Formation conditions and reservoir-forming models of the Ordovician buried hill reservoirs in the Jizhong depression

The buried hill in the Jizhong depression contains abundant petroleum reserves and are important production areas.The Ordovician buried hill has restricted the discovery of new oil and gas exploration targets because of its strong reservoir heterogeneity and complex reservoir-controlling factors.Based on a large volume of core,thin section,logging,seismic,and geochemical data and numerous geological analyses,the reservoir-forming conditions and modes were systematically analyzed to guide the exploration and achieve important breakthroughs in the Yangshuiwu and Wen an slope buried hills.The study revealed that three sets of source rocks of the third and fourth members of the Shahejie Formation from the Paleogene and Carboniferous-Permian were developed in the Jizhong depression,providing sufficient material basis for the formation of buried hill oil and gas reservoirs.The reservoir control mechanism involving the three major factors of“cloud-karst-fault”was clarified,and karst cave,fracture fissure-pore,and cloud pore type reservoir models were established,thereby expanding the exploration potential.Controlled by the superposition of multi-stage tectonic processes during the Indosinian,Yanshanian,and Himalayan,two genetic buried hill trap types of uplift-depression and depression-uplift were formed.Based on the analysis of reservoir-forming factors of the Ordovician buried hill,three buried hill oil and gas reservoir-forming models were identified:low-level tectonic-lithologic composite quasi-layered buried hill,medium-level paleo-storage paleo-block buried hill,and high-level paleo-storage new-block buried hill.Comprehensive evaluations indicate that the reservoir-forming conditions of the low-level tectonic-lithologic composite quasi-layered buried hill in the northern portion of the Jizhong depression are the most favorable and that the Sicundian and Xinzhen buried hills are favorable areas for future exploration.

Inversion of breakout data from inclined boreholes for stress state of the upper crust in Jizhong depression

The forward and inverse problems of studying crustal stress state from breakout data of inclined boreholes are concisely stated. direction of the maximum horizontal principal stress (compressive) and relative magnitudes of the horizontal stresses to the vertical stress in the upper crust in two regions of the Jizhong depression, the North of China, are obtained by analyzing the breakout data of 6 inclined wells. To get stable results in the analysis wesearched for the unknown parameters both forwardly and inversely. The results show that the maximum azimuths of the horizontal Principal compressive stresses in the central and southern part of the Jizhong depressionare N86°E and N77°E, respeCtively, while the relative magnitudes of the three principal stresses in the uppercrust (about 1000-4000 m) of the depression are variable. In the centra; part of the Jizhong depression we havefound SH : Sv: SK= 1. 38: 1. 00: 0. 57, where SH, SV and Sh are the maximum horizontal, vertical and minimum horizontal stress, resistively. This indicates that the present stress regime in this area is of strike-slipfaulting type. In the southern part of the depreSSion we have obtained SH: Sv: Sh=0. 80: 1. 00 1 0. 62, indicating a normal faulting stress regime in the shallow Part Of the crust.

Application of active-source surface waves in urban underground space detection: A case study of Rongcheng County, Hebei, China

Active-source surface wave exploration is advantageous because it has high imaging accuracy,is not affected by high-speed layers,and has a low cost;thus,it has unique advantages for investigating shallow surface structures.For the development and utilization of urban underground space,two parameters in the shallow surface are important,namely,the shear wave velocity(V_(S))and the predominant period of the site,which determine the elevation and aseismic grade of the building design.The traditional method is mainly to obtain the two above-mentioned parameters through testing and measuring drilling samples.However,this method is extremely expensive and time consuming.Therefore,in this research,we used the multichannel surface wave acquisition method to extract the fundamental dispersion curve of single-shot data by using the phase shift method and obtain the V_(S) characteristics in the uppermost 40 m by inversion.We arrived at the following two conclusions based on the V_(S) profile.First,the study area can be roughly divided into five layers,among which the layers 0−8 m,14−20 m,and 20−30 m are low-velocity layers,corresponding to miscellaneous fill,a water-bearing sand layer,and a sand layer;therefore,the V_(S) is relatively low.In contrast,the layers at 8−14 m and 30−40 m are high-velocity layers that are mainly composed of clay,with a relatively better compactness and relatively high V_(S) values.In addition,a low-speed anomaly appears abruptly in the high-speed area at 20−40 m.This anomaly,when combined with geological data,suggests that it is an ancient river channel.Second,from the V_(S) value,the V_(Se)(equivalent shear wave velocity)was calculated.The construction site soil was categorized as class III,with good conditions for engineering geology.In addition,we calculated the predominant period of the site to be 0.56-0.77 s based on the V_(S).Therefore,in the overall structural design of the foundation engineering,the natural vibration period of the structure should be strictly controlled to avoid the predominant period of the site.