A detailed view of the injection-induced seismicity in a natural gas reservoir in Zigong, southwestern Sichuan Basin, China
ABSTRACT  Seismicity at a gas reservoir located in the relatively stable Sichuan Basin, China, mirrors the injection pressure of unwanted water, suggesting that the seismicity is injection induced. Injection under high pressure on a routine basis began on 9 January 2009 and continued to July 2011. During the injection period, over 120,000 m3 of water was pumped under a wellhead pressure of up to 6.2 MPa into the limestone formation of Permian 2.45 to 2.55 km beneath the surface. The injection induced more than 7000 surface-recorded earthquakes, including 2 M4+ (the largest one was ML4.4), 20 M3+, and more than 100 M2+ events. Data observed by a nearby local seismic network and five temporal stations provide a detailed view of the spatiotemporal distribution of the induced earthquakes. Most events were limited to depths ranging from 2.5 to 4 km, which is consistent with the limestone formation of Permian. In a map view, hypocenters are concentrated in a NNW extended ellipsoidal zone approximately 6 km long and approximately 2 km wide centered approximately at the injection well. Multisources of evidence such as the shear mechanism, pattern of hypocenter distribution, and small elevated pore pressure as compared with the least principal stress in the region show that the induced earthquakes occurred as a result of lowering of the effective normal stress on known or unknown preexisting blind faults which are critically loaded under the regional stress field. Epidemic-type aftershock sequence modeling results indicate that injection inducing and earthquake triggering are both important during earlier periods of injection, while later periods are dominated by forced (injection-induced) seismicity.
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Article: A detailed view of the injection-induced seismicity in a natural gas reservoir in Zigong, southwestern Sichuan Basin, China
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- "Event rate fluctuates following changes of injection rate and injection frequency and tapered quickly after shut down. Detailed studies on some recent and well monitored cases demonstrate that most events, particularly larger ones, mirror the reactivation of pre-existing faults (including joints and fractures) in the sedimentary formations or faults underlying/overlying the reservoir (Lei et al., 2013b; Wang et al., 2012). As a typical example, Fig.1 shows hypocenter distribution of injection-induced earthquakes superimposed on the simplified geological cross section and stratigraphy of a gas Asian R reservoir were de gas rese and play clouds, migratio faults of largest e depleted behavior injection integrate Here from typ were per for many Fig. geolog "
ABSTRACT: Injection-induced seismicity associated with geoengineering applications, in which fluids are intensively pressed into the deep formations of the earth's crust such as Enhanced Geothermal System (EGS), shale gas fracking, geological sequestration of CO2, have attracted growing attentions. Motivated by the desire to better understand the mechanism of damaging events so that they can be avoided or mitigated, we have started an integrated study on rock fracturing and fault reactivation in multiscales. In this paper, we present some preliminary investigation results of an ongoing experimental study utilizing acoustic emission technique in laboratory scale. We systematically carried out rock fracture tests using samples of typical sedimentary rocks collected from the Sichuan Basin, China, where a number of injection-induced seismic swarms with sizable earthquakes ranging up to M4~5 have been observed in some gas/oil reservoirs. Since most injection-induced earthquakes are located in sedimentary strata of a wide range of lithology and depth, the fracturing behaviors of such rocks are thus important. Our results indicate that the Pre-Triassic rocks in the Sichuan Basin, including dolomite or dolomitic limestone and shale demonstrate strong brittle fracturing behaviors in the laboratory. Such properties are necessary conditions for maintaining high level reservoir stress and resulting seismic fracturing.ARMS8 - 2014 ISRM International Symposium - 8th Asian Rock Mechanics Symposium - Rock Mechanics for Global Issues - Natural Disasters, Environment and Energy -, Sapporo, Japan; 10/2014
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ABSTRACT: CO2 geological storage, when combined with deep saline water recovery (CO2-EWR), not only achieves the relatively secure storage of CO2 that was captured from the coal chemical industry, due to lower pressure, but also enhances saline water for drinking and industrial or agricultural utilization. This storage will undoubtedly become a win–win choice for the enhancement of energy security and for the promotion of regional development in China, particularly for western regions with a relative shortage of water resources and a more fragile ecological environment. In this paper, a three-dimensional injection–extraction model is established that uses the TOUGH2/ECO2N program according to typical formation parameters of a coal chemical industry in the Xinjiang Uyghur Autonomous Region. Numerical results showed that under the guarantee of sufficient water conditions, 1.73 × 108 tons of saline water could be produced when the CO2-EWR is adopted. Well arrangements and formation parameters are also analyzed, and the following conclusions can be drawn: arrangements of pumping wells, such as pumping well number, pumping rate and distance, have considerable influences on the reservoir pressure, and in addition, the sensitivity of pressure on the distance and pumping rate decreases as their values increase. In view of these features, it is necessary to find an optimal point to achieve the best combination of pressure, the leakage time and the amount of dissolution. Formation parameters primarily control the mechanism of CO2 migration and dissolution. Salinity in the salt water has the greatest impact on CO2 dissolution trapping followed by permeability and porosity. The arrival time that is allowable for saline water production primarily depends on porosity followed by the permeability ratio and the arrangements of pumping wells. The reservoir pressure change that is caused by parameters is not obvious compared with setting pumping wells. Overall, CO2-EWR technology is a potential strategic choice for China, particularly in western regions. Additionally, the analysis results provide a reliable guide and reference for CO2 storage site selection, as well as the practical arrangements of wells.Applied Energy 03/2014; 116:101–110. DOI:10.1016/j.apenergy.2013.11.050 · 5.61 Impact Factor