Lithologic Trap Prediction Of Ns₂-1 Formation In Chunguang Block, Chepaizi Uplift

Chunguang block of Chepaizi uplift is located in Zhunger Basin. Because of the continuing uplift over a long period of time, it is favorable for oil accumulation, and the sedimentary formation in this area are in low burial depth which were not buried too deep in the history of geologic evolution, so the area has a very favorable oil and gas geology condition. Chunguang block is a gently monocline structure uplifted northward, and the types of the traps mainly are lithologic trap and unconformity trap, so the exploration of subtle trap is more important in the block. In the early exploration of this area, it had obtained great breakthrough in the well of Pai2, Pai8 and Pai206, but the prospecting wells which were deployed later were all stepped out, the main reasons are that the traps are not so clearly located and the geologic condition of hydrocarbon accumulation is unclear.To solve these problems, in this paper the author applies the sequence stratigraphy, seismic strarigraphy, sedimentology and structural geology as the theoretical guidance, and use the Ns₂-1 formation as the research object. On the basis of well log, seismic data and previous studies, and according to the technology of waveform analysis the reflection of sandstone in the framework of sequence stratigraphy is identified, the distribution of sandbody and sedimentary faces are confirmed. And then, based on the analysis of hydrocarbon migration pathway, the favorable traps are predicted. Main progress and understanding obtained are as follows:1) A new method, which could be used to better identify sandstone, based on the method of waveform analysis, from lithofaces to seismic faces, then back to lithofaces, is preliminary formed, the condition is that the sandy ratio must be less than 0.5. 2) The velocity of sandstones is more lover than mudstones of Ns₂-1 formation, resulting in apparently seismic reflection, and the character of reflection is skew symmetric waveform (trough-crest).3) The sandbody of Ns₂-1 formation distributes as band in the direction from northeast to southwest along the lake strandline. The sands which mainly distribute in the south of the connection of Chun7, Chun6, Pai206 and Pai2-30, are the beach bar sandstone of shore-shallow lake facies and favorable for hydrocarbon accumulation,4) The Shawan formation of Neogene develops a series of strike-slip shear normal faults, and the strikes of the faults mainly are in the direction of NWW and northwestward to southeastward. They are the well migration path for hydrocarbon.5) Find 13 lithologic traps, and predict 3 favorable exploration targets, and the area is 1.6km2, but the shortcoming is that the area of every target is a little small.