An Algorithm for Improving Mud Invasion Modeling Through Inversion of Resistivity Logs

Mud invasion occurs in permeable formations because of overbalance drilling. During mud invasion, liquid phase of mud invades into formation, and the solid phase accumulates on the borehole wall (mud cake). Rate, volume and geometry of mud invasion are controlled by (1) mud properties, (2) petrophysical properties of formation and (3) pressure difference between mud and reservoir. The invasion of mud severely damages reservoirs and reduces its productivity. In addition, it has negative impact on the acquired data, e.g. wireline logs, formation tester and also rock and fluid sample. Different mathematical and experimental models have been developed to model mud invasion considering different aspects of the problem. Implementing these models in real cases does not have satisfactory results because they need major modifications. In this paper, we adjust mud cake permeability as the main controlling parameter of mud invasion. It is accomplished by inversion of resistivity logs. We developed different workflows using Petrel software to simulate the mud invasion and invert the resistivity log. The objective function of the inversion was the difference between modeled and real resistivity logs. After optimizing the mud cake permeability, the mud invasion profile significantly improved.