The vast number of wells and unique operating conditions in Alaska's Prudhoe Bay field have presented many opportunities for those involved in remedial wellwork. Among the technologies that have either been pioneered, tested, or applied there, coiled tubing (CT) ranks as one of the most long lasting and widely used. This paper highlights the more recent applications of CT in the field. The paper begins with a brief overview of the Prudhoe Bay Unit's (PBU) CT wellwork program and then follows with discussions on eight CT applications that have been developed or expanded in the last two years. Some are new technology and others are old techniques with a new design. Descriptions and procedures ate given for each in addition to performance results thus far.
The Prudhoe Bay Field contains approximately 1,200 wells which produce over 900,000 barrels of oil per day. Along with this large oil rate, 1.2 million barrels of water and 7.5 billion cubic feet of gas are produced each day. As water processing costs are very high and gas is currently not marketed from the North Slope, the search for reliable water and gas shut-off techniques is never ending.
In the continual effort to optimize oil production, PBU wellwork has become a major program. Many tools and technologies have been used over the years in the program, but CT has risen to be one of the most significant pieces of it because of its versatility, capabilities, and cost effectiveness. Typical CT remedial operations cost 5% to 15% of conventional rig options. The large wellwork program and its diverse challenges have provided countless opportunities for CT technology. Many of these advancements have been presented in past papers. As the field ages, wellwork becomes more and more challenging which requires continual improvement in technology to keep pace. This paper highlights the most recent advancements and applications of CT in remedial work.
The CT program on the North Slope has grown to be one of the largest in the world. Between the two operators of the nine fields there, 8 coiled tubing units (CTU) are contracted to run on a near daily basis. Two service companies maintain and operate these units and provide critical expertise. In PBU alone, over 1000 CTU operating days are spent on some 600 wellwork jobs striving to keep wells operating efficiently and oil production at a maximum.
Applications. There are many applications of CT in the wellwork program at PBU. They range from simple nitrogen lifts to complex remedial completions. Below are the major categories of applications and many of the associated jobs performed.
Reservoir Surveillance - Memory surveys and CT electric line logs of all types
Capacity Sustainment - Stimulations, perforating, fill clean-outs, nitrogen lifts.
Gas & Water Shut-offs - Cement and chemical squeezes, mechanical and inflatable plugs, mechanical straddles.
Injection Control - Profile modifications with cement, chemicals, and mechanical devices.
Mechanical Repairs - Tubing patches & straddles, cement packer repairs, liner repairs, etc.
Miscellaneous - Fishing, ECP's, velocity strings, etc.
Prior to the technological advancements of CT, many of these jobs could not have been performed in certain wells or would have been left for a rig workover (RWO). Now, these jobs are often routine events due to the ever expanding use of CT.
Technologies. With the variety of CT wellwork being performed naturally comes a variety of associated technologies. Some of the more prominent ones that are advancing the applications of CT are: