A rapid paleosalinity calculation method for marine carbonate rocks

Abstract

The present invention belongs to the field of petroleum exploration and development, and discloses a rapid paleo-salinity calculation method applicable to marine carbonate rocks. The method comprises the following steps: determining multiple lithology combinations of carbonate rock formations; establishing volume percentage calculation formulas for various lithologies according to volume models and well logging curves corresponding to various lithologies in each lithology combination; establishing a calculation formula for seawater salinity during deposition of each lithology combination formation using seawater salinity assignments during deposition of various lithologies and established volume percentage calculation formulas for various lithologies, and then calculating the seawater salinity during deposition of carbonate rock formations. The method of the present invention can be preferably applied to marine carbonate rock formations.

Description

Technical Field

[0001] The invention belongs to the field of petroleum exploration and development, and more specifically, relates to a rapid paleo-salinity calculation method applicable to marine carbonate rocks. Background Art

[0002] Seawater salinity is the ratio of all dissolved solids in seawater to the weight of seawater, usually expressed in grams per kilogram of seawater, and is used to indicate the mass fraction of salt substances in seawater. The average salinity of the world's oceans today is 35‰, with the highest being the Red Sea, which is as high as 41‰, and the lowest being the Baltic Sea, which is 10‰. In the geological history, the salinity of seawater has been constantly changing, and the types of rocks formed by sedimentation under different salinities vary greatly. By restoring the salinity of the sedimentation period to judge the rock deposition environment, we can further analyze the possible distribution patterns of source rocks or reservoirs.

[0003] There are many methods to restore paleo-salinity. Geochemical methods (such as B / Ga, Sr / Ba, Mg / Ca, Sr / Ca and Na / Ca, etc.) have been widely used in China to reconstruct the paleo-salinity of different sedimentary strata. Some studies have used the Mn isotope range, Mn / Sr value and carbon-oxygen isotope intersection to analyze salinity. Some studies have used the content of major elements such as geochemical MgO, CaO, Na2O, K2O and the content of rare earth elements to identify the paleoenvironment. Some studies have used the boron content of mudstone as a paleo-salinometer to reconstruct the paleo-salinity change curve of lake sediments. In addition, some scholars have used the salinity test of fluid inclusions in rock veins to restore the paleo-fluid salinity during diagenesis.

[0004] At present, the only research related to the research method of fluid salinity is CN201711418008.X, which is mainly based on the salinity of cement inclusions to restore the later fluid salinity. The steps are as follows: determine the order of formation rock cements, screen samples with multi-stage cements and rich fluid inclusions; select fluid inclusions of different orders, conduct homogenized temperature and salinity tests, and obtain multiple homogenized temperature and salinity data; combine the burial history to determine the corresponding relationship between geothermal evolution and geological time, and draw the trend line of salinity change with geological time based on the homogenized temperature and salinity data of multiple fluid inclusions, so as to obtain the evolution history of paleofluid salinity.

[0005] The marine carbonate rock field has always been the main front for deep oil and gas exploration. The large oil and gas fields such as Anyue, Shunbei, Puguang, Yuanba, and western Sichuan that have been recently broken through in my country all belong to the marine strata. The environment when the large oil and gas fields in the marine strata were formed was very different. The Ordovician strata in Shunbei belonged to normal seawater deposition of limestone, the formation environment of the Changxing Formation in Puguang and the Longwangmiao Formation in Anyue was dolomite deposition, and the seawater was slightly salinized when they were formed. The Majiagou Formation in the Jingbian gas field and the Leikoupo Formation in western Sichuan formed with greater salinity. It can be seen that the salinity of different strata varies greatly, and the salinity changes greatly in the same stratum, and the correlation with the reservoir is also different. Through the analysis of salinity, the change process of sea level during stratum deposition can be restored, and then the spatial distribution range of the reservoir can be inferred. In the past, salinity analysis required a large amount of rock geochemical analysis, which was time-consuming and economically expensive. Therefore, it is urgent to propose a rapid paleo-salinity calculation method suitable for marine carbonate rocks. Summary of the invention

[0006] The purpose of the present invention is to propose a rapid paleo-salinity calculation method applicable to marine carbonate rocks in view of the deficiencies of the prior art. The method of the present invention can be well applied to marine carbonate rock formations. The seawater salinity during the deposition of carbonate rock formations is calculated by logging curves, which is fast and simple, does not necessarily require rock geochemical analysis, saves time and economic costs, and lays an important foundation for further analysis of source rocks and reservoir distribution laws. It has been well applied in the Ordos Basin.

[0007] In order to achieve the above object, the present invention provides a rapid paleo-salinity calculation method applicable to marine carbonate rocks, the method comprising the following steps:

[0008] S1: Determine the various lithological combinations of carbonate formations;

[0009] S2: Establish a calculation formula for the volume percentage of various lithologies in each lithology combination based on the volume model and well logging curve corresponding to each lithology combination;

[0010] S3: Using the seawater salinity values ​​assigned during the deposition of various lithologies and the volume percentage calculation formula of various lithologies in each lithology combination established in step S2, a calculation formula for the seawater salinity during the deposition of each lithology combination is established, and then the seawater salinity during the deposition of the carbonate rock formation is calculated.

[0011] The beneficial effects of the technical solution of the present invention are as follows:

[0012] (1) The present invention provides a method suitable for identifying ancient seawater salinity in marine carbonate rocks, laying an important foundation for further analyzing the distribution patterns of source rocks and reservoirs.

[0013] (2) The present invention forms a method suitable for marine carbonate rocks to quickly and quantitatively identify ancient seawater salinity using well logging curves, which solves the problem of being able to identify ancient seawater salinity only by relying on geochemical analysis, saving time and economic costs.

[0014] (3) The method of the present invention is highly operable, and the identification is intuitive, clear, and simple, and has high application value. The method steps can be easily promoted and applied to the exploration and development of marine carbonate formations. The method of the present invention can also be used to obtain the vertical salinity changes in sections, and then infer the changes in the seawater environment in different time periods.

[0015] Other features and advantages of the present invention will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0016] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0017] The present invention provides a rapid paleo-salinity calculation method applicable to marine carbonate rocks, the method comprising the following steps:

[0018] S1: Determine the various lithological combinations of carbonate formations;

[0019] S2: Establish a calculation formula for the volume percentage of various lithologies in each lithology combination based on the volume model and well logging curve corresponding to each lithology combination;

[0020] S3: Using the seawater salinity values ​​assigned during the deposition of various lithologies and the volume percentage calculation formula of various lithologies in each lithology combination established in step S2, a calculation formula for the seawater salinity during the deposition of each lithology combination is established, and then the seawater salinity during the deposition of the carbonate rock formation is calculated.

[0021] In the present invention, the volume of pores in carbonate rock formations is relatively small, so the influence of pore volume is ignored.

[0022] According to the present invention, preferably, in step S1, the sedimentary microfacies and diagenesis of the carbonate rock formation are analyzed to determine various lithology combinations of the carbonate rock formation.

[0023] According to the present invention, preferably, the plurality of lithology combinations include a dolomite+limestone+mudstone combination, a dolomite+limestone+anhydrite+mudstone combination, and a dolomite+anhydrite+salt rock+mudstone combination.

[0024] According to the present invention, preferably, the mineral composition of the dolomite+limestone+mudstone combination per unit volume of formation includes dolomite, calcite and mud.

[0025] According to the present invention, preferably, the volume percentage calculation formulas of various lithologies in the dolomite + limestone + mudstone combination are:

[0026] V dol1 =2.242*ρ b1 -0.142*U1-4.077 (1);

[0027] V lim1 =1.132*ρ b1 +0.261*U1-5.753 (2);

[0028] V sh1 =-3.375*ρ b1 -0.119*U1+10.830 (3);

[0029] Among them, V dol1 、V lim1 、V sh1 are the volume contents of dolomite, calcite and mud in the dolomite + limestone + mud combination per unit volume of the formation, respectively;

[0030] ρ b1 is the density logging value;

[0031] U1 is the photoelectric absorption cross-section logging value;

[0032] The volume model corresponding to the dolomite + limestone + mudstone combination is V dol1 +V lim1 +V sh1 =1;

[0033] The coefficients before each term in formula (1), formula (2) and formula (3) are obtained by solving the relationship between the density logging curve and the photoelectric absorption cross-section logging curve corresponding to the dolomite + limestone + mud combination established according to the volume model corresponding to the dolomite + limestone + mud combination and the volume content of each mineral component in the dolomite + limestone + mud combination in a unit volume of the formation.

[0034] In the present invention, the volume model corresponding to the dolomite + limestone + mud combination is that the sum of the volume contents of each mineral in the dolomite + limestone + mud combination per unit volume of the stratum is 1, that is: V dol1 +V lim1 +V sh1= 1. The relationship between the "density logging curve and photoelectric absorption cross-section logging curve" established by the volume model and the "volume content of each mineral composition in the dolomite + limestone + mudstone combination in the unit volume of the formation" is: the density logging value ρ b1 The photoelectric absorption cross-section logging value U1 is respectively the sum of the product of the density logging value and the photoelectric absorption cross-section logging value of the above three minerals and the volume content of each corresponding mineral. Then, by using the volume model corresponding to the dolomite + limestone + mudstone combination, the coefficients before each term in formula (1), formula (2) and formula (3) are obtained.

[0035] According to the present invention, preferably, the mineral composition of the dolomite + limestone + anhydrite + mudstone combination per unit volume of formation includes dolomite, calcite, anhydrite and mudstone.

[0036] According to the present invention, preferably, the volume percentage calculation formulas of various lithologies in the dolomite + limestone + anhydrite + mud combination are:

[0037] V dol2 =0.715*ρ b2 -0.188*U2-0.003*DT1+1.235 (4);

[0038] V lim2 =-3.609*ρ b2 +0.116*U2-0.010*DT1+10.742 (5);

[0039] V anhy1 =3.120*ρ b2 +0.095*U2+0.007*DT1-10.855 (6);

[0040] V sh2 =-0.226*ρ b2 -0.023*U2+0.007*DT1-0.122 (7);

[0041] Among them, V dol2 、V lim2 、V anhy1 、V sh2 are the volume contents of dolomite, calcite, anhydrite and mud in the dolomite + limestone + anhydrite + mud combination in a unit volume of the formation;

[0042] ρ b2 is the density logging value;

[0043] U2 is the photoelectric absorption cross-section logging value;

[0044] DT1 is the acoustic logging value;

[0045] The volume model corresponding to the dolomite + limestone + anhydrite + mudstone combination is V dol2 +V lim2 +V anhy1 +V sh2 =1;

[0046] The coefficients before each term in formula (4), formula (5), formula (6) and formula (7) are obtained by solving the relationship between the density logging curve, photoelectric absorption cross-section logging curve and acoustic logging curve corresponding to the dolomite + limestone + anhydrite + mud combination established according to the volume model corresponding to the dolomite + limestone + anhydrite + mud combination and the volume content of each mineral component in the dolomite + limestone + anhydrite + mud combination in unit volume of formation.

[0047] In the present invention, the volume model corresponding to the dolomite + limestone + anhydrite + mudstone combination is that the sum of the volume contents of each mineral contained in the unit volume of the stratum is 1, that is: V dol2 +V lim2 +V anhy1 +V sh2 =1; the relationship between the "density logging curve, photoelectric absorption cross-section logging curve and acoustic logging curve" established by the volume model and the "volume content of each mineral composition in the dolomite + limestone + anhydrite + mud combination in a unit volume of the formation" is: the density logging value, the photoelectric absorption cross-section logging value and the acoustic logging value are respectively the sum of the products of the density logging value, photoelectric absorption cross-section logging value, and acoustic logging value of the above four minerals and the volume content of each corresponding mineral. Then, by using the volume model corresponding to the dolomite + limestone + anhydrite + mud combination, the coefficients before each term in formula (4), formula (5), formula (6) and formula (7) are obtained.

[0048] According to the present invention, preferably, the mineral composition of the dolomite+anhydrite+salt rock+mud in a unit volume of formation includes dolomite, anhydrite, halite and mud.

[0049] According to the present invention, preferably, the volume percentage calculation formulas of various lithologies in the dolomite + anhydrite + salt rock + mud combination are:

[0050] V dol3 =0.946*ρ b3 -0.196*U3-0.003*DT2+0.547 (8);

[0051] V anhy2 =-0.265*ρ b3 +0.204*U3-0.003*DT2-0.779 (9);

[0052] V hal =-1.647*ρ b3 +0.053*U3-0.005*DT2+4.903 (10);

[0053] V sh3 =0.966*ρ b3 -0.061*U3+0.010*DT2-3.672 (11);

[0054] Among them, V dol3 、V anhy2 、V hal 、V sh3 are the volume contents of dolomite, anhydrite, halite and mud in the dolomite + anhydrite + salt rock + mud combination per unit volume of the formation;

[0055] ρ b3 is the density logging value;

[0056] U3 is the photoelectric absorption cross-section logging value;

[0057] DT2 is the acoustic logging value;

[0058] The volume model corresponding to the combination of dolomite + anhydrite + salt rock + mud is V dol3 +V anhy2 +V hal +V sh3 =1;

[0059] The coefficients before each term in formula (8), formula (9), formula (10) and formula (11) are obtained by solving the relationship between the density logging curve, photoelectric absorption cross-section logging curve and acoustic logging curve corresponding to the dolomite + anhydrite + salt rock + mud combination established according to the volume model corresponding to the dolomite + anhydrite + salt rock + mud combination and the volume content of each mineral component in the dolomite + anhydrite + salt rock + mud combination in a unit volume of the formation.

[0060] In the present invention, the volume model corresponding to the dolomite + anhydrite + salt rock + mudstone combination is that the sum of the volume contents of each mineral contained in the unit volume of the formation is 1, that is: V dol3 +V anhy2 +V hal +V sh3 =1; the relationship between the "density logging curve, photoelectric absorption cross-section logging curve and acoustic logging curve" established by the volume model and the "volume content of each mineral composition in the dolomite + anhydrite + salt rock + mud combination in the unit volume of the formation" is: density logging value ρ b3, photoelectric absorption cross-section logging value U3 and acoustic logging value DT2 are respectively the sum of the products of the density logging value, photoelectric absorption cross-section logging value, acoustic logging value and the volume content of the corresponding minerals of the above four minerals. Then, by using the volume model corresponding to the dolomite + anhydrite + salt rock + mud combination, the coefficients before each term in formula (8), formula (9), formula (10) and formula (11) are obtained.

[0061] According to the present invention, preferably,

[0062] The calculation formula for seawater salinity when the dolomite + limestone + mudstone combination strata are deposited is:

[0063] S1=(k*V dol1 +l*V lim1 ) / (V dol1 +V lim1 ) (12);

[0064] The calculation formula for seawater salinity when the dolomite + limestone + anhydrite + mudstone combination strata are deposited is:

[0065] S2=(k*V dol2 +l*V lim2 +m*V anhy1 ) / (V dol2 +V anhy1 +V lim2 ) (13);

[0066] The calculation formula for seawater salinity when the dolomite + anhydrite + salt rock + mud combined strata are deposited is:

[0067] S3=(k*V dol3 +n*V hal +m*V anhy2 ) / (V dol3 +V anhy2 +V hal ) (14);

[0068] Among them, V dol1 、V lim1 are the volume contents of dolomite and calcite in the dolomite + limestone + mudstone combination per unit volume of the formation;

[0069] V dol2 、V lim2 、V anhy1 are the volume contents of dolomite, calcite and anhydrite in the dolomite + limestone + anhydrite + mudstone combination per unit volume of the formation;

[0070] V dol3 、V anhy2 、V halare the volume contents of dolomite, anhydrite and halite in the dolomite + anhydrite + salt rock + mud combination per unit volume of the stratum;

[0071] k is the value assigned to the seawater salinity when the dolomite was deposited, which is determined based on the current dolomite deposition environment. In the present invention, the salinity in the lagoons and tidal flats of Texas and Kuwait where the dolomite was deposited is 42-44‰, so the value of k is preferably 43‰.

[0072] l is the salinity of seawater at the time of limestone deposition, which is determined based on the current limestone deposition environment. In the present invention, the salinity at the time of limestone deposition is roughly similar to that of current seawater, so the preferred value of l is 35‰.

[0073] m is the salinity of seawater when anhydrite is deposited, which is determined based on the current anhydrite deposition environment. In the present invention, the salinity when anhydrite is precipitated is significantly higher than the salinity when limestone and dolomite are deposited. Therefore, the value of m is preferably 100‰.

[0074] n is the salinity of seawater during salt rock deposition, which is determined based on the current salt rock deposition environment. In the present invention, the salinity during salt rock deposition can be as high as 260‰, so the preferred value of n is 260‰.

[0075] S1 is the salinity of seawater when the dolomite + limestone + mudstone combination of carbonate strata was deposited;

[0076] S2 is the salinity of seawater when the carbonate rock formations were deposited with dolomite + limestone + anhydrite + mudstone combination;

[0077] S3 is the salinity of seawater when the carbonate rock formations of dolomite + anhydrite + salt rock + mud were deposited.

[0078] The present invention is specifically described below by way of examples.

[0079] Example 1

[0080] This embodiment provides a rapid paleo-salinity calculation method applicable to marine carbonate rocks, which calculates the salinity of carbonate rock formations at a depth of 3056.6 m in a well in a block of the Ordos Basin during deposition.

[0081] The method comprises the following steps:

[0082] S1: Determine that the lithology combination of the carbonate rock formation of the well is a combination of dolomite + limestone + mudstone; the mineral composition of the dolomite + limestone + mudstone combination per unit volume of formation includes dolomite, calcite and mudstone.

[0083] S2: Based on the volume models and well logging curves corresponding to the dolomite, limestone and argillaceous lithologies in the dolomite + limestone + argillaceous combination, the volume percentage calculation formulas of various lithologies in the dolomite + limestone + argillaceous combination are established:

[0084] V dol1 =2.242*ρ b1 -0.142*U1-4.077 (1);

[0085] V lim1 =1.132*ρ b1 +0.261*U1-5.753 (2);

[0086] V sh1 =-3.375*ρ b1 -0.119*U1+10.830 (3);

[0087] Among them, V d o l1 、V lim1 、V sh1 are the volume contents of dolomite, calcite and mud in the dolomite + limestone + mud combination per unit volume of the formation, respectively;

[0088] ρ b1 The density logging value of the well at this depth is 2.810 g / cm 3 ;

[0089] U1 is the photoelectric absorption cross section logging value of the well at this depth, which is 11.286 B / cm 3 ;

[0090] The volume model corresponding to the dolomite + limestone + mudstone combination is V dol1 +V lim1 +V sh1 =1;

[0091] The coefficients before each term in formula (1), formula (2) and formula (3) are obtained by solving the relationship between the density logging curve and the photoelectric absorption cross-section logging curve established according to the volume model corresponding to the various lithologies and the volume content of each mineral composition in the dolomite + limestone + mud combination in a unit volume of the formation.

[0092] From this we can get: V dol1 62.6%, V lim1 31.2%, V sh1 0.2%;

[0093] S3: In this embodiment, the seawater salinity calculation formula for the deposition of dolomite + limestone + mudstone combination strata is established by using the seawater salinity assignment during dolomite deposition, the seawater salinity assignment during limestone deposition, and the volume percentage calculation formulas (1), (2), and (3) of various lithologies in the dolomite + limestone + mudstone combination established in step S2:

[0094] S1=(k*V dol1 +l*V lim1 ) / (V dol1 +V lim1 ) (12);

[0095] Among them, V dol1 is 62.6%, V lim1 31.2%

[0096] k is the value assigned to the seawater salinity at the time of dolomite deposition, which is determined to be 43‰ based on the current dolomite deposition environment;

[0097] l Assign a value to the seawater salinity at the time of limestone deposition, which is determined to be 35‰ based on the current limestone deposition environment;

[0098] It was further calculated that the salinity of seawater during the deposition of the dolomite + limestone + mudstone combination of carbonate rock strata was 40.4‰.

[0099] Example 2

[0100] This embodiment provides a rapid paleo-salinity calculation method applicable to marine carbonate rocks, which calculates the salinity of carbonate rock formations at a depth of 3097.1 m in a well in a block of the Ordos Basin during deposition.

[0101] The method comprises the following steps:

[0102] S1: Determine that the lithology combination of the carbonate rock formation of the well is a combination of dolomite + limestone + anhydrite + mud; the mineral composition of the dolomite + limestone + anhydrite + mud combination per unit volume of formation includes dolomite, calcite, anhydrite and mud.

[0103] S2: Based on the volume models and well logging curves corresponding to the dolomite, limestone, anhydrite and argillaceous lithologies in the dolomite + limestone + anhydrite + argillaceous combination, the volume percentage calculation formulas of various lithologies in the dolomite + limestone + anhydrite + argillaceous combination are established:

[0104] V dol2 =0.715*ρ b2 -0.188*U2-0.003*DT1+1.235 (4);

[0105] V lim2=-3.609*ρ b2 +0.116*U2-0.010*DT1+10.742 (5);

[0106] V anhy1 =3.120*ρ b2 +0.095*U2+0.007*DT1-10.855 (6);

[0107] V sh2 =-0.226*ρ b2 -0.023*U2+0.007*DT1-0.122 (7);

[0108] Among them, V dol2 、V lim2 、V anhy1 、V sh2 are the volume contents of dolomite, calcite, anhydrite and mud in the dolomite + limestone + anhydrite + mud combination in a unit volume of the formation;

[0109] ρ b2 The density logging value of the well at this depth is 2.825 g / cm 3 ;

[0110] U2 is the photoelectric absorption cross section of the well at this depth, which is 10223 B / cm 3 ;

[0111] DT1 is the acoustic logging value of the well at this depth, which is 154.768 μs / m;

[0112] The volume model corresponding to the dolomite + limestone + anhydrite + mudstone combination is V dol2 +V lim2 +V anhy1 +V sh2 =1;

[0113] The coefficients before each term in formula (4), formula (5), formula (6) and formula (7) are obtained by solving the relationship between the density logging curve, photoelectric absorption cross-section logging curve and acoustic logging curve established according to the volume models corresponding to the various lithologies and the volume content of each mineral composition in the dolomite + limestone + anhydrite + mud combination in a unit volume of the formation.

[0114] From this we can get: V dol2 81.0%, V lim2 10.8%, V anhy1 0.2%, V sh2 8.0%;

[0115] S3: In this embodiment, the seawater salinity assignment k during dolomite deposition, the seawater salinity assignment l during limestone deposition, the seawater salinity assignment m during anhydrite deposition, and the volume percentage calculation formulas (4), (5), (6) and (7) of various lithologies in the dolomite + limestone + anhydrite + mud combination established in step S2 are used to establish the seawater salinity calculation formula during dolomite + limestone + anhydrite + mud combination stratum deposition:

[0116] S2=(k*V dol2 +l*V lim2 +m*V anhy1 ) / (V dol2 +V anhy1 +V lim2 ) (13);

[0117] Among them, V dol2 81.0%, V lim2 10.8%, V anhy1 0.2%;

[0118] k is the value assigned to the seawater salinity at the time of dolomite deposition, which is determined to be 43‰ based on the current dolomite deposition environment;

[0119] l is the value of seawater salinity at the time of limestone deposition, which is determined to be 35‰ based on the current limestone deposition environment;

[0120] m is the value of seawater salinity at the time of anhydrite deposition, which is determined to be 100‰ based on the current anhydrite deposition environment.

[0121] It was further calculated that the salinity of seawater during the deposition of the dolomite + limestone + anhydrite + mud combination of carbonate rock strata was 42.2‰.

[0122] Example 3

[0123] This embodiment provides a rapid paleo-salinity calculation method applicable to marine carbonate rocks, and calculates the salinity of carbonate rock formations at a depth of 3661.9 m in a well in a block of the Ordos Basin during deposition.

[0124] The method comprises the following steps:

[0125] S1: Determine that the lithology combination of the carbonate rock formation of the well is a combination of dolomite + anhydrite + salt rock + mud; the mineral composition of the dolomite + anhydrite + salt rock + mud combination per unit volume of formation includes dolomite, anhydrite, halite and mud.

[0126] S2: Based on the volume models and well logging curves corresponding to the dolomite, anhydrite, salt rock and mudstone in the dolomite + anhydrite + salt rock + mudstone combination, the volume percentage calculation formulas of various lithologies in the dolomite + anhydrite + salt rock + mudstone combination are established:

[0127] V dol3 =0.946*ρ b3 -0.196*U3-0.003*DT2+0.547 (8);

[0128] V anhy2 =-0.265*ρ b3 +0.204*U3-0.003*DT2-0.779 (9);

[0129] V hal =-1.647*ρ b3 +0.053*U3-0.005*DT2+4.903 (10);

[0130] V sh3 =0.966*ρ b3 -0.061*U3+0.010*DT2-3.672 (11);

[0131] Among them, V dol3 、V anhy2 、V hal 、V sh3 are the volume contents of dolomite, anhydrite, halite and mud in the dolomite + anhydrite + salt rock + mud combination per unit volume of the formation;

[0132] ρ b3 The density logging value of the well at this depth is 2.730 g / cm 3 ;

[0133] U3 is the photoelectric absorption cross section logging value of the well at this depth, which is 11.187 B / cm 3 ;

[0134] DT2 is the acoustic logging value of the well at this depth, which is 194.093 μs / m;

[0135] The volume model corresponding to the combination of dolomite + anhydrite + salt rock + mud is V dol3 +V anhy2 +V hal +V sh3 =1;

[0136] The coefficients before each term in formula (8), formula (9), formula (10) and formula (11) are obtained by solving the relationship between the density logging curve, photoelectric absorption cross-section logging curve and acoustic logging curve established according to the volume models corresponding to the various lithologies and the volume content of each mineral composition in the dolomite + anhydrite + salt rock + mud combination in a unit volume of the formation.

[0137] From this we can get: V dol3 41.8%, V anhy2 21.0%, V hal 6.9%, V sh3 30.3%

[0138] S3: In this embodiment, the seawater salinity assignment during dolomite deposition, the seawater salinity assignment during anhydrite deposition, the seawater salinity assignment during salt rock deposition, and the volume percentage calculation formulas (8), (9), (10), and (11) of various lithologies in the dolomite + anhydrite + salt rock + mud combination established in step S2 are used to establish the seawater salinity calculation formula during dolomite + anhydrite + salt rock + mud combination stratum deposition:

[0139] S3=(k*V dol3 +n*V hal +m*V anhy2 ) / (V dol3 +V anhy2 +V hal ) (14);

[0140] Among them, V dol3 41.8%, V anhy2 21.0%, V hal 6.9%;

[0141] k is the value assigned to the seawater salinity at the time of dolomite deposition, which is determined to be 43‰ based on the current dolomite deposition environment;

[0142] m is the value assigned to the seawater salinity at the time of anhydrite deposition, which is determined to be 100‰ based on the current anhydrite deposition environment;

[0143] n is the value assigned to the seawater salinity at the time of salt rock deposition, which is determined to be 260‰ based on the current salt rock deposition environment.

[0144] It was further calculated that the salinity of seawater during the deposition of the dolomite + anhydrite + salt rock + mud combination in the carbonate rock strata was 81.7‰.

[0145] It can be seen from Examples 1-3 that the method of the present invention can also be used to obtain longitudinal salinity changes in sections, and then infer changes in seawater environment in different time periods.

[0146] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A rapid paleosalinity calculation method applicable to marine carbonate rocks, characterized in that: The method comprises the following steps: S1: Analyze the sedimentary microfacies and diagenesis of the carbonate rock formation, and then determine multiple lithological combinations of the carbonate rock formation; the multiple lithological combinations include dolomite + limestone + mud combination, dolomite + limestone + anhydrite + mud combination and dolomite + anhydrite + salt rock + mud combination; S2: Establish a calculation formula for the volume percentage of various lithologies in each lithology combination based on the volume model and well logging curve corresponding to each lithology combination; S3: using the seawater salinity values ​​assigned during the deposition of various lithologies and the volume percentage calculation formula of various lithologies in each lithology combination established in step S2, a calculation formula for the seawater salinity during the deposition of each lithology combination is established, and then the seawater salinity during the deposition of the carbonate rock formation is calculated; The calculation formula for seawater salinity when the dolomite + limestone + mudstone combination strata are deposited is: S1=(k*V dol1 +l*V lim1 ) / (V dol1 +V lim1 ) (12); The calculation formula for seawater salinity when the dolomite + limestone + anhydrite + mudstone combination strata are deposited is: S2=(k*V dol2 +l*V lim2 +m*V anhy1 ) / (V dol2 +V anhy1 +V lim2 ) (13); The calculation formula for seawater salinity when the dolomite + anhydrite + salt rock + mudstone combination strata are deposited is: S3=(k*V dol3 +n*V hal +m*V anhy2 ) / (V dol3 +V anhy2 +V hal ) (14); in, V dol1 、V lim1 are the volume contents of dolomite and calcite in the dolomite + limestone + mudstone combination per unit volume of the formation; V dol2 、V lim2 、V anhy1 are the volume contents of dolomite, calcite and anhydrite in the dolomite + limestone + anhydrite + mudstone combination per unit volume of the formation; V dol3 、V anhy2 、V hal are the volume contents of dolomite, anhydrite and halite in the dolomite + anhydrite + salt rock + mud combination per unit volume of the stratum; k is the value assigned to the seawater salinity at the time of dolomite deposition, which is determined based on the current dolomite deposition environment; l is the value of seawater salinity at the time of limestone deposition, which is determined based on the current limestone deposition environment; m is the value of seawater salinity at the time of anhydrite deposition, which is determined based on the current anhydrite deposition environment; n is the value assigned to the seawater salinity when the salt rock was deposited, which is determined based on the current salt rock deposition environment; S1 is the salinity of seawater when the dolomite + limestone + mudstone combination of carbonate strata was deposited; S2 is the salinity of seawater when the carbonate rock formations were deposited with dolomite + limestone + anhydrite + mudstone combination; S3 is the salinity of seawater when the carbonate rock formations of dolomite + anhydrite + salt rock + mud were deposited.

2. The rapid paleo-salinity calculation method applicable to marine carbonate rocks according to claim 1, wherein: The mineral composition of the dolomite+limestone+mudstone combination per unit volume of formation includes dolomite, calcite and mudstone.

3. The rapid paleo-salinity calculation method applicable to marine carbonate rocks according to claim 2, wherein: The volume percentage calculation formulas of various lithologies in the dolomite + limestone + mudstone combination are: V dol1 =2.242*ρ b1 -0.142*U1-4.077 (1); V lim1 =1.132*ρ b1 +0.261*U1-5.753 (2); V sh1 =-3.375*ρ b1 -0.119*U1+10.830 (3); Among them, V dol1 、V lim1 、V sh1 are the volume contents of dolomite, calcite and mud in the dolomite + limestone + mud combination per unit volume of the formation, respectively; ρ b1 is the density logging value; U1 is the photoelectric absorption cross-section logging value; The volume model corresponding to the dolomite + limestone + mudstone combination is V dol1 +V lim1 +V sh1 =1; The coefficients before each term in formula (1), formula (2) and formula (3) are obtained by solving the relationship between the density logging curve and the photoelectric absorption cross-section logging curve corresponding to the dolomite + limestone + mud combination established according to the volume model corresponding to the dolomite + limestone + mud combination and the volume content of each mineral component in the dolomite + limestone + mud combination in a unit volume of the formation.

4. The rapid paleo-salinity calculation method applicable to marine carbonate rocks according to claim 1, wherein: The mineral composition of the dolomite+limestone+anhydrite+mudstone combination per unit volume of stratum includes dolomite, calcite, anhydrite and mudstone.

5. The rapid paleo-salinity calculation method applicable to marine carbonate rocks according to claim 4, wherein: The volume percentage calculation formulas of various lithologies in the dolomite + limestone + anhydrite + mud combination are: V dol2 =0.715*ρ b2 -0.188*U2-0.003*DT1+1.235 (4); V lim2 =-3.609*ρ b2 +0.116*U2-0.010*DT1+10.742 (5); V anhy1 =3.120*ρ b2 +0.095*U2+0.007*DT1-10.855 (6); V sh2 =-0.226*ρ b2 -0.023*U2+0.007*DT1-0.122 (7); Among them, V dol2 、V lim2 、V anhy1 、V sh2 are the volume contents of dolomite, calcite, anhydrite and mud in the dolomite + limestone + anhydrite + mud combination in a unit volume of the formation; ρb2 is the density logging value; U2 is the photoelectric absorption cross-section logging value; DT1 is the acoustic logging value; The volume model corresponding to the dolomite + limestone + anhydrite + mudstone combination is V dol2 +V lim2 +V anhy1 +V sh2 =1; The coefficients before each term in formula (4), formula (5), formula (6) and formula (7) are obtained by solving the relationship between the density logging curve, photoelectric absorption cross-section logging curve and acoustic logging curve corresponding to the dolomite + limestone + anhydrite + mud combination established according to the volume model corresponding to the dolomite + limestone + anhydrite + mud combination and the volume content of each mineral component in the dolomite + limestone + anhydrite + mud combination in unit volume of formation.

6. The rapid paleo-salinity calculation method applicable to marine carbonate rocks according to claim 1, wherein: The mineral composition of the dolomite+anhydrite+salt rock+mud in a unit volume of formation includes dolomite, anhydrite, halite and mud.

7. The rapid paleo-salinity calculation method applicable to marine carbonate rocks according to claim 6, wherein: The volume percentage calculation formulas of various lithologies in the dolomite + anhydrite + salt rock + mud combination are: V dol3 =0.946*ρ b3 -0.196*U3-0.003*DT2+0.547 (8); V anhy2 =-0.265*ρb3+0.204*U3-0.003*DT2-0.779 (9); V hal =-1.647*ρ b3 +0.053*U3-0.005*DT2+4.903 (10); V sh3 =0.966*ρ b3 -0.061*U3+0.010*DT2-3.672 (11); Among them, V dol3 、V anhy2 、V hal 、V sh3 are the volume contents of dolomite, anhydrite, halite and mud in the dolomite + anhydrite + salt rock + mud combination per unit volume of the formation; ρ b3 is the density logging value; U3 is the photoelectric absorption cross-section logging value; DT2 is the acoustic logging value; The volume model corresponding to the combination of dolomite + anhydrite + salt rock + mud is V dol3 +V anhy2 +V hal +V sh3 =1; The coefficients before each term in formula (8), formula (9), formula (10) and formula (11) are obtained by solving the relationship between the density logging curve, photoelectric absorption cross-section logging curve and acoustic logging curve corresponding to the dolomite + anhydrite + salt rock + mud combination established according to the volume model corresponding to the dolomite + anhydrite + salt rock + mud combination and the volume content of each mineral component in the dolomite + anhydrite + salt rock + mud combination in a unit volume of the formation.