INTRODUCTION
The ability to custom synthesize a scale inhibitor product for any specific scaling regime would be extremely advantageous. This paper presents the results of an R&D initiative in developing such a product range. These polymeric scale inhibitors incorporate patented, phosphorus based monomer species utilizing end-capped technology that allows specific performance characteristics of the product to be altered. Presented within the paper are the results of the product development along with details of the laboratory testing undertaken to determine the performance envelope for these inhibitors.
Operators, service companies and suppliers are constantly examining means of achieving better downhole scale control. The driver for this is not only financial but also out of necessity due to increasingly complicated well completion technology and increasing production from high temperature/high pressure reservoirs. Governmental legislation for many countries, but most notably Norway, has also dictated the need for environmentally friendly chemicals for offshore usage. In recent years, a raft of scale inhibitor chemistries and deployment techniques has been developed to meet these demands. For example, pre-emptive squeeze treatments using non-aqueous products ~ have become increasingly popular. Such treatments can be used in wells where severe scaling is predicted with the onset of water production. A pre-emptive squeeze before water production provides protection against scale formation and ensures well inflow performance. A further means of controlling downhole scale has been through continuous injection within the gas lift stream 2 or by deployment of encapsulated scale inhibitors 3. However, by far the most popular means of downhole scale control is by squeeze treatment, which will be the focus of this paper. In this context, our attention was drawn to novel technology 4 where scale control polymers could be "end-capped" to modify their properties and the decision was taken to focus on this area.
Through our experience of existing scale inhibitor chemistries it was recognized that there are several
performance characteristics that could, potentially be enhanced.
a . Control of scale at a lower minimum scale inhibitor concentration (MIC). If an end capped polymer could be optimized in such a way that it was capable of controlling scale at lower concentration there would be a potential for increasing squeeze lifetimes.
b. An enhancement in the quantity of scale inhibitor adsorbed. An increase in the amount of adsorption would again potentially increase squeeze lifetime. Furthermore, increased adsorption might result in a decrease in the amount of wasted scale inhibitor. From previous experience, it is recognized that only one third, or thereabouts, of the chemical deployed is effective at scale control. The remainder is either back produced during initial flowback or is lost to the formation. In this respect, squeeze treatments are highly inefficient with significant quantities of waste chemicals entering the environment.
c. Environmental performance. For environmentally sensitive regions many scale inhibitors are excluded due to a combination of poor biodegradation, bioaccumulation and toxicity. By utilizing end capped polymer technology it was hoped that we could synthesize products with better environmental performance.
The points made above were used as the basis for the defining an R&D program to investigate end capped polymer technology as a means of custom synthesizing scale inhibitor products to meet specific performance targets. The R&D program was divided into two phases.
Phase 1. Define base line parameters by comparing the perfo
