In this work, shale hydration Inhibition performance of tallow amine ethoxylate as a shale stabilizer in water based drilling fluid, was investigated through these tests: bentonite hydration inhibition test, bentonite sedimentation test, drill cutting recovery test, dynamic linear swelling test, wettability test, isothermal water adsorption test, and zeta potential test. The results showed that bentonite particles are not capable of being hydrated or dispersed in the mediums containing tallow amine ethoxylate; tallow amine ethoxylate had shown a comparable and competitive inhibition performance with potassium chloride as a common shale stabilizer in drilling industry.
Pezhman Baratia, Khalil Shahbazia, Mosayyeb Kamarib, Amir Aghajafaria
aDepartment of Petroleum Engineering, Ahwaz Faculty of Petroleum Engineering, Petroleum University of Technology, Ahwaz, 63431, Iran. bReservoir Evaluation Department, National Iranian South Oil Company, Ahwaz, Iran.
Received 25 September 2016, Accepted 15 May 2017
Some amine functional groups exist in tallow amine ethoxylate structure which are capable of forming hydrogen bonding with surfaces of bentonite particles. This phenomenon decreased the water adsorption on bentonite particles’ surfaces which results in reduction of swelling. Tallow amine ethoxylate is also compatible with other common drilling fluid additives.
A large part of underground formations consists of shaly rocks which face with swelling and disintegration when meeting the aqueous phase of drilling fluids. This event causes the wellbore washouts and drill string sticking in the borehole, wasting 1 billion USD per year worldwide during the drilling operations , , . Drilling fluid designers are always seeking for high performance drilling fluids which are resistant to shale hydration and disintegration, so they are more willing to use oil-based drilling fluids. But this sort of drilling fluids also has severe degenerative effects on the environment in addition to its high operation and disposal costs. This makes them less desirable to the drilling fluid designers in recent years , . In most recent researches, amines and their derivatives are of high interest to the researchers because of their sufficiency in controlling the shale hydration and capability to extend their specification to almost any drilling operation conditions , .
Qu et al. (2009) synthesized polyoxyalkyleneamine (POAM) and investigated its inhibitive properties to Na-montmorillonite. Based on their results, POAM is completely water soluble, low toxic and compatible with other common drilling fluid additives. The reaction between POAM molecules and clay minerals can involve several mechanisms including hydrogen bonding and compete with water molecules for reactive sites . A new modified polyethylene glycol (M-PEG) was introduced by Souza et al. (2010) as a new shale inhibitor additive which could adsorbed via hydrogen bonding on the clay particles’ surfaces. It had much greater effect on reducing the water uptake by the clays and increasing their stabilities than those of polyethylene glycol . The ability of poly(oxypropylene)diamine in suppressing the montmorillonite hydration was investigated by Wang et al. (2011).
They showed that poly(oxypropylene)diamine adsorbed on particle surfaces via hydrogen boning and could form a hydrophobic shell around them, and in some cases intercalate into the montmorillonite interlayers which results in clay swelling reduction . The inhibition performance of polyether diamine (PEDA) was studied by Zhong el al. (2011). Their research showed that PEDA stabilized shales by exchanging protonated diammonium ion to native sodium ions and expelled the water molecules out of the clay galleries which could bind the plates together and improve their hydrophobicity against the water molecules .
Poly(oxyprolylene)-amidoamine (POAA), a new counteractive agent, was examined by Zhong (2012) in order to neutralize the negatively charged sites of clay minerals which make them more hydrophobic and stable against hydration . Other new introduced amine-based additives could be referred to bis(hexamethylen)triamine (BHMT) and dopamine (DA) , . Recently, Nano additives were used to improve the sealing ability of muds during drilling through shaly formations by plugging of pore throats and micro fractures , . Some researchers have turned to investigate the performances of plant-based additives such as horse tail in inhibiting the shaly formations against hydration and disintegration .
In this work, shale hydration inhibition performance of tallow amine ethoxylate along with its mechanisms have been investigated through bentonite hydration inhibition, bentonite sedimentation, hot rolling shale particle disintegration, dynamic linear swelling, wettability alteration, isothermal water adsorption, and zeta potential measurement tests. Also the compatibility of tallow amine ethoxylate with other common drilling fluid additives has been checked using drilling fluid making tests.
Materials and methods
Tallow amine ethoxylate (CAS No. 61791-26-2) with chemical name of tallow amine polyethylene glycol ether has been purchased from Kimyagaran Chemical Industries Company. The theoretical structure of this tertiary amine has been shown in Fig. 1.
Fig. 1. Theoretical structure of tallow amine ethoxylate .
This polyamine is known as KETALO (trade name) and is a non-ionic surfactant with a certain number of ethylene oxide unites (EOn). In this study, KETALO with EO15 (KETALO15) has been used. This kind of polyamine is cationic in nature because of existence of amine groups in its molecules structure, which can be protonated . KETALO15 properties presented by the company has been summarized in Table 1.
Table 1. KETALO15 properties.
Bentonite with high percentage of sodium montmorillonite has been purchased from Pars Drilling Fluid Company, Tehran, Iran. The drilling cuttings have been obtained from Asmari formation of Maroon oilfield in southwest of Iran, well number 281, and in depth of 4001–4008 m. Bentonite and drilling cuttings’ CECs (Cation Exchange Capacities) (CEC) were have been determined to be 18 and 3 mmol/g respectively, by sodium acetate method according to ISRIC soil analysis procedures . Potassium hydroxide and potassium chloride have been supplied by Merck Company, Germany. Other drilling fluid additives (PAC-LV, PAC-R, starch-HV, PHPA, Xanthan gum, anti-foam, biocide, and barite) have been purchased from Pars Drilling Fluids Company, Tehran, Iran. All materials have been used without any further purification treatments.
Bentonite hydration inhibition test
To assess the inhibition performance of KETALO15 against the bentonite hydration in aqueous phases, the bentonite hydration inhibition test has been used. In this test, at first, the aqueous solutions of KETALO15 with concentrations of 0, 0.5, 2 and 3 wt% have been prepared and then 10 wt% bentonite powder has been added, mixed and aged at atmospheric conditions for 24 h. Then their filtration and rheological properties (i.e. yield point, apparent and plastic viscosities) have been obtained using API low pressure–low temperature filter press and 35SA Fann rotational viscometer respectively, according to API recommended practice on the rheology and hydraulic of oil-well drilling fluids . At the last part, inhibition performance of KETALO15 has been compared with potassium chloride as a common shale stabilizer.
Bentonite sedimentation test
Instability of dispersed bentonite particles in aqueous mediums containing KETALO15 has been determined via bentonite sedimentation test. In this test, 3 wt% bentonite powder has been added to KETALO15 aqueous solutions with concentrations of 0, 1, 2 and 3 wt%, mixed thoroughly using magnetic stirrer, poured into the glass test tubes and kept in static-atmospheric conditions for 24 h. Then, by measuring the distance from the clearly formed horizontal interference (between sediment and supernatant) to test tube cap (h) and dividing it by internal length of test tube (H), the ratio h/H can be calculated and plotted for each test tubes containing different KETALO15 concentrations. Finally, the h/H ratios have been compared to those of potassium chloride as a common shale stabilizer.
In order to investigate the compatibility of KETALO15 with the other common drilling fluid additives, two different formulated drilling fluids have been selected (Table 2). Then the effects of 2 wt% KETALO15 addition on their rheological and filtration properties have been determined. For this purpose, drilling fluids have been aged at 70 °C using hot rolling oven (with the speed of 22 rpm) for 4 h. Then their filtration and rheological properties (i.e. yield point, 10 s and 10 min gel strengths, apparent and plastic viscosities) have been determined according to API recommended practice on the rheology and hydraulic of oil-well drilling fluids .
Table 2. Test fluid formulation used in compatibility test.
Hot rolling shale particles disintegration test
Hot rolling shale particles disintegration test has been employed to evaluate the inhibition performance of KETALO15 in preventing shale cuttings from hydration, disintegration and dispersion in (or to) the aqueous phase of drilling fluids according to API recommended practice of standard procedure for laboratory testing drilling fluids . In this test, 10 g sized shale drill cuttings (between 2 and 4 mm) have been in contact with drilling fluid at 70 °C in hot rolling oven aging cells (with the speed of 22 rpm). After 16 h, the recovery of drill cuttings (ratio of final oven dried weight to its initial weight) over mesh 35 has been determined.
Dynamic linear swelling test (DLST)
This test has been used to investigate the effect of KETALO15 on the bentonite wafers linear swelling which were in contact with different test fluids at low (26 °C) and elevated (65 °C) temperatures. In this test, 9.5 g bentonite wafers (with 28.3 mm diameter) have been produced under 27.58 MPa (4000 psi) for 2 h using hydraulic compactor, and then their initial thickness have been measured using caliper (with accuracy of 0.01 mm). Then, the prepared bentonite wafers have been left in contact with test fluids for 4000 min in the dynamic linear swell meter cup assembly at desired temperature, and their swellings have been recorded versus time. The anti-swelling ability of KETALO15 has been compared by that of potassium chloride at low temperature. On the other hand, the performance of KETALO15 has been investigated in different formulated drilling fluids at elevated temperature.
Wettability alteration test
Some shale stabilizers can change the clay minerals surface wettability properties from hydrophilic to hydrophobic state; that is why this test has been employed. In this test, the procedure illustrated by Wu  has been employed (Fig. 2A), which uses smeary glass microscopic slides to the homogeneous bentonite-water dispersions (2 wt% bentonite) with and without KETALO15 (2 and 0 wt%, respectively). Then, the water droplet contact angle on the prepared air-dried glass slides (Fig. 2B) has been measured at atmospheric conditions by automatic Attension theta optical tensiometer (Biolin Scientific Instrument Company).
Fig. 2. Smeary glass microscopic slides to the homogeneous bentonite-water dispersion: A) Before drying, B) After drying.
Isothermal water adsorption
Tendency reduction of clay mineral surfaces to the water molecules has a significant impact on their stability and is needful for having a safe drilling operation through shaly formations . In this test, the effect of KETALO15 adsorption on the tendency reduction of bentonite particles’ surfaces to water molecules has been investigated. To do so, an aqueous bentonite dispersion with concentration of 1.5 wt% has been prepared and left for 24 h at atmospheric conditions. Then the prepared dispersion has been split into two parts.
One part has been left without any further treatment (blank dispersion) and the other part has been treated by the addition of KETALO15 at 2 wt% concentrations (modified dispersion). Then, both parts have been centrifuged at 6000 rpm for 30 min. Sediments have been collected, and oven has been dried at 105 °C for 24 h, pulverized and screened by sieve mesh no. 200. 1 g of each sediment has been left in a well-sealed desiccators containing distilled water at the bottom (water activity of unit). After 11 days, the amount of adsorbed water molecules has been calculated based on the mass changes in atmospheric conditions.
Zeta potential measurement test
Some of shale stabilizers will adsorb the negatively charged clay particles and affect their surface charge density and colloidal stability. Colloidal stability reduction of clay particles can lead into increasing their durability against hydration and disintegration. In this test, effect of KETALO15 adsorption on the colloidal stability of the well-dispersed bentonite particles has been studied. To do so, KETALO15 has been added to an aqueous bentonite dispersion with concentration of 0.5 wt%, which leaded into different KETALO15 concentrations. After shaking for 24 h, zeta potential of all samples has been measured at atmospheric conditions using zeta potential analyzer (Zetasizer Nano ZS, Malvern Instrument Ltd.).
Results and discussion
Bentonite hydration inhibition test
The effect of KETALO15 on the filtration and rheological properties (i.e. apparent viscosity (AV), plastic viscosity (PV) and yield point (YP)) of aqueous bentonite dispersion has been investigated and results have been shown in Fig. 3. In the absence of KETALO15, bentonite particles have been well hydrated in the aqueous mediums, resulting in high AV, PV and YP and low filtration volume.
Fig. 3. Bentonite hydration inhibition test results.
When KETALO15 was added to the medium, even at low concentration of 0.5 wt%, bentonite hydration has been retarded, and the rheological properties are very low along with high filtration volume. In KETALO15 concentrations greater than 2 wt%, the aqueous medium inhibition potency has not improved significantly. When potassium chloride with 2 wt% concentration was added into the medium, hydration potential of bentonite particles reduced as much as when KETALO15 is added at the same concentration. This is shows that KETALO15 has a comparative performance with respect to potassium chloride as a common shale stabilizer and could be used in drilling fluids during drilling operation through shaly formation.
Bentonite sedimentation test
Bentonite sedimentation test has been performed to measure the stability of colloidal bentonite particles in an aqueous solution (Fig. 4). Bentonite particles have been well hydrated in the distilled water and converted to a stable colloidal dispersion. In the presence of KETALO15 at 1 wt%, bentonite colloids flocculated and settled down to form a sediment at the bottom of the test tubes. By increasing the KETALO15 concentration, bentonite colloids have become more flocculated and settled down in a faster rate to form a denser sediment. When potassium chloride was added into the aqueous mediums, similar phenomena occurred. By comparing the compactness of sediments at the bottom of the test tubes in case of the KETALO15 and potassium chloride it could be concluded that KETALO15 has a comparable potency in inhibiting bentonite particles with respect to the potassium chloride.
Fig. 4. Bentonite sedimentation behavior in KETALO15 and potassium chloride aqueous solutions.
Based on the results (Fig. 5), addition of KETALO15 to the both base and high performance drilling fluids has no adverse effect on their filtration and rheological properties. In simple words, KETALO15 is perfectly compatible with other common drilling fluid additives and even the filtration volumes are lower than those of untreated (i.e. absence of KETALO15) drilling fluids.
Fig. 5. Effect of KETALO15 addition on the filtration and rheological properties of base and high performance drilling fluids.
Hot rolling shale particles disintegration test
Shale drill cutting recovery in distilled water, 2 wt% KETALO15 and potassium chloride aqueous solutions has been measured and presented in Fig. 6. Distilled water has a great ability in hydrating and dispersing the shale drill cuttings, so the cutting recovery is as low as 43%. In the presence of KETALO15 and potassium chloride, both at 2 wt%, cutting recovery has increased by 26% and 28%, respectively, which is an indication of KETALO15 ability to inhibit aqueous mediums leading to reserving the shale drill cuttings from disintegration. Inhibition performance of KETALO15 in drilling fluids has been demonstrated by conducting the test on two different formulated drilling fluids (Table 2). In this case, the cutting recovery has been increased by 8% and 5% for base and high performance drilling fluids, respectively.
Fig. 6. Hot rolling shale particles disintegration test results, A) Distilled water, B) 2.0 wt% potassium chloride, C) 2.0 wt% KETALO15, D) Base drilling fluid, E) Base drilling fluid + 2.0 wt% KETALO15, F) High performance drilling fluid, G) High performance drilling fluid + 2.0 wt% KETALO15.
Dynamic linear swelling test (DLST)
At first step, swelling behavior of bentonite wafers in contact with distilled water, 2 wt% KETALO15 and 2 wt% potassium chloride has been investigated by conducting DLST at low temperature (Fig. 7 (A)). According to the figure, the swelling curves of all samples display a similar trend with sharp increases during the initial times. Bentonite wafer in contact with distilled water has swelled sharply and reached to the 130% after 4000 min, while in case of 2 wt% KETALO15 aqueous solution, the bentonite wafer swelling has started to reduce even at initial test times and finally reached to only 84% at the end of the test. In case of 2 wt% potassium chloride, bentonite wafer swelling behavior has been nearly the same as distilled water before 500 min, then the swelling has reduced sharply to reach the final value of 78%.
The anti-swelling performance of KETALO15 and potassium chloride at initial test times shows that the presence of KETALO15 in aqueous medium postpones the bentonite wafer swelling even at initial test times, while in case of potassium chloride it has not happened and bentonite wafer has swelled the same as distilled water. This indicates that if potassium chloride is the only presented shale stabilizer in the drilling fluid, the shale hydration risk exists more severely in comparison with KETALO15. At last, the effect of KETALO15 on inhibition performance of different formulated drilling fluid has been investigated at high temperature (Fig. 7 (B)). Based on the results, presence of KETALO15 in both base and high performance drilling fluids has improved the inhibition performance of both drilling fluids, resulting in swelling reduction of bentonite wafers by of 11% and 7%, respectively.
Fig. 7. Dynamic linear swelling test results: (A) aqueous solutions at low temperature of 26 °C, (B) Different drilling fluid at high temperature of 65 °C.