Deepwater drilling presents significant issues and uncertainties, especially when there is no prior drilling experience in country or only limited offset information is available. Uncertainties about the drilling conditions create additional risk to operators and can cause project budget increases. Therefore, innovative technologies are often implemented to help ensure that the well is drilled efficiently and safely, operators obtain well data and important geological data that can help identify potential reservoirs and wells in the area. Petrobras Colombia undertook the challenge of drilling the first deepwater well in Tayrona BLock located in the Colombian Caribbean, in approximately 1,840 ft water depth. Drilling fluid selection was a key decision to the success of the project due to the nature of the exploratory project, formation uncertainty, environmental footprint, wellbore stability and protecting any potential reservoirs.
A high-performance water-based fluid (HPWBF) was selected to drill the well based on the following criteria;
The ability to discharge to the sea without environmental impact
Effective inhibition capability to drill reactive clay formations
Non-dispersed, low-solids formulation to improve rate of penetration (ROP)
Shear-thinning behavior for excellent hole cleaning
High and low temperature as well as high-pressure stability
Lubricity, wellbore stability and low equivalent circulating density (ECD) values.
The HPWBF provided excellent performance as demonstrated by trouble-free trips, casing, cementing and wireline logging operations. Rheological properties remained stable during changes in temperature and pressure, confirming reliable fluid stability and reducing costs associated with non productive time (NPT).
Although the inhibition provided by the fluid system was excellent, the wellbore exhibited some mechanical instability related to stress distribution. No bit balling problems were observed and ROP was acceptable most of the time. Wiper trips required less time than expected and did not present any issues. In conclusion, the HPWBF demonstrated excellent performance in all aspects and contributed to the overall project success in obtaining important formation data, minimizing NPT and reducing costs related to fluid and cuttings disposal.
Deepwater exploration activity in the oil and gas industry continues to present new hurdles requiring innovative technical solutions. These difficult wells can increase the risk factor and result in potentially higher operational costs. In most cases an oil-base drilling fluid is selected as the first option in light of the high daily costs associated with a deepwater operation, and the advantages gained in wellbore stability and ROPs compared to conventional water-based systems. However, tightening environmental regulations and high costs associated with cuttings and oily fluid disposal is sufficient to seek viable water base fluid alternatives that could yet provide an oil base drilling fluid performance.
For this reason, drilling fluid companies constantly investigate and design state-of-the-art water based drilling fluid systems that can provide performance similar to an oil-based fluid but can be discharged directly to the sea with a reduced environmental footprint.