Main Characteristics and Evaluation of Bedrock Reservoirs in the Eastern Segment of Altun Piedmont

Based on the field outcrop survey,core observation,section identification,scanning electron microscopy and cathodoluminescence method,combined with conventional logging,image logging,pore infiltration test data,etc.,main characteristics and evaluation of bedrock reservoirs in the eastern segment of the Altun Piedmont were studied. The results show that the lithology of the bedrock reservoirs in the eastern segment of Altun Piedmont mainly includes magmatic rocks and metamorphic rocks. The magmatic rocks are mainly granite,and the metamorphic rocks are mainly gneiss and schist. The types of reservoir space mainly include incompletely filled fractures,dissolved pores and matrix micropores. The maximum porosity of bedrock reservoir is 9.76%,the minimum is 0.004%,and the average is 1.663%~3.844%. The maximum permeability of bedrock reservoir is 33.239 mD,the minimum is 0.002 mD,and the average permeability is 0.020~3.836 mD. There is no obvious correlation between porosity and permeability. The main controlling factors of bedrock reservoirs include lithology and mineral combination,paleogeomorphology,pre-existing faults and fracture zones,late magmatic intrusion and hydrothermal action. Combined with the physical properties and the main controlling factors of the bedrock reservoir,the evaluation criteria of bedrock reservoir controlled by many factors are put forward. The reservoir is divided into four categories:good,average,fair,and poor. The results of evaluation show that the study area is mainly composed of type Ⅱ reservoirs,mainly found in granitic gneiss,followed by granite,plagioclase gneiss,feldspar hornblende schist,etc. The Dongping nasal and Niuzhong-Niubei slopes are mostly type Ⅰ reservoirs,the Jianbei slope,Niudong nasal and Lengbei slope are mostly type Ⅱ reservoirs.