Smart Well Design aligned with Geological Objectives to Deliver Value and Cost Efficiency

Abstract A good well design is essential for any drilling project where the primary objective is to deliver value for the entire life-cycle of the well. It becomes imperative that Geological objectives are considered in the design phase to ensure that targets will be achieved optimally with minimum challenges and the lowest financial impact. This paper describes an approach followed by the drilling team to design a deep gas well to maximize the efficiency of drilling operations. The drilling team analyzed the short-term and long-term objectives of the well and utilizing in-house developed software tools addressed all the associated challenges. The biggest challenge facing the team was a tight, flow-capable zone, which would be combined with the reservoir section in the same hole. Through the use of heat maps, flow risk was determined, and an appropriate drilling fluid density was selected. Moreover, drilling several zones of the same size without running a liner provided flexibility in terms of side-tracking and yielded immense cost savings. Deviating from a typical well profile, the team developed a design that offered flexibility while maintaining cost efficiency. The main requirement from the Geological team was to drill a pilot hole and then decide either to do a small nudge away from the mother-bore, termed ‘twinning the well’, or to perform a full side-track away from the mother-bore based on log results. Drilling of this well commenced with a typical slim-bore design, with one exception that two known reservoir intervals were combined in one section without running a 7-in liner that separates both. The liner would have to be milled in order to side-track the well, which would have a huge time and cost impact; however, with optimized engineering design, this was not required. This section also contained the unpredictable tight flow zone that could jeopardize the project if encountered. However, with a thorough risk assessment and control measures in place, drilling operations were concluded successfully. Well was side-tracked from the open hole after placing two cement plugs and using open hole whip-stock, and in the subsequent lateral, the two reservoir sections were isolated from each other with a 7-in liner, which also covered a high-pressure water layer just above the production interval. State-of-the-art data analysis and visualization tools helped to identify and mitigate risks associated with combining two reservoir sections, which also contained a tight, unpredictable flow zone. In addition, with a novel approach to well design, the requirement of milling a 7-in liner in order to side-track the well was eliminated, which led to significant time and cost savings. All the Geological objectives were achieved successfully, thereby validating the smart approach to well design.