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Picture a bowl of prepared oatmeal. Now, take a spoonful of oatmeal and place it on a sponge. If you watch that oatmeal, you will see that the sponge soaks up the water present in the oatmeal, but leaves behind the oatmeal and anything else that is to big to fit through the pores of the sponge. While this visual is not very impressive in and of itself, it is still a decent way to explain the need for fluid loss control when drilling a well. Mud or slurry is often used as part of the drilling process. When this slurry impacts a porous rock, the water present in the slurry can seep into the porous rock, thus decreasing the effectiveness of the slurry. Water present in cement can similarly seep out into porous rock during a drilling process. When this happens, the water loss can damage the rock formation and decrease the efficacy of the slurry or cement. Fluid loss control is the term used to describe the efforts of the drilling crew to prevent lost fluids. Let's return for a moment to the oatmeal on the sponge. There are ways to prevent the fluid from seeping out of the oatmeal mixture. There are many chemicals and additives that you could use to prevent fluid loss from the oatmeal. Few of the additives would be edible, but petroleum engineers don't have to worry about how palatable the slurry they use is. Fluid loss into spongy layers of rocks used to be a real problem, but thanks to the efforts of modern chemical engineers, fluid loss does not the problem that it once was. On the other hand, the problem of fluid loss control is not as simple as grabbing a bottle of seepage stopper and dumping it into your drilling mud. There are many different rheology modifiers and fluid loss additives available. Each additive has its own optimal range. Different modifiers work best within a certain range of temperatures, with certain rock types, and for certain types of slurry and/or mud. There is a science to designing a slurry to make sure that it works the way it is supposed to. If the slurry is not designed properly, then it can end up causing problems for the future of the well. When a slurry does not work right, steps must be taken to correct problems created by the improper use of the slurry. It is better to get the slurry right to begin with rather than to try to clean up the mess later. One fluid loss modifier worth discussing is carboxy methyl starch. Carboxy methyl starch, or CMS is a natural compound. Thus, when you use CMS, you don't have to worry about introducing dangerous contaminants into the well system. Carboxy methyl starch helps to improve the viscosity, or thickness, of a slurry or mud. When you use CMS, you don't have to worry as much about fluid loss, but you will still need to monitor the fluid in question to make sure it continues to function as it should. While CMS is not right for all drilling operations, it is still one worth knowing about. Fluid loss control is an important part of modern drilling operations. Porous rocks act as sponges to soak up fluids and extract them from drilling mud or cement. In order to maintain the integrity of the mud or cement, it is important to use rheology modifiers and fluid loss additives to maintain the right amount of fluid in the drilling fluid. Carboxy methyl starch is one of many choices that can help with fluid loss control.
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