Abstract
Coiled tubing (CT) services in India are positioned as highly tailored services with operations such as cleanout, nitrogen kickoff, and matrix stimulation in vertical or slightly deviated well. With the advent of horizontal wells in India, the scope of CT applications has increased considerably, especially for multistage fracturing in tight reservoirs.
This paper deals with well performance optimization in a tight gas reservoir in the Cambay basin situated along the western coast of India. Most of the reservoirs in the basin are very low permeability, and hydraulic fracturing may be the only way to achieve economic production from the reservoirs in most cases. The successful execution implied tapping into the unconventional gas reservoirs in India, which are expected to account for 75% of gas production in India by 2035. The plan was to fracture stimulate eight zones in four stages and later mill the isolation plugs to put the well into production from all eight zones. An innovative perforation technique of using dual firing head guns—an electronic firing head and circulation ball drop-activated firing (CBF)—in the same run to selectively perforate two clusters was used.
The presence of gas in the CT-tubing annulus while perforating the upper formations and the adequate isolation through the flow-through plug to provide appropriate pressure differential for the CBF were the major challenges faced whilst perforating. Previous failure in the offset well was carefully analyzed to identify the root cause and come up with appropriate job design and operating procedures. The job was designed to keep backpressure in a balanced condition to the reservoir pressure to prevent any inflow of gas through plug, and the electronic firing head was optimally programmed above the cushion reference pressure. A rise in the wellhead pressure and shock at the wellhead were the surface indications observed for both the electronic and CBF firing heads while the latter also exhibited sudden rise and then drop in circulation pressures.
The project was executed in a defined timeline as per client expectations. The well was completed with eight fractures in four stages placing the designed amount of proppant. Initial production estimates have been very encouraging, with increased Oil Gas Ratio (OGR) leading to 20% greater production than forecast. This operation has opened new possibilities for the use of CT services in horizontal wells in the same formation.
