Autonomous decision-making against induced seismicity in deep fluid injections

The rise in the frequency of anthropogenic earthquakes due to deep fluid injections is posing serious economic, societal, and legal challenges to geo-energy and waste-disposal projects. We propose an actuarial approach to mitigate this risk, first by defining an autonomous decision-making process based on an adaptive traffic light system (ATLS) to stop risky injections, and second by quantifying a "cost of public safety" based on the probability of an injection-well being abandoned. The ATLS underlying statistical model is first confirmed to be representative of injection-induced seismicity, with examples taken from past reservoir stimulation experiments (mostly from Enhanced Geothermal Systems, EGS). Then the decision strategy is formalized: Being integrable, the model yields a closed-form ATLS solution that maps a risk-based safety standard or norm to an earthquake magnitude not to exceed during stimulation. Finally, the EGS levelized cost of electricity (LCOE) is reformulated in terms of null expectation, with the cost of abandoned injection-well implemented. We find that the price increase to mitigate the increased seismic risk in populated areas can counterbalance the heat credit. However this "public safety cost" disappears if buildings are based on earthquake-resistant designs or if a more relaxed risk safety standard or norm is chosen.Comment: 8 pages, 4 figures, conference (International Symposium on Energy Geotechnics, 26-28 September 2018, Lausanne, Switzerland

Advies over seismische activiteiten en bodemdaling

Ze vindt het geweldig om als onderzoeker te werken aan onderwerpen die in onze samenleving heel actueel zijn. Denk hierbij bijvoorbeeld aan allerlei aspecten rond de gas- en zoutwinning in ons land. Dr. Karin van Thienen-Visser is medeverantwoordelijk voor de technisch-geomechanische adviezen hierover aan de overhei

Inversion of double-difference measurements from optical levelling for the Groningen gas field

Hydrocarbon extraction lead to compaction of the gas reservoir which is visible as subsidence on the surface. Subsidence measurements can therefore be used to better estimate reservoir parameters. Total subsidence is derived from the result of the measurement of height differences between optical benchmarks. The procedure from optical height difference measurements to absolute subsidence is an inversion, and the result is often used as an input for consequent inversions on the reservoir. We have used the difference measurements directly to invert for compaction of the Groningen gas reservoir in the Netherlands. We have used a linear inversion exercise to update an already existing reservoir compaction model of the field. This procedure yielded areas of increased and decreased levels of compaction compared to the existing compaction model in agreement with observed discrepancies in porosity and aquifer activity

Compaction and subsidence of the Groningen gas field in the Netherlands

The Groningen gas field in the Netherlands is Europe’s largest gas field. It has been produced since 1963 and production is expected to continue until 2080. The pressure decline in the field causes compaction in the reservoir which is observed as subsidence at the surface. Measured subsidence is characterized by a delay at the start of production. As linear compaction models cannot explain this behavior, alternative compaction models (e.g. Rate Type Compaction Model and Time Decay model) have been investigated that may explain the measured subsidence. Although the compaction models considered in this study give a good match to this delay, their forecasts are significantly different. Future measurements of subsidence in this area will indicate which type of compaction model is preferred. This will lead to better forecasts of subsidence in future. The pattern of over- and underestimation of the subsidence is similar for the compaction models investigated and tested. The pattern can be explained by differences in modeled porosity and aquifer activity illustrating the improvement of subsurface knowledge on the reservoir using subsidence measurement

Subsidence due to gas production in the Wadden Sea: How to ensure no harm will be done to nature

The Wadden Sea is a shallow tidal sea in the north of the Netherlands where gas production is ongoing since 1986. Due to the sensitive nature of this area, gas extraction induced subsidence must remain within the "effective subsidence capacity" for the two tidal basins (Pinkegat and Zoutkamperlaag) affected. We present a probabilistic method to monitor the "effective subsidence capacity" and ensure that subsidence is below the long term (18.6 years) volumetric rate for relative sea level rise that can be accommodated by the tidal basins without environmental harm. The role of sedimentation volume rate, relative sea level rise and subsidence volume rate due to gas depletion are taken into account including their uncertainties. The probability of exceeding the acceptable subsidence limit for the period 2012 to 2050 is 2.8% for the tidal basin called Zoutkamperlaag and 1% for the tidal basin of Pinkegat for climate scenarios that fit the current relative sea level rise observations on the Dutch coast. The values are shown to be dominated by the effect of relative sea level rise, and not due to subsidence induced by gas depletion in the Wadden Sea. To current knowledge no harm is done to nature. Copyright 2015 ARMA, American Rock Mechanics Association

Isotach formulation of the rate type compaction model for sandstone

This paper presents a new formulation of the Rate Type Compaction Model (RTCM) for sandstone based on the isotach concept. The RTCM was originally developed to explain the loading rate dependent compaction behaviour observed in laboratory test on unconsolidated and consolidated sandstone samples and the delayed subsidence behaviour above depleting reservoirs. The original RTCM equation has the limitation of being unable to describe transitions between different loading rates, including the transition to a loading rate of zero (creep). The new formulation combines the features of the original RTCM with the isotach concept developed is soft soil geotechnics, which enables transitions between different loading rates, thereby overcoming the limitations of the original RTCM. The isotach formulation of the RTCM model is used to simulate a multiple loading rate experiment on a Rotliegend sandstonwe core sample. The agreement between results of the lab experiment and the proposed isotach RTCM model is excellen

Compaction and subsidence of the Groningen gas field in the Netherlands

The Groningen gas field in the Netherlands is Europe's largest gas field. It has been produced since 1963 and production is expected to continue until 2080. The pressure decline in the field causes compaction in the reservoir which is observed as subsidence at the surface. Measured subsidence is characterized by a delay at the start of production. As linear compaction models cannot explain this behavior, alternative compaction models (e.g. Rate Type Compaction Model and Time Decay model) have been investigated that may explain the measured subsidence. Although the compaction models considered in this study give a good match to this delay, their forecasts are significantly different. Future measurements of subsidence in this area will indicate which type of compaction model is preferred. This will lead to better forecasts of subsidence in future. The pattern of over- and underestimation of the subsidence is similar for the compaction models investigated and tested. The pattern can be explained by differences in modeled porosity and aquifer activity illustrating the improvement of subsurface knowledge on the reservoir using subsidence measurements

Geomechanics response and induced seismicity during gas field depletion in the Netherlands

In this paper we present a review of controlling geological, tectonic and engineering factors for induced seismicity associated to gas depletion in the Netherlands and we place experiences from extensive Dutch geomechanical studies in the past decade in the context of generic models for induced seismicity. Netherlands is in a mature gas production phase, marked by excellent subsurface structural and stratigraphic characterization. Over 190 gas fields of varying size have been exploited. No more than 15% of these fields show seismicity. Geomechanical studies show that, similar to the EGS stimulation phase, largest seismicity is localized on pre-existing fault structures. However, the prime cause for seismicity in gas depletion is differential compaction, whereas in EGS stimulation related pressure build-up and fluid pressure diffusion along the faults form the prime mechanism. On the other hand, our study has a close theoretical analogy to reservoirs where the fluid volumes extracted are significantly larger than the re-injected volumes, and which can result in (differential) reservoir compaction.The observed onset of induced seismicity in the Netherlands occurs after a considerable pressure drop in the gas fields. Geomechanical models show that both the delay in the onset of induced seismicity as well as the non-linear increase in seismic moment observed in the induced seismicity, can be explained using a model of differential compaction, if the faults involved in induced seismicity are not critically stressed at the onset of depletion. The presented model serves to highlight key aspects of the interaction of initial stress and differential compaction in the framework of induced seismicity in Dutch gas fields. It is not intended as predictive model for induced seismicity in a particular field. To this end, a much more detailed field specific study, taking into account the full complexity of reservoir geometry, depletion history, mechanical properties and initial stress field conditions is required