| 其他摘要 | Feldspars are one of the most aboundant kinds of minerals in the rock of the earth crust. As framework granules of sand rock reservoirs, feldspar's dissolution can form secondary pores and enhance the porodity of the deep sand stones, Especially when the sand stones have low intergranular porosity or high content of feldspars. On the base of sum of thermodynamic properties of feldspars, the effects of temperature, acidity, compostion of feldspars and organic acids (acetic acid and oxalic acid) on the dissolution of feldspars are study by the means of thermodynamic. The result indicates that: In high acidity or high basicity, the solubility of feldspars is positive correlations with acidity or basicity; in nearly neutral and neutral fluid, the solubility of feldspar is minimum. In acidic solution and Al~(3+) is main speciation of Aluminums, with temperature increase, the solubility of feldspars reduce; in basic solution and Al(OH)~-_4 is main speciation of Aluminums, with temperature increase, the solubility of feldspars increase. Disorder feldspar's solubility (high albite, sanidine) is higher than that of order feldspar's (low albite, microcline). The solubility of alkali feldspar and plagioclase feldspar solid solution is higher than that of correspond end-member feldspar. For alkali feldspar, the solubility of solid solution is posotive correlations with the content of Na-feldspar; for plagioclase feldspar, solubility increase with the increase of content of Ca-feldspar in acid solution. In basic solution, the solubility of plagioclase feldspar have no significant differences with the change of composition. Al-acetate complex only occurs in partial acid aqueous. With the increase of temperature, the pH complexion occurred decrease and the ability of acetate to complex aluminum decrease, too. Al-acetate complex's contribution to the solubility of feldspar is of negligible, not excess one time. But acetate acid can buffer pH to improve the dissolution of feldspar. Al-oxalate complex occurs in weakly alkaline to acid solutions. With the increase of temperature, the ability of oxalate to complex aluminum increases. Al-oxalate complexion can significantly enhance the solubility of feldspar by 1-2 order of magnitude in proper pH. Due to low content in solution, oxalic acid can't improve the solubility of feldspar by buffer pH in a low value. Whether acetic and oxalic acid can promote secondary porosity development depends on pH and the buffer system of fluid in basin. According to the conclusions, to understand the devolopment of secondary porosity, we must know the evolutive history of basin's fluid, the history of diagenesis, the composition of mineral and the evolution of orgnaic matter. Jurassic coal measures bed is the main reservoir in Tu-Ha basin, whose character is low porosity and low permeability or medium porosity and iow permeability. Based on the study on the history of deposition, diagenesis and fluid evolution in Tabei sag and the analysis of reservoir's character and the effect factor, we concluded: The research area is characted by close provenance, quick rate of deposition, high content of feldspaes and volcanic rock (or pyroclastic rock), low textural maturity and composition maturity, which is the basic reason led to the reservior's low porosity and low permeability. Besides the sedimentary environment and facies, the stage of diagenesis also affects the quality of reservoir in Tabei sag. The content of organic acid in the fluid is the main factor that decides the discrepancy of the quality of reservoir. Middle and Lower Jurassic upper reservoir (especially Sanjianfang formation) of Tabei sag in Tn-Ha basin have better reservoir-quality, and therrfore is the main block of oil exploration, while the lower reservoir (especially Xishangyao formation and Badaowan formation) have bad reservoir-quality and high thermoevolution degree. Which is benefit to the gas's formation and accumulation. So, we can predict that the Jurassic upper reservoir has oil and that the lower reservoir has gas. |
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