Drilling for oil and gas requires sensitive viscosity instrumentation, especially at low-shear rates, to insure that production is optimized. Field viscosity measurements on drilling and fracturing fluids are required to predict flow performance under the extremely low shear conditions applicable to solids transport down hole. Brookfield's LVDV-II+ PRO Viscometer provides sensitive, low-shear rate viscosity (LSRV) measurements and is rapidly becoming the instrument of choice when oil/gas service companies need to verify performance of expensive fracturing fluids and drilling muds immediately prior to use.
For analyzing drilling fluid rheological properties in the field, Brookfield's LVDV-II+ PRO Viscometer used with the LV-1 cylindrical spindle or Small Sample Adapter with SC4-18 spindle provides the complete solution for LSRV measurement under a variety of tough field conditions.
* While a particular model/version may be used as an example in this method, any current or past model/version from the same series may also be used. Please consult a sales associate to discuss the most current instrumentation and software available.
Having chosen one of the spindle geometries mentioned above in Required Equipment, the procedure involves running a test at two or more different rotational speeds. The objective is to run at a very low speed between°.01 and°.1 rpm and a second rotational speed between 1.0 and 6.0 rpm. These speeds would generally equate to shear rates below°.1 sec-1 and 10 sec-1 respectively. If the instrument has sufficient viscosity measurement range, a higher speed test at 200 rpm can also be considered.
On tests run by a field service company on three different fracturing fluids, the following values were obtained:
|Shear Rate||Fluid A (cP)||Fluid B (cP)||Fluid C (cP)|
The above values show that the three different fluids would exhibit very similar viscosity behavior at shear rates around 5.11 sec-1 and higher, but drastically different viscosity values at the lower shear rate of°.06 sec-1. In order to suspend particles down hole, the higher viscosity value at very low shear rate is important; therefore, Fluid B is a much better solution for the application.
A more detailed test can be created using Brookfield's Wingather™ software which provides automatic data collection. In addition, the software will calculate yield point and plastic viscosity by using the appropriate mathematical model which is included in the software.
Higher shear rate measurements can be made if appropriate. The Brookfield LVDV-II+ PRO Viscometer with SC4-18 spindle is capable of measuring shear rates up to 333 sec-1. The Brookfield PVS Rheometer can measure up to and beyond 511 sec-1 with the sample pressurized up to 1000 psi. For making measurements at low shear rates under pressurized conditions, please refer to Brookfield Application, Oil/Gas Exploration and Drilling.