A Comprehensive Analysis of Filter Cake Breakers for Non-Aqueous Drilling Fluids

Non-aqueous drilling fluids (NADF) have become widely used due to their ability to provide failure-free drilling in difficult conditions. During the drilling, the filter cake is being built on the wall of the borehole providing the integrity of the wellbore and preventing formation damage. However, filter cake can cause long-term bringing-in of a well and an increased value of the drawdown required for inflow stimulation. Hence, the filter cake has to be successfully removed in order to maximize the well's productivity. The goal of the research is to provide a comprehensive analysis of various formulations used for NADF filter cake removal. NADF is typically formulated using oil as a continuous phase, brine as a dispersed phase, emulsifiers, wetting agents, and gellants. Depending on the reservoir, the filter cake may have a complex structure due to the particles’ intermixing with the emulsion to create the internal and external layers. Destruction of this system is an intricate task, particularly in horizontal and multilateral wells. An effective breaker must be able to separate the mud into component phases and simultaneously dissolve the weighting agents. The design of an effective treatment requires accounting for the mud composition, formation type, downhole conditions, and type of a completion. The variety of available solutions as well as their advantages and limitations are described in this article. The results of the research demonstrate that state-of-the-art systems and technologies can be divided into several groups depending on the number of stages and the required alteration of the rock wettability. To dissolve the external filter cake built by the hydrophobic weighting materials the chelating reagents, acids or acid precursors are commonly utilized. An internal filter cake formed by the emulsion drops and emulsion blockage in the damaged zone can be removed by solvents, mutual solvents, de-emulsifiers or microemulsions. Modern eco-friendly technologies as well as multifunctional thermochemical fluids used for removing the barite filter cakes are also highlighted in the publication. It is shown that many factors affect the filter cake removal efficiency, including mud oil-water ratio, types of solids present and their concentration, salinity, and temperature. Furthermore, a preliminary assessment of breakers’ performance should be performed in a laboratory while considering the individual characteristics of each well. Although many formulations have been introduced to remove barite filter cake in NADF, the need for a low-cost, compatible, and efficient breaker still prevails. Based on the research findings, a new thoroughly selected composition of chelates, surfactants, and additional reagents as a breaker with high de-emulsifying properties, and barite-dissolving ability is expected to be developed to break down the filter cake after completion of drilling with NADF.