Damage Mechanism and Experimental Evaluation Method of Fractured Reservoir during Drilling Process
Based on the study of rock pore structure,stress sensitivity and percolation rules,the method of artificial fracture was used to simulate rock fracture width of the formation to evaluate the drilling fluid damage degree by the means of measuring the different permeability both before and after the core pollution induced by mud.By taking Kazakhstan Kenkiyak Oilfield for example,reservoir damage mechanism was experimentally evaluated during drilling process.The results show that solid particles block core surface when fracture width is very small,however,they invade into the depth of core and cause serious damage as fracture width is greater than 100μm.The wider the fracture is,the serious the formation damage is.Therefore,for the fractured reservoir,balance drilling or underbalanced drilling should be used to the protect reservoir if the fracture is quite wide.