The Relationship Between The Distribution Of The Igneous Rocks And The Oil And Gas In Tazhong Area

Tazhong area is the central uplift of Tarim Basin, which consist of three structural units: Bachu Faulted Uplift, Tazhong Uplift, Tadong Uplift from west to east. Generally speaking, Tazhong area includes east part of Bachu Faulted Uplift, Tazhong low-relief Uplift and west part of Tadong Uplift, which, covering an area of 75000km2, consists of five blocks: west Pintuoguole, Katake 1, Adong, east Hetian river and west Hetian river.Carboniferous and Permian is the most important period in the structural evolve-ment of Tarim Basin. In late period of the early Permian, ocean basin of the southern Mountain-Tian and ancient ocean died out, so continental plate of Tarim collided with plate of Mid-Mountain Tian and Kazakhstan plate-Junggar plate and pieced together finally. Continental plate of Tarim became one part of Eurasia plate and ancient orogenic belt of Mountain Tian formed, leading to Permian riftogenesis in Tarim Basin, and giant volcanic rocks formed.In this paper, the author has thoroughly analyzed the sedimentary system, the tectonic evolution, the distribution of the igneous rocks in each formation, the methods to recognize igneous rocks, the geochemical characteristics of the igneous rocks and their forming environment, the methods how to recognize the igneous rock strata sequence and their correlation, the controlling facts for the distribution of the igneous rocks, the relationships between the igneous rocks and oil and gas and the reservoir types in igneous rocks etc. Firstly, In order to recognize the igneous rocks in this area, much data such as drilling, wire line well -logging and seismic, many methods such as drilling, wire line well - logging, synthetic seismogram, seismic facies, seismic data specially processing, foreward modeling , impedance inversion and 3-D horizontal slice are used in this paper. This is the first time to make a synthetic seismogram with resistivity curve then to study the distribution lateral and vertical of the igneous rocks in Tarim basin. Secondly, the igneous rock cores and the micro element are used to study the geochemical characteristics and the forming environment of Permian igneous rocks in Tazhong area , and then to recognize the strata sequence of the igneous rocks and their eruption pe-riods of the rocks which were from four to six. Finally, the author summarized the types of reservoirs in igneous rocks on the basis of the analyzing the active periods of the volcano and the relationship with the generation, migration, and accumulation of oil and gas. On the basis of a lot of studies, the author has gotten the following point of views:1. The igneous rocks in Tazhong area are widely and unevenly distributed, and their thickness are charged very much. The Permian igneous rocks in this area are mainly neutral to basic.2. In Tazhong and its vicinity area, the Fast experience formula (V = KH1/6Rt1/6) can be used with resistivity to get sonic velocity. The Fast constant in Tazhong area is K = 756.645.3. Because thin layers' seismic events of the top and the bottom are stacked, the instantaneous frequency is usually high. Whereas the instantaneous frequency in the interior of the igneous rocks is usually low as the shielding functions of the top igneous rocks. Based on the point of views above, the high instantaneous frequency on the instantaneous frequency profiles can be used to study the lateral and vertical distributions of the igneous rocks, and the low even instantaneous frequency can be used to study the plane distribution of the igneous rocks in this area. The top of the igneous rocks usually has high reflection, positive instantaneous phases, and the absolute value of that is minimum.4. The eruption of the volcano of Permian in Tazhong area was mainly through rift, and companied by heart— style. The type of the volcano in Tazhong area was continental rifting and island arc. The Tazhong No. 1 fault, which is extended to the subduction zone, could be the passing way to the magma. There were two eruption periods in early Permian in this area, of which the Kupukuaman period, occurred in the Xixia epoch of early Permian, the other one, Kaipaizleike, was occurred in Maoko epoch of early Permian. Bachu—Manxi volcano is belonged to the second one. *5. One molten melt which is cooled be called a lava unit. A group of lava, which represents the combination of several times eruption, consists of many lava units. The division and correlation show that there were 4 — 6 time eruptions during Permian in Tazhong area.6. There is a close relationship between the volcano's activities and the generation, migration, and accumulation of oil and gas. Volcano's activities can offer affluent mineral materials, can enhance the organic material abundance, can generate caloric to speed up the generation of oil and gas, can offer micro elements and transition metallic element as activators to improve organic material change into petroleum, can offer volcano material which can be deposited in some area to form reservoir. Meanwhile, the heat the vol-cano generated can destroy the source rocks and oil and gas reservoirs which were formed early. The rifts which were formed with the volcano's activities can be the sound migration way for the oil and gas. If the volcano's activities were earlier than the migration of oil and gas, then these sorts of activities can be helpful to the formation of oil and gas reservoir, otherwise, could be harmful.7. There are many types of oil and gas reservoirs in Taxzhong area: typel, uplifting and percolating in Silurian and Permian;type2 , rock sill pierced in Carboniferous} type3, invasion rocks to be lateral seal in Cambrian, Ordovician and Carboniferous;type4, draping anticline in Permian and Triassic.