Jimusar Depression Permian Lucaogou Group Tight Oil Reservoir Characteristics And Reservoir Evaluation

A set of dolomitic rock and volcaniclastic rocks reservoir developed in Permain Lucaogou Formation in Jimusar sag of Junggar Basin. It’s an important tight oil exploration area. The tight oil in this area characterized by source-reservoir one body or source-reservoir interbeded, forming a good source-reservoir matching relationship. Lucaogou Formation in this area can be divided into two sections:the member1of Lucaogou Formation (P2l1) and the member2of Lucaogou Formation (P2l2). Compared to the member2of Lucaogou Formation, the member1of Lucaogou Formation have more tuffaceous rocks and less dolomite, greater single layer thickness and better oiliness.According to core and thin sections observation, combined with X-ray diffraction, electron microprobe, scanning electron microscopy of Argon ion polished thin sections and mercury injection data, we think that tight oil reservoir rocks in study area can be divided into five types:tuff, sedimentary tuff, tuffaceous micrite dolomite, tuffaceous containing micrite dolomite and micrite dolomite. Among them, tuff and sedimentary tuff have the best reservoir property. These tuffaceous rocks have high organic content, forming a set of source-reservoir one body tight oil. Rocks in the whole Lucaogou Formation were seen fluorescent light display, including two oil enrichment member called upper and lower "sweetspot". The average thickness of "upper sweetspot" is25-35m, and the average thickness of "lower sweetpot" is40-60m. Upper and lower "sweetspot" spread across large continuous areas in our study area, but the "lower sweetspot" have a wider distribution and more stable thickness.Reservoirs in our study area is (ultra) low Porosity/(extra) low permeability reservoirs. Intergranular pore is the main pore type, the others are emposieu and microfracture. According to mercury injection data, the pore structure can be divided into two categories, micro-throat and thin-throat, but they have some common characteristics:pore throat radius is too small, poor connectivity and strong microscopic heterogeneity. Most of these tuffaceous rocks have abundant intergranular pore, emposieu and microfracture, have better reservoir property. Especially in the interval microfracture developed, reservoir property has been significantly improved.According to thin sections fluorescent observation and organic geochemistry analysis, tuffaceous rocks in Lucaogou Formation have high organic content. Preliminary analysis show that tuffaceous rocks, as a new type of hydrocarbon source rock, have important effect on the forming of tight oil.