New Magnetite Nanoparticles Allow Smart Drilling Fluids With Superior Properties

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This work focuses on using custom-made (CM) magnetite (Fe3O4) nanoparticles (NPs) to improve the properties of bentonite-based fluids. The microstructure qualities and modes of interaction have been identified, helping to optimize the rheological and fluid-loss properties of these drilling fluids. The better performance of the CM Fe3O4 NPs can be attributed to their extremely small size, which leads to stability in suspensions and effective linking with the bentonite particles, thus allowing the formation of a rigid microstructure network.

Introduction

The effects of adding iron oxide NPs on the rheological and filtration properties of aqueous bentonite suspensions have been studied by several researchers. The results showed that the addition of iron oxide NPs at low concentrations significantly improves drilling-fluid-filtration characteristics and maintains optimal rheological properties compared with the base fluid (BF). Moreover, the creation of a thin and impermeable filter cake and its effectiveness depend on the NP concentration. 

The main objective of the research detailed in the complete paper is to study the performance of aqueous bentonite suspensions (7 wt%) containing CM Fe3O4 NPs at 0.5 wt% concentration in terms of their rheological and fluid-loss properties. Rheological analysis for the fluid samples with and without dynamic thermal aging identifies the degree of thixotropy of the developed fluids. The study outlines the effect of temperature on the yield stress, presents an integrated approach to characterizing raw materials by use of various methods, and explores techniques used to examine the produced-filter-cake properties and the size of NPs. Combination of such an integrated analytical approach regarding the evaluation of the properties of such suspensions together with the development and use of CM Fe3O4 NPs with made-to-order properties can lead to the development of multifunctional smart drilling fluids. The results of the experiment are discussed in detail in the complete paper.

Experimental

Materials and Sample Preparation. The bentonite, in powder form, had a relative density of 2.6 g/cm3 and was supplied without any polymer additives. It was tan in color with a pH range of 8–10. X-ray-diffraction (XRD) and X-ray-fluorescence analyses confirmed that the bentonite was sodium-based, with small quantities of illite and quartz. The bentonite had a mean particle size of 36 μm.

The CM Fe3O4 NPs were synthesized by a chemical-coprecipitation method, including reaction of ferrous and ferric salts with NaOH. The synthesized NPs were characterized with XRD and a high-resolution transmission electron microscope (TEM). The XRD pattern of the CM Fe3O4 NPs showed peaks corresponding to pure crystallites of magnetite with no impurities, while the TEM image revealed the spherical shape of the NPs, with a mean diameter of 6–8 nm. Their surface area was 100–260 m2/g. 

Bentonite (45.16 g) was added to 600 mL of deionized water to give 7% mass concentration and was mixed at high speed for 20 minutes. The suspension was left for 16 hours to hydrate at room temperature in plastic containers. After hydration of bentonite, the CM Fe3O4 NPs were added slowly in the water/bentonite suspension while agitating at high speed for 20 minutes. The samples were left in the plastic containers until the rheological or fluid-loss measurements were performed. The pH of all samples ranged from 7.8 to 8.2.

Temperature was controlled using a circulating water bath allowing the water to circulate around the viscometer cup, keeping water-circulating temperature constant, with an accuracy of ±0.5°C. Once the desired temperature was achieved, the sample to be measured was stirred for 5 minutes. The sample was then placed into the measuring cup, and the measurements were conducted immediately. An initial step of agitation at 600 rev/min for 200 seconds was implemented before recording any values. This step was added in order to achieve a temperature equilibration of the sample. The temperature of the experiments was monitored by a temperature sensor embedded into the viscometer cup. 

The effect of dynamic thermal aging on the rheological and filtration properties of the prepared samples was also investigated in order to examine the ability of the developed fluids to maintain their properties under such extreme conditions. The samples were placed in an aging cell and pressurized at 300 psi and then placed in a rolling oven for 16 hours. After cooling down, the appropriate rheological or filtration measurements were obtained.

The same sample was used to run the rheological measurements and, afterward, the fluid-loss measurements. For all the tested samples, the rheological and fluid-loss measurements were conducted at 1 and 2 days after the initial preparation of the samples, respectively. Before any measurement and filtration measurements were obtained, the samples were mixed at high shear for 5 and 10 minutes, respectively. The sample-preparation procedure for each sample was followed strictly to ensure consistency.

Rheological Measurements. The rheological properties of the produced fluids were measured at ambient pressure and different temperatures of 77, 104, and 140°F with a rotational standard viscometer. Rheological measurements were determined at fixed speeds. The yield stress is estimated from the rheograms (shear stress vs. shear rate) after extrapolating the curves to zero shear rate and fitting an appropriate rheological model. The readings were taken from high to low speeds, while rotation lasted for 60 seconds at each rotational speed, with readings recorded every 10 seconds, thus giving six measurements for each rotational speed. These six values were averaged and recorded. The total duration of the rheological measurement for each sample was 8 minutes per cycle. The rheological parameter estimation was performed according to the Herschel-Bulkley model.

After dynamic aging of the samples at 350°F, the same measurement protocol was followed to record the rheological properties of the aged samples. 

High-Pressure/High-Temperature (HP/HT) Filtration Measurements. Filtration properties of the fresh and the thermally aged samples were obtained following American Petroleum Institute procedures. Data were collected with an HP/HT filter press operating at 300‑psi differential pressure at a temperature of 250°F. The apparatus includes a 500‑mL cell furnished with a standard cell inlet cap, four 200-W heaters, and a scribed outlet cap for the ceramic filter disks (used as the filter medium). The ceramic disks are of 0.25-in. thickness and 2.5-in. diameter, with a permeability of 15 darcies and a mean pore throat of 50 µm. The samples were poured into the cell, and the cell was then sealed and put into the heating jacket. A controlled-pressure nitrogen source was used to adjust the pressures at the desired values. The filtration volume was recorded as a function of time for 30 minutes. The thickness of the filter cake was measured immediately at the end of the filtration period using a digital caliper. The filter cakes were examined for their morphology and particle interactions.

Discussion

A bentonite-based fluid system was developed with the addition of 0.5 wt% CM Fe3O4 NPs. Extensive rheological analysis and filter-loss experiments revealed the exceptional rheological and filtration characteristics of the new fluids. On the basis of the results obtained, the following conclusions can be drawn:

  • The samples of BF and of nanobased fluid (NF) exhibited a yield stress followed by a shear-thinning behavior, with trends becoming more Newtonian at higher temperatures.
  • The three-parameter Herschel-Bulkley rheological model provided a best fit with all of the experimental data.
  • Yield stress and apparent viscosity became increasingly sensitive to temperature. Yield stress increased linearly with temperature up to 250°F. Apparent viscosity also increased at higher temperatures over the entire range of shear rates. The linear dependence of yield stress with temperature was identified for the first time.
  • The NF exhibited a flat type of gel-strength profile compared with the progressive-type gel strength of the BF.
  • Dynamic thermal aging of the fluids at 350°F for 16 hours affected the properties of the BF adversely. On the other hand, the NF maintained its good rheological properties, and its filtration properties were considerably improved.
  • Addition of 0.5 wt% CM Fe3ONPs yielded a 40% decrease of HP/HT fluid loss compared with that of the BF before aging, and an even greater reduction of 43% after thermal aging.
  • The spurt losses decreased by 100% upon addition of CM Fe3O4 NPs. Filter-cake thicknesses increased upon addition of NPs before aging, but decreased after thermal aging. 
  • The complex morphology of the filter cakes produced upon addition of NPs, a process that gives rise to superior filtration characteristics, was investigated, showing that the CM Fe3O4 NPs are finely dispersed among the bentonite plate-like particles.
  • Use of the CM Fe3O4 NPs increases the ability of bentonite-based fluids to control filtration losses at

HP/HT conditions and shows the ability of the NFs to build a thin and impermeable filter cake, resulting in improved and cost-effective drilling operations. 

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 18731, “A Comprehensive Approach for the Development of New Magnetite Nanoparticles Giving Smart Drilling Fluids With Superior Properties for HP/HT Applications,” by Z. Vryzas, Texas A&M University at Qatar; V. Zaspalis, Aristotle University of Thessaloniki; L. Nalbantian, Centre for Research and Technology Hellas; O. Mahmoud and H.A. Nasr-El-Din, Texas A&M University; and V.C. Kelessidis, Texas A&M University at Qatar, prepared for the 2016 International Petroleum Technology Conference, Bangkok, Thailand, 14–16 November. The paper has not been peer reviewed. Copyright 2016 International Petroleum Technology Conference. Reproduced by permission.

New Magnetite Nanoparticles Allow Smart Drilling Fluids With Superior Properties

01 November 2017

Volume: 69 | Issue: 11

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