| The Keshen-2 gas reservoir belongs to fractured pore type tight sandstone reservoir in Kuqa Depression,and has the characteristics of deep burial,strong compaction,lack of mature research experience and technical reference.This paper not only used basic data of casting thin sections,SEM,high pressure hg injection,negative pressure pore permeability,all diameter pore permeability,but also adopted some new methods of CT scan,laser scanning confocal,field emission scanning electron microscope according to the features of study area.Further study on pore structure,fracture,physical properties,petrological characteristics and diagenesis features of the reservoir is carried out.Combined with reservoir elements and fracture elements,develop synthetic classifying evaluation of the reservoir in study area.The main achievements are as follows.1)Pore structure is very complex in the study area.Throats are very small,mainly are on the scale of micro-to nano-meters.Pores are mostly made up by original intergranular pores and vugular pores.Pore throats are distributed widely and among them,the throat with diameter of 0.1 ?m could control the fluid mechanics in porous medium.In 2-D space,the smaller the pores,the shape is more like a circle;in 3-D space,the smaller the pores,the shape is more like a sphere.However,the bigger the pore,the shape is more unpredictable.This is caused by pore erosion.Bigger original intergranular pore and corrosive pore are the main reservoir space.Smaller corrosive pore contribute to both reservoir space and seepage capacity.Lamellar throat play a role of linking pores.2)Fracture is the main seepage pathway in Bashijiqike Formation.Fractures in the study area are mainly with a high angle or vertical.Its trend is west-east and south-north and strike is northeast to southwest.The fracture opening is generally 0.2mm,half of which are filled.Fracture with small opening shows low level of filling,but fracture with small opening have little contribution to porosity.Most of the crack porosity are below 0.1%.Fracture with high porosity have high degree of filling.3)The tight reservoir in study area is caused by sedimentary,diagenesis process and structural movement.The composite maturity is low in the study area with strong diagenesis process such as compaction,cementation and corrosion.The main types of cements are carbonates like calcite and dolomite.The reservoir experienced four diagenesis stages:early compaction and cementation;Supergene dissolution and leaching,the middle stage,compaction,cementation and alkaline dissolution,late generation of fracture of the late tectonic extrusion,and dissolution.4)Bashijiqike Formation is made mainly of type ? tight sandstone reservoir(based on tight sandstone reservoir classification method of Jia Chengzao).Porosity range from 3%to 7%and permeability from 0.003 to 0.1 mD;there is no apparent relation between porosity and permeability in the reservoir.In sandstone,the larger the particle size,the better the reservoir physical properties;Reservoir quality index,short for RQI,increase with quartz content increasing and decrease with the rock fragment content and mud matrix content decreasing.This indicates that the reservoir pore structure becomes better with higher sandstone composite maturity and becomes worse with more mud matrix content;reservoir stress sensitivity is moderate to low and permeability stress sensitivity is better than that of porosity.5)According to the basic features,the reservoir can be divided into four types.Based on fracture occurrence the reservoir can be divided into five types.When combining the above two classification,we can come to an integrated classification method which divide the reservoir into five categories.The reservoir in this study area is mainly type II and type ?,and type I and type ? follows.Reservoir type has a close relation with gas well production capacity.Fracture has a strong impact on early stage production capacity on single well.This classification has practical implication. |
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