Modeling of Mud Filtrate Invasion and Damaged Zone Formation

Filtration loss and circulation loss in drilled pay zone during drilling operation cause wasting a lot of money in oil and gas drilling industries. In addition, they cause damage to hydrocarbon reservoirs in term of productivity reduction of pay zone and cause increasing the cost of well stimulation operation. In this study, invasion depth of mud filtrate from water-based mud is investigated and a model that includes the presence of mud cake layer and irreducible water saturation is developed to estimate the radius of invasion and mud filtrate concentration in the hydrocarbon formation. Here, a linear flow system is considered. The mud cake thickness and filtration velocity is derived from mass conservation and Darcy law equations, respectively. In this study, the invasion depth is obtained from mud filtrate profile in the formation. Also, it is clear that the filtration velocity in a flow system depends on formation permeability, overbalance pressure, mud cake characteristics (porosity, permeability and density), and invasion time. Finally, the effect of different parameters such as connate water, cake permeability, formation permeability and porosity on mud concentration and filtration velocity is showed. By studying the trends of changes in mud concentration profile and filtrate velocity profile, it is obvious that cake permeability and formation permeability have the most effect on mud filtration depth and concentration profile.

Keywords:

Mud Invasion , Modeling , Mud Cake , Invasion Radius