Method for calculating total organic carbon content of formation by combining acoustic and electrical logging

Abstract

The present application relates to the technical field of oil and gas exploration, in particular to a method for calculating total organic carbon content of formation by combining acoustic and electrical logging. The method comprises the following steps: selecting clay content of a standard layer as a background value; calculating clay content of a target layer section by using deuranium gamma data; calculating a resistivity correction factor according to the background value and the clay content of the target layer section; dividing the target layer into pore structure phases; establishing a calculation model of conversion coefficient based on the pore structure phases; obtaining the conversion coefficient according to the pore structure phases and the corresponding conversion coefficient model; constructing an improved formula of delta log R method; and obtaining the total organic carbon content of the formation by using acoustic time difference and resistivity on this basis. The present application introduces a resistivity correction factor for the first time, establishes a calculation model of conversion coefficient K, realizes the improvement of the delta log R method, and extends the application of the delta log R method from marine shale to continental shale, which has strong practicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas exploration, and particularly relates to a method for calculating total organic carbon content of a formation by combining acoustic logging and electrical logging. BACKGROUND

[0002] Shale gas is a new field of global oil and gas exploration, and has a broad development prospect. Organic matter is the basis of shale gas generation, and its abundance is closely related to the gas production capacity of shale. Prediction of total organic carbon content is crucial for the evaluation of organic matter abundance.

[0003] At present, the organic carbon parameters obtained from core samples by organic geochemical analysis and testing have high precision, but the results have discreteness due to the limitation of the number of test samples, and it is difficult to meet the needs of fine exploration. Well logging data are widely used in the prediction of organic carbon content because of its continuous longitudinal data and high longitudinal resolution. The commonly used prediction methods include natural gamma-ray spectroscopy, bulk density method, multiple linear regression method and Delta log R method.

[0004] Natural gamma-ray spectroscopy is based on the correlation between natural gamma-ray spectroscopy logging response and organic matter. According to the characteristics of high natural gamma-ray, high uranium, low thorium and potassium of organic matter shale, and the correlation analysis results of TOC, a fitting model of radioactive elements and TOC is established, and finally the continuous TOC prediction results are obtained by inversion.

[0005] The bulk density method proposes that there is a negative correlation between shale density and TOC, and an inverse proportional model of density and TOC is established.

[0006] The multiple linear regression method determines the logging signals with strong correlation with TOC, such as acoustic travel time and resistivity, and then establishes a multiple regression model to finally obtain the prediction results of TOC.

[0007] The traditional delta log R method is a TOC prediction method based on logging curves (acoustic travel time, resistivity, etc.) and maturity parameters (LOM), which can obtain continuous TOC distribution in the vertical direction, and has achieved good results in many foreign regions. However, due to various geological factors, the application effect is not ideal in China. Scholars have proposed corresponding improvement methods for different influencing factors. In 2012, Liu L et al. used the modified coefficient delta log R method to predict the TOC of Shahejie Formation in Liaohe Oilfield, and achieved good results. In 2012, Guo Zeqing et al. summarized that for the layer with more samples, there is a linear relationship between organic carbon TOC and delta log R, which simplifies the cumbersome process of predicting TOC corresponding to the LOM maturity chart. In 2014, Liu Chao et al. proposed a variable coefficient delta log R method to reduce the error of traditional delta log R TOC prediction. In 2016, Hu Huiting proposed a generalized delta log R method to solve the problems that the resistivity curve does not have obvious anomalies due to the high content of conductive components in continental sedimentary strata, and the acoustic travel time is small due to strong compaction when the source rock is deeply buried. The prediction accuracy is greatly improved compared with the traditional method. In 2020, on the basis of Hu Huiting's work, Wang Xiang, Ma Jinfeng et al. added a parameter representing density to the TOC calculation formula to reduce the error of TOC prediction results. In addition, machine learning can also predict the total organic carbon content (TOC) of the stratum, and the accuracy is very high, but it requires rich and complete data.

[0008] In summary, the delta log R method has been improved many times and has good results in predicting the total organic carbon content (TOC) of the stratum. However, there are still defects in calculating the total organic carbon content (TOC) of continental shale using the delta log R method. SUMMARY

[0009] The purpose of the present application is to overcome the defects of the prior art, and to provide a method for calculating the total organic carbon content of the stratum by combining acoustic and electrical logging, which can solve the defect that the traditional delta log R method is not suitable for continental shale by increasing the resistivity correction factor and modeling the conversion coefficient, and achieve the effect of improving the calculation accuracy of TOC in continental shale.

[0010] The method for calculating the total organic carbon content of the stratum by combining acoustic and electrical logging provided by the present application comprises the following steps:

[0011] Step 1, select a standard layer, and calculate the clay content of the standard layer as a background value;

[0012] Step 2, calculate the clay content of the target layer according to the deuranium gamma;

[0013] Step 3, calculating resistivity correction factor g according to the background value and the clay content of the target interval;

[0014] Step 4, dividing the target interval into pore structure phases;

[0015] Step 5, establishing a calculation model of conversion coefficient K based on the pore structure phases;

[0016] Step 6, obtaining the conversion coefficient according to the pore structure phases of the target interval and the corresponding calculation model of conversion coefficient;

[0017] Step 7, constructing an improved ΔlogR formula and obtaining the total organic carbon content according to the acoustic travel time curve, the resistivity curve, the resistivity correction factor and the conversion coefficient.

[0018] Preferably, in step 1, the standard interval is selected as an interval with stable and same trend of resistivity and acoustic travel time curves.

[0019] Preferably, the clay content of the standard interval and the clay content of the target interval are calculated by the following formula:

[0020] I=(KTH-KTH min ) / (KTH max -KTH min );

[0021] SH=(2 Gcur*I -1) / (2 Gcur -1);

[0022] Wherein, KTH, KTH max , KTH min are the deuranium gamma, the maximum value of deuranium gamma and the minimum value of deuranium gamma of the target interval respectively; Gcur is an empirical coefficient related to the formation; SH is the clay content.

[0023] Preferably, in step 3, the resistivity correction factor g is calculated by the following formula:

[0024] g=SH / SH bl ;

[0025] Wherein, SH is the clay content of the target interval; SH bl is the clay content of the standard interval.

[0026] Preferably, in step 4, dividing the target interval into pore structure phases includes:

[0027] Dividing by total porosity of 3% and 4% as the boundary;

[0028] Total porosity greater than 4% is type I;

[0029] Type II is that the total porosity is greater than 3% and less than or equal to 4%;

[0030] Type III is that the total porosity is less than or equal to 3%.

[0031] More preferably, in the step 5, the conversion coefficient K is obtained according to core fitting, wherein the K value of Type I is 0.035, the K value of Type II is 0.033, and the K value of Type III is 0.031.

[0032] More preferably, in the step 7, the improved ΔlogR method formula is constructed as follows:

[0033]

[0034] TOC = 10 (1.5374-0.944R0) ΔlogR + ΔTOC;

[0035] Wherein, R, R 基线 are resistivity and resistivity baseline value respectively; Δt, Δt 基线 are acoustic time difference and acoustic time difference baseline value respectively; ΔTOC is total organic carbon content background value.

[0036] The present application has the beneficial effects that: the present method is a calculation method of total organic carbon content of formation by using resistivity curve and acoustic time difference curve. It selects the clay content of standard layer as background value; calculates the clay content of target layer by using deuran gamma data; calculates the resistivity correction factor according to the clay content background value and the clay content of target layer; divides the pore structure phase of the target layer; establishes the calculation model of conversion coefficient relying on the pore structure phase; obtains the conversion coefficient according to the pore structure phase of the target layer and the corresponding conversion coefficient model; constructs the improved ΔlogR method formula; on this basis, the total organic carbon content of formation can be obtained by using acoustic time difference and resistivity. The present application firstly introduces the resistivity correction factor, establishes the calculation model of conversion coefficient K, realizes the improvement of ΔlogR method, expands the application of ΔlogR method from marine shale to continental shale, and has strong practicability. Thus, the defects of low calculation accuracy of existing ΔlogR method in continental shale are overcome. It is proved by practice that the total organic carbon content (TOC) of target formation can be accurately obtained by using the method, and the accuracy of reservoir evaluation is improved, and the method has strong universality. The present application provides a better and faster method for obtaining the total organic carbon content (TOC) of formation for continental shale reservoir. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The present application is a method flowchart;

[0038] Figure 2A resistivity vs. TOC correlation diagram for the present application;

[0039] Figure 3 A resistivity vs. TOC correlation diagram for the present application after adding a resistivity correction factor;

[0040] Figure 4 A TOC calculation diagram for the present application. DETAILED DESCRIPTION

[0041] In order to make the technical problems to be solved, technical solutions and beneficial effects of the present application clearer, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0042] It should be understood that when used in the specification and the appended claims of the present application, the term "comprising" indicates the presence of the described features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0043] It should also be understood that the term "and / or" used in the specification and the appended claims of the present application means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0044] As used in the specification and the appended claims of the present application, the term "if" can be interpreted as "when" or "upon" or "in response to a determination" or "in response to detecting" depending on the context. Similarly, the phrases "if determined" or "if detected [the described condition or event]" can be interpreted depending on the context as meaning "upon determining" or "in response to determining" or "upon detecting [the described condition or event]" or "in response to detecting [the described condition or event]".

[0045] In addition, in the description of the present application and the appended claims, the terms "first", "second", "third", etc. are only used for differentiation in description, and cannot be understood as indicating or implying relative importance.

[0046] Reference to "one embodiment" or "some embodiments" or "one implementation" or "some implementations" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase "in one embodiment" or "in some embodiments" or "in one implementation" or "in some implementations" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily referring to some, but not all, embodiments. The terms "including," "comprising," "having" and variations thereof are meant to encompass the items listed thereafter, but do not exclude other items from also being present. The term "consisting of" is meant to exclude any item not specified. The term "consisting essentially of" means excluding any item not specified except for impurities or other minor nonessential components.

[0047] Embodiment One

[0048] Figure 1 A structure diagram of a method for calculating total organic carbon content of a formation by acoustic-electric logging is shown. For the convenience of description, only the part related to the embodiment is shown, and the details are as follows:

[0049] The method for calculating total organic carbon content of a formation by acoustic-electric logging provided by the application comprises the following steps:

[0050] Step 1, selecting a standard layer and calculating the clay content of the standard layer as a background value;

[0051] Step 2, calculating the clay content of the target layer section according to the deuranium gamma;

[0052] Step 3, calculating the resistivity correction factor g according to the background value and the clay content of the target layer section;

[0053] Step 4, dividing the target layer into pore structure phases;

[0054] Step 5, establishing a calculation model of the conversion coefficient K based on the pore structure phases;

[0055] Step 6, obtaining the conversion coefficient according to the pore structure phases of the target layer and the corresponding calculation model of the conversion coefficient;

[0056] Step 7, constructing an improved ΔlogR formula, and obtaining the total organic carbon content according to the acoustic travel time, the resistivity curve, the resistivity correction factor, and the conversion coefficient.

[0057] In one embodiment, in step 1, the standard layer is selected from a layer section with stable and same trend resistivity and acoustic travel time curves.

[0058] In one embodiment, the clay content of the standard layer and the clay content of the target layer section are calculated by the following formula:

[0059] I = (KTH - KTH min ) / (KTH max -KTH min );

[0060] SH = (2 Gcur*I -1) / (2 Gcur -1);

[0061] Wherein, KTH, KTH max , KTH min are the deuranium gamma, the maximum value of deuranium gamma, the minimum value of deuranium gamma of the target interval, unit API; Gcur is an empirical coefficient related to the formation, Gcur is 3.7 for new formation (Tertiary formation), Gcur is 2.0 for old formation, dimensionless; SH is the clay content, unit %.

[0062] In one embodiment, in step 3, the resistivity correction factor g is calculated by the following formula:

[0063] g = SH / SH bl ;

[0064] Wherein, SH is the clay content of the target interval, unit %; SH bl is the clay content of the standard layer, unit %.

[0065] In one embodiment, in step 4, the pore structure phase division of the target layer includes:

[0066] Divided by total porosity 3% and 4% as the boundary;

[0067] Total porosity greater than 4% is type I;

[0068] Total porosity greater than 3% and less than or equal to 4% is type II;

[0069] Total porosity less than or equal to 3% is type III.

[0070] In one embodiment, in step 5, the conversion coefficient K is obtained according to core fitting, wherein the K value of type I is 0.035, the K value of type II is 0.033, and the K value of type III is 0.031.

[0071] In one embodiment, in step 7, the improved ΔlogR method formula constructed is as follows:

[0072]

[0073] TOC = 10 (1.5374-0.944R0) · ΔlogR + ΔTOC;

[0074] Wherein, R, R基线 respectively, resistivity, resistivity baseline value, unit ohmm-m; Δt, Δt 基线 respectively, acoustic travel time, acoustic travel time baseline value, unit us / ft; ΔTOC is total organic carbon content background value, unit %.

[0075] The method first uses the deuranium gamma curve to calculate the clay content of the target layer section, selects the clay content of the standard section as the background value, and the ratio of the two is the resistivity correction factor g.

[0076] As shown in Figure 2 , Figure 3 : after introducing the resistivity correction factor, the fitting degree of total organic carbon content and resistivity increases from 0.0778 to 0.3446, making the correlation between resistivity and total organic carbon content (TOC) stronger. Then, according to the divided pore structure phase, the conversion coefficient K of the corresponding layer section is obtained. Finally, the resistivity correction factor g and the conversion coefficient K are substituted into the improved ΔlogR method to calculate the total organic carbon content of the formation.

[0077] The method uses the acoustic travel time curve, the resistivity curve and the deuranium gamma curve to calculate the resistivity correction factor g and the conversion coefficient K, and finally obtains the total organic carbon content of the target layer section as shown in Figure 4 . As shown in Figure 4 The last black solid line shows that the total organic carbon content calculated by the improved ΔlogR method is basically consistent with the measured total organic carbon content.

[0078] It should be understood that the specific order or hierarchy of steps in the disclosed processes is an example of an example order or hierarchy of steps. Based on design preference, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of protection of the present disclosure. The appended method claims give the elements of various steps in an exemplary order, and are not intended to be limited to the specific order or hierarchy described.

[0079] The above-described embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A method for calculating total organic carbon content of a formation by acoustic and electrical well logging, characterized in that, The method comprises the following steps: Step 1, selecting a standard layer and calculating the clay content of the standard layer as a background value; Step 2, calculating the clay content of a target layer section according to deuterium gamma; Step 3, calculating a resistivity correction factor g according to the background value and the clay content of the target layer section; Step 4, dividing the target layer into pore structure phases; Step 5, establishing a calculation model of a conversion coefficient K based on the pore structure phases; Step 6, obtaining the conversion coefficient according to the pore structure phases of the target layer and the corresponding calculation model of the conversion coefficient; Step 7, constructing an improved ΔlogR method formula and obtaining the total organic carbon content according to the interval transit time, the resistivity curve, the resistivity correction factor and the conversion coefficient; In the step 4, the pore structure phase division of the target layer comprises: Dividing the pore structure phases according to the total porosity of 3% and 4% as boundaries; When the total porosity is greater than 4%, it is type I; When the total porosity is greater than 3% and less than or equal to 4%, it is type II; When the total porosity is less than or equal to 3%, it is type III; In the step 5, the conversion coefficient K is obtained according to core fitting, wherein the K value of type I is 0.035, the K value of type II is 0.033, and the K value of type III is 0.

031.

2. The method of determining total organic carbon content of a formation from acoustic and electrical well logs according to claim 1, wherein: In the step 1, the standard layer is selected as a layer section with stable and same trend resistivity and interval transit time curves.

3. The method of claim 1, wherein the total organic carbon content of the formation is calculated using acoustic and electrical logs. The clay content of the standard layer and the clay content of the target layer section are calculated by the following formula: I = (KTH - KTH min ) / (KTH max - KTH min ); SH = (2 Gcur*I -1) / (2 Gcur -1); Wherein, KTH, KTH max , KTH min Respectively, the purpose of the segment of deuranium gamma, deuranium gamma maximum, deuranium gamma minimum; Gcur is the experience coefficient related to the formation; SH is the clay content.

4. The method of claim 1, wherein the total organic carbon content of the formation is calculated using acoustic and electrical logs. In the step 3, the resistivity correction factor g is calculated by the following formula: g = SH / SH bl ; where SH is the clay content of the target interval; SH bl is the clay content of the standard interval.

5. The method of claim 1, wherein the total organic carbon content of the formation is calculated using acoustic and electrical logs. In the step 7, the improved ΔlogR method formula is constructed as follows: wherein R, R 基线 respectively are resistivity, resistivity baseline value; Δt, Δt 基线 respectively are acoustic travel time, acoustic travel time baseline value; ΔTOC is total organic carbon content background value.

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