Abstract

Paraffin related problems of deposition, congealing oil and interface/tank bottoms cost the gas and oil industry hundreds of millions of dollars each year. Most of this money is spent without a clear understanding of the problems being experienced or their cost. If the real cost of a problem is not calculated before a treatment program is started it may not be possible to know if that program is cost effective. This paper will attempt to explain the difference between an inexpensive program and a cost effective program. Case histories will be presented.

Introduction

The paraffin or n-alkane components account for a significant portion of a majority of crude oils that are > 20° API. These paraffins have a straight chain linear structure composed entirely of carbon and hydrogen. The melting points vary from –295°F for methane gas (CH4) to >240°F for Hectane (C100H202) and above.1 It is not known what the longest naturally occurring n-alkane in crude oil is, the longest observed by this author was a C103H208. The paraffins >C24 H50 are the ones that can cause deposition or congealing in crude oil systems.2 The paraffins can deposit anywhere from the fractures in the formation rock to pipelines that deliver oil to the refineries.3 The deposits can vary in consistency from rock hard for the longest chain length paraffin to very soft, mayonnaise like congealing oil deposits caused by shorter chain paraffin. Crude oils have congealing points from < –90° F to >130°F.

Paraffin can cause a great many types of problems including deposition from in the formation to the refinery, congealing oil, interface problems, tank bottoms, stabilized emulsions, high line pressures, plugged flow lines, paraffin coated solids, under deposit corrosion, plugging of injection wells and filter plugging.4 One or all of these problems can occur in a production system. Paraffin problems in flowing wells will differ from those in gas lift systems and pumping wells. Pumping wells on time clocks or pump off controllers can have a number of the problems mentioned above at the same time. Any type of production system at any stage in its production life may experience paraffin problems based on the chemistry of the crude oil, the production temperatures and what we decide to do to the well. Many of our paraffin problems are aggravated by the procedures we use.

Many different types of treating programs have been used to control all of the various types of problems in different systems. Down hole problems have been treated by cutting or wire lining, rod scrappers, heated tubing, coated tubing, fiberglass tubing, hot water circulation, hot oiling down the casing, hot oiling down the tubing, hot water down the tubing or casing, cold water truck treatments down casing with chemical, bacteria, magnets, enzymes, steam injection, solvent or condensate treatments, continuous down hole chemical injection using a beam pump, neat chemical dump treatments down casing, squeeze treatments of crystal modifiers (PPD's) and chemical or solvent combined with any of the above not using chemical. In the past 100 years we have used some or all of these treatments thinking that they were cost effective until a major problem occurred and we switched to some other treatment that was supposed to be better. In this paper I hope to shed a little light on a method to find a cost effective treatment program for paraffin problems.

Individual Well Problem

The first paraffin treatment idea that needs to be changed is that all problems are the same in every well in the field or lease. If I believe this I can make life simpler by treating all the wells the same. Hot oil monthly or magnets on every well or rod scrapper type programs always seem to work on some wells and fail on others. Eventually it may quit working on the wells it was working on. This usually leads to a belief that paraffin is hard or impossible to treat effectively, much less control cost effectively.

In fact in each well in a field or lease the oil varies in the amount of gas it makes, the percent paraffin content, the chain length of the paraffins present, the cloud point, the viscosity, the oil/water ratio, the wellhead temperature, and its deposition tendencies. Each well is an individual. A field's paraffin problems will vary from well to well.

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