NANOFIBRILLATED CELLULOSE FOR USE IN FLUIDS FOR PRIMARY OIL RECOVERY

Abstract

The present invention relates to nanofibrillated cellulose (NFC) for use in drilling fluids, fracturing fluids, spacer fluids etc. The fluids contain NFC as a viscosifier with an aspect ratio of more than 100 and where the nanofibrils have a diameter between 5 and 100 nanometer and a length of more than 1 m.

Claims

1. A fluid containing nanofibrillated cellulose (NFC) as a viscosifier, wherein the fluid is a drilling fluid, a fracturing fluid, or a spacer fluid, wherein the NFC has an aspect ratio of more than 100 and where the nanofibrils have a diameter between 5 and 100 nanometer and a length of more than 1 m.

2. A fluid as claimed in claim 1, wherein the aspect ratio of NFC is more than 500 and where the nanofibrils have a diameter between 5 and 50 nanometer and a length of more than 5 m.

3. A fluid as claimed in claim 1, wherein the NFC is nanofibrillated lignocellulose having a lignin content of up to 20 wt % based on dry matter.

4. A fluid as claimed in claim 3, wherein the NFC is nanofibrillated lignocellulose having a lignin content of up to 10 wt % based on dry matter.

Description

FURTHER DESCRIPTION OF THE INVENTION

[0016] The NFC materials used in the examples below were produced in the laboratory as described in the literature as follows. [0017] 1) TEMPO mediated NFC (TEMPO-NFC) was produced according to the publication of Saito et al. (Saito, T. Nishiyama, Y. Putaux, J. L. Vignon M. and Isogai. A. (2006). Biomacromolecules, 7(6): 1687-1691). TEMPO is 2,2,6,6-tetramethylpiperidine-1-oxyl radical. Generally, TEMPO-NFC has a diameter less than 15 nm and an aspect ratio of more than 100. The charge density is typically in the range 0.2-5 mmol/g. [0018] 2) Enzymatic assisted NFC (EN-NFC) was produced according to the publication of Henriksson et al, European polymer journal (2007), 43: 3434-3441 (An environmentally friendly method for enzyme-assisted preparation of microfibrillated cellulose (MFC) nanofibers) and M. Pkk et al. Biomacromolecules, 2007, 8 (6), pp 1934-1941, Enzymatic Hydrolysis Combined with Mechanical Shearing and High-Pressure Homogenization for Nanoscale Cellulose Fibrils and Strong Gels. ME-NFC has a diameter less than 50 nm and an aspect ratio of more than 100. The charge density is typically less than 0.2 mmol/g. [0019] 3) Mechanically produced MFC (NE-NFC) was produced as described by Turbak A, et al. (1983) Microfibrillated cellulose: a new cellulose product: properties, uses, and commercial potential. J Appl Polym Sci Appl Polym Symp 37:815-827. ME-MFC can also be produced by one of the following methods: homogenization, microfluidization, microgrinding, and cryocrushing. Further information about these methods can be found in paper of Spence et al. in Cellulose (2011) 18:1097-1111, A comparative study of energy consumption and physical properties of microfibrillated cellulose produced by different processing methods. ME-NFC has a diameter less ca. 50 nm and an aspect ratio of more than 100. The charge density (carboxylate content) is typically less than 0.2 mmol/g. [0020] 4) Carboxymethylated NFC (CM-NFC) was produced according to the method set out in The build-up of polyelectrolyte multilayers of microfibrillated cellulose and cationic polyelectrolytes Wigberg L, Decher G, Norgen M, Lindstrom T, Ankerfors M, Axnas K Langmuir (2008) 24(3), 784-795. CM-NFC has a diameter less than 30 nm and an aspect ratio of more than 100. The charge density is typically in the range 0.5-2.0 mmol/g.

[0021] The equipment used to measure the various properties of the produced NFC included a mass balance, a constant speed mixer up to 12000 rpm, a pH meter, a Fann 35 viscometer, a Physica Rheometer MCR-Anton Paar with Couette geometry CC27, and a heat aging oven (up to 260 C. at pressure of 100-1000 psi) and a core flooding system.

Example 1

Core Flooding Tests

[0022] Core flooding tests on NFC fluids were performed using different types of cores, both sandstone and limestone, under different conditions such as various NFC concentrations, various types of NFC, at various temperatures, flow rate and different pressures.

[0023] The procedure used for the core flooding tests was as follows:

1. The core was dried at 250 F. for 4 hours and weighed to obtain its dry weight. Then the core was saturated with brine solution (5 wt % KCl in deionized water) for 6 hours under vacuum and its wet weight was measured. The pore volume (PV) was calculated using these measurements and the density of the brine solution (density=1.03 g/cm3 at 70 F.).
2. The core was placed inside a core holder. The brine (5 wt % KCl) was pumped through the core in the production direction. If elevated temperature was required, the temperature was raised to the target value (250 F.) and kept constant during the test. The pressure drop across the core was monitored and recorded until it was stabilized. The initial permeability was calculated.
3. The treatment fluid was prepared by diluting 1.0 wt % NFC dispersion with 5 wt % KCl brine to NFC concentration of 0.4 wt %. A 400 g NFC solution was mixed into 600 g KCl brine (5 wt %) to make the 0.4 wt % NFC as a treatment fluid.
4. The treatment fluid containing NFC and/or other chemicals was pumped, in the injection direction (reversed to production direction), at the back pressure of 1100 psi. The pressure drop across the core increased as the fiber fluid was injected. The injection was stopped when 2 PV was injected. The pressure drop across the core was recorded.
5. The direction of flow was then reversed to the production direction and the brine (5 wt % KCl) was injected into the core until the pressure drop across the core was stabilized. The return permeability after fluid treatment was calculated.

Example 1: Test of ME-NFC Using Cores with Different Permeabilities

[0024] In this test, ME-NFC having an aspect ratio above 100 and a diameter of less than 50 nm was tested for core-flooding using sandstone core with permeability of 20, 100, and 400 mD, respectively.

TABLE-US-00001 TABLE 1 Test of ME-NFC using various cores. The tests were conducted at 250 F. Core flood no. Test 1 Test 2 Test 3 Low permeability Medium permeability High permeability Core (20 mD) (100 mD) (400 mD) NFC 0.4% 0.4% 0.4% concentration Pressure Permeability, Pressure Permeability, Pressure Permeability, Drop, psi mD Drop, psi mD Drop, psi mD Initial 81.6 20.1 21.6 75.8 8.0 409 After Fiber 93.1 17.6 24.0 68.2 15.2 215 Return 88 90 53 permeability (%)

[0025] The example above indicates that a regular NFC grade with a diameter of ca. 30 nm and length of more than 5 micrometers poses less or no damage to low and medium permeability cores. The return permeability was above 88% for cores with initial permeability <100 mD. This indicates that NFC fibrils with long fibrils of more than 5 micrometer are large enough to penetrate medium to low permeability formations such as tight gas. It was observed the fibrils were filtered out at the core surface from the injection direction. As the permeability increases, the pore-throat becomes big and nano-fibrils might invade the core. This was the case for the core with an initial permeability of 400 mD where the return permeability was just 53%. This indicates that fibrils penetrated the core and impaired the formation. A post treatment such as enzymatic or chemical breakers is required to remove NFC from the formation.

Example 2: Test of Various Types of NFC Using Berea Sandstone Core with Medium Permeability (100 mD) and Comparing with Guar Gum and Viscoelastic Surfactant

[0026] This example compares the return permeability of 3 types of NFC with guar gum, modified guar gum (hydroxypropyl guar gum) and viscoelastic surfactant as viscosifiers. The treatment fluids were prepared as shown in Table 2.

TABLE-US-00002 TABLE 2 Recipes for treatment fluids NFC 1 wt % KCl 5% brine Total Mass in (gm) Mass in (gm) concentration ME-NFC 800 200 0.8 wt.-% ENZ-NFC 800 200 0.8 wt.-% TEMPO-NFC 800 200 0.8 wt.-% Guar gum 8 992 0.8 wt.-% Modified guar gum 8 992 0.8 wt.-% Viscoelastic surfactant 40 ml 960 ml 4 vol. %

TABLE-US-00003 TABLE 3 Test of various types of NFC using Berea sandstone core with medium permeability (100 mD) and comparing with guar gum and viscoelastic surfactant. The tests were conducted at 250 F. Core flood no. Test 4 Test 5 Test 6 Test 7 Test 8 Test 9 Viscosifier ME- ENZ- TEMPO- Guar gum Modified Viscoelastic NFC NFC NFC guar gum surfactant Concentration 0.8% 0.8% 0.8% 0.8% 0.8% 4 vol % Initial 75.8 79.1 89.5 74.4 83.1 81.5 permeability Permeability 68.2 78.4 86.6 15.8 49.9 78.7 after fluid injection Return 90 99 97 21 60 97 permeability (%)

[0027] This example 2 shows that regardless of the charge density on the surface of the fibrils at the same concentration the return permeabilities were above 90% for medium permeability core such as Berea sandstone. The return permeability for NFC materials was significantly higher than that for guar gum and for modified hydroxypropyl guar gum.

[0028] If an enzymatic or chemical pretreatment is used before the defibrillation step to produce NFC, it should be monitored and controlled to avoid shortening the fiber, which can pose damage to the oil & gas reservoir afterword.