Forward Modeling Of AVO Characteristics Of Gas Tight Sandstone

The Sulige gas field is rich in geological reserves and belongs to typical low-porosity and low-permeability tight sandstone reservoirs.Such reservoirs have the characteristics of diverse pore types,complex gas-water relationships,large changes in reservoir thickness,and small impedance differences between the gas-bearing layer and the surrounding rock,which makes the geophysical characteristics of such reservoirs insignificant,which brings great challenges to oil and gas identification.In this paper,combined with the actual reservoir and seismic parameters in this area,a combination of seismic physics simulation and rock physics is used to design two types of reservoir models with connected and unconnected pores,taking into account the small wave impedance difference between the reservoir and the surrounding rock,the method of adding hollow microspheres and silica gel particles has successfully reduced the speed and density of the connected reservoir,The low-speed epoxy resin/silicone rubber mixture is used to fill the small particles to obtain the unconnected reservoir material.Reservoir materials have successfully completed the production of gas-bearing tight sandstone models with 40 parameters,connected and disconnected.Finally,numerically simulated the response characteristics of Class II and Class III AVO of various types of reservoirs with physical model seismic parameters.Through the processing and analysis of the two-dimensional data of the model,the following conclusions can be drawn:the unconnected pore sandstone,regardless of the porosity of the reservoir,the impedance when gas is contained is greater than that when oil is contained,and the impedance when gas is contained is the largest.For the connected pore sandstone,with the gradual increase of porosity,the impedance of the sandstone when it is dry and fully saturated also decreases in sequence,and the impedance difference with the surrounding rock also appears to decrease first and then increase.When the porosity of the dry and fully saturated sandstone samples is equal,regardless of the porosity,the reflection amplitude under fully saturated water at different porosities is stronger than under dry conditions.When the porosity is constant,the change of impedance with water saturation is not obvious.Sandstone generally shows that the impedance when fully saturated is greater than that when completely dry and greater than when it is not fully saturated.