First Subsea Deployments of Permanent Electrical Distributed Temperature Array Enable OOZI Monitoring in Perdido
Authors: Byrne Devin , Gurses Sule , Orzechowski Diana , Puccini Piero , Klein Mark 
Published: November 2018

Abstract
The first permanent electrical distributed temperature array system (EDTA-S) was installed with a single trip in water injection wells in the Perdido fold belt, Gulf of Mexico. The oil field is offshore in the Alaminos Canyon block ultradeepwater environment, which consists of heavily faulted sand formations. Water injection is part of field development, and the risk of out-of-zone injection (OOZI) has a negative impact on the pressure support in the oil zone and causes part of the injected water to be allocated to an undesired formation and reducing hydrocarbon recovery.
The EDTA-S was identified as a technology solution to monitor OOZI. It comprises a permanent array of high-resolution temperature sensors distributed across the formation and overlying caprock with discrete dual-sensor pressure and temperature (PT) gauge measurements. A subsea acquisition card interfaces with the subsea control module, sending power and telemetry to the system via an electric cable installed across the completion. The sensors are installed below the feedthrough packer and positioned on a shroud offset from the tubing to thermally decouple the sensors from the tubing and enable monitoring of the formations. The installation is supported with a data interpretation platform that the operator’s technical teams review to assess whether injected water has been rerouted from the reservoir to some other sink, such as a fractured caprock. This ensures that production is maximized by establishing all the injected volume in the reservoir zone.
The first operator to deploy the permanent EDTA-S subsea used it in one water injector in 2016, and one in 2017. To deploy the array system in a single-trip completion, several enabling components were developed and qualified, including an electrical feedthrough system for the tree/hanger, subsea and topside control integration, shrouded tubing for the array sensors, and a feedthrough control line set packer. The completion operations went according to plan, and the sensors were positioned to monitor 100 m of formation above the perforations. The monitoring system was successfully integrated with the subsea controls and topside system and provides real-time monitoring of the injection and warmback periods. A biweekly system data health check shows good quality of data. Warmback data analysis indicates cooling in the nonperforated sand formation and possible water invasion is moving upward. To date, there is no evidence of OOZI into the caprock or channeling to the wellbore. Advanced thermal modeling software was used for interpretation, and a good match has been obtained with sensor measurements. Modeling of warmbacks confirms the data analysis result with no evidence of OOZI currently in caprock. However, continuous monitoring provides value in that it will capture any behavior changes over time.
The paper details the integration of components, execution, and data interpretation of EDTA-S in the Perdido fold belt. There is a significant potential for implementation of this system in deepwater developments to increase recovery factors.