--> Recent Advances and Future Prospects of Tight Oil in China

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Recent Advances and Future Prospects of Tight Oil in China

Abstract

Since 2011, tight oil has been a practical exploration target in China. Up to now, three large tight oil plays, each one more than 100 million tons oil in place, have been exploited. For example, more than 100 horizontal wells have been drilled in Chang 7 member of Upper Triassic in Ordos basin, and tight oil production is greater than 20 thousand barrels per day. Moreover, six new plays have been discovered, such as Shasan formation of Paleocene in Shulu depression of Bohai Bay basin, Upper Ganchaigou formation of Miocene in Zahaquan block of Qaidam basin and lucaogou formation of Middle Permian in Santanghu basin. It is expected that tight oil production will be more than 1.2 million tons in 2014. Tight oil in China is different from that in North America. Tight oil in China completely comes from lacustrine mudstones and shales, while that in U.S. mostly derives from marine shales. There are three kinds of tight oil reservoirs in China, including sandstones, carbonates and mixed rocks. Most of high production reservoirs are sandstones and mixed rocks. Many wells which aimed at carbonates are uneconomic, but production is pretty high if natural fractures are abundant. Source rocks can also be divided into three types, including laminar algal shale, massive mudstone and marlstone. Laminar algal shale is high abundance of organic matter, TOC content typically more than 3%; mudstone and marlstone are medium or low abundance of organic matter, TOC content averagely less than 2%. Laminar algal shale is the main source of high yield plays according to oil-source correlation. Four factors cause high production of lacustrine tight oil plays in China. The first one is that plays are located in or immediately adjacent to distribution area of mature organic-rich source rocks. Secondly, porosity of sandstone and mixed rock reservoir is more than 8%, or that of carbonate rock is more than 5%. Thirdly, there are abundant natural fractures, but large faults are undeveloped. The last one is high thermal maturity, the vitrinite reflectance 0.9%–1.3%, and high GOR(gas oil ratio) results in low oil viscosity. Finally, a number of favorable blocks are pointed out, and technically recoverable resources of tight oil in China is forecast, while expanded exploration potential of lacustrine tight oil is expected.