Not Too Hot to Handle: Water Based Fluid Drills High Temperature Wells

Most high temperature (HT) wells are drilled with oil or synthetic-based drilling fluids (O/SBM) for a variety of reasons. These O/SBM drilling fluids are naturally lubricious due to the hydrocarbon continuous phase, which also contributes to improved wellbore stability, as the fluids are relatively inert to the formations being drilled. These fluids also have acceptable temperature stability and drilling performance, which makes them suitable for several applications. Downhole losses with O/SBM can be costly and difficult to cure. Additional O/SBM can be mixed at the rig site, but this requires a supply of base oil to be available and the fluid can take time to prepare. The ideal scenario is to have a facility close to the rig location that can supply the high volumes of premixed O/SBM and base oil required. Exploratory wells are often drilled in remote locations with no convenient liquid mud plant close by to service the O/SBM requirements. Acquisition of good quality logging data from exploratory wells is crucial to understanding the field potential for commercial development. Some of the more sophisticated logging tools available in the industry are incompatible or difficult to run and interpret in an O/SBM environment. In such cases a water based drilling fluid (WBM) can be the solution. The logistic requirement for WBM is significantly lower than for O/SBM, as chemicals can be stored on location and water can be supplied from a nearby water well. WBM is much simpler to prepare than O/SBM, so WBM can be quickly prepared as required, and WBM downhole losses can often be cured more easily. Typical polymer-based WBM does not have high temperature stability, and is usually restricted to wells where the bottomhole temperature is less than 300°F. This paper will discuss the design, testing, and field application of a WBM for HT applications. To design a temperature stable HT-WBM fluid requires the use of drilling chemicals that can function adequately in a harsh environment. These wells required temperature tolerant polymers that provide an acceptable rheological profile and controlled fluid loss, so the wells can be safely drilled with no major complications. The HT-WBM was used to successfully drill, core, log, and case wells with bottomhole temperatures higher than 375°F.