Unconventional Resources
nXis Well Integrity Inspection in Unconventional Wells Last Reviewed August 2017


The goal of this project is to develop a novel well-integrity inspection system capable of providing enhanced information about the flaw structure and topology of conventional and unconventional gas-filled wells.  This will be achieved by developing a novel combined X-ray/neutron backscatter imaging device, suitably sized for operation in well bores.

GE Global Inc., Niskayuna, NY
Starfire Industries, Champaign, IL

Unconventional mining poses many challenges for well inspection at both the construction and operational stages. This is particularly true in the environmentally sensitive aquifer depth region, as well as in the vicinity of lateral perforation zones, where accurate assessment of well integrity is of paramount importance to minimize environmental impact. The presence of challenging structures, such as concentric well casings, only heightens the need for novel inspection methodologies. The nXis technology is based on a new dual-particle imaging technique, which combines imaging information obtained from X-ray and neutron backscatter in a single instrument. The resultant data will be obtained from electromagnetic and acoustic principles to achieve results that are intrinsically more accurate than individual modality results.

GE is studying a dual approach for gamma ray generation, relying on both a radioisotope source as well as developing an electrical non-radioisotope based generation. An additional test was conducted to test the ability of the electromagnetic system to track the edge of the casing pipe. In order to improve defect visualization capability with the electromagnetic system, a new set of pickup coils was designed and manufactured.

The potential impacts and benefits of this new technology include improved environmental safety and resource recovery for unconventional wells via the collection of better data to ensure long-term borehole integrity.  Operators will be able to remedy well integrity flaws with the nXis inspection system, which will be capable of providing enhanced information about the flaw structure and topology of conventional and unconventional gas wells. Environmental impacts caused by unconventional energy activities during construction and operations will be identified in both the aquifer depth region and lateral perforation zones. The new technology will be capable of analyzing geometrically challenging structures and minimizing false negatives in existing well integrity data. Effective monitoring and mitigation will also reduce environmental impacts on surface and groundwater sources.

Accomplishments (most recent listed first)
The team has outlined fault detection algorithms for each modality. With x-ray use, defects down to 1/4” in concrete and 1/8” in steel pipes can be identified. Testing of the modalities is planned at a GE facility in Houston, TX, which has a 20’ long test well.

The team has studied eccentricities between different casing strings in combination with material loss in each casing. Initial test bed experiments suggest multiple defects can convolute sensor data and therefore more advanced data analysis is required to accurately extract desired sensor information. Due to its asymmetric design, the triple coil configuration can provide directional information. The small coil has higher resolution and is more sensitive to material loss in small regions of the first casing. However, it cannot detect eccentricities between casings nor material loss in the second casing. Dr. Kasten presented project results on August 17, 2016, at the 2016 Mastering the Subsurface through Technology Innovation and Collaboration: Carbon Storage and Oil and Natural Gas Technologies Review Meeting in Pittsburgh, PA.

The original detector was redesigned and the new geometry was modeled showing stronger collimation within the tight confines of narrow diameter casings. The updated detector design is expected to enable better sensitivity to voids in the well casing or concrete. Researchers performed component-level fabrication and bench-level testing for the various components of the neutron generator prototype integrated system. Presently the performance of this second prototype neutron generator is not up to the expected level due to conflicting operation of various power supplies, and is currently being investigated.

Testing of X-ray and neutron sources were completed by modeling defect detection tests utilizing a variety of emitting sources. Based on the results, it is more likely that a high energy photon source would be able to produce the energy needed to detect defects in the outer rings of a well as X-rays have not shown enough energy to date. Experiments are planned to confirm the modeled results.

Neutron modality testing continued. The neutron flux distribution throughout the cylindrical steel/cement test assembly was calculated. The results show the penetrating power of the neutron through multiple casings and cement layers. GE was notified by a subcontractor that they are no longer comfortable participating in the project due to changes in the specifications for the X-ray sources, as they feel the new specifications are outside of their expertise and existing infrastructure. GE had discussions with potential replacement subcontractors. The choices have been narrowed down to three manufacturers of X-ray sources experienced in the design and build of X-ray sources of high acceleration voltages.

Researchers are using Monte Carlo N-Particle (MCNP) modeling of transport properties to determine the entitlement for the high energy modalities of X-ray and neutron. A basic modeling configuration of concentric cylinders of steel and cement has been developed to represent concentric casings in the unconventional well and the soil field. Results show the penetrating capability of the X-ray photons through multiple casings and cement layers. These preliminary results demonstrate that the MCNP code is functioning and the neutron and photon transport properties can be used to examine the wellbore steel and cement structure.


GE has submitted the task four report which includes the entitlement results and risk analysis from modality testing.  X-rays, neutrons, ultrasound and electromagnetic were tested for their applicability to well integrity tests through modeled experiments. A high energy X-ray source is the most promising for the limited space and the thickness of the well walls.

Current Status (August 2017)
The developed nXis prototype tools were tested at a high-energy facility at GE Global Research and at an industrial oil and gas test facility using an inground test pit. For the entitlement analysis of the nXis system, multiple wellbore phantoms with engineered casing and annulus defects were inspected. Wellbore integrity defects past the first casing/cement interface could be detected by the neutron modality. Detection capabilities with azimuthal resolution for outer annulus channel defects show promise of this technology to enhance safety and to improve environmental protection for hydrocarbon producing wellbores.

Project Start: October 1, 2014
Project End: March 31, 2017

DOE Contribution: $2,488,688
Performer Contribution: $622,172

Contact Information:
NETL – Sandy Borek (sandra.borek@netl.doe.gov or 412-386-4533)
GE – Matthias Kasten (kasten@ge.com or 518-387-6915)