A Study On The Genesis And Evaluation Of Tight Sand Reservoir In Daniudi Gasfield

The researches on reservoir of Daniudi gasfield of Ordos basin are not systematic.By the theory of present sedimentation and reservoir geology, based on the comprehensive application of core,well logging,logging,production testing,and analytic data,the sedimentation characteristics,reservoir characteristics,controlling factors and evaluation of effective reservoirs of Carboniferous-Permian formation were systematically studied.The depositional setting of Daniudi gasfield is braid river delta sediment systems, types of microfacies include braid river delta plain and front deposition.The results show that the reservoirs mainly is clastic and consist of conglomerate, glutenite and sandstone.The reservoir has high compositional maturity and low texture maturity. The diagenetic stage of reservoirs is divided into early diagenetic stage B,middle diagenetic substage A1 and A2 and middle diagenetic stage B,mainly developed compaction,cementation,metasomasis and dissolution.The pore of reservoir is divided into primary pore,secondary pore and fracture by origin,the mostly is secondary pore.Following depth increasing primary pores decrease whereas secondary pores and fractures increase and developed two secondary pores zones in vertically. Micr-fractures on one hand make the pores conneet improve the reservoir quality of the sandstones.On the other hand,act as the role that transporting fluid medium.Porosity and permeability of Carboniferous- Permian reservoir is low and pore texture is mid-microbore-microthroat.The controlling factors of physical property of reservoir in macroscopic is tectonism,on vertically is diagenesis and on plane is sedimentation. High compaction and argillaceous content made reservoir became more tight and has a poor physical property,otherwise,has a good physical property.Considering these controlling factors,the evalution standard of reservoir is established and classified into four categories,of which,â… andâ…¡is effective reservoirs.The result indicate that the effective reservoirs concentrate in the central and southwest of Daniudi gasfield.The sedimentation of effective reservoirs mainly is braid river delta front and sand body mostly is subaqueous distributary channel.Reservoir mainly is silicarenite and lithic silicarenite with macrograin and mesograin.