A novel adsorption type gel plugging agent (ATGPA) was prepared using acrylamide (AM), acrylic acid (AA), diallyl dimethyl ammonium chloride (DMDAAC), 2-acrylamido-2-methylpropanesulfonate (AMPS), formaldehyde (HCHO), resorcinol (C6H6O2), and thiocarbamide (CH4N2S) as raw materials under mild conditions. ATGPA was characterized by infrared (IR) spectroscopy, elemental analysis, and scanning electron microscope (SEM). It was found that ATGPA exhibited higher elastic modulus (
Gel plugging agent plays an important role in the field of enhanced oil recovery (EOR) for high water cut oilfield [
In general, while increasing the concentration of gel plugging agent is beneficial to enhance the sealing strength, the antiscouring ability of the gel plugging agent is not helpful. And this method will lead to a substantial increase in the cost of gel plugging agent. Recently, many studies have demonstrated that the adsorption property of composite material could be significantly improved by copolymerization with a cationic functional monomer with high charge density [
Furthermore, many research works have indicated that functional polyacrylamide with -
Keeping in mind these fundamental conditions, herein, diallyl dimethyl ammonium chloride and AMPS were introduced into gel plugging agent aiming to obtain satisfying antiscouring ability, temperature resistance, and salt tolerance.
Acrylamide (AM, ≥99.0%), acrylic acid (AA, ≥99.5%), 2-acrylamido-2-methylpropanesulfonate (AA, ≥99.5%), diallyl dimethyl ammonium chloride (DMDAAC, ≥99.5%), sodium hydroxide (NaOH, ≥96.0%), polyoxyethylene (10) octylphenyl ether (OP-10, ≥99.5%), sodium hydrogen sulfite (NaHSO3, ≥58.5%), ammonium persulfate ((NH4)2S2O8, ≥98.0%), ethanol (C2H5OH, ≥99.7%), formaldehyde (HCHO, 37% aqueous), resorcinol (C6H6O2, ≥99.7%), thiocarbamide (CH4N2S, ≥98.0%), sodium chloride (NaCl, ≥99.5%), magnesium chloride hexahydrate (MgCl2·6H2O, ≥98.0%), calcium chloride anhydrous (CaCl2, ≥96.0%), potassium chloride (KCl, ≥99.5%), sodium sulfate (Na2SO4, ≥99.0%), and sodium bicarbonate (NaHCO3, ≥99.5%) were purchased from Chengdu Kelong Chemical Reagent Factory (Sichuan, China). All chemicals and reagents were used as received without any further purification. Water was deionized by passing through an ion-exchange column and doubly distilled.
The AM/AA/AMPS/DMDAAC copolymer was synthesized by free radical copolymerization. 17.58 g AM, 4.53 g AA, 3.87 g AMPS, 4.02 g DMDAAC, 2.51 g NaOH, 0.12 g OP-10 (used as emulsifier), and 0.15 g NaHSO3-(NH4)2S2O8 initiator (1/1 mol ratio) were taken along with 70 g distilled water in a three-necked flask. Residual oxygen was removed by nitrogen (N2) being bubbled through the solution for 30 min under constant stirring at 35°C. The three-necked flask was kept in a water bath with magnetic stirring unless otherwise indicated. Copolymerization was carried out at 35°C under N2 atmosphere for 6 h. After being cooled to room temperature (25°C), the products were separated by precipitation using ethanol and dried in vacuum oven at 40°C for 24 h to give the powdered copolymer samples. 6.08 g HCHO (37 wt% aqueous), 0.60 g C6H6O2, and 0.15 g CH4N2S were added into a solution of copolymer (3.0 g) in 1000 mL distilled water at room temperature with magnetic stirring to yield ATGPA.
The AM/AA copolymer without AMPS and DMDAAC (replaced by additional AM and AA) was synthesized by using the same synthesis method. The AM/AA gel plugging agent (AAGPA) was prepared using the AM/AA copolymer, HCHO, C6H6O2, and CH4N2S via the same method.
ATGPA and AAGPA solutions (0.6 wt%) were prepared with distilled water. These solutions were placed in a constant temperature box, and the cross-linking reaction took 72 h. All characterization and evaluation were carried out until all of the plugging agent was cross-linked unless otherwise indicated. Infrared (IR) spectra of ATGPA and AAGPA were measured with potassium bromide (KBr) pellets using a PerkinElmer RX-1 spectrophotometer. The elementary analysis of ATGPA and AAGPA was carried out with a Vario EL-III elemental analyzer. The microstructures of ATGPA and AAGPA were observed by a scanning electron microscope (SEM).
ATGPA and AAGPA solutions (0.6 wt%) were prepared with distilled water. These plugging agents were placed at different temperature, and the time required for the formation of the gel was 72 h. Then the apparent viscosity of these plugging agents was tested using Brookfield DV-III viscometer at different temperatures.
The plugging agents solutions were prepared by using brine with different salt concentration (NaCl or CaCl2). These plugging agents solutions needed to be aged for 72 h at 65°C. The apparent viscosity of these plugging agents was measured via Brookfield DV-III viscometer at 65°C.
Viscoelasticity measurements of ATGPA and AAGPA were conducted on a HAAKE RS 600 Rotational Rheometer (Germany). The test system was cone-plate system and the rotor was P35TiL in viscoelasticity measurements. The stress was 1.0 Pa, and the scanning range of frequency (
Two sandstone cores were used for core plugging experiments. The cores were dried at 65°C, and then their diameter, length, gas permeability, and porosity were measured by using a SCMS-B2 core multiparameter measurement system. A Hassler core holder was used with 3.5 MPa confining pressure and 1.5 MPa backpressure [
Composition and TDS of injecting water.
Composition | Na+ + K+ | Ca2+ | Mg2+ |
|
Cl− |
|
TDS |
|
|||||||
Content (wt%) | 0.0232 | 0.0099 | 0.0024 | 0.0009 | 0.0321 | 0.0473 | 0.1158 |
Flow chart of the core plugging experiments is shown in Figure
Flow chart of the core plugging experiments.
The structures of ATGPA and AAGPA were confirmed by IR spectra as illustrated in Figure
IR spectra of ATGPA and AAGPA.
The elementary analysis of ATGPA and AAGPA was carried out using a Vario EL-III elemental analyzer. The content of different element in these plugging agents can be obtained by detecting the gases, which are the decomposition products of the samples at high temperature. The test results of ATGPA and AAGPA are shown in Table
The test results of elementary analysis of ATGPA and AAGPA.
Element | AAGPA | ATGPA | ||
---|---|---|---|---|
Theoretical value (%) | Found value (%) | Theoretical value (%) | Found value (%) | |
C | 47.2 | 48.2 | 47.2 | 49.4 |
H | 6.5 | 6.9 | 6.7 | 7.5 |
N | 8.8 | 9.1 | 7.7 | 8.3 |
S | 1.1 | 1.0 | 2.0 | 1.9 |
The microscopic structures of ATGPA and AAGPA were observed through SEM at room temperature. ATGPA and AAGPA solution samples (0.6 wt%) were prepared with distilled water and cooled with liquid nitrogen, and then these samples were evacuated to keep original appearance as far as possible. As shown in Figure
SEM images of ATGPA and AAGPA.
ATGPA and AAGPA solutions were prepared with distilled water. These plugging agents were placed at different temperatures for 72 h. The apparent viscosity of these plugging agents was tested using Brookfield DV-III viscometer at different temperatures. The apparent viscosity versus temperature curves of ATGPA and AAGPA solutions are shown in Figure
Apparent viscosity versus temperature for ATGPA and AAGPA. The apparent viscosity of these plugging agents (0.6 wt%) was measured by Brookfield DV-3 viscometer at 7.34 s−1.
The ability against Na+ of ATGPA was shown in Figure
Salt tolerance ((a) NaCl and (b) CaCl2) of ATGPA and AAGPA (0.6 wt%) at 65°C. The apparent viscosity of these plugging agents was measured by Brookfield DV-3 viscometer at 7.34 s−1.
ATGPA and AAGPA solutions (0.6 wt%) were prepared with distilled water. These plugging agents were placed at 65°C, and the time required for the formation of the gel was 72 h. The viscoelasticity curves of ATGPA and AAGPA were shown in Figure
Viscoelasticity of ATGPA and AAGPA at 65°C. These plugging agents (0.6 wt%) were prepared with distilled water.
As shown in Table
The parameter of core and the results of core plugging experiments.
Plugging agent | Cores | Length (cm) | Diameter (cm) | Porosity (%) |
|
|
|
---|---|---|---|---|---|---|---|
ATGPA | 1# | 6.56 | 2.51 | 24.18 | 822.6 | 22.7 | 97.2 |
AAGPA | 2# | 6.15 | 2.52 | 23.31 | 802.4 | 32.4 | 95.7 |
Core plugging experiments results of ATGPA and AAGPA (0.6 wt%) at 65°C.
ATGPA was prepared using AM, AA, DMDAAC, AMPS, HCHO, C6H6O2, and CH4N2S as raw materials. ATGPA was characterized by IR spectrum, elemental analysis, and scanning electron microscope. The solution properties, such as viscoelasticity, temperature resistance, salt tolerance, and plugging ability of ATGPA, were investigated under different conditions. The results indicated that ATGPA possessed moderate or good viscoelasticity, temperature resistance, salt tolerance, plugging ability, and antiscouring ability as EOR chemical.
The authors declare no possible conflict of interests.
This work was supported by the Major Project of Jidong Oilfield (2013A06-08) and the Science and Technology Project of the exploration and production company (2014B-1113).