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AAPG Bulletin

Abstract

AAPG Bulletin, V. 100, No. 1 (January 2016), P. 23-39.

Copyright ©2016. The American Association of Petroleum Geologists. All rights reserved.

DOI: 10.1306/08031514030

Identification and calculation of transfer overpressure in the northern Qaidam Basin, northwest China

Changyu Fan,1 Zhenliang Wang,2 Aiguo Wang,3 Suotang Fu,4 Liqun Wang,5 Yongshu Zhang,6 Hongxi Kong,7 and Xiao Zhang8

1State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, Xi’an 710069, China; [email protected]
2State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, Xi’an 710069, China; [email protected]
3State Key Laboratory of Continental Dynamics and Department of Geology, Northwest University, Xi’an 710069, China; [email protected]
4Qinghai Oilfield Company, CNPC, Dunhuang, Gansu 73200, China; [email protected]
5Exploratory Development Institute, Qinghai Oilfield Company, CNPC, Dunhuang, Gansu 73200, China; [email protected]
6Exploratory Development Institute, Qinghai Oilfield Company, CNPC, Dunhuang, Gansu 73200, China; [email protected]
7Exploratory Development Institute, Qinghai Oilfield Company, CNPC, Dunhuang, Gansu 73200, China; [email protected]
8Department of Geology, Northwest University, Xi’an 710069, China; [email protected]

ABSTRACT

The origin of the overpressure in the northern Qaidam Basin has not been clearly understood, which has caused some difficulties in hydrocarbon exploration. Using a compaction study, we applied a modified acoustic-velocity and effective-stress diagram to identify the overpressure transfer in the study area. This phenomenon has not been discussed in previous studies. For the present study, we approximately calculated the magnitude of the transfer overpressure and analyzed the cause of the overpressured aquifer at the crest of the anticline in the study area. Our study indicates that the effect of overpressure transfer is very distinct, and the largest contribution to the total overpressure is 57%. The main media of overpressure transfer include vertical faults and lateral conducting layers. The vertical faults can connect deep overpressured strata, and the lateral conducting layers can connect overpressured strata at the top and wing of the anticline. During anticline formation, the crest fractures, and then the overpressured water in the anticline wing flows into the fractured crest and forms the overpressure compartment that prevents the charging of deeper natural gas.

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