Electro-Map: A Novel Method of Hydraulic Fracture Analysis

In the present day, there are three main practical issues that most engineering solutions are aiming to address: environmental effect, completeness of information, and cost effectiveness. Engineers and designers around the world are trying to implement solutions that address these three main practical issues. There are two main common methods that are currently used by engineers in order to detect cracks that are created by hydraulic fracturing: radioactive tracers and microseismic monitoring. However, both of these methods present some practical issues, which our proposed solution aims to address and avoid.

Effect on the Environment:

The main mechanism through which radioactive tracers work is by coating the proppant particles with these tracers, which then emit gamma rays that can be detected using a radioactive sensor. As a result of the signals received by this sensor, the various characteristics of the cracks can be determined. However, using these radioactive materials can be extremely harmful for the environment. This is one of the practical issues with using radioactive tracers, and this was one of the main motivations behind undertaking this project. Therefore, despite its effectiveness, the method of radioactive tracers is not a preferred method of application. Our proposed method of using a LFEI tool does not require the use of any radioactive material that would be harmful towards the environment in any way.

Completeness of information and cost effectiveness: 

The technique of microseismic monitoring presents the idea of installing geophones at different ground locations, which are a type of acoustic sensor that work by detecting vibrations in the ground that are caused by seismic waves. Engineers and geophysicists can gather the information from several adjacent sensors and then compare the data. The difference in the data will allow them to effectively determine the geometric structure of these cracks. However, some of the basic challenges with microseismic monitoring is the incompleteness of information (such as the propped length of these fractures), distribution of the proppants within these fractures, and its cost effectiveness. There are two main practical issues with microseismic monitoring: completeness of information and cost effectiveness. Our proposed solution aims to provide information both on propped fracture lengths and the distribution of these proppants, through a set of data that will be used for generating a graph. Additionally, the use of geophones in microseismic monitoring is very expensive, since multiple geophones need to be installed in multiple locations. On the other hand, our project requires only the use of one triaxial transmitter and two triaxial receivers, which are relatively less expensive than the installation of multiple geophones at different locations.

1. Ability to infer concentrations of proppants and their conductivity within the fracture distributions.

Through our research, current industry technologies used to characterize fracture distributions such as microseismic mapping offer no data on the concentration of proppants within a given fracture. This information is important as it provides a means of assessing the hydraulic conductivity (i.e., the ability which oil and gas can flow through a given pathway) and therefore the productivity of a given fracture. Without this data, well operators cannot adjust and optimize proppant injection. Our LFEI prototype characterizes proppant concentration by replacing a portion of the proppant mixture with a conductive substance called calcined petroleum coke. Since our tool maps out fractures by inducing a time-varying current through the cracks, the magnitude of the signals picked up by the tri-axial receivers can determine the proppant density. This information allows well operators to accurately estimate hydraulic conductivity and by extension, the productivity of any given fracture.

2. Can characterize the following fracture distribution parameters: aspect ratio, dip angles, and radii.

Extracting as much information out of fracture distributions is paramount for optimization studies and determining the productivity of hydraulic fracking wells. Our LFEI prototype tool can characterize not only the length and size of fractures, but also its aspect ratio, radii, and lastly, dip angles. By mapping out fracture distributions with more detail, drilling companies have the information and resources to determine which mechanisms for creating these fractures have the greatest potential to extract the most oil and gas.

3. Modularity. Can add more Tx/Rx pairs to increase resolution or capture more information along the wellbore. 

Our LFEI prototype tool is modular as it has the capacity to extend its range of data collection along the wellbore by adding more sets of Tx/Rx pairs to the array. Whether the application is to map out a short horizontal section of fracture distributions or to collect data for the entire wellbore, our system can accommodate any application and range.

The main working principle of our technique is to detect and characterize fractures using electromagnetic induction. These fractures are created when a fracturing fluid is pumped into the wellbore at an extremely high pressure. Proppants are an important part of the fracturing fluid as they are responsible for holding these newly created fractures open. The trapped oil and gas underneath the shale formation can travel up to the surface through these cracks. Our technique is unique because it substitutes a portion of traditional proppants (typically sand) with an electrically conductive substance, specifically Calcined Petroleum Coke (CPC). The idea is that a sufficient quantity of this substance will be used and as a result, the fractures, which will be filled with this substance, can then be modelled as metallic conductors.

Our proposed solution uses a changing magnetic field to be incident upon a conductor, which is the proppant filled fracture. As a result of this incident magnetic field, eddy currents are generated within the fracture (conductor), which then create a secondary magnetic field that varies with respect to time. Our solution uses this basic principle of electromagnetic induction in order to detect fractures created during the process of hydraulic fracturing.

In order to produce the incident magnetic field described, a time-varying current will be run through a triaxial transmitter coil. This incident magnetic field on the fracture component will cause eddy currents to run through the interior of the fracture. The secondary signal produced by the eddy currents will be received by a triaxial receiver coil. The results received from this can then be analyzed to infer the geometric characteristics of the fracture from which the signal originated.

For the actual constructed prototype, each block comprising the solution had a QAQC report that was completed. The collected data were mainly qualitative and they were measured by analysing different design attributes. The transmitter consisted of impedance and inductance testing, the power amplifiers, voltage gain and power efficiency testings, The pre-amp for the receiver was tested for output efficiency and for the lock-In Amplifier, functionality and lowest output range was tested. Based on these subtestings, the team is able to validate the working process of the whole prototype design solution.

The project also includes a simulation that is run on FEKO to support the expected results of the whole prototype. Since the prototype is an electromagnetic tool, the simulated tool and the associated data are an ideal representation for verifying expected data which is then comparable to results from the physical tool. The process can be followed with the figure below.

An experimental setup was constructed, which consisted of the prototype being used in a built small-scale wellbore to get data as close to as if the tool was used in a real underground wellbore setting. The resulting data is compared to the simulation data for validation.

Our idea needed to be of high potential as well as a feasible solution for our sponsor and the oil and gas industry in general.

To start, each component has been made to produce high quality results while still being relatively inexpensive in comparison to some of the other current methods. This not only ensures a cost effective solution, but also an easily reproducible product. 

While small in size, the tool can be easily scaled up to be used in a real world scenario and this is supported with resulting data from simulations conducted.

The team has also kept a well detailed log of the design process that will be transformed into a technical document for the sponsor to continue this project  for further research and development.