Method for Determination of Gel Strength of Cellulose Ether

To measure the strength of cellulose ether gel, the article introduces that although cellulose ether gel and jelly-like profile control agents have different gelation mechanisms, they can use the similarity in appearance, that is, they cannot flow after gelation In the semi-solid state, the commonly used observation method, rotation method and vacuum breakthrough method for evaluating the strength of jelly are used to evaluate the strength of cellulose ether gel, and a new positive pressure breakthrough method is added. The applicability of these four methods to the determination of cellulose ether gel strength was analyzed through experiments. The results show that the observation method can only qualitatively evaluate the strength of cellulose ether, the rotation method is not suitable for evaluating the strength of cellulose ether, the vacuum method can only evaluate the strength of cellulose ether with a strength below 0.1 MPa, and the newly added positive pressure This method can quantitatively evaluate the strength of cellulose ether gel.

Key words: jelly; cellulose ether gel; strength; method

0.Preface

Polymer jelly-based profile control agents are most widely used in oilfield water plugging and profile control. However, in recent years, the temperature-sensitive and thermally reversible gel cellulose ether plugging and control system has gradually become a research hotspot for water plugging and profile control in heavy oil reservoirs. . The gel strength of cellulose ether is one of the most important indicators for formation plugging, but there is no uniform standard for its strength test method. Commonly used methods to evaluate jelly strength, such as observation method – a direct and economical method for testing jelly strength, use the jelly strength code table to judge the level of gel strength to be measured; rotation method – commonly used instruments are Brookfield viscometer and rheometer, the temperature of the Brookfield viscometer test sample is limited within 90 °C; breakthrough vacuum method – when the air is used to break through the gel, the maximum reading of the pressure gauge represents the strength of the gel. The gelling mechanism of jelly is to add a cross-linking agent to the polymer solution. The cross-linking agent and the polymer chain are connected by chemical bonds to form a spatial network structure, and the liquid phase is wrapped in it, so that the entire system loses fluidity, and then transforms For jelly, this process is not reversible and is a chemical change. The gel mechanism of cellulose ether is that at low temperature, the macromolecules of cellulose ether are surrounded by small molecules of water through hydrogen bonds to form an aqueous solution. As the temperature of the solution rises, the hydrogen bonds are destroyed, and the large molecules of cellulose ether The state in which molecules come together through the interaction of hydrophobic groups to form a gel is a physical change. Although the gelation mechanism of the two is different, the appearance has a similar state, that is, an immobile semi-solid state is formed in three-dimensional space. Whether the evaluation method of jelly strength is suitable for evaluating the strength of cellulose ether gel needs exploration and experimental verification. In this paper, three traditional methods are used to evaluate the strength of cellulose ether gels: observation method, rotation method and breakthrough vacuum method, and a positive pressure breakthrough method is formed on this basis.

1. Experimental part

1.1 Main experimental equipment and instruments

Electric constant temperature water bath, DZKW-S-6, Beijing Yongguangming Medical Instrument Co., Ltd.; high temperature and high pressure rheometer, MARS-III, Germany HAAKE company; circulating water multi-purpose vacuum pump, SHB-III, Gongyi Red Instrument Equipment Co., Ltd.; sensor, DP1701-EL1D1G, Baoji Best Control Technology Co., Ltd.; pressure acquisition system, Shandong Zhongshi Dashiyi Technology Co., Ltd.; colorimetric tube, 100 mL, Tianjin Tianke Glass Instrument Manufacturing Co., Ltd.; high temperature resistant glass bottle , 120 mL, Schott Glass Works, Germany; high-purity nitrogen, Tianjin Gaochuang Baolan Gas Co., Ltd.

1.2 Experimental samples and preparation

Hydroxypropyl methylcellulose ether, 60RT400, Taian Ruitai Cellulose Co., Ltd.; dissolve 2g, 3g and 4g of hydroxypropylmethylcellulose ether in 50 mL hot water at 80 ℃, stir well and add 25 ℃ of 50 mL cold water, the samples were completely dissolved to form cellulose ether solutions with concentrations of 0.02g/mL, 0.03g/mL and 0.04g/mL respectively.

1.3 Experimental method of cellulose ether gel strength test

(1) Tested by observation method. The capacity of the wide-mouth high-temperature-resistant glass bottles used in the experiment is 120mL, and the volume of the cellulose ether solution is 50mL. Put the prepared cellulose ether solutions with concentrations of 0.02g/mL, 0.03g/mL and 0.04g/mL in a high temperature resistant glass bottle, invert it at different temperatures, and compare the above three different concentrations according to the gel strength code The gelling strength of the cellulose ether aqueous solution was tested.

(2) Tested by the rotation method. The test instrument used in this experiment is a high-temperature and high-pressure rheometer. The cellulose ether aqueous solution with a concentration of 2% is selected and placed in a drum for testing. The heating rate is 5 ℃/10 min, the shear rate is 50 s-1, and the test time is 1 min. , The heating range is 40～110 ℃.

(3) Tested by breakthrough vacuum method. Connect the colorimetric tubes containing the gel, turn on the vacuum pump, and read the maximum reading of the pressure gauge when the air breaks through the gel. Each sample is operated three times to obtain the average value.

(4) Test by positive pressure method. According to the principle of breakthrough vacuum degree method, we have improved this experimental method and adopted the method of positive pressure breakthrough. Connect the colorimetric tubes containing the gel, and use a pressure acquisition system to test the strength of the cellulose ether gel. The amount of gel used in the experiment is 50mL, the capacity of the colorimetric tube is 100mL, the inner diameter is 3cm, the inner diameter of the circular tube inserted into the gel is 1cm, and the insertion depth is 3cm. Slowly turn on the switch of the nitrogen cylinder. When the displayed pressure data drops suddenly and sharply, take the highest point as the strength value required to break through the gel. Each sample is operated three times to get the average value.

2. Experimental results and discussion

2.1 The applicability of the observation method to test the gel strength of cellulose ether

As a result of evaluating the gel strength of cellulose ether by observation, taking the cellulose ether solution with a concentration of 0.02 g/mL as an example, it can be known that the strength level is A when the temperature is 65 °C, and the strength begins to increase as the temperature increases , when the temperature reaches 75 ℃, it presents a gel state, the strength grade changes from B to D, and when the temperature rises to 120 ℃, the strength grade becomes F. It can be seen that the evaluation result of this evaluation method only shows the strength level of the gel, but cannot use the data to express the specific strength of the gel, that is, it is qualitative but not quantitative. The advantage of this method is that the operation is simple and intuitive, and the gel with the required strength can be screened cheaply by this method.

2.2 Applicability of the rotation method to test the gel strength of cellulose ether

When the solution is heated to 80 °C, the viscosity of the solution is 61 mPa·s, then the viscosity increases rapidly, and reaches a maximum value of 46 790 mPa·s at 100 °C, and then the strength decreases. This is inconsistent with the previously observed phenomenon that the viscosity of hydroxypropyl methylcellulose ether aqueous solution begins to increase at 65 °C, and gels appear at around 75 °C and the strength continues to increase. The reason for this phenomenon is that the gel is broken due to the rotation of the rotor when testing the gel strength of cellulose ether, resulting in incorrect data of gel strength at subsequent temperatures. Therefore, this method is not suitable for evaluating the strength of cellulose ether gels.

2.3 Applicability of breakthrough vacuum method to test the gel strength of cellulose ether

The experimental results of cellulose ether gel strength were evaluated by the breakthrough vacuum method. This method does not involve the rotation of the rotor, so the problem of colloidal shearing and breaking caused by the rotation of the rotor can be avoided. From the above experimental results, it can be seen that this method can quantitatively test the strength of the gel. When the temperature is 100 °C, the strength of the cellulose ether gel with a concentration of 4% is greater than 0.1 MPa (the maximum vacuum degree), and the strength cannot be measured greater than 0.1 MPa. The strength of the gel, that is, the upper limit of the gel strength tested by this method is 0.1 MPa. In this experiment, the strength of cellulose ether gel is greater than 0.1 MPa, so this method is not suitable for evaluating the strength of cellulose ether gel.

2.4 The applicability of the positive pressure method to test the gel strength of cellulose ether

The positive pressure method was used to evaluate the experimental results of the cellulose ether gel strength. It can be seen that this method can quantitatively test the gel with a strength above 0.1 MPa. The data acquisition system used in the experiment makes the experimental results more accurate than the artificial reading data in the vacuum degree method.

3. Conclusion

The gel strength of cellulose ether showed an overall increasing trend with the increase of temperature. The rotation method and the breakthrough vacuum method are not suitable for determining the strength of cellulose ether gel. The observation method can only qualitatively measure the strength of cellulose ether gel, and the newly added positive pressure method can quantitatively test the strength of cellulose ether gel.