High-performance, low friction resistance, low-cost, low-molecule clear fracturing fluid; NS-DUPAC system additives interchangeable with Guar system.
NS-DUPAC Composition：
NS-DUPAC is a low- molecular polymer system that consists of the following products.
Table 1 Composition of low- molecular clean fracturing fluid system
| Low-molecular clean fracturing fluid NS-DUPAC (based on preparation of 100m3 ) | ||||
| Medicine Description | Percentage (%) | Dosage | Unit | |
| 1 | Thickener | 0.3~0.6 | 0.3~0.6 | t |
| 2 | Cleanup agent | 0.5~1.0 | 0.5~1.0 | t |
| 3 | Clay stabilizer | 0.5~1.0 | 0.5~1.0 | t |
| Delay-action cross-linker | ||||
| 4 | Delay-action crosslinker | 0.4~0.6 | 0.4~0.6 | t |
| Gel breaker: | ||||
| 5 | Gel breaker | 0.02~0.04 | 20~40 | kg |
| Remarks |
(1) Thickener is subject to slight adjustment based on different physical properties of formations; (2) Select different delay-action cross linkers based on the reservoir temperature: • NS-A is a low-temperature delay-action cross linker, which is applicable to fracturing of reservoirs at under 60℃； • NS-B is a medium-high-temperature delay-action cross linker , which is applicable to fracturing of reservoirs at 60-90℃； • NS-C is a high-temperature delay-action cross linker, which is applicable to fracturing of reservoirs at 90-140℃； • NS-D is a super high-temperature delay-action cross linker, which is applicable to fracturing of reservoirs at 140-180℃； |
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Working Mechanism of Low molecular Clean Fluid NS-DUPAC ：
(1).The successful application of low-molecular copolymer based on monomer copolymerization in sulfonic acid group improves the temperature resistance and salt resistance of polymer and inhibits the hydrolysis of amide group. In addition, the rigid side chain group of low-molecular copolymer improves its shear resistance and mechanical degradation resistance. The structural characteristics of this low-molecular copolymer provide a theoretical basis for fracturing fluid thickener.
(2).This low- molecular copolymer in aqueous solution can react with many amphoteric metal salts to form gel by cross-linking. Cross-linking principle is as follows: In an acidic environment (pH<7), hydrated cation of hydroxyl group connects with hydroxyl bridge to form a polynuclear complex, and can be cross linked with the low- molecular copolymer containing active group in the aqueous solution. The amphoteric metallic ion’s polynuclear hydroxyl bridge complex ion developed on this principle for delay-action cross linker FRK-JL3 has a positive valence (2n+6). The cross linked points in the spatial network structure are mutually exclusive and the network is stretched , thereby forming the gel with good viscosity.
(3).Metallic ions as an auxiliary agent of delay-action cross linker for fracturing fluid has strong thickening capability, wide range of application and good temperature resistance, especially reducing the formation damage in an acidic environment.
(4).In order to improve the complexing capability of delay-action cross linker, to improve the properties of cross-linked gel, and to control its cross-linking time, and apply cross-linking coordination products . The use of this auxiliary agent is conducive to the formation of complex ion, and can control the cross-linking time at 45-180s.
After a series of indoor evaluation tests, we can see this clean fracturing fluid system obviously has a temperature resistance and can at least be applied to the formations at 90-1600C. In the meantime, the fracturing fluid is characterized by shear resistance and salt resistance, and has broad prospects for development due to its thorough gel breaking, less filtration residue and less formation damage.
