The operational realities of deepwater well testing

Ndubuisi Ezumba is Reservoir Performance Sales Engineer for SLB in Angola and Central East Africa, where he supports deepwater reservoir performance evaluation and intervention operations across some of the industry’s most technically demanding offshore environments. Over a career spanning more than two decades with SLB, he has held operational, maintenance, field leadership, and commercial roles across Angola, Nigeria, Kenya, Uganda, and Romania, with experience that includes deepwater drill stem testing (DST), technology lifecycle management, equipment reliability, service quality, and offshore operational execution. His work has involved supporting exploration and appraisal campaigns in high-cost offshore environments where testing decisions directly influence reservoir understanding, development planning, and project economics.

In this interview, Ndubuisi discusses the operational realities of deepwater well testing, including the growing role of real-time downhole visibility, the challenges associated with offshore execution under changing reservoir conditions, and how testing teams balance efficiency, technical discipline, equipment reliability, and decision-making during complex appraisal programmes.

Ellen Warren: Ndubuisi, you began your career as a field engineer and have spent more than 20 years working across offshore operations, reservoir performance, and well testing environments. What originally drew you to the oil and gas industry, and how did you develop a particular focus on deepwater DST and reservoir evaluation work?

Ndubuisi Ezumba: I have always been drawn to engineering and science. My interest in the oil and gas industry began while I was studying Mechanical Engineering at university. At the time, my older brother was working for an oilfield services company in one of Nigeria’s major oil and gas hubs, and visiting him regularly exposed me to the industry and the people working within it. Those experiences sparked my curiosity and helped me develop a strong interest in oil and gas operations.

The university I attended was also located near one of Nigeria’s key oil-producing regions, so careers in the industry were frequently discussed among engineering and science students. Between those conversations and my exposure to the operational side of the business, I became increasingly interested in the industry and decided early in my studies that I wanted to build my career in oil and gas.

My focus on deepwater well testing and reservoir evaluation developed later through my field experience. Working on exploration and appraisal projects showed me how important well testing is in reducing uncertainty and helping operators make critical development decisions. I became particularly interested in the role that high-quality reservoir data plays in understanding reservoir behaviour, optimising development plans, and ultimately improving project economics.

EW: One of the recurring themes in offshore testing is uncertainty during execution. What are some of the most common situations where downhole conditions or reservoir behaviour diverge from the original test plan, and how do experienced teams adapt in real time without compromising the technical objectives of the test?

NZ: Uncertainty is one of the defining characteristics of well testing. Before an exploration or appraisal well test takes place, operators typically have seismic data, wireline logs, and other subsurface information available. While these data sets provide valuable insight, they are collected under static conditions. The most accurate understanding of reservoir behaviour can only be obtained once the well is allowed to flow and the reservoir responds dynamically, which is the primary objective of well testing.

Because of this, it is not uncommon for actual reservoir behaviour to differ from pre-test expectations. Teams may encounter pressure responses, fluid characteristics, productivity levels, or flow behaviour that were not fully anticipated during planning. Experienced testing teams adapt by continuously monitoring real-time data and adjusting operations while remaining focused on the technical objectives of the test.

One example is hydrate formation during deepwater operations. Under certain pressure and temperature conditions at the seabed, ice-like crystalline solids can form and create restrictions within the flow path. Through real-time monitoring, teams can track seabed conditions and adjust methanol injection rates as needed to prevent hydrate formation and maintain safe operations. The ability to make those adjustments in real time allows the test to continue safely while preserving the quality of the reservoir data being collected.

EW: Deepwater DST programmes often operate under significant time and cost pressure. From your experience, what operational decisions during a DST campaign tend to have the greatest impact on overall efficiency and data quality?

NZ: Deepwater DST programmes operate under significant time and cost pressures, so several operational decisions can have a major impact on both efficiency and data quality. Some of the most important include choke-size management, determining appropriate flow and buildup periods, establishing sampling timing and volumes, optimising methanol or glycol injection strategies, and ensuring efficient fluid separation and metering.

Each of these decisions directly influences the quality of the reservoir data collected and the overall success of the test. The challenge is balancing the need to acquire sufficient reservoir information while minimising unnecessary rig time and operational risk.

EW: Reservoir evaluation during offshore appraisal campaigns often shapes much larger development and investment decisions after the test is completed. From your perspective, how does the quality and timing of data gathered during a DST campaign influence appraisal strategy, development planning, and long-term project economics?

NZ: The quality and timing of data gathered during a DST campaign can have a significant impact on both development planning and long-term project economics. A well-executed test reduces uncertainty by providing critical information about reservoir connectivity, productivity, fluid characteristics, pressure behaviour, and reservoir boundaries. These insights help operators make more informed decisions about field development.

From a planning perspective, the data influences decisions related to well architecture, well count, completion design, and production-facility sizing. It also helps operators better understand reservoir continuity and identify potential faults or compartmentalisation that could affect future production performance.

The economic implications are equally important. Development decisions are only as good as the data supporting them. If reservoir potential is overestimated, operators may commit capital to facilities, infrastructure, and development plans that do not deliver the expected returns. High-quality reservoir data helps reduce that risk by supporting more accurate reserve estimates, optimising capital expenditure (CapEx) decisions, and improving the long-term operating efficiency of the asset. Ultimately, better reservoir understanding leads to better investment decisions and stronger project economics.

EW: You have supported operations across multiple offshore regions in Africa. How do logistical constraints, rig conditions, and regional operating environments influence the way deepwater testing programmes are planned and executed from one basin to another?

NZ: Across the regions in Africa where I have supported operations, logistics and supply-chain constraints have consistently been among the biggest challenges affecting deepwater well testing. Mobilising specialised equipment, personnel, vessels, and materials often requires extensive planning, and any delays can have a significant impact on both operational schedules and overall project costs.

As a result, operators frequently begin planning DST operations more than a year in advance. While this level of preparation cannot eliminate logistical challenges, it helps reduce the risk of costly delays and minimises the need for expedited shipments of critical equipment and materials.

Regional operating conditions also influence how testing programmes are planned and executed. In parts of southern Africa, for example, stronger currents and more demanding metocean conditions can affect vessel operations, equipment deployment, and overall execution strategy. These factors must be incorporated into the planning process to ensure that testing operations are conducted safely and efficiently.

EW: In conventional DST operations, surface teams often relied heavily on indirect indicators while waiting for post-test confirmation from memory gauges. How has the increasing use of real-time telemetry changed the way operational decisions are made during live testing?

NZ: For many years, testing teams relied primarily on surface indicators such as flow rates, choke-size changes, wellhead pressure, and temperature trends to understand what was happening downhole. While these measurements provided valuable information about what was happening at the surface, they offered only indirect insight into reservoir behaviour and limited the ability to optimise operational decisions in real time.

The introduction of real-time telemetry has fundamentally changed that. Teams can now monitor bottomhole pressure and reservoir response as the test progresses, providing a much clearer understanding of reservoir behaviuor during both flow and buildup periods. This allows operators to optimise cleanup periods, adjust flow durations, identify the appropriate sampling window, and conclude buildup periods once sufficient data has been acquired. As a result, operational decisions can be made with greater confidence, improving both efficiency and the quality of the reservoir information collected during the test.

EW: There is often a perception that improving efficiency in offshore testing simply means reducing operational time. In practice, how do experienced testing teams determine whether a sequence, flow period, or intervention is still adding meaningful reservoir information?

NZ: The objective during a well test is not simply to finish as quickly as possible. The goal is to maximise the value of the data collected and ensure that each stage of the test contributes meaningful reservoir information. To determine whether a particular flow period, buildup period, or operational sequence is still adding value, experienced teams focus on the reservoir response being observed in real time. As long as the data continues to reveal new information about reservoir behaviour, connectivity, boundaries, or productivity, there is a clear justification for continuing the test.

However, once pressure and flow responses begin to stabilise and no new flow regimes or reservoir features are emerging, extending the test further often provides limited additional insight. At that point, teams can make informed decisions about concluding a sequence while still meeting the technical objectives of the test.

EW: Your background includes both field operations and technology lifecycle management. How does equipment reliability influence the success of offshore testing campaigns, particularly in deepwater environments where intervention opportunities can be limited and operational delays become extremely expensive?

NZ: Equipment reliability is fundamental to the success of any well-testing operation, particularly in deepwater environments where intervention opportunities are limited and operational downtime can be extremely costly. From my experience across both field operations and technology lifecycle management, reliable equipment is essential for maintaining operational efficiency, protecting data quality, and ensuring that the test achieves its technical objectives.

When equipment failures occur, the consequences can extend well beyond operational delays. A failed downhole gauge or valve, for example, can compromise an entire DST programme and may require a costly rerun of the test string. Similarly, improperly calibrated gauges can produce inaccurate measurements that affect reservoir interpretation and ultimately influence development decisions.

For that reason, equipment reliability influences every aspect of a well-testing operation, from operational execution and risk management to data integrity and reservoir evaluation. Reliable equipment gives operators confidence that the reservoir information being collected is accurate, complete, and suitable for making important technical and commercial decisions.

EW: Many offshore projects now involve increasingly complex coordination between reservoir engineers, offshore crews, service companies, and client decision-makers. In your experience, how do testing teams maintain operational alignment and clear communication during critical phases of a deepwater campaign, particularly when conditions begin changing during execution?

NZ: Maintaining alignment during a deepwater testing campaign depends on having a disciplined communication structure and a shared understanding of the test objectives across all teams involved. Because decisions made during a live operation can have significant technical and economic consequences, it is important that communication pathways are clearly defined before the operation begins.

In practice, this starts with detailed pre-job planning and briefing sessions where operational procedures, responsibilities, and lines of communication are established. Both the operator and service provider typically designate key points of contact who are responsible for coordinating information flow and ensuring that decisions are communicated consistently across the broader team.

The same principle extends to onshore support teams. Reservoir engineers, well-testing specialists, and data-interpretation centers often work together in real time, using live data streams and regular communication to evaluate reservoir response and support operational decisions. Those established communication channels become especially important when conditions change during the test, allowing teams to evaluate new information quickly, align on the appropriate response, and implement decisions efficiently while remaining focused on the overall test objectives.

EW: You have also worked extensively in sales and commercial leadership roles tied directly to offshore operations. How does commercial pressure influence technical decision-making during deepwater testing campaigns, particularly when operators are balancing reservoir evaluation goals against rig-time exposure and project economics?

NZ: Commercial pressure has a significant influence on technical decision-making during deepwater testing because every additional hour of rig time carries a substantial cost. At the same time, acquiring high-quality reservoir data is essential for reducing uncertainty and supporting critical development decisions. The challenge is finding the right balance between those competing priorities.

Operators address this challenge long before the test begins through detailed planning, modeling, and the establishment of decision criteria that help define the information required to meet the objectives of the programme. These preparations provide a framework for evaluating whether additional testing time is likely to deliver meaningful value.

The availability of real-time telemetry has further improved this process. By combining live reservoir data with pre-test modeling, teams can optimise flow and buildup periods based on actual reservoir response rather than assumptions. This allows operators to acquire the information needed to characterise the reservoir effectively while minimising unnecessary rig exposure and controlling overall project costs.

EW: Offshore appraisal campaigns frequently generate large volumes of operational and downhole data. In your view, how do experienced teams determine which real-time information is operationally meaningful during live testing, and how should decision pathways be structured before the operation begins?

NZ: Before a well test begins, experienced teams spend considerable time defining the key uncertainties they are trying to address. These may involve reservoir permeability, reservoir boundaries, fluid characteristics, productivity, connectivity, or other factors that will influence future development decisions. Once those objectives are established, the team can identify the measurements and indicators most likely to provide the information required to evaluate them.

This preparation is important because deepwater testing operations generate large volumes of data, and not all of it is equally relevant to operational decision-making. During live testing, the focus is on information that directly supports reservoir interpretation and helps determine whether the test objectives are being achieved. Pressure trends, drawdown and buildup responses, cleanup indicators, and rate stability often provide some of the most meaningful insights because they influence decisions about extending flow periods, initiating buildups, adjusting operations, or concluding the test.

Establishing those decision pathways before operations begin allows teams to respond more quickly and confidently when conditions change. It also helps ensure that the operation remains focused on acquiring decision-quality data rather than simply collecting more data.

EW: Across your career, you have seen deepwater testing operations evolve significantly in terms of telemetry, operational responsiveness, and execution strategy. Which operational practices or technical capabilities do you believe have most improved the industry’s ability to reduce uncertainty during offshore reservoir evaluation, and what do you foresee as the next evolution in deepwater testing?

NZ: Several operational and technological advances have significantly improved the industry's ability to reduce uncertainty during offshore reservoir evaluation. One of the most important has been the evolution of real-time data acquisition and interpretation. High-frequency downhole pressure measurements, improved surface-rate monitoring, and live data transmission allow teams to evaluate reservoir behaviour as the test progresses rather than waiting until operations have been completed.

Advances in pressure-transient analysis, well-test modeling, and integrated digital workflows have also improved the speed and quality of reservoir interpretation. These capabilities enable operators to gain a better understanding of reservoir properties, connectivity, and boundaries while often achieving the required objectives in shorter testing periods.

The next phase of evolution will likely involve greater integration of advanced analytics, AI-assisted interpretation, and remote operational support. These technologies will not replace engineering judgment, but they will help teams process large volumes of data more efficiently, identify important trends more quickly, and make better-informed decisions during live operations.

Ultimately, the objective remains the same as it has always been: reducing uncertainty and providing operators with the information they need to make confident development decisions. The difference is that the industry now has far more powerful tools available to achieve that goal.

Read the article online at: https://www.oilfieldtechnology.com/offshore-and-subsea/26062026/the-operational-realities-of-deepwater-well-testing/