INHIBITIVE EFFECT OF POTASSIUM METHYLSILICONATE ON HYDRATION SWELLING OF MONTMORILLONITE
© 2014 г. G. Jiang",b, Y. Xuan", b, Y. Li", b, J. Wang", b
"State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum (Beijing), Changping District,
Beijing 102249, China
bMOE Key Laboratory of Petroleum Engineering, China University of Petroleum (Beijing), Changping District,
Beijing 102249, China e-mail: firstname.lastname@example.org Поступила в редакцию 17.09.2013 г.
Herein we report on a study on the inhibition effect of potassium methylsiliconate on hydration swelling of montmorillonite. The results of linear swelling tests showed that potassium methylsiliconate exhibits a high performance as an effective shale inhibitor in drilling fluids. The inhibition mechanism was investigated by means of a variety of methods including Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and zeta potential measurements. The high degree of inhibition is a result of the synergy of action of potassium cations and methylsiliconate anions. Methylsiliconate anions form a hydro-phobic shell around each montmorillonite particle through the adsorption on the edge sites, thus inhibiting the penetration of water into the interlayer. The potassium ions promote the formation of a less hydratable structure of montmorillonite through cation-exchange interaction.
The problem ofwellbore stability in water-sensitive shale formation has frustrated oil-field engineers from the beginning of the oil and gas drilling. When water-based drilling uids encounter clay-rich shale formation, the resulting swelling of hydrated clay can cause instability of wells. This instability manifests itself by building up of solids in the drilling fluids, tightening or enlargement of drill pipes, which significantly increases construction costs, and in the worst case, can result in total abandonment of the well . During the past 50 years, a variety of drilling fluid additives known as 'shale inhibitors' or 'clay stabilizers' have been developed and utilized to prevent clay from hydration swelling. Along with the inorganic salts such as KCl , the shale inhibitors involves organic polymers or surfactants , which present functional groups reducing swelling through the interactions with clays.
A chemical structure of typical alkali metal organic siliconates such as potassium methylsiliconate (PMS) and sodium methylsiliconate (SMS) is shown below.
(M represents alkali metal such as K, Na, Li).
Friedel and Ladenberg  first obtained these alkali salts in their studies on alkyl silanetriols in 1870; the
first study on their properties was performed by Meads and Kipping  in 1914. According to , alkali metal organic siliconates in dilute aqueous solutions predominantly exist in a monomeric form [CH3Si(OH)2O]-M+ as shown above. Concentrated solution of alkali metal organic siliconate probably contains dimers ([CH3SiOH(OM)]2O) and larger polysiloxanes. They are easily formed since silicon does not form double bonds with oxygen.
After have been used as water repellent in 1950's, alkali metal organic siliconates have been applied as additive in drilling fluids. In 1970's, SMS has been first introduced in Soviet Union as a viscosity reducer to stabilize the properties of water-based drilling fluids . Since 2000's, China has been widely used SMS, especially in Daqing [8, 9], Henan , Huabei and Liaohe oilfields .
To our knowledge, the usage of alkaline metal organic siliconates in drilling fluids has been mostly limited by viscosity reducing additives. We founded, however, that PMS could act as a high-performance shale inhibitor due to the unique synergistic inhibition effect of potassium ions and methylsiliconate anions on clay swelling in water. In this work, we report a comprehensive investigation of the inhibitive effect of PMS on hydration swelling of montmorillonite (2 : 1 type smectite clay). The inhibition performance of PMS was evaluated via clay linear swelling test and the mecha-
nism of this inhibition was corroborated by using a variety of characterization methods.
2. EXPERIMENTAL 2.1. Reagents and Materials
Potassium methylsiliconate (PMS) and sodium methylsiliconate (SMS) were obtained as 30% aqueous solutions from Xinghua Silicone Ltd., China. Montmorillonite (MMT), with cation exchange capacity of 81.3 mmol/100 g was purchased from Xinjiang Xiazijie Bentonite Inc., China. The raw samples were characterized by X-ray diffraction method and FT-IR spectroscopy. Quartz, potash feldspar, anorthose, and gibbsite were the most abundant impurities accompanying pristine clay. The elemental composition of the raw sample was determined by ICP-AES analysis: Si, 58.7 wt %; Al, 20.2 wt %; Na, 4.6 wt %; Fe, 8.1 wt %; Mg, 3.6 wt %; K, 3.1 wt %; Ca, 0.8 wt %; Ti 0.9 wt %. Other reagents were obtained from local chemical companies. All materials were used without further purification.
2.2. Clay Linear Swelling Test
The linear swelling tests of MMT in inhibitor solutions were performed using CPZ-2 dual channel shale expansion instrument (Qingdao, China). 5 g MMT was placed inside the test container equipped with a hydraulic press operating under 10 MPa for 5 min. Then the container was fitted to the shale expansion instrument and the inhibitor solution was poured into it. Once the MMT contacted the inhibitor solution, the linear swelling of MMT in vertical direction was started to record.
2.3. Inhibition Characterization
2.3.1. Sample preparation. PMS aqueous solutions with different PMS concentrations (0, 0.5, 1, 3, 5, 12, and 20 wt %) were prepared. Then 9 g MMT was dispersed in 300 g of PMS solutions to make MMT/PMS aqueous suspensions with 3 wt % of MMT The suspensions were stirred vigorously at 4000 rpm for 30 min and then shaken in a thermostated chamber at 25°C for 16 h to equilibrate.
The MMT/PMS suspensions were centrifuged for 15 min at 11000 rpm, and then the supernatant was decanted. The wet MMT with adsorbed PMS was washed with deionized water for 5—6 times to remove the remaining PMS from the surface until the pH value of the decanted water reached 7. Then, the wet MMT/PMS mixture was divided into portions. One portion was sealed, stored at room temperature and then used for the XRD analysis. Another portion was dried in the oven at 100°C overnight, stored being exposed to air for the investigations by using XRD, FT-IR, TEM, and water contact angle methods.
2.3.2. X-ray diffraction (XRD). XRD patterns of the MMT/PMS complex were analyzed by D8 Advance Diffractometer (Bruker, Germany) operating at a voltage of 40 kV and a current of40 mA, and employing CuZ"a filtered radiation (X = 1.5406 nm). Diffraction patterns were collected by sample scanning in the 29-angle mode between 2° and 15°.
2.3.3. Fourier transform infrared (FT-IR) spectroscopy. FT-IR spectra of MMT/PMS were recorded by Magna-IR 560 spectrophotometer (Nicolet, USA) within the wavelength range 4000—400 cm-1 and the resolution of 4 cm-1.
2.3.4. Transmission electron microscopy (TEM).
TEM analysis was performed by a JEM-2100 transmission electron microscope (JEOL, Japan). The samples were prepared by dispersing the MMT and MMT/PMS complex in deionized water to form 0.1 wt % aqueous suspensions, which were further ultrasonicated for 30 min. The as-prepared suspensions were dipped onto the amorphous carbon-coated copper TEM grids and dried under an infrared lamp.
2.3.5. Zeta potential measurements. Zeta potential values of the MMT colloidal particles in PMS aqueous solutions were measured using Zetasizer Nano ZS instrument (Malvern, U.K). The series of samples was prepared by dispersing 0.1 wt % MMT in PMS solutions with different concentration to form MMT/PMS suspensions, which were ultrasonicated for 30 min before measurements.
2.3.6. Water contact angle measurements. For this test, the self-supporting MMT films was prepared according to the method of Wu . The dried MMT/PMS complex was dispersed in water again to form 1 wt % suspensions, which were ultrasonicated for 30 min. Then the aliquots of 10 mL suspensions were withdrawn with pipettes and distributed evenly onto clean glass slides (2 cm x 5 cm), which were placed strictly horizontal. The glass slides were left air-dried for at least one night until the smooth and thin MMT films formed, and then the films coated on the slides were peeled off for the test. Contact angles of water droplets on the MMT films were determined with the static sessile drop method using JC2000D contact angle measuring instrument equipped with a digital camera (Powereach, China).
2.4. Yield Point Measurements
The yield points of the MMT/PMS suspensions were calculated from measurements for 600 and 300 rpm (0600 and 0300), which were performed with ZNN-D6L viscometer (Qingdao, China). The calculations were done using the following formula from API Recommended Practice of Standard procedure for field testing drilling fluids : Yield point = (0300 - 0600)/2 (Pa).
Linear swelling, mm - i • 1 '2 5 r * 3 4 5 6 * 7 -8 4 b 9 10
0 2 4 6
8 10 12 14 16 Time, h
Linear swelling, mm 2.5
2.0 1.5 1.0 0.5
0 2 4 6
8 10 12 14 16 Time, h
Fig. 1. Linear swelling curves of MMT in PMS solutions with different concentrations: 0 (1), 0.5 (2), 1.0 (3), 2.0(4), 3.0 (5), 5.0 (6), 7.0 (7), 9.0 (8), 12 (9), and 20 wt % (10).
Fig. 2. Linear swelling curves of MMT in PMS, SMS and KCl solutions with different compositions: 5 wt % of KCl (1), 10 wt % of KCl (2), 5 wt % of SMS (3), and 5 wt % of PMS (4).
3. RESULTS AND DISCUSSION 3.1. Inhibition Degree Evaluation
The linear swelling curves of MMT immersed in deionized water and PMS solutions with different concentrations, respectively, are presented in Fig. 1. For all samples, the swelling curves show a clos
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