BLOG

8 Benefits of Distributed Acoustic Sensing (DAS) in the Oil & Gas Industry

Samuel Burrows

Samuel Burrows

Distributed Acoustic Sensing in the Oil & Gas Industry

An Unmatched Technology 

Distributed Acoustic Sensing (DAS) is a fiber optic system based on Rayleigh scattering. The fiber optic cable acts as the sensing element making measurements that are processed and analyzed to relay critical data, some examples of which we will explore in this post. 

A DAS system detects acoustic frequency strain signals, sometimes over large distances and in challenging conditions. Rayleigh scatter-based sensing is made possible by a laser pulse sent along an optic fiber, scattering within the fiber and causing it to act as a distributed interferometer with a gauge length approximately equal to the pulse length. The reflected light’s intensity is measured as a function of time after the transmission of the laser pulse. The pulse travels the entire fiber length and back before the next laser pulse is sent along the fiber. The system is extremely sensitive to strain and temperature, resulting in highly accurate readings. 

DAS is a technology that serves many applications to benefit production quality and efficiency in the Oil & Gas Industry. It is typically used in the continuous monitoring of pipelines, checking for interference, obstructions, leaks, and faults; for surveying private perimeters; and in oil well monitoring applications, where real-time monitoring is essential to production. Due to the capability of the technology to perform in challenging conditions with such a high degree of sensitivity and accuracy, its potential is unmatched, and here are eight standout reasons that justify investing in fiber optics in the Oil & Gas Industry:

1. Seismic Streamers

The ocean can be difficult to monitor due to the vast area and harsh conditions, so specialist methods that relay accurate data are required. Seismic streamers are surface marine cables that monitor the ocean, which is necessary to understand coastal and ocean dynamics, vulnerabilities at different temporal and spatial scales, and to interpret the impact of global and local conditions. An essential function of monitoring the ocean for the Oil & Gas industry is to pinpoint and locate the optimal area for oil drilling. 

The need to monitor the ocean is more crucial now than ever. The world’s oceans, coasts, and marine ecosystems are undergoing significant changes due to increasing greenhouse gas emissions, coastal pollution, overfishing, coastal development, and the pressure resulting from the increasing population. Oil drillers need to monitor the ocean accurately and locate the best location for drilling, and, as much as possible, reduce the risk of threatening consequences to the marine ecosystem. Accurate monitoring of the ocean prevents dangerous mistakes. 

Seismic streamers are surface marine cables that connect hydrophones. The hydrophones have a net of sensors to catch the vibration responses caused onshore by a heavy weight being punched into the ground. The sensors relay data to the seismic recording vessel that deployed the seismic streamers. Seismic data is three-dimensional data acquired at different times over the same area. It is used to monitor any changes that have occurred over time, including changes in fluid movement and saturation, pressure, and temperature. 

Distributed Acoustic Sensing (DAS) is the technology that transforms marine cables into seismic receivers. The fiber optic cable within the marine cable design produces seismic images of the seafloor and underlying geological structures. The images are created via the echoes that are relayed from the signal bouncing from the receivers and the vessel. Seismic images acquired from DAS are used to support geohazard analysis and other subsurface exploration activities. 

2. Ocean Floor Cables

Oceans present the most demanding environmental challenges and contribute to the majority of the Earth’s surface; exploring and monitoring the oceans is therefore vital to our understanding of the world and extremely difficult. In addition to the challenging environmental conditions, the sheer volume of the ocean floor presents another challenge, requiring the equipment to perform over a massive area and be resilient. 

By understanding more about the oceans, we can advance our knowledge of marine geology, offshore earthquakes, ocean currents, ocean waves, sediment transport, and marine mammals, amongst many other activities. In addition, by probing changes in an ocean environment, we can ultimately create a map of previously unknown fault systems and detect subsea dynamic processes. 

Ocean floor cables – also known as subsea or submarine cables – with Distributed Acoustic Sensing (DAS) capabilities are fiber optic cables installed on the ocean floor to record seismic data and relay that data to a recording vessel. An underwater fiber optic network can predict waves, tsunamis, and earthquakes by analyzing the stress, strain, and pressure on the long-haul submarine cables at the bottom of the ocean. 

DAS utilizes optical fiber as a sensor and transforms submarine telecommunication cables into powerful seismic receivers that survey the ocean floor. Compared to other methods of measuring, DAS measurements offer significant advantages due to the quality of the data they can assess in a marine environment. In addition, ocean floor cables with Distributed Acoustic Sensing capabilities can rapidly transmit massive amounts of information, often thousands of kilometers in length. Therefore, the ability to create longer distances of FIMT (Fiber in Metal Tube), the protective element that enables the optical cable to perform in challenging conditions, is a crucial advantage. 

NBG recently made a significant leap in creating FIMTs of a longer continuous length by constructing a new cladding line for 50 km FIMT. The advantages of the Subsea Cable Industry are clear. Longer FIMT saves our clients a significant amount of money because it requires less splicing, which can be a considerable expense for the project. 

3. Downhole Seismic Surveying

Downhole Seismic Surveying in the Oil & Gas Industry is used to find out what is underneath the Earth’s surface during the exploration phase of Oil and Gas development. Therefore, it is vitally important to an excavation project that the exploration crew gain as much insight into the nature of what elements are underneath the surface before drilling. 

Three primary methodologies are regularly used to find hydrocarbons in the subsurface: Geophysical, Remote Sensing, and Wildcatting. Selecting the best method will lead to pinpointing the areas with the richest resources, resulting in a better return on investment.  

Downhole Seismic Surveying is conducted to assess compressional and shear wave velocity versus depth. The velocity data is used to assist a particular site’s geology and seismic response. 

Fiber optic sensor cables with Distributed Acoustic Sensing capabilities are used as geophones to analyze soil and rock mechanics/structure. A seismic source is positioned at the surface with the fiber optic sensor cables placed down the hole. The collected data are the travel times for compressional and shear waves from the source positioned at the surface through the hole, measured by the fiber optic sensor cables. 

Distributed Acoustic Sensing delivers the most accurate data possible, and it does so in real time, providing excellent value.  

The many benefits of Downhole Seismic Surveying include the following: 

  • Calculating elastic moduli and dynamic rock and soil properties 
  • Vs30 calculations for seismic site classification 
  • The detection of faults, shear zones, and voids 
  • Diagnosing problem areas in 2-D or 3-D 
  • Pre- and post-grouting surveys 
  • Quality control for structural repairs 
  • Quantitative evaluation of material by seismic velocity analysis 
  • Seismic shear-wave and compressional wave velocity soundings 
  • Determining the rock or concrete quality through the estimation of the material’s dynamic coefficients 
  • Detection of bedrock faults and shear zones 

4. Sand Detection

Many forms of mechanical systems for sand control aren’t effective, leading to sand ingress and poor production results. Sand production affects the pipeline design and overall operations in three main areas. The first is that sands in the pipeline will rapidly increase pipeline erosion. The second is that the fluid velocity would need to be high enough to carry and remove the sand from the flowline to prevent a sand deposit from blocking the flow within the pipeline. The third reason is that sand deposits inside the pipeline may prevent inhibition chemicals, such as corrosion chemicals, from contacting the pipe wall, nullifying the purpose of chemicals. 

Ineffective sand control can lead to a loss of well integrity. Sand ingress across reservoir sections results in reduced output of hydrocarbon production. Overcoming the problem will drastically increase the quality of production while making it much easier to maintain the lifetime of the application. 

Distributed Acoustic Sensing is the leading candidate technology for downhole sand detection. The optical-fiber-based acoustic sensing systems use the light backscatter injected into an optical fiber to detect acoustic perturbations throughout the fiber, which acts as the sensing element.  

Distributed Acoustic Sensing processes data at the source and in real time, allowing for the following applications: 

  • Monitoring the sand flowline 
  • Monitoring sand ingress during production 
  • Increasing hydrocarbon production 
  • Informing and implementing a targeted sand-shutoff operation 
  • Controlling and managing sand-related risks during well ramp-up and production operations 
  • The optimization of oil production 
  • Assessing the reliability of the sand-control equipment during production, which helps to improve future designs 

5. Perimeter Intrusion Detection Systems (PIDS) on Wellbore Sites

A wellbore site is an asset in the Oil & Gas Industry that needs protection to maintain the security of the site and the integrity of production. If an ineffective security method is selected, the site is vulnerable to production being affected, causing negative financial implications. 

A wellbore site that can guarantee the presence of an intruder attempting to gain unpermitted access is in a much better position to ensure the integrity of production. An intrusion system that stands up to all conditions without any decrease in its performance is a necessity. Detecting an intruder before they have even attempted entry and alerting the control center at the earliest stage possible are factors that must be considered and prioritized when selecting the intrusion detection method. 

Perimeter Intrusion Detection Systems (PIDS) is a generic term that covers various technologies that are produced to detect an unwanted intruder attempting to gain access to a secure area. PIDS are vital for any high-security site. They keep organizations fully secure and reduce operational risk. 

PIDS don’t replace security camera surveillance; they work alongside existing surveillance systems, providing early intrusion detection in real-time. In addition, the technology is resilient and robust against extreme weather conditions and electromagnetic interference and is mainly passive. 

Fiber optic technology presents many advantages over conventional means of surveillance. For example, a single detection unit buried under the ground or mounted on a wall or fence provides fully scalable and robust security for areas of all sizes. In addition, fiber optic surveillance systems are more cost-effective solutions compared to rival technologies, and they offer a lower full-life cost of ownership. 

As Perimeter Intrusion Detection Systems are one of our core fields of expertise, we can provide the following: 

  • Monitoring solutions for wellbore sites 
  • Solutions for a perimeter of any length 
  • Future-proof technology that matches your requirements 
  • One software platform 
  • A system that can integrate with existing security systems 
  • For different terrains: soil, sand, and gravel 

We supply a fiber optic monitoring system with the highest possible security for wellbore sites, with innovative technology and resilient materials to perform in even the most challenging environments. 

6. Fracture Monitoring

Fracking has been a viable method of drilling the ground for gas since the 1940s. Regardless, it has only become popular relatively lately due to the increased difficulty in finding natural resources underground. Traditional gas sources in the US are becoming exhausted, and fracking is viewed as an attractive and profitable method. 

A shaft is drilled several hundred meters underground, and a horizontal hole is drilled into the oil and/or gas-bearing rock. Next, high-performance pumps move the fracking fluid into the ground, penetrating the rock layer and producing cracks. Sand is also pumped into the rock layer, and its function is to prevent the cracks from closing so the oil or gas can easily be driven out of the rock.  

When properly employed, fracking helps meet the demand for low-cost energy. In addition, accurate deployment with the ability to monitor the conditions of the wells will massively reduce the chances of contaminating any water sources, which is one of the most pressing concerns of fracking operations. Successful fiber optic deployment will also prevent hazardous and toxic materials, including greenhouse gases, from being unintentionally released into the environment. 

Fiber optic monitoring provides real-time and actional insights from data obtained from Distributed Temperature Sensing (DTS) and Distributed Acoustic Sensing (DAS). Operators with this insight will be better placed to comprehensively understand the subsurface conditions and make decisions and adjustments that help determine the best fracture placement and the application’s performance. 

The outcome of implementing DAS and DTS is a more precise process that produces better results and reduces the chances of operational inefficiency and errors. 

7. Frac Hits during Hydraulic Fracturing

The pressure from the hydraulic fracturing of a well can impact the nearby wells, either horizontal or vertical, which is referred to as a ‘frac hit.’ Though they range in intensity, this communication between two wells causes a pressure spike and issues with sand in offset laterals, which are disastrous to production.  

The following factors will determine the severity of the frac hit: 

  • Well Spacing: How close are the old wells to the new wells that are being fracked? 
  • Formation Characteristics: How permeable is the formation of the fluid/flow in the reservoir? Are there any faults in the well? 
  • Pressure Depletion: If the pressure has decreased, you can create a pressure sink for a new frac. You are more likely to get a harder frac hit on a well that has been there longer. 
  • Parent-Child Wells: You are more likely to get a harder frac hit on a well that has been there longer, which would be referred to as a parent well. 

Combating the effects of Frac Hits 

The first step is to communicate with the owners of the parent wells and notify them of any work. Also, an operator should ensure their equipment has been modified to handle a frac hit, reducing the chance of damage. But fiber optic technology plays the most significant role in combatting the effects. 

The most effective method to mitigate and even nullify the effects of a frac hit is a mapping technique: fiber optic microseismic monitoring. By monitoring the well pressure, an operator can assess when a frac hit will come and how severe it will be. Monitoring the production of the well also indicates an oncoming frac hit – a sign that one is imminent is a rapid decrease in production. Increased water volumes indicate that fluids from the newly fracked well are entering an already-producing well. 

Fiber optics is a tool that offers an improved diagnostic approach. Distributed Acoustic Sensing (DAS) and even Distributed Temperature (DTS) Sensing can measure critical data to determine the condition of wells. DAS provides vital data regarding the strain response as the fractures interact with the neighboring wells. This is supported by the fiber optic microseismic analysis that shows the time sequence of microseismic events and reveals the fracture networks. A microseismic analysis is a cost-effective solution allowing operators to acquire necessary information. 

NBG can deliver a comprehensive microseismic solution fitted with DAS and DTS that helps operators understand the conditions and characteristics of downhole wells. In addition, the fiber optic solution is robust and easily deployable, making it an essential inclusion in hydraulic fracturing applications in the Oil & Gas Industry. 

8. Pipeline Monitoring

Pipeline Monitoring is an essential measure in Midstream Oil & Gas applications, preventing expensive leakages with potentially catastrophic consequences for the environment, assets, and personnel. Fiber optic sensing technology presents the most efficient and reliable method; Distributed Acoustic Sensing (DAS) in Pipeline Monitoring guarantees the integrity of the pipelines and the product throughout the downstream process by delivering immediate leak detection and pinpointing the exact source of the leak. 

NBG’s FIMT (Fiber in Metal Tube) is ideal for Pipeline Monitoring because it can cover vast distances, is resilient and durable in challenging conditions, requires little to no maintenance once installed on-site, and perform well in various meteorological conditions. Functioning in challenging situations is an absolute prerequisite in heavy industries; for example, the Oil & Gas Industry has complex processes involving large and heavy products, equipment, and facilities. Our FIMT is the protective element that enables the optical fiber to perform in some of the most challenging environments in the world. 

The optical fiber in the FIMT works as a sensor that is capable of temperature and acoustic monitoring over the entire course of a pipeline, which can be hundreds of meters long. By monitoring the pipeline with this technology, any disruption caused by external influences, attempted thefts, or leaks will be detected immediately and located within an accuracy of meters. 

Other events within the pipeline are also detectable through the use of fiber optic monitoring systems, such as Negative Pressure Waves (NPW), flow constrictions due to waxing or hydrate formation, scrapers, pigs, and liquid accumulations. DAS and DTS technologies can be implemented alone or within the same cable to deliver comprehensive pipeline leak detection and continuous monitoring for onshore and offshore pipelines throughout all operational conditions: fluids, gases, and multiphase flow regimes. 

Managing a pipeline that stretches hundreds of meters without the use of fiber optic monitoring is an impossible task. In addition, the financial and environmental consequences of failing to recognize a leak or being unable to detect the leak’s exact location are enormous. 

NBG’s Distributed Acoustic Sensing Products

NBG specializes in producing custom-built FIMTs (Fiber in Metal Tubes), which are the protective element that houses the optical fiber. FIMT ensures that DAS and many other data transmission and sensing applications can be implemented in even the harshest conditions imaginable. Three popular FIMTs for Distributed Acoustic Sensing in the Oil & Gas Industry are SonoSens, the Polymer Layered FIMT, and the Trisens Cable. 

1. SonoSens

SonoSens is the most advanced acoustic sensor on the market, offering a 40% better acoustic transmission than common FIMT (Fiber in Metal Tube) constructions. In addition, the sensor is protected with a resilient metallic layer, creating a robust cable that guarantees the maximum lifetime of the application in challenging environments.

2. Polymer Layered FIMT

The Polymer Layered FIMT is ideal for umbilical cable solutions for Distributed Acoustic Sensing in subsea umbilical applications. The polymer-protected optical cable has increased impact resistance and excellent durability against mechanical stress. In addition, it allows for greater elasticity and weighs less than extra metallic layers. 

3. Trisens Cable

The Trisens cable is an ultra-thin optical sensor optimized for Distributed Acoustic Sensing (DAS), Distributed Strain Sensing (DSS), and Distributed Temperature Sensing (DTS). The outer polymer sheath and high-grade steel tube give the cable enhanced flexibility and high resistance to mechanical stress, and it’s an excellent solution for leak and strain detection. 

Are you searching for a DAS solution?

This post covers only eight applications and three products for Distributed Acoustic Sensing in the Oil & Gas Industry. However, the innovations of fiber optic technology offer an extensive range of benefits to practically every industry. We are constantly innovating to improve the potential of fiber optic technology further to benefit our clients. 

Contact us today to discuss any of the applications or products mentioned within this article with an NBG expert. We approach every project uniquely to ensure we find the best solution for each client, so introduce your challenge to us now.

More insights

Benefit from over 25 years of expertise in fiber optics.

Get the latest fiber news.

Sign up to our newsletter!