Removal of Filter Cake Formed by Manganese Tetraoxide-Based Drilling Fluids

Abstract

Abstract Manganese tetraoxide (Mn3O4) has been recently used as a weighting material for water-based drilling fluids (Al-Yami et al., 2007). Mn3O4 particles are spherical, 1–2 µm in diameter, and have a specific gravity of 4.8 g/cm3. A mud (102 ± 5 pcf) was developed to drill deep gas wells. The filter cake formed by this fluid contained polymers (starch, XC-polymer, and polyanionic cellulose polymers), Mn3O4 and a small amount of CaCO3. Unlike CaCO3, Mn3O4 is a strong oxidizer and, as a result, HCl not recommended to be used to remove the filter cake. The objective of this work is to develop a new cleaning fluid to effectively and safely remove the filter cake that contains large amounts of Mn3O4. Various organic acids, chelating agents, enzymes, and a combination of these chemicals were tested up to 300 °F. Characterization of filter cake before and after soaking in several cleaning fluids were conducted using XRD/XRF/SEM techniques. Solubility of Mn3O4 was conducted using various acids and chelating agents at different temperatures up to 284 °F and 200 psi. The concentration of manganese in spent chemicals was measured using Inductivity Coupled Plasma (ICP). Extensive lab testing indicated that Mn3O4 particles in the filter cake were coated by polymeric materials that acted as a barrier. The coating material reduced the ability of cleaning fluids to remove filter cake. The efficiency of cleaning fluid was improved by soaking filter cake in a starch specific enzyme, and then applying the cleaning fluids. HCl, citric, and in-situ lactic acid were found to be the most effective fluids in dissolving Mn3O4 particles. This paper will discuss the characteristics of filter cake and the effectiveness of various cleaning fluids. New cleaning fluids were designed to remove Mn3O4 filter cake, while maintaining the integrity of the formation and well tubulars. Introduction Drilling horizontal/multilateral wells is utilized to enhance both hydrocarbon recovery and total well productivity from many types of reservoirs (Yildiz 2005 and Tronvoll et al., 2001). Drilling, workover and production operations may result in near-wellbore formation damage that in most cases cannot be prevented e.g. Pore plugging by calcium carbonate particles from drilling fluid, drilled solid particles, or particles from the formation (Ismail et al., 1994). Manganese tetraoxide was introduced to potassium formate drilling fluid back in 1995 to overcome the main drawback of potassium formate, which is the production of brine of density 1.7 g/cm3 (106 lb/ft3). Due to the partial solubility of barite in concentrated formate brines and the decision not to acidize prior well completion of the well, CaCO3 and barite were excluded as options to increase the density of the fluid. The most effective breaker fluid of the filter cake formed by this drilling fluid found to be 10 wt% citric acid with formate brine. (Sevendsen et al., 1995) Mn3O4 was introduced as a weighting material to oil-based drilling fluid due to the achievement of the very low plastic viscosity at the fluid density requirement and the ability to suspend the solid particles, Mn3O4, at lower fluid viscosity (Franks et al., 2004). In 2007, a water-based drilling fluid weighted with manganese tetraoxide and small amount of CaCO3 were developed. CaCO3 were added to control the filtration properties of the drilling fluid. The needs for using a drilling fluid with high rheological properties were achieved using manganese tetraoxide particles. (Al-Yami et al., 2007) Current approaches introduced to remove filter cake include the use of live acids, strongly buffered organic acids (Ali et al., 2000), chelating agents, oxidizing agents (Brady et al., 2000), enzymes (Butler et al., 2000, Al-Otaibi et al., 2000, and 2005), in-situ organic acids (Al Moajil et al., 2007), or combinations of these chemicals.