The invention discloses a quantitative evaluation method for the stability of a
tight oil reservoir
cement sheath, which comprises the following steps: 1) acquiring well cementation
cement, measuring basic parameters of main substances in the well cementation
cement, carrying out an underground cement well cementation
simulation experiment, and measuring basic parameters of a
cement sheath sample after reaction; 2) taking the particle size as a separation point, dividing the cement substance into an unreacted inclusion and a full-reacted body, calculating the average thickness of the outer ring of the unreacted inclusion, obtaining a thickness-
diameter curve, calculating the ratio of the thickness to the particle size of the unreacted inclusion with different particle sizes, and re-representing the large-particle-size combination distribution state of the substance after the cement reaction; and 3) calculating the filling degree of the small-particle-size substances according to the
porosity and the
effective porosity of the cement sample, defining the unfilled small-particle-size substances and the unreacted inclusion substances as free substances, and calculating a
stability coefficient according to the composition state of the free substances to evaluate the well cementation quality. The stability is determined according to the particle distribution state before and after the
cement sheath reaction, and the method is more scientific and economical.