Contact with the Damage

Add treatments will always preferentially seek the path(s) of least resistance. This results in only partial treatment of the target interval or spot removal of skin damage. The longer the interval is and/or the more heterogeneous it is with respect to permeability, the greater will be the difficulty in effectively contacting the full interval and the full extent of the damage. 

Limited interval coverage can be overcome to a degree by maximizing matrix acid injection rate. Greater coverage can be accomplished with chemical diversion or, preferably, mechanical placement— including coiled-tubing/injection-nozzle methods. 

Shut-in of an HF acid treatment in a sandstone near the wellbore, increases the chance of damage in the formation from precipitation of HF reaction products. Acid, especially spent HF, should be produced back out immediately or as soon as possible. If immediate turnaround cannot be accomplished, then acid should be kept moving and a healthy overflush should be employed. This is so that reprecipitation of acid reaction products, which inevitably takes place, will be far enough beyond the near wellbore that its effect on radial permeabihty will be insignificant. 

In carbonate formations, there is usually not much concern about reprecipitated species. However, if iron is present or H S gas is expected, certain scales and solids reprecipitation can occur. These can be substantially damaging if fluids are shut-in and allowed to remain static for long periods of time (a few hours or more). 

A shut-in period may be unavoidable, as a result of logistics and the time it takes to repipe lines and turn a well around. Sometimes a well does not produce back immediately, and assistance, such as swabbing and jetting with nitrogen, is required. Hopefully, the shut-in period can be limited to two to eight hours. Beyond that range, there is cause for concern, especially with lower-permeability sandstone formations with complex mineralogy, which are conducive to spent-acid reprecipitation reactions. 

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In any case the engineer can make one of the following decisions after this first contact with the damaged structure ... 

The scraper or knife discharge consists of a blade that removes the cake from the dmm by direct contact with the filter cake. It is normally used for granular materials with cake thickness greater than about 6 mm. In order not to damage the filter cloth, a safety distance of 1 to 3 mm between the blade and the cloth must be observed. If the residual layer is made not of filter aid but of the product, there is danger of its blocking by fine particles and by successive consoHdation by the scraper blade. 

Type 2 On the other hand. Type 2 degree of protection limits the extent of damage in the case of a short-circuit. Now under short-circuit conditions, the contactor or the starter will present no risk to the operator or the installation and will remain suitable for further service. In other words, no damage to the contactor or the OCR is permitted. It may, however, be interpreted that contact welding may be permissible to the extent that the contactor can be put to service once again after a brief period by separating the contacts with the help... 

Contamination from Process Gas. Contamination from process gas can occur when there is insufficient supply of sealing gas into the seal, allowing process gas to come into direct contact with the seal ring faces. Contaminants existing within the process gas can then damage the seal. 

Corrosion in these areas is sometimes effectively controlled by cathodic protection with zinc- or aluminium-alloy sacrificial anodes in the form of a ring fixed in good electrical contact with the steel adjacent to the non-ferrous component. This often proves only partially successful, however, and it also presents a possible danger since the corrosion of the anode may allow pieces to become detached which can damage the main circulating-pump impeller. Cladding by corrosion-resistant overlays such as cupronickel or nickel-base alloys may be an effective solution in difficult installational circumstances. 

The anode is not recommended for use in water at above 50°C, where the consumption rate increases rapidly and erratically. It is no longer the practice to use this material in cooling water plant where secondary attack from contact with the relatively noble pieces of anode may occur, should damage take place. 

If water is required below 5°C, the approach to freezing point brings considerable danger of ice formation and possible damage to the evaporator. Some closed systems are in use and have either oversize heat exchange surfaces or high-efficiency-type surfaces. In both of these, the object is to improve heat transfer so that the surface in contact with the water will never be cold enough to cause ice layers to accumulate. 

Central damage region, corresponding to the site where a particle first contacts with the surface, undergoes the greatest stress, which leads to crystal lattice deformation. 

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