Research On Two-component Ester Drilling Fluids For Ice Drilling In Polar Region

The scientific expedition in Polar Regions has not only the major scientific significance but also the profound and lasting politic meaning. China scientific expeditions in the Antarctica and Arctica have achieved significant success. The China Dome A deep ice coring scientific engineering get the great progress in the south east of Antarctica. It stands out as one of the notable landmarks in the development of the polar exploration engineering in China. Three ice cores with the length of3.83m,3.57m and3.59m were retrieved and the drilling depth reached134.0m. A project titled “Non‐pipe core drilling equipment for subglacial bedrock in Polar Regions” is being conducted by Polar Research Center at Jilin University, which is funded by the National Natural Science Foundation of China (NSFC). One of the aims of the project is to develop the suitable equipment for subglacial bedrock drilling in the Dome A region.Drilling fluid of deep ice core drilling plays an important role to ensure the smooth work of the drill rig. The two main purposes for the use of drilling fluid are: firstly, the presence of a density‐balanced fluid in the hole prevents the hole from closure through viscoplastic deformation. Secondly, a circulating fluid in the borehole can sweep chips away from the drill head. Three types of borehole fluids have been used in deep ice core drilling:(i) two‐component petroleum base fluids;(ii) alcohol compounds; and (iii) ester compounds. Not all of them are qualified as intelligent choices from the view of physical properties, safety, environmental and other technological standpoints. The search for a new environmental‐friendly drilling fluid for coring in Antarctica is still one of the most pressing problems of future drilling projects.Density and viscosity are two of the most important drilling fluid properties that should be considered. Density and corresponding hydrostatic pressure of the fluid column should be sufficient to prevent closure of the borehole. Viscosity of the fluid influences the travel time of the drill string, winching power requirements and, finally, the total time of drilling. The proposed method in this dissertation presents a method to choose the proper fluid density and the fluid level below the surface for the concrete drilling site and to ensure an accident‐free drilling in ice sheets. For example, if the pressure equilibrium is decided at the depth of2500m (this is quite reasonable for deep holes with target depth in the range of3000‐3200m), the desirable average density of the drilling fluid should be9314kg/m3, assuming that the fluid level is maintained at the depth of70‐90m. The required viscosity can be considered as low as20‐25mm2s‐1.It is probable that the new stage of ice drilling fluid technology evolution will develop with the introductions of ESTISOL and low molecular fatty acid esters, which are declared as non‐hazardous substances. Linear density‐temperature relationship of ESTISOL esters is obtained according to the experimental results of this dissertation. The results show that the density of ESTISOL140is equal to the ice density at temperature of–40.5℃. Therefore it is almost sufficiently dense by itself to compensate for ice‐overburden pressure, but to provide a long‐term stability of the borehole walls in some cases, ESTISOL165or ESTISOL F2887in small quantities (2‐6%) could be used as an densifier for ESTISOL140‐based drilling fluid. ESTISOL140is totally miscible with ESTISOL165or ESTISOL F2887, and the density‐temperature relationship is also linear. Viscosity of single ESTISOL140ester is7.65mm2s‐1at‐30℃and25.59mm2s‐1at‐50℃. Single ESTISOL165and F2887esters have much higher viscosity compared with ESTISOL140, but the addition of these esters to ESTISOL140hardly effects the viscosity of two‐component mixture. Viscosities of single ESTISOL140, two‐component fluids ESTISOL140‐ESTISOL165or ESTISOL140‐ESTISOL F2887are reasonable at borehole temperatures down to‐30℃～‐40℃. At lower temperature, ESTISOL140based fluids have relatively high viscosity that may influence the travel time of the drill and therefore the total drilling time.Low molecular fatty acid esters such as ethyl butyrate, n‐propyl propionate, n‐butyl butyrate, n‐amyl butyrate, and hexyl acetate can also be used as single or two‐component drilling fluid. It is observed in this dissertation that at the temperature ranging from‐30℃to‐50℃, the density of two‐component drilling fluid based on low molecular fatty acid esters can be adjusted within the range of910‐938kg/m3according to demands. Both the single low molecular fatty acid ester and the corresponding two components drilling fluid have a low viscosity (less than16mm2s‐1at temperatures down to‐60℃) and can meet the demand as a drilling fluid for deep ice core drilling. More detailed researches regarding health and environmental hazard, electrical resistivity properties, reaction with materials that used in drills (especially elastomers), etc. should be carried out in order to prove the possibility of these materials applied in drilling operations. The drilling fluids for Polar Regions are studied deeply domestic and overseas. The topic in this dissertation is studied on the base of general theory and experimental method. Its results will provide the reference and support for the following research work.