Characteristics and assessment of the Chang 2 low permeability sandstone reservoir in the Dingbian oilfield of Ordos Basin

The Chang 2 reservoir in the Dingbian oilfield of Ordos Basin contains medium-fine feldspathic sandstone in delta plain distributary channel deposit,with average porosity of 16.36% and average permeability of 9.58×10-3μm2,belonging to medium porosity and mid-low permeability reservoir.The Chang 2 reservoir has been studied and evaluated based on analytical data of intrusive mercury curve and casting thin section as well as the results of production test and mud logging.It is concluded that the Chang 2 reservoir involves primary porosity and secondary porosity,and the latter had developed feldspar dissolved pores which had improved reservoir property;the diagenesis mainly involves compaction,cementation and denudation,the first two were severely destructive to reservoir property,and denudation had enlarged reservoir space and improved reservoir property;the Chang 2 reservoir can be divided into Class I,II,III and IV these four types;the Chang 2 reservoir is a mid-low permeability reservoir mainly composed of Class I and II reservoir,with high quality reservoir distributed in the mid-low part of the distributary channel deposit.