Further Discussion of Application of Oil Muds
- M.J. Benning (Don Ray George and Assocs.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- March 1987
- Document Type
- Journal Paper
- 86 - 86
- 1987. Society of Petroleum Engineers
- 1.11 Drilling Fluids and Materials, 1.14 Casing and Cementing, 1.6 Drilling Operations
- 1 in the last 30 days
- 179 since 2007
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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.
I agree entirely that lost circulation is a worse problem with oil-based muds than water-based muds because of the cost per barrel of the oil muds. and I also agree that mud-handling costs should be considered part of the cost of the drilling fluid. In my experience they were. They are not included in the mud bill unless they are provided by the same company. It is my understanding that the major drilling-fluids companies will buy back the used oil-based muds at a substantial percentage of the initial purchase price. This buy-back policy reduces the final cost of using oil-based fluids considerably.
Frequently, the cost benefits occur later in the well history. For example, in the Williston basin, oil-based fluids consistently reduced the incidence of casing failure after completion, by ensuring a better cement job through the massive salt sections that occur in that area.
Handling and disposal of oil-based muds offshore is indeed costly and difficult. These costs can be estimated, however, and measured against the positive economics of improved drilling performance. I was under the impression that washed cuttings could be disposed of offshore, although frequently the detergent used in the washing is more toxic than the oil being removed. The less-toxic muds currently gaining favor on the gulf coast are considerably more than just "slightly less toxic. "Toxicity studies run on our muds by an independent laboratory for our own use showed the mineral-oil muds to be less toxic by an order of 100 times or more. In fact, some of the muds tested would fall in the nontoxic category as specified by the MMS. Because it is now standard for most of the major drilling-fluid companies to formulate their liquid additives with a mineral-oil base, the toxicity is further reduced.
Because these muds do contain an oil, however, they will leave a sheen on the water and still fall into the category of oil-based fluids. For this reason, they are subject to the same regulations as the conventional oil muds.
I don't think anyone who works with oil-based drilling fluids would recommend them as the best fluid for use in all cases, or even most cases. They are, however, unbeatable in certain circumstances, such as deep, hot holes, massive salt sections, water-sensitive shales, and deviated holes. As always, each well must be evaluated on its own merits.
Related papers:SPE 13001, SPE 11356, SPE 13158
Related discussions and replies:SPE 15965, SPE 16445, SPE 16456, SPE 17012
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