RESEARCH ARTICLE


Study on Wellbore Stability of Shallow Sediments in Deepwater Drilling



Jun Zhang1, *, Chi Ai1, Bo Zeng2, Yuwei Li1, Jia Zeng1
1 School of Petroleum Engineering, Northeast Petroleum University, Daqing, 163318, P.R. China
2 Research Institute of Petroleum Exploration & Development-Langfang Branch, PetroChina, Langfang, 065007, P.R. China


Article Metrics

CrossRef Citations:
0
Total Statistics:

Full-Text HTML Views: 1888
Abstract HTML Views: 884
PDF Downloads: 624
ePub Downloads: 244
Total Views/Downloads: 3640
Unique Statistics:

Full-Text HTML Views: 1014
Abstract HTML Views: 516
PDF Downloads: 441
ePub Downloads: 164
Total Views/Downloads: 2135



© 2017 Zhang et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this authors at Northeast Petroleum University, Daqing, P.R. China, No.199, Fazhan Road, High-Tech Development District, Daqing City, Heilongjiang Province, P.R. China; Tel: +86-13091693160; E-mails: zhangjun410410@163.com, 2:406684545@qq.com


Abstract

Background:

The deepwater shallow formation has low fracture pressure and narrow safe window of mud density, which results in a high risk of wellbore instability in this kind of formation.

Objective:

Without considering the plastic state of shallow formation around the borehole or the influence of in-situ stress difference on wellbore stability, the prediction accuracy of the traditional wellbore stability analysis models are relatively low. This paper can provide a reliable method to accurately predict the safe window of drilling fluid density.

Method:

In this paper, the shallow formation around the borehole is divided into plastic zone and elastic zone considering it under non-uniform in-situ stress. The collapse pressure formula of shallow formation is derived by taking the shrinkage rate of the borehole as the instability criterion. The fracturing pressure calculation model of shallow sediment under non-uniform in-situ stress is derived by combining the theory of excess pore pressure and hydraulic fracturing.

Conclusion:

The calculated results indicate that the horizontal in-situ stress difference has a significant effect on the shape of the plastic zone, the shrinkage rate of borehole, collapse pressure and fracturing pressure. The calculated results are in good agreement with the field test results, and the prediction accuracy of this model is higher than that of other traditional models.

Keywords: Wellbore stability, Borehole shrinkage rate, Collapse pressure, Excess pore pressure, Fracture pressure, Drilling fluid density.