Combined downhole temperature and pressure sensing with DTS and fiber F-P sensors

Project background: from isolated alarms to continuous risk assessment

Combined downhole temperature and pressure sensing with DTS and fiber F-P sensors addresses the long-term safety and condition management of oil and gas wells, thermal-recovery wells, geothermal wells, injection/production wells, wellbores and surface acquisition systems. Such assets commonly span multiple spaces, process sections or asset identifiers; risks can move along routes, equipment boundaries and structural weaknesses rather than appearing at predetermined measuring points. Key concerns include high downhole temperature and pressure, crossflow, changing injection/production profiles, power constraints for electronic sensors and long-term reliability. Point sensors, manual inspections and video provide local evidence but may not capture the complete development of an anomaly from onset to response.

The solution uses high-temperature DTS, fiber Fabry–Pérot pressure sensors and BOTDA, placing sensing fiber along the paths that need observation to create continuous, localized and replayable records. Its objective is to obtain continuous wellbore thermal profiles with one or more fiber cables and add F-P pressure points at critical depths for combined interpretation, rather than add isolated equipment. Start design with an asset-risk inventory and verifiable monitoring objectives, then specify range, spatial resolution, sampling, sensing-cable construction, software interfaces and alarms.

Risk progression and monitoring boundaries

For oil and gas wells, thermal-recovery wells, geothermal wells, injection/production wells, wellbores and surface acquisition systems, distinguish initiating factors, early signs, developing conditions and consequences. Risks including high downhole temperature and pressure, crossflow, changing injection/production profiles, power constraints for electronic sensors and long-term reliability may occur independently or arise from combined load, environmental, construction and maintenance effects. Capture measurable changes in temperature, acoustics, vibration, strain or local condition and associate them with specific assets and distances.

Sensing principles and technology selection

An integrated solution places continuous DTS temperature, dynamic DAS acoustics/vibration, slow BOTDA/BOTDR strain and sensitive FBG or silicon photonic point measurements in one spatial coordinate system. Different mechanisms provide complementary evidence: temperature indicates thermal anomalies; acoustics/vibration describes event timing and dynamics; strain reveals cumulative structural change; and point sensors add local equipment condition.

The recommended combination is high-temperature DTS, fiber Fabry–Pérot pressure sensors and BOTDA. Check monitoring distance, spatial resolution, localization accuracy, channel count, dynamic range, sampling cycle, operating temperature and communications together. Specifications should support the objective to obtain continuous wellbore thermal profiles with one or more fiber cables and add F-P pressure points at critical depths for combined interpretation, rather than be compared individually. For long routes, prioritize signal-to-noise ratio, reliable localization and far-end stability; for localized high-risk areas, assess coupling, effective sensing length and response time.

System architecture: sensing, interrogation, software and response

The system comprises sensing cable or fiber sensors, splicing and protection units, interrogation equipment for high-temperature DTS, fiber Fabry–Pérot pressure sensors and BOTDA, edge processing, application software and supervisory interfaces. Returned signals undergo quality checks, distance calibration and parameter calculation before mapping to asset records. Outputs include live curves, time-space plots, event lists, risk zones, historical trends and reports, rather than an unexplained waveform.

Connect to oilfield or geothermal production databases and remote monitoring for depth profiles, injection/production analysis and long-term trends. Define the data dictionary, time synchronization, alarm acknowledgment, offline buffering and recovery upload. For important projects, use tiered retention of raw or feature data to support incident reviews, algorithm improvement and threshold changes.

Sensing cable and field installation

Recommended installation: select permanent or temporary downhole cable for the completion, managing wellhead sealing, armor, hydrogen-induced loss and minimum bend radius, with interrogators in safe surface areas. Installation quality directly affects results; the same interrogator can respond differently with different mounting, jacket materials and coupling. Design documents should identify start/end distances, slack loops, splice boxes, zone boundaries, fastening intervals, bend radius, pulling tension and protection.

Data analysis and graded alarms

Instead of simply connecting several interrogators, establish unified distance coordinates, asset identifiers and timestamps. Validate data quality within each parameter before cross-checking between parameters. For example, coincident acoustic/vibration and temperature anomalies may increase risk priority; a short impact without subsequent temperature or strain change can enter observation or manual verification.

Initial application criteria: synchronize depth-temperature gradients, transient injection/production responses and pressure changes, interpreting anomalies against well conditions and operation logs. Use advisory, early-warning, alarm and emergency levels, each with defined confirmation times, verification and actions. Calibrate thresholds against actual conditions during trial operation and record every revision, reason and effective date. Display position, asset name, measured value, baseline deviation, duration and supporting evidence together.

Commissioning, acceptance and performance verification

Integrated acceptance must verify each sensing chain and test clock synchronization, distance mapping, asset identifiers and response logic across systems. Simulated events should cover individual and simultaneous multi-parameter anomalies, communication loss and sensing-cable faults, confirming clear indications during degraded operation.

Maintenance and sustained effectiveness

Maintenance assessment should cover valid-alarm rates, confirmation time, false-alarm causes, missed-event reviews, closed work orders and detected trends, not just equipment uptime. Continued labeling of real events can improve recognition models and sustain practical performance after commissioning.

Integration with existing systems

Connect to oilfield or geothermal production databases and remote monitoring for depth profiles, injection/production analysis and long-term trends. Let the fiber platform handle interrogation, curve analysis and original evidence, while the supervisory system manages consolidated displays, duty workflows and work orders. Depending on the project, interfaces may use Modbus TCP, OPC UA, IEC protocols, REST APIs, message queues or dry contacts. Avoid transferring only an unexplained aggregate alarm.

Every alarm on a map, plan or process diagram should link back to original curves and historical trends. Feed dispositions from supervisory systems back into event records, closing the loop between monitoring, confirmation, response, review and threshold improvement.

Benefits, operating conditions and technical boundaries

The solution replaces sampled inspections of oil and gas wells, thermal-recovery wells, geothermal wells, injection/production wells, wellbores and surface acquisition systems with continuous observation, retaining traceable early indications of high downhole temperature and pressure, crossflow, changing injection/production profiles, power constraints for electronic sensors and long-term reliability. Passive fiber, electromagnetic immunity and multiple sensing locations on one fiber can reduce distributed power and maintenance requirements on long routes, at unattended sites or in hazardous environments. Locations and trends help teams narrow inspections, plan condition-based maintenance and prioritize risk.

Equipment selection and detailed design

Begin with five questions: which parts of oil and gas wells, thermal-recovery wells, geothermal wells, injection/production wells, wellbores and surface acquisition systems require protection; which indications of high downhole temperature and pressure, crossflow, changing injection/production profiles, power constraints for electronic sensors and long-term reliability must be detected; what localization, response and sampling performance is needed; what routing, power, communications and cabinet facilities are available; and who confirms alarms and owns the response workflow?

Then specify the combination of high-temperature DTS, fiber Fabry–Pérot pressure sensors and BOTDA, cable construction, single- or double-ended optical paths, channel redundancy, software licensing and interfaces. For phased projects, reserve fiber, rack space, network addresses and platform capacity. For long-distance or multisite projects, evaluate centralized interrogation, distributed edge nodes and remote maintenance together.

Application-specific validation and limitations

DTS measures temperature distributed along well depth; F-P pressure sensors generally measure at their installed positions. Their spatial coverage is different. Sharing a link requires checking wavelengths, splices and interrogation arrangements; a common outer sheath does not establish optical compatibility.

Depth coordinates must account for deviation, stored cable and surface lead-outs. Record the completion and sensor positions at commissioning. Interpret injection, production, shut-in and thermal recovery separately. Assess survival under heat, pressure, hydrogen and mechanical loading for the actual construction, and cross-check production interpretation against wellhead and process data.

Installation, optical-path calibration and acceptance checklist

Related products and technical resources

Explore the product categories below according to distance, spatial resolution, channels, response and site conditions. Published specifications support preliminary selection; final configuration must account for optical loss, installation and acceptance objectives.