CN109298064B - Carbonate rock ancient buried hill unconformity recognition method based on strontium isotope analysis - Google Patents
Carbonate rock ancient buried hill unconformity recognition method based on strontium isotope analysis Download PDFInfo
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Abstract
The inventionThe method for identifying the unconformity of the carbonate rock ancient buried hill based on the strontium isotope analysis comprises the following steps: (1) obtaining a rock core sample or a rock debris sample of carbonate rock ancient buried hill drilling; (2) subjecting the sample obtained in step (1) to isotope analysis to obtain87Sr/86The Sr ratio; (3) with the product obtained in step (2)87Sr/86The Sr ratio is an abscissa, the depth data corresponding to the sample in the step (1) is an ordinate, and an intersection graph is drawn; (4) and (4) identifying the unconformity surface of the carbonate rock ancient buried hill according to the intersection drawing in the step (3). The method for identifying the unconformity surface of the carbonate rock ancient buried hill based on the strontium isotope analysis is a method for searching and judging the unconformity surface of the carbonate rock ancient buried hill, and is used for identifying the unconformity surface of the carbonate rock ancient buried hill based on the change rule of the strontium isotope in the processes of formation and later evolution of the carbonate rock.
Description
Technical Field
The invention relates to a carbonate rock ancient buried hill unconformity recognition method based on strontium isotope analysis, and belongs to the technical field of oil-gas geological exploration.
Background
Carbonate rock ancient buried hill hydrocarbon reservoirs are an important field of marine oil and gas exploration. In the seventies of the last century, a major breakthrough of depression of 11 wells for yang-saving depression in the basin of Bohai Bay, depression of 4 wells for depression in the basin of Bohai Bay and other high-yield well positions reveals the great potential of carbonate ancient buried mountain type oil and gas reservoirs in China. Through exploration for decades, a plurality of high-yield oil and gas fields are sequentially obtained from a plurality of series of systems in a plurality of regions of large basins such as Bohai Bay, Tarim, Orthon basin and the like in China, such as an Olympic system Majiagou group in the Bohai Bay basin, an eagle mountain group in the Orthon basin in the Tarim basin, a Border dam group and the like. In recent years, with the successive high yield of the Nindong 1 well, the Annao 1 well, the thousand 16-16 wells and the Ross 2 well, the new climax of the carbonate rock ancient buried hill oil and gas exploration is raised.
The carbonate rock ancient buried hill is an oil-gas reservoir with good reservoir performance formed after a carbonate rock stratum formed by early deposition is lifted and exposed out of the earth surface due to tectonic movement in the later evolution process, is subjected to weathering leaching action and corrosion action of earth surface fluids such as atmospheric fresh water, mixed water and the like, and is superposed with tectonic cracks and other actions; the method is characterized in that the method is subjected to lifting and denudation, and a non-integration surface widely existing in an area is formed: the unconformity surface can be used as an advantageous channel for oil and gas migration on one hand; on the other hand, the strata near the unconformity, especially below the unconformity (mainly in the depth range of 0-300 meters below the unconformity) are better in physical properties than the overburden and underburden strata of the unconformity, and are main hydrocarbon reservoir segments, and the main producing zones such as the depression high-producing well promote 7, the depression high-producing well promote 2, the depression high-producing well promote 6 and the Su 6 well are all located in the depth range of 50 meters below the unconformity. Therefore, accurate identification of unconformity is a prerequisite and key for carbonate rock ancient buried hill type hydrocarbon reservoir oil and gas exploration.
The traditional method for judging the unconformity mainly comprises methods such as an earthquake recognition method, field outcrop, core observation and the like, but with the deepening of oil-gas exploration, most of shallow carbonate rock ancient buried mountains are discovered, and most of the existing exploration objects are deep buried mountains or hidden buried mountains. The buried hill type buried hill has large buried depth, complex structure and poor seismic data quality and is difficult to depict; the contrast of field outcrop is poor; and the core sampling limitation is strong, typical brecciated carbonate rocks near the unconformity are difficult to observe, and the coring sample is often rock debris due to technical limitation and cost control in addition to deep-layer and ultra-deep layers, so that the difficulty of geological identification is greatly increased.
Therefore, providing a carbonate rock ancient buried hill unconformity recognition method based on strontium isotope analysis has become an urgent technical problem to be solved in the field.
Disclosure of Invention
In order to solve the defects and shortcomings, the invention aims to provide a carbonate rock ancient buried hill unconformity identification method based on strontium isotope analysis.
In order to achieve the above object, the present invention provides a method for identifying unconformity of ancient buried hill of carbonate rock based on strontium isotope analysis, wherein the method for identifying unconformity of ancient buried hill of carbonate rock based on strontium isotope analysis comprises the following steps:
(1) obtaining a rock core sample or a rock debris sample of carbonate rock ancient buried hill drilling;
(2) subjecting the sample obtained in step (1) to isotope analysis to obtain87Sr/86The Sr ratio;
(3) with the product obtained in step (2)87Sr/86The Sr ratio is an abscissa, the depth data corresponding to the sample in the step (1) is an ordinate, and an intersection graph is drawn;
(4) and (4) identifying the unconformity surface of the carbonate rock ancient buried hill according to the intersection drawing in the step (3).
According to the embodiment of the invention, in the method, because the carbonate rock texture is complex and is easily influenced by the later diagenesis transformation, the argillaceous crystal matrix which is most representative of the intergrown-quasi-intergrown period and is weak by the later diagenesis transformation is selected as an experimental sample.
According to a specific embodiment of the present invention, in the method, the obtaining of the core sample of the carbonate rock ancient buried hill drilling comprises: selecting a relatively-developing area of the core matrix, and drilling a powder sample by using a millimeter-grade micro-sampling drilling machine.
According to a specific embodiment of the present invention, in the method, the obtaining of the core sample of the carbonate rock ancient buried hill drilling comprises: and selecting a relatively-developing area of the core matrix according to research needs (considering well positions, horizons and specific research requirements) and sample characteristics, and drilling a powder sample by using a millimeter-scale micro-sampling drilling machine.
In the embodiment of the present invention, the millimeter micro-sampling drilling machine may be, for example, a Strong 204 millimeter micro-sampling drilling machine from Precision.
According to a specific embodiment of the present invention, in the method, the obtaining of the rock debris sample of the carbonate rock ancient buried hill drilling comprises:
1) selecting the rock debris which can represent the target layer most;
2) washing the sample to remove impurities including mud;
3) the samples were crushed and sieved.
According to a specific embodiment of the present invention, in the method, the selection principle of the selection in step 1) includes: a) the color and the size of the rock debris are the dominant components; b) obvious tooth marks are formed on the section of the rock debris.
According to a specific embodiment of the present invention, in the method, the sample washed in step 2) may be washed using an ultrasonic washer, and the sample crushed using an agate-milling bowl in step 3).
According to a particular embodiment of the invention, in said method, said sieving in step 3) is a 200 mesh sieve.
According to a specific embodiment of the present invention, in the method, the isotopic analysis of the sample obtained in step (1) in step (2) comprises: and (3) carrying out isotope analysis on the sample obtained in the step (1) by adopting a thermal ionization isotope ratio mass spectrometer (TIMS) or a multi-receiving cup plasma mass spectrometer.
In the embodiment of the present invention, the amount of the sample used for the isotope analysis is generally about 200mg, and before the isotope analysis is performed on the sample, the sample is further subjected to a chemical purification operation, which is a means of ordinary skill in the art.
According to a specific embodiment of the present invention, in the method, if the core sample configuration is complex, the isotopic analysis of the sample obtained in step (1) in step (2) comprises: and directly carrying out in-situ micro-area analysis on the core solid sample by using a multi-receiving cup plasma mass spectrometer.
According to the specific embodiment of the invention, in the method, if the core sample has a complex structure and the micro-drilling sampling is difficult, the multi-receiving cup plasma mass spectrometer can be used for directly performing in-situ micro-area analysis on the core solid sample, and a slicer, a piece grinder and the like are required to prepare a test sample meeting the requirements before the in-situ micro-area analysis; the specific dimensional specification of the test sample is based on the size of the laser ablation cell of the laser connected to the multi-receiving cup plasma mass spectrometer (MC-ICP-MS) used for the test.
In embodiments of the invention, the test sample may be, for example, 50 μm to 1000 μm thick; the size is as follows: a rectangular parallelepiped sample of 0.5cm by 0.5cm to 7.5cm by 2cm or 0.5cm by 0.5cm to 4.5cm by 3cm, or a circular sample within the above specification range.
According to a specific embodiment of the present invention, in the method, if the rock debris sample particles are large, the isotope analysis of the sample obtained in the step (1) in the step (2) comprises: after the rock debris which can represent the target layer most is selected, the rock debris is adhered to a glass plate by using an adhesive to manufacture a rock debris slice, and then the in-situ micro-area analysis of the core solid sample is directly carried out by using a multi-receiving cup plasma mass spectrometer.
According to a specific embodiment of the present invention, in the method, the selection principle of the selection comprises: a) the color and the size of the rock debris are the dominant components; b) obvious tooth marks are formed on the section of the rock debris.
According to a specific embodiment of the invention, in the method, if the rock debris sample particles are large, after the rock debris which can represent the target layer most is selected, the rock debris is adhered to a glass plate by using an adhesive to prepare a rock debris slice, and then the in-situ micro-area analysis of the rock core solid sample is directly carried out by using a multi-receiving cup plasma mass spectrometer; before in-situ micro-area analysis, a test sample meeting the requirements is prepared by using a slicing machine, a sheet grinding machine and the like; the specific dimensional specification of the test sample is based on the size of the laser ablation cell of the laser connected to the multi-receiving cup plasma mass spectrometer (MC-ICP-MS) used for the test.
In embodiments of the invention, the test sample may be, for example, 50 μm to 1000 μm thick; the size is as follows: a rectangular parallelepiped sample of 0.5cm by 0.5cm to 7.5cm by 2cm or 0.5cm by 0.5cm to 4.5cm by 3cm, or a circular sample within the above specification range.
According to a specific embodiment of the present invention, in the method, the step (4) of identifying the unconformity of the carbonate rock ancient buried hill according to the cross plot drawn in the step (3) includes:
determine the presence on the cross-plot87Sr/86Peak value of Sr ratio, if at formation boundary, the87Sr/86The peak value of the Sr ratio is obvious, and the Sr ratio is considered to be87Sr/86The depth range corresponding to the peak value of the Sr ratio is the unconformity of the target layer of the carbonate rock ancient buried hill.
The carbonate rock ancient buried hill is firstly lifted and exposed to weathering, leaching and denudation, and later-stage settlement is subjected to redeposition, and the differences of the carbonate rock ancient buried hill on lithology are obvious, namely, the carbonate rock ancient buried hill has an obvious stratum boundary.
According to an embodiment of the present invention, in the method, the judgment cross map appears87Sr/86Peak Sr ratio, comprising: judging the appearance of the cross plot by combining the sample background and the regional geological background87Sr/86Peak value of Sr ratio.
In the specific embodiment of the present invention, the sample background and the regional geological background are all conventionally available to those skilled in the art.
According to a particular embodiment of the invention, in said method, said87Sr/86The peak value of the Sr ratio obviously means that the peak value is 0.712-0.740.
Sr is a ubiquitous element in nature, with four stable isotopes:84Sr、86Sr、87Sr、88sr, wherein87Sr is a stable isotope of a radioactive origin and is derived from87Radioactive decay of Rb. In the actual use process, mainly utilize87Sr/86The Sr ratio changes with the depth, and the existence of unconformity is judged according to the following:
1. the residual time of Sr in seawater (about 2.5Ma) is much longer than the mixing time of seawater (about 1.6Ka), so that the marine phase Sr element is uniform in isotope composition in any time all over the world;
2、87Sr/86the Sr ratio is mainly controlled by the strontium material source and is not influenced by the fractionation of chemical and biological isotopes. After Sr in seawater is added to marine carbonate rock in the same-growth-quasi-same-growth period in a similar manner, unless exogenous Sr is added in the later period87Sr/86The Sr ratio value is kept stable for a long time and is consistent with the seawater value in the same period;
3. the Sr source comprises shell source Sr and valance source Sr, wherein the shell source Sr is mainly from a land surface weathering system, and the valance source Sr is mainly from a hot liquid circulation system in the ocean;
4. during the process of lifting, exposing and forming an unconformity surface of the carbonate rock ancient buried hill, a large amount of debris such as quartz, feldspar, clay and the like can be brought in due to the wind effect, the river effect and the like of an earth surface weathering system. The Sr in the shell source material is added into carbonate rock minerals such as calcite and dolomite in a similar form, so that the early formed strontium isotope composition is changed, and the increase of Sr is realized87Sr/86The Sr ratio.
In the production application process, a sample (rock core or rock debris) is selected to obtain87Sr/86After the Sr ratio, the87Sr/86The Sr ratio is plotted on the abscissa and the depth is plotted on the ordinate as a data relationship (cross plot). The existence of the unconformity can be judged by the peak value appearing on the data map. Marine carbonate rock87Sr/86The Sr ratio is generally lower and is 0.707-0.711; without integrating samples below the vicinity of the surface87Sr/86The Sr ratio is often larger than 0.711, and the peak value can reach 0.712-0.740, even higher.
The method for identifying the unconformity surface of the carbonate rock ancient buried hill based on the strontium isotope analysis is a method for searching and judging the unconformity surface of the carbonate rock ancient buried hill, and is based on the change rule of the strontium isotope in the processes of formation and later evolution of the carbonate rock, wherein the strontium isotope is mainly utilized to be free from chemistry, biology and buryingThe reservoir-forming process is mainly governed by the source of the material. During the weathering exposure of the carbonate rock ancient buried hill, the addition of a large amount of shell source strontium changes the strontium isotope ratio, so that87Sr/86Sr is greater and is in87Sr/86The intersection of the Sr ratio and the depth shows a peak value, thereby identifying an unconformity.
Drawings
Fig. 1 is a schematic process flow diagram of a specific process flow of the carbonate rock ancient buried hill unconformity identification method based on strontium isotope analysis according to embodiment 1 of the present invention;
FIG. 2 shows the results of example 1 of the present invention87Sr/86An intersection of Sr with depth, and a comparison of the intersection with a lithology histogram of a synchysis 4 well;
FIG. 3 is a schematic view of unconformity (breccid limestone) and discontinuous deposition (breccid dolomite) observed in field profile of Zhao-Wuzhuang Zhuang (mountain, Changshan) and Handan Peak-ao pottery systems in Tang mountain;
FIG. 4 is a diagram of a Utility 4 well in example 1 of the present invention87Sr/86The change of Sr with depth and the comparison of the change of Sr with the change of Fe and Sr element contents with depth are shown schematically.
Detailed Description
In order to clearly understand the technical features, objects and advantages of the present invention, the following detailed description of the technical solutions of the present invention will be made with reference to the following specific examples, which should not be construed as limiting the implementable scope of the present invention.
Example 1
The embodiment provides a method for identifying an unconformity surface of a carbonate rock ancient buried hill based on strontium isotope analysis, which takes a depression in a Bohai Bay basin wing as an example to verify the effectiveness of the carbonate rock ancient buried hill unconformity surface, and a specific process flow chart of the method is shown in FIG. 1.
The depression in the late stage of Ordovician pottery in the Ji is affected by the movement of the Carinodon, the whole area is lifted out of the earth surface, and after one hundred million years of weathering leaching and degradation in the Zhi-Shi basin, the stone and charcoal rise and fall again to receive debris deposition, so that an unconformity surface in the whole area is formed. The overburden stratum of the unconformity surface is a carboniferous indigenous group, and the underburden is a main reservoir type and a main purpose stratum of the depressed ancient buried mountain type oil-gas reservoir in the hope, such as any 4 wells and 1 well for Anmo, and has huge potential according to the fact that the denudation strength is an Ordovician peak group or a Majia ditch group and the like. However, over the years of exploration, the ancient buried mountains in the shallow layer are basically explored, and the rest are mostly buried deep buried mountains or hidden buried mountains with the buried depth of more than 5000 meters, so that the discovery is difficult. Therefore, judging the unconformity of the ancient buried hill of the Ordovician carbonate rock and finding the ancient buried hill of the carbonate rock are important difficulties in the next oil-gas exploration.
The Ugu 4 well is a carbonate rock ancient buried mountain exploration well which is arranged at the north of the depression in the wing and is designed for exploring an Ordovician ancient buried mountain oil and gas reservoir. Due to the large burial depth (over 5000 meters) and cost control, only the cuttings sample was taken.
1) Selecting the rock debris which can represent the target layer most; the selection principle is as follows: a) the color and the size of the rock debris are the dominant components; b) obvious tooth marks are formed on the section of the rock debris.
2) Cleaning the sample by using an ultrasonic cleaning instrument to remove impurities including mud;
3) crushing the sample by using an agate grinding bowl, sieving the sample by using a 200-mesh sieve, and taking 200mg of the sieved powder sample to send to a strontium isotope analysis room (carbonate rock reservoir key laboratory of China oil and gas Limited company, Sr isotope analysis instruments and models are as follows: thermal ionization isotope ratio mass spectrometer, Triton Plus; fe. The Sr element content analytical instrument and the model are as follows: x fluorescence Spectroscopy, Panalytical Axios XRF), analysis87Sr/86Sr ratio, data are shown in table 1 below.
TABLE 1
According to the data in Table 1, to87Sr/86Sr ratioThe value is plotted on the abscissa and the sampling depth is plotted on the ordinate87Sr/86Sr and depth, and comparing the cross plot with the lithology histogram of the ancients 4 well, the cross plot, the lithology histogram of the ancients 4 well and the effect of the comparison are shown in fig. 2.
As can be seen from fig. 2, the depth is from shallow to deep,87Sr/86the Sr ratio has 4 peaks, wherein,87Sr/86the Sr ratio is at its maximum at about 5000 m (4998 m), with a maximum of 0.719353, and decreases with depth (0.711376) to a value slightly above the subject background (0.709-0.710), after which there are three secondary peaks with increasing depth.
The comprehensive geological analysis of the data and the lithologic histogram of the Ugu 4 well and the like shows that:87Sr/86the maximum Sr ratio (4998-5070) is at the junction between the aotao peak group and the carbolite Benxi group, the downward deposition discontinuity 1 and the deposition discontinuity 2 are the deposition discontinuities at the high-altitude areas of the peak group and the Majia ditch group, and the upper and lower Majia ditch groups inside the Majia ditch group, and the bottom deposition discontinuity 3 is the deposition discontinuity formed by the formation lifting (high-altitude area) caused by late distance movement of the leuca group, which can be directly verified by the field outcrop section, as shown in fig. 3.
As can be seen from FIG. 3, karst weathering crust developed at the interface between the Audo peak group and the benxi rock-charcoal group, which is represented by gravelly limestone, and high-angle seams and wide seams are developed, and the cracks are completely filled; in addition, three sets of typical breccid dolomite are found at the lower layer of Ordovician, which correspond to the boundary between the Armand mountain group and the lower Ma ditch group, the boundary between the lower Ma ditch group and the upper Ma ditch group, and the boundary between the upper Ma ditch group and the peak-peak group, respectively, are typical deposition discontinuity products. This confirms the judgment of fig. 2 for the inconformity surface of the syncretic 4 well by the Sr isotope.
Meanwhile, analyzing corresponding Fe and Sr contents, Fe contents, Sr contents and Fe content in rock debris samples in the Ugu 4 well87Sr/86FIG. 4 shows the relationship between Sr and depth
As can be seen in fig. 4, at the non-integration plane,87Sr/86peak of SrThe value is more consistent with the peak value of the Fe content, and the Sr content has no obvious peak value; and in the deposition intermission, except that a peak value of the Fe content appears at the corresponding position of the lower Ma ditch group and the upper Ma ditch group, other peaks are not obvious. This indicates the discrimination of the unconformity surface, strontium isotope (b) ((b))87Sr/86Sr) has better analysis effect, which is consistent with the reality.
Claims (9)
1. A carbonate rock ancient buried hill unconformity recognition method based on strontium isotope analysis is characterized by comprising the following steps:
(1) obtaining a core sample or a rock debris sample of a carbonate rock ancient buried hill well drilling, wherein the sample is a mud crystal matrix sample which can represent the most of a syngeneic-quasi-syngeneic period and is weak to later-stage diagenesis transformation;
the principles for selecting the rock debris samples include: a) the color and the size of the rock debris are the dominant components; b) obvious tooth marks are formed on the section of the rock debris;
(2) subjecting the sample obtained in step (1) to isotope analysis to obtain87Sr/86The Sr ratio;
(3) with the product obtained in step (2)87Sr/86The Sr ratio is an abscissa, the depth data corresponding to the sample in the step (1) is an ordinate, and an intersection graph is drawn;
(4) identifying the unconformity surface of the carbonate rock ancient buried hill according to the intersection drawing in the step (3), comprising the following steps of:
determine the presence on the cross-plot87Sr/86Peak value of Sr ratio, if at formation boundary, the87Sr/86The peak value of the Sr ratio is obvious, and the Sr ratio is considered to be87Sr/86The depth range corresponding to the peak value of the Sr ratio is the unconformity surface of the target layer of the carbonate rock ancient buried hill;
the above-mentioned87Sr/86The peak value of the Sr ratio clearly means that the peak value is greater than 0.711.
2. The method of claim 1, wherein obtaining a core sample of a carbonate rock ancient buried hill well bore comprises: selecting a relatively-developing area of the core matrix, and drilling a powder sample by using a millimeter-grade micro-sampling drilling machine.
3. The method of claim 1, wherein the obtaining of the sample of cuttings from the carbonate rock drilling of the ancient buried hill comprises:
1) selecting the rock debris which can represent the target layer most;
2) washing the sample to remove impurities including mud;
3) the samples were crushed and sieved.
4. The method of claim 3, wherein the sieving in step 3) is 200 mesh sieving.
5. The method according to any one of claims 1 to 4, wherein the step (2) of performing isotope analysis on the sample obtained in the step (1) comprises: and (3) carrying out isotope analysis on the sample obtained in the step (1) by adopting a thermal ionization isotope ratio mass spectrometer or a multi-receiving cup plasma mass spectrometer.
6. The method according to claim 1, wherein if the core sample configuration is complex, the step (2) of performing isotope analysis on the sample obtained in the step (1) comprises: and directly carrying out in-situ micro-area analysis on the core solid sample by using a multi-receiving cup plasma mass spectrometer.
7. The method according to claim 1 or 3, wherein if the rock debris sample particles are large, the isotope analysis of the sample obtained in the step (1) in the step (2) comprises: after the rock debris which can represent the target layer most is selected, the rock debris is adhered to a glass plate by using an adhesive to manufacture a rock debris slice, and then the in-situ micro-area analysis of the core solid sample is directly carried out by using a multi-receiving cup plasma mass spectrometer.
8. The method of claim 1, wherein the determining the presence on the cross-plot is performed by a computer87Sr/86Peak Sr ratio, comprising: judging the appearance of the cross plot by combining the sample background and the regional geological background87Sr/86Peak value of Sr ratio.
9. The method of claim 1, wherein the step of applying the coating comprises applying a coating to the substrate87Sr/86The peak value of the Sr ratio obviously means that the peak value is 0.712-0.740.
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