A ternary copolymer of 2-acrylamide-2-methyl propane sulfonic acid (AMPS), acrylamide (AM), and allyl alcohol polyoxyethylene ether (APEG) with a side chain polyoxyethylene ether
Water-based drilling muds including bentonite were well-known and widely used in the petroleum industry recently [
To make sure the fluid loss additive has an excellent ability of absorption, the monomer with strong absorption groups, such as amino-group, are introduced [
AMPS and AM were from Chengdu Kelong Chemical Reagent Factory (China). APEG-1000 were of industrial grade from Jiangsu Haian petrochemical factory (China). Potassium persulfate, sodium hydroxide, and sodium bisulfite were analytical grade from Chengdu Kelong Chemical Reagent Factory (China).
APEG (0.006 mol) was added in a three-necked flask, using moderate amount of water to dissolve in a heated water bath. And then AMPS (0.029 mol) and AM (0.084 mol) were added to the mixed solution. The pH was adjusted to 7-8 with NaOH. Finally, 0.2 wt% potassium persulfate and sodium bisulfite were added into the system. The reaction was performed under 60°C with stir speed of 300 rmp. After completion of the reaction, the product was extracted with ethanol, shear granulation, vacuum drying, and grinding to obtain a white powdery polymer fluid loss additive. Chemical structure of SJ-1 was shown in Scheme
Chemical structure of SJ-1.
In laboratory studies, the best parameters of copolymer SJ-1 were obtained: monomer concentration was 15 wt%; molar ratio of
The pellet samples were prepared by pressing the mixture of the SJ-1 and KBr and then measured with FTIR (WQF-520, China) spectrophotometer at range between 4000 and 500 cm−1.
The molecular weight distribution of SJ-1 was measured by GPC (Waters e2695, USA). The polymer was dissolved into distilled water forming the solution with concentration of 2 mg/mL. The measurement was performed at the room temperature (23°C) for 90 min.
Freshwater base mud containing 4 wt% of sodium bentonite and 0.2 wt% of Na2CO3 was prepared by mixing the raw bentonite, Na2CO3, and freshwater at a certain ratio, stirring for 20 min at a high speed of 10000 rpm, and aging for 24 h at room temperature. Salt-water base mud was prepared by adding different concentration of NaCl into the above freshwater base mud and then submitted to a prehydration period of 24 h. Calcium-water base mud was prepared by adding different concentration of CaCl2 into the above freshwater base mud and then submitted to a prehydration period of 24 h. Polymer based mud was prepared by adding different concentration of SJ-1 into the freshwater base mud, salt-water base mud, and calcium-water base mud, respectively, and then submitted to a prehydration period of 24 h.
Drilling fluid filtrations were measured according to American Petroleum Institute (API) specifications and Chinese SY/T5621-93. The API filtrate volume (FLAPI) of the mud was determined with a medium-pressure filtration apparatus (ZNS-2 type, China).
Apparent viscosity (AV), plastic viscosity (PV), and yield point (YP) were measured by rotational viscometer (ZNN-D6, China) at different temperatures.
Aging experiments of bentonite-polymer fluids were carried out in a frequency conversion rolling oven (BRGL-7 type, China) at a series of temperatures for 16 h.
The filter cake of the sample was tested by SEM (JSM-7500F, Japan) analysis and the filtrate of the sample was tested by zeta electric potential (Zeta PALS/90plus, Brookhaven, America) at different conditions.
The chemical structure of SJ-1 was analyzed by FTIR after being purified; the results were shown in Figure
FTIR spectrum of polymerization product.
A strong absorption peak of 3330.64 cm−1 was assigned to the stretching vibration of N–H. The absorption peaks observed at 2933.20 cm−1 and 2863.77 cm−1 were due to the stretching vibration of –CH3 and –CH2, respectively. The absorption peak of 1673.91 cm−1 was attributed to the stretching peak of C=O. The absorption peak of 1544.70 cm−1 was due to the stretching vibration of C–N, while 1201.43 cm−1 was attributed to C–O–C. Moreover, absorption peaks of 1112.72 cm−1 and 1041.37 cm−1 were according to the bending vibration of
The molecular weight and its distribution of SJ-1 which was synthesized under the best optimum synthesis condition mentioned in Section
Different concentration of SJ-1 was added to the freshwater base mud. The rheological and API fluid loss properties have been measured by rotational viscometer and medium-pressure filtration apparatus, respectively. The results were shown in Table
Relationship between SJ-1 concentration and fluid loss.
SJ-1 concentration |
AV |
PV |
YP |
API filter loss |
---|---|---|---|---|
0.0 | 12.5 | 7.0 | 5.62 | 23.0 |
0.1 | 16.0 | 10.0 | 6.13 | 11.8 |
0.3 | 19.5 | 13.0 | 6.64 | 11.2 |
0.6 | 23.5 | 16.0 | 7.67 | 10.4 |
0.9 | 30.0 | 21.0 | 9.20 | 9.4 |
1.2 | 37.0 | 26.0 | 11.24 | 9.2 |
1.5 | 44.0 | 31.0 | 13.29 | 9.2 |
1.8 | 52.5 | 36.0 | 16.86 | 9.1 |
According to Table
1.2 wt% SJ-1 was added to the freshwater base mud, then, rolling in frequency conversion rolling oven for 16 h at different levels of temperature. The rheological and API fluid loss have been measured by rotational viscometer and medium-pressure filtration apparatus, respectively. The results were shown in Table
Fluid loss of drilling fluid changed with aging temperature.
Experimental conditions | AV |
PV |
YP |
API filter loss |
---|---|---|---|---|
120°C, 16 h | 43.5 | 34.5 | 9.20 | 10.6 |
140°C, 16 h | 38.5 | 32.0 | 6.64 | 10.6 |
160°C, 16 h | 20.8 | 17.0 | 3.83 | 11.5 |
180°C, 16 h | 13.0 | 9.5 | 3.58 | 12.1 |
200°C, 16 h | 13.0 | 11.0 | 2.04 | 12.5 |
220°C, 16 h | 12.5 | 11.0 | 1.53 | 13.0 |
The value of API fluid loss of drilling fluid raised with the increase of temperature, when the concentration of SJ-1 was equal to 1.2 wt%. The API fluid loss of drilling fluid was still below 13 mL even at 220°C showing its property of temperature resistant. Three reasons account for this phenomenon. Firstly, the main chain of the polymeric molecule is connected by C–C, which is stable at high temperatures. Secondly, the
With the increase of temperature, the rheological property of drilling fluid which reflected on apparent viscosity, plastic viscosity, and yield value decreased. Some of the SJ-1 was degraded at high temperature, which can lead to breaking up the network structure to a certain extent. But this negative influence held within limits and control. The little change on the performance of the drilling fluid was less affected.
1.2 wt% SJ-1 and different concentration of NaCl were added to the freshwater base mud and, then, aged 16 h at 120°C. The rheological and API fluid loss have been measured by rotational viscometer and medium-pressure filtration apparatus, respectively. The results were shown in Table
Performance evaluation of salt resistance of drilling fluid at high temperature.
Experimental conditions | NaCl concentration |
AV |
PV |
YP |
API filter loss |
---|---|---|---|---|---|
Aging temperature 120°C, aging time 16 h | 0.0 | 32.0 | 27.5 | 4.60 | 10.6 |
2.0 | 20.0 | 17.5 | 2.56 | 16.0 | |
5.0 | 17.5 | 15.0 | 2.56 | 13.0 | |
10.0 | 18.0 | 16.0 | 2.04 | 12.6 | |
15.0 | 17.0 | 15.0 | 2.04 | 12.6 | |
20.0 | 17.0 | 15.0 | 2.04 | 12.6 | |
25.0 | 17.5 | 15.0 | 2.56 | 10.4 | |
30.0 | 19.5 | 18.0 | 1.53 | 7.5 |
Table
Five reasons account for this phenomenon. Firstly, when the NaCl was added to the freshwater base mud, the value of the zeta electric potential of the clay particles would decrease and the hydration shell would be reduced, which would lead to generating the flocculated structure in the freshwater base mud. So, the API filter loss increases. Secondly, when the NaCl was added to the freshwater base mud, the adsorption of the fluid loss additive on the surface of the clay particles would increase, which would lead to the increase of the zeta electric potential of the clay particles and the thickening of hydration shell. So, the API filter loss would decrease. When the concentration of the NaCl was 2 wt%, the effect of the NaCl on the clay particles played a leading role, and the API filter loss was increased. Meanwhile, with the increase of the concentration of the NaCl, the effect of the NaCl on the fluid loss additive was increased and the API filter loss was decreased. When the concentration of the NaCl was 25 wt%, the effect of the NaCl on the fluid loss additive played a leading role, so the API filter loss was lower than that without the NaCl. Thirdly, the SJ-1 with good temperature resistant remains at a comparatively high level. And it is beneficial for adsorbing clay particles and free water to form aggregate, which forms a thin and dense mud cake on the wall. The appearance of mud cake effectively reduces the filtrate loss. Lastly, because of the adding of fluid loss additive SJ-1, the hydrophilic radical of this treating chemical mainly includes sulfonic acid and polyoxyethylene side chain which enjoy a favorable hydrophilicity and good solubility in a saline environment. It can bring enough hydrated film to clay and ensure the drilling fluid system has good salt tolerance.
1.2 wt% SJ-1 and different concentration of CaCl2 were added to the freshwater base mud and, then, aged 16 h at 120°C. The rheological and filtration properties have been measured by rotational viscometer and medium-pressure filtration apparatus, respectively. The results have been shown in Table
Performance evaluation of calcium resistance of drilling fluid under high temperature.
Experimental conditions | CaCl2 concentration |
AV |
PV |
YP |
API filter loss |
---|---|---|---|---|---|
Aging temperature 120°C, aging time 16 h | 0.0 | 32.0 | 27.5 | 4.60 | 10.6 |
2.0 | 9.5 | 9.0 | 0.51 | 26.0 | |
4.0 | 10.0 | 9.0 | 1.02 | 19.0 | |
6.0 | 9.0 | 8.0 | 1.02 | 17.0 | |
8.0 | 8.5 | 8.0 | 0.51 | 12.6 | |
10.0 | 8.5 | 8.0 | 0.51 | 12.0 |
Table
Two reasons account for this phenomenon. Firstly, the
1.2 wt% SJ-1 was added to the freshwater base mud in different temperatures. The zeta electric potential and API filter loss have been measured by zeta potential analyzer and medium-pressure filtration apparatus, respectively. The results were shown in Figure
The impact of zeta electric potential and API filter loss on mud system in different temperatures.
Figure
1.2 wt% SJ-1 and different concentration of NaCl were added to the freshwater base mud at 25°C. The zeta electric potential and API filter loss have been measured by zeta potential analyzer and medium-pressure filtration apparatus, respectively. The results were shown in Figure
The impact of zeta electric potential and API filter loss on mud system in different salt contents.
Figure
In order to explore the microstructure of the filter cake formation and the filtration mechanism research, the formation of the filter cake was observed by type JSM7500F SEM.
Freshwater base mud and polymers of 1.2 wt% density are added into drilling fluid to test the API filter loss in normal temperature. After drying, the appearance of filter cake can be seen through SEM in Figure
SEM photos of (a) API filter cake formed by base mud and (b) API filter cake modified with SJ-1 (both of aging temperature 120°C).
Figure
Figure
Freshwater base mud polymers of 1.2% density are added into freshwater base mud, which is then stirred up speedily for 10 minutes. Next, NaCl is mixed into it and then stirred up for 10 minutes. API filtrate loss is tested and Figure
SEM photos of (a) API filter cake formed by base mud + SJ-1 + 30 wt% NaCl and (b) API filter cake formed by base mud + SJ-1 + 30 wt% NaCl after the aging process of 30 min.
Figure
Figure
With FTIR analysis, the composition of the synthetic polymer SJ-1 was consistent to the designed structure. The weight average molecular weight of SJ-1 was
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors thank the Engineering Research Center of Oilfield Chemistry, Ministry of Educational Key for experiment support.