Reservoir Characteristics Of Bedrock Buried Hill In Tanan Depression

Tanan depression is a negative structure unit located in the south of central rift zone in Hailer- Tamtsag Basin. In recent years, people find better oil and gas show in the buried hill reservoir. Because of complex geological conditions and the conditions of hydrocarbon accumulation, the unclear geological knowledge of bedrock buried hill reservoir which include the formation mechanism and distribution of holes, features, which can not meet the needs of speeding up the exploration and development. So this paper is comprehensively used of seismic, well logging, logging, core and production testing to study the reservoir characteristics of bedrock buried hill in Tanan Depression. We stressly analyze petrologic characteristics, the type and logo of diagenesis, diagenesis sequence, the division of diagenesis stages and physical characteristics and the type of reservoir space and characteristics of the bedrock reservoirs. Because the distribution of the poor property feature determine the quality of reservoir properties. This paper prospects the development and distribution of bedrock feature by many methods. At the same time, combinating the ancient geomorphological features, we have pointed out the favorable exploration blocks by combining evaluation of the reservoir and provided foundation for the oilfield development.The result shows that the bedrock buried hill reservoir includes pyroclastic rocks and clastic rock and the main clastic rock is feldspathic lithic sandstone and lithic feldspathic sandstone and its maturity is low. Main diagenesis types include mechanical compaction, cementation, metasomatism, dissolution, fracture diagenesis, cavity filling and so on. Compaction, cementation and cavity filling damage the reservoir properties, but metasomatism, dissolution and fracture diagenesis is favorable for the formation of secondary pore. The main lithology of pyroclastic rock is tuff, sedimentary tuff, tuffaceous sandstone, tuffaceous sandy conglomerate, etc. The important diagenesis include mechanical compaction, mechanical filtration, de-vitrified role, alteration, cementation, clay minerals, dissolution, etc. The main diagenesis stage is A period of middle diagenesis stage and B period of middle diagenesis stage is the second one.The bedrock buried hill reservoir's physical characteristics is low porosity and permeability - low porosity and low permeability in Tanan depression. The main type of fracture is tectonic origin type which is the main type of reservoir pore. The paper has prospected the reservoir fracture by well logging interpretation, MVE and core observation. At the same time, by the burial history research of single well ,we discuss characteristics of the ancient topography of the area. The ancient landform of small elevation difference may be the main reason for less developed secondary porosity. The various researches shows that the overall reservoir properties is worse, and the proportion of the good reservoir is 12%. Excellent reservoir is main located in the central of the rift zone.