Abstract
With the scarcity of new field discoveries and depletion of existing mature fields, operators in Pakistan are keen on cost-effective rigless solutions to enhance production. In the northern region, one operator was looking to curb the water production of an oil well completed with a jet pump installation. The subhydrostatic nature of the well, naturally fractured reservoirs, and large producing units with multiphase reservoir fluids and active aquifers posed significant challenges for rigless well intervention for water control and zonal isolation. High water cut resulted in oil production loss and made the well uneconomic. An innovative zonal isolation method was required to overcome those challenges.
The proposed solution comprised coiled tubing (CT) capable of acquiring real-time downhole measurements through fiber optic telemetry and delivering a through-tubing inflatable packer. The 2 1/8- in. packer was to be set in 4 1/2-in. liner with an expansion ratio of ~2:1. Planning and design considerations included selecting the bottomhole assembly (BHA) and performing pre-job quality checks of the inflatable packer and fiber optic cable. Downhole measurements verified accurate packer setting depth using a casing collar locator (CCL). To achieve adequate packer inflation without jeopardizing the packer integrity and to confirm proper anchoring of the packer onto the casing, downhole CT internal and annulus pressures were continuously monitored. During the first run, the liner tubulars were conditioned across the planned packer setting depth using a high-pressure rotary jetting nozzle. In the second run, the through-tubing inflatable packer was anchored, tested, and ultimately released at the target depth, providing a mechanical isolation above the water-invaded interval.
Water shutoff is one of the most challenging remedial operations in the oil and gas industry. During the design stage for mechanical isolation, key steps such as proper wellbore conditioning, accurate placement technique, and effective sealing across the water-bearing zones must be carefully reviewed to increase the chance of success. Conventional CT solutions fall short when it comes to actual tool depth with errors as high as 0.3% being accepted as common. Likewise, critical factors for CT operations in subhydrostatic wells, such as precise control of fluid flow in pressure-sensitive tools and understanding of changing well conditions, are very difficult to validate through conventional CT. An advanced CT solution relying on real-time downhole data combined with a high-pressure rotary jetting nozzle and a through-tubing inflatable packer was able to deliver precise results, reducing the water production from 1,253 B/D to 93 B/D and increasing oil production from 48 B/D to 224 B/D. Furthermore, the production tubing remained in place, eliminating the need for a workover rig. Real-time downhole measurements also served as a safety net so the packer would not inflate prematurely, and to allow validation of downhole conditions throughout the intervention. By leveraging the use of real-time downhole measurements to accurately control the positioning and actuation of high-pressure jetting tools and through-tubing inflatable packers, critical interactions with the formation or the completion are achieved, improving operational reliability while reducing risk of failure for water shutoff operations in subhydrostatic wells with a narrow depth margin between intervals.
