Pipelines are utilized, universally, to transport oil, gas, water, chemicals and slurry. The subject of this paper is to provide a method for the removal of wax from oil pipelines especially in offshore gathering and transmission pipelines. The process described in this document, although directed at offshore oil pipeline systems, may not be confined to offshore systems or exclude the process for dealing with build-up of contaminates in other types of pipelines. 

Paraffin wax or Asphaltite tend to drop out of crude oil as the oil cools, usually below 140 degrees F. Oil leaving the wellhead has a substantially higher temperature often in excess of 250 degrees F. As the oil flows through the offshore pipeline, a cooling process occurs. 

In another context, pipelines are used to load crude oil from on-shore tank farms to offshore tanker loading facilities for transportation of product by sea. Dependent on the distance from land to the loading facility, oil can cool and form a wax or asphaltite build-up, according to the composition of the crude oil. The build-up of wax may not be confined to one small area of the pipeline due to the fact that the wax forms its own insulation or barrier against heat loss, which extends the area of deposit, and so this process is normally an on-going problem. 

As the deposits increase, there is a resultant loss of flow and/or increased energy requirement to maintain flow condition. The methods currently utilized to reduce the contaminate deposits are varied. The most common is to batch solvents, which is rarely effective against hardened deposits and extremely costly in time, lost revenues and the high cost of solvent. Other methods include the use of undersized Polly Pigs, which may contribute to a line blockage or become disintegrated. One extremely high cost partial solution is to "Hot Tap" the line at close intervals and flush with hot oil. A further method used in the past is to batch "Moth Balls" this method is little used due to being non-effective and out dated by more effective solvents. 

The best solution to the problem at this time has been carried out by the Baker Chemical Performance Company who, in conjunction with Shell Developments, have designed a chemical process known as "N-Situ". The composition is comprised of two or more components which include Hydrochloric acid and Ammonia, and additional pacifying and time delaying agents. The purpose of these chemicals is to cause an exothermic reaction in order to melt the wax deposits. 
 
 

The process is not limited to the use of the two chemicals as previously mentioned as there are many other chemical compositions which can create the same effect such as Ammonia Nitrate and Sodium Nitrite with a Hydrochloric additive in order to adjust the pH thus causing time delay. These chemicals are pre-mixed by the utilization of two separate tanks linked to a manifold by valves as shown in diagram ( I ). Chemicals are mixed at the manifold prior to entering into the Pipeline System. 
 
 

In severe circumstances, the pipeline may become completely blocked. This creates an extreme loss of revenue to the operating company and will prove costly, as the pipeline usually requires replacement with new line. The basic cause of this problem has been due to the lack of regular maintenance pigging which would eliminate or certainly limit the deposit of wax on the pipeline wall. 

The object of the Jetstream Operation is to demonstrate methods, which may be used to clean wax or asphaltite contaminates and restore the pipeline to normal flow conditions. 

Methods:

In order to remove the deposits of wax or asphaltite from a pipeline, requires a combination of heat to melt the wax, in conjunction with jetting or turbulent action to remove the contaminate from the pipe wall and to maintain the action in order to keep any particles in suspension. 

The system is run in the form of a bathed train headed by a slug of Gel. Each component is designed specifically for the system in operation and calculations are made which take into consideration the length of the pipeline and the flow conditions that may be related to the extent of blockage or build-up of contaminate. 

JETSTREAM PIG:

Such a process may be carried out by use of StarTrak special pipeline pig (exhibit ii) known by the trade name "Jetstream". 

This pig is comprised of a steel body supported by bidirectional urethane disks that are separated by either steel or urethane spacers. A magnetic circuit that is encapsulated in urethane separates the rear disks. The purpose of the magnetic circuit is to ensure detectability of the pig from the outside of the pipeline. Two pole plates are utilized in conjunction with magnets in order to guide the magnetic flux to the wall of the pipeline as demonstrated in earlier Ernest Lloyd Ltd. (Ernest D Casey) patents. Such a field may be utilized to activate magnetic pig passage indicators, and in turn valve actuators, etc. The exact position may be located by a fluxgate gradiometer. 
 
 

The nose chamber of the pig is designed with a pressure release valve, which can be set to activate at a pre-determined delta "P" factor. The nose is completed with drilled jetting nozzles. 

CHEMICAL:

The function of the chemical components is to generate an exothermic reaction that takes place when the first becomes contaminated with the second chemical. By use of Hydrochloric acid acting as the first chemical and Anhydrous ammonia as the second chemical, a high temperature is developed at the point where the two chemicals react as they come in contact with each other. 

This is by way of an example, as there are other chemical compositions, which may be utilized to carry out a similar function or include chemical additions such as Sodium Nitrite, which act as a time reaction delay. 

There has been similar developments in the past for cleaning pipelines and addressing wax build-up, however, the efforts have had limited success. The limitations have been due to a factor of not using the jetting type of action in order to create the combination of exothermic reaction and mechanical action at the point of deposit, subject of this proposed patent. 
 
 

THE SYSTEM:

Wax/Asphaltite removal can be achieved by the following procedures. The insertion of a Hydrochloric base Gel followed by a batch of Hydrochloric acid, quantity and strength to be ascertained at the commencement of each job due to size of line, length and chemical formulation of product. 

After the batch of HCL has been loaded, it would be followed by the "Jetstream" pig. The pig to be propelled by a quantity of Anhydrous Ammonia which in turn may be followed by an agent such as Xylene, separated by a pig, in order to eliminate the possibility of crystallization. 

When the batch or system reaches the point where build-up of wax/asphaltite has started, the pig will become impeded by the build-up. By this stoppage of the pig, the Delta "P" factor will increase until it reaches the predetermined factor where the pressure release valve becomes activated allowing the Anhydrous Ammonia to jet through the pig's nozzles at a high velocity. The jetting force factor plus the exothermic reaction will cause the contaminate build-up to be released from the pipeline wall. The turbulent flow created will cause the melted contaminate to be held in suspension. 

Due to the pig's magnetic circuit, the pig can be traced at all times and in the event of a problem situation where the operators are forced to back off the intrusive contaminate, the actual location of obstruction can be determined. 
 
 

CONCLUSION:

For many years, offshore pipeline companies have been troubled with the problem of wax and asphaltite deposits that adhere to the inner wall of their marine pipeline systems so reducing the overall efficiency of the system. The fear of a pig becoming obstructed during routine maintenance operations has caused operators to shy away from using pigs. 

Various operators have utilized spheres or spherical pigs in an attempt to lower the frequency of wax contaminate deposit, but no one can rightfully claim that spherical pigs have any realistic cleaning power. They do have least tendency to become obstructed although many Gulf Coast operators have been forced to contend with this problem. 

The solution which StarTrak offers in conjunction with their associates C.S.I. Hydrostatic Testers of Lafayette, Louisiana may not be the solution to all problems associated with contaminate build-up, but it does however, offer advancement towards eliminating many of today's problems associated with this subject. 

The system, a combination of the "Jetstream" pig and the Chemical, as described, will provide an answer to many problems for the removal of wax deposits from the internal wall of an oil pipeline either on land or sub-sea operations. 

In the event that the pig becomes obstructed it can-easily be located by StarTrak "Pathfinder" methods. Knowledge of the pig's whereabouts, plus careful monitoring of product, will provide information of where the contaminate build-up is occurring. Further information detailing the quantity of chemical #2 jetting into chemical # 1 can be calculated. 

Additional information of an operation may be gained by introducing a temperature-monitoring probe at the surface of the jetting chamber of the pig and including an odometer with associated circuitry that may be housed within the pig body. The resultant information will allow a record of temperature against time against footage traveled. This information provide a good indication of the temperature required to remove wax deposits also the exact position of the contaminate build-up and the total length of the deposit. This information will assist by lending additional support to final reporting. 

Patents Pending

Ernest D Casey 7th July 1995