Construction And Application Of Fluid Identification Factors Based On Porous Media

With increasing difficulties of oil and gas exploration, more accurate reservoir predictionmethods are needed. In order to identify fluid and predict reservoir better, we must built moreaccurate fluid identification factors.At present, most fluid identification factors are proposed based on the single-phasemedium theory, which simplifies underground reservoir into ideal isotropic homogeneousmedium model. This practice is feasible when the reservoir porosity is small, but its predictedresults will be biased when large reservoir porosity exists. So, to create high-precision fluididentification factors, we must innovate in terms of the media and establish fluid identificationfactors on the basis of more accurate petrophysical model.Based on the two-phase medium theory, we build fluid identification factors A andN. A and N are two elastic parameters for the two-phase medium, which are similar toLame constants and shear modulus in isotropic medium. The two new factors containfast P-wave velocity, S-wave velocity, density, porosity, fluid velocity and fluid densityinformation in porous medium reservoir. They take into consideration the effects of solidskeleton and pore fluid on stratum, which more accords with the actual geological formations,so they can improve the precision and accuracy of fluid identification.In order to have a more thorough understanding of the establishment of fluididentification factors, we start from the rock physical basis of fluid identification factors,including spatial averaging model theory, Gassmann equation, Biot theory and the basicequation Biot-Gassmann equation for poroelastic media. Also we analyze the changes of rockproperties with different pore-filling fluids and theoretically summarize the sensitivity of thefluid. In order to introduce the main media for the two-phase fluid identification factors, wediscuss the classification of two-phase media in detail; and in order to analyze the attenuationand dispersion characteristics of wave in porous media, we analyze the porous medium BISQmechanisms minutely. What’s more, the reflection and transmission at the interface oftwo-phase media is discussed and related parameters are calculated. Finally，we get the mainparameters of two-phase medium fluid identification factors, A and N.Three typical Hilterman sandstones and25sets of synthetic sandstone models are used to test A and N, and the identification effects of A and N are compared with that of theisotropic medium fluid identification factors. The results show that the identification effects ofand is much better than that of the single-phase media recognition factors. Theformer has the characteristics of high precision, high sensitivity, strong ability to predict thereservoir. To determine the effect of changes in porosity on and, we observe therecognition effects of and with reservoir porosity reduced and rock porosityunchanged. When reservoir porosity is very small, and can still identify the reservoirvery well, they are barely affected by the porosity. and are applied to the actualreservoir data, and the results show that they not only recognize gas reservoir very well, butalso have certain ability to indicate oil reservoir. They have promising practical value.