Borregaard operates one of the world’s largest biorefineries that specializes in the sustainable processing of Norwegian spruce tree into a spectrum of bio-based products as well as bioenergy. For example, Borregaard’s lignin-based biopolymers are a wood-based alternative to fossil-fuel based chemicals and have been utilized in the oil and gas industry for over 90 years in numerous applications.
Similarly, another component of the wood, cellulose fibrils or Borregaard’s microfibrillated cellulose (MFC), shows efficacy as a suspending agent for cuttings, fines, proppant, and solids with superior shear-thinning ability as compared to typical hydrocolloids (CMC, guar, xanthan, and HEC) and should always be considered in performance testing where a rheological additive is needed especially in completions with high TDS brines, high pressure high temperature (HPHT), in the presence of oxidizers, acids, and bases as well as systems with a high water cut or water-based drilling muds for horizonal drilling for conventional oil.
Limitations with the Fann 35® and ultra-low sheer
One of the challenges impacting the potential use of MFC in the oil and gas industry is due to the industries methods to measure the viscosity and qualify a rheological additive suspending capability. In most cases, the industrial standard to measure a rheological modifier suspending ability in a drilling fluid or mud utilizes the Fann Model 35, which can measure the viscosity from a shear rate of 0.24 to 1021 s¯¹. When the viscosity of MFC is compared to typical hydrocolloids (HEC, CMC, guar, and xanthan) at a low shear rate, there is a clear performance differentiation between HEC, CMC, and guar as compared to BioDrill RX as seen in Graph 1.
On the other hand, the performance differentiation between xanthan and MFC is not clear at the shear rate of 0.1 s¯¹, as seen in the red box. Furthermore, drilling a well is a stop and go process. The fluids in the well bore may experience static periods for an extended time. Therefore, is determining the suspending ability of a rheological additive utilizing the Fann 35 indictive of how the fluids are behaving in the field at rest or near static conditions? Can an alternative instrument be used to provide viscosity values at a lower shear rate more representative of fluids at rest or closer to static conditions?
Graph 1. Graphical depiction of the measured viscosity of BioDrill RX (MFC) as compared to xanthan, HEC, CMC, and guar from a shear reate of 0.1 to 100 s¯¹
Why measuring viscosity at ultra-low sheer is important
Due to the sensitivity of the rheometer to measure the viscosity at ultra-low shear (0.0001 s¯¹) as compared to the Fann 35 (0.24 s¯¹), a more realistic understanding can be obtained of how a rheological modifier is performing in the field at rest or closer to static conditions. Therefore, when a flow sweep from 1000.0 to 0.0001 s¯¹ is obtained with the rheometer of a 0.28wt.% solution of xanthan and BioDrill RX in 3.5% NaCl, a significant differentiation in performance can be observed as seen in Graph 2.
In this case, at an ultra-low shear rate of 0.0001 s¯¹ or closer to static conditions, BioDrill RX and xanthan have a measured viscosity of 2182300.0 and 175596.0 cP. Therefore, by lowering the shear rate from 0.1 s¯¹ by utilizing the rheometer to 0.0001 s¯¹, the measured viscosity of BioDrill RX was 124 x the magnitude of xanthan. Now there is an observed performance differentiation showing the superior suspending capability of solids, cuttings, and proppant of BioDrill RX as compared to xanthan under static conditions and closer to rest.
Graph 2. Flow viscosity sweep of BioDrill RX and xanthan from a shear rate of 0.0001 to 1000 s¯¹
Microfibrillated Cellulose's superior suspending capability
In some cases, the industrial standard (Fann 35) doesn’t always depict the entire performance profile of a rheological additive due to the instruments inability to measure the viscosity at a low enough shear rate. Therefore, in the case of MFC, another instrument should be utilized to evaluate the rheological additives benefit to suspending particles, cuttings, fines, and proppant due to the instruments ability to measure the viscosity at ultra-low shear (0.0001 s¯¹), which is more indicative of static conditions than the minimal shear rate of 0.24 s¯¹ provided by the Fann 35.
If you haven’t utilized the rheometer or another instrument to evaluate MFC’s unique physical properties, superior shear-thinning ability as well as suspending capability in high water cuts, it is recommended that you obtain a sample and compare BioDrill RX performance characteristics to many other hydrocolloids in the market at ultra-low shear. Addition of BioDrill RX to your next drilling mud may prevent your team’s next blow-out or shutdown by maintaining the hydrostatic pressure.