Unwanted water production is a serious issue in oil-and gas-producing wells. It causes corrosion, scale, and loss of productivity. One method of treating this problem is to chemically reduce unwanted water. This paper discusses the use of polymer systems for this purpose and presents a thorough review of available literature over the last decade. In this paper, field-application data for various polymer systems are summarized over the range of 40 to 150 C (104 to 302 F). These applications cover a wide range of permeabilities from 20 to 2,720 md in sandstone and carbonate reservoirs around the globe. Moreover, the review revealed that the last decade of developments can be categorized into two major types. The first type is polymer gels for total water shutoff in the near-wellbore region, in which a polymer is crosslinked with either an organic or an inorganic crosslinker. The second type is concerned with deep treatment of water-injection wells diverting fluids away from high-permeability zones (thief zones). These thief zones take most of the injected water, which results in a large amount of unrecovered oil. For the total-blocking gels, various systems were identified, such as polyurethane resins, chromium (Cr 3þ ) crosslinking terpolymers, Cr 3þ crosslinking foamed partially hydrolyzed polyacrylamide (PHPA), and nanoparticle polyelectrolyte complexes (PECs) sequestering Cr 3þ for elongation of its gelation time with PHPA. In addition, polyethylenimine (PEI) was identified to crosslink various polyacrylamide-(PAM-) based polymers. The Petróleos de Venezuela S.A. (PDVSA) Research and Development Center developed a PAM-based thermally stable polymer and an organic crosslinker. The system is applicable for a wide temperature range from 50 to 160 C (130 to 320 F).For the deep modification of water-injection profiles in waterinjection wells, two systems were identified: microspheres prepared from PAM monomers crosslinked with N,N 0 -methylenebisacrylamide and microspheres produced by crosslinking 2-acrylamido-2-methylpropane sulfonic acid (AMPS) with diacrylamides and methacrylamides of diamines (thermally activated microparticles known as Bright Water). This paper highlights all major developments in these areas. Important Factors for Successful CITsThe identification of the water source is a key factor for successful CITs. The characterization of water production can be performed

Polymeric gels are used to reduce or shut off excess water in petroleum reservoirs. The strength of polymeric gels needs to be high enough to withstand the water flow. This study investigates the strength of an organically crosslinked polyacrylamide (PAM) with polyethylenimine (PEI) as crosslinker. Dynamic testing measurements at high temperatures up to 130 C (266 F) and high pressure (500 psi) were used. During the gelation process, the rate of crosslinking increases with increased temperature. However, after the crosslinking reactions were completed, G 0 was lower at higher temperatures than at lower temperatures. Polymer concentration has a stronger impact on G 0 in comparison with the crosslinker. Salinity of mixing water has a negative impact on G 0 . High G 0 was observed in distilled water (1044 Pa) in comparison with field water (725 Pa) at 130 C (266 F). Moreover, samples prepared at alkaline and acidic conditions produced stronger gels compared with samples prepared at neutral conditions. However, the gelation time is longer at a pH of 7. Ammonium chloride is found to be a very effective retarder in comparison with NaCl. The yield stress of the gel was correlated to the pressure gradient for the gel extrusion through fractures. It was found that gels with 7:0.3 and 5:0.3 wt% PAM/PEI gave pressure gradients of 155.5 kPa/m (55.2 psi/m) and 3572 kPa/m (518 psi/m), respectively. The decrease or increase in gel strength was explained through the impact of the different parameters on PAM hydrolysis.

A polymer gel is one of the common remediate methods to either reduce or totally block excessive water production in oilfields. Some systems demonstrated an excellent performance in treating the problem like polyacrylamide tert-butyl acrylate (PAtBA)/polyethylenimine (PEI). In this study, polyacrylamide (PAM) was introduced as a cheap alternative to PAtBA that can tolerate high salinity reservoirs. The thermal stability of the PAM/PEI polymeric gel in saline water was examined at 150 C (302F). Samples prepared in sea water showed better stability compared with distilled and field water. Dynamic rheology and core-flooding experiments were used to evaluate the PAM / PEI gel system at high temperatures. NaCl and NH 4 Cl were evaluated as a possible retarders for delaying the gelation time in order to achieve a successful placement. NH 4 Cl was found to be more effective retarder. Core-flooding tests were conducted in sandstone and carbonate cores. The subject polymer gel was injected at rates typical of those in field applications. The injectivity of PAM/PEI was tested in Berea sandstone cores with initial permeability of 45 mD. The posttreatment of the system showed a permeability reduction of 94% for a period of two weeks. The injectivity in low permeability carbonate cores required more retardation compared with the injectivity in sandstone cores. The gel reduced the permeability to brine in Indiana limestone core by 99.8% for more than 5 months. Rheology of cured gel samples indicated that the gel strength needs about one day of curing in the core for the strength to stabilize.

Water production in the oilfields has a negative impact on the production and economy. It is highly desired to shut off water paths without affecting the hydrocarbon zones. Polymer gels are frequently used for water control in oil and gas wells. However, a risk will be taken, which is blocking the oil-producing zones alongside the water zones. Hence, a selective system is proposed, which is based on emulsified polymer gel that contains a water phase which will form a gel, and an oil phase remains mobile to secure the flow of oil. The gels formed in situ by breaking up of an emulsified gel made of an oil phase and an aqueous water-soluble polymers (gelant). Breaking of the emulsion and the subsequent gelation is a function of temperature, time, salinity of mixing water, and concentration of the various components, including surfactants and salts. The gelant was prepared by mixing polyacrylamide (PAM) with a mixing brine and then adding polyethylenimine (PEI) as a cross-linker. Diesel and a surfactant were used to form the emulsified gel. In this study, differential scanning calorimetry (DSC) is utilized to study the emulsified gel reaction kinetics for the first time. The rate of increase in temperature and the final temperature used in DSC were chosen to approximate (mimic) the field injection conditions. The impact of parameters such as temperature, water salinity, surfactant, and retarder type on gelation is investigated to compare the kinetics of the polymeric gels and their emulsified forms. At a given emulsifier concentration, emulsified PAM/PEI has a lower rate of cross-linking (gelation) when compared to that of PAM/PEI. This is most likely due to less heat conducted to the gelant. As a result, the cross-linking density will be less. Ammonium chloride is found to be more efficient than sodium chloride in retarding the gelation process. The type of surfactant is an additional parameter which can be used to control gelation in emulsified gel systems.

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