Investigating fluid invasion control by Colloidal Gas Aphron (CGA) based fluids in micromodel systems

Abstract

Recently, Colloidal Gas Aphron (CGA) based fluids have been introduced to further develop depleted hydrocarbon reservoirs. This fluid system has been employed in an attempt to control drilling fluid invasion and, thus, reducing formation damage occurred during drilling operations. Understanding the mechanisms of fluid invasion control is of great importance for successful design and application of CGA-based fluids in drilling operations. Although fluid flow of conventional foams has been studied extensively in the available literature, little attention has been paid to CGA fluids flow, especially in heterogeneous fractured porous media.Here, an experimental study was conducted to achieve maximum knowledge of CGAs blocking mechanisms in heterogeneous unfractured/fractured porous media using a micromodel setup. Fluid invasion control was studied with the aids of direct observations, injection pressure of CGA fluids, and return permeability calculations. Microscopic mechanisms such as bubbly flow, trapping of CGAs, aggregations of bubbles within fracture, and configuration of different phases were observed in the experiments. Observations revealed that CGA fluids reduce fluid invasion through creation of nonbonding aggregation of CGAs in the fracture. Injection pressure data of CGA fluids were employed to compare performance of two CGA fluid samples prepared by Sodium Dodecyl Sulfate (SDS) and Sodium Dodecyl Benzene Sulfonate (SDBS) surfactants. Results showed that CGA sample prepared by SDBS provides a better fluid invasion control capability, possibly due to its wider bubble size distribution compared to that of CGA sample prepared by SDS surfactant. Furthermore, during production phase, CGAs were easily removed by produced oil, and a higher return permeability (about 80%) was achieved for CGA fluids prepared by SDBS. Finally it has been shown that aqueous CGA fluids perform better in oil wet conditions than in water-wet conditions. This study provides a helpful reference for understanding blockage ability of CGA fluids occurred in drilling operations.