Abstract
Crosslinkable polymers, such as polyacrylamide (PAM), are widely applied for water control in oil and gas reservoirs. Organic and inorganic crosslinkers are used to formulate a gel with PAM. Although chromium has a high level of toxicity, it has been implemented as an effective crosslinker combined with carboxylates because of the controllability of crosslinking time at low temperatures. The objective of this work was to develop greener d-metal inorganic crosslinkers based on cobalt, copper, and nickel to replace chromium for application at reservoir conditions. The obtained results showed that the gelation chemistry of the developed systems depends on the metal charge density. The gelation of PAM with d-metals depends on pH and temperature for low- and high-charge density, respectively. Cobalt (II) acetate (CoAc) was effective at high temperatures (130–150 °C) and forms (4% CoAc + 9%PAM) stable, and strong gels at a pH > 7 with a storage modulus exceeding 4300 Pa. However, Nickel Acetate and Cupper Acetate formed stable weak gels at low temperatures (50–70 °C) and a pH > 6 and gel decomposition was observed upon increasing the temperature. The developed formulations were compatible with low-salinity water (1000 ppm NaCl).
Highlights
The productivity of oil and gas wells is highly affected by the coproduction of water from water zones as well as the heterogeneity of the formations [1]
Nickel Acetate and Cupper Acetate formed stable weak gels at low temperatures (50–70 ◦ C) and a pH > 6 and gel decomposition was observed upon increasing the temperature
Inorganic crosslinkers are preferred for the low-temperature range because of their fast gelation at high temperatures ( 90 ◦ C) compared to organic crosslinkers such as polyethyleneimine (PEI), which results in stable gel after crosslinking with PaM at high temperatures
Summary
The productivity of oil and gas wells is highly affected by the coproduction of water from water zones as well as the heterogeneity of the formations [1]. Sandstone reservoirs are associated with high permeability zones, whereas carbonates are naturally fractured. Crosslinked by organic or inorganic crosslinkers is the most commonly applied type of polymer because of the ability to withstanding reservoir salinity and high-temperature conditions as well as its relatively low cost for field applications [2,6,7,8,9,10]. Inorganic crosslinkers are preferred for the low-temperature range because of their fast gelation at high temperatures ( 90 ◦ C) compared to organic crosslinkers such as polyethyleneimine (PEI), which results in stable gel after crosslinking with PaM at high temperatures (>90 ◦ C) [11]. Aluminum (III), chromium (III), zirconium (IV), and titanium (IV) have been used to crosslink polyacrylamides and polysaccharides [12,13]
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