and the atomic number sensitivity factor calculation formula is as follows:

[0088]

[0089] In the formula, j is the serial number of the element in the stratum, j is a positive integer and 1≤j≤m, m is the number of types of elements in the stratum; S j is the atomic number sensitivity factor of element j, j is the serial number of the element in the stratum, y j is the yield of element j, n j is the atomic number of element j; y o is the yield of oxygen element, n o is the atomic number of oxygen element.

[0090] When the non-elastic atomic number sensitivity factor of each element in the stratum is calculated, the yield y j is the non-elastic yield of element j, the yield y o is the non-elastic yield of oxygen element, the calculated atomic number sensitivity factor S j is the non-elastic atomic number sensitivity factor of element j;

[0091] When the capture atomic number sensitivity factor of each element in the stratum is calculated, the yield y j is the capture yield of element j, the yield y o is the capture yield of oxygen element, the calculated atomic number sensitivity factor S j is the capture atomic number sensitivity factor of element j.

[0092] Step 2.2, based on the atomic number normalization closed model, the atomic number sensitivity factor of each element in the stratum is combined to determine the stratum atomic normalization coefficient.

[0093] In this embodiment, the atomic number normalization closed model is used to calculate the stratum atomic non-elastic normalization coefficient and the stratum atomic capture normalization coefficient respectively, the stratum atomic non-elastic normalization coefficient is calculated according to the non-elastic atomic number sensitivity factor and the non-elastic yield of each element in the stratum, the stratum atomic capture normalization coefficient is calculated according to the capture atomic number sensitivity factor and the capture yield of each element in the stratum, and the stratum atomic non-elastic normalization coefficient and the stratum atomic capture normalization coefficient are determined.

[0094] The atomic number normalization closed model is shown in formula (4):

[0095]

[0096] wherein F is a formation atomic normalization factor;

[0097] When calculating the formation atomic inelastic normalization factor, the yield y j is the inelastic yield of element j, the atomic sensitivity factor S j is the inelastic atomic sensitivity factor of element j, the calculated formation atomic normalization factor F is a formation atomic inelastic normalization factor;

[0098] When calculating the formation atomic capture normalization factor, the yield y j is the capture yield of element j, the atomic sensitivity factor S j is the capture atomic sensitivity factor of element j, the calculated formation atomic normalization factor F is a formation atomic capture normalization factor.

[0099] Step 2.3, based on the formation atomic normalization factor, determining the atomic percentage of each element in the formation, determining the inelastic atomic percentage and the capture atomic percentage of each element in the formation, and establishing the inelastic atomic percentage data set and the capture atomic percentage data set of the formation elements.

[0100] In this embodiment, the inelastic element atomic percentage of each element in the formation is calculated according to the inelastic yield of each element in the formation and the formation atomic inelastic normalization factor, and the capture element atomic percentage of each element in the formation is calculated according to the capture yield of each element in the formation and the formation atomic capture normalization factor, to determine the inelastic element atomic percentage and the capture element atomic percentage of each element in the formation.

[0101] The atomic percentage calculation formula of the formation element is:

[0102]

[0103] wherein n' j is the atomic percentage of element j in the formation;

[0104] When the yield y j is the inelastic yield of element j, the atomic sensitivity factor S j is the inelastic atomic sensitivity factor of element j, the formation atomic normalization factor F is a formation atomic inelastic normalization factor, and the calculated atomic percentage n' j is the inelastic atomic percentage of element j in the formation.

[0105] When the yield y j is the capture yield of element j, the atomic sensitivity factor S jis the number of captured atoms of element j, F is the stratum atom normalization coefficient, and n′ is the calculated atomic number proportion j is the number of captured atoms of element j in the stratum.

[0106] The non-elastic atomic number proportion dataset of the elements in the stratum is established according to the non-elastic atomic number proportions of the elements in the stratum, and the captured atomic number proportion dataset of the elements in the stratum is established according to the captured atomic number proportions of the elements in the stratum.

[0107] Step 2.4, the non-elastic atomic number proportions of carbon, oxygen and magnesium elements are extracted from the non-elastic atomic number proportion dataset of the elements in the stratum, and then the captured atomic number proportions of the elements other than carbon, oxygen and magnesium elements are extracted from the captured atomic number proportion dataset of the elements in the stratum, to construct the atomic number proportion dataset of the elements in the stratum.

[0108] Step 2.5, according to the atomic number proportion dataset of the elements in the stratum, the mass fraction of each element in the stratum is calculated by using formula (6), and the mass fraction dataset of the elements in the stratum is constructed according to the mass fraction of each element in the stratum.

[0109] The calculation formula of the mass fraction of the elements in the stratum is:

[0110]

[0111] In the formula, i is the serial number of the element in the atomic number proportion dataset of the elements in the stratum, i is a positive integer and 1≤i≤m; w i is the mass fraction of element i in the atomic number proportion dataset of the elements in the stratum, n i ′ is the atomic number proportion of element j in the atomic number proportion dataset of the elements in the stratum, M i is the mass number of element j in the atomic number proportion dataset of the elements in the stratum.

[0112] The content of chlorine element in the stratum is calculated based on the atomic number proportion under different stratum water salinity conditions by using the method of the present application, as shown in Figure 3 It is found by comparison that the absolute error of the chlorine element content calculated by using the atomic number proportion based mass fraction calculation method of the elements in the stratum of the present application is less than 0.01%, which is much smaller than the absolute error 1.72% of the chlorine element content calculated by using the oxygen closure model, thereby verifying the accuracy of the calculation of the content of the elements in the stratum based on the atomic number proportion.

[0113] Step 3, the time spectrum measured by the single detector element logging instrument is processed, the first time window and the second time window are selected in the time spectrum, and the macroscopic capture cross section Σ of the stratum is calculated by using the gamma count in the first time window and the second time window, as shown in formula (7):

[0114]

[0115] In the formula, ∑ is the macroscopic capture cross section of the formation, N1 is the gamma count in the first time window, N2 is the gamma count in the second time window, and ΔT is the interval between the first time window and the second time window.

[0116] Step 4: Extracting the mass fraction w of chlorine element from the formation element mass fraction set Cl In combination with the macroscopic capture cross section ∑ of the formation and the formation porosity φ and the formation density ρ obtained from the open hole data, a comprehensive calculation model of the formation water salinity and the oil saturation is established, as shown in formula (12):

[0117]

[0118] In the formula, ∑ is the macroscopic capture cross section of the formation, ∑ ma is the capture cross section of the formation skeleton, is the capture cross section of the salt water in the formation, ∑ oil is the capture cross section of the oil in the formation, is the capture cross section of the fresh water in the formation; C w is the formation water salinity, w Cl is the mass fraction of chlorine element, ρ is the formation density, and φ is the formation porosity.

[0119] The formation water salinity and the oil saturation of the formation are simultaneously calculated by using the comprehensive calculation model of the formation water salinity and the oil saturation.

[0120] Meanwhile, according to the instrument structure of the single-detector element logging instrument, a calculation model of different formation water salinity and oil saturation is constructed by using a numerical simulation method, the detection process of the single-detector element logging instrument in the formation is simulated, the non-elastic gamma spectrum, the capture gamma spectrum and the time spectrum of the single-detector element logging instrument are simulated, the content of the chlorine element in the formation is obtained by using the method, the double-parameter information is simultaneously obtained by using the time spectrum, and the simulation value of the formation water salinity and the simulation value of the oil saturation of the formation are simultaneously determined. The simulation value of the formation water salinity is compared with the calculated value of the formation water salinity, and the simulation value of the oil saturation is compared with the calculated value of the oil saturation. Figure 4 It can be known that the error of the oil saturation calculated by using the method is controlled within 5%, according to Figure 5 It can be known that the error of the formation water salinity calculated by using the method is controlled within 5Kppm, thereby verifying the accuracy of the method for calculating the oil saturation and the formation water salinity.

[0121] The present application is based on the accurate acquisition of the mass fraction of each element in the formation by the atomic number proportion, effectively solves the negative influence of the uncertainty of formation water salinity on the quantitative monitoring of oil saturation, realizes the acquisition of the two formation parameters of formation water salinity and oil saturation, widens the application range of element logging, and is beneficial to the oil-bearing evaluation of the formation and the guidance of reservoir development.

[0122] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the spirit and scope of the present application should also be within the protection scope of the present application.

Claims

1. A method for comprehensively calculating formation water salinity and oil saturation based on lithological scanning, employing a measurement system equipped with a DT neutron source and at least one gamma detector for in-well measurement, characterized in that... Specifically, the following steps are included: Step 1: Use the measurement system to measure the original energy spectrum of the strata, obtain the elemental yield of the strata based on the original energy spectrum collected by the standard spectrum analysis of the strata elements, and determine the inelastic yield and capture yield of each element in the strata. Step 2: Based on the fact that the sum of the atomic percentages of each element in the stratum is 1, the non-inelastic yield of each element in the stratum is converted into the non-inelastic atomic percentage, and the captured yield of each element in the stratum is converted into the captured atomic percentage. This constructs a dataset of non-inelastic atomic percentages and a dataset of captured atomic percentages of stratum elements. The non-inelastic atomic percentages of carbon, oxygen, and magnesium are extracted from the dataset of non-inelastic atomic percentages of stratum elements. Combined with the captured atomic percentages of elements other than carbon, oxygen, and magnesium in the dataset of captured atomic percentages of stratum elements, a dataset of atomic percentages of stratum elements is constructed. The mass fraction of each element in the stratum is determined, and a set of mass fractions of stratum elements is constructed. Step 3: Calculate the macroscopic capture section of the formation by processing the time spectrum obtained by the measurement system through a selected time window; Step 4: Extract the mass fraction of chlorine from the mass fraction set of formation elements. Combine the macroscopic capture section of the formation with the formation porosity and density obtained from naked-eye data to establish a comprehensive calculation model for formation water salinity and oil saturation. Use the comprehensive calculation model for formation water salinity and oil saturation to perform calculations and determine the formation water salinity and oil saturation of the formation. In step 4, based on the relationship between formation porosity, formation density, and formation oil saturation, the mass percentage of freshwater in the formation is expressed as: （8） In the formula, The percentage of freshwater by mass. The density is that of fresh water. For the volume of fresh water, For the density of the formation, The volume of formation pores. Formation porosity, This represents the oil saturation of the formation. Formation water salinity is expressed as: （9） In the formula, Formation water salinity, This refers to the mass percentage of the salt water. This represents the mass fraction of chlorine. An oil saturation volumetric model based on the macroscopic trapping section of the formation is established, as shown in formula (10): （10） in, （11） In the formula, This is a macroscopic capture section of the strata. This is the capture section of the stratigraphic framework. This is the capture section of brine in the formation. This is the cross section for oil capture in the formation. This represents the capture section of freshwater in the strata. By combining formulas (9) to (11), a comprehensive calculation model for formation water salinity and oil saturation is obtained, as shown in formula (12): （12）。 2. The method for comprehensively calculating formation water salinity and oil saturation based on lithological scanning according to claim 1, characterized in that, In step 1, the original measured energy spectrum includes the inelastic gamma energy spectrum and the captured gamma energy spectrum, and the formation element yield includes the inelastic yield and captured yield of each element in the formation. First, the inelastic gamma spectrum is analyzed using the weighted least squares method to determine the inelastic yield of each element in the formation. Then, the captured gamma spectrum is analyzed using the weighted least squares method to determine the captured yield of each element in the formation. The formula for calculating the elemental yield of the formation is as follows: （1） in, （2） In the formula, For stratigraphic element production; T is the standard spectrum matrix of stratigraphic elements, where each column vector corresponds to the standard spectrum of different elements in the stratigraphic unit; T is the transpose matrix. This is the weight matrix; The first in the original measured energy spectrum The weight of the channel count, The first in the original measured energy spectrum The counting of the Tao; When calculating the inelastic yield of formation elements, the formula for calculating the yield of formation elements includes the following: The inelastic gamma spectrum, weight matrix Substituted from The first in the non-elastic gamma spectrum The weight of the channel count, substituted into The first in the non-elastic gamma spectrum The counting of channels and the calculation of the elemental yield of the formation. Non-bullet production; When calculating the capture yield of formation elements, the formula for calculating the yield of formation elements includes the following: To capture the gamma spectrum, the weight matrix Substituted from To capture the first gamma energy spectrum The weight of the channel count, substituted into To capture the first gamma energy spectrum The counting of channels and the calculation of the elemental yield of the formation. In order to capture production.

3. The method for comprehensively calculating formation water salinity and oil saturation based on lithological scanning according to claim 2, characterized in that, Step 2 specifically includes the following steps: Step 2.1: Obtain the atomic number sensitivity of each element in the formation based on the elemental yield of the formation; First, calculate the non-explosive atomic number sensitivity factor of each element in the stratum based on the non-explosive yield of each element in the stratum. Then, calculate the captured atomic number sensitivity factor of each element in the stratum based on the captured yield of each element in the stratum. This yields the non-explosive atomic number sensitivity factor and the captured atomic number sensitivity factor of each element in the stratum. Step 2.2: Based on the atomic number normalization closed model and combined with the atomic number sensitivity factor of each element in the formation, determine the formation atomic normalization coefficient; First, based on the non-explosive atom number sensitivity factor and non-explosive yield of each element in the stratum, the stratum atom non-explosive normalization coefficient is calculated. Then, based on the captured atom number sensitivity factor and captured yield of each element in the stratum, the stratum atom capture normalization coefficient is calculated. The stratum atom non-explosive normalization coefficient and the stratum atom capture normalization coefficient are determined. Step 2.3: Determine the atomic percentage of each element in the formation based on the formation atomic normalization coefficient, and establish a dataset of non-elastic atomic percentage and a dataset of captured atomic percentage of formation elements. First, based on the non-explosive yield of each element in the stratum and the non-explosive normalization coefficient of stratum atoms, calculate the proportion of non-explosive element atoms of each element in the stratum. Then, based on the capture yield of each element in the stratum and the capture normalization coefficient of stratum atoms, calculate the proportion of captured element atoms of each element in the stratum. Determine the proportion of non-explosive element atoms and the proportion of captured element atoms of each element in the stratum. Establish a dataset of non-explosive atom proportion of stratum elements based on the proportion of non-explosive atoms of each element in the stratum. Then, establish a dataset of captured atom proportion of stratum elements based on the proportion of captured atoms of each element in the stratum. Step 2.4: Extract the non-elastic atomic percentages of carbon, oxygen, and magnesium from the non-elastic atomic percentage dataset of formation elements, and then combine them with the captured atomic percentages of elements other than carbon, oxygen, and magnesium extracted from the captured atomic percentage dataset of formation elements to construct the formation element atomic percentage dataset. Step 2.5: Based on the data set of the proportion of atomic numbers of formation elements, calculate the mass fraction of each element in the formation and construct a set of mass fractions of formation elements.

4. The method for comprehensively calculating formation water salinity and oil saturation based on lithological scanning according to claim 3, characterized in that, In step 2.1, based on the fact that the sum of the atomic percentages of each element in the formation is 1, the atomic number sensitivity factor of oxygen is set to 1, and the atomic number sensitivity factor of each element in the formation is calculated. The formula for calculating the atomic number sensitivity factor is as follows: （3） In the formula, This refers to the sequence number of the stratigraphic element. are positive integers and , This represents the number of types of elements in the formation. For elements The atomic number sensitivity factor, This refers to the sequence number of the stratigraphic element. For elements output, For elements The number of atoms; The production of oxygen. This represents the number of oxygen atoms. When calculating the non-elastic atomic number sensitivity factor for each element in the formation, the yield substituted into the atomic number sensitivity factor calculation is... For elements Non-elastic production, substituted with oxygen production The atomic number sensitivity factor is calculated based on the non-elastic yield of oxygen. For elements The non-elastic atomic number sensitivity factor; When calculating the capture atomic number sensitivity factor for each element in the formation, the yield substituted into the atomic number sensitivity factor calculation is... For elements The captured output, substituted with the oxygen element output The atomic number sensitivity factor is calculated to represent the capture yield of oxygen. For elements The sensitivity factor for the number of captured atoms.

5. The method for comprehensively calculating formation water salinity and oil saturation based on lithological scanning according to claim 4, characterized in that, In step 2.2, the inelastic normalization coefficient of formation atoms and the normalization coefficient of formation atoms capture are calculated using the atomic number normalization closed model, as shown in formula (4): （4） In the formula, This represents the normalization coefficient of the formation atoms; When calculating the inelastic normalization coefficients of formation atoms, the yield substituted into the atomic number normalization closed model is... For elements Non-elastic production, substituted with the atomic number sensitivity factor For elements The non-elastic atom number sensitivity factor, and the calculated formation atom normalization coefficient. The inelastic normalization coefficient of the atom in the formation; When calculating the normalized coefficient of formation atomic capture, the yield substituted into the atomic number normalization closed model is... For elements The captured yield, substituted into the atomic number sensitivity factor For elements The captured atom number sensitivity factor, and the calculated formation atom normalization coefficient. This is the normalized coefficient for atomic capture in the formation.

6. The method for comprehensively calculating formation water salinity and oil saturation based on lithological scanning according to claim 5, characterized in that, In step 2.3, the formula for calculating the atomic percentage of formation elements is as follows: （5） In the formula, This represents the percentage of atoms of element j in the stratum. When the yield is substituted into the formula for calculating the atomic percentage of elements in the strata... For elements Non-elastic production, substituted with the atomic number sensitivity factor For elements The non-elastic atom number sensitivity factor, substituted into the formation atom normalization coefficient. The inelastic normalization coefficient of the strata atoms is used to calculate the percentage of atoms. Elements in the strata The percentage of non-elastic atoms; When the yield is substituted into the formula for calculating the atomic percentage of elements in the strata... For elements The captured yield, substituted into the atomic number sensitivity factor For elements The number of captured atoms sensitivity factor, substituted into the formation atom normalization coefficient The normalized coefficient for atomic trapping in the formation is used to calculate the percentage of atoms. Elements in the strata The percentage of captured atoms.

7. The method for comprehensively calculating formation water salinity and oil saturation based on lithological scanning according to claim 6, characterized in that, In step 2.5, the formula for calculating the mass fraction of formation elements is as follows: （6） In the formula, This represents the index of the element in the dataset representing the percentage of atoms of elements in the formation. are positive integers and ; The elements in the data representing the percentage of atoms of elements in the strata The mass fraction, The elements in the data representing the percentage of atoms of elements in the strata The percentage of atoms, The elements in the data representing the percentage of atoms of elements in the strata The mass number.

8. The method for comprehensively calculating formation water salinity and oil saturation based on lithological scanning according to claim 1, characterized in that, In step 3, a first time window and a second time window are selected within the time spectrum. The macroscopic capture section of the formation is calculated using the gamma counts within the first and second time windows, as shown in formula (7): （7） In the formula, This is a macroscopic capture section of the strata. For the gamma count within the first time window, For the gamma count within the second time window, This is the interval between the first time window and the second time window.

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