Page 172 - Handbook Of Multiphase Flow Assurance

168 5. Flow restrictions and blockages in operations

• Comparative economics of remediation techniques
Regional availability and operator experience with a wax removal technique are often
more important than the relative cost savings or effectiveness because safety of a method
application should increase with the operator's familiarity with the method.
Mechanical methods are usually the most cost-effective ones for wax removal. While
scraping and wireline scraping are commonly used to maintain production operations, the
coiled tubing jetting is used to clear wax from completely plugged pipes and for hydrocarbon
removal during pipeline decommissioning.

Environmental impacts of remediation techniques

• Thermal
Thermal methods are usually cost-effective for downhole onshore well applications be-
cause earth around the wellbore provides heat retention. Hot oiling is usually ineffective in
offshore wells or in flowlines both onshore and offshore because of the requirement for the
high initial temperature of the heating medium (hot oil) and the significant heat loss to the
ambient environment.
Thermal methods such as hot oiling may not be applicable in cold regions production such
as permafrost areas.
• Mechanical
Mechanical methods such as scraping, wireline cutting or jetting can be applied in onshore
wells and in flowlines both onshore and offshore. Un-scrapable lines may require solvent
remediation of wax deposit.
• Chemical
Lab selection of solvent should focus on chemical compatibility with the production sys-
tem including valve seals material. Chemical should also be effective in dissolving samples
of wax from a given field in the least amount of time at the lowest operationally possible tem-
perature. Higher temperature usually increases the solvent effectiveness, but it also increases
the flashing off of solvent vapor which may create environmental and safety hazards.

Measurement techniques

Laboratory measurements focus on determination of conditions, usually temperature but
sometimes both pressure and temperature at which solid paraffins start to precipitate from
oil, and on the comparison of amounts of wax deposition with various additives.
Finding the temperature of wax precipitation may be done with a number of methods,
categorized in Table 5.7 below.
An example in Table 5.8 below illustrates how the mass of a paraffin deposit from a cold
finger laboratory test as shown in Fig. 5.36 may be used to estimate the wax diffusion coeffi-
cient, in order to test other diffusion coefficient evaluation methods such as flow loop deposit
measurement. The initial rate of deposition is used to calculate flux in this method.
Compositional analysis of oils or wax deposits is performed using HTGC, described earlier.
The amount of wax deposition can be measured quantitatively using in a laboratory using
the methods of a cold finger, cold plate, rotating shear cell, flow loop or in field conditions using
flow spools. The methods of cold finger or a mini-flow loop can be used to compare the effects
of various chemical additives on the mass, consistency and melting point of the wax deposit.