New Generation Nano Technology Drilling Fluids Application Associated to Geomechanic Best Practices: Field Trial Record in Bahia - Brazil
Authors: Barroso A. L. , Marcelino C. P. , Leal A. B. , Odum D. M. , Lucena C. , Masculo M. , Castro F. 
Published: April 2018

Abstract
A Brazilian Client drilling in the Reconcavo Basin, drilling the 12 ¼" interval of the 1-UR-2-BA well, which presented challenges due a fresh water zone near the surface and an unstable shale section below the sandstone formation. An important choice to ensure success would be selecting a drilling fluid specifically designed without chlorides so that the freshwater zone being drilled would not risk contamination, provide adequate shale inhibition as well as characteristics to provide optimum drilling performance. Nano-Fluids can be produced by adding Nano-sized particles in low volumetric fractions to a fluid providing enhanced properties. In relation to the geomechanical effect, the fracture formations, such as the Pojuca, Maracangalha and Candeias, there is potential to drill unstable shale formations with rich deep clay, that have an affect on the drilling fluids, even with synthetic based muds. The fluid penetration may cause collapse of the rock during drilling, particularly affected by time lapse. A very challenging field trial was performed drilling more than 1300m of 12 ¼″ hole to 1830m with a new generation water base fluid based on Nanotechnology. The field data captured showed additionaly benefits with this trial when compared with the field data captured of SBM which is historically used in this area: drilling faster with lower pressure loss, Easier and more economical, as well as much more environmentally friendly. The NanoFluid, without chlorides, presented excellent performance while drilling reactive shale formations. Low drilling torque values captured the evidence that the fluids had good lubricity in the field as was observed in the lab. The drill cuttings on the shakers ran freely over the shakers screens, dried inside indicating a good level of shale inhibition, which was confirmed by fluid analysis. After drilling out at 1324m with Nano Fluid System through the Pojuca formation, while tripping caving associated to mechanical instability was observed possiblydue to dehydration, osmosis effect and under-balanced fluid density. A Geomechanic study, that included the rock & fluid interaction effect on collapse pressure with exposure time was developed. Recently, a 2nd 12 ¼″ interval was drilled on a different well, reusing the Nano Fluid utilized on a previous well then stored in the Mud Plant for 100 days, and it showed a good performance while drilling, tripping, and running in the hole with casing as well as performing cement job, breaking a paradigm about reuse of water base mud. The potential to reuse the Nano Fluid from well to well could have a significant impact in reducing the overall well cost in the wells drilled utilizing this fluid. Additional benefit related to fluid reservoir characterization was highlighted by geologists. Recent investigations as presented by Mortatha Saadoon Al-Yasiri & WaleedTareq AlSallami (2015) have demonstrated that Nano-Fluids have engaging features for applications where mechanical stability control is of interest. For a better understanding before the application a careful analysis of Recôncavo Baiano typical formations was conducted. For this, the shales were characterized by CEC, XRF, XRD and LSM. Drilling oil and gas wells with Nano Technology Drilling Fluids System represents a major shift for the Industry.