靖安油田上三叠统长6储层成岩作用研究

Diagenetic Characteristics of the Chang 6 Oil-bearing Interval of the Upper Triassic in the Jin'an Oilfield,Ordos Basin

通过对5条剖面和11口探井的综合研究确定了长6储层的成岩作用阶段,对影响储层物性重要的自生矿物形成进行了探讨,认为靖安油田上三叠统延长组6段储层经历了压实、胶结、溶蚀等一系列复杂的成岩作用,成岩现象十分丰富,特征明显。从储层成岩作用研究表明,早成岩期的压实作用、多种矿物胶结作用是使储层物性变差、孔隙度降低的两个重要的成岩作用;而溶蚀作用,特别是浊沸石胶结的溶蚀是储层物性变好的重要成岩控制因素。

Abstract An intensive study has been done in the Jingan oil-field by observing five cross sections and eleven wells, analyzing 108 samples with thin section, cathodelumination, SEM, X-ray diffraction and related test materials. It is believed that Chang 6 oil-beating beds underwent a series of diagenesis, such as compaction, cementation, dissolution and so on. The diagenetic phenomenona are very rich and the According to the analysis of petrology, it is found that Chang 6 diagenetic oil-beating characters are very obvious and complex. interval is composed of middle size sand- stone and fine sub-sand. After analyzing of the whole situation, granularity is much smaller. Little of them are rock fragments feldspar sandstone. Diagenesis of Chang 6 oil-beating interval can be divided to two stages, early and late stage. Furthermore, they can also be subdivided into two sub-phases, A and B sub-phase. The diagenetic processes that control reservoir properties include the mechanic compaction, cementation and dissolution of grains. At the early diagenesis, mechanical and chemical compaction is very strong, which reduced the primary porosity. Cementation is an important factor to reservoir, including carbonate, clay and laumontite cementation and so on. Laumontite is special mineral in Ordos Basin and is very abundant. Cementation filled the space among grains and blocked the path between grains are another factors resulting in sandstone compaction and very low permeability. But, at the same time, cements also protect grains from further compaction. At the late diagenesis phase, the dissolution of framework grains, especially the dissolution of feldspar and laumontite, is the key to form secondary porosity. They changed the porosity characteristics of sandstone; engendering new benefit storing beds consisted with secondary porosity. Feldspar is dissolved very commonly and severly. They often form dissoluble porosity among grains. Laumontite has deficient dissoluble forms and its dissolution mostly appear along rein, forming irregular size room among grains. This indicates the direction of exploration and development for oilfield. In a word, the diagenetic study of reservoir property show that mechanical compaction and cementation is two important diagenetic controlling factors, which make oil-bearing physical property bad and porosity down in reservoir. Dissolution, particularly dissolution of laumontite and feldspar is one of most important diagenetic factors controlling the physical property of oil-bearing interval and forming better reservoir.