Influence of solid bitumen on reservoir physical properties and logging parameters and its quantitative evaluation method

The occurrence of solid bitumen in the reservoir will not only block the throat and reduce the physical properties of the reservoir, but also interfere with the conventional logging interpretation conclusions and affect the effective production layer logging identification. Taking the high-mature pryobitumen of Guanwushan Formation in northwestern Sichuan Basin and low-mature solid bitumen of Baikouquan Formation in Mahu Sag as examples, based on high-temperature cyclic dissolution and artificial core simulation experiments, the effects of solid bitumen on reservoir physical properties and logging parameters were studied by analyzing and testing reservoir physical properties, acoustic time difference (AC), resistivity and nuclear magnetic resonance before and after bitumen dissolution, and a quantitative evaluation method of solid bitumen logging was established. After the dissolution of solid bitumen, the physical properties of the reservoir become better, the resistivity decreases significantly, the AC increases, and the change value of the S-wave transit time is more obvious than that of the P-wave transit time. The content of solid bitumen is linearly correlated with the increase of porosity and permeability, and the increase of AC, and exponentially correlated with the decrease of resistivity. The greater the maturity of solid bitumen, the smaller the influence on reservoir physical properties, the greater the influence on resistivity, but the influence of AC is not obvious. The influence of solid bitumen filling state on resistivity is more obvious, but the influence on AC is not obvious. The more concentrated the distribution of solid bitumen in the reservoir, the greater the influence on resistivity. The transverse relaxation time (T2) of solid bitumen in nuclear magnetic resonance is less than 4000μs, and the main peak is distributed in 60 ~ 100 μs, which overlaps with the response range of bound water. The higher the maturity of solid bitumen, the more left the T2 peak and the weaker the response amplitude. The porosity of density logging minus the porosity of nuclear magnetic resonance logging can characterize the content of high-maturity solid bitumen. The inversion porosity of No.1 peak of nuclear magnetic resonance T2 spectrum minus the porosity of irreducible water characterizes the content of low-maturity solid bitumen, which can greatly improve the effectiveness evaluation and logging interpretation accuracy of bitumen-bearing reservoirs.