Reservoir characteristics and favorable area prediction of Devonian Kizirtag formation in Bashituo area, Tarim Basin

摘要

Tarim Basin is the largest petroleum potential in the west of China. As a co-prospecting project, some wells of the Devonian Kizirtage formation in Bashituo area have gained encouraging industrial oil flow. The basic characteristics of the reservoir beds are described in detail in this paper by collecting and processing plenty of existing data. The results of petrologic analysis show that the pore types of the Kizirtag formation are mainly residual primary intergranular pores and intergranular dissolution pores, and the lithology is mainly fine grain quartz sandstone. Based on the analyses of reservoir physical properties, the reservoir porosities of Kizirtag formation in study area mainly range from 2% to 8% with an average of 6.14%, and the reservoir has a lower permeability with a range less than 1 × 10~(-3) pm~2 with average of 1.86 × 10~(-3) pm~2. The core analyses indicate there is a distinct positive correlation between porosity and permeability, and members 4 to 6 are the main reservoir section. The inversion prediction of reservoir physical properties shows that the distributions of favorable zones are similar to the distribution of sand body and sedimentary facies. The favorable zones of reservoir physical property of member 6 in Kizirtag formation range from well BK8 to well BK2 and the northern area. Well Q003 and the south eastern area have the poorest physical properties. The favorable zones of reservoir physical property of member 5 distribute in the northwestern and south central area of the study area. The favorable zones of reservoir physical property of member 4 distribute in well BK8 area. Through the statistics analysis, it was found that the reservoir physical properties in study area were controlled by primary sedimentary environment and diagenetic transformation and was especially influenced by the carbonate cementation. There is an obvious negative correlation between the carbonate content and porosity and permeability. Based on the tectonic characteristics, reservoir distributions and hydrocarbon test results of the study area, the favorable areas of main productive layers in the Kizirtag formation were divided to I type, II type and III type. The I type area with the optimum forming conditions is the most favorable part for oil and gas accumulation. So it is suitable to immediately implement drilling, which poses a low drilling risk. The I type areas of the sixth member in the Kizirtag formation is mainly distributed in the intensive areas of exploration wells. The I type areas of the fifth member are mainly concentrated in east in the study area, and the distribution of I type areas in the fourth member of Kizirtag formation is similar to that of the sixth member, but the range is reduced. The distribution of the fourth member is concentrated in the Q002 well to BK9 well range. The II type area has better reservoir forming conditions, and belongs to a more favorable area for hydrocarbon accumulation. However, there are also some exploration risks . In II type areas it is appropriate to carry out drilling to explore objects combined with other hydrocarbon bearing series. The II type areas of the sixth member in Kizirtag formation is concentrated in the east of the study area,; that of the fifth member basically covers the scope of the two traps that are interpreted in this study. In addition, there are larger distribution areas in the east of the study area, and a small distribution area in the south western part of the study area. The II type area distribution of the fourth member in the Kizirtag formation is diminshed, and is mainly distributed in the north of the study area. The reservoir formation conditions of III type zone are poor, so there is no drilling under its current condition. It was considered that this research can provide a new method for future exploration of this area.