A STUDY OF ORGANIC COMPOSITION IN MUDSTONE AND SILTSTONE USING LASER SCANNING CONFOCAL MICROSCOPY

In the study of tight oil, we have found that tight sand is usually interbeded by mudstone and they are both fractured to produce oil during oil testing. However, whether oil is stored in sand or not and their occurrence state are still in debate. In this study, we have collected samples of crude oil, saturated hydrocarbon, aromatic hydrocarbon, non-hydrocarbon, asphaltene and kerogen. Using 3D reconstruction technique of Laser Scanning Confocal Microscopy (LSCM) to research their laser spectral characteristics.Here, main peak position and peak shape characteristics of different components can be to study spatial distribution of organic composition, oil occurrence state, and relative volume percentages of light components, heavy components (free oil), kerogen and its adsorbed hydrocarbons.

The samples are from Songliao Basin, NE China .The well Qiping 1, located in Xingshugang nose structure of Qijia depression in central depression area , obtained industrial oil flow of 10.2t/d during well testing in 2012 and it’s a major breakthrough of unconventional tight oil exploration in Songliao Basin. We sampled from a section of Gaotaizi oil layer with 20m of successive core and got a total of 45 samples: 16 mudstone samples, 15 silty mudstone samples and 14 siltstone samples.

Using LSCM to study oil occurrence state in different lithology, we have found that different reservoirs were different in oil content. As can be seen from the 3D space distribution, in mudstones and silty mudstones, light components, heavy components, kerogen and its adsorbed complex hydrocarbons are overlapped; however, in siltstones, the three components are staggered, especially between light-heavy components and mixing components of kerogen and its adsorbed hydrocarbons. From quantitative components, the content of light components and heavy components in siltstone is high, with the value between 4.79% and 54.09% (17.02% in average). The content of light components and heavy components in mudstone is between 4.77% and 21.68% with an average of 13.55%, while the value in silty mudstone is between 4.69% and 13.92% with an average of 7.95%. It indicates that the content of free oil in siltstone is higher, while in mudstone and silty mudstone is lower. The result is consistent with rock slice observation.