A New Method to Restore Paleogeomorphology of Deeply Buried Hill: A Case from BZ Condensate Field in Bozhong Sag, Bohai Bay Basin

Abstract The BZ Archaean hill is deeply buried and has experienced the influence of multi-stage tectonic movement. The fracture development law is complex, and the reservoir heterogeneity is strong. However, due to the low seismic resolution, it is difficult to predict the dominant reservoir. It is well known that paleogeomorphology has an obvious controlling effect on the distribution of fractured reservoirs, but conventional palaeogeomorphic restoration methods cannot restore the uplift and denudation amount in each deformation stage of BZ buried hill. Therefore, it is urgent to find a new palaeogeomorphic restoration method to provide technical support for the prediction of superior reservoirs in deeply buried hill. Firstly, the denudation amount of the denudation interface at different tectonic periods of key wells in the buried hill is obtained based on the low temperature thermochronology technique. Then, based on the mechanical parameters of the rock, the numerical simulation of the tectonic stress field is carried out according to the results of the tectonic evolution profile and the amount of denudation on the wells. The uplift and subsidence of the whole working area in different tectonic periods are obtained. Finally, under the constraint of structural simulation, the paleogeomorphology of the buried hill in different tectonic periods is restored.The result shows that the uplift rate around Bozhong sag ranges from 7.7 to 19.1m/Ma, and the amount of denudation ranges from 1000 to 2500m according to the multi-low temperature thermochronology data. The denudation rate of BZ buried hill is 8.8m/Ma, and it is estimated that the denudation amount of BZ buried hill in Indosinian and Yanshannian is 1800±300 m. Based on the results of the tectonic evolution profile and the amount of denudation on the wells, the quantitative results of the multi-stage tectonic uplift and subsidence of the typical profile is obtained through repeated forward iteration, and then the quantitative results of three-dimensional paleogeomorphology are obtained. Lastly, the favorable block of the development zone is predicted based on the results of seismic facies, stress field and paleogeomorphology. It can provide the basis for the implementation of oilfield development.Paleogeomorphology of deeply buried hill is restored by using low temperature thermochronology and numerical simulation forward iteration based on the evolution process analysis of the buried hill. By estimating the amount of denudation in different tectonic periods of the working area, the paleogeomorphology in different tectonic periods of the buried hill is finally obtained, which is the first attempt to solve the difficult problem of paleogeomorphology restoration of deep buried hill affected by multi-stage tectonic movements. This method will be used to guide the research of more similar oilfields in Bohai Bay Basin.