Category: Insights

13 Jul 2017

Real-time Cluster Efficiency

Distributed fiber optic sensing for uniform fracture stimulation

Evaluating stimulation performance and well spacing early in development can increase a projects Net Present Value. This is especially true when developing stacked intervals.  For example, studies have shown that plug-and-perf completions often produce under-performing perforation clusters and undesired inter-well communication.

To address under-performing perforation clusters, operators are combining Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS)measurements to calculate the amount of fluid and proppant placed in each cluster on the fly to enable optimized decision-making throughout a project ensure more effective fracturing on current and future wells.

Recent observations from fiber optic DAS and DTS indicate that a majority of treatment volume is limited to only one or two dominate clusters near the heel-side of a treatment stage—leaving the remaining stage clusters under stimulated.

With a large majority of perforation clusters failing to contribute to production, you can’t help but ask: Where’s my proppant going and why?

Assessing cluster efficiency, fluid distribution and diverter effectiveness

There are many possible reasons for uneven reservoir stimulation, such as stress shadowing interference between fractures, local heterogeneity, the effectiveness of zonal isolation between stages, stimulation design (pumping schedules and fluid/proppant selection), and the variation in natural fracture systems surrounding the well.

Fiber optic monitoring, such as DAS and DTS can be used to assess cluster efficiency, fluid and sand distribution and diverter effectiveness.

On a recent spacing pilot in the Anadarko Basin, home to several stacked interval reservoirs, a five-well project equipped with OptaSense Distributed Fiber Optic Sensing offered another explanation for the heel-side bias. For this project fiber optic derived DAS and DTS measurements provided the operator an opportunity to monitor fluid movement during fracture stimulation and warm-back before the well was produced.

Monitoring distribution

During treatment, acoustic and temperature data confirmed inadvertent diversion away from toe-side clusters, and acceleration of the already-dominant heel-side clusters. Using algorithms applied to DAS data, proppant volumes per cluster were calculated revealing highly uneven proppant distribution among multiple clusters even when fluid is uniformly distributed

The DAS measurements captured in this pilot project suggested a strong heel bias was present in a majority of stages. The uneven distribution, caused by interference between adjacent fractures within a given stage and from preceding fracture stages, resulted in a consistent geometric predominance for fracture growth toward the most heel-ward perforation cluster.

A variety of completion variables, such as perforation designs, fluid systems, diverter and proppant size, were tested to identify the optimal treatment for improved fluid distribution.

Simulating distribution

Using these measurements, the operator used calculated proppant placement to monitor diversion efficiency in real-time during the fracture and took action to modify the treatment, which resulted in more even fluid and treatment distribution. After modeling the improved distributions derived from fiber optic monitoring, a new well completion and stimulation design resulted in more equal fracture heights and half lengths, as well as increased the overall effective fractures in the wellbore.

Multiple optimizations in pressure pumping strategy were discovered during the variable testing using real-time DAS and DTS. The pumping schedule was altered to test different rations of slick water and high viscous fluids, ratios in proppant sizes and concentrations of proppant within the various fluids.

Optimizing distribution

Using DAS and DTS to estimate fluid and proppant placement enabled the operator to identify the root problem and implement an effective proppant and fluid treatment (aligned with an optimized pressure pump schedule) that mitigated the uneven stimulation. The result, improved cluster efficiency and more uniform proppant/fluid distribution on current and future stages and wells.

15 Dec 2016

Enabling Cost-Effective Sweep Efficiency with DAS-VSP

Offshore brownfield exploitation generally involves operating in remote, environmentally sensitive areas that have geologic basins with complex overburden, structure and stratigraphy.

In these geologically challenging areas, Ocean Bottom Node (OBN) seismic acquisition is the technology of choice for a number of reasons; the most important being its ability to capture a high quality seismic image, which is critical for characterizing time-lapse response of the reservoir.

Due to the high acquisition cost, many mature reservoirs using an OBN approach for time-lapse imaging are surveyed several years apart, resulting in the missed opportunity to effectively manage and understand the reservoir.

To eliminate this risk, a supermajor operating in the Gulf of Mexico contacted the OptaSense team with the goal of identifying a low-cost alternative that would enable comparable or better quality seismic surveys at more frequent intervals.

Rethinking borehole seismic

Technology plays crucial role in providing the information to make sound exploration decisions. Given the complexity and high cost of deepwater development, there is great value in being able to identify the best spots to drill wells and manage production methods for field exploitation. This skill hinges on generating an accurate picture of the subsurface. Seismic technology lies at the heart of this process and was a key research priority for our client.

Vertical Seismic Profiling (VSP) has long been considered a possible solution for deepwater seismic imaging; however, high cost and practicality have made it unfeasible for many operators. Since the introduction of Distributed Acoustic Sensing (DAS) VSP technology, these concerns have essentially been eliminated.

Putting DAS to the test

Concept testing for the low-cost, on-demand DAS-VSP solution included several aggressive objectives, one being surveying reservoirs lying below thick salt formations which are notoriously challenging to image. Additional objectives included demonstrating repeat DAS acquisition using multimode fiber, acquiring DAS on active production and injection wells, and providing quick on-demand service for time-lapse monitoring of sweep efficiency.

To meet these objectives, OptaSense recommended running their DAS-VSP borehole seismic acquisition service, capable of acquiring 2D, 3D and 4D VSP data, and the fourth generation ODH-4 DAS interrogator unit (IU) for its unmatched imaging and measurement performance.

The ODH-4 provides a 6 dB improvement in signal-to-noise ratio over its predecessor—delivering the highest fidelity VSP measurements available. In addition to higher quality seismic imaging, the ODH-4 offers increased sensitivity, finer spatial sampling (1.02m) and finer spatial resolution of (4.02m gauge length) to capture high-caliber image resolution.

Subsalt imaging

Oil and gas is commonly trapped subsalt, or near salt flanks.Incidentally, imaging near and below the large salt structures is naturally problematic for any surface or OBN seismic program. One of the best known methods to properly image these areas is a VSP survey, which enables access to these obscure locations. However, these wellbores commonly have high deviation and high entry to access costs, making the use of conventional geophones unfeasible.
The ODH-4 IU instead transformed the operators existing fiber optic cable attached to production casing into an array aperture to acquire VSP data across the entire wellbore.

Multimode fiber acquisition

By retro-fitting our DAS technology to pre-existing multimode fibers, OptaSense provided permanent, on-demand DAS-VSP access at no extra cost to the operator. Although DAS was originally developed for single-mode fibers, most legacy fiber optic installations are multimode.

By continuously pioneering the evolution of DAS technology, OptaSense has proven quality DAS measurement can be acquired on either single-mode or multimode fiber—enabling on-demand acquisition of quality seismic surveys from wellbores with existing fiber.

VSP acquisition on active production and injection wells

With OptaSense DAS-VSP borehole seismic acquisition service, the operator successfully acquired VSP data on actively producing and injecting wellbores during acquisition operations. Such a practice would be unthinkable with geophones.

In some cases, a mature field may not have suitable placement for, or the existence of, an observation well. This can impact an operator’s ability to monitor production, as well as optimize future well placement. Our DAS-VSP eliminates the requirement of observation wellbores for VSP imaging, while providing on-demand, direct monitoring of production and injection zones.This ensures operators receive the subsurface insight required to control current operations and optimize future placement of injector and producer wells.

OptaSense DAS-VSP also provides the ability to acquire data on active wellbores without shutting in operations—resulting in greater VSP imaging coverage at favorable economic costs.

On-demand 4D time-lapse

Due to cost, 4D VSP acquisition at shorter intervals may not be feasible. However, the OptaSense DAS-VSP service is flexible, quickly mobilized and offers favorable economics for repeat acquisition monitoring.
Through the use of our DAS-VSP 4D time-lapse service, the operator effectively monitored conditions throughout the reservoir over time—increasing recovery, optimizing cost, reducing risk and extending the life of the field.

Unmanned VSP services

Manned operations for recording instruments can amount to significantly increased risk and cost depending on the duration and location of the program. Through the use of a suitable internet connection OptaSense can provide unmanned VSP services through remote monitoring of OptaSense equipment and data. This significantly reduced cost and HSE exposure for our client by reducing lodging, substance and day rates for an onsite operator, in exchange for a daily remote monitoring fee.

Exceeding expectations

The quality of the DAS-VSP acquired using our ODH-4 IU surpassed our client’s expectations. This included data collected on multimode fiber, actively producing and injecting wellbores and those positioned subsalt.

Imaging objectives for 4D reservoir monitoring continues to be successfully met and our client is looking forward to expanding DAS-VSP service for regular time-lapse monitoring of their asset. In just a short period of monitoring, our client is moving forward with DAS-VSP service as an integral part of sustainable field development. They have realized added value with the service’s seamless application and the capability to remotely monitor the equipment and program. Our client highly advocates the installation of fiber optic cables for new offshore wells, and utilizing existing fibred wells to take full advantage of DAS for VSP acquisition.

13 Jul 2016

Permanent Well Monitoring Solutions for Optimal Fracture Design

With the growing pressure to optimize data value and reduce costs, operators are continually seeking better ways to maximize value from exploration and production. One effective solution is to optimize the hydraulic fracture stimulation design of a shale gas well. However, a gap of understanding exists in how completion design relates to long-term reservoir production. Our motivation is to provide the data necessary to fill in the gaps and ultimately leverage unrealized production potential and cost savings.

The inability to effectively understand the dynamic and varying production behavior of a shale gas well lies within the sparse sampling of data.  One method for wellbore production monitoring combines the use of a Production Logging Tool (PLT) and analysis. As a point sensor wireline tool, a PLT is not suitable for permanent, continuous measurement across a large producing zone. At best, a wellbore is logged at a few discrete points within its production life. To improve completion design, long-term observation of inflow production behavior is required.

The OptaSense permanent well monitoring solution provides long-term Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS). It features a permanent hardware system and portal service. Field data is processed with a flow/no flow algorithm to produce a real-time cluster efficiency metric. Field data and processed data are then streamed to the portal for online viewing and downloading. The portal and data are supported by OptaSense DxS Pro software, allowing users to download and perform in-depth analysis to generate quantitative results on demand. Through this setup, real-time and long term trends of individual stages and clusters can be observed. Observation of contributing cluster performance over a long period of time demonstrates whether cluster performance is influenced by completion design. The OptaSense permanent monitoring solution shows long-term behavior of a reservoir section, including regions of diminishing influence and changing cluster response, allowing for better reservoir management. The OptaSense permanent well monitoring solution also removes the requirement for multiple field acquisitions and provides continuous data.

With a long-term monitoring solution from OptaSense, you can develop smarter completion designs that optimize field development, from improving well, stage, and perforation spacing for maximized recovery to increasing operational efficiency that saves time and money.

For more information about our permanent well monitoring solutions, contact your local sales representative.

27 Mar 2016

Microseismic Interferometry: Transforming dots in a box into a 3D seismic image

Traditionally, operators plan and execute a hydraulic fracturing project based in part on available seismic data, which lacks the resolution needed to see fine-scale geophysical features and reservoir extent. Without a detailed understanding of a reservoir’s geophysical characteristics, the chosen fracturing parameters may not be optimal, resulting in diminished performance and wasted money.

OptaSense has released an advanced method of imaging called microseismic interferometry that uses the microseismic events themselves as seismic sources to generate high-resolution three-dimensional images. Using data recorded on either DAS fiber optic tools or conventional three-component receivers, microseismic interferometry  improves upon traditional microseismic processing which produces event locations (dots in a box) along with some event attributes but no image.

OptaSense’s new technique employs thousands of microseismic events to build up a 3D image of the stimulated reservoir volume and supply a high resolution image of the subsurface geology around event locations.

Microseismic interferometry works by gathering data from a long borehole seismic array, ideally with 3C sensors straddling the stimulation zone. The data is then processed in a conventional manner to produce event locations and magnitudes. Following this initial analysis, the full waveform data is processed using interferometry – imaging the P and S wave fields to produce a local image for each microseismic event. These local images are combined into one large 3D volume covering the entire extent of the frac zone.  This analysis can be performed on newly-acquired microseismic data or on existing surveys.

The 3D interferometric image volume can be analyzed using standard seismic analysis tools and can be integrated with existing surface seismic interpretations, well logs, formation tops, horizons or geomechanical analyses to build a better understanding of  the reservoir and its geology. This improved understanding may be particularly useful for planning additional wells in nearby areas or re-fracturing wells in the imaged area.

OptaSense’s microseismic interferometry method extracts high-resolution information from existing data. Customers benefit from optimizing the costs of completion and drilling as they can use the information to plan subsequent fracs in nearby areas, re-fracs in the same formation or for time-lapse reservoir characterization.

To read more, download the paper by clicking here.