Regional environmental geological background

4.1.1 Meteorological characteristics

The Yellow River Delta region belongs to the warm temperate monsoon climate zone, with continental climate characteristics and four distinct seasons. Spring warms up quickly and precipitation is low; summer temperatures are high, the weather is hot and humid, and precipitation is concentrated; autumn temperatures drop sharply, rainfall decreases sharply, and there are more droughts than floods; winters are dry and cold, with less rain and snow.

The average precipitation in the area from 1956 to 1998 was 537.3mm (see Table 4-1), and the precipitation is extremely uneven in time and space. Geographically, it decreases from south to north. In terms of time, the year is mainly concentrated in the flood season, especially July and August; the inter-annual changes are large, and the wet and dry periods occur alternately. The maximum annual precipitation is 2.88 times the minimum annual precipitation; the average annual water surface evaporation intensity is 1194.2mm, and in summer , is larger in spring, accounting for 70% of the whole year; the evaporation ratio is 2.2:1.

Table 4-1 Precipitation scale with different guaranteed rates for various districts and counties in Dongying City Unit: mm

4.1.2 Stratigraphy and lithology

The oil and gas accumulation area is located in North China The northeastern part of the Jiyang Depression in the platform area is a subsidence area of ??the Mesozoic and Cenozoic Era, with a subsidence amplitude of 12,000 m. The strata and structures before the Mesozoic Era are covered by thousands of meters of Cenozoic Era.

The crystalline basement of the North China Depression is Archaean metamorphic rocks, the Lower Paleozoic Cambrian and Ordovician are a set of marine sediments dominated by carbonates; the Mesozoic Jurassic, The Cretaceous is a set of extremely thick clastic rocks and volcanic rocks; the Cenozoic is a coastal lacustrine-fluvial facies deposit with a thickness of up to 7000m. The Tertiary System is a set of extremely thick oil-bearing, salt-mud sandstone formations, divided into the Lower Tertiary System and the Upper Tertiary System. The Lower Tertiary is divided from older to younger into the Kongdian Formation, Shahejie Formation and Dongying Formation. The Shahejie Formation is the high-yield oil layer of Shengli Oilfield; the Upper Tertiary is divided into the Guantao Formation and Minghuazhen Formation from bottom to top. , thousands of meters thick. The Quaternary Plain Formation is 200-400m thick and covers the Minghuazhen Formation.

Lower Pleistocene (Q1): 85~175m thick, 250~400m buried depth. Mainly silty clay, mixed with silt, silty sand, and fine sand. The color is mostly brown, brown, red, gray green, etc. The structure is dense, the fracture surface is developed, and it is rich in calcium nodules.

Mid-Pleistocene (Q2): 65-102m thick, 90-200m deep, with two marine transgressions in the entire area. Mainly silty clay, mixed with silt, silt sand and fine silt sand. The color is mostly grayish-yellow or brownish-yellow, containing calcium nodules, and fracturing surfaces are rare.

Upper Pleistocene (Q3): 40-50m thick, 80-100m deep at the bottom, and there are two marine transgressions in the area. The lithology is mainly silty clay, mixed with silt and fine silty sand. The color is mostly gray-yellow and earthy yellow, with thin layers of silt.

Holocene (Q4): 10~32m thick, there was a marine transgression in the area. The upper part is khaki, gray-yellow silt and silty clay; the middle part is mostly gray-black silty soil or silt; the lower part is mainly silty fine sand. The structure is loose, containing calcareous nodules and containing iron.

4.1.3 Structure and earthquakes

The basic form of geological structure is the negative geological structural unit surrounded by deep faults since the Mesozoic and Cenozoic. The interior of the plain is divided by a number of basement faults and deep faults. These large basement faults strictly control the distribution and arrangement of secondary (III) structural units. They open in the northeast and converge in the south and west, with the characteristics of a knob structure. From the end of the Mesozoic to the Early Tertiary, the uplift and depression of the primary structural unit were divided into smaller uplift and depression IV structural units by secondary faults. Late northwest-trending fault activity caused them to be generally transformed. The basement structure and seismic intensity in the area are shown in Figure 4-1, and the structural units in the area are shown in Table 4-2.

The main faults in the area are northeast and northeast, followed by north-northwest and northwest. The track measurement of each fault shows activity. The main faults from north to south are:

(1) Chengzikou fault: the trend changes from northeast to nearly east-west, with a basement fault difference of 500m. Tends south to southeast. The Tertiary system was deposited on the fault dip side under strict control.

Table 4-2 Division of Yellow River Delta tectonic units

(2) Yinan fault: trending northeast, leaning southeast, with the lower part cutting into the basement, it is the link between Chezhen Sag and Zhanhua Sag Boundaries break.

(3) Gubei Fault: trending northeast to nearly east-west, leaning north to northwest, with fault distances from east to west, from small to large (45-200m), controlling Lower Tertiary sedimentation inclined to the fault.

(4) Chennan fault and Shengbei fault: They are the boundary faults between Chenjiazhuang uplift and Dongying sag, distributed in nearly east-west direction. The two appear as two separate faults in the shallow part, but merge into one in the deep part. The two faults dip southward in the same direction, with an angle of 60° to 70°.

Figure 4-1 Basement structure and seismic intensity The schematic diagram shows that the drop is greater than 300m, and the Tertiary system is controlled to be deposited on the tilt side.

(5) Dongying Fault: It is distributed in the Dongying Depression in a nearly east-west direction and is a shallow fault formed since the Cenozoic.

(6) Changle-Guangrao fault: It is a branch of the Yidu-Wudi fault, trending northwest and leaning northeast, cutting the Guangrao-Qihe fault and controlling the deposition of the Tertiary system.

This area is located in the North China earthquake zone and is surrounded by strong earthquake areas.

According to historical records: Since 692 AD, the region has experienced 54 earthquakes, of which 14 have occurred in the region, and have been affected by intensity VII intensity 3 times: July 25, 1668, Tancheng Ju County 8.5 During the magnitude 7.5 earthquake in Lijin, "many houses collapsed" in Lijin, with the intensity reaching level Ⅶ; during the 7.5-magnitude Bohai earthquake on June 13, 1888, "many houses collapsed" in Lijin; during the 7.4-magnitude Bohai earthquake on July 18, 1969, Kenli, The three counties of Lijin and Zhanhua suffered severe earthquake damage. "A ground fissure about 1km long and 0.3-0.4m wide appeared on the isolated island, and the northern end sank 30cm." Zuojiazhuang, Jianlin, Xin'an and Huanghe Farms in Kenli County There were many cracks, water and sand came out, and the house collapsed. On July 28, 1976, during the 7.8-magnitude earthquake in Tangshan, abnormal cracking areas appeared in Zhanhua and Lijin: two cracks in the Yellow River dam in Lijin County, more than 100 places where water and sand gushed out, 560 houses collapsed in Zhanhua County, and many There are cracks in the ground and spots where water and sand are emitted. To sum up, the actual damage caused by the earthquake in this area has reached intensity VII.

Based on the time distribution characteristics of seismic activity, the statistics of missing earthquakes in destructive earthquakes within 100 years, and the analysis of the impact of historical earthquake intensities, the area will mainly face one strong earthquake of magnitude VII in the next 100 years. In view of the historical earthquake intensity in the area, Earthquakes rarely occur, and the main risk of seismic damage comes from strong earthquakes outside the region. It is predicted that late strong aftershocks with magnitudes up to 6.5 will occur in the Bohai District in the next 100 years; moderately strong earthquakes (magnitude 6-6.5) will occur in Anqiu-Yidu District in the next 100 years, with the greatest possibility of epicenter intensity VII: Bin County - There will be an earthquake of magnitude 5.56 (epicenter intensity VII to VIII) occurring in Boxing District in the next hundred years. The new activities of the Chennan Fault and Shengbei Fault in the area are relatively prominent, and there is a background of earthquakes of around magnitude 5 (degree) within the area.

According to the comprehensive seismic intensity map in the area compiled by the "Shandong Province Intensity Zoning Map" published in 1977, the seismic intensity in the area is determined as: No. 5 Pile - the area west of the pile is Ⅷ degree; Hekou, Ken Li, Dongying and Lijin are all at degree VII; Boxing-Bin County is at degree VIII; Zhanhua is at degree VI.