This common problem occurs when something happens to the formation near the wellbore, slowing oil production. For example, excessive buildup of water saturation in the vicinity of the wellbore impedes oil flow. A mud block, an accumulation of drilling mud around the wellbore producing zone, can also reduce the rate of oil flow, In a shaly producing formation, the drilling mud used in a workover operation can cause clay swelling and completely stop oil flow.
Wells with such formation damage may be treated with acids, mud cleanout agents, wetting agents, and/or other special-purpose chemicals. These materials are pumped into the formation and are eventually produced to the surface. These are highly specialized operations, requiring special pump trucks and equipment, and they are usually performed by oilwell service companies specializing in this type of work.
Emulsions of oil and water are a fourth common production problem. Under certain conditions, oil and water may form an emulsion that will not separate at the surface without special treatment. This is a problem because the process to break up the emulsion is very expensive. Methods of breaking up such emulsions include heat treatment, chemical treatment, and various combinations of chemical treatment. Since the chemical composition of crude oil varies from one field to another, the nature of the chemicals used to break up emulsions also varies.
Corrosion of equipment is one of the most costly problems plaguing the oil industry. Salt water produced with oil is highly corrosive, and most crude oils contain varying amounts of hydrogen sulfide, which is also quite corrosive. Anticorrosive measures include the injection of a chemical corrosion inhibitor down the casing/tubing annulus; the use of plastic-coated tubing; and the use of special corrosion-resistant alloys and cement-lined pipe. Each of these methods has distinct advantages and disadvantages. Frequently the cost of reducing the corrosion rate is so high that it cannot be justified, in which case no anticorrosion measures of any kind are taken and the equipment is replaced at the end of its useful life.