DRILLING CONSIDERATIONS FOR CHARACTERIZATION EFFORT OF CO2 GEOLOGICAL STORAGE

Storing CO₂ into a suitable underground geological formation is considered the most effective way for a safe and definitive CO₂ sequestration. This interdisciplinary and environmental-related topic holds broad prospects and it was believed with great potential for the global capacity to store CO₂ in the underground. So far, a large amount of information and experience were gained for the CO₂ injection and storage from the existing CO2-related projects application. While rare research/technical attention was drawn on the concerns when drilling the well used for geological storage of CO₂ (Class VI well). In this paper, the PRRC inputs the efforts on several critical considerations when conducting the well design and drilling scenario, aiming to clarify some uncertainties and provide reliable support on San Juan Basin CarbonSAFE Phase III Project.

Drilling fluids are added to the wellbore to facilitate the drilling process with multi-functions. Selecting the proper drilling fluid is critical to the success of the CO₂ injection/monitor well drilling operation. Typically, the oil-based mud (OBMs) has an extensive application with high drilling rates and good borehole integrity maintenance. While research and investigation had been conducted and proved that the OBMs are not a good candidate for Class VI well with several drawbacks. First, compared to the water-based mud (WBMs), the OBMs can change the rock wettability to oil-wet, and reduce the drilling invasion zone permeability thus causing severe formation damage and a reduction to injectivity. These and other properties together with techniques such as Pneumatic Percussion Drilling (PPD) are also discussed.

Another consideration when drilling a Class VI well is the logging tool/method selection for the formation test. Normally the drill stem test (DST) will be conducted to acquire the reservoir pressure, the fluid samples, and other reservoir properties such as permeability, productivity, etc. While facing the challenges from the regulation and technical side, the Modulus Dynamic Tester (MDT) from Schlumberger is an excellent game-changer with extra functions armed. Properties in relation to CO2 class VI wells are detailed in this study. Other factors emphasized are Fiber optics and vertical seismic profiles (VSP) as data acquisition techniques.