Every rotary drilling operation consists of three systems that work simultaneously in boring a hole; a rotating system which rotates the drill bit, a hoisting system that raises and lowers the drill string into the hole, and a circulating system that moves fluid around from the drill stem, out of the drill bit and up again to the hole at the surface (Dyke & Baker, 1998). The type of fluid chosen for a particular well depends on 3 important factors; Cost, Technical performance, Environmental impact. The cost of products is very important, but should only be considered on a cost-performance basis. Technical performance of the drilling mud is the most important factor (Hawker, 2001) (Devereux, 1999). The task focuses on investigating the effect of bone dust on the different mud samples and studying their behaviors when subjected to different conditions. In order to do this, they would all be subjected to a number of experiments. In doing so, the different mud samples with varying amount of bone dust would be used and at certain varying conditions such as varying temperatures and aging times, to help the mud samples perform maximally. Amongst the tests to be carried out are filtration or water loss test, swell tests, lubricity, investigations to determine the rheological properties of the different mud samples, aging and temperature tests.
1.1 DRILLING FLUIDS
Drilling fluid, in its liquid form, may be water or a mixture of water and oil, clay with some additives is used to aid the drilling of boreholes into the earth. A drilling fluid is any fluid which is circulated through a well in order to remove cuttings from a wellbore. Drilling fluid is often used while drilling oil and natural gas wells.
1.2 TYPES OF DRILLING FLUIDS
a) Water Base Muds (WBM): WBM having water as the continuous phase is predominantly used in the industry due to its environmentally acceptable nature, and also because it is relatively cheap to operate with. It also called aqueous drilling fluid and it consists of about 90–95% of fresh water, salt or sea water and several dissolved substances (Devereux, 1999), (Skalle, 2010)). WBM is the drilling mud type which would be focused on and used in this project. There are several types of WBM as seen below;
• Dispersed Muds: These mud type are used at greater depths requiring higher densities or in problematic hole conditions where heightened treatments are required. The mud system would be dispersed with specific additives to give specific properties to the mud e.g. thinners or dispersants.
• Non – Dispersed Muds: These mud type are used for shallow wells or top hole sections. Clear or native water such as spud muds, natural muds and other lightly treated systems
b) Oil Base Muds (OBM): These muds have oil as their continuous phase, usually diesel oil, mineral oil or low toxicity mineral oil, and although they may contain little formation water, no additional water or brine is added. This is due to the fact that they contain water-emulsifying agents. The ratio of the oil percentage to the water percentage in the liquid phase of an oil-based system is called its oil/water ratio. Oil-based systems generally function well with an oil/water ratio in the range from 65/35 to 95/5, but the most commonly observed range is from 70/30 to 90/10.
c) Synthetic-Base Muds: In SBMs, the continuous phase is the synthetic liquid while brine serves as the dispersed phase. During drilling, the solids in the mud system and the formations are exposed to the synthetic liquid and not to the aqueous phase, preventing swelling and degradation of borehole walls. As with OBMs, drill cuttings are less likely to disperse into the mud. SBMs are used where OBMs are commonly used in difficult drilling situations, such as high downhole temperatures, hydratable shales, or salt, where the properties of WBMs would limit performance. Out of an increased desire to reduce the environment impact of offshore drilling operations, synthetic-base muds were developed.