Abstract
High-pressure, high-temperature fractured shale reservoirs are types of unconventional reservoirs that need proper drilling operations for adequate efficiency. Proper measurement of drilling fluid's rheological properties is of importance for drilling operations that may increase the penetration rate on the one hand with proper design. Therefore, the success of drilling operations strongly depends on the proper design of drilling fluids. In this paper, we experimentally investigated the effect of potassium and sodium formate fluid on the rheological properties of drilling fluid for fractured shale core samples. The yield point and apparent viscosity for muds consisted of cellulose polyanionic and cellulose polyanionic-ultralow polymers higher than base muds. It indicates the effect of formate salts in increasing thermal stability. In addition, in polymer-based muds, more amounts of formate salts have been used, indicating the low fluid loss volume. Consequently, the shale recovery rate for potassium formate fluids is higher than sodium formate fluid.