Study On Numerical Simulation Of Formation Mechanism And Evaluation Method Of Bound Water In Complex Sandstone Reservoirs

Bound water saturation is one of the important parameters of reservoir evaluation,but its influencing factors are numerous and the formation mechanism of bound water is still unclear.Therefore,it is of great significance to study the formation mechanism and evaluation method of bound water.In this paper,the formation mechanism of the bound water of complex sandstone in the study area is studied from the macroscopic and microscopic levels,and the evaluation method is proposed.Firstly,on the macroscopic level,the correlation analysis of the influencing factors of bound water saturation is carried out.It is concluded that the main controlling factor is the pore structure,which can be evaluated by the Reservoir Quality Index RQI.The bound water saturation is negatively correlated with RQI logarithmically.With the increase of RQI,the linear correlation between bound water saturation and ln(RQI)increases.Then,on the microscopic level,a pore network seepage model is established to simulate the formation of bound water by simulating oil flooding.The core experiment shows that the model can reflect the effect of micropore structure changes on macroscopic properties.Next,from five aspects of coordination number,aspect ratio,pore throat radius,throat length and shape factor,it is concluded that coordination number and pore throat radius are positively correlated with RQI and negatively correlated with bound water saturation;aspect ratio is negatively correlated with RQI and positively correlated with bound water saturation;throat length has little influence on RQI and bound water saturation.The pore throat radius has a significant influence on the permeability of the model.As the pore throat radius increases,the permeability of the model increases rapidly.RQI decreases slightly and bound water saturation is almost invariable with the increase of shape factor when the cross-sectional shape of pores and throats elements does not contain a circular shape.Finally,bound water saturation of the three layers in the study area is evaluated.Multivariate regression based on AC and RHOB of conventional logging data can well fit the RQI in the layer of K1y2+3,and then quantitatively evaluate the bound water saturation with better results.And another method of evaluating bound water saturation based on the echo data of nuclear magnetic resonance logging using exponential sine function integral transform with T_c and m calibrated by the core experiments is more accurate than the integral transform method using exponential sine function without core calibration,traditional inversion-based method and multivariate regression fitting method of conventional logging data.