Adam Baig

Microseismic moment tensors: A path to understanding frac growth

Microseismic monitoring is a valuable tool in understanding the efficacy of hydraulic fracture treatments. Determination of event locations and magnitudes leads to estimations of the geometry of the fracture zone and certain dynamics of the fracturing process. With sufficient resolution, the hypocenters may even reveal failure planes or other underlying structures controlling the distribution of events and of interest to petroleum engineers to test various hypotheses on fracture growth.

Identifying Reservoir Drainage Patterns From Microseismic Data

Microseismic data provides insights on the efficiency of a hydrocarbon field stimulation program. Current interpretation is often limited to assessing stimulated fracture geometry and number of events. Classical flow patterns, based on symmetric and homogeneous flow, are then often assumed to predict drainage areas and production volumes. In an attempt to link geophysical data with reservoir engineering, we here present a novel approach, using in situ measurements on the strain imparted on the rock mass by individual rock failures. Moment tensor inversion of the microseismic events yields the failure mechanism and orientation of each event. Historically, the resultant strain field of all events has been used to mapping compartments of parallel strain. Here, we here extent this approach assuming that tensile strain on the rock mass opens preferred flow path ways. By mapping stream lines through the strain field it is thus possible to identify drainage patterns of individual ports throughout the stimulated reservoir volume.

After a Decade of Microseismic Monitoring: Can We Evaluate Stimulation Effectiveness and Design Better Stimulations

Over the past decade, microsesimic monitoring has become the approach most oftenused to gain an in-situ understanding of the rocks response during hydraulic fracture stimulations. From initial monitoring performed in the Barnett Shale to monitoring currently being carried out for example in the Horn River and Marcellus formations, we review the evolution of microseismic monitoring from the viewpoint of data collection (single versus multi-well array configurations, utilization of long lateral stimulation wells), to data analysis, to the incorporation of microseismic parameters to constrain and validate reservoir models. Generally, we have observed that overall fracture height, width and length, orientation, and growth vary from formation to formation and within each formation, thereby highlighting the ongoing necessity for microseismic monitoring. Additionally, through the use of advanced microseismic analysis techniques, such as Seismic Moment Tensor Inversion (SMTI), details on rupture mechanisms have been used to assess stimulation effectiveness, define complex Discrete Fracture Networks (DFN) and provide estimates of Enhanced Fluid Flow (EFF), which assist in calibrating and validating reservoir models. Utilizing spatial and temporal distributions in DFN and EFF, along with estimates of fracture interconnectivity and complexity, the role of pre-existing fractures and fault structures in the rock matrix can be established and used to provide more realistic estimates of stimulation parameters such as Stimulated Reservoir Volume (SRV).

Long-term assessment of reservoir integrity utilizing seismic source parameters as recorded with integrated microseismic-pressure arrays

Summary In this paper, we investigate how an integrated approach to long-term reservoir monitoring utilizing pressure and micorsiemic data can be used to identify changes in reservoir behaviour leading to compromises in reservoir integrity. In particular, we examine the observations related to a cyclic steam operation and subsequent loss of steam containment. Based on these observations, we suggest that the integration of real-time microseismic monitoring provides an opportunity to investigate reservoir integrity over long-term field development.

Rupture Behaviour of Induced Seismicity

With a hybrid monitoring array of 15 Hz downhole sensors and lower frequency sensors on the surface, we can look in detail at the differences in rupture processes between lower magnitude seismicity usually associated with hydraulic fractures (M 0). We find that in the dataset we examine from the Horn River Basin in NE BC, that the lower magnitude events are associated with more lubricated, slower slip, and simple rupture processes whereas the larger magnitude events are more consistent with a more complicated rupture process with less of a fluid component. These findings are important to develop an understanding of the generating processes behind larger magnitude events observed during hydraulic fracture completions.

Linking Microseismicity to Geomechanics through Seismic Moment Tensor Inversion

Moment tensor inversion of microseismicity can be used to image the strain tensor through space and time around the injection volume, resolve the associated dynamic stress variations, and determine the orientations of fractures in the discrete fracture network (length scales of these ruptures can be observed in the frequency content of the waveforms). All of these quantities are of direct import to geomechanical models and may be directly used to as inputs in terms of the stimulated DFN as well as establishing the dynamism of the stress and strain conditions to allow for better understanding of the fracturing process.

Establishing Flow and Drainage Potential as Related to Well Production

Microseismicity can occur in dense concentrations in time and space during injection processes. We discuss imaging the deformation from the microseismic events in terms of streamlines that highlight the optimal drainage pathways in the reservoir. Furthermore, we introduce dynamic fracture parameters. One such parameter, the plasticity index, shown. Both the drainage patterns and the plasticity index are compared to production logs from different wells to validate their responses.

The Potential for Predicting Production by Characterizing Fluid Flow and Drainage Patterns Using Microseismicity

We apply a continuum approach to describe the dynamics of seismicity observed during a hydraulic fracture of a multiple horizontal well pad. By exploiting the multi-well observation geometry, we are able to resolve the seismic moment tensors of the high-quality events. Not only does this information constrain the fracture orientations, but it can be used to reconstruct the state of stress/strain in the reservoir. We use the strain to drainage of the reservoir through a strain-flow analysis. Furthermore we examine the spatial and temporal variations in the microseismicity, as well as the energy release characteristics, to image the regions of the reservoir where plastic damage is most confined around the wellbores. To validate both approaches we use PLT data.

4D Tomography and Deformation from Microseismic Data

Microseismic data are used to calculate seismic deformation in response to hydraulic fracturing throughout a reservoir. This information is incorporated into a 4D tomography code that calculates changes in seismic velocity over the volume of the reservoir and as a function of time as deformation progresses. Changes in velocity are attributed to either deformation or the presence of fluids. A comparison is made between the velocity anomaly and deformation fields and is used to help distinguish between fluid induced changes in velocity and damage induced changes.

Resolving Time Dependant Stress Variations through Analysis of Microseismicity Recorded During Hydraulic Fracturing

Hydraulic fracturing of shale reservoirs enhances productivity of reservoirs by propping open fractures in the reservoir. In order to map the extent of the successfully stimulated zones, microseismic monitoring is increasingly used; typical outputs of such monitoring efforts are the geometry of the microseismic event distribution. To relate these event distributions to production decline curves, geomechanical modelling of the injection using these event distributions as a constraint is frequently performed. However, a basic assumption of such efforts is that the stress regime under which the events are occurring is invariant. By using multiple-well recordings of microseismic events, the mechanisms of the microseismicity may be determined. These mechanisms are proportional to the strain rate (deformation) that is imparted to the medium at the point of rupture, and as such constrain the stress regime through the treatment. Observations indicate that the stress/strain conditions in the reservoir can be highly variable, implying that microseismicity needs to be coupled to geomechanical models at a more basic level, in that the dynamic stress regime controls both the occurrence of these events and the propagation of fluid and proppant in the reservoir.