Due to spreading of Helan and Qinling rift valleys during the Ordovician period, a L-shaped swell belt formed in the western and south - ern parts of the basin.
奥陶纪由于西边贺兰裂谷和南面秦岭裂谷发生扩张裂离，在盆地西缘和南缘产生裂谷肩翘升，形成l形隆起带。
2
The formation water in L area, M Basin is fresh. The natures of drilling mud vary with different drilling depth. There is a complicated relationship between electric properties of water and oil.