From Wish-List to To-Do List: A Summary of the 5^th EAGE Passive Seismic Workshop 

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Introduction

The 5^th EAGE Passive Seismic Workshop held in Lisbon/Portugal from Sep. 29^th to Oct.1^st attracted more than 50 specialists from all over Europe, North America and New Zealand. In order to generate some tangible deliverables, this workshop focused only on issues around “Induced Seismicity”, “Fracture Mechanics and Interpretation“ and “Integrated Interpretation”, with each of the three days focusing on one of the topics. Compared to previous workshops the general format was significantly changed to facilitate a more focused discussion among experts from academia, operators and service companies. The morning sessions were reserved for invited keynote speakers describing the current status of the day’s focus topic and pointing out knowledge gaps. The topic was further explored before lunch through related poster sessions already sparking lively discussions among the participants. In the afternoon the workshop participants could attend one of three breakout groups that worked on some of the issues identified in the keynote addresses under the guidance of discussion facilitators. The results of these discussions were reported back to the whole group with the intent to create a To-Do list identifying specific topics that need to be addressed in order to advance the application and usefulness of microseismic and passive seismic technologies.

ASL Geoscientist William Wills who is on the technical committee presented a paper Reducing velocity model uncertainty and improving microseismic event location accuracy: crosswell seismic tomography using a repeatable downhole sparker source.

Outcome 1: Data exchange

Almost universally the discussions identified the need for a better information exchange between academia, service providers and operators. However without a clear protocol for data exchange based upon an anonymized system of data submission, the flow of information from the operators would be unlikely to happen. Establishing such a protocol is now placed on our wish-list.

Although many of the challenges in the application of microseismic data are well-known throughout the industry, the publishing and updating of these challenges will help research and development institutions to focus on industry relevant problems. Similarly, an overview of capabilities and current work programs of research groups will help connecting academia with industry and support development of required products by the service providers.

A new LinkedIn group EAGE-PSW has been created with the intent to discuss and follow up the outcomes of the workshop and to determine topics for the next workshop. In addition, informal meetings for PSW members will be organized for any upcoming major geoscientific convention to further facilitate information exchange. Check the EAGE-PSW discussion group for details.

Outcome 2: Definition

The growing demand for regulatory compliance in certain jurisdictions requires us to standardize the meaning for key terms. Presently the specific meaning of terms such as natural, induced and triggered seismicity vary. Actions need to be discussed in order for a standardized definition and to gain acceptance for this definition. Geophysically there is no measurable difference between these three categories.

Outcome 3: Seismic hazard and risk

Some of the more recent regulation requires the use of monitoring systems to detect seismicity and estimate Magnitude. So far it has not been proven that such regulations are effective. It is necessary to document any instance of the application of these regulations in order to determine if they are useful in mitigating the risk of induced seismicity.

Discussions surrounding the use of probabilistic and deterministic methods for estimating seismic risk tentatively concluded that adaptive probabilistic methods should be used, whereby continued model update would provide a better constraint upon future risk.

Since building codes most often use peak ground velocity or acceleration as a criterion for potential damage it would make much more sense if our probabilistic models also make forecasts including particle motion at the surface along with Magnitude.

Although probabilistic models often better reflect our understanding of the data than deterministic models, the often unintuitive nature of inverse or probabilistic modelling requires a transparency of approach and a process of stakeholder education, such that public acceptance and trust become the norm.

Outcome 4: Geomechanical models

The critical role of geomechanical models linking microseismic attributes with relevant deformations in the ground is recognized. Although it is not necessary to agree on a single universally applicable geomechanical model, it is important to determine how the different models should be applied. In addition, it is important to understand what key input parameters for geomechanical need to be collected in order to validating some of the model conclusions.

Outcome 5: Uncertainty and non-uniqueness

The use of inverse models requires an understanding of both uncertainty and the non-uniqueness of the modeling process. However, as a community we need to better drive home the standardization and quantification of error in the process of delivering microseismic results.

The decomposition of seismic moment tensors in anisotropic media is non-unique. Ideally, individual terms of the decomposition should allow for an interpretation in terms of the physics of the source mechanism.

Outcome 6: Integration with other data

The basic value proposition for the use of microseismic results relies upon the input of length and height as a geometric constraint on frac models.

Yet the information content of microseismic data is much greater. Attempts to use microseismic information as input to fracture network representations are showing promise. However, the validations of such workflows are not yet broadly recognized. Such direct validation is difficult to obtain for suggested interpretations of microseismic attributes such as the correlation of moment tensor solutions and fluid movements, r-t diffusivity values, etc. Often some indirect validation evidence exists but these results are not accessible in a systematic manner. A summary of all direct and indirect validation data for microseismic interpretations would help identify and close knowledge gaps. Data gathering could start from published sources supplemented by available data from industry.

When looking at the overall disciplines involved in a complete integration approach, laboratory tests are seen as key to evaluate actual geomechanical properties under stress. However there is a recognized up scaling limitation of lab test models when considering the formation’s behavior at the scale of a production pad or field. As a result, existing hydraulic fracture modelling tools must accommodate simplifications and short cuts that potentially render the link between lab and field much more difficult to assess.

Overall, microseismic information has the potential to link a wide range of data sets together by providing the connection between near field information (stress/imaging logs, mineralogy samples, lab tests, etc.) to the far field information provided mainly by 3D seismic structural and seismic attributes information. Where microseismic events can be used to calibrate and tie far field data with near field data, one can develop stronger predictive models of the formations response to certain stimulations.

End users of microseismic data need to establish clear decision workflows based on validated interpretations of microseismic and other diagnostic data.

Conclusions

The new workshop format facilitated plenty of discussion. The smaller the individual groups were the more productive these discussions appeared to be which lead to a suggestion to limit future workshops to 70 participants. The combination of keynote presentations and poster presentations worked equally well with the poster sessions sparking plenty of discussions. Most microseismic datasets are still being collected in North America but the challenges and possible applications are different in places like Europe and the Middle East. While these places most certainly can benefit from the learnings in North America, transfer of workflows and problem solutions might require adaptation to the local technical, logistical and regulatory environment.

No final To-Do list was generated at the end of the workshop, but several action items were discussed with the main topic being the continued information exchange between workshops. The current organization committee will stay in place for a little while longer to realize or initiate as many of the suggestions as possible.

The organization committee and all participants in the workshop hope that the discussions initiated in Lisbon will carry on with the ultimate goal not only to create a specific To-Do list but actually solve some of the identified challenges in the wide range application of microseismic data.