Researches On The Formation Mechanism Of Reservoirs In Shahejie Formation Of Dawangzhuang Area

Based on the full use of all kinds of abundant data of petroleum industry and previous studies, the writer researches the formation mechanism of reservoirs in Shahejie Formation of Dawangzhuang area in the paper, by analyzing the basic accumulation conditions, dissecting the typical reservoirs, analyzing the controlling factors and summarizing the accumulation models of hydrocarbons.Study on the formation mechanism of reservoirs is conducted from six aspects.The quality third member and the general lower half of the first member of Shahejie Formation are main source rocks, and they have produced lots of hydrocarbons. Braided river delta formations are the main potential reservoirs. Sandstones and small percentage of carbonates are the main composition of Shahejie reservoir, which are characterized by the particularly low to low porosity and permeability. There are two kinds of source-reservoir-cap assemblages: one is self generation and self reservation in the oil source strata, another is lower source rock generation and upper reservoir reservation in the non-oil source strata. The vertical passage is the fault, and the lateral one is the sand body. The passage system is characterized by three fault-stepped breaks style and the graben-like style. Main power of hydrocarbon migration is abnormal pressure in the source rocks, which is widespread in Shahejie Formation. Low porosity and permeability rocks sealed, reservoir up dip pinch out and lenses are three representative types of traps in this area. Lithological-structural trap is common. There is no extensive tectonic movement in later Paleogene, so hydrocarbons have been well preserved from then on.Reservoirs distributed in the higher area, the majority of them are adjacent to faults for too many faults in the area. Then the writer chooses four typical reservoirs and carefully analyses on them. Both of the reservoirs in Liu 70-39 well area and Liu 430 well area are wrapped in the source rock, so they are two kinds of lithological-structural traps; Liu 77 pool is a faulted anticline reservoir in the lower half of the first member of Shahejie Formation; Liu 70 pool is a faulted block reservoir over the source rock.For all these workloads, the writer compares the different reservoirs and analyses the controlling factors and summarizes the accumulation models of hydrocarbons. The source rock, the historic environment controlled by tectonics and sedimentation, the oil migration condition are dominating factors for the lithological-structural reservoirs in this area. The matching performance of faults and sand bodies, and the position of the traps are dominating factors for the structural reservoirs. Judging from the dominating factors and the formation time of oil accumulation conditions, here we summarize four models for characterizing hydrocarbon accumulation. Based on the above,thirteen favorable targets for natural gas exploration in the third member and the lower half of the first member of Shahejie Formation are predicted in this paper.