| The long-lived Songliao Basin in the northeast China located on one of the largest sedimentary landmasses during Cretaceous, is an excellent candidate from which to recover a nearly complete Cretaceous terrestrial sedimentary record based on basin-filling history. The Continental Scientific Drilling Project in the Cretacous Songliao Basin is a drilling initiative under the framework of International Continental Scientific Drilling Program (ICDP), with the aim of recovering a continuous?high resolution and complete terrestrial sedimentary record from Paleogene to the top of Upper Jurassic. This scientific drilling project conducted in two stages, combined with two wells includes four holes, about 10,000 m cores will be abtained. The first stage, the SKI drilling was finished in 2007, with a total core length of 2,485.89 m and a recovery ratio of 96.46% from Mingshui Formation to the upper part of Quantou Formation (Danian-Turonian). The second stage, the SK2 drilling operation has implemented in April 13,2014, to recover rock strata from Quantou Formation to Huoshiling Formation (Early Cretaceous-Late Jurassic) and basement of the basin (Permian-Carboniferous), with an estimated cores of 7,400 m. Combined with SKI, the recovered cores of SK2 will provided unique opportunities for the geoscience community to further understand the environmental/climate change in the Cretaceous greenhouseworld and terrestrial oil and gas exploration and development.In this doctoral thesis, under the guidance of the goals and key scientific problems of continental scientific drilling, the following 4 main contents were studied detailedly, based on a great deal of geological and geophysical data including regional geological survey, petroleum exploration and exploitation and scientific results in the Songliao Basin. (1) To meet the drilling strategies and feasibility of drilling, a "one well with two holes" drilling plan was implemented, and the target areas and well sites of both holes of SK2 were confirmed. (2) The stratigraphical sequence of fault depression in the Songliao Basin, including Yingcheng Formation, Shahezi Formation, and Huoshiling Formation, were summarized systematically. A new lithostratigraphy and chronostratigraphy of Huoshiling Formation was established. (3) The bottom hole geotemperature, formation pressure and formation fracture pressure of target strata of SK2-e were predicted, according to the relationship between depth and geotemperature, geothermal gradient and formation pressure. (4) The simulated stratigraphic column of SK2-e was established, based on the prediction of the depth of the main formation boundaries and the lithology of each member or formation. These studies are the most important fundamental and pilot research for the following research, such as the marine-terrestrial correlation of stratigraphy, the response of the terrestrial environment to the geological events, the new field of middle-deep oil and gas exploration in the Songliao Basin and adjacent areas, and so on. The results also directed the whole scientific drilling process. The principal results as follows:1. Well site selection of SK2(1) Target area and well site selection of SK2-wIn order to recover the most continuous and complete core of Quantou Formation and Denglouku Formation, a series of trans-basinal setions and hundreds of wells were coMPared. As a result, the Changchunling anticline and Daqing Placanticle in the Central Depressional Zone of Songliao Basin are two candidate target areas for SK2-w, which shows the most complete strata and least hiatus with the simplest tectonic structure. However, in Changchunling anticline, the strata thickness of Denglouku Formation is relativety thin and mudstone less developed. On the other hand, in Daqing Placanticle, the buried depth of Quantou Formation is relativety deep, but well developed thick target strata and mudstone coordinate with the drilling strategies completely. And the cost and risk of drilling could be controlled in the further studied. Therefore, the Daqing Placanticle is the most ideal target area for SK2-w. The southwest part of Daqing Placanticle close to the Qijia-Gulong Depression, with the most thick target strata and mudstone.3D seismic investigation has been conducted for this area, which allows us to estimate the thickness of target strata, also allows us to understand the tectonic development and avoid structural complications. Based on the seismic data, lithologic information from existing cores, and discussions at the Daqing workshop, we chosen a site for SK2-w (124° 40' 50" E,46° 04'26" N) in the north part of the basin, which located to 4.0km to the northwest of Bajingzi Town, Datong District, Daqing City, Heilongjiang Provence. The plan call for continuous coring of 3,670m, from 1,555m depth to 5,225m depth, from the top of Quantou Formation to the bottom of Denglouku Formation. The recovery ratio will be above 95%, based on SKI core recovery.(2) Target area and well site selection of SK2-eIn order to recover the most continuous and complete core of Yingcheng Formation to Huoshiling Formation and basement of the basin, the main fault depressions in Songliao Basin and dozens of deep wells were coMPared. As a result, the Lishu Fault Depression in the south and the Xujiaweizi Fault Depression in the north part of the basin are two candidate target areas for SK2-e; which shows the most complete strata and least hiatus with fine sediment in depocenter. However, in Lishu Fault Depression, the buried depth of basement is about 7,000m, the cost and risk of drilling may be out of control. On the other hand, in Xujiaweizi Fault Depression, the depth of the top surface of Yingcheng Formation is relativety deep, but the total thickness of target strata is moderately and the buried depth of basement is relativety shallow. Therefore, the Xujiaweizi Fault Depression is the most ideal target area for SK2-e. The Songshen3 well field in Anda Depression in the north part of Xujiaweizi Fault Depression was refined in the further studied, with relativety shallow buried depth of basement, huge thickness fine sediment and the sandstone reservoir surrounded by dark source rocks, which shows a favorable exploratory potential.3D seismic investigation has been conducted for this area, which allows us to estimate the thickness of target strata, also allows us to understand the tectonic development and avoid structural complications. Based on the seismic data, lithologic information from existing cores, and discussions at the Daqing workshop, we chosen a site for SK2-e (125° 21'47.03" E; 46° 14'26.89" N) in the north part of the basin, which located to 0.25km to the southeast of Liucuofang Country, Anda City, Heilongjiang Provence. The plan call for continuous coring of 3,655m (includes 120m cores of Nenjing Formation), from 2,865m depth to 6,400m depth, from the bottom of Denglouku Formation to the top of the basement. The recovery ratio will be above 95%, based on SKI core recovery.2. The stratigraphical sequence of fault depression in the Songliao Basin The stratigraphical sequence of fault depression is the main target strata of SK2-e, which the most important strata for series key scientific problems of continental scientific drilling. We summarized systematically the sequence stratigraphic subdivision and correlation of Yingcheng Formation, Shahezi Formation, and Huoshiling Formation in descenting order. On the basis of lithologic correlation and seismic cross-sections correlation, the remain controversial lithostratigraphy of Huoshiling Formation was discussed.(1) The stratigraphical sequence of Yingcheng Formation The Yingcheng Formation is the last rifting basin stage with the filling sequence of mainly volcanic rocks. It could be divided into four lithologic members. From bottom to top, the 1st member consists mostly of acidic lava and pyroclastic, and intermediate-basic lava developed at the bottom of this member. The 2ed member is mostly of clastic rocks with tuff and coal streak as interlayers. The 3rd member is mainly composed of massive intermediate-basic lava, while at the top and bottom of the member interbeded with acidic volcanic rocks. The 4th member consists mostly of tuffaceous conglomerate, sandstone and mudstone, and only exists in the Xujiaweizi Fault Depression. Further study shows that, the 1st and 3rd member could be divided into 7 volcanic eruption cycles totally. The 1st member includes intermediate-basic lava cycle, acidic pyroclastics cycle, massive acid lava cycle, and acidic pyroclastics cycle in ascending order, and the thickness ratio of these 4 cycles is about 1:2:4:1. The 3rd member includes acidic pyroclastics cycle, massive intermediate-basic lava cycle, and acidic lava-pyroclastics cycles in ascending order, and the thickness ratio of these 3 cycles is about 1:3:1.(2) The stratigraphical sequence of Shahezi FormationThe Shahezi Formation is the middle rifting basin stage with the filling sequence of mainly clastic rocks with several coal beds as interlayers. In general, the Shahezi Formation shows two normal cycles which thining-and fining-upward, correspond to two lithologic member respectively. From bottom to top, the 1st member consists mostly of massive conglomerate and dark mudstone with several commercial beds. The upper part of the 2ed member is mostly of dark mudstone with thin sandstone and conglomerate, while the lower part interbedded with mudstone and grey conglomerate, and a small amount of coal streak and tuff also developed.(3) The stratigraphical sequence of Huoshiling FormationThe Huoshiling Formation is the first rifting basin stage with the filling sequence of mainly volcanic rocks in northeastern China and adjacent areas. Laterally, it is characterized by the widespread distribution, remarkable variation in volcanic eruption time and scale between fault depressions. It could be divided into two lithologic members.The 1st member mostly interbedded with dark mudstone and grey sandstone, while coarse clastic rocks developed in the margin of the fault depressions. And lava and pyroclastic rocks dominate in the 2ed member. Further study shows that, the 2ed member includes 5 volcanic eruption cycles, intermediate lava cycle, acidic pyroclastics cycle, intermediate-basic lava cycle, alkalic-intermediate lava cycle and acid lava cycle in ascending order, and the thickness ratio of these 5 cycles is about 3: 2:2:6:1.3. The chronostratigraphy of Huoshiling Formation in the Songliao BasinTime (geological age) and duration is the fundamental subjects to establish the marine-terrestrial correlation of stratigraphy in the Cretaceous Songliao Basin, as well as to form the basis for the marine-terrestrial correlation of environmental/climate change. The geologic period of Yingcheng Formation and Shahezi Formation belong to Early Cretaceous has been accepted widely. However, quite different opinions upon Huoshiling Formation were proposed based on different types of evidences.In this part, the chronostratigraphy of Huoshiling Formation was discussed and summarized on the basis of biostratigraphy, isotopic dating, lithostratigraphy as well as magnetostratigraphy.The Huoshiling Formation yielded plant megafossils in a wide range of periods. The sporo-pollen assemblages show a blooming age of the early Cretaceous. Characteristic megaspore fossil and magnetostratigraphy indicate the age of the Jurassic. Overlying sequence of the Huoshiling Formation is also concerned in order to constrain its time span. The bottom of Yingcheng Formation is 130Ma, the duration of Shahezi Formation is about 10Ma, so that the top age of the Huoshiling Formation should be ca.140Ma. The minimum duration of Huoshiling Formation is calculated ca.8Ma, and its bottom age ought to approach about 150Ma. The isotopic age dating on the volcanic rocks of Huoshiling Formation mainly ranges from 140Ma to 150Ma. All these evidences above suggest that the age of Huoshiling Formation can be well constrained from the Tithonian to the Berriasian or to the bottom of the Valanginian. The Jurassic-Cretaceous boundary (J/K boundary) in the Songliao Basin probably exist inside the Huoshiling Formation.4. The bottom hole geotemperature, formation pressure and formation fracture pressure prediction of SK2-eThe designed depth of SK2-e is 6400m, and previous studies shows that the Xujiaweizi Fault Depression falls in the high geotemperature area, the high geotemperature and possible abnormal pressure are the main challenges for continental scientific drilling. According to the relationship between depth and stastistic of present geotemperatures, geothermal gradients and formation pressures, we predicted the bottom hole temperature, formation pressure and formation fracture pressure of target strata of SK2-e.(1) Prediction of the bottom hole geotemperatureA refined analysis of 3 sets of system geotemperatures and 154 test geotemperatures from the SK2-e well field suggested that, the geotemperature increases and the geothermal gradient decreases with the increasing of the depth. According to the relationship between depth and geotemperatures of Yingcheng, Shahezi and Huoshiling Formation in Xujiaweizi Fault Depression, we calculated the bottom hole geotemperature is 260.40 ?.The geotemperature is 144 ? in 3816m of well Songshen3, which located in 680m south to SK2-e. According to the relationship between depth and geothermal gradients in Yingcheng Formation and Shahezi Formation, and average geothermal gradient below 3800m, we calculated the bottom hole geotemperature is 235.99 ? and 240.64 ? respectively.So far the deepest well in Songliao Basin has reached the depth of 6300.84 m, named well Gulongl, which located in 83 km southwest to SK2-e. According to the calculated geothermal gradient of well Gulongl (4.14 ?/100 m), we calculated the bottom hole geotemperature of SK2-e is 265.14 ?.Synthesizes above several predictions, the bottom hole geotemperature of SK2-e probably range from 235.99 ? to 265.14 ?.(2) Prediction of formation pressure and formation fracture pressureAccording to the relationship between depth and formation pressures, we calculated the formation pressure of Yingcheng Formation range from 30.62 MPa to 37.72 MPa. The average formation pressure coefficient is 1.06, and DrillWorks software calculated result is 1.05, we calculated the formation pressure of Yingcheng Formation range from 30.83 MPa to 34.52 MPa and range from 30.54 MPa to 34.20 MPa respectively. Based on the above results, the formation pressure of Yingcheng Formation probably range from 30.54 MPa to 37.72 MPa.The average formation pressure coefficient of Shahezi Formation is 1.07, and DrillWorks software calculated result is 1.02, we calculated the formation pressure of Shahezi Formation range from 34.85 MPa to 59.52 MPa and range from33.22 MPa to 56.74 MPa respectively. Based on the above results, the formation pressure of Shahezi Formation probably range from 33.22 MPa to 59.52 MPa.There is no test formation pressure below Shahezi Formation at present. The integrated average formation pressure coefficient includes Yingcheng Formation and Shahezi Formation is 1.07. We calculated the formation pressure of Huoshiling Formation-the bottom of the hole range from 59.52 MPa to 67.18 MPa.According to the average formation fracture pressure coefficient of Yingcheng Formation, Shahezi Formation and Huoshiling Formation-the bottom of the hole is 1.8, 1.9,1.88, and integrated DrillWorks software calculated results, we calculated the formation fracture pressure range from 52.35 MPa to 58.62 MPa, from 61.88 MPa to 105.68 MPa, from 104.57 MPa to 118.03 MPa respectively.5. The simulated stratigraphic column prediction of SK2-eThe simulated stratigraphic column is the main reference for the whole scientific drilling process bases on the experience of SKI. First of all, the depth of the main formation boundaries was predicted according to structural maps, seismic profiles and adjacent wells. Secondly, we predicted the detail lithology of each member or formation, based on regional stratigraphic-lithologic characteristics, geophysical data, and well Songshen3 and other adjacent wells. Finally, the designed coring horizon, contents, oil, gas and water bearing layers, probable drilling failures etc. were integrated into the comprehensive simulated stratigraphic column of SK2-e.From top to bottom, the lithology of main target strata of SK2-e as follows:Yingcheng Formation can be divided into two parts in SK2-e, the upper part consists mostly of grayish green coarse sand, conglomerate, and glutinite, with dark purple mudstone as interlayers, and massive tuff, andesite- basalt and rhyolite, dominated in the lower part, while massive dark grey conglomerate developed at the bottom of this member.The Shahezi Formation mostly of dark mudstone, with grey fine sand, dark grey siltstone, silty mudstone, and coal streak as interlayers, while interbeded with grey glutinite, coarse sand and grey dark mudstone at the bottom of this member.The lithology of Huoshiling Formation possiblely correspond to regional stratigraphic-lithologic characteristics, the upper part mainly composed of grey tuff, mudstone, and grayish green dacite and andesite, while the lower part consists mostly of dark mudstone, with fine-siltstone and coal streak as interlayers.The basement probably composed of mottled-green conglomerate and green "metamorphic rock". And the Permian-Carboniferous "metamorphic rock" probably very high diagenesis or very low-grade metamorphism sedimentary rocks. |
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