The Research On Damage Mechanism Of Low Permeability And Micro-fracture Of Nanyishan Reservoir

Unconventional fractured reservoir contains abundant hydrocarbon resources in northwest of CHD basin. The thesis makes a comprehensive, systematic study about the damage mechanism of Nanyishan reservoir which is one of reservoirs in northwest of CHD basin.Through the study and analysis on the petrology and fluid properties of the reservoir, the experimental test of formation sensitivity, the experimental evaluation of fluid into the wells and expansion experiment and the experimental method that is established by the thesis for evaluating formation sensitivity, the following knowledge and achievements have been primarily obtained:(1)Reservoir rock of Nanyisan is complex, its lithological property is divided into four types, that is, lime mudrocks, sandstones, mudstones and tempestite, and lime mudrocks are the main rock types. The reservoir physical properties is poor as a whole, belong to typical in-low porosity and low-low permeability reservoir. Main types of the pores have intergranular micropore, dissolving pores and micro-fracture.(2)The main clay minerals are illite, chlorite, their content generally about 25%, and some amorphous clay are included. They are major sensitive material. Special pore structure of the reservoir is combination of microfracture and pores, the width of micro-fracture is mainly in the 1～30μm, and the main flow channel of fluid. The micro-fracture is vulnerable and one of the main factors of formation damage.(3) The formation damage of Nayishan reservoir is strong water sensitivity, strong salt sensitivity, strong acid sensitivity, moderately strong alkali sensitivity and velocity sensitivity, and strong stress sensitivity. In particular, when micro-fracture reservoir rocks experience strong stress sensitivity, it is difficult for their permeability to be recovery.(4) It is very serious for the drilling fluids, killing fluid, injected water and fracturing fluid which are used to damage the formation. The degree of damage is middle-strong. The damage of Guan gel fracturing fluid is relatively the strongest, the second is low polymer fracturing fluid. The cleaning fracturing fluid has the lowest damage. All water-based fluid may lead to the expansion of the reservoir rocksx, the role of anti-swelling agent is very limited. However, kerosene is able to make the rock contract and can inhibit expansion of the rock.In this study, the paper puts forward the protection measures of Nanyishan reservoir. The results of the paper establish the foundation for understanding of the mechanism of formation damage and protection of Nanyishan reservoir. At the same time, also there is important guiding significance on the similar low permeability reservoirs.