In this paper, we present a thorough analysis of drilling methods and fluid and mechanical solutions to mitigate lost circulation (LC), as well as risk control measures undertaken, while drilling 5 wells on two platforms with severe LC zones in the reservoir. The drilling rate of penetration (ROP) was significantly reduced compared to the ROP utilized in the sections above the reservoir, along with the pump rate, to minimize enhancing fractures in a highly permeable zone. A combination of bridging, cement and resin based materials were also used in the 5 wells to mitigate and partially/fully cure losses. Risk control measures included only having a maximum of two rigs drilling in the reservoir section at the same time, rig capacities to sustain bad weather without support from boats, each rig in the vicinity having barite, lost circulation materials (LCM), and other resin based LCM materials available and having cement retainers (CRs) on standby and using them not only when curing losses but also to secure the well in the event mud/barite/chemicals on the rig could not sustain hole filling during bad weather. Even though the losses were not completely cured in wells B and E, which led to the cessation of drilling operations before reaching the planned total depth, the LC mitigation methods used ensured access to 20 % of the net payzone in well B and 30 % in well E, a significant achievement in such severe LC zones. Evaluation of three fluid solutions used to mitigate losses showed that spotting cement through a cement retainer (CR), set close to the previous casing shoe, gave a higher possibility of curing losses compared to conventional LCM resin based LCM and directly spotting cement on loss zone with open ended drillpipe (OEDP).

No abstract

Drilling offshore gas wells is a very challenging operation since it involves a high number of offshore rigs, mud losses into formation, well control and adverse weather conditions. All of which minimize the drilling efficiency on those wells with huge attendant cost, if no proper arrangement is put in place to mitigate these challenges. In the current setting where we can sometimes see rapid increase in offshore drilling operation challenges such as coping with severe drilling fluid losses into formations, the main challenge is to support offshore rigs with drilling fluid in a timely and seamless manner. As on-shore mud plant keeps up with a very high operational demand, launched and successfully implemented a new floating mud facility ("HUB") to improve supply and deliver mud materials and fluids to offshore drilling rigs. This floating mud and chemicals storage plant (HUB) spot successfully reduced transit times, minimized delays and nonproductive time previously experienced by the drilling rigs operating in offshore gas fields. These delays were due to late drilling fluid deliveries from the onshore mud plant and extended times to mix high-density fluids on the rigs. This innovative model guarantees significant savings in terms of saving mixing times, providing chemical storage capacity, consequently minimizing unnecessary rig site operations. There is also a significant reduction in environmental, health, safety, and risk exposure resulting in optimized shipping, distribution, back loading of drilling fluids, reduction in the utilization of supply vessels and rig resources, to support severe lost circulation or well control events. The HUB floating plant provides a full array of scalable fluids, mixing equipment and facilities to meet offshore operational requirements while eliminating the cost, extended lead-time, and specialized shipping. This plant encompasses a floating installation to mix and store drilling and completion fluids and chemicals. The HUB floating plant is equipped with twin mixing systems with the ability to mix and safely store more than 20,000 bbl of different fluid sets. It was recently utilized to mix high-density MICROMAX (manganese tetroxide) based completion fluid with excellent performance, despite the complexity of mixing over 2,500 metric tons (super-sacks), and still was able to handle different fluids seamlessly. This HUB is anchored within equal distance to the three largest gas fields. The reduction in delivery time is estimated to be 90% in both normal and emergency operations. Weighting materials and mud chemical storage capacity provides an additional platform to minimize rig deck utilization and drilling mud mixing construction capabilities, minimizing the huge coping pressure on the alternative onshore mud plant operations. Over the last 3 years of being in operation, the HUB floating plant has mixed more than 916,000 bbl of heavy mud and completion fluid, received over 19,000 bbl for storage, and stored up to 400,000 ft3 of barite, with more than 600,000 workhours, without any near misses, incidents, or accidents.

After experiencing massive lost circulation in an exploratory well in Colombia, it became necessary to drill without returns and stop the job upon various occasions of waiting for water. Upon completion of the job, water uptake limits were exceeded and various community relation issues were encountered, increasing both operational costs and nonproductive time (NPT). By the next well, the operator decided to develop a strategic plan to drill the well with the same scenario in the same location, but using a comprehensive strategy to help reduce the volume of water uptake while managing community relations and associated costs. The operator achieved a drill section in the well from the surface to 2,800 total ft, without additional water uptake, in less time. The logistical plan was executed in the field successfully, complying with the allowable uptake water permitted by the licensure without exceeding uptake limits. No NPT or health, safety, or environmental (HSE) incidents occurred during operations. No penalties or breaches of licensure were committed. No damage to the environment occurred. The community felt fulfilled that operational management protected its resources and the operator achieved a savings of nearly USD one million compared to the previous well. This strategy allowed analyzing a drilling fluid system alternative involving the use of aerated fluids to improve the operation and minimize the necessity to uptake water. The logistical plan developed helped build structures that currently support the operations of nearby wells, providing operational savings to execute drilling operations in the same area. Using the lessons learned from this operation, the operator successfully drilled two additional wells in the same area, implementing similar strategies (use of aerated fluids system) and complying with outlined environmental regulations. This helped the operator reduce operational costs. All personnel involved during operations were mindful of environmental impact and the importance of compliance with outlined environmental regulations. IntroductionThe Piedemonte área in Colombia is one of the most complex regions for drilling wells globally, wherein unexpected events or issues can often be faced. planning for and anticipation of such activities can help operators achieve optimal operational performance, based on lessons learned, to help minimize the risk of events of the past being repeated this kinds of events has been discussed, facing and solved in other areas with similar formations in Colombia (Delgado et al. 2014). Fig. 1. illustrates a profile of the lithological structure in the Piedemonte area.Considering the particular lithology of this area, is important to briefly describe the following formations.Guayabo Formation. This formation is composed predominantly of mudstone intercalated with irregular beds of sandstone and thin discontinuous layers of sand, conglomeratic sandstone, and minor siltstone interbedded toward the base. The mudstone is soft to moderately consolidated, plastic, sticky, ...