Origin Of Abnormal Formation Pressure And Its Relationship With Hydrocarbon Accumulation In Raoyang Sag,Jizhong Depression

Based on the multidisciplinary theory?petroleum geology,hydrocarbon accumulation dynamics,hydrocarbon geochemistry,reservoir geology and mineral petrography,etc.?,a comprehensive study on the origin of abnormal high pressure of the Paleogene strata and its relationship with hydrocarbon accumulation in Raoyang sag are conducted in this paper.Firstly,the effective stress theorem of Bowers rock,is used to conduct a qualitative-semi quantitative analysis of the mechanism of abnormal high pressure in different areas of Raoyang sag.Secondly,based on the genetic types of formation overpressure,Eaton method is used to predict and establish the single well profile of formation pressure,and clearly defines the distribution characteristics of abnormal high pressure in Raoyang sag.Thirdly,Basin-Mod software and homogenization temperature measuring of inclusions are used to identify the evolution history of the strata,hydrocarbon source rock,abnormal high pressure,hydrocarbon charming,pore in the Shahejie formation.This paper specify the development of abnormal high pressure and its coupling relationship with hydrocarbon accumulation elements and the hydrocarbon accumulation model under the control of abnormal high pressure has been constructed in the study area.The research results are as follows:?1?Abnormal formation pressure is widespread from the Dongying formation to the Shahejie formation in Raoyang sag,The origin of abnormal high pressure include disequilibrium compaction,hydrocarbon generation and high pressure fluid injection?hydrocarbons?in the study area.The main mechanism of high pressure is hydrocarbon generation and disequilibrium compaction in the central region of sub-sags,but disequilibrium compaction and high pressure fluid injection in the edge of sub-sags and the slope areas.From the point of horizons,disequilibrium compaction is the main mechanism of high pressure in Dongying formation.Disequilibrium compaction is the main mechanism of high pressure in Es₁.Mechanism of high pressure is hydrocarbon generation in the lower part of Es₁ which is also the source rock layer.The disequilibrium compaction is the main mechanism of high pressure in the upper part of Es₁.Disequilibrium compaction and high pressure fluid injection are the main mechanism of high pressure in Es₂.The hydrocarbon generation is the main mechanism of high pressure in Es₃ which is the main source rock in this area.?2?According to the analysis of the actual geological conditions and the mechanism of abnormal high pressure,the Eaton method is selected to predict the formation pressure in Raoyang sag with constraint of the measured formation pressure data.The values of the Eaton index are 0.5⁰.8 in Raoyang sag,and the values in sub-sag region are larger than slope region.70 single well profiles of formation pressure have been constructed.Based on the prediction results of formation pressure,it can be conclued that the Raoyang sag generally developes abnormal high pressure?except Wuqiang-Yangwuzhai?from the bottom of the Dongying formation to Es₃.The formation pressure coefficients are 1.1¹.5,indicating weak overpressure and middling overpressure.?3?There is strong regularity of distribution of abnormal high pressure in Raoyang sag.From the profile of Raoyang sag,Es₃ and Es₁^L?source rock?are the mainly high-pressure centers.The initial depth of high pressure is the shallowest in Maxi region.The initial depth of Renxi,Liuxi-Liuchu,Hejian-Suning region are in the middle,and Wuqiang-Yangwuzhai are the deepest.From the point view of horizons,the initial depth of high pressure is in the bottom of the Dongying formation in Renxi,Maxi,Hejian-Suning,and Liuxi-Liuchu region.Hower,the initial depth of high pressure is in Es₁ in Wuqiang-Yangwuzhai region.From the plane view,the extent of high pressure is the largest in Hejian-Suning region where the maximum pressure coefficient is up to 1.5.Liuxi-Liuchu and Maxi region are in the middle and Renxi and Wuqiang-Yangwuzhai are minimum.The range of high pressure extend from the central area to the part of the sub-sag and slope as the extent of formation pressure extend from high pressure to normal pressure.?4?Abnormal high pressureis closely related to hydrocarbon accumulation elements,Abnormal high pressure can not only inhibit the thermal evolution,and cementation of organic matter,but also slow down the mechanical compaction of the overlying strata and protect primary pores and indirectly promote dissolution.Therefore,the development of abnormal high pressure is the important reasons of the development of abnormal high porosity in the moderately to deeply buried reservoirs of Raoyang sag.?5?The evolution history of hydrocarbon generation,hydrocarbon charming,pore,formation pressure shows that the period of hydrocarbon generation and the period of hydrocarbon charming obviously correspond to the period of high abnormal pressure.That is also an important factor for the development of abnormal high pressure.And the development of abnormal high pressure can also be the motive force of hydrocarbon migration.At the same time,hydrocarbon charming can inhibit the destructive diagenesis?cementation?and the unstable minerals of the acid can also be dissolved in organic acids,and have a positive effect on the improvement of the porosity of the reservoir.Therefore,the high pressure development and evolution,hydrocarbon generation and evolution of source rocks,hydrocarbon charming and pore evolution of the reservoir have good coupling relationship in time in the study area.?6?5 hydrocarbon enrichment types under high pressure control are classified according to the hydrocarbon enrichment rules in Raoyang sag:high pressure sealing-high pressure enrichment in source rock?type??,high pressure sealing-normal pressure enrichment in source rock?type??,high pressure sealing-high pressure enrichment out of source rock?type??,high pressure sealing-normal pressure enrichment out of source rock?type??,normal pressure sealing-normal pressure enrichment out of source rock?type??.Finally,2 hydrocarbon accumulation models are constructed in the study area,include the“early high pressure driving-high pressure sealing-hydrocarbon accumulation in sand of source rock”and the“late high pressure driving-high pressure/faultsealing-hydrocarbon accumulation in sand out of source rock”.