A new flow-diagnostics resource delivers continuous flow profiles across a variety of completion and reservoir scenarios, including fractured formations. Article featured in Harts E&P Magazine   Horizontal wells offer increased reservoir contact and generally deliver much higher levels of productivity than their vertical counterparts, but these performance gains come at a cost. Managing horizontal wells and understanding their interactions with the reservoir are extremely complex challenges for petroleum engineers and asset management teams. New diagnostics technology from TGT, specifically designed to assess flow in horizontal wells, can deliver a much clearer picture of well system behavior.   Operating companies want to maximize hydrocarbon recovery in the safest, cleanest and most economical way possible. To do this, they need reliable information on fluid behavior within the well system, that is, the wellbore and the immediately surrounding reservoir rocks. Having an accurate picture of fluid flow in these areas gives teams greater confidence in the decisions they take to enhance production, maximize recovery and rectify well problems.   Flow analysis in horizontal wells is notoriously challenging. Variations in well angle and the extended reservoir contact as well as the presence of mixed fluids and segregated flow, formation changes, fractures and intricate completions all add to the complexity. Conventional production logging tools designed for flow assessment in vertical wells often struggle to deliver what is required.   Under favorable conditions, production logging technology may be able to map the multiphase flows encountered in a horizontal wellbore, but it cannot quantify the flow of fluids exiting or entering the reservoir behind the completion. This means that teams that rely exclusively on flow profiles from wellbore production logs are not seeing the true flow dynamics across the well system. Basing development, production or remediation plans on an incomplete or incorrect flow diagnosis may lead to flawed decisions, lower productivity and reduced asset performance.   More accurate horizontal flow diagnostics  For many years, petroleum engineers have been looking for ways to overcome the drawbacks of conventional production surveys in horizontal wells. Specifically, they wanted a system that could deliver continuous flow profiles across a variety of completion and reservoir scenarios, including fractured formations. The team at TGT has addressed these needs by creating the Horizontal Flow product, which is a new flow-diagnostics resource powered by Cascade3 technology. Figure 1. Horziontal Flow leverages Cascade3 and the True Flow system to deliver the truest picture of inflow and outflow downhole, even in the most challenging wells. The basis of this new technology is an advanced modeling and simulation engine that predicts the hydrodynamic and thermodynamic behavior of fluids and their surroundings as those fluids flow through the well reservoir system. Purpose-built for horizontal wells, it combines advanced hydrodynamic (fluid motion) and thermodynamic (heat and energy transfer) modeling technologies to translate temperature, pressure and other well system data into continuous reservoir flow profiles.   Crucially, the flow profiles produced reflect flow into and out of the reservoir, thereby delivering a true picture of inflow and outflow in even the most challenging wells, including those with natural or hydraulically induced fractures. This is important because, although fractures can boost the performance of a well or reservoir, they can also provide pathways for water or gas breakthrough. The new technology evaluates all three common types of flow pattern (radial, spherical and linear/fracture) encountered in horizontal well systems. This makes it possible to provide an accurate assessment of the linear flow that is occurring in fractures and to determine fracture contribution. This is particularly useful when combined with the Chorus acoustic sensing system that identifies fracture locations along the wellbore.   Armed with detailed insights into the complex flow regimes in well systems, asset teams can manage well and reservoir performance much more effectively. The new approach enables them to Establish reliable flow profiles; Locate water or gas breakthroughs; Reduce carbon footprint; Maintain a more accurate reservoir model; Measure effective pay length; Make more accurate reserves assessments; Reveal crossflows; Assess inflow control devices and packers; Assess fractures; Make more accurate production forecasts; and Optimize completion designs.   The new workflow can also be used to estimate or validate other key parameters such as reservoir pressure, permeability and skin factor. This independent verification of key parameters can help reservoir engineers to resolve uncertainties, improve history matching and optimize their dynamic reservoir model.   Horizontal wells represent a significant resource investment. Production engineers, reservoir engineers and the wider asset team need to ensure that each well system performs to expectations by achieving production targets and maximizing recovery. TGT’s new Horizontal Flow diagnostics technology solves key challenges and helps keep well and reservoir performance on track.

Predictive modeling using digital technologies and data analytics will help reduce carbon emissions Article featured in Harts E&P Magazine   If only we could inoculate subsurface wells against future integrity or flow issues it would be a dream come true. But there are many ways to proactively diagnose and keep them healthy and immune from unexpected “disease.”   Never has health been more in the spotlight—the health of our communities and the health of our planet. The pandemic has elevated the world’s focus on the environment and on driving down carbon emissions.   The energy sector has come under intense scrutiny as the world strives to tackle climate change. A major challenge is striking the balance between the continued need for fossil fuels, as part of a wider energy portfolio, while offsetting the associated carbon emissions. Energy outlook The DNV 2020 Energy Transition Outlook estimates that by 2050 oil and gas will account for 74% of the world’s energy-related CO2 emissions (Figure 1) and more than 80% emissions including CO2 equivalents. Emissions from the entire oil and gas value chain is on course to fall one-third by 2050.   The oil and gas sector is not alone in its endeavor; many major world economies have set ambitious goals to reach net-zero emissions by 2050, some even sooner. It is no longer a solitary cause. FIGURE 1. DNV GL predicts that oil and gas will still play key roles in the energy mix in 2050 when their value chains will account for most energy-related emissions. Proactive and predictive diagnostics We are constantly reminded that it is important to visit the doctor for routine checkups to ward off potential issues and/or treat issues early. We all know that prevention is better than treatment. Staying healthy does not only apply to humans or businesses, but also to wells that produce, inject or store hydrocarbons.   The road to net zero has many paths, but keeping wells healthy through proactive monitoring, diagnosing and subsequent remedial work is not only a duty, it’s good business. Furthermore, it would drastically reduce environmental fallouts as well as unplanned costs or reputational damage.   Well diagnostic companies, like TGT, can help. Application-led diagnostic products provide operators with the right information to act in advance and thus reduce potential emissions. A proactively diagnosed well has the best chance of staying healthy versus a well that is only diagnosed when problems start to appear. Optimizing resources But it’s not only about catching leaks and holes, it is also about optimizing resources that can have a detrimental effect on the environment. An activity that has a huge potential for improvement is fluid injection into a well system to enhance reservoir pressure and hydrocarbon recovery. Thousands of barrels of water are injected daily, but is the flow going where it should? On numerous occasions, TGT’s diagnostics have revealed the actual path and volume of injected water is different to the expectation or the plan—and this is sometimes after years of operating. With these findings, operators can reduce the amount of wasted water, cut down on water transportation and treatment, and ultimately reduce their energy intensity and drive down their emissions.   Equally important are idle wells—wells that are either abandoned or neglected. Routinely diagnosing the integrity of these wells to provide assurance they are “quiet” is highly advisable. More often than not, there are signs of subsurface activity. These wells represent a potential emission source that may prove difficult to remedy if neglected further.   A focus in the pursuit of net zero is carbon capture and storage (CCS)—capturing CO2 at the source, compressing it for transportation and then injecting it deep into a rock formation, where it is permanently stored. Routinely diagnosing the integrity of this storage facility to provide assurance that the plug is holding tight and that the CO2 is not migrating to water reservoirs or the surface will become essential, if not a legal requirement. Data are gold Pursuing routine diagnostics of subsurface wells to detect potential issues before they escalate is common sense, but what’s next?   Like many sectors, data are gold. With a wealth of diagnostic data at our fingertips, we can employ digital technologies and methodologies that predict when a diagnosis is needed or when a failure is imminent. With sufficient field or reservoir diagnostic data, we will be able to predict its behavior and failure modes with acceptable accuracy. Predictive modeling using digital technologies and data analytics will help reduce carbon emissions by boosting the energy efficiency of production.   It’s good for the environment and for business to stay healthy. To do this, we need to have a bold and visionary mindset that encourages proactive well diagnostics and soon makes use of predictive diagnostics. “Pursuing routine diagnostics of subsurface wells to detect potential issues before they escalate is common sense, but what’s next?”   Mohamed Hegazi, CEO

Integrity and corrosion assessment for successful slot recovery and plugging & abandonment (P&A) applications Article featured in Oilfield Technology   For all plug and abandonment applications, either permanent or for slot recovery, the sealing performance of well system components needs to be assured, and remain intact.    Well systems are complex and need to work perfectly to perform safely, cleanly, and productively. Understanding the condition and sealing performance of well system barriers can be challenging once the well has been brought onstream and access to these elements and components is restricted.     Current mainstream technologies only provide partial answers, leading to an incomplete assessment. However, through-barrier diagnostics look at the well system in a far more holistic and uncompromising way. These technologies have the capability of seeing through multiple barriers to provide a more complete picture of the condition of the metal tubulars and the flow around them to see if the seals are holding, prior to plug and abandonment.     In the case of permanent abandonment, natural barriers that prevent the movement or migration of downhole fluids, must be restored. And the performance of the well system barriers  must remain intact indefinitely.     In the case of slot recovery, the well components must be in good enough condition to be used again for the upcoming production cycle.   A comprehensive integrity assessment is required for either scenario.  Optimising P&A operations Planning and executing a flawless plug and abandonment requires prior knowledge of the integrity of the well barriers, and the precise position of all downhole completion elements. Operators armed with this information can determine the location of the permanent plugs and the best depths for the casing cuts for an optimised retrieval procedure.     During the productive life of a well it may experience several operator changes, perhaps after concessions expire or following divestment decisions. This can often lead to historical data being lost which, when it comes to well decommissioning, can increase the potential for making decisions without knowing all the facts about the well system, particularly the position of the casing collars, fins, centralisers or other components that impede successful decommissioning.     Using a simple multifinger caliper or an ultrasound survey, the location of the first-barrier casing collars can be determined, but the locations of the collars in the subsequent casing strings remain unknown. This approach contains an element of risk and may result in a cut planned directly in line with a thick section of metal, like a casing collar, or fin. Cutting across a collar or a fin, would mean an increase in the rig and intervention time of several hours, or potentially days.    TGT’s Multi Tube Integrity product uses the Pulse electromagnetic sensing platform to provide accurate barrier-by barrier assessment of up to four concentric tubulars (up to 20” diameter) in one single through-tubing deployment. Pulse can also pinpoint to within 1ft the location of completion elements.    The ‘electromagnetic signature’ of each tube or metal completion component, contains information about its wall thickness. The Pulse platform harnesses this information and through 3D modeling, can decipher metal loss as well as metal gain, in multiple casing strings throughout the entire well system.     Pulse can identify the location of known completion elements, but also identify new ones, not expected including welded fins on the outer casing string, often inaccessible to other evaluation technologies.     If Multi Tube Integrity is used prior to the P&A planning, the diagnostic results would remove the uncertainty allowing operators to confirm the optimum cutting window location in all casings, thus minimising the intervention time and reducing rig time and costs.  Integrity & corrosion assessment for slot recovery Slot recovery offers operators a way of capitalising on existing assets, by providing a new means of extending a well’s productive life.     It is a robust solution which utilises the existing surface and downhole infrastructure, to create a “new” offshoot well, which would reduce the costs associated with drilling. However, before this can become a reality, the inspection of downhole completion elements such as surface casing and its cemented annulus are a must.     Limitations in current technologies have meant that barrier verification is performed while the rig is in place, and once the tubulars (production and intermediate casings) have been retrieved.     Key input parameters, such as the cement condition and the integrity of the casing are obtained at the last stage of the planning. The late arrival of this critical information results in a complex well intervention plan, with several contingent scenarios based on a range of potential outcomes from the downhole integrity assessment.     The industry is calling for a new solution. One which can determine the condition and sealing performance of the cement and the metal barriers, prior to planning the slot recovery.  Pulse data showing wall thickness, collars and completion elements in 5 ½ in., 9 5/8 in., 13 3/8 in. and 20 in. tubulars. A powerful diagnostic combination TGT’s Multi Tube Integrity product used together with the Multi Seal Integrity product is the answer. This powerful combination utilises TGT’s Pulse electromagnetic platform, the Chorus acoustic platform and the Indigo multisense platform, and it can be deployed in one through-tubing deployment.   Pulse is used to evaluate the metal thickness of multiple tubulars, including the surface casing. It also has the unique capability of being able to confirm the position of critical completion components, including collars, centralisers, and casing shoes.   Chorus is used to assess the hydraulic seal integrity of the cement barrier to determine where the cement is sealing and where it is not. Fluid flow in the well system creates a rich spectrum of acoustic energy that penetrates the surroundings. This acoustic wave is encoded with information that Chorus can convert into acoustic spectra that can locate leaks and flowpaths throughout the well system, from the wellbore to the outer annuli.   The Pulse, Chorus and Indigo platforms are part of TGT’s True Integrity System which provides a clear diagnosis of integrity dynamics throughout the well system. The key to success It is critical that before slot recovery can be executed, there is an understanding of the collective integrity of the tubes, seals and barriers of the mother well. Only in doing this can there be a guarantee of the secure passage for pressurised fluids.   The key to success for any P&A or slot recovery operation is knowing all the facts about the integrity of the well system prior to planning and execution. This delivers the potential to reduce costs, minimise schedule overruns, and ensures the integrity of the final outcome.

Production logging is an essential resource for managing well and reservoir performance, but traditional methods only see half the picture. In this article, we look at a new approach that looks further to reveal the true flow picture. Article featured in Harts E&P   The last few decades have brought impressive advances in ‘production logging’ technology, especially in the context of new sensor designs and diagnosing complex flow downhole. Fibre optics are also playing an increasing role in production surveillance. However, the fundamental technique of using wellbore-confined production logging tools (PLT’s) to infer total well and reservoir flow performance still dominates the industry.   Basically, PLT measurements are used to monitor fluid properties and flow dynamics in the wellbore and importantly, to determine production and injection ‘flow profiles’ where fluids enter or exit the wellbore, such as via perforations or inflow control devices. These measured and calculated flow profiles are used to assess the production and injection performance of the entire well system.   However, the validity and accuracy of this approach depends on many factors, and chief amongst them is the ‘integrity of communication’ between the wellbore and reservoir formations at the entry/exit points. Analysts and operators using PLT’s must assume that fluids entering or exiting the wellbore are flowing radially from or to the formations directly behind the entry/exit points. And unfortunately, this is often not the case. Flowpaths can exist through annular cement channels, formation packers or natural fissures, and fluid will always find the path of least resistance. From a compliance, environmental and performance perspective, these unwanted flowpaths are bad news. Decisions made assuming wellbore flow correlates directly to target reservoir flow can lead to complex reservoir and field management issues, and compromised asset performance. From a diagnostics perspective, it’s clear that analysts and operators can’t rely on PLT’s alone to diagnose and manage well system performance – a more powerful diagnostic approach is needed. Seeing further The challenge of behind-casing ‘cross-flow’ is not new and the industry has made several attempts over the decades to diagnose this insidious phenomenon. Some of the early techniques used nuclear activation, chemical tracers and noise logging to try to detect and map flow behind pipe, but these methods generally lacked the precision demanded of modern-day diagnostics and were, at best, qualitative. However, fueled by an increased operator focus on compliance, the need for better asset performance, and pure ingenuity, a new diagnostic capability has emerged that is rapidly becoming the new industry standard for diagnosing flow downhole. True Flow system Understanding the dynamics and connectivity of wellbore and reservoir flow downhole with any degree of precision and accuracy is a highly complex task that extends beyond the capabilities of conventional ‘logging’.   Which is why ‘True Flow diagnostics’ utilises a more powerful ‘system-based’ approach. The True Flow system combines experience and expertise with proprietary technology and an industry proven workflow to deliver a more complete picture of well system flow dynamics, and enable better informed well, reservoir and field management decisions (Figure 1). Programmes and methods The first ingredient and stage in the workflow is ‘Programmes & methods’. Following an initial customer consultation, analysis of well performance history, completion design, reservoir and fluid properties and assessment of diagnostic objectives, analysts customise a survey programme that will effectively ‘stress-test’ the well system to expose its flow dynamics in a number of scenarios. This can be likened to a heart specialist exercising a patient on different treadmill settings whilst scanning physiological parameters such as heart-rate, blood pressure and electro-cardio signals. Typical programmes will include a precisely-timed sequence of flowing and non-flowing surveys that allow the entire well system to warm-up and cool-down between surveys. Tools and measurements The second stage and ingredient is the application of high-fidelity ‘Tools & measurements’ by engineers that survey the well according to the diagnostic programme. The measurements come from basic and advanced PLT-type wellbore probes, and a combination of proprietary acoustic and high-precision temperature sensors. Fluids flowing throughout the well system generate acoustic signals encoded with flow information. The acoustic sensing technology used by the True Flow system captures this information in the form of sound pressure across a wide frequency and amplitude range. Importantly, the remarkable dynamic range of this technology means it can sample absolute sound levels from deafeningly loud to imperceptibly quiet without losing clarity or detail. This means that a wide variety of flow scenarios can be located and characterised throughout the well system, from the wellbore to several metres into the reservoir formation. The temperature sensor in itself is unremarkable, being an industry standard fast-response, high-precision type capable of resolving to decimals of degrees. However, correlating temperature changes observed during the diagnostic programme and combining it with the acoustic data, wellbore flow measurements and other well and reservoir information is the key to quantifying flow by the next ingredient of the system – ‘Processing & modeling’. Processing and modeling During the processing and modeling stage, data acquired during the survey programme are enhanced further by analysts using a proprietary digital workspace and a number of processing and modeling ‘plug-ins’. High-resolution acoustic data are transformed into an ‘Acoustic Power Spectrum’ to reveal the characteristic signatures of different types of flow. Analysts can select from a catalogue of digitally enhanced spectra to illuminate particular aspects of the flow and extract maximum information from the acoustic signals.   The subsequent flow modeling is integral to the entire True Flow system and represents another significant advancement in flow diagnostics. Precision temperature measurements acquired during all stages of the diagnostic programme are assimilated together with all other data to derive ‘reservoir flow profiles’. These are distinct from conventional PLT-derived wellbore flow profiles because they quantify flow exiting or entering formation layers whether or not casing or perforations are present. Built on more than a decade of R&E and commercially proven in thousands of wells, the flow modeling engine solves complex thermohydrodynamic physics by matching simulated and measured temperature and other responses in the flow scenarios created during the diagnostic programme. The result is ‘quantified reservoir flow’ that together with wellbore flow measurements complete the total flow picture. Analysis and interpretation The previous True Flow stages are curated under the watchful eye of analysts who also administer the final important stage of the workflow – ‘Analysis & interpretation’. Armed with all available well data, processed and modeled results, and an expert knowledge of true flow applications, the analyst will derive and compile the diagnostic result. Whilst more complex scenarios can take a number of days to complete, the final result is a more comprehensive and accurate diagnostic of reservoir and wellbore flow that ultimately leads to better well management decisions and improved asset performance.   The True Flow system is used to provide a range of diagnostic answer products that address most flow-related applications. These products include ‘Total Flow’, which combines both wellbore and reservoir flow (Figure 2), ‘Sand Flow’ for sand management applications, ‘Fracture Flow’ to optimise fracturing programmes, ‘Stimulate Flow’, ‘Horizontal Flow’, and many more. FIGURE 2. A typical Total Flow answer product derived using the True Flow system is depicted. The PLT-derived wellbore flow profile (left) shows oil and water entering the wellbore at P2 only, suggesting the source of production is from the target reservoir at the same depth. However, the True Flow system reveals that several other formation layers are contributing to this flow, including that the main oil production is coming from the upper and lower sections of the A1 formation, and the water is emanating from deeper layers. By seeing the total flow picture, the operator has a more accurate and complete understanding of well and reservoir behavior and is able to target appropriate remediation. A bright future The old thinking cannot answer today’s new challenges. As well systems become more complex and older, managing performance will remain a priority and continue to task the industry. Wells are built to connect the right fluids to the right places, safely and productively, but forces, materials and age conspire to undermine this perfect balance. Traditional production logging will continue to play an important role in managing production, but it’s clear that we need to look beyond the wellbore, to the reservoir itself, in order to see the true picture.

Challenge In cyclic steam stimulation and steam-assisted gravity drainage, the reservoir fluids are heated through steam flooding to increase the mobility of heavy oils.   The steam is transported to the reservoir through the producing well. Consequently, the well’s casing metals and cement sheath are exposed to temperatures up to 300°C.   A common problem in cyclic steam injection operations is the failure of casing connections due to induced coaxial stress, which requires quick and reliable verification. To optimise cost operators need to identify issues downhole, such as casing collar breaks, without retrieving/pulling the tubing. In this case, an operator in northeastern Alberta, Canada, wanted to check the integrity of a producing well with 73 mm tubing inside a 168.3 mm slotted liner. Well sketch shows a range of typical collar condition scenarios that Collars Tube Integrity can diagnose. Solution The operator selected TGT’s Collars Tube Integrity product to provide an accurate assessment of the casing connections in the well through tubing.   Powered by TGT’s True Integrity diagnostic system using the Pulse (electromagnetic) platform, Collars Tube Integrity reveals collar condition from a single through-tubing deployment. Collars Tube Integrity can be used to investigate a specific integrity breach or routinely to support ongoing integrity management programs. Its ability to assess up to four concentric tubulars simultaneously means that most of the collars can be evaluated in a single deployment.   TGT’s diagnostic systems combine several proprietary technology platforms that share a common structure and four-stage workflow: programs and methods; tools and measurements; processing and modeling; and analysis and interpretation. The collar break at depth depicted by Line A was detected by using the Pulse platform and was verified by MFC data. Result In the subject well, Collars Tube Integrity located a casing break (see Line A) that coincided with the depths of collars (Figure 1). The Operator confirmed this when forced to pull the tubing to run a Multi-Finger Caliper (MFC) in casing.   The Collar Tube Integrity data acquisition and processing approach enabled time and resource optimisation by indicating the location and severity of casing collar breaks while the completion was still in the hole. This resulted in more focused well intervention planning and resource allocation. Over the past five years, the technique has been successfully applied in more than 100 wells across the province of Alberta and identified multiple casing collar breaks in single runs.

Challenge Multistage fracturing is an effective stimulation technique for heterogeneous, low-permeability oil reservoirs. However, after a fracturing campaign, there may be a risk of increased communication between the water-bearing formation, which may cause a high water cut in the stimulated well.   In this case from the Volga-Ural region of Russia, the operator wanted to identify unexpected water sources in a horizontal well in a low-permeability carbonate reservoir. The well had been subjected to a multistage acid fracturing job and it was necessary to determine the most effective strategy for a workover to shut off the water producing zones. Well sketch shows flow scenarios before and after fracturing that Fracture Flow can evaluate. Fracture Flow provides the clarity and insight needed to manage well system performance more effectively. Solution The operator selected TGT’s Fracture Flow product to understand the flow dynamics of the well system and identify the water sources. Fracture Flow is delivered by the True Flow diagnostic system. TGT’s diagnostic systems combine several proprietary technology platforms that share a common structure and workflow comprising programs and methods; tools and measurements; processing and modeling; and analysis and interpretation.   The Chorus (acoustic) platform records and analyses the acoustic energy produced by fluid flow; its role in this case was to help pinpoint unexpected flow activity behind casing. The Fracture Flow product uses a multi-sensor tool, adopts a unique data acquisition programme and utilises a processing and modelling software plugin which varies from the other True Flow products.   In combination, the technique is able to identify the location and determine the distance of the acoustic signal from the receiver. It is therefore able to distinguish reservoir flows from those generated by completion leaks. Integrated logging suite results: Acoustic signal source identification Result An acoustic signal was recorded in a narrow interval above the target reservoir. This signal had a broadband spectrum that could have been generated by reservoir flow or by a completion leak (see Line A in Figure 1).   Taking into consideration the well design and the acoustic wave propagation in the wellbore and rocks, TGT’s Chorus diagnostics determined that the location of the acoustic source extended beyond the wellbore. It was deduced that the signal was generated by turbulent flow from an unexpected fracture above the target reservoir. The inflow fluid from this unwanted fracture flowed back down the well completion, entering the wellbore through the topmost perforation. It was this rogue fracture that was the cause of water in the well production.   Thanks to Fracture Flow’s diagnostic results, the operator changed the hydraulic fracturing design programme, to optimise production while preventing the reoccurrence of rogue fractures in the future.