In early 2007 Exxon Neftegas entered the record books when it completed the design, engineering and construction of the extended-reach Z-11 well in the Sakhalin-1 project, based on Sakhalin Island off the east coast of Russia. It is the longest well of its type in the world, and it reaches a total depth of 11,282m. The well includes three offshore fields – Chayvo, Odoptu and Arkutun Dagi. It has potential recoverable resources of 2.3 billion barrels of oil and 485 billion cubic metres of gas.
Sakhalin-1 is operated by Exxon Neftegas, a subsidiary of Exxon Mobil, with a 30% interest, on behalf of the Japanese consortium Sakhalin Oil and Gas Development Co, which has another 30% ownership, ONGC Videsh, the Indian state-owned oil company, which has a 20% share, and affiliates of Rosneft, the Russian state-owned oil company, RN-Astra (8.5%) and Sakhalinmorneftegas-Shelf (11.5%). Exxon Neftegas has worked to minimise the environmental impact of its Sakhalin-1 infrastructure.
Using extended reach drilling (ERD) – which allows the project to reduce its offshore operations by exploiting remote reservoirs from a central area, in most cases onshore – Exxon has brought down costs and reduced environmental concerns.
The high capital and operating costs associated with building, installing and maintaining large offshore structures has been reduced, while sensitive inshore areas and marine communities essential to Russia's economy are protected.
Chayvo was the first field to be exploited in Sakhalin-1. Located between five and seven miles offshore, the field came on stream in October 2005. Initial production of up to 50,000 barrels of oil per day was fed into Russia's Far East domestic market infrastructure until the project's export system was fully commissioned. Production of natural gas, averaging 60 million cubic feet per day, began at Chayvo shortly thereafter. Chayvo is being developed from both onshore and offshore facilities.
The Chayvo Yastreb land rig, launched in June 2002, was engineered and constructed especially for Sakhalin-1. Like the project itself, its existence was no mean feat. Yastreb is one of the largest and most powerful land rigs in the industry. It was specifically designed to create extended-reach drilling wells to offshore targets from land-based locations.
ENGINEERING DOWN THE COST
Sakhalin-1’s well Z-11, the 17th extended-reach producing well to be finished in the project, was drilled in just 61 days – 15 days ahead of schedule. Gradual improvements in the way the drill crew carried out operations helped bring down costs and ensure that there were no significnt safety or environmental incidents.
According to ExxonMobil, since the first Sakhalin-1 well was drilled in 2003, the time required to drill these wells has been reduced by more than 50%. Compared with industry benchmarks, Sakhalin-1 wells are the fastest-drilled extended-reach wells in the world.
The improvements in the speed of drilling the wells followed intense research work carried out by ExxonMobil’s project team. It developed a number of proprietary technologies to deliver the Z-11 well, including Exxon's integrated hole-quality (IHQ) technology and its Fast Drill process.
President of ExxonMobil upstream research, Steve Cassiani, says: "The physics-based modelling and experimental validations of our IHQ technology allowed us to successfully design and drill the Z-11.
"With this technology we were able to take into account a broad range of interdependent design variables, including rock strengths, stresses and wellbore hydraulics, to successfully drill this well."
In conjunction with IHQ technology Exxon used the optimization process called Fast Drill. This energy-based analysis tool allows rig site and drilling engineering personnel to maximise performance when drilling. A fundamental component of this drilling system is the Baker Hughes company INTEQ’s AutoTrak G3.0 rotary steerable system. AutoTrak is essentially a rotary closed-loop drilling system that integrates drilling and measurement-while-drilling / logging-while-drilling information to provide precise directional control, while allowing continuous drill string rotation. This improves performance and hole quality in directional wells, especially in geosteering, by minimising the possibility of stuck pipe.
The second drilling front is centred on the Orlan offshore platform, on the south-western flank of the main Chayvo zone. To maximize drilling space on Orlan, minimal integral processing facilities were constructed offshore. The well stream is exported to the onshore processing facility, where it joins the Chayvo stream. This facility is designed to produce at the rate of approximately 250kb/d and 22.4 million cubic metres of gas.
The stabilised crude oil is shipped to the newly constructed DeKastri terminal in the Khabarovsk Krai terminal for export, while the natural gas is supplied to the Russian Far East or injected back into Chayvo for reservoir support.
A large crude oil export system was commissioned in August 2006 to transport crude from this onshore processing facility across Sakhalin Island and the Tatar Strait to DeKastri. This was based on a 24in, 225km pipeline to the Chayvo onshore processing
Meanwhile, gas deliveries to Khabarovsk Krai totalled 1 billion cubic metres through February 2007. These gas supplies are expected to satisfy demand until 2025. The Chayvo field overall reached its peak production rate of 250kb/d in February 2007.