The Palaeogeomorphic Recovery Of Late Ordovician And The Section Of O1m5 Reservoir Prediction In YanChang Exploration Area Of Ordos Basin

The Yanchang exploration area is located in the eastern part of Jingbian gas field of Ordos basin, covering 10 thousand square kilometers. Ordovician Majiagou carbonate reservoir rocks are widely developed and controlled by the karst reservoir, crack and paleogeomorphology. It showed poor reservoir regular, complex forms, strong heterogeneity. Exploration wells and evaluation wells'drilling success rate has always been low. Similar with Jingbian gas field in reservoir development and gas bearing feature, the recovery of the eroded trough and paleogeomorphy of top Ordovician crust play an important role in Yanchang gas exploration.Carry out the paleogeomorphic recovery and seismic reservoir identification is necessary when several gas wells were obtained. On one hand, a pre-upper Paleozoic geological map relative to paleogeomorphy is constructed based on a dedicated thin bed division and correlation of Ordovician Majiagou Formation on well-linked sections. The thickness map of the Benxi Formation overlying immediately above the unconformity surface made from seismic and well data also display some correlation with the paleogeomorphology, a seismic forward model is used to find out the relationship between the eroded trough depth and seismic reflection. It is found that there were two NW-SE trend eroded troughs on the top Ordovician unconformity, the low impedance suggests the distribution of good dolomite reservoir, whose positions are rightly on both sides of eroded trough. present gas productin and indication wells are all located in the same position. On the other hand, compared with cores, slices, test data, single well phase and connected well profiles, the main production section Olm51, which in gypsum-bearing dolomitite flat of supralittoral zone and dolomitic flat of intertidal zone, were the favorable reservoir facies, solution pores, intercrystalline solution pores and small amount of joint-shaped pores constitute the network gas migrate channel. Combined with many controlling factors, mainly include carbonate reservoir geological response characteristics, post-stack seismic attributes analysis, and the ancient karst landform, the karst-type reservoir prediction were achieved.