A correction method for the effect of source rock organic matter on overpressure logging parameters

Abstract

The present invention belongs to the field of well logging technology, and specifically relates to a correction method for the influence of organic matter in source rocks on overpressure logging parameters. The method comprises: step 1: dividing the source rock into four parts, namely, mudstone skeleton, organic matter, hydrocarbons and formation water, taking unit volume as the correction unit, the sum of the volume percentages of the four parts is 1, wherein the total volume percentage of hydrocarbons and formation water is the porosity (Φ); step 2: on the basis of step 1, establishing a calculation formula for the acoustic well logging value of the source rock section and a calculation formula for the density well logging value of the source rock section; step 3: calculating the volume of organic matter in the source rock according to the organic carbon content measured in the laboratory; step 4: on the basis of the volume of organic matter in the source rock and the volume of the rock skeleton of the source rock layer section obtained in step 3, respectively calculating the masses of the four parts; step 5: substituting the volume of organic matter in the source rock in step 3 and the masses of the four parts in step 4 into the calculation formula for the acoustic well logging value of the source rock section and the calculation formula for the density well logging value of the source rock section in step 2.

Description

Technical Field

[0001] The invention belongs to the technical field of well logging, and in particular relates to a correction method for the influence of organic matter in source rocks on overpressure logging parameters. Background Art

[0002] Different from ordinary mudstone, source rock contains a lot of organic matter, so its logging curve characteristics are also significantly different from ordinary mudstone. Compared with ordinary mudstone, source rock has a larger acoustic time difference (theoretical value is 550us / m) and a smaller density (theoretical value is 1.1g / cm 3 )(, which is also the basis for using logging data to identify and evaluate source rocks. When using logging data to identify overpressure and determine its cause, the difference in logging responses between overpressure section mudstone and normal pressure section mudstone is mainly used. Therefore, the logging response of organic matter in the source rock section is bound to affect the accuracy of using logging data to identify overpressure and determine its cause. In view of this, in order to accurately understand the cause of overpressure, it is particularly necessary to correct the influence of organic matter in the source rock section on logging parameters. Since the acoustic time difference and density logging data are mainly used when determining the cause of overpressure, the present invention mainly corrects the acoustic time difference and density logging parameters of organic matter in the source rock section. Summary of the invention

[0003] In view of the problems existing in the above-mentioned prior art, the present invention proposes a correction method for the influence of organic matter in source rock on overpressure logging parameters, and uses acoustic time difference and density logging data to realize the correction of acoustic time difference and density logging parameters by organic matter in source rock intervals.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A correction method for the effect of source rock organic matter on overpressure logging parameters, comprising:

[0006] Step 1: Divide the source rock into four parts: mudstone skeleton, organic matter, hydrocarbons and formation water. The unit volume is used as the calibration unit. The sum of the volume percentages of the four parts is 1, and the total volume percentage of hydrocarbons and formation water is the porosity (Φ).

[0007] Step 2: Based on step 1, establish a calculation formula for the acoustic logging value of the source rock section and a calculation formula for the density logging value of the source rock section;

[0008] Step 3: Calculate the volume of organic matter in the source rock based on the organic carbon content measured in the laboratory;

[0009] Step 4: Based on the volume of organic matter in the source rock and the volume of the rock skeleton in the source rock layer obtained in step 3, calculate the masses of the four parts respectively;

[0010] Step 5: Substitute the volume of organic matter in the source rock in step 3 and the masses of the four parts in step 4 into the calculation formula for the acoustic logging value of the source rock section and the calculation formula for the density logging value of the source rock section in step 2.

[0011] Preferably, the step 2 is specifically:

[0012] Step 2: Based on step 1, establish the calculation formula (2-1) for the acoustic logging value of the source rock section and the calculation formula (2-2) for the density logging value of the source rock section:

[0013] Δt s =Δt ma v ma +Δt om v om +Δt H v H +Δt w v w (2-1)

[0014]

[0015] v ma +v om +v H +v w =1 (2-3)

[0016] v H +v W =φ (2-4)

[0017] Where:

[0018] △t s —Sonic time difference logging value of source rock layer, us / m;

[0019] △t ma —Sonic wave time difference of rock skeleton in source rock layer, us / m;

[0020] △t om —Organic matter acoustic time difference in source rock layer, us / m;

[0021] △t H —Sonic time difference of hydrocarbons in source rock layer, us / m;

[0022] △t w —Sonic time difference of formation water in source rock layer, us / m;

[0023] ρ s — is the logging density of the source rock layer, g / cm 3 ;

[0024] Φ—porosity of source rock, %;

[0025] v ma —Volume percentage of rock skeleton in source rock layer, %;

[0026] v om —Volume percentage of organic matter in source rock layer, %;

[0027] v H —Volume percentage of hydrocarbons in the source rock layer, %;

[0028] v w —Volume percentage of formation water in source rock layer, %;

[0029] m ma —Rock skeleton mass of source rock layer, g

[0030] m om —Mass of organic matter in source rock layers, g;

[0031] m H —Mass of hydrocarbons in the source rock layer, g;

[0032] m w —Mass of formation water in source rock layer, g.

[0033] Preferably, the step 3 is specifically:

[0034] Calculate the volume of organic matter in source rocks based on the organic carbon content measured in the laboratory:

[0035]

[0036] Where: k is the organic carbon conversion coefficient, w TOC The organic matter content was measured in the laboratory.

[0037] Therefore, the rock skeleton volume of the source rock layer is expressed as:

[0038]

[0039] Preferably, the step 4 is specifically:

[0040] Step 4: Based on the volume of organic matter in the source rock and the volume of the rock skeleton in the source rock layer obtained in step 3, calculate the mass of the four parts:

[0041] Quality of rock skeleton in source rock layer:

[0042]

[0043] Organic matter quality of source rock layers:

[0044] m om =ρ ma kw TOC(2-8)

[0045] Hydrocarbon quality of source rock layer:

[0046] m H =ρ H (φ-v w ) (2-9)

[0047] Formation water quality in source rock layers:

[0048] m w =ρ w v w (2-10).

[0049] Preferably, the step 5 is specifically:

[0050] Substituting equations 2-5 to 2-10 of steps 1.3 and 1.4 into equations 2-1 and 2-2 of step 1.2 yields:

[0051]

[0052]

[0053] For non-source rocks:

[0054] Δt m =Δt ma (1-φ)+Δt w φ (2-13)

[0055] ρ m =ρ ma (1-φ)+ρ w φ (2-14)

[0056] Then, the correction model of the acoustic time increment △t' and density reduction ρ' caused by organic matter in the source rock layer is:

[0057]

[0058]

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] The present invention provides a correction method for the effect of organic matter content in source rocks on logging parameters, quantitatively evaluates the contribution of organic matter content and overpressure in shale to well logging curves such as acoustic time difference and density, clarifies the mechanism of overpressure of different origins on well logging curves, and solves the problem that the contribution of undercompaction-induced overpressure to overpressure is easily overestimated due to the lack of quantitative evaluation of the effect of organic matter content on well logging parameters in overpressure intervals in previous overpressure cause identification. The accuracy of overpressure cause identification is improved, and the current research status of overpressure in sedimentary basins is changed, which is mainly due to undercompaction. It is believed that overpressure in source rock intervals is mainly caused by hydrocarbon generation and fluid expansion, and its conduction is caused in the reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0062] In the attached picture:

[0063] Figure 1 is a flow chart of the method of the present invention;

[0064] Figure 2 This is the equivalent volume model diagram of the source rock of the present invention;

[0065] Figure 3 This is a comparison chart of the overpressure cause identification results before and after the correction of the logging curve combination method;

[0066] Figure 4 This is a comparison chart of overpressure cause identification results before and after Bowers method correction;

[0067] Figure 5 This is a comparison chart of overpressure cause identification results before and after correction by velocity-density comparison method;

[0068] Figure 6 This is a comparison chart of the overpressure cause identification results before and after porosity comparison method correction. DETAILED DESCRIPTION

[0069] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0070] Example:

[0071] A correction method for the effect of source rock organic matter on overpressure logging parameters, such as Figure 1 As shown, including:

[0072] Step 1: Figure 2The source rock is divided into four parts: mudstone skeleton, organic matter, hydrocarbons and formation water. The unit volume is used as the calibration unit. The sum of the volume percentages of the four parts is 1, and the total volume percentage of hydrocarbons and formation water is the porosity (Φ).

[0073] Step 2: Based on step 1, establish the calculation formula (2-1) for the acoustic logging value of the source rock section and the calculation formula (2-2) for the density logging value of the source rock section:

[0074] Δt s =Δt ma v ma +Δt om v om +Δt H v H +Δt w v w (2-1)

[0075]

[0076] v ma +v om +v H +v w =1 (2-3)

[0077] v H +v W =φ (2-4)

[0078] Where:

[0079] △t s —Sonic time difference logging value of source rock layer, us / m;

[0080] △t ma —Sonic wave time difference of rock skeleton in source rock layer, us / m;

[0081] △t om —Organic matter acoustic time difference in source rock layer, us / m;

[0082] △t H —Sonic time difference of hydrocarbons in source rock layer, us / m;

[0083] △t w —Sonic time difference of formation water in source rock layer, us / m;

[0084] ρ s — is the logging density of the source rock layer, g / cm 3 ;

[0085] Φ—porosity of source rock, %;

[0086] v ma—Volume percentage of rock skeleton in source rock layer, %;

[0087] v om —Volume percentage of organic matter in source rock layer, %;

[0088] v H —Volume percentage of hydrocarbons in the source rock layer, %;

[0089] v w —Volume percentage of formation water in source rock layer, %;

[0090] m ma —Rock skeleton mass of source rock layer, g

[0091] m om —Mass of organic matter in source rock layers, g;

[0092] m H —Mass of hydrocarbons in the source rock layer, g;

[0093] m w —Mass of formation water in source rock layer, g.

[0094] Step 3: Calculate the volume of organic matter in source rocks based on the organic carbon content measured in the laboratory:

[0095]

[0096] Where: k is the organic carbon conversion coefficient, w TOC The organic matter content was measured in the laboratory.

[0097] Therefore, the rock skeleton volume of the source rock layer is expressed as:

[0098]

[0099] Step 4: Based on the volume of organic matter in the source rock and the volume of the rock skeleton in the source rock layer obtained in step 3, calculate the mass of the four parts:

[0100] Quality of rock skeleton in source rock layer:

[0101]

[0102] Organic matter quality of source rock layers:

[0103] m om =ρ ma kw TOC (2-8)

[0104] Hydrocarbon quality of source rock layer:

[0105] m H =ρ H (φ-vw ) (2-9)

[0106] Formation water quality in source rock layers:

[0107] m w =ρ w v w (2-10).

[0108] Step 5: Substitute equations 2-5 to 2-10 from steps 1.3 and 1.4 into equations 2-1 and 2-2 from step 1.2 to obtain:

[0109]

[0110]

[0111] For non-source rocks:

[0112] Δt m =Δt ma (1-φ)+Δt w φ (2-13)

[0113] ρ m =ρ ma (1-φ)+ρ w φ (2-14)

[0114] Then, the correction model of the acoustic time increment △t' and density reduction ρ' caused by organic matter in the source rock layer is:

[0115]

[0116]

[0117] Take the values ​​of the calibration model parameters established in step 5

[0118] 1. Organic matter conversion coefficient k

[0119] The organic carbon conversion coefficient k is mainly affected by the type of organic matter and the diagenetic stage. Considering that the source rock of the Pinghu Formation in the Xihu Sag is mainly type III kerogen, its value range is as shown in Table 1:

[0120] Table 1 Organic matter conversion coefficient k value table

[0121] stage Type I kerogen Type II kerogen Type III kerogen Diagenesis 1.25 1.34 1.48 End of epigenetic effect 1.20 1.19 1.18

[0122] 1.2 Organic carbon content w TOC

[0123] The organic carbon content is determined based on the measured data of source rocks. When there is no measured data, the average value of adjacent sections is taken.

[0124] 1.3 Acoustic Time Difference Parameters

[0125] Acoustic time difference Δt of source rock mudstone skeleton ma According to the normally compacted non-source rock section, the corresponding value when the porosity is 0 is obtained;

[0126] Organic matter sound wave time difference Δt om Take the theoretical value, 550us / m, the hydrocarbon sound wave time difference Δt H Take the theoretical value, which is 780us / m, and the formation water acoustic wave time difference Δt w The theoretical value is 620us / m.

[0127] 1.4 Density parameters

[0128] Source rock mudstone skeleton density ρ ma According to the measured value, take 2.7~2.8g / cm 3 ;

[0129] Source rock organic matter density ρ om Take the empirical value of 1.1g / cm 3 ;

[0130] Hydrocarbon density ρ H The values ​​are taken according to the measured physical property data of natural gas in the study area;

[0131] Formation water density ρ w The value is taken according to the measured data of formation water in the study area.

[0132] 1.5 Oil / water saturation

[0133] The calculation of oil / water saturation in source rocks can be obtained by using Archie's formula and nuclear magnetic resonance data, among which Archie's formula is currently the most commonly used one. w :

[0134]

[0135] Where: R W — formation water resistivity, which is determined based on actual logging data and experimental data; R— logging resistivity value of source rock layer; constants a, b, m and n can be obtained through rock electrical tests. Since there is no experimental data in source rocks, empirical values ​​a=0.62, b=1, n=2 and m=2.15 are taken. The average water saturation in the source rocks in the study area calculated according to formula 2-17 is 40%, and the average oil and gas saturation is 60%. This value is taken for calibration.

[0136] Experimental verification

[0137] 1. Logging curve combination method

[0138] Taking the East China Sea Basin as an example, Figure 3 As shown, the overpressure cause identification result before correction using this method is undercompaction, and the overpressure cause identification result after correction using this method is hydrocarbon generation and pressurization.

[0139] 2. Bowers Act

[0140] Taking the East China Sea Basin as an example, Figure 4 As shown in the figure, before correction using this method, the cause of overpressure identification result is a combination of undercompaction and hydrocarbon generation pressurization, and after correction using this method, the cause of overpressure identification result is hydrocarbon generation pressurization.

[0141] 3. Speed-density comparison method

[0142] Taking the East China Sea Basin as an example, Figure 5 As shown in the figure, before correction using this method, the cause of overpressure was identified as undercompaction, while after correction using this method, the cause of overpressure was identified as hydrocarbon generation and pressurization.

[0143] 4. Porosity comparison method

[0144] Taking the East China Sea Basin as an example, Figure 6 As shown in the figure, before correction using this method, the cause of overpressure was identified as undercompaction, while after correction using this method, the cause of overpressure was identified as hydrocarbon generation and pressurization.

[0145] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A correction method for the effect of organic matter in source rocks on overpressure logging parameters, characterized in that: include: Step 1: Divide the source rock into four parts: mudstone skeleton, organic matter, hydrocarbons and formation water. The unit volume is used as the calibration unit. The sum of the volume percentages of the four parts is 1, and the total volume percentage of hydrocarbons and formation water is the porosity (Φ). Step 2: Based on step 1, establish a calculation formula for the acoustic logging value of the source rock section and a calculation formula for the density logging value of the source rock section; Step 3: Calculate the volume of organic matter in the source rock based on the organic carbon content measured in the laboratory; Step 4: Based on the volume of organic matter in the source rock and the volume of the rock skeleton in the source rock layer obtained in step 3, calculate the masses of the four parts respectively; Step 5: Substitute the volume of organic matter in the source rock in step 3 and the masses of the four parts in step 4 into the calculation formula for the acoustic logging value of the source rock section and the calculation formula for the density logging value of the source rock section in step 2; The step 2 is specifically as follows: Step 2: Based on step 1, establish the calculation formula (2-1) for the acoustic logging value of the source rock section and the calculation formula (2-2) for the density logging value of the source rock section: Δt s =Δt ma v ma +Δt om v om +Δt H v H +Δt w v w (2-1) v ma +v om +v H +v w =1 (2-3) v H +v W =φ (2-4) Where: △t s —Sonic time difference logging value of source rock layer, us / m; △t ma —Sonic wave time difference of rock skeleton in source rock layer, us / m; △t om —Organic matter acoustic time difference in source rock layer, us / m; △t H —Sonic time difference of hydrocarbons in source rock layer, us / m; △t w —Sonic time difference of formation water in source rock layer, us / m; ρ s — is the logging density of the source rock layer, g / cm 3 ; Φ—porosity of source rock, %; v ma —Volume percentage of rock skeleton in source rock layer, %; v om —Volume percentage of organic matter in source rock layer, %; v H —Volume percentage of hydrocarbons in the source rock layer, %; v w —Volume percentage of formation water in source rock layer, %; m ma —Rock skeleton mass of source rock layer, g m om —Mass of organic matter in source rock layers, g; m H —Mass of hydrocarbons in the source rock layer, g; m w —Mass of formation water in source rock layer, g.

2. The correction method for the effect of organic matter in source rocks on overpressure logging parameters according to claim 1, characterized in that: The step 3 is specifically as follows: Calculate the volume of organic matter in source rocks based on the organic carbon content measured in the laboratory: Where: k is the organic carbon conversion coefficient, w TOC is the organic matter content measured in the laboratory, ρ ma is the rock skeleton density, ρ om is the density of organic matter; Therefore, the rock skeleton volume of the source rock layer is expressed as:

3. The correction method for the effect of organic matter in source rocks on overpressure logging parameters according to claim 2, characterized in that: The step 4 is specifically as follows: Step 4: Based on the volume of organic matter in the source rock and the volume of the rock skeleton in the source rock layer obtained in step 3, calculate the mass of the four parts: Rock skeleton quality of source rock layer: Organic matter quality of source rock layers: m om =ρ ma kW TOC (2-8) Quality of hydrocarbons in source rock layers: m H =ρ H (φ-v w ) (2-9) Among them, ρ H is the organic matter density, Formation water quality in source rock layers: m w =ρ w v w (2-10).

4. The correction method for the effect of organic matter in source rocks on overpressure logging parameters according to claim 3 is characterized by: The step 5 is specifically as follows: Substituting equations 2-5 to 2-10 of steps 1.3 and 1.4 into equations 2-1 and 2-2 of step 1.2 yields: For non-source rocks: Δt m =Δt ma (1-φ)+Δt w f (2-13) r m =ρ ma (1-φ)+ρ w f (2-14) Then, the correction model of the acoustic time increment △t' and density reduction ρ' caused by organic matter in the source rock layer is:

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