四川广元天井山古油藏剖析

Characteristics of Tianjingshan Destroyed Oil Reservoir in Guangyuan Area,Sichuan

根据赋存方式,天井山古油藏的沥青主要可分为:(1)下泥盆统平驿铺组石英砂岩中的孔隙型沥青;(2)下寒武统杂砂岩中的孔隙型沥青;(3)下寒武统杂砂岩中顺层分布的"扁豆状"沥青;(4)下寒武统脉沥青。这几组沥青的反射率分别为:1.07%(一期),0.23%(二期);3.99%;0.98%(一期),0.23%(二期);0.37%～0.42%。氯仿沥青"A"的含量较高,其中下泥盆统沥青可达4244.1×10^(-6),反映沥青的演化程度较低。低反射率的沥青不是源自下古生界自身,而是源自较新的地层;有机地球化学资料显示其源于二叠系和下三叠统。两组低反射率的沥青还反映了区内存在两期油气成藏与演化。下泥盆统石英砂岩沥青含量分布自下而上表现为高—较高—低—较高—低(以至无)的变化现象,其间并无隔层,这可能是由天然气的幕式充注及气洗作用和构造抬升后处于开启环境的水洗氧化、生物降解等多因素综合作用的结果。

The bitumen in the destroyed Devonian and Cambrian sand- stone reservoirs at Tajinshan,based on the occurrence of it, can be divided into four groups,which show values of R_o 1.07% (D_1p,the 1st stage)and 0.23% (D_1p,the 2nd stage),R_o 3.99%(∈1);R_o 0.98% (∈_1,the 1st stage)and 0.23%(∈_1,the2ndstage);and Rvo 0.37 %～0.42 % (∈_1). Chloroform bitumen"A"is high (up to 4 244.1×10^(-6) in D_1 bit- umen),which indicates low grade of bitumen evolution and two stages of hydrocarbon accumulation and evolution in this area.The data of organic geochemistry indicate that the bitu- men with low reflectivity derived from earlier Permian and Low- er Triassic carbonate source rocks,instead of Lower Paleozoic rock of own itself.Content of bitumen in the Lower Devonian quartz sandstone shows a gradual change of high—higher—low —higher—low (to absent) distribution from the bottom to the top,in which there is none of interval beds,as a result of com- bining actions of the intermittent-filling and gas-washing of nat- ural gas and the water-washing and biodegradation after tec- tonic uplifting,