Production in mature offshore Mexico fields is mostly driven by gas
injected from surface. With time, injected gas flows directly through natural
fractures in the low-pressure carbonate reservoirs, leaving oil trapped in the
low-permeability matrix and reducing crude production. Over the past few years,
the gas-oil contact has rapidly moved across those fields making conventional
gas shutoff techniques both unsuccessful and uneconomic. An innovative approach
introducing a fit-for-purpose polymer foam system (PFS) and its accurate
placement using coiled tubing (CT) real-time telemetry addresses those
challenges with an unprecedented success rate while optimizing both logistics
and operational time.
To selectively shut off unwanted gas in these naturally fractured
reservoirs, the PFS was designed to have a high foam quality and low density.
Thanks to a delayed crosslinker, this formulation enables deep penetration
along the fractures and fissures before the gel strength develops. To ensure
effective placement of the PFS and its activation at the right depth, CT
downhole gauges monitor pressure and temperature throughout the pumping stages.
Any deviation from the downhole schedule can swiftly be addressed to maximize
shutoff effectiveness at depth.
Monitoring of downhole parameters is not only instrumental to the PFS
placement, it is also critical to other services associated with conformance
operations. Thanks to the casing collar locator and gamma ray signals, it
enables accurate depth control during perforating and stimulation phases. This
system also facilitates the evaluation of the wellbore response after each main
stage of the intervention. Finally, it can help perforate new intervals with
minimum impact to the already pumped conformance treatment through the use of a
new perforating firing head whose activation is controlled through fiber optics
rather than triggered by hydraulics. The introduction of this methodology in
offshore Mexico led to an increased success rate in gas shutoff operations. Of
the nine wells that had interventions performed in 2015, eight were initially
closed to production due to high gas production. Following the shutoff
interventions, those wells were put back in production with an average
reduction of 8.0 MMscf/d in gas produced per well and an average increase of
600 BOPD in oil produced per well. Near the end of the campaign, average oil
produced per well reached 830 BOPD thanks to further improvements in the
This approach constitutes a significant step forward in terms of
efficiency and economic sustainability. The use of CT to perform all the stages
of conformance operations greatly improved logistics on the platforms. In
addition, the real-time monitoring capabilities of the system and flexibility
of its downhole toolstring enabled an enhanced level of evaluation throughout
the interventions, which, in turn, optimized the outcome and saved days of
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