Distribution of Platform Edge Reefs and Beach As Well As Their Major Controlling Factors Over the Changxing-Feixianguan Formations in Northeast Sichuan Basin, China
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+ MODEL Available online at www.sciencedirect.com ScienceDirect Journal of Natural Gas Geoscience xx (2017) 1e10 http://www.keaipublishing.com/jnggs Original research paper Distribution of platform edge reefs and beach as well as their major controlling factors over the Changxing-Feixianguan formations in northeast Sichuan Basin, China Mancang Liu*, Wei Yang, Hui Jin, Wulin Mo, Saijun Wu, Nan Su Institute of Natural Gas Geology, Research Institute of Petroleum Exploration & Development, PetroChina, Langfang 065007, China Received 9 February 2017; revised 12 April 2017 Available online ▪▪▪ Abstract The platform facie, platform edge facie, slope, and basin facie were developed in the Chengkou-Western Hubei Trough zones during the Upper Permian Changxing Formation's Early Triassic Feixianguan period; during this time the platform edge had the most favorable sedimentary facie. The Changxing Formation was composed of three sections in which the second section was rich in framework reef, whereas the third one was rich in micro-reefs at the bottom. Recently, it has been discovered that abundant platform edge shoals are developed in the third member and that oolitic shoals with large thickness are widely distributed. This paper systematically investigated the influence of the changes in reef-building organism system on the development of organic reefs. The results show that the distribution of bank belts is determined through paleogeography framework. The rapid change of relative sea level affects the formation and movement of bank belts. In addition, the regional tectonic activity controls the distribution and transformation of the bank belts. Finally, the prospective zone in the Chengkou-Western Hubei area was evaluated and divided into four favorable zones, in which the Wanyuan-Yunyang area was deemed to be most advantageous. Copyright © 2017, Lanzhou Literature and Information Center, Chinese Academy of Sciences AND Langfang Branch of Research Institute of Petroleum Exploration and Development, PetroChina. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Keywords: Organic reefs; Oolitic beach; Changxing Formation; Feixianguan Formation; Development and distribution; Chengkou-Western Hubei; Sichuan Basin 1. Introduction Wuxi, Fengjie, and Fengdu in Chongqing, Lichuan and Enshi in Hubei, and so on (Fig. 1). With the same formation mechanism, The Changxing and Feixianguan formations are rich in reefs the Chengkou-Western Hubei Trough and the Kaijiang- and shoals with a wide distribution range in the Sichuan Basin. Liangping Trough are worth exploring. Recently, most re- Thus far, a number of abundant big industrial gas pools have been searchers aimed to study the characteristics of reefs and shoals as discovered, such as the Longgang, Puguang, Tieshanpo, Luo well as their distribution patterns and controlling factors [4e9]. Jiazhai, and Wubaiti, which have become the most important Their research provides abundant materials for gas prospecting prospecting areas after the Carboniferous in the Kaijang- in Chenkou-Western Hubei Trough. These findings are all based Liangping Trough [1e3] within northeastern Sichuan. The on the investigations of outcrop and well observation using a study area, Chengkou-Western Hubei zone, is located in the variety of geological, logging, and seismic methods. north-eastern Sichuan Basin. It refers to the Zhenba County in We studied the controlling factors of platform edge reefs Shanxi, Wanyuan in Sichuan, Chenkou, Kai County, Yunyang, and shoals' distribution and the development of the Changxing-Feixianguan formations in Chenkou-Western * Corresponding author. Hubei Trough areas within Sichuan Basin. Furthermore, we E-mail address: [email protected] (M. Liu). analyzed the exploration prospect of this region which could Peer review under responsibility of Editorial office of Journal of Natural Gas be helpful for oil-gas prospecting. Geoscience. http://dx.doi.org/10.1016/j.jnggs.2017.06.002 2468-256X/Copyright © 2017, Lanzhou Literature and Information Center, Chinese Academy of Sciences AND Langfang Branch of Research Institute of Petroleum Exploration and Development, Petro- China. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Please cite this article in press as: M. Liu, et al., Distribution of platform edge reefs and beach as well as their major controlling factors over the Changxing- Feixianguan formations in northeast Sichuan Basin, China, Journal of Natural Gas Geoscience (2017), http://dx.doi.org/10.1016/j.jnggs.2017.06.002 + MODEL 2 M. Liu et al. / Journal of Natural Gas Geoscience xx (2017) 1e10 frequent. It is rich in nutrient substance; therefore reef- building organisms were abundant. They lead to high pro- ductivity in carbonate rock. According to the features of reef- building organisms, it could be further divided into skeleton reef and lime-mud mound characterized by light gray to gray thick-blocky sponger limestone, algal limestone, reef dolo- stone, and microbialite. The types of the organisms in the sedimentary environment that were abundant include sponges, hydrozoans, corals, and other reef-attached organisms. Framework reefs mainly developed in the mid-bottom of the Changxing Formation (Fig. 4aed), while lime-mud was widely developed in the upper-mid section (Fig. 4eeh). The scale of the platform edge reefs was large on the plane, but not continuous in the horizon. It kept string beads distributed along the platform edge. 2.2. Platform edge shoals The platform edge shoals, often developed in the high en- ergy environment of the platform edge, blocks the wind and faces the wide sea. Its depth ranged from 5 to 10 m above the sea level. In addition, it's also characterized by recycled well water, abundant oxygen, formal salt, and visible current. It contained grayewhite to light gray thick-blocky sparry bio- clastic limestone, sparry intraclast limestone, and sparry grain limestone (Fig. 5aed). It is also accompanied by large middle cross bedding and wedge cross bedding. It was popular during Fig. 1. Location and local structural map showing the study area. the sea lever falling act of the Changxing-Feixiangaun phase, depositing bioclastic bank, intraclast bank, and oolitic bank, 2. Characteristic of platform edge reefs and shoals respectively. This is common in many outcrop profiles and well-drilling profiles, such as the Tianba, Manyue, Shuanghe, On the basis of petrography, sedimentary structure, and Miaoba, Well Feng 1, Well Jinzhu 1, Well Luojia 2, and Well ' paleontology feathers, in combination with an areas sediment- Jian 27. With the rapid change in relative sea level, the plat- tectonic background, we divided the Changxing Formation- form edge bank transformed observably. Feixianguan Formation into four facies belts (Figs. 2 and 3): platform, platform edge, slope, and basin. The platform edge 3. Deposition situation and distribution of reefs and shoals is rich in reefs and shoals. at the Changxing-Feixianguan formations The platform edge is located in the narrow area between the platform edge and slope where the terrain is higher than the 3.1. Reefs of the Changxing Formation others. The said area is intensely affected by waves and tides. Its boundary comes in contact with the wave base. Thus, Study areas suffered from transgression that leads to the developing platform edge reef-shoals on the side of the wide water deepening from west to east during the early to middle sea and forming the rimmed platform between the platform Changxing phase. In response to the change, it successively and the slope boundary. It exposes itself to a certain sea level developed the platform, platform edge, slope, and basin that causes it to suffer from atmospheric water eluviation and (Fig. 6). The area of the Tiechanghe, Fengtong, Panlongdong, e mixed dolomitization [10 12]. The typical sediments were and Jiantianba is regarded as the geological boundary of the reef limestone and grain limestone with fine grain sorting and sedimentary facies division, of which the west developed the roundness, as well as sparry cement, all of which reflects that open platform. The dominant sediment was intra-platform the sedimentary environment was of high energy. Based on the shoals or reefs in the higher geomography of the intra- sedimentary features, the platform edge could be divided into platform. The framework reefs could be seen in many places a reef and bank sub-phase. such as Fengtong in Wanyuan City, Panlongdong in Xuanhan County, Manyue in Kai County, Well Feng 1 and Jiantianba. 2.1. The platform edge reefs They kept the state of string beads and broken chain along the edge. The slope was located on the outside of the platform The platform edge reef was one of the important sedi- edge and it gradually became steep and narrow due to the mentary types on the carbonate platform edge. It faces the effect of the powerful facies of the platform edges. The basin wide sea where waves and upward current processes are facies mainly developed in the east of the slope facie, Please cite this article in press as: M. Liu, et al., Distribution of platform edge reefs and beach as well as their major controlling factors over the Changxing- Feixianguan formations in northeast Sichuan Basin, China, Journal of Natural Gas Geoscience