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CN-122017204-A - Tracing method for geothermal liquid activity of sedimentation basin

CN122017204ACN 122017204 ACN122017204 ACN 122017204ACN-122017204-A

Abstract

The invention discloses a tracing method for geothermal liquid activity of a sedimentation basin, and belongs to the technical field of geochemistry and isotope tracing. The tracing method comprises the steps of preprocessing a mixed mineral sample, separating and purifying lithium elements, measuring delta 7 Li carb values, carrying out correlation analysis on delta 7 Li carb values and main trace element characteristics of the sample, correcting measured delta 7 Li carb values of the mixed mineral sample, carrying out correlation analysis on corrected data of the mixed mineral sample, hydrothermal activity indexes and anti-weathering indexes, determining delta 7 Li After correction background values in a research layer sequence, and judging a hydrothermal activity enhancement period, a hydrothermal activity weakening period or a non-hydrothermal dominant period by comparing the lithium isotope ratio of a continuous layer section with the difference of the background section values. The method has the advantages of continuous high resolution, wide temperature range sensitive response, clear mechanism, strong anti-interference capability and strong universality.

Inventors

  • CAO JIAN
  • Xia Liuwen
  • ZHANG JINGKUN
  • ZHANG RUIJIE

Assignees

  • 南京大学

Dates

Publication Date
20260512
Application Date
20260414

Claims (10)

  1. 1. A method for tracing geothermal fluid activity of a sedimentary basin, comprising the steps of: S1, carrying out pretreatment, separation and purification of lithium elements and delta 7 Li carb value measurement on a mixed mineral sample; S2, carrying out correlation analysis on the delta 7 Li carb value and the main trace element characteristic of the sample, and when delta 7 Li carb has no obvious correlation with the main trace element characteristic of the sample, entering a step S3 to carry out hydrothermal intensity judgment; S3, correcting the measured delta 7 Li carb value of the mixed mineral sample by the following correction formula: δ 7 Li After correction =δ 7 Li carb -k×[f Alkali /(1+f Alkali )]; Wherein f Alkali is the content ratio of alkali mineral to calcium magnesium carbonate; k represents the inherent difference in fractional values of the two classes of minerals, k=Δ 7 Li Alkali -Δ 7 Li Calcium and magnesium ; S4, carrying out correlation analysis on delta 7 Li After correction value data of the mixed mineral sample, a hydrothermal activity index and an anti-weathering index to verify whether a cooperative change relation exists among the three, thereby confirming the reliability and mechanism consistency of delta 7 Li After correction value response to hydrothermal activity; S5, determining a background value of delta 7 Li After correction value in the research layer sequence, and judging the hydrothermal activity enhancement period, the hydrothermal activity weakening period or the non-hydrothermal dominant period by comparing the difference between the lithium isotope ratio of the continuous layer section and the background section value.
  2. 2. A tracing method according to claim 1, wherein in step S1, the mixed mineral sample is an unconsolidated core taken from a sedimentary basin.
  3. 3. A tracing method according to claim 1, wherein in step S1, the specific operation of pre-treating the mixed mineral sample is: washing, drying and crushing the mixed mineral sample, and then using 0.5-1M ammonium acetate solution to shake and rinse the mixed mineral sample; and then the residual sample is subjected to oscillation reaction for 2-6 hours at room temperature by using 0.5-1M acetic acid solution, the acetic acid leaching solution is collected, and the nitric acid system is converted after evaporation.
  4. 4. The tracing method according to claim 1, wherein in step S1, the specific operations of separation and purification of lithium element are: purified lithium solution was obtained using AG50W-X12 cation exchange resin column with 0.15-0.3M hydrochloric acid as eluent.
  5. 5. A tracing method according to claim 1, wherein in step S1, the specific operation of lithium isotope ratio determination is: Measuring the purified lithium solution by MC-ICP-MS, performing instrument quality fractionation correction by using international standard substances USGS LSVEC by adopting a standard-sample crossing method, and expressing the result by delta 7 Li carb values (per mill); the calculation formula is that ：δ 7 Li carb = [( 7 Li/ 6 Li) Sample of /( 7 Li/ 6 Li) LSVEC -1]×1000.
  6. 6. The tracing method according to claim 1, wherein in step S2, when the mixed mineral sample is collected from the sedimentary basin, it is confirmed that δ 7 Li carb has no significant correlation with Al/Ca, rb/Ca, mn/Ca, mg/(ca+mg).
  7. 7. A tracing method according to claim 1, wherein in step S3, the k value is 0.1-1.0%.
  8. 8. A tracing method according to claim 1, wherein in step S4, the hydrothermal activity index comprises: Europium positive anomaly: eu/eu=2eu N /(Sm N + Gd N ); Wherein Eu N 、Sm N and Gd N are the Eu, sm and Gd contents after PAAS standardization; the content of alkali minerals refers to the total content of the alkali minerals, and abnormal enrichment of the alkali minerals often indicates deep hydrothermal substance input; The reverse weathering index includes: the content of the autogenous silicon is Si auto =Si Sample of -Al Sample of multiplied by 3.11; Wherein 3.11 is the Si/Al background ratio of the upper crust, and positive values represent the autogenous silicon of non-debris sources and directly reflect the concentration of water soluble silicon; The high ratio of Li/Al to K/Al, significantly above the UCC background, is a direct geochemical evidence of the formation of lithium-rich and potassium-rich authigenic clay minerals by reverse weathering.
  9. 9. The tracing method according to claim 8, wherein in step S4, a multi-index cooperative variation evidence chain is established by systematically analyzing the correlation between δ 7 Li After correction and hydrothermal activity index and anti-wind index: If delta 7 Li After correction is significantly positively correlated with the hydrothermal activity index and the anti-wind index, it shows that delta 7 Li After correction can effectively respond to the anti-wind effect driven by the hydrothermal activity, and the reliability of delta 7 Li After correction as the hydrothermal activity tracing index is verified, and the step S5 can be entered for hydrothermal intensity judgment.
  10. 10. The tracing method according to claim 8, wherein in step S5, the background value is delta 7 Li carb average value of no obvious hydrothermal index layer segment, no obvious hydrothermal index layer segment is layer segment which simultaneously satisfies Eu/Eu < 1.05, alkali mineral content < 5%, and anti-weathering index satisfies that Si auto is within 3±3%, K/Al is within 0.3±0.3, and Li/Al is within 3±3 ppm/%; when the delta 7 Li carb average value of the continuous layer segments is larger than the sum of the background value and twice of the standard deviation, judging that the continuous layer segments are in the hydrothermal activity enhancement period; When the delta 7 Li carb average value of the continuous layer segments is equal to the sum of the background value and twice of the standard deviation, judging the continuous layer segments as a non-hydrothermal dominant period; when the delta 7 Li carb average value of the continuous layer segments is lower than the sum of the background value and twice the standard deviation, the hydrothermal activity weakening period is judged.

Description

Tracing method for geothermal liquid activity of sedimentation basin Technical Field The invention belongs to the technical field of geochemistry and isotope tracing, and particularly relates to a tracing method for geothermal liquid activity of a sedimentation basin. Background The hydrothermal activity in the sedimentary basin has key influence on oil gas generation, mineral enrichment and ancient environment evolution, and the accurate evaluation of the hydrothermal activity intensity has important significance on oil gas exploration, shale gas reservoir prediction and mineral deposit cause research. Currently, the tracing technology generally relied on in the industry mainly covers three major categories, including specific minerals (such as zeolite and dawsonite), element ratios (such as Fe/Ti), rare earth element anomalies (such as Eu anomalies, and Eu/Eu is usually greater than 1.05 as a criterion), and radioactive isotopes (such as 87Sr/86 Sr). However, these methods suffer from the significant disadvantage that, first, index specialization is generally weak. Many widely used indices, such as the Fe/Ti ratio and 87Sr/86 Sr values, are essentially "mixed indices" of volcanic-hydrothermal activity and do not effectively distinguish between the specific properties of the deep matter source (e.g., fe/Ti). Second, the sensitivity and temporal-spatial continuity of the index are severely inadequate. For example, the formation of Eu positive anomalies typically requires a higher hydrothermal temperature (> 200 ℃) and therefore it is insensitive to moderate to low temperature hydrothermal activity. More importantly, most existing indicators (such as first appearance of specific minerals, abnormal enrichment of certain metallic elements) are recorded in an event or intermittently. They can mark the "presence or absence" or "peak" of hydrothermal activity, but cannot faithfully record the dynamic fluctuations and long-term evolution trend of the relative intensity of hydrothermal activity with high resolution like a continuous curve. In summary, the art has long lacked a new technology for realizing continuous, sensitive, exclusive and strong anti-interference tracing on hydrothermal activity in sedimentary basins, especially on intensity changes thereof. The technical bottleneck limits the fine description of the time-space evolution law of the hydrothermal activity and also limits the deep understanding of the roles of the hydrothermal activity in resource enrichment and environment evolution. Disclosure of Invention Aiming at the defects existing in the prior art, the technical problem to be solved by the invention is that the existing hydrothermal activity tracing technology has defects in continuity, sensitivity and specificity, and the invention provides a tracing method for the hydrothermal activity of a sedimentation basin, which has the advantages of continuous high resolution, wide temperature range sensitivity response, clear mechanism, strong anti-interference capability and strong universality. In order to solve the technical problems, the invention adopts the following technical scheme: In a first aspect of the invention, there is provided a method of tracking the geothermal fluid activity of a sedimentation basin, comprising the steps of: S1, carrying out pretreatment, separation and purification of lithium elements and delta 7Licarb value measurement on a mixed mineral sample; S2, carrying out correlation analysis on the delta 7Licarb value and the main trace element characteristic of the sample, and when delta 7Licarb has no obvious correlation with the main trace element characteristic of the sample, entering a step S3 to carry out hydrothermal intensity judgment; S3, correcting the measured delta 7Licarb value of the mixed mineral sample by the following correction formula: δ7Li After correction =δ7Licarb-k×[f Alkali /(1+f Alkali )]; Wherein f Alkali is the content ratio of alkali mineral to calcium magnesium carbonate; k represents the inherent difference in fractional values of the two classes of minerals, k=Δ 7Li Alkali -Δ7Li Calcium and magnesium ; S4, carrying out correlation analysis on delta 7Li After correction value data of the mixed mineral sample, a hydrothermal activity index and an anti-weathering index to verify whether a cooperative change relation exists among the three, thereby confirming the reliability and mechanism consistency of delta 7Li After correction value response to hydrothermal activity; S5, determining a background value of delta 7Li After correction value in the research layer sequence, and judging the hydrothermal activity enhancement period, the hydrothermal activity weakening period or the non-hydrothermal dominant period by comparing the difference between the lithium isotope ratio of the continuous layer section and the background section value. Preferably, in step S1, the mixed mineral sample is an unconsolidated core taken from a sedimentary basin.