LLC JV Vanyoganneft operates the Vanyogan and Ai-Yogan licenses around 120 km to the northeast of Niznevartovsk in Western Siberia. LLC JV Vanyoganneft is a joint venture between Occidental Petroleum and TNK-BP, each holding 50 percent.
The licenses were awarded to the company in 1993, production having started in 1987 from deep formations in the fields. Vanyogan has many productive formations ranging from the Upper Pokur (PK) through to Jurassic formations. There are currently 54 zones under development, 22 in the PK and Achimov, 11 in the A sands, and 21 in the B and J sands.
Over the past few years, production from all zones at Vanyogan has been at around 2.5 mln t per year. Now the water cut is increasing and efforts are focused on maintaining the production rate and developing the untapped zones in the field. The largest of these are the PK1 and PK2 formations.
Vanyogan PK1-2 Development
The PK1-2 formations at Vanyogan contain significant reserves of heavy, viscous oil. The oil in place in these formations may equal that in place in all the other productive zones at Vanyogan, some of which have been in production since 1987. This year, efforts have increased to develop this resource. Why isn't development of these formations already well under way?
Worldwide experience indicates that the production and processing difficulties of this kind of formation are considerable and that many issues need to be resolved to enable development to be economic. Fortunately, BP has experience of some very similar fields in Alaska and specialists from there have been involved in the technical work that is now being done.
The oil has a density of 0.95 g/cc and its viscosity may exceed 200 cp (the equivalent numbers for more normal crude oil are a gravity of 0.85g/cc with a viscosity less than 10 cp). In the whole Russian Federation, out of a total production in excess of 420 mln t per year only around 2.5 mln t is this heavy. Other areas producing significant volumes of oil of this type are in North and South America, especially Venezuela, California, Canada and Alaska.
These formations are generally quite shallow (900 m at Vanyogan). The high viscosity means that the productivity of the wells is low, requiring long horizontal completions to achieve economic rates. Injection of steam or hot water is often used to reduce the viscosity and increase production. Experience elsewhere indicates that the key to making economic developments with this type of oil is reducing the cost of providing well completions. This requires highly efficient drilling techniques and potentially multilateral wells - where multiple horizontal completions are drilled from a single vertical wellbore.
Completing Appraise Stage
The adverse mobility ratio between the oil and water means that rapid water breakthrough can be expected and this can be a particular problem when injecting water for pressure maintenance. Injection plans may also involve the use of hot water or steam to help reduce the viscosity of the oil and encourage it to flow more easily into the wells. Much of the formations also have a gas cap and gas breakthrough can be a particular problem for production.
There is a likelihood that significant amounts of sand will be produced, so the control of sand at the completion, and tolerance to sand in the downhole pumps and surface facilities is vital to avoid production problems. Experience from other fields shows that produced sand can cause significant production downtime.
The oil is also likely to form stable emulsions or foams once at the surface, requiring the right mix of heat and chemicals to give efficient processing.
These challenges mean that so far, efforts to produce the lower more normal zones have been more rewarding, but the time has come to bring this oil into production.
Last year a short horizontal well was drilled in a good area of the PK2 zone, and this year it has produced at a rate of around 30 tpd. This year GETEK, based at the Gubkin Oil & Gas University in Moscow, prepared a plan for initial pilot production from four more wells in the same area. The first of these additional wells is now being drilled.
A project team is now being set up to move the development of the PK1-2 ahead at a faster pace. In October, a bpSTART workshop was held to begin looking at the options and issues for the full development of the PK1-2. The process will provide the information to complete the planning of the Appraise stage of the development, and submit an Appraise FM to fund the future work. This will align the major project development with CPP.