The Influence and Formation Environment of Chlorite Coatings in the Clastic Rock

Key words: 
• chlorite coatings /
• reservoir physical property /
• protectivemechanism /
• formation environment

Abstract: Unifying the domestic and international research information and using chlorite cement as the research object in the Daniudi Gas Field, we have discussed the cause of chlorite coatings and its influence on reservoir physical property, moreover studies on its environment designating signification. The chlorite cement of Daniudi Gas Field which thickness is 10~20 μm formed in early stage of diagenesis, and the crystal becomes better, the particlebecomes bigger gradually from the edge of primary intergranular pores to the center. Chlorite coatings can be divided into in autochthonous genesis and allochthonous genesis according to the source of ferruginous. The autochthonous chlorite coatings existing as mixed layer clay and the smaller crystal coatings was generated from the undischarged Fe-rich fluid which was produced by precursory clay mineral and the dissolution of rock fragment. The allochthonous chlorite coatings crystallizing fully and well was generated from the Fe-rich fluid which was produced by Fe-rich minerals and cuttings dissolution flocculating offsite through rivers. Mechanism of reservoir protection of chlorite coatings: ①inhibition of secondary quartz increases; ②increased mineral particle compaction strength and restrain pressure solution; ③inhibition of carbonate cementation and promote corrosion. The chlorite coatings of Daniudi Gas Field mainly developed in H1(63%) and S2. Porosity rises linearly with the increase of content of chlorite when chlorite content below 15%. Chlorite coatings can be used as delta (braided river delta) front of underwater distributary channel (underwater braided rivers) and other microfacies marker of strong hydrodynamic conditions.