An Acoustic Approach to Identify Shallow Gas and Evaluate Drilling Risk in Deep Water Based on Simulation Experiment Study
- Huanhuan Wang (China University of Petroleum) | Jin Yang (China University of Petroleum) | Lei Li (China University of Petroleum) | Jiajun Xu (China University of Petroleum) | Lingyu Meng (China University of Petroleum) | Jiayao Hong (China University of Petroleum) | Qiuxuan Zhao (China University of Petroleum) | Mailun Wang (China University of Petroleum)
- Document ID
- International Society of Offshore and Polar Engineers
- The 29th International Ocean and Polar Engineering Conference, 16-21 June, Honolulu, Hawaii, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. International Society of Offshore and Polar Engineers
- deep water, Shallow gas, drilling risk assessment, prediction
- 3 in the last 30 days
- 46 since 2007
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In this paper, a new prediction and evaluation method for shallow gas pressure in deep water was described. The innovation of this method lies in the establishment of the multivariate function relationship between acoustic velocity and shallow gas pressure and formation porosity, so that the risk degree of shallow gas geological disaster can be predicted more accurately in the actual prediction.
Shallow gas refers to small gas reservoirs gathered within 1000m below the mudline. Shallow gas sometimes exists in the form of gasbearing sediments, high-pressure airbags under overpressure, and also directly sprays to the seabed (Gu, 2013; Fleischer,2003 and Adams, 1991). According to the International Council for the Exploration of the Sea (ICES), 22% of blowouts are caused by shallow gas, which is one of the most destructive shallow geological hazards in deepwater drilling. In the process of deep water drilling, shallow soil has the characteristics of low overburden pressure and weak cementation strength (Weber, 1997; Mayer,2002). Once high pressure shallow gas is drilled, it will cause wellbore gushing or even blowout. Moreover, blowout preventers are not installed during shallow drilling, which makes well control difficult (Savvides,2001). Therefore, it is necessary to improve the pre-drilling prediction accuracy of shallow gas.
The surface layer of deep water has a two-phase medium consisting of seawater and surface solids. The propagation of longitudinal wave in surface solids is affected by many factors, including surface density, porosity, clay content and other surface solids mechanical parameters(Hou, 2013; Long, 2015 and Bu, 2007). The change of mechanical parameters may cause the obvious change of P-wave propagation velocity.
Based on the geological characteristics of deep water surface soil and the characteristics of shallow gas formation (Azadpour, 2015 and Carcione, 2001), this paper designs a simulation experiment scheme for identifying the acoustic characteristics of deep water surface drilling geological hazards based on shallow seismic principle, seismic wave velocity propagation theory, similarity principle and wavelet analysis, and carries out a simulation experiment for identifying the acoustic characteristics of deep water surface drilling geological hazards. A two-parameter shallow gas prediction model with P-wave velocity, shallow gas pressure and formation porosity was established, and prediction templates with different formation porosity were made. The method has been applied in South China Sea, and the model has good adaptability after successful application in 20 wells.
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