塔里木盆地有机酸来源、分布及对成岩作用的影响

塔里木盆地寒武-第三系储层油田水实测表明:有机酸浓度高峰值分布于４３００ｍ以下及不整合面附近；来源于干酪根热成熟作用、原油微生物降解和热化学硫酸盐还原作用等；有机酸浓度多占总碱度３０%～７０%，可达９２%，对油田水的ｐＨ值影响甚大。油田水中Ａｌ浓度在含油层中可高达３.１～５.４ｍｇ/Ｌ，Ａｌ可能以有机络合物形式存在。用国际上常用的水-岩反应地化软件ＳＯＬＭＩＮＥＱ.８８，对石炭、三叠和侏罗系主要造岩矿物溶解-沉淀进行模拟，结果表明，斜长石在储层温度８１℃～１３８℃范围内均可发生溶解作用；低于１３２℃时，高岭石处于超饱和状态，可沉淀；在有机酸参与下，斜长石溶解是该区次生孔隙的主要成因。这与岩观察吻合。

The Source, Distribution of Organic Acids in Oilfield Waters and Their Effects on Mineral Diagenesis in Tarim Basin

The source, distribution and effects of organic acid anions( OAA) in sedimentary basins were notsystematically studied and were poorly understood in China. The paper presented 185 OAA data and 100samples of dissolved Al, Si, Ba and other 12 elements in oilfield waters from Cambrian to Tertiary reser-voirs of the Tarim basin. The above data showed that OAA of high concentration (> 800× 10- 6) oc-curred in reservoirs deep than 4 300 m and nearby unconformities. OAA are thought to be sourced fromthermal maturation of kerogen biodegradation and thermochemical sulfate reduction of crude oils, whichis supported by high reservoir temperature( 115 ℃ to 139 ℃ ), abundance of dissolved H 2 S in oilfield waters( 600 × 10- 6to 780 × 10- 6), and occurrence of tas mats. OAA may contribute 30 % ～ 70 %, up to 92 % oftotal alkalinity; thus it controls pH values of oilfield waters. The concentration of dissolved aluminumranges up from 3. 1 mg /L to 5. 4 mg /L in oil- bearing reservoirs, and it indicates the existence of organ-ic- complexing agents.Selected mineral equilibrium calculation from Carboniferous, Triassic and Jurassic reservoirs wascarried out by computer code SOLMINEQ. 88 for geochemical modeling of water- rock interaction, andshowed that oligioclase is unsaturated and can be dissolved at 81 ℃ to 138 ℃ while kaolinate is over- sat-urated and tends to precipitate at the temperature lower than 132 ℃; quartz is near equilibrium; K-feldspar is stable between 81 ℃ to 105 ℃. From the above, it can be concluded that oligioclase dissolu-tion and kaolinite precipitation are the main diagenesis, and control secondary porosity. And it is consis-tent with the petrographic observation.