Further Discussion of Application of Oil Muds

Abstract

Abstract After reading Bloemendal's "Discussion of Application of Oil Muds" (Oct. 1986 SPEDE, Page 395), I felt compelled to reply. I have 6 years of experience with Dresser, Magcobar in various capacities, including mud engineer, instructor in the in-house schools, and finally technical service engineer. I was first based in south Texas and later in Houston, where I spent time in the field dealing with oil-based muds in Alaska, Wyoming, North Dakota, California, Texas, and Louisiana, both onshore and offshore. I will address Bloemendal's objections in the order in which they occurred. Shortly after the higher-fluid-loss oil muds came into use, I put together a study comparing rates of penetration (ROP's) between oil-based and conventional (usually chrome lignosulfonate) muds in south Texas. I chose wells drilled in the same area, at the same depths, and as much as possible, with the same bits. None of the wells used a polycrystalline bit. Without a doubt, the oil-based muds outperformed the water-based fluids. Bloemendal attributes the increased penetration to higher API-FL, lower effective bottomhole density, better lubricity, and more favorable rheology. Undoubtedly, he is correct in his choice of possible reasons for the increased penetration. But why question the increased ROP with oil-based muds because of these factors? They are inherent in the oil-based system, and all these attributes are used as selling points for oil-based muds. That they are simply mechanical factors in no way negates their importance. Bloemendal mentions the possibility of an oil-based mud flipping under certain circumstances. Flipping is the sudden change from a water-in-oil emulsion to an oil-in-water emulsion. He neglects to mention that these circumstances are extremely rare and usually avoidable. In my 6 years dealing with muds, I have seen a few in bad condition, but I have yet to see one flip.