Increasing the temperature stability of environmentally friendly drilling and completion fluids based on organic brine.

Abstract

Formates provide an already superior system, designed to complement synthetic polymers and extend their temperature capabilities as drilling fluids. However, as HPHT drilling continues to move into more harsh environments with expected bottom-hole temperatures of over 300°C; further research is required to improve the temperature ceiling of eco-friendly formate drilling fluids. The overall aim of the project was to develop a well construction fluid capable of withstanding ultra and possibly extreme HPHT temperature measures. As a result of this research, a measured combination of polyglycol sacrificial agent and MagOx has been found to inhibit the degradation of xanthan gum in formate brine so it remains stable after 16 hours dynamic ageing at 200ºC without the use of any synthetic materials. However; a formate system comprised of xanthan gum and synthetic HE® polymer was proven to function incredibly well at ultra-HPHT temperatures in excess of 250ºC for >64 hours. Thus, through utilization of improved HPHT testing equipment, it is hypothesized that the formate system and HE® polymers will remain stable in extreme HPHT circumstances i.e. over 260ºC. Further, there has been some dissimilarity to the literature with regards to the solubility of biopolymers in formate solutions where it has been discovered that viscosity actually increases with even less water available for hydration. It was found that the highly alkaline environment and/or buffer effect was inhibiting viscous characteristics and not the extreme concentration of salts dissolved in formate solution. The present study has also confirmed that; the order of stabilizing effects of individual cations in formate solutions generally follows the Hofmeister series of cations; Li+, Cs+, Na+, K+ with the response becoming more pronounced at higher salt concentrations. Thus, increased temperature stability of polymers and other additives can easily be achieved through simple manipulation of the formate base brine. Additionally, a significant increase in xanthan Tm of 177ºC in 2.20g/cm3 caesium formate was measured in the current stock - 20ºC higher than original values recorded for the Formate Manual.