Polymer Gelants for High Temperature Water Shutoff Applications
- Steven L. Bryant | Martin Bartosek | Thomas P. Lockhart | Diego Giacca
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- December 1997
- Document Type
- Journal Paper
- 447 - 454
- 1997. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 4.3.3 Aspaltenes, 3 Production and Well Operations, 2.2.2 Perforating, 2.4.3 Sand/Solids Control, 1.6.9 Coring, Fishing, 5.1 Reservoir Characterisation, 1.14 Casing and Cementing, 5.3.1 Flow in Porous Media, 4.3.4 Scale
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Polymer gelants are a well established means for shutting off water in lower temperature formations, but extending their application to hot reservoirs (>80°C) presents a number of technical challenges, particularly in matrix reservoirs. Achieving reliable high temperature performance requires programmable gelation delay, good injectivity good propagation of gelant components and durability of the permeability reduction. The performance of a gelant against these criteria is dictated by a relatively small set of chemical and physical phenomena. A discussion of these phenomena provides a rational background for assessing the advantages and disadvantages of currently available gelants This also helps to identify the best avenues for improving polymer gelant systems. This approach is particularly relevant when seeking gelants for high temperature matrix applications. because increased temperature renders it much more difficult to satisfy the four performance features simultaneously.
Lower operating margins have led to a strong push to identify and eliminate problems that add to operating costs. This focus has drawn close attention to the problem of produced gas and water in oil wells over the last few years.
Several technological alternatives are available to the field engineer faced with such water production problems. These include relatively simple procedures such as setting a bridge plug or using cement to isolate the lower portion of a well. These low cost procedures may be extremely effective if the water is known to enter at the bottom of the well. More expensive and less reliable interventions include remedial cementing to reduce channeling behind pipe and well workover in order to mechanically isolate the water producing zone.
Polymer gel treatments have emerged as another effective tool. These treatments are carried out with aqueous polymer solutions that are pumped into the formation while still fluid. Cross-linking of the polymer solution, by means of which it is transformed into a robust, viscoelastic solid (gel), is triggered by the formation temperature. Presently, the most widely used polymer gel-forming compositions (gelants) employ a polyacrylamide (PAAm) or an acrylamide co-polymer and a chromium [Cr(III)] cross-linker.1,2 Gelants using organic cross-linkers are being applied with increasing frequency in high temperature formations.3,4
Polymer gels can greatly reduce the permeability of porous rock and can be formulated to resist considerable drawdown.5 The ability of polymer gelants to penetrate deeply within a fracture (>10 m) and to a significant depth (>1 m) in matrix formations means that fluid flow can be blocked or redirected even at a significant distance from the wellbore. This can be very important to the success of water and gas shut-off treatments, and constitutes an essential difference between this technology and mechanical isolation or cement treatments. Gels also have the mechanical strength to shut off flow through conductive fractures, and have been widely employed for this purpose in naturally fractured formations.6 The ability of fluid polymer gelants to penetrate through narrow openings also makes them an attractive alternative to remedial cementing to shut off flow behind pipe.
The versatility of polymer gels is not a substitute for careful analysis of the causes of the unwanted fluid production. Without a good knowledge of the nature of the problem, it is much more difficult to design an effective treatment, both from technological and economic points of view. Whatever the application, four characteristics of a gelant are generally desirable:
programmable gelation delay
good propagation of gelant components
durability of the permeability reduction
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