Implementing Innovative Technology to Provide Pore Pressure Prediction During Drilling Operations: A Case Study of the ‘White Tiger’ Offshore Oilfield
Authors: Melikov R. , Krasnikov A. , Tatur O. , Stishenko S. , Lobashov V. , Chaschin S. , Anh Nguyen Lâm , Chung Ho Nam , Sustavov V. , Âu Pham Viet 
Published: January 2025

Pore pressure assessment and determining the safe drilling window are critical tasks aimed at reducing risks in drilling and well construction operations, especially in offshore fields where the cost of well construction is very high, and errors can lead to serious consequences. Solving these tasks at the "White Tiger" oilfield requires consideration of unique challenges due to the complex geological structure of the formation and the need to ensure high drilling rates (penetration rate and commercial drilling speed) in intervals with abnormally high formation pressures while minimizing delays related to traditional geophysical studies and measurements. This article describes an approach to building a pre-drilling geomechanical model, adapted to the project's goals and objectives. A methodology for calculating of overpressure and the safe drilling window based on real-time measurements of petrophysical properties from drilling cuttings is presented. Using this approach improves the quality of well construction projects, enhances the accuracy of modeling results, and reduces uncertainties inherent in drilling forecasts in data-limited environments.

1. INTRODUCTION

The study area is located in the central part of the "White Tiger" oilfield, situated on Vietnam's continental shelf. This giant field, part of the Cuu Long Basin, produces hydrocarbons from crystalline basement rocks (Bogoyavlensky, 2016) as well as from Oligocene-Miocene reservoirs situated above them (Nemchenko, 2007). To enhance and optimize oil recovery, there is a pressing need to drill new wells with hydraulic fracturing in the Lower Miocene and Lower Oligocene reservoirs (Nguyen et al., 2010), which are characterized by high heterogeneity and complex geological features (Nhu et al., 2014).

Drilling in this field is complicated by geological factors such as numerous tectonic faults, abnormally high formation pressure in the upper Oligocene rocks, and reduced pressure in the reservoirs of the lower Oligocene, caused by uneven depletion and waterflooding of the formations through pressure maintenance systems. Figure 1 presents a seismic-geological section with a structural map of the seismic horizon SH-11 at the drilling site of the planned Well No. 5xx MSP-5, illustrating the complexity of the geological structure.

The primary reasons for these works were regularly occurring complications: borehole instability, mud losses, and oil-gas-water influxes during drilling. These factors negatively affect the duration of well construction operations, increase their cost, deteriorate the quality of reservoir penetration, and reduce the efficiency of casing cementing and well operation (Fig. 2).

For these reasons, pre-drill pore pressure assessments and safe mud window predictions, as well as real-time updates during drilling, are crucial for minimizing risks and reducing non-productive time during well construction. Another important aspect of the project is a reduction of the capital expenditures for drilling by implementing new approach for pore pressure and safe mud window prediction.