Research On The Relationship Between Abnormal Pressure And Hydrocarbon Accumulation Of Lower Yanchang Formation In The Central And Western Erdos Basin

Abnormal pressure is an important global geological phenomenon in oil and gas bearing basin, of which formation and distribution are closey related to generation, migration, accumulation of oil and gas. There are also high-pressure anomalies in Erdos Basin. Its history of geological evolution basically contains two abnormal pressure peak, the first peak in the Yanchang group of Mesozoic strata which is the purpose of our study; the second peak appeared in the Upper Paleozoic which is more development than in the Yanchang Formation. It’s very bright and tremendous that the oil and gas exploration prospects of the lower layer of Yanchang group, which has appeared very important exploration potential in the Erdos Basin.There lie compactness reservior and simple ectonic, so that it’s particularly important to select abnormal formation pressure for the study. There are more than200wells’mudstone compaction curves that are researched to study the mudstone compaction law, and use the equivalent depth method to calculate abnormal pressure in mudstone, which depicts the development form of abnormal pressure in detailed, and systematic analysis of abnormal pressure distribution characteristics. In addition, by combining with the laws of reservoir distribution of the lower Yanchang Group in the survey region, this dissertation discusses the relationship between abnormal pressure and hydrocarbon migration and accumulation, as well as illustrating the laws of hydrocarbon accumulation from the perspective of abnormal pressure.According to the study, the results and conclusion can be drawn as follows:1) There are two types of abnormal pressure from the single wells of the lower Yanchang group. The first one is Gradation:the gradation gradient type with two peaks which producing most oil, and the second one is Mutation:the mutant gradient type with single peak which producing oil less.2) The abnormal pressure of the lower Yanchang group in the survey region is obviously and closely related to the oil migration and accumulation on the geological profile. Oil is mainly with the vertical migration, and it will be favorable to its accumulation with a lower overpressure gradient lengthways. While, abnormal overpressure bodies of local development would affect its oil producing capacity.3)The relatively low value area of overpressure from the plane of the lower Yanchang group in the survey region is an advantageous area for petroleum reservoir distribution. In the distribution area of source rocks, the gradation of overpressure reflects the degree of hydrocarbon-expulsion to some extent. High overpressure means that hydrocarbon production strands seriously, and low overpressure means the the hydrocarbon expulsion completes fully, and its expulsion environment is a necessary material base for oil accumulation.4) In the lower Yanchang group in Central and Western Erdos Basin, the oil distribution shows some features of scattering. The dispersion characteristics from Chang8to Chang10do not overlap, instead that Multi-layers of oil accumulation in some areas with development of both Chang7and Chang9overlaps in the south area. We all know that hydrocarbon accumulation in priority to select the best reservoir filling, while the rate of longitudinal sand and the gradient of overpressure determine the filling layer, with the region of overpressure showing the advantage position as the high capacity area, when sand bodies laminate.