As oil reserves mature around the world, oil companies are focusing more attention to methods of improving the recovery of existing assets and tapping into unconventional reserves, such as gas shale, tight gas, etc. There has been a natural progression to larger sizes and premium material grades of coiled tubing (CT) and jointed tubing (JT) to adapt to these new and extended applications. However, situationsexist, such as in long horizontal or ultradeep wells, where either the CT or JT is unable to provide the required reach efficiently and safely. The JT is stronger but is limited to the stroke of the hydraulic jack, whereas CT has twisting and buckling issues on extended-reach wells. This paper presents details on a novel concept of combining CT and JT into a hybrid string to attain the speed and efficiency of CT and rigidity of JT.
This simple-sounding concept required significant modification to surface equipment and the development of new downhole tools to create a field-deployable system. One key piece of technology was a safety valve required at the CT/JT junction to be able to make or break the connection while isolating the well pressure. A safety valve was designed, built, tested, and deployed in the field that isolated the flapper mechanism from the flow pathand provided remote-activation capability between blowout preventers (BOPs) and bubble-leak well-pressure isolation.
A second newly designed safety valve was developed for the bottomhole assembly (BHA)that provided well isolation during trip in and trip out. Several modifications to the hydraulic workover (HWO) unit and CT unit were made that enhanced their operation and safety.
This paper presents details of equipment modifications, tool development, and case histories where the technology was applied.
Most conventional reservoirs are either sandstone or carbonate formations with high porosity and permeability, which allow a good flow of hydrocarbons and do not require large-scale stimulation treatment. Shale formations have always been known to carry hydrocarbons and have been known as more of a source rock for conventional reservoirs. Unconventional reservoirs, such as shale, usually have permeability in the microdarcy range and have always been thought to be uneconomical to produce. These reservoirs are divided into the following categories:
• Tight sand.
• Shale gas.
• Coalbed methane (CBM).
Shale reservoirs are abundant around the world in countries such as the USA, Russia, France, Poland, and Argentina, and a large number are known to be producible. Until now, production of these shales was thought to be uneconomical because of gaps in available technology. However, technological advancement in horizontal drilling and multistage fracturing hastotally changed the economics of unconventional reservoirs. Wells in excess of 10,000-ft long horizontal sections and stimulation treatments exceeding 30 stages are becoming common. Formationsonce deemed uneconomical are now producing with increased service intensity and longer laterals. There is a global rush for both the service and production companies to tap into unconventional reservoirs. This has led to the development of several new tools and processes. This paper presents details on a new method of completing horizontal wells using a CT/JT combination and multistage fracturing process that has redefined well-intervention techniques. Successful case histories of field deployment are also presented.
