Method for evaluating content of organic carbon in marine facies hydrocarbon source rock of Yanan gas field based on logging curve

Abstract

The invention belongs to the technical field of oil and gas well logging, and particularly relates to a method for evaluating the content of organic carbon in marine facies hydrocarbon source rock of a Yanan gas field based on a well logging curve. The invention discloses a method for evaluating the organic carbon content of Yanan gas field marine facies hydrocarbon source rock based on a logging curve. The method comprises the steps that a conventional logging curve and an actually-measured TOC value of a rock sample are obtained; constructing fusion parameters; and fitting the actually measured TOC values of the rock samples of the same well and the same depth with the fusion parameters to obtain a fitting relational expression, namely a TOC prediction model. According to the method, the fusion parameters are constructed instead of being directly fitted with a conventional logging curve, and the fusion parameters are reasonably selected and accord with the organic matter enrichment rule; the method has the advantages of being low in cost, high in efficiency and high in practicability, the hydrocarbon source rocks in the work area can be accurately and integrally depicted in a fine mode, and data support is provided for oil and gas exploration, development and evaluation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oil and gas logging, and in particular to a method for evaluating the organic carbon content of marine hydrocarbon source rocks in the Yan'an gas field based on logging curves. BACKGROUND

[0002] Hydrocarbon source rock refers to rock rich in organic matter that can generate oil or natural gas, and is usually quantitatively described using the organic matter abundance index, i.e. organic carbon content (TOC). Marine hydrocarbon source rocks are mainly composed of carbonate rocks, and have a deeper sedimentary water body and greater burial depth, and are more obviously affected by compaction, compared with terrestrial hydrocarbon source rocks. The marine hydrocarbon source rocks in the Yan'an gas field have the characteristics of low organic matter abundance and high thermal evolution degree, and usually, part of the samples are analyzed and tested using organic geochemical methods to evaluate the entire block. Although this method has high accuracy, due to the limitations of the samples and the relatively high cost of manpower, material resources and financial resources for analysis and testing, it is difficult to meet the requirements of exploration and development deployment when evaluating the development of hydrocarbon source rocks in the entire work area of the Yan'an gas field. The logging curve data has the significant advantages of continuous measurement data, large quantity and easy availability compared with other data, and part of the curves are more sensitive to hydrocarbon source rocks, so the logging curves are used to identify and calculate the organic carbon content of the hydrocarbon source rocks, to provide well site deployment basis for oil and gas exploration, and are more in line with the actual situation.

[0003] Currently, the methods for quantitatively interpreting TOC using logging data mainly include single-parameter logging interpretation method, acoustic time difference and resistivity curve overlap method (ΔlgR method) and multiple regression fitting method. The single-parameter logging interpretation method usually establishes a fitting relationship between a certain curve in the logging curve and the TOC content, such as establishing a fitting relationship formula between the natural gamma ray GR curve or the compensated density DEN curve and the TOC. Since the geological conditions in the Ordos Basin are complex, a single curve is usually affected by multiple factors, so this method is not suitable for this work area. The ΔlgR method was proposed in the 1990s, and this technology uses the TOC prediction formula established by the acoustic time difference (Δt), the resistivity (R) and the hydrocarbon source rock maturity (LOM), and makes the resistivity curve and the acoustic time difference curve coincide at the position of the fine-grained non-hydrocarbon source rock, i.e. the baseline (R 基 , Δt 基 ), and the distance between the two curves is the amplitude difference (ΔlgR), and the calculation formula is as follows: ΔlgR=lg(R / R 基 )+0.02(Δt-Δt 基 ) (1) TOC=10 (2.297-0.1688LOM) ΔlgR+ΔTOC (2) In the above formula: ΔlgR is the amplitude difference; R is the resistivity; Δt is the acoustic time difference; R 基 , Δt 基Baseline values of resistivity curve and acoustic time curve respectively; LOM is thermal alteration index; ΔTOC is background value of organic carbon content; the traditional ΔlgR technology is based on normal compaction formation, is not suitable for logging evaluation of high-conductive components of source rock, especially deep strong compaction source rock, and the LOM value range in the fitting formula is 7-12, that is, only suitable for source rock in mature-high mature range, and the source rock in the work area is mostly above 12, that is, belongs to over-mature source rock.

[0004] The multiple regression method refers to using several logging curves most sensitive to TOC change, and then establishing a fitting relationship through the multiple regression method, which overcomes the limitation of single logging parameter, and improves the accuracy of the fitting formula through the combination of multiple parameters, and since the fitting result is obviously affected by regional characteristics, the parameters used in different regions and different layers are quite different, and the fitting relationship has the characteristics of diversity and complexity. SUMMARY

[0005] In order to solve the above problems, a method for identifying and evaluating the organic carbon content of marine source rock in Yan'an gas field by logging is established, and the method adopts multiple logging curves such as deuranium gamma KTH curve, natural gamma GR curve, natural gamma spectrum uranium U curve, natural gamma spectrum thorium TH curve, compensated acoustic time difference AC curve, compensated density DEN curve, compensated neutron CNL curve and deep exploration resistivity RT curve to identify the source rock and calculate the TOC content, solves the problem that the traditional logging fitting relationship is not obvious in response to the low organic matter abundance, high thermal evolution degree and obvious compaction of marine source rock in Yan'an gas field, improves the prediction accuracy, and provides necessary basic data support for deep Paleozoic oil and gas exploration.

[0006] The technical scheme of the present application is characterized in that: A method for evaluating the organic carbon content of marine source rock in Yan'an gas field based on logging curves, which adopts the following formula: TOC=a×(1-KTH / GR)+b×(U / TH)+c×(AC-150) / (200×(DEN-2))+d×CNL / (60×(DEN-2)) (1) In the formula, TOC is the organic carbon content; KTH is deuranium gamma; GR is natural gamma; U is natural gamma spectrum uranium; TH is natural gamma spectrum thorium; AC is compensated acoustic time difference; DEN is compensated density; CNL is compensated neutron; a, b, c and d are constants.

[0007] A method for evaluating the organic carbon content of marine source rock in Yan'an gas field based on logging curves, and the method is as follows: Obtain the conventional logging curve and measured TOC value of the rock sample; The conventional logging curve comprises a uranium-free gamma KTH curve, a natural gamma GR curve, a natural gamma spectrum uranium U curve, a natural gamma spectrum thorium TH curve, a compensated acoustic time difference AC curve, a compensated density DEN curve and a compensated neutron CNL curve. The fusion parameter is constructed, specifically including: 1-KTH / GR, U / TH, (AC-150) / (200(DEN-2)) and CNL / (60*(DEN-2)); Since the TOC value is closely related to the development characteristics and sedimentary environment of the hydrocarbon source rock in the work area, and the natural gamma GR curve is greatly affected by radioactive elements, the (1-KTH / GR) parameter is used to eliminate the influence of part of the radioactive elements, so as to be more closely related to the organic matter content in the hydrocarbon source rock, can reflect the enrichment characteristics of organic matter, and is usually positively correlated with the TOC value; (U / TH) usually reflects the oxidation-reduction environment of the water body and is positively correlated with TOC; The compensated acoustic time difference AC curve is affected by organic matter, and the value will increase with the increase of the TOC value, and the compensated density DEN curve is affected by organic matter, and the value will decrease with the decrease of the TOC value, so the two curves are normalized respectively, and then combined to judge the TOC value; similarly, the compensated neutron CNL curve is affected by organic matter, and the value is positively correlated with TOC, and also normalized and combined with the compensated density DEN curve to judge TOC.

[0008] The measured TOC value of the rock sample at the same depth in the same well is fitted with the above fusion parameter to obtain a fitting relationship (1), that is, a TOC prediction model.

[0009] Before obtaining the conventional logging curve of the rock sample, the rock sample is core homing.

[0010] The technical effect of the present application is that: 1. The present application does not directly fit the conventional logging curve, but constructs a fusion parameter; wherein the ratio of KTH / GR is to eliminate the influence of shale content on the fitting result, the ratio of U / TH is to consider the influence of the sedimentary environment (oxidation or reduction environment) on the fitting result, and the purpose of (AC-150) / (200(DEN-2)) and CNL / (60(DEN-2)) is to normalize and combine the two to comprehensively identify, so as to improve the accuracy of the fitting result of the curve to the organic carbon content. The fusion parameter is reasonable and conforms to the enrichment law of organic matter; 2. Compared with the traditional organic geochemical experimental method, the present application can comprehensively and completely reflect the continuous development and distribution characteristics of the hydrocarbon source rock in a certain well; 3. Compared with traditional methods, this invention is more suitable for source rocks with low exploration depth, low organic matter abundance, and high thermal evolution. It also features low cost, high efficiency, and strong practicality. It can accurately and finely characterize the source rocks in the work area, providing data support for oil and gas exploration, development, and evaluation. Attached Figure Description

[0011] Figure 1 These are plots showing the intersection of measured TOC values ​​of rock samples with GR and 1-KTH / GR curves in specific application cases.

[0012] Figure 2 These are plots showing the intersection of measured TOC values ​​of rock samples with U and U / TH curves in specific application cases.

[0013] Figure 3 These are plots showing the intersection of the measured TOC values ​​of rock samples with the AC and (AC-150) / (200*(DEN-2)) curves in specific application cases.

[0014] Figure 4 These are plots showing the intersection of the measured TOC values ​​of rock samples with CNL and CNL / (60*(DEN-2)) curves in specific application cases.

[0015] Figure 5 These are plots showing the intersection of measured TOC values ​​of rock samples with DEN and RT curves in specific application cases.

[0016] Figure 6 This is a comparison chart of the predicted TOC content of rock samples and the measured TOC content of some rock samples in specific application cases. Detailed Implementation

[0017] Specific application case - taking the Y2251 well in the Yan'an Gas Field of the Ordos Basin as an example A method for evaluating the organic carbon content of marine source rocks in the Yan'an gas field based on well logging curves is as follows: Step 1: Core alignment and correction of source rock samples with logging depth, as shown in Table 1; Table 1 Rock Sample Relocation Table .

[0018] Step 2: Obtain the measured TOC values ​​of source rock samples at different depths and their corresponding natural gamma ray GR, natural gamma ray energy spectrum uranium U, compensated acoustic transit time AC, deep probe resistivity RT, compensated density DEN, and compensated neutron CNL curve values, as shown in Table 2. Table 2. Statistical Table of Rock Samples and Corresponding Well Logging Curve Values .

[0019] Step 3: The statistical table of rock samples and corresponding fusion parameters is shown in Table 3; Table 3 Statistical table of rock samples and corresponding fusion parameters The measured TOC values of rock samples at each well depth are correlated with the corresponding GR, 1-KTH / GR, U, U / TH, AC, (AC-150) / (200x(DEN-2)), CNL, CNL / (60x(DEN-2)), DEN, RT curves, as shown in Figures 1-5 The fitting correlation of measured TOC values and fusion parameters is better than that of single parameter fitting, and the RT curve has no significant linear relationship with the measured TOC value.

[0020] Step 4: According to the data in Table 3, the fitting of predicted hydrocarbon source rock organic carbon content is carried out, and the fitting relationship is as follows: TOC=0.185x(1-KTH / GR)+0.098x(U / TH)+0.032x(AC-150) / (200x(DEN-2))+0.215xCNL / (60x(DEN-2)).

[0021] Step 5: The correlation analysis of the predicted TOC content predicted value obtained by the method provided by the present application and the measured TOC content value of part of rock samples is carried out, and it is found that the correlation is strong, as shown in Figure 6 The predicted TOC content predicted value obtained by the method provided by the present application is reasonable and reliable.

[0022] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this. Any change or replacement within the technical range disclosed by the present application can be easily thought by those skilled in the art, which should be covered within the protection scope of the present application.

Claims

1. A method for evaluating the organic carbon content of marine hydrocarbon source rocks in the Yan'an gas field based on well logging curves, characterized by, The following formula is used: TOC=a×(1-KTH / GR)+b×(U / TH)+c×(AC-150) / (200×(DEN-2))+d×CNL / (60×(DEN-2)) (1) In the formula, TOC is a predicted value of the organic carbon content; KTH is deuranium gamma; GR is natural gamma; U is natural gamma energy spectrum uranium; TH is natural gamma energy spectrum thorium; AC is compensated acoustic time difference; DEN is compensated density; CNL is compensated neutron; and a, b, c and d are all constants.

2. The method for evaluating the organic carbon content of marine source rock in Yan'an gas field based on logging curve according to claim 1, characterized in that, The method is as follows: Obtain the conventional logging curves and the measured TOC value of the rock sample; The conventional logging curves include: deuranium gamma KTH curve, natural gamma GR curve, natural gamma energy spectrum uranium U curve, natural gamma energy spectrum thorium TH curve, compensated acoustic time difference AC curve, compensated density DEN curve and compensated neutron CNL curve; The fusion parameters are constructed, specifically including: 1-KTH / GR, U / TH, (AC-150) / (200×(DEN-2)) and CNL / (60×(DEN-2)); The measured TOC value of the rock sample at the same depth in the same well is fitted with the above fusion parameters to obtain the fitting relationship (1), which is the TOC prediction model.

3. The method for evaluating the organic carbon content of marine source rock in Yan'an gas field based on logging curve according to claim 2, characterized in that, Before obtaining the conventional logging curves of the rock sample, the rock sample is returned to the original position.

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