A New Production Model by Considering the Pressure Sensitivity of Permeability in Oil Reservoirs

摘要

Most of the “easy” oil in high permeability reservoirs has been explored and developed to a great extent. More and more “difficult” oil has been discovered. There are many problems in developing the “difficult” oil in low or extremely low permeability reservoirs. One of the problems is the pressure sensitivity of permeability which declines significantly as pore pressure decreases or net overburden pressure increases. There have been a few mathematical models to calculate oil or gas production by considering the pressure sensitivity of permeability. However most of the models have not been verified using field production data. In this study, a new production model has been derived theoretically with the pressure sensitivity of permeability considered. Using the production data from a low permeability (less than 1.0!10-3μm2) oil field (Yushulin, Daqing), the model has been tested and verified. The pressure sensitivity coefficient of permeability has been calculated by using the new model with the field data. The results calculated using the new model also showed that the permeability near the well bottom decreased significantly because of the drop in pressure in low permeability reservoirs. An obvious permeability decline funnel could be formed even the formation was homogeneous before development. It was found that the productivity index is no longer a constant in low permeability reservoirs with serious pressure sensitivity of permeability. According to this study, it is necessary to consider the pressure sensitivity of permeability when low permeability reservoirs are being developed. Otherwise, the production will be greatly overestimated.