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 impactEffective inhibition capability to drill reactive clay formationsNon-dispersed, low-solids formulation to improve rate of penetration (ROP)Shear-thinning behavior for excellent hole cleaningHigh and low temperature as well as high-pressure stabilityLubricity, 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. Introduction 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.

As wells increase in complexity, new challenges must be addressed in order to produce hydrocarbons in the best way possible. Some wells should be cemented in two stages because of the risks of fracturing the lower zone. Running a long casing string increases the equivalent circulating density (ECD) and also increases the chance of damaging that zone, so running a liner is the best option. Cementing liners in two stages has been performed with conventional liner hangers for some time because of their capability to run an inner string and their capacity for manipulation after the hanger is set. Now, new technologies allow those treatments to be completed with expandable liner hangers (ELH). The ELH provides a premium liner top seal (Williford, Smith, 2007) and excellent tensile capabilities. They also help to improve the cement bond by allowing the movement of the string while the cement is being pumped in place. ELHs have proven to be a reliable tool (Jimenez, C., et al., 2009), and every year their popularity increases tremendously. This paper discusses the first true two-stage cement job with an ELH performed in Kazakhstan. The use of the ELH helped the operator reach total depth (TD), cement the two zones without issues, and create a premium barrier at the top of the liner.

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