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SPE 156992 Novel Nanoparticle-Based Drilling Fluid with Improved Characteristics Mohammad F. Zakaria,SPE, Maen Husein, SPE, Geir Hareland,SPE Department of Chemical and Petroleum Engineering, University of Calgary
Copyright 2012, Society of Petroleum Engineers This paper was prepared for presentation at the SPE International Oilfield Nanotechnology Conference held in Noordwijk, The Netherlands, 12–14 June 2012. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.
Abstract The success of drilling operations is heavily dependent on the drilling fluid. Drilling fluids cool down and lubricate the drill bit, remove cuttings, prevent formation damage, suspend cuttings and also cake off the permeable formation, thus retarding the passage of fluid into the formation. Typical micro or macro sized loss circulation materials (LCM) show limited success, especially in formations dominated by micropores, due to their relatively large sizes. In the current work, a new class of nanoparticle (NP) loss circulation materials has been developed. Two different approaches of NP formation and addition to oil-based drilling fluid have been tested. All NPs were prepared in-house either within the oil-based drilling fluid (in-situ), or within an aqueous phase (ex-situ), which was eventually blended with the drilling fluid. Under low pressure low temperature API standard test, more than 70% reduction in fluid loss was achieved in the presence of NPs compared to only 9% reduction in the presence of typical LCMs. The filter cake developed during the NP-based drilling fluid filtration was thin, which implies high potential for reducing the differential pressure sticking problem and formation damage while drilling. Moreover, at the level of NPs added, there was no material impact on drilling fluid viscosity and the fluid maintained its stability for more than 6 weeks. Inroduction The cost of the drilling fluid loss often represents one of the single peak capital expenditure during drilling. Current experience, nevertheless, shows that it is often impossible to reduce fluid loss successfully with micro and macro type fluid loss additives due to the fact that their physio-chemical and mechanical characteristics still falls short of the best that can be conceived. This impacts the economy of drilling since it increases the non-productive drilling time (Fraser et al., 2003; Amanullah et al., 2011; Chenevert and Sharma, 2009). LCM with diameters in the range of 0.1-100 µm may play an important role when the cause of fluid loss occurs in 0.1 µm-1 mm porous formation. In practice, however, the size of pore opening in shales that may cause fluid loss varies in the range of 10 nm-0.1 µm, where NPs as a loss circulation material could fulfill the specific requirements by virtue of their size domain, hydrodynamic properties and interaction potential with the formation (Abdo and Haneef, 2010; Amanullah et al., 2011; Srivatsa, 2010). NPs are defined as particulate dispersions or solid particles with a size in the range of 1-100 nm. Amanullah and Al-Tahini (2009) defined nano fluids as any fluids (drilling fluids, drill-in-fluids, etc) used in the exploitation of oil and gas that contain at least one additive with particle size in the range of 1-100 nm. These particles are smaller than micro particles, have a high surface to volume ratio and may provide superior fluid properties at low concentrations of the additives (Amanullah and Al-abdullatif, 2010). The main application of NPs would be to control the spurt and fluid loss into the formation and hence control formation damage. The presence of NPs can lead to better sealing at an earlier stage of filter cake formation and, subsequently, a thinner impermeable mud-cake. Due to its high surface to volume ratio the particles in the mud cake matrix can easily be removed by traditional cleaning systems during completion stages. Thus, the NPs can be used as rheology modifiers, fluid loss additives and shale inhibitors at low concentrations (Amanullah et al., 2011; Amanullah and Al-abdullatif, 2010; Zakaria et al., 2011) without the fear of particles lingering in the drilled well. Oil-based muds offer a good solution to shale instability problems. However development of water-based mud is also needed for environmentally sensitive areas. Chenevert and Sharma (2009) investigated permeability reduction of shale formations using specific NPs in the water-based drilling fluids. By identifying the pore throat radii of shale samples, the investigators were able to select fine particles that would fit into the pore throats during the drilling process and create a nonpermeable shale surface. Sensoy et al. (2009) showed that adding NPs to water-based mud decreases mud invasion in shale. Berret (2004) investigated the interaction of NPs with co-polymers and observed the formation of “super-micellar” aggregates. NPs having hydroxyl groups (-OH) on the surface led to NP agglomeration, which was controlled by addition of
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surfactants. This work was aimed at investigating in-house prepared NPs in order to control fluid loss in porous media with very small pore size such as shale formations. This investigation was based on the hypothesis that in-house prepared NPs will mix better with, and interact with, the rest of the oil-based drilling fluid. NPs based drilling fluid formulation The oil-based drilling fluid used in this study was supplied by a Calgary based drilling fluid company. One mix of the drilling fluid was tested; namely 90% oil: 10% water (V/V). Commercial NPs (Nano structured and amorphous materials Inc, Houston, Texas, USA) were used primarily to provide bench marking. Similar NPs can be prepared from its precursors inhouse. In order to provide fair comparison, the same amount of ex-situ as well as in-situ prepared in-house NPs were added into the drilling fluid, and their fluid loss mitigation was compared. In-situ approach refers to preparing the particles within the drilling fluid. Drilling Fluid characterization The filtration characteristics of the different drilling fluids involved in this study were evaluated according to API 30-min test. Data was collected using a standard FANN filter press (Fann Model 300 LPLT, Fann Instrument Company, USA) and filter paper (Fann Instrument Company, USA). Three replicates were prepared for every sample and the 95% confidence intervals were reported in the results. The cake thickness was measured using a digital caliper (0-6˝ TTC Electronic digital calipers model # T3506, Canada). A rotational Fann 35 viscometer (Fann Instrument Company, USA) was used to measure the shear characteristics of the drilling fluid at six different speeds. Results and Discussion Electron microscopy. The TEM photographs and the corresponding particle size distribution histogram for the in-house ex-situ prepared NPs are shown in Figure 1(a-b). The histogram shows size distribution falling in the range between 1-30 nm, in addition to some aggregates with larger sizes. The TEM image shows that the ex-situ prepared NPs are not uniform in size and shape. It should be noted that the ex-situ particles were prepared without the addition of a surfactant, which could have capped the particles. Dispersing the ex-situ prepared NPs by ultrasonication in methanol for 10 min before deposition on the TEM grid did not seem to eliminate all aggregates, despite the fact that the NPs were not found to exhibit magnetic properties at room temperature. Therefore, it is concluded that this agglomeration at room temperature is not due to magnetic attraction, but rather due to the high interfacial energy of the particles (Bumajdad et al., 2011). Once mixed with the drilling fluid, the surfactant rich oil-based fluid limits the aggregation of the ex-situ prepared particles, especially since the concentration of NPs in the drilling fluid is kept low. On the other hand, in-situ prepared NPs are expected to be very well dispersed by virtue of the surfactant component of the drilling fluid mix. The results of this investigation are detailed below.
a)
b)
TEM Photographs Figure 1 : a) TEM Photographs and b) the corresponding particle size distribution histogram for the ex-situ in-house prepared NPs
Stability of NP-based Fluid. Visual observation was used to assess the stability of the NP-based fluids. Stability against agglomeration and sagging relates here to the „shelf life‟ of the NP-based fluid. Figure 2 shows photos of samples representing the original drilling fluid without NPs and NP-based fluids. The photos show no sign of sagging or aggregation even after 6 weeks of setting at room temperature and confirm that, at the concentration of the added NPs, no agglomeration or sagging takes place. Therefore, no extra additives were required to stabilize the NP-base drilling fluid. NPs that grow or agglomerate to sizes beyond the stabilization capacity of oil-based fluid might settle under gravity, which was not apparent in the figure.
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NP-based Fluid (NDF)
Original Drilling Fluid (DF)
Figure 2: Photos comparing NP-based and original drilling fluids
LPLT Filtration. Filtration property is dependent upon the amount and physical state of colloidal materials used in the mud. When mud containing sufficient colloidal material is used, fluid loss can be minimized. The spurt loss of the drilling fluid is considered as one of the sources of solid particles and particulate invasion to the formation, which can cause serious formation damage as a results of internal mud cake formation in the vicinity of the wellbore. Internal pore throat blockage may create a flow barrier which reduces oil and gas flow. Moreover, higher particle flocculation in drilling fluid leads to a thicker mud cake which increases the probability of differential sticking and stuck pipe problems (Amanullah et al., 2011). This highlights the importance of using dispersed NPs in fluid design with virtually no spurt loss, low filtrate volume and good quality filter cake. At first, commercial NPs were introduced into the commercial oil-based drilling fluid as per literature procedure (Amanullah et al., 2011; Srivatsa, 2010; Cai et al., 2011). This experiment served as bench marking. The performance towards fluid loss prevention was very poor as shown in Table 1. It is to be noted that the original drilling fluid (DF) and NPbased drilling fluid was completely LCM free. A large amount of small „fish eyes‟ (lump of un-dissolve commercial NPs) on the commercial NPs based mud cake were clearly apparent in Figure 3. Even high shear mixing did not improve its quantitative fluid loss property. Following the hypothesis outlined earlier, in-house prepared NPs may better interact with the drilling fluid, especially in-situ formed NPs (in-house prepared NPs were formulated inside the drilling fluid or added to the drilling fluid after formation. In-house NPs had better plugging performance than commercial NPs as shown in Table 2. „Fish eyes‟, which appeared in the mud cake using commercial NPs, were minimized in the presence of in-house formulated NPs; both ex-situ and in-situ. The characteristics of the resultant filter cake depended on the degree of peptization or flocculation of the suspension. Stable (peptized) suspensions form dense and compact sediments, while flocculated suspensions form more voluminous sediments and particles are associated in the form of a loose, open network. In general, filter cake formed from stable dispersed NPs is dense and relatively impenetrable and display more flow resistance in comparison to that formed from flocculated commercial NPs. Table 1: API LPLT Fluid loss of drilling fluid samples using commercial NPs. LPLT Fluid Loss (mL) Samples Types
90:10 (v/v) Oil: Water
NPs
Commercial NPs (20-40 nm)
Time (min)
7.5 30
Fluid Loss Reduction %
DF
DF with commercial NPs
1.7±0.6
1.7±0.6
0
4.5±0.6
4.2±0.6
6.67
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Commercial NP- based mud cake
In-house NP-based mud cake
Figure 3: Mud Cakes of drilling fluid with commercial NPs and in-house NPs
It is believed that the in-house prepared NPs in drilling mud adsorbed into the pore space of the clay platelets and formed well dispersed plastering effect on the filter paper. This implies lower penetration of fluid into the formation and, hence lesser damage to the formation. It appears that the in-house prepared NPs progressively builtup on the surface of the filter cake and acted as a “shut off valve”. Effective mud cake resulted in much lower fluid loss as can be clearly seen in Table 2. Drilling fluid (DF) without NPs and LCM considered as a baseline drilling fluid for comparative evaluation of fluid loss property of ex-situ and in-situ prepared nano-based fluid which is completely LCM free. Based on the original DF, fluid loss over a period of 30 min decreased by 9 vol% for the drilling fluid with LCM only, while it decreased by 70 vol% for the drilling fluid containing the ex-situ prepared NPs and more than 80 vol% for the drilling fluid containing the in-situ prepared NPs. Shale has macro to nanopores. Conventional LCM will not properly seal the nanopore due to its micron size. Therefore, smaller particles are needed to better fit the nanopore. Those NPs interact with the formation and eventually plug the pore either internally or externally. External pore plugging is more desirable, since pore channel plugging results in formation damage and oil and gas production would be interrupted. Once a primary bridge is established, NPs down to fine colloids and, then, larger particles are trapped leading to much lower filtrate invasion to the formation. The better dispersed in-situ prepared NPs were able to immediately adsorb on clay platelets during cake formation, filled the pores and gaps of clay interstices, and hence tremendously lowered the fluid loss compare to the ex-situ prepared NPs. On the other hand, for the typical LCM, only particles larger than pore opening cannot enter the pore at first and might be swept away by the mud stream. Table 2: Comparative study of API LPLT fluid loss property of in-house prepared NP-based drilling fluids. LPLT Fluid Loss (mL) Samples Types
90:10 (v/v) Oil: Water
Time (min) DF
DF with LCM 1.4±0.2
DF with In-house ex-situ NPs 0.15±0.1
DF with In-house in-situ NPs -
7.5
2.0±0.2
30
3.96±0.2
3.6±0.1
1.25±0.2
0.9±0.2
During spurt loss period (t< 7.5 min), mud particles attempt to flow with the filtrate through the filter paper. NPs bridge across pore throats to form the external mud cake immediately, and thus lowering the spurt loss. There could be an additional effect from the generation of sticky NPs in the preferred method. More laboratory work could help to elucidate these mechanisms in depth. Fluid loss control of drilling muds using similar approach was not reported in literatures. Most of the literature on NP-based drilling muds considered water-based muds employing commercial NPs, and loss reduction of 40% maximum was reported for 1-30 wt% NPs (Amanullah et al., 2011; Srivatsa, 2010; Cai et al., 2011). In order to prevent drilling and completion problems, mud cake quality and build up characteristics are also very important. Figure 4(a-d) shows the mud cake formed in the presence and absence of NPs. Compared with LCM-based cake, the NP-based drilling fluid produced a thin mud cake. Addition of NPs did not cause an increase in the thickness of the mud cake, since the NPs are believed to be located at the interstice of clay and filled the gap or holes in the clay platelets. The NPs are subsequently captured within its multiple layer clay structure. This multiple layer structure provides much better sealing, prevents further flow through the pores, and subsequently lower clay deposit and results in a thinner filter cake. It should also be noted that the surface of the mud cake was essentially occupied by the NPs. This suggests that, in addition to participating into the build up of the filter cake, NPs also occupied the very small pores left at the surface and provided the perfect sealing. This layer, in turn, led to a crack-free and smooth surface. This suggests a high potential for reducing the differential pressure
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sticking problem while drilling. On the other hand, large sized LCM could not lodge in the porous space of the cake and the cake exhibited sufficient porosity to permit continued flow through it as filtration proceeds. This, in turn, led to more clay depositing onto the cake and particles accumulation. Because the fluid loss performance is improved dramatically with these NP additives, it raises the question as to whether conventional LCM are still needed to control the fluid loss. Current test results proved that NPs give dramatic improvement in performance and confirmed that they were very effective even when used alone. a)
b)
c)
d)
Figure 4: Mud Cakes of a) DF only, b) DF+LCM, c) DF with in-house ex-situ NPs and d) DF with in-house in-situ NPs
Rheology of NP-based fluids. Drilling fluid with good pumpability exhibit lower viscosity at high shear rate and higher viscosity at lower shear rate. This property of drilling mud is used widely where high viscosities are required during tripping operation and low viscosities during drilling operation to clean the cuttings from the bottom of the hole (Chenevert and Sharma, 2009; Fraser et al., 2003). The plot of apparent viscosity and shear rate as shown in Figure 5 resembles the nonlinearity of the curves at low shear rates and approach linearity at high shear rates. The fact that addition of NPs created a slight change in the rheology supports the theory that NP behavior is governed by NPs grain boundary and surface area/unit mass (Amanullah, 2011; Srivatsa, 2010). Although the addition of NPs is not sufficient to cause material rheology changes in the system compared to the drilling fluid (DF) without LCM and NPs, particle size, nature of particle surface, zeta potential of the particles, surfactants, pH value and particle interaction forces may play significant role in altering the viscosity.
Figure 5: Rheology behavior of drilling fluid containing ex-situ NPs and in-situ NPs
Fluid with high viscosity may cause excessive pumping pressure and decreased rate of drilling. Therefore, it is an important issue to design a suitable fluid rheology. Lee et al., (2009), who investigated the application of NPs for maintaining viscosity of drilling fluids at high temperature and high pressure, reported that the rheological behavior may depend on the particle type, size, concentration and inter-particle distance of NPs within the fluid. The rheological properties of the in-house NP-based drilling fluid thus could suitably fulfill the drilling requirements. Potential for Field application. Oil-based muds containing in-house NPs have been formulated for the first time. According to the above results, these NPs formulated within or outside the fluid offer a great potential to properly seal the formation, prevent fluid loss and reduce formation damage and contamination. Delicate formations such as shales with highly porous nano-sized structures may benefit so much from the technology addressed in this study, since the NPs possess the proper sizes to block throats and thereby decrease fluid loss and increase wellbore stability. Furthermore, it may be possible to reduce the differential pressure sticking problem as in-house NPs form a well dispersed thin mud cake and also can improve the rate of penetration (ROP), and consequently reduce drilling costs significantly. Conclusions
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The incorporation of custom prepared NPs in oil-based drilling fluid system reduced the fluid loss substantially by virtue of their ability to block small sized pores and ability to interact with the clay particles. A reasonably low fluid loss value and thin mud cake, thickness < 1 mm, reflected superior performing drilling fluid compare with the drilling fluid with the conventional LCM. The engineered NPs alone provided sufficient plugging, because they sealed most of the holes in a typical mud cake, or mud cake with typical LCM, structure. However the use of NPs in the drilling fluid at a right concentration and adpotion of a specific preparation method led to a stable drilling fluid with desirable rheological behavior. Tailor made NPs with specific characteristics is thus expected to play a promising role in helping to solve the circulation loss and other technical challenges faced with commercial drilling fluid during oil and gas drilling operation. References Amanullah,MD. And Al-Tahini,M.A. 2009.Nano-Technology – Its Significance in Smart Fluid Development for Oil and Gas Field Application.SPE Saudi Arabia Section Technical Symposium, AlKhobar, Saudi Arabia. Amanullah,MD. Al-Abdullatif,Z.2010.Preliminary test results of a water based nanofluid. The 8th International Conf.& Exhib. on chemistry in industry, Manama, Bahrain,18-20 October. Amanullah,MD. Al-Arfaj, K. M. and Al-Abdullatif,Z.2011.Preliminary Test Results of Nano-based Drilling Fluids for Oil and Gas Field Application. SPE/IADC 139534,1-9. Zakaria,FM.Mostafavi,V. Hareland,G. and Husein,M. 2011.Design and Application of Novel Nano Drilling Fluids to Mitigate Circulation Loss Problems during Oil Well Drilling Operations”, presented at the World Nano Conference and Expo 2011 in Boston,Massachusetts, U.S.A on June 13-16, 2011,Chapter 9: Cleantech & Nanotech in Oil, Gas & Traditional Energy,ISBN: 978-1-4398-8189-7. Chenevert,E M. and Sharma,M.M.2009.Maintaining shale stability by pore plugging. US Patent 0314549. Sensoy,T. Chenevert,M.E. and Sharma,M.M.2009.Minimizing water invension in shale using nanoparticles. SPE 124429,SPE Annual Technical Conference and Exhibition, New Orleans, LA, 4-7 October. Berret,JF.2004. Interactions between Polymers and Nanoparticles: Formation of Hybrid aggregates, arxiv.org/pdf/cond-mat/0411669. Fraser,L.J. Harrington,b. Albarrazin,C.Snyder,G.and Donham,F.2003. Use of Mixed Metal Oxide fluid to combat losses in porous and fractured formations: two case histories, AADE-03-NTCE-40. Abdo,J.and Haneef,D.2010.Nanoparticles: Promising solution to overcome stern drilling problems,”NSTI-Nanotech 2010, www.nsti.org,ISBN 978-1-4398-3415-2,Vol.3. Bumajdad,A. Ali,S. and Mathew,A.2011.Characterization of iron hydroxide/oxide nanoparticles prepared in microemulsions stabilized with cationic/non-ionic surfactant mixtures.Journal of Colloid and Interface Science 355,pp282–292. Srivatsa,T.J.2010. An Experimental Investigation on use of Nanoparticles as Fluid Loss Additives in a Surfactant – Polymer Based Drilling Fluid.Texas Tech University,M.Sc thesis. Cai,J.Chenevert,E. M. and Sharma,M.M. and Friedheim,J.2011.Decreasing water invasion into Atoka Shale using non-modified silica nanoparticles.SPE 146979,1-12. Lee,J-K. Sefzik,T. Son,Y-H. Phuoc, T.X. Soong,Y. Martello,D. and Chyu,M.K.2009.Magnetic nanoparticles for smart drilling fluid. NTCE 18-04, AADE.
