Coiled Tubing was introduced to the Karachaganak Field in 1997 as part of a package of technical enhancements designed to improve field productivity. Initially planned only for acid stimulation work during the summer, the service has been extended into an all year round support to the Workover, Stimulation and Well Service programs. Examples of the type of operations performed are described. These include tubing cutting, cleaning and acid washing as required to remove tailpipes during workovers. Fishing to clean up old wells prior to the workover. Inflatable packer isolations for acid stimulation and wellhead repairs.
Introducing a new service, such as coiled tubing, to any location, presents an interesting challenge. Developing and applying the techniques within the service, particularly on an established, corrosive, gas/condensate production field with old, high rate, well stock, located in a remote area with extreme weather conditions, challenges the technical application of Engineers, operators and support services.
The Karachaganak field was discovered in 1979 and is located in the Uralsk region of West Kazakhstan (Fig 1). This large gas and condensate field is a micro-fractured carbonate formation; pay height 100 to 600 meters at 4050 to 5250 meters true vertical depth with an oil rim. The structure is sealed with a salt layer that varies in thickness across the field from 10 meters to 4000meters. The field covers an area of 500 square kilometers and contains over 1200 million tonnes (9.4 billion barrels) of oil and condensate and more than 1350 billion cubic meters (48 tcf) of gas. Limited field production commenced in 1984.
The reservoirs are Permian and Carboniferous in age and comprise low permeability limestone and dolomite. The reservoir fluid can be classed as highly corrosive, with high levels of both Carbon Dioxide (7.5%) and Hydrogen Sulfide (5%) see appendix 1 for further details.
Karachaganak Integrated Organisation (KIO) participants are BG International (32.5%) AGIP (32.5%) Texaco (20%) and LUKOIL (15%), operating in Kazakhstan as Karachaganak Petroleum Operating b.v. (KPObv.) under a production sharing agreement since 1995.
A major investment is underway to expand the field production facilities. Planned peak production after 2006 is estimated at 37000 tonnes (290000 bbls) of oil per day and 70 million cubic meters (2.5 bcf) of gas per day. The ability of the operating contractor to provide well stock for this expansion by working over old wells, drilling new wells and stimulating wells, has been enhanced by the introduction and development of coiled tubing techniques to the field well operations.
Initial Coiled Tubing Services
Well Operations requirements for the field can be split into four key components:-
Well preparation for workover
Workover and completion
In the next few years vertical and horizontal deepening of existing wells and new well drilling are programmed. The utilization of coiled tubing will increase still further (Fig. 2).
A single 1¼" coiled tubing unit was introduced to the field operations in 1996. This was part of an overall technology improvement programme agreed within the contract with the operator. Coiled tubing was identified as a means to increase production through stimulation improvements, mainly by washing the perforations with Hydrochloric Acid and removing drilling and workover damage. Field operations are limited by extremes in temperature (+40C in summer -40C in winter), site access to wells, logistics and technical support. In view of this the initial stimulation work was carried out in the form of a summer campaign.
The scope of the initial coiled tubing services was designed to support only the stimulation component of the well operations requirements.