Research On The Rock Physical Response Mechanism Of Micro-nano Pores In Shale Reservoirs

The focus of exploration and development has been focused on unconventional oil and gas reservoirs in recent years.As an important type of unconventional reservoir,shale reservoir owns huge development potential due to its rich reserves,so it has become one of the hot spots in current research.Compared with the conventional reservoir,shale reservoir usually have some special properties,such as low porosity,low permeability,extensive development of micro-nano pores,kerogen abundant organic matter and diverse,complex pore structure,etc.The conventional rock physical model cannot accurately describe the shale reservoir,often leading to the predicted rock physical results and the actual produce larger deviation,which affect the accuracy of the seismic inversion process next.As the main storage space of shale gas,micro-nano pores have a great influence on the overall elastic parameters of shale.As an important organic matter mineral in shale,kerogen occurs in different states with different maturity,and is also the main development site of micronano pores.The rock physical response mechanism of these two components mentioned above is not yet clear,so it is necessary for us to focus on the research.Rock physics is the bridge to connect reservoir's seismic elastic parameters and its physical parameters.In this paper,we firstly introduce and summarize the basic rock physics theories.Secondly,two kinds of micronano pores theories are explored,and the macroscopic response of micro-nano pores and pore fluid of rock is analyzed.Then we mainly consider micro-nano pores and the state of kerogen under different maturities,using a micro-nano pores model to describe shale micro-nano pore features,while considering the strong anisotropy of shale,compactness,kinds of features such as pore types,to establish a new shale reservoir rock physical model.We then analyze the sensitivity of the shale reservoir physical parameters.The model is verified by using a shale gas well in a certain working area in southwest China.We use another kind of micro-nano pores model to describe the micro-nano pores fluid flow mechanism of shale gas,with fractional derivative is used to characterize the solidity of the pores fluid.Under the Biot theory framework,with the geometric equations,constitutive equation and kinematics differential equation,we construct a kind of wave equation of orthogonal anisotropic porous media based on fractional order,then analyze the equation using plane wave method.Two-phase anisotropic medium wave equation is used to carry out forward modeling,and the influence of reservoir physical parameters on seismic wave field is also analyzed.