Migration-based event location for DAS-geophone hybrid microseismic monitoring from a single monitoring well: Hydraulic stimulation case studies for oil/gas and geothermal applications

A precise velocity model is necessary to obtain reliable locations of microseismic events, which provide information about the effectiveness of the hydraulic stimulation. Seismic anisotropy plays an important role in microseismic event location by imposing the dependency between wave velocities and its propagation direction. Building an anisotropic velocity model that accounts for that effect allows for more accurate location of microseismic events. We have used downhole microseismic records from a pilot hydraulic fracturing experiment in Lower-Paleozoic shale gas play in the Baltic Basin, Northern Poland, to obtain accurate microseismic events locations. We have developed a workflow for a vertical transverse isotropy velocity model construction when facing a challenging absence of horizontally polarized S-waves in perforation shot data, which carry information about Thomsen’s [Formula: see text] parameter and provide valuable constraints for locating microseismic events. We extract effective [Formula: see text], [Formula: see text] and [Formula: see text], [Formula: see text] for each layer from the P- and SV-wave arrivals of perforation shots, whereas the unresolved [Formula: see text] is retrieved afterward from the SH-SV-wave delay time of selected microseismic events. An inverted velocity model provides more reliable location of microseismic events, which then becomes an essential input for evaluating the hydraulic stimulation job effectiveness in the geomechanical context. We evaluate the influence of the preexisting fracture sets and obliquity between the borehole trajectory and principal horizontal stress direction on the hydraulic treatment performance. The fracturing fluid migrates to previously fractured zones, while the growth of the microseismic volume in consecutive stages is caused by increased penetration of the above-lying lithologic formations.

Download Full-text

Single Well Microseismic Monitoring Leveraging Hybrid Cable Combining Both DAS and Traditional Geophones

10.2118/204613-ms ◽

2021 ◽

Author(s):

Takashi Mizuno ◽

Joel Le Calvez ◽

Theo Cuny ◽

Yu Chen

Keyword(s):

Cost Effective ◽

Microseismic Monitoring ◽

Arrival Times ◽

Monitoring Well ◽

Location Uncertainty ◽

Event Location ◽

Single Well ◽

Using Data ◽

Array Aperture ◽

Montney Formation

Abstract The single monitoring well configuration is a favorable option for microseismic monitoring considering risk and cost. It has commonly been used in various industries for decades. When using a single monitoring well, we rely among other things on the waveforms’ polarization information to accurately locate detected microseismic events. Additionally, using a large array aperture reduces hypocenter's uncertainty. Instead of solely relying on 3C geophones to achieve such objectives, we propose to combine 3C sensors and distributed acoustic sensing (DAS) equipment. It is quite a cost-effective solution, and it enables us to leverage each system's strength while minimizing their respective limitations when considered individually. We present the technical feasibility of such a hybrid microseismic monitoring system using data acquired during a monitoring campaign performed in the Montney formation, Canada. In this dataset, the optic fiber (DAS) is located in the wireline cable used to deploy the 3C geophones; themselves located at the bottom of the DAS wireline cable. Though different acquisition systems are employed for the geophone array and the DAS array, both datasets are GPS time stamped so that data can be processed properly. We scan the DAS data using an STA/LTA event detection, and we integrate with the 3C geophone data. We find the microseismic waveform in both the DAS and the geophone sections and confirm the arrival times are consistent between DAS and geophones. Once datasets are merged, we determine hypocenters using a migration-based event location method for such hybrid array. The uncertainty associated with the event located using the hybrid DAS – geophone array is smaller than for any of the systems looked at independently thanks to the increased array aperture. This case study demonstrates the viability and efficiency of the next generation of a single well acquisition system for microseismic monitoring. Not only does it lower event location uncertainty, but it is also more reliable and cost-effective than the conventional approaches.

Download Full-text

A Closer Look at Hydraulic Fractures: Case Studies of Microseismic Results from Horizontal Monitoring Wells

10.2118/205707-ms ◽

2021 ◽

Author(s):

Zhanwu Gao ◽

Kai Li ◽

Guanghui Gao ◽

Haiyu Liao ◽

Yadong Zhang ◽

...

Keyword(s):

Case Studies ◽

Hydraulic Fracture ◽

Horizontal Well ◽

Horizontal Wells ◽

Microseismic Monitoring ◽

Long Distance ◽

Fracture Geometry ◽

Monitoring Wells ◽

Monitoring Well ◽

Microseismic Events

Abstract Amongst different options of hydraulic fracture geometry detection or measurement, microseismic monitoring is a commonly used method to reveal the hydraulic fracture geometry in three-dimensional space. Microseismic monitoring typically requires one or several monitoring wells within an effective range from the treatment well, in which the geophones are set to detect the microseismic events occurring during or after the treatment. In the past, most of the monitoring wells have been vertical wells. We present several recent case studies in which both the treatment and monitoring wells were horizontal wells, which produced some unique and interesting observations beyond the initial expectations. One of the prerequisites of a proper microseismic monitoring of hydraulic fracturing treatment is to place the geophone in the proper position because a long distance between the actual fracturing events and the geophone may result in signal deterioration, which influences the processing and increases the uncertainty. This problem is more severe if the treatment well is a horizontal well because the distance from the geophone to the microseismic events varies between stages. One of the methods to solve this issue is to monitor the microseismic events in a horizontal offset well. As horizontal wells are often batched drilled in clusters for tight or unconventional resource nowadays, the availability of the monitoring well is less of a problem, and the constant distance from the monitoring well to the treatment well may help to generate better data quality and more accurate interpretation result. We implemented horizontal well monitoring in two difference cases between 2018 and 2019. For case A, one horizontal monitoring well was used to monitor 54 fracturing stages in three offset wells, and for case B, we monitored 24 fracturing stages in one offset well. In both cases, the geophone arrays were shifted in multiple positions to fit the distance requirements, and both cases generate satisfying interpretation results. The microseismic results from the two cases showed less uncertainty and better precision of microseismic events after processing, as we expected. What is surprising is this type of monitoring showed a unique physical phenomenon a couple of times, which is a casing background noise indicating excessive fracturing extension over a long distance. This phenomenon was captured in both cases, even with small injection rate and fluid volumes, which can be important information for us to better understand the dynamics of fracture propagation in such geomechanical environment and help to set a new guideline and design reference in the same region.

Download Full-text