Induced seismicity caused by underground fluid injection occurs because of pore pressure changes that lead to stress changes in the reservoir and the surrounding formations. Despite that noticeable seismic events from fluid injection is very rare, proper assessment of possible seismic events is important. The objective of this study is to develop numerical models that simulate stress changes, fault slips, and ground floor movements induced by underground fluids injection.
The numerical analysis process presented in this work consists of three steps. First, stress changes around the reservoir due to fluid injection are analyzed using a FEM-BEM (Finite Element Method - Boundary Element Method) coupled model. Secondly, the stability of faults located near the reservoir is evaluated using the displacement discontinuity method. Thirdly, elastic waves caused by the fault slip is simulated using a FEM model where seismic response on the surface are calculated. A field case study is also presented to demonstrate the applicability of the numerical model developed in this work.
The numerical analysis results indicate that stress concentration occurs around a boundary between the basement and sandstone beneath the reservoir. This affects the stability of existing faults in this region. As a result, when the fault is slipped, seismicity may be triggered. It is assumed that the slip is caused by stress changes in the faulted region as well as a pore pressure change in the fault, which is caused by volumetric strain changes of the fluid in the fault. A field case study based on wastewater injection in the Southwestern region of the United States where injection induced seismicity events have been recently reported, is also performed in this work. In this case study, the variation of rock strength is considered one of important factors in induced seismicity events.
The novelty of our model is the ability to quantitatively assess the risk of induced seismicity due to wastewater injection, which can be also applied to other applications such as CCS and underground gas storages. Moreover, conducting risk assessment by these numerical models can improve safety of underground fluid injection operations.
Diagnostic fracture injection tests (DFIT's), or "mini-fracs" are often used to gauge many reservoir and fracture design parameters. However, DFITs are not always conducted in conjunction with the main completions work. This paper proposes a novel workflow to determine the instantaneous shut-in pressure (ISIP) from readily available completions data. This is a valuable parameter in itself as related to the least principal in-situ stress states as demonstrated by the stress change relationships near faults in
Directly using completions data from fracture stimulation operations, the authors have leveraged on the water-hammer signature in bottom-hole pressure data during completions to process the ISIP for each completions stage. Within this study, completions data from ~2100 stages from ~300 horizontal Montney formation wells were analyzed. A MATLAB script was used to automate the derived ISIP stress trends over the Montney formation and to deduce the ISIP in a consistent format.
This novel workflow also validates the expected in-situ stress trends at depth, with a relationship of high ISIP gradients closer to fault zones similar to stress change behaviour as shown in
Considering the continued push for higher fluid and sand loading in industry in the development of unconventional assets as an economic driver, there also exists a large and tangible corporate citizenship opportunity of mining real time completions dark data with the possibility of relating that live feed as a prescriptive tool to mitigate reactivation of critically stressed faults. This case study focuses on the Montney formation as a basis for processing easily available data from standard operations in an effort of systematically designating areas prone to seismicity risk in future hydraulic fracturing operations based on automated real-time analytics of dark data.
Induced seismicity from the injection of fluids into the earth remains a significant concern for oilfield activities such as saltwater disposal and hydraulic fracturing operations. The number of induced earthquakes occurring in the oil and gas producing regions of the Central United States and Western Canada has been declining over the past few years, highlighting the successful implementation of improved regulations and effective operational practices. However, technical engineering and geoscience challenges remain. This opening session will explore the current state of learnings and progress since the last workshop in November 2017, and highlight forward opportunities and challenges. Differences in geology, industry practices, population, politics, and other factors lead to various regulatory responses and requirements.
This paper describes a coreflooding program performed with sandpacks at different permeabilities, water qualities, and injection conditions. ProSep’s Osorb Media Systems are providing a unique solution for treating the water coming from chemical enhanced oil recovery operations and removing the dissolved hydrocarbons. Rising oil production in the Permian Basin has created an opportunity for midstream companies to acquire and expand pipeline infrastructure to handle a predicted spike in produced water. The company makes good on a pledge to reduce freshwater use and replenish the fresh water it uses. In a recent acquisition, H2O Midstream will own and operate Encana’s produced-water gathering system in Howard County, Texas, and will expand it to also serve third parties.
The UK shale operator will move forward with fracturing and testing its second well at its Lancashire site despite strict constraints on induced seismicity that hampered fracturing work on its first well. UK’s first horizontal shale well has yielded positive results after an initial flow test. But further testing—and fracturing of a second well—will have to come amid a continuation of UK’s stringent regulations on induced seismicity. Small quantities of gas and water are flowing to the surface from the UK’s first horizontal shale well—just days after operator Cuadrilla paused injection work for a second time amid earthquakes. Cuadrilla has encountered its first bumps in the road while fracturing its Preston New Road shale gas well, with two quakes already temporarily halting injection operations.
The green light for Santos Energy’s drilling program in the McArthur Basin comes after a moratorium on hydraulic fracturing in the Northern Territory was lifted in 2018. The UK shale operator will move forward with fracturing and testing its second well at its Lancashire site despite strict constraints on induced seismicity that hampered fracturing work on its first well. As the country pushes for higher output from its emerging unconventional sector, nature is pushing back. To get better results, operators there are increasing their reliance on technology. UK’s first horizontal shale well has yielded positive results after an initial flow test.
Researchers mapped 251 faults in the North Texas home of the Barnett Shale, the birthplace of the shale revolution, finding that wastewater injection there “significantly increases the likelihood for faults to slip.” Stanford geoscientists have found a way to detect thousands of tiny tremors around hydraulic fracturing operations that could serve as predictors of eventual larger earthquakes. One of Oklahoma’s top government officials announced recently that it could be many more months before the full scope of the state’s regulatory response plan for induced seismicity is proven effective. Earthquake in Cushing, OK -- home to the largest oil storage facility in the world -- leads to further regulatory action on disposal wells in the area. Research and development firm Battelle is working on a new induced-seismicity study that aims to help wastewater disposal well operators in Ohio stay on the good side of state regulators.
Stanford geoscientists have found a way to detect thousands of tiny tremors around hydraulic fracturing operations that could serve as predictors of eventual larger earthquakes. It is known that a well injecting a lot of water near a big fault can lead to earthquakes. The problem is, more often than not those faults are not known until after a tremor. Top US seismic experts say they are keeping a watchful eye on ground shaking in the state as new concerns are raised in neighboring Texas. One of Oklahoma’s top government officials announced recently that it could be many more months before the full scope of the state’s regulatory response plan for induced seismicity is proven effective.
In recent years, deformation of the reservoir host rocks has become a subject of great interest, prompted in part by the dramatic subsidence observed at Ekofisk platforms in the North Sea. One method of monitoring deformation is by passive seismic monitoring. It is called "passive" because the geopysicist does not activate a seismic source, but rather uses existing geophones to monitor ongoing changes in the rocks due to downhole conditions. Deformation is an important aspect of reservoir production, even without a significant compaction drive in many cases. Previous studies have been published in the scientific and earthquake literature relating earthquakes to oil/gas production and to injection practices.
The geologic setting of geothermal resources is similar to deposits of metal ores, and geothermal systems are thought to be the modern equivalent of metal ore-forming systems. Hence, exploration draws most heavily on the techniques of the mining industry. Development of the resource and its production as hot fluid uses the techniques of the oil/gas industry with modifications because of the high temperatures and the much higher flow rates needed for economic production. Exploration begins with selection of an appropriate area based on general knowledge of areas with above average heat flow. The best guides for more detailed investigation are the presence of thermal springs (the equivalent of oil seeps).