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^
Improved productivities can be obtained from wells if clean fluids are used for workovers and completions. All clays, silts, or sands that are suspended in wellbore fluids can be deposited in the producing formation and the perforation channels where they will reduce a well's production rate. Filters are often used to clean up fluids. Although two micron cotton filters are commonly used for this purpose, there are other types of filters and filtration systems available that could do a more efficient job for less cost. A study has been made of the efficiency and life of various filter elements. Some of the factors evaluated were: filter materials of cotton and polypropylene; micron size ratings of 2 microns to polypropylene; micron size ratings of 2 microns to 75 microns; and flow rates of 1 to 3 barrels per minute. Due to the extremely large number of variables, this study is continuing, but some important conclusions have been reached. These conclusions are: Conclusions Filter life is longest at low rates. When more than one barrel per minute rate is required, the flow should be split into 2 or more filter pots in parallel. Series filtration through 50 micron and 2 micron rated filters provides good filtration and filter life at flow rates to 3 BP per pot. per pot. Sock type polypropylene filters showed best overall efficiency of the three types of filters tested. Cotton sock type filters have best efficiency at low flow rates, but fail at higher flow rates. Polypropylene filters should be changed when the pressure differential reaches 35 psi. A better understanding of filters and filtration technology can provide cleaner fluids and reduce the high costs and wastes of ineffective filter systems. Introduction Formation damage by solids in completion and workover fluids can result in considerable loss of production from oil and gas wells. Solids injected production from oil and gas wells. Solids injected into the formation may be trapped by the matrix or in the perforation tunnels and reduce productivity. This problem frequently occurs in operations such as acidizing, washing perforations, killing a well, injecting chemicals into a formation and in sand control jobs. It is very difficult to remove these solids once they have been placed into the formation, especially if they invade some distance into the formation matrix. The pore sizes of typical productive miocene sands in the Gulf Coast are between productive miocene sands in the Gulf Coast are between 0.2 and 7.5 micron diameters. Thus, solids of these sizes can invade into the formation sand where they may be trapped. To estimate the volume of this size range of solids required to significantly damage a formation sand, one may calculate the amount of solids that will completely fill a pore volume of the formation sand l' radially around the well bore. For instance, one foot radial volume around a 7" well bore would require only one quarter of a cubic foot of solids to completely fill the pore spaces of a one foot interval assuming twenty percent porosity. Using this calculation, 7.14 barrels of water containing only one thousand parts per million (0.1%) of solids, would completely fill the pores if all of these solids were trapped in the first radial foot of the formation.
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