The push is on to reduce well construction costs as we enter the new century. This is not news. But some recent initiatives by the oil companies and the US government bear watching.
At the beginning of 1999, Shell Expro introduced a concept called Deliver the Limit (DTL). It was a comprehensive philosophy that embodied planning, defining the well's ideal technical system or limit, design review and analysis. Shell Expro coined the phrase Technical Limit Times to describe the discrete hundred or so tasks required to construct a wellbore. The key to a step change in performance was the early involvement of the drilling contractor and service subcontractors who together embraced the DTL concept.
The first implementation of the DTL approach was carried out on the Goldeneye prospect appraisal well in the UK Continental Shelf. A breakthrough in performance was achieved. The Transocean John Shaw drilled the well in 21.6 days against an original application for expenditure time of 35 days. The technical limit set by the team was 15 days. The final well cost was about US $5 million (£3 million) vs. a $7.4 million (£4.5 million) budget. The results indicate significant improvements are available with sufficient time and resources for planning and preparation, an enabling environment and the offshore team's true "can-do" attitude.
World-class step change
BP Amoco's Valhall field on Norway's continental shelf required drilling of extended-reach wells that typically experienced unacceptable trouble costs of 35% to 50%.
BP Amoco organized a select group of service suppliers into an aligned team that really made a difference. Drilling difficulties included subsidence; disproportionate overburden to reservoir pressure differential due to reservoir depletion; gas-charged overburden zones; circulation losses; fracturing; extensive faulting, including active faults severing pipe and transmitting pressure through the overburden; and platform rig equipment being repeatedly pushed to the limit.
A primary service provider established for each major section of the program worked closely with other service companies, the rig contractor and company personnel. The team members accepted responsibility for delivering discrete aspects of the well and learned to interact directly. Slot recovery was completed in 18 days instead of 29 days. The extended-reach well concluded 31 days (30%) ahead of past performance.
Novel sand screen completion
Shell Petroleum Development Co. in Nigeria has optimized horizontal well economics by employing expandable sand screen/liner (ESS) technology. One thousand feet of ESS was installed in a horizontal well in Shell's Nigeria operation. This approach delivers the optimum drain hole from a slimmer well with downhole equipment that needs minimal re-entries and remedial work, resulting in increased productivity, reduced well construction costs and lower operating costs.
Shell representatives in Nigeria expect to improve production 60% in the short term and more than 200% to 2.5 million b/d of oil by 2010. Most new wells are completed horizontally with production rates on the order of 3,000 b/d of oil. The application of ESS in these types of wells is a challenge. There had been about only four installations in wells up to 60° deviation and maximum deployed length of about 240ft. More details are available in SPE/IADC Paper No. 59142.
Advanced gas drilling research
The US Department of Energy (DOE) has long been a supporter of advanced drilling research. Examples of successes from past programs include development of the near-bit sensor, carbon dioxide/sand fracturing stimulation and air motors, which are used for most new wells drilled in eastern US gas formations.
Strategic investments in "zero footprint" drilling, rigless drilling, self-drilling well technology, designer stimulation treatments and single-well drainage capabilities are part of the forward plan.
Drilling rig time is a prime target, and programs that address drilling efficiency are funded to reduce rig equipment failures, extend drill bit life and reach the target zone with minimum number of course corrections.
Deep gas drilling efforts in hard rock formations pose challenges. The most efficient strategy is to focus on the brittle nature of the rock itself. When hit or hammered, this type of rock will break into large chips. This turns out to be a more effective strategy than crushing or grinding using roller cone bits. Other formations are sensitive to the type of drilling fluid used, and in these cases it's best to use air.
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