Polymer Drilling Fluids in the 1990's: Will They Replace Oil-Based Muds?
- S. Dwight Strickland (Baroid Drilling Fluids)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- August 1994
- Document Type
- Journal Paper
- 691 - 714
- 1994. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 2.2.3 Fluid Loss Control, 1.11.4 Solids Control, 6.5.4 Naturally Occurring Radioactive Materials, 1.6 Drilling Operations, 1.11 Drilling Fluids and Materials, 2.1.7 Deepwater Completions Design, 4.2.3 Materials and Corrosion, 4.3.1 Hydrates
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Technology Today Series
The 1990's have seen a surge in new water-soluble polymers available to thedrilling industry. Many new polymers offer enhancements or significantimprovements. It has often been said that "This polymer system is just asgood as oil mud," or "This product will replace oil mud." Theseclaims have negatively affected acceptance of new polymers, retarding theirfield applications regardless of technical and/or economic merit.
Many new polymers are gaining acceptance because of unique performancecharacteristics and are proving to be cost-effective. Other polymers have beenslow to gain acceptance, not because of improper claims, but because ofless-than-satisfactory technical and/or economic performance. Some polymerswill never achieve stated claims, but others will be optimized or modified andfind an application niche in the industry. No one polymer chemistry or systemwill replace all the performance characteristics of oil-based fluids; however,some polymers are being used successfully in some oil-mud applications.
Polymer Classification Overview
Polymers are used in virtually all water-based fluids, so the term"polymer" should not have a negative connotation. However, many in theindustry view polymers negatively because of a lack of understanding. Also,many drillers, drilling superintendents, and drilling engineers have seen onlocation that polymers fail to achieve claims.
Polymers are classified as natural, modified natural, and synthetic. Naturalpolymers originate in nature (i.e., starch). Modified natural polymers are theresult of a chemical reaction or modification to a natural polymer (i.e.,carboxymethyl starch). Synthetic polymers are chemically reacted monomers[i.e., partially hydrolyzed polyacrylamides (PHPA's)]. The primary benefits ofmodified and synthetic polymers over natural polymers are increased temperaturestability and contamination resistance.
A general understanding of polymer classification and knowledge of thestrengths, weaknesses, molecular weight, and functionality can facilitateselection and treatment strategy for polymers.
The following performance characteristics desirable in a drilling fluid areselected from a list of advantages of oil-based drilling fluids and will beused to compare the performances of polymers and oil-based drilling fluids.
-Protection of production zone.
-Lubricity and torque/drag reduction.
-Resistance to contamination.
Thermal Stability. Synthetic polymer chemistry has probably made its mostsignificant contribution to the drilling industry inhigh-temperature/high-pressure applications. During thedeep-gas/high-bottomhole-temperature (BHT) drilling of the 1970's and 1980's,oil muds prevailed. During the late 1980's and early 1990's, numerous syntheticpolymers proved technically capable and cost-effective at high BHT's andpressures. Synthetic polymers specifically formulated for deflocculating,fluid-loss control, and gel inhibition at high temperature proved to have wideutility. In 1989, Elsen et al. reported the use of a lime-based fluid atdensities exceeding 18.0 lbm/gal with calculated BHT's above 350#F. Using limemuds at these hostile conditions would have been impossible without natural,modified, and synthetic polymers. Polymers used in this challenging environmentincluded lignite, starch, polyanionic cellulose (PAC), polyanionic lignon,polymer-grafted lignosulfonate, modified polyacrylate terpolymer, and vinylamide/vinyl sulfonate copolymer. Numerous water-based systems incorporatingvarious polymers have been used successfully and economically above 400 F withdensities ranging from 15.0 to 18.0 lbm/gal.
Successful completion of these wells with water-based polymers requiresprespud planning and laboratory optimization specific to the drillingobjective. These prerequisites must not be compromised. Special programs mustbe in place with wellsite laboratory equipment and laboratory confirmation forthis technology to be applied successfully.
Formation Stability. Various developments in the late 1980's and early1990's focused on improving formation stability by increasing the concentrationof shale-inhibiting additives or by combining polymer additives that inhibitreactive shales. Preventing the hydration of swelling and/or reactive shaleswith water-based systems became the technical challenge of the drilling-fluidindustry. A long list of polymers and polymer enhancers were thrust on theindustry. Examples are saturated salt/PHPA, polyalcohol, polyglycol,cloud-point polyols, polyglycerine, cationic polymers, cationic starch,carboxymethyl starch, cationic PHPA, black liquids, black powders, potassiumpolyacrylates, potassium cellulosic polymers, polyamino acids, MMH, MMS, andmethyl glucoside.
Cationic polymer systems received increased attention in the early 1990's.The industry saw a major operator and a major service company introduce andpromote cationic chemistry as a replacement for oil-based muds. The reviews ofthese systems were mixed. While some reports indicate the success of thesesystems, more field experience is needed to determine long-termapplicability.
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