Hydrocarbon Distribution Based On The Claracteristics Of Current Pressure Field, Es4 Formation, In Bonan Sag

As one of the subsags in Zhanhua Depression, Bonan Sag is oil-enriched showing abnormal pressure. The 4^th member of Shahejie Formation in Eogene has been confirmed to be an important oil producing interval of huge potential for exploration activity, and it is also one of the overpressure layers. Base on the measured data on formation pressure, the paper analyzes the pressure characteristics of Es4 in different depths, and plane pattern of Es4.By the principle of balance depth,vertical formation pressure distributions of typical wells are reconstructed in different structures, Bonan Sag, and then the pressure distribution in profiles could be displayed through comparative analysis on the wells in different structures combining the distribution of oil, gas and water. The relationships between oil and pressure field are discussed, which can be summed up into three coupled modes. The paper makes the relationship between oil and pressure field quantification and deals the pressure data with grid mesh through Witson algorithm, then the area for oil-gas enriching can be forcasted effectively by simplifying geologic model.The main knowledge can be gotten as below:(1)Normal pressure of Es4 in different depth grows, meanwhile the abnormal pressure grows brightly from 2500m to 4000m, of which transition type dominate firstly and anomalous pressure secondly. A big distinction on single-welled pressure profile for the different structures in Bonan Sag. Abnormal pressure doesn't usually exist in actic region near fault and in gentle slope near uplift, comparing with low-lying belt near fault which is a main place for abnormal pressure growing.(2)Bonan Sag is composed of kinds of superposed pressure fields, which present as lenticulars. Pressure fields vary from the centre where they are unified to border of sag where little and discrete. All of lenticulars superposes and effect each other.(3)Oil layers distributed in the actic region near the border of sag, gentle slope and the centre of sag. Aqueous layer usually distribut in the uplift where heavy oil reservoir of minor production also exist. Combining the characteristics of distribution of oil, gas and water with tectonic position, the oil reservoirs in Bonan Sag can be classified into three types:lithologic hydrocarbon reservoir, fault block hydrocarbon reservoir and structural- lithologic hydrocarbon reservoir.(4)The distribution of Oil reservoirs have something with the superimposition of pressure fields. The relationship between them can be generalized such three patterns as anomalous pressure type, transitional pressure type and normal pressure type. The upper layer have obvious link on oil and accumulation in its underlying bed if the reservoirs in underlying bed are sealed both by lithology and abnormal pressure. In that case, the reservoirs in underlying bed have great reserves and outcome. According to these mentioned aboved, the Es4 in middle-deep zone has huge potential of exploration activity if it is sealed both by lithology and abnormal pressure.(5)High pressure formation sealing can be described quantitatively by pressure coefficient, based on which, the areas for oil and gas enriching in Bonan sag can be forecasted. Favorable area for oil and gas accumulation is on vicinity of Well-Luo601 and on the north of Well-luo58 where the high pressure sealing of Es3 is obvious, and great outcome of oil is expected. However, the middle of work area such as Well-Luo354 area is unfavorable, where high pressure sealing doesn't exist, and the known outcome is very low. Southern work area is secondary range of profitability, where the outcome in commercial wells is moderate.