Hydrate formation poses an ever-increasing risk as pipeline conditions contain both water and natural gas. The ability for a gas saturated with water to form a hydrate will also increase over time as methane is extracted leaving higher concentrations of heavier gases. These hydrates can continuously precipitate to the point where they have developed as long stretches of uniform pipeline restriction or accumulated as a large mass that results in complete plugging. The solid-like nature of the hydrate makes them a difficult and often expensive pipeline issue to avoid or remedy.
One common solution for pipeline hydrate remediation are changes to physical conditions of the pipeline, either changes in temperature or pressure that prevent the formation of hydrates. However, this is not always possible, especially in deep water pipelines where the conditions are what they must be for successful transportation of the produced gas. The other solution is continuous inhibitor addition, being either Methanol or MEG, but the problem with this solution is the massive volumes needed of the selected inhibitor and the fact that the inhibitor needs to be present in the free water phase of gas fluid to prevent hydrate formation. Surface and pipeline conditions can make this very difficult if not impossible.
A more cost conscience method is routine hydrate removal. The hydrate structure is an equilibrium phase of the water and gas. A routine cleaning slug can push the equilibrium away from the hydrate formation and revert the formed hydrates back into their base components. This can be done with minimal cost and effort by implementing an appropriate cleaning gel and elastomer pig. This requires minimal equipment and time to launch the gel and pig and requires no equipment to catch the pig as it will just break apart through any orifice smaller than 50% the diameter of the pig.
Mono Gel Pig
To ensure a properly functioning pipeline system, routine maintenance is required. The maintenance required will depend on the properties of the fluid within the pipeline as well as any physical modification that is to be done to the pipeline. The most common threats to a pipelines longevity are wax, asphaltene, and scale deposition. The potential damage that each of these poses can be monitored using the ReNu (Hyperlink to ReNu paragraph) process. If deposition is left unchecked, then the mechanical pig that is typically recommended might do far more harm than good by getting stuck due to either pipeline geometry or deposit buildup.
Mechanical Pig Aides
The highest cost during normal mechanical pigging operations is bypass. Pipeline gels reduce bypass and provide lubrication that reduces runtimes 30 to 50%. The use of debris removal or suspension gels eliminate the stuck pig risk from “snow plowing”. If the mechanical pig does happen to get stuck, then it can be a very costly endeavor. Prior to sending an expensive wireline or coiled tubing crew a series of solvents, gels, and gel pigs should first be tried to recover the pig. They are more cost-effective and have no chance of doing more harm. If this method doesn’t dislodge the pig and wireline or coiled tubing is required, their operations can be assisted with the use of a gelled system to assist with the removal of the mechanical pig out of the pipeline.
Profitable Transportation for as Long as Possible
Pipeline Modification, Inspection, Repairs, and Hydro Testing
If a testing procedure is to be performed, then dewatering or deoiling steps may be necessary. This can be done easily and effectively with a dewatering or deoiling gel train with an elastomer pig backing. This removes the risk of the pig getting stuck and allows for the pipeline to be prepared for testing with minimal volumes and cost.
If there is to be a modification on the pipeline, then a deoiling or dewatering step may be used. But an encroachment prevention gel should be used. A segment to be added can be plugged using elastomer pigs with solvent or inhibitor treatments enclosed that can be used once the segment is installed. The section being opened for installation can be isolated by a gel slug between elastomer pigs completely preventing contamination from the environment. This minimizes the risk of introducing damage mechanisms during the modification as well as allows for installation of segments with build in pipeline treatments immediately ready to use.
Inline Inspection (ILI) Smart Pigs
ILI pigs are a tremendously useful tool if they can be utilized, however ILI pigs frequently have wax buildup on their location wheels that result in bad runs. This buildup occurs even after the ILI pig immediately follows a mechanical pig run. By calculating bypass rate of the specific pipeline geometry, customized solvent slugs can be pumped to insure location accuracy. Specifically, designed wax dispersant or solvent stages can be added between mechanical pigs during the initial ILI preparatory process. This further reduces the risk of wax accumulation on the ILI tool.
Organic and Inorganic Deposits
To combat this problem, wax and asphaltene removal or descaling treatments should be designed and implemented to prevent the development of deposits that cannot be chemically removed. These treatments can be performed as a liquid or gelled system to best fit the conditions of the pipeline. If deposits have developed beyond the remedial capability of a routine low volume treatment, then a mapping of the restrictions should be performed. This can be done with a surveillance pig which allows for alterations in pressure and flow rate to pinpoint the location of large restrictions while also determining the approximate magnitude of the restriction. After the restrictions are located then an effective batch treatment of the deposits can be performed which include customizable chemicals to remove debris, de-oil pipe surfaces, optimize bacterial control to achieve both quick kill and preservation as well as remove biomass/microbial deposits.