The Study On Rock Physics Experiment And Modeling For Heavy Oil Clastic Rock Reservoir

With the deepening of exploration and development and the increase of energy demand,unconventional resources have received more and more attention.As an important non-conventional energy source,heavy oil has abundant reserves in Liaohe Oilfield,Shengli Oilfield and Bohai Bay.However,the heavy oil is usually accompanied by the characteristics of large viscosity and poor fluidity,and the nature of the clastic rock heavy oil reservoir is also different from that of conventional reservoirs.Therefore,it is necessary to carry out rock physics experiments of clastic rock reservoirs to determine the relationship between physical parameters and elastic parameters of clastic rock heavy oil reservoirs,and to establish rock physics models suitable for clastic rock heavy oil reservoirs.In this paper,a total of 22 rock samples were collected,including 18 well-consolidated rock samples and 4 artificially prepared rock samples.Their density and porosity were measured first,then their P-wave velocities and S-wave velocities were measured over a temperature range of 20°C to 100°C.Analysis of experimental data shows that the P-wave velocity of heavy oil rocks decreases with increasing temperature,but the P-wave velocity and S-wave velocity ratio increases with increasing temperature at low temperatures,and decrease with increasing temperature after reaching around 60°C.which is determined by the nature of the pores filled with heavy oil.At low temperatures,the viscosity of heavy oil decreases sharply with increasing temperature,which causes the shear modulus and shear wave velocity of heavy oil to drop sharply with increasing temperature,making the rate of decline of S-wave velocity in heavy oil rock higher than that of P-wave velocity.which shows that the ratio of the P-wave velocity and S-wave velocity of heavy oil rock increases with the increasing temperature at low temperature.When the temperature reaches about 60°C,the viscosity of the heavy oil is basically reduced to 0,resulting in S-wave velocity of heavy oil rock tends to stabilize with increasing temperature,while the P-wave velocity decreases with the expansion of the volume.which shows that the ratio of the P-wave velocity and S-wave velocity of heavy oil rock decreases with the increasing temperature at low temperature.In this paper,the relationship between the shear modulus of heavy oil and temperature isstudied firstly.The theory shows that the shear modulus of heavy oil at low temperature can not be neglected and does not conform to the assumption of Gassmann equation.Therefore,the conventional clastic rock physics model no longer suitable for heavy oil clastic reservoirs.The establishment of rock physics model for clastic rock heavy oil reservoirs must take into account the effects of temperature.This paper combines the Xu-White theory and Gassmann equation to proposes a new model called XWGG,the theoretical data that using the XWGG model to calculate with experimental data show the same trend,but there is still an error,which is due to deformation of the rock skeleton and part of the heavy oil will adhere to the inner wall of the pore at low temperatures.Therefore,the temperature-related skeleton deformation factor and the solid heavy oil proportional factor are proposed.With the improved XWGG model,the theoretical data obtained with the improved model agrees well with the experimental data,demonstrating the validity of the XWGG model.Finally,the AVO forward modeling was carried out using the established rock physical model of clastic rock heavy oil reservoirs,and the seismic response characteristics of clastic rock heavy oil reservoirs under different physical conditions were analyzed.