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 operational workflow.
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 operation.
