Shale Membrane Efficiency Experimental Study Using Water-Based Muds

Drilling operations rely heavily on the use of water-based muds. These muds tend to invade the formation and alter the stress state condition of the exposed rock and can lead to instability such as wellbore collapse. In the case of shales, muds that have good membrane efficiencies offer a way to provide more stability. Such muds are, therefore, desired. Oil-based muds have proven to have high membrane efficiencies, however, they are usually more expensive than water-based muds and certainly more toxic to the environment. Water-based muds have historically evidenced low membrane efficiencies; however, innovative water-based muds, now available in the industry, appear to be promising in producing higher efficiencies. The objective of this study was to evaluate the membrane forming performance of four water-based muds using different shale types. The water-based muds tested were Ultradril (MI Swaco), Hydroguard (Baroid), Deepdrill (Newpark) and BHDF (also known as Performax) (Baker Hughes). The shales tested were designated as C3, C4, C5, and Arco China. In this study membrane efficiencies varied between 0% and 7.3%, and were found to depend on both the mud properties and the shale properties (such as porosity). Low porosity shales showed high membrane efficiencies. Correlations of membrane efficiency with other parameters such as mineralogy or shale water activity were inconclusive and need additional data. These water-based mud membrane efficiencies are low compared to those of oil-based muds (up to 52%), as reported by Al-Bazali (2005).