有机质热演化过程中地层压力的作用与影响

Effects and Influences of Pore Pressures on Organic Matter's Maturation

压力对有机质演化的影响长期以来争论不断,共有3种不同意见:压力对有机质演化没有影响,压力促进有机质的演化,压力抑制有机质的演化。通过对前人所做实验的实验设备、实验样品及实验结果的分析对比发现:不同实验结果主要是由于不同实验条件引起的,特别是实验系统和加压方式的不同,对实验结果影响最大,所代表的地质意义也不同。综合分析结果表明,当压力的增加表现为沉积有机质受到的有效应力增加时可以促进有机质生烃;当压力的增加表现为孔隙流体压力增加时,有机质生烃过程将受到抑制;另外,这两种情况都可能使干酪根的镜质组反射率降低,易使人得出压力增加抑制有机质演化的结论。进一步对压力影响有机质演化的成因机制进行了分析,发现在有机质演化的不同阶段因异常压力的增压机制不同,压力在有机质演化过程中所表现出来的作用也有差异。

Three contradictive conclusions on the effect of pore pressures on organic matter＇s maturation（OMM） have been obtained from previous experimental studies： pore pressures may play a positive, null and negative role on organic matter＇s maturation. After systematic review of the literature about this subject, the authors found that these contradictive conclusions probably resulted from different experiment conditions, especially the equipments＇ structures and ＂pressure＂ loaded on samples. After an analysis of the mechanisms of the effects of pressures on OMM, it is denoted that when the increase of ＂pressure＂ on the samples is the increase of effective stress, the stress acts directly on solid OM and the maturating rate will be accelerated. On the Contrary, if increasing ＂pressure＂ acts on pore fluid to augment pore pressure, then the maturating rate will be decelerated. It is previously proved that the vitrinite reflectivity corresponding to the OM appears relatively lower in these experiments of both types of cases. In actual basins, the effect of overpressures on OMM must be so different that the overpressuring occurs underground with different mechanisms at different burial depths and sedimentary environments.