While laboratory tests show that polyacrylamides candecrease permeability to water while only slightlydecreasing permeability to oil, there is much confusionabout why this occurs. This study focuses on determiningwhich properties are most important for reducingpermeability to water and how they relate to successfulfield treatments. Introduction Polyacrylamide polymers have been used for years toreduce water production in oil wells and for mobilitycontrol in injection wells. The unique property ofpolyacrylamides that makes them attractive for reducingthe water production from oil wells is their ability toreduce the permeability to water of a porous media withonly a minor effect on the permeability to oil. This has been demonstrated by many laboratory tests, but somefield results have been disappointing.A description of 19 polyacrylamide treatments of producing wells within Continental Oil Co. over thepast several years is shown in Table 1. Results of somejobs were excellent. For instance, Job 11 resulted innearly a tenfold increase of oil production rate and4,000 bbl of additional oil. However, only seven jobswere economically successful. Although the number ofsuccessful jobs is discouraging, several that did notpay out did reduce water production significantly butdid not improve oil production. Jobs 4, 11, 18 and 19were all run in the same field and formation; but t hefirst two were very successful and the others failed.To remove some confusion from this technology, thisstudy was conducted on polyacrylamides currently beingused in the field for water control. The differencesbetween the polymers and the importance of thesedifferences in treating various types of formationswere studied. We attempted to define where polymersmost likely will reduce water production and improveoil production as well as where they should not be used.This study led to several conclusions that areimportant to improving the success ratio of future polymertreatments in producing wells. Commercial Water-ControlPolyacrylamides Currently available commercial polyacrylamides can bedivided into five types as shown in Table 2. Thesepolymers are provided in dry powdered form or concentratedin a water-and-oil emulsion. In its dry form, the polymer is dissolved in water at the wellsite by variousmeans. An advantage of the emulsion polymers isthat they will dissolve readily and uniformly in water, thus facilitating control of the polymer concentrationduring a job. However, the emulsion polymers are usuallymore expensive than dry polymers.The average molecular weights and activities listedin Table 2 were provided by the polymer suppliers astypical of the polymer analyses. The higher molecular-weightpolymers generally yield higher-viscosity solutions inthe same water. The activity numbers indicate the relativenumber of reactive sites or degree of hydrolysis in thepolymer. Nonionic polyacrylamides usually have less than10-percent activity. An anionic polyacrylamide will becompatible only with fresh-water or soft-water brines, while nonionic polymers are compatible with a wide varietybrines.Table 3 gives some chemical analyses of variouspolyacrylamide samples. JPT P. 906^