We have carried out a field trial of a time-lapse continuous electromagnetic profile (CEMP) method for monitoring gas reservoir development. Several data acquisition methods were tested to establish a field-worthy practical procedure that maintained the consistency of time-lapse CEMP acquisition and ensured the reliability of collected data. An effective denoising and static correction algorithm has also been developed to sufficiently suppress noise and disturbance for data processing purposes. The resistivity variation with time was recovered using a time-lapse inversion method. Three continuous acquisition tests on a gas reservoir in western China produced results that clearly indicated the relationship between resistivity change and the change in gas and water ratio as well as pressure decreases. The field trial was a successful experiment in monitoring gas reservoir development with high-precision time-lapse CEMP surveys. The established data acquisition procedure, data processing algorithm, and the inversion-based interpretation have general applicability, and these may open new avenues for time-lapse monitoring in oil and gas production.
Successful geophysical exploration projects in the Gucheng–Yaxi area located in Gaochun District, Jiangsu Province, China, have been limited partly due to the complex geological conditions of the area and high artificial noise in data acquired using electrical and electromagnetic methods. In this study, we deployed the new anti-interference spread-spectrum-induced polarization method (SSIP) and the audio-magnetotelluric (AMT) method to detect a copper–polymetallic deposit in the area. Two-dimensional inversion results in the Gucheng–Yaxi area revealed a high chargeability anomalous zone on the SSIP profile that coincided with a zone of moderate resistivity located between two resistor bodies on the AMT profile. A follow-up 1200 m drill hole was established at this high-chargeability, moderate-resistivity zone which encountered polymetallic (copper, lead, zinc, gold, and silver) mineralization at a depth of ≥400 m. Drill hole data analysis showed that mineralization occurred interspaced in the marble rock mass at varying depths. Furthermore, several low-resistivity, weak-chargeability sections were revealed and attributed to Cretaceous sediments and faults. These faults are thought to have played a critical role in the polymetallic mineralization genesis. In summary, this study demonstrated the successful of application of SSIP and AMT in detecting a metallic deposit in an area with high artificial noise. Hence, the geophysical prospection potential of the Gucheng–Yaxi area is great.
A successful case history of reservoir mapping of the geothermal water using a high frequency<br>EM method is presented in this paper. The high frequency electromagnetic system (MT-U5A with<br>frequency range from 10KHz to 1Hz) is used for the data acquisition, which is its first time using in<br>China, remote reference was used for high quality field data. J County has a known hot spring and<br>several wells were drilled for geothermal water used by sanatoriums. The water temperature ranges<br>from 30 Centigrade to 93 Centigrade. But the geothermal water distribute only in a little area. High<br>frequency EM method was used to map the reservoir of the geothermal water and to explore the<br>source of it. We found the geothermal water is saltwater here and another very useful event, that is,<br>the apparent resistivity beyond here is quite different to the other area. Based on this, we carried out<br>467 high frequency EM sites here. 2-D inversion is used for data processing. Distribution area of<br>geothermal water of different depth has been mapped by this method. Finally, we gave a acceptable<br>interpretation of the geothermal water source.
The Mashan structural belt, which extends several hundred km east-west and 8–12 km north-south, is in the east section of the southern faulted tectonic belt at Bachu uplift of Tarim Basin. It is mainly controlled by two large faults—one in the south and one in the north. Commercial gas has been discovered in the area and it is considered to have further exploration potential despite the huge obstacles its topography presents to seismic prospecting. Seismic data quality in the south Mashan is poor and the reflection from top Ordovician limestone, the exploration target, is not clear.
Traditionally, the Mashan structural belt was regarded as a single anticline with a northern high as the principal feature (Figure 1). However, comprehensive nonseismic geophysical studies (gravity, magnetic, and electromagnetic methods) have resulted in a different view—one that has attracted oil explorationists. Figure 1.
Seismic interpretation profile of the Mashan tectonic belt.
The Mashan structural belt was formed during Himalayan orogeny. Drilling data show that the Quaternary and Tertiary consist of sandstone, shale, and lagoon sediments; the upper Permian mainly is sandstone-shale; the lower Permian has a basalt section and shale section; the Carboniferous is the continental-oceanic interaction sediment; and the Ordovician mainly consists of the marine sediment. Based on core density measurements and the P-wave interval velocity, we conclude that the interface between the Permian-Carboniferous and Ordovician (−0.15g/cm3) and the interface between the Cenozoic and Permian-Carboniferous (nearly −0.15g/cm3) are the principal density interfaces in this area. The lower Permian basalt has stronger magnetism but its thickness is no more than 200–350 m. Basement metamorphic rock has middle or weak …
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