| A set of dense drainage system and unique geomorphology combinations were created under the fluvial karstification in early Hercynian of Tahe Oilfield. As a result, a large carbonate karst fracture-cave system was produced and the karst features in east and west areas vary a lot. Karst water has special representative motion style and enrichment pattern in different geological structure, geomorphic background and the state of karst development. And the motion style and distribution style play an important role in the development and distribution of karst reservoir. So this is the essential question in the study of karst reservoir. At present, the domestic and foreign scholars have made some research on the development and control of karst reservoir in ancient landform and water system. But they don’t study from the hydro-geomorphological system and karst landform evolution angle of karst water structure style, hydrodynamic characteristics, the water yielding and runoff routing theory, and expounds the hydro geomorphological system, karst landform evolution and cave development of relations between the "structure and function".Address the above problems, we rebuilt paleo-gemorphology and paleo-drainage system at the depth of over 5,000 meters, then precisely described and compared the hydro-geomorphologic characteristics between east and west areas, and lastly identified their karst evolution stages, divide the karst hydrological and karst platform, In this process, modern karst theory and seismic attributes extracting and related imaging techniques based on high resolution 3-D seismic data were utilized. Secondly, using the logging interpretation porosity data to establish the non-cave type reservoir classification template, and division the region 971 single well reservoir type. The region’s Underground River Cave is forecasted through hydrology and geomorphology principle method and seismic methods, and development characteristics are compared in the different hydro geomorphological system karst reservoir layer. Finally, through the anatomy of different hydro geomorphological system in the karst water yielding and runoff routing theory and reservoir development, and combined with the modern karst landforms field investigation to discuss different hydrological and geomorphological development pattern. The main research is as follows: 1. There are great differences in characteristics of hydrology and geomorphology in different areas of Tahe Oil field in the early stage of Hercynian.1) The secondary ancient karst landform unit Divided into karst plateau, karst slope, karst basin in Tahe Oilfield. Different secondary hydrological features of karst landform units have obvious difference. The karst, plateau, karst slope develops in karst plateau, and peak cluster and karst hill acted as the primary landform units with high relief. Developed a large karst canyon. Surface drainage shows large dendritic, deep valleys and Cascade shape profile formed by strong vertical erosion from surface water. Capture stream appear in the border of the karst plateau and karst slope, the surface water developed in the mature stage. Moreover, the evolution degree of surface water tended to be mature because a large amount of them were shifted to subsurface leading to a integrated underground hydrologic network, which reflected a long stable karstification period, karstification landform evolution stages is in mature stage. The karst basin developed in karst depression and gentle topography gradient and karst hills with relatively lower relief were found. Obviously, the evolution stage of surface water displayed much younger as snaking steam developed well, that is, surface water was stored mainly on the ground rather than underground and the lateral erosion was highly prominent. Therefore, a limited karstification period was revealed, karstification landform evolution stages is in young stage.2) According to the structural characteristics of the watershed boundary,water system, hydrodynamic conditions and the characteristics of water cycle, Tahe Area Early Hercynian basin system is divided for Karst Plateau hydro geomorphological system, karst slope geomorphology and hydrology system, karst basin geomorphology and hydrology system and shallow overburden cover area hydro geomorphological system.3) River terraces, flow concentration and onlap termination, were utilized to subdivide karst platforms architecture. Karst platforms in Tahe Oilfield can be subdivided into 4 levels, and platform I was first formed, while the area of platform III was the maximum, experience a long stable tectonic stage. 2. Karst reservoir distribution characteristics of the development has obvious differences in different hydrological landscape system.Underground river caves in the hydrological landscape system of karst plateau appear single type, network type in the plane, and they have the large scale in the development, buried depth, and good connectivity characteristics. Blind valley, swallet steam and the underground river which formed by the capture phenomenon are abnormal developed. And the most of these underground river developed in the boundary of the plateau and the slope. Epikarst reservoir has higher development degree in the wing of the pepino hill than the top and bottom. Closer to the main river (Valley) senior stream (Valley) parts surface karst reservoir more development, and away from the main Valley lower sub drainage (Valley) surface karst belt karst reservoir layer on a smaller scale; The caves in the hydrological landscape system of karst slope area developed into large scale branch work passage system, the branch system developed well, and they have the large scale in the development, buried depth, and good connectivity characteristics. The caves in the hydrological landscape system of karst basin mainly appeared to be isolated, but they aren’t formed into continuous underground river network. And caves developed in the small scale and buried shallow; there are two sets of isolated caves in the hydrological landscape system of the shallow coverage area. Most of Yijianfang Formation are reef flat facies sedimentary. Even though it has experienced the late diagenetic transformation, parts of them has been destroyed, and some primary pores and secondary pores are still preserved. In the region, the all caves shows the obvious characteristics of stratification and complexity in vertical direction. The cave layer presents the formation time sequence which up layer is old and down layer is young.3. The valley, pepino hill epikarst zone reservoir development pattern are established, syncline confluence type underground river cave development pattern, watershed and fault controlled underground river cave development pattern in the karst plateau hydro geomorphological system. The surface and subsurface double structure of caves development pattern in the canyon area and development pattern of the double controlled by the canyon and the fault cave are established in Karst slope hydrology and geomorphology system. The development pattern of the bedding karst and the karst development pattern of the deep hydrothermal fluid were established in the shallow coverage area. Based on the relationship between the hydrogeology and space-time evolution of the karst reservoir response, the rule of karst reservoir development are discussed. The development model of the cave layer under the constraint of karst platforms is established.1) The joint and fracture in the wing of the pepino hill provide a good condition for infiltration and corrosion of the meteoric fresh water into the surface rock mass. And the meteoric fresh water infiltrate into the subcutaneous hydrological layer strongly. It produces subcutaneous flows which is lateral diffusion flow and excrete to valley. The meteoric fresh water infiltrates in the surface fracture for a long time, so the surface karst zone reservoir of the wing of the pepino hill develops well. Because of the flow’s great vertical erosion, the most of main river (Valley) surface on both sides of the branch river (valley) become into the dry condition. Surface water transports into the underground through the bottom of valley. That makes the branch valley system "leakage in". So it controls the development of the branch valley system surface karst reservoir.2) Two large watershed enclosed by the limit of the syncline structure as favorable catchment area, plenty of meteoric fresh water supply conditions and surface water strong vertical to erosion in plateau hydrology and geomorphology. It makes surface valley system degraded into dry valley, subterranean streams, and a blind valley. And a large number of drowning holes and shafts, the hydrological network has disintegrated and gradually to the underground transformation. Internal syncline rock joint surface and fracture development provides channels for the infiltration of Groundwater. It causes in the formation of the syncline axis development of large-scale underground river cave system. Due to the core of watershed’s deep fracture is developed, some water along the watershed wings along deep faults infiltration, and become watershed-fault controlled underground river cave.3) Canyon area has larger landform gradient, which provide larger hydrodynamic conditions for surface water. Surface water system with a strong vertical erosion, and eventually down to underground, make the surface system loses its ability to drainage, Developed drainage system parallel to the original surface valleys, formed a surface-underground cave system; canyon control hydro-dynamic field, make regional surface and groundwater discharge to canyon, the fracture provides specific path for groundwater infiltration. After many time fall of base level, formed many layers of caves in the canyon.4) Northern of shallow coverage area provide strong hydrodynamic conditions, fracture and cave and cave in grain limestone provide a advantage path, Part of the water along fault discharge to down-cutting river. Another part of the water upward to the surface through fault, formed the rising spring, to form the complete recharge runoff-drainage system. Deep thermal fluid flow upward along deep fracture, carry a lot of strong chemical activity of material components and generate hydrothermal karstification, Which contributed to the development of reservoir in deep area.5) Karst plateau experience a long stable karstification period. The complete surface karst watershed drainage network combinations consist of dry valley, blind valley, swallet steam and function of comprehensive underground water cave system is the product of mature period of karst landform evolution. The karstification time in Karst basin region is limited, the isolation cave is the product of young period of karst landform evolution.6) Three cave levels were identified, distributing to be layered, and the scale of the cave level controlled by platform Ⅲ was the largest. Actually, this three cave levels are not overlaid in vertical except some part of the cave level confirm to platform Ⅲ extending to platform Ⅱ. This feature above proved that the cave level controlled by platform Ⅲ resulted from a long stable tectonic stage, while the other two cave levels were created in a relatively restricted tectonic stage. |
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