OBTAINING A WATER-SOLUBLE INHIBITOR BASED ON EPICHLOROHYDRIN

ABSTRACT

In this paper, a series of poly ammonium shale inhibitors were prepared from diethylamine, epichlorohydrin, and melamine and their inhibition to shale were evaluated by bentonite linear expansion test, anti-swelling experi- ments, and mud ball experiments. Additionally, other properties of drilling fluid treated by poly ammonium were evaluated. Anti-swelling results showed that anti-swelling rate of DEM-8 reaches up to 97.8% when its concentration reaches to 0.8%.

АННОТАЦИЯ

В этой статье из диэтиламина, эпихлоргидрина и меламина была приготовлена серия ингибиторов полиаммонийного сланца, и их ингибирование в сланце оценивалось с помощью теста на линейное расширение бентонита, экспериментов по борьбе с набуханием и экспериментов с грязевыми шариками. Кроме того, были оценены другие свойства бурового раствора, обработанного полиаммонием. Результаты по борьбе с набуханием показали, что скорость борьбы с набуханием DEM-8 достигает 97,8%, когда его концентрация достигает 0,8%.

Keywords: Melamine, Cross-linked polycation, Inhibitor, Clay, Swelling

Ключевые слова: Меламин, Сшитый поликатион, Ингибитор, Глина, Набухание.

Introduction

During the synthesis, reactions of organic substances to N storage in EXG were carried out at a temperature of 60 degrees. The yield of the produced inhibitor was based on temperature and EXG ratio. During the drilling, borehole stability problems such as bit balling, disinte- gration of cuttings, borehole wash-out and stuck pipe mostly occur in shale formations due to hydration and swelling of water-sensitive shales [1–3]. When water-sen- sitive shales (high montmorillonite content) are exposed to water-based drilling fluids, depending on the chemical characteristics of the shale or drilling fluid, this can result in a rapid swelling or dispersion of the shale [4]. Conse- quently, a high level of shale inhibitor has been utilized widely in drilling operations [4,5], but same additives may be unfavorable due to the environmental protec- tion requirements, which limits their usage or restricts their discharge [6]. Recently, organic amine compounds with high performance as shale inhibitor have drawn much attention of the researchers. This kind of inhibitor has obtained wide application around the world with great success because of its excellent inhibition, lubrica- tion and stable rheological property and so on [7,8]. As the polyamine salt has higher inhibitory and anti-balling abilities, and it is not poisonous and hazardous, the use of this drilling fluid could decrease the cost of oil con- taminated drilled cuttings disposal [9,10]. Currently, polyamine compound can be used in various kinds of water-based oilfield working fluid and has superior com- patibility with traditional additives, and it can meet envi- ronmental protection requirements, due to its oxidation product is harmful for animals [11]. In the current work, the inhibitive properties of a melamine cross-linking agent are evaluated through experiments including lin- ear expansion, mud balls, particle distribution measure- ments, thermogravimetric analysis and scanning electron microscopy. Furthermore, the inhibitive mechanism is discussed in detail.

In this paper, a new shale inhibitor with high stability has been synthesized from diethylamine, epichlorohy- drin, and melamine (EXG) and their inhibitions to shale have been evaluated in detail. Both the effect of the poly- mer to the properties of drilling fluid and the proposed inhibition mechanism have also been disused.

Synthesis of EXG

Diethylamine and epichlorohydrin with the mole ratio of 1:1 as well as melamine used as the cross-linking agent were employed to synthesize shale inhibitor under 60 °C [12,13], as shown in Scheme 1, and the final product, melamine cross-linking agent, was abbreviated as EXG in the following text.

Swelling inhibition and mud ball immersing test

The hydration swelling of bentonite is tested by a NP-01 shale expansion instrument (Haitongda, Co., Ltd., Qing- dao, China), in accordance with Chinese petroleum and natural gas industry standards SY/T6335-1997 and SY/ T5971-1994. Mud ball immersing test is as follows: ben- tonite (10 g) was used to make a mud ball, and the mud ball was immersed in 80 mL tap water or other aque- ous solutions for 24 h [14,15]. Then the details of the immersed mud balls were evaluated, including a check whether there are cracks or dilapidation on the surface.

Figure. Particle distribution test

Table 1.

Table of values

4% (m/m) bentonite dispersion was prepared and pre- hydrated for 24 h. Inhibitors with certain concentrations were added into the dispersion and stirred for 20 min, after aged for 24 h, and then the size distribution of the particles was measured by LS-13320 laser particle size analyzer based on the light scattering principle (Beckman Coulter, Inc., USA) using equipment operating procedure under the pump speed of 40%.

TGA and SEM

After the bentonite was dispersed in inhibitor solutions for 24 h, the bentonite was separated and dried at 105 °C for thermogravimetric analysis (TGA) and scanning elec- tron microscopy (SEM). TGA experiment was performed on a TGA/DSC 1/1600 thermal analysis machine (MET- TLER TOLEDO, Inc., Switzerland) at a ramp of 20 °C/ min from room temperature to 825 °C under nitrogen flow. The surface morphology of the sample under study in the absence and presence of inhibitors was investigat- ing using a Digital Microscope Imaging scanning electron microscope (model SU6600, serial No. HI-2102-0003) at accelerating voltage of 40.0 kV. Samples were attached on the top of an aluminum stopper by means of carbon con- ductive adhesive tape. All micrographs of the specimen were taken at 5009 times magnification.

Table 2.

The conditions of synthesis polycation inhibitors

The influence of the amount of cross-linking agent and synthesis temperature on the performance of the inhibi- tor was investigated by the clay-swelling rate, and the results were shown in Table 1. Obviously, when the con- centration of cross-linking agent is 0.1%, the anti-swelling rate of clay is the lowest. So it is advisable to choose 0.1% cross-linking agent in the following experiment. Further- more, under different temperature, 0.1% cross-linking agent was investigated on the effect of clay-swelling rate. The  results  show  that  the  product  synthesized  under 90 °C, DEM-8, displays most potent inhibition with the lowest clay-swelling rate of 53.75% within 90 min. The possible reason may attribute to the proper ratio of cross- linking agent helping to form a cross-linked net work, and the low ratio and low temperature is not efficient to cross link the polyammonium while the high ratio and high temperature may lead the polyammonium to cross link and assemble into a tight agglomeration. So DEM-8 was selected for the further study in detail.

Inhibitive mechanism analysis

Figure 4 shows the particle size distribution of the ben- tonite dispersions when these are treated in different ways. Compared to the un-hydrated control sample, the average size of hydrated bentonite particles increased from 16.25 to 32.94 μm. This is different when DEM was added before the hydration of bentonite. When DEP was added before the virgin bentonite was dispersed into water, after 16 h, the average size of clays changed slightly, and it is just a litter larger than that of virgin bentonite, from 16.25 to 25.00 μm, which indicates that DEM-8 can inhibit the bentonite swelling effectively.

Conclusions

In this work, cross-linked polycation inhibitor (EXG) was synthesized with epichlorohydrin, diethylamine and melamine. The inhibitive properties of EXG to clays swelling were investigated linear expansion test, mud ball immersing test etc. The results indicate that, compared with a blank solution, EXG shows stronger inhibition to hydration and swelling of bentonite. The anti-swelling rate of 0.5% EXG reaches up to 85%. The hydration expansion degree of the mud ball in the EXG solution was significantly weaker than that of blank. The inhibi- tion mechanism of EXG to shales may be due to the ion exchange, hydrogen bonding, anchoring effect and modification of surface affinity toward water. This was found by thermogravimetric analysis, ion exchange test and scanning electron microscope analysis.

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