A Quantitative Estimation Method of Cement Clay in Clayey Sandstone and Its Rock Physics Application

When building the rock physics model for clayey sandstones, it is very important to know the contact type and content of cement clay in clayey sandstone for correctly understanding the influence of the cementation on acoustic velocity of clayey sandstone and how to reasonably establish rock physical model. At present, there is no laboratory method to directly quantitatively estimate the content of the cement clay, which leads to large errors in predicting acoustic velocities when using the cemented sands model for cemented sands formation because of the over-estimated of the cement clay. In this paper, a method for distinguishing cemented clay is proposed by observing the contact relationship and relative distribution between clay and particles in thin sections. The cement clay is used as the input parameter of the constant cement model. The comparison shows the velocities error predicted in our method is 20% lower than the original model, and the predicted results are significantly improved. The method proposed in this paper is a suitable rock physics model for weak cemented formation. It can predict acoustic velocity to identify favorable reservoirs and quantitatively evaluate reservoir parameters by combining seismic and logging data.