Unleashing the Potential: Geomechanics and Fracture Gradient Modelling Reshape the HPHT Landscape in SA Gas Field, Gulf of Thailand
Authors: Kongsumrit W. , Adisornsupawat K. , Chansawad P. , Santadgarn P. 
Published: February 2025

The SA Gas Field, a high-pressure and high-temperature (HPHT) reservoir, holds significant potential for petroleum resource development. However, unlocking this potential has proven challenging, with considerable non-productive time (NPT) attributed to drilling complications on previous platforms, SA-1, and SA-2. Between 2022 and 2023, drilling operations on these platforms encountered circulation losses, well ballooning, premature total depth issues, and gaps in essential subsurface data, all of which increased risk and affected timelines. To address these issues and improve drilling efficiency for upcoming wells, a 1D Mechanical Earth Model (1D-MEM) and geomechanical models, including fracture gradient models, were developed, and implemented across the SA Gas Field to predict and manage wellbore stability, thereby reducing NPT and associated costs.

The 1D-MEM, tailored for HPHT application in the SA Gas Field, integrates essential geomechanical parameters such as in-situ stress profiles, pore pressure data, and rock mechanical properties, creating a robust model that supports predictive wellbore stability analysis. This approach optimises mud weight, casing points, and Equivalent Circulating Density (ECD) for specific drilling conditions. The model was calibrated using data from multi-stage triaxial (MTXC) tests on reference wells, providing critical parameters like static Young's modulus, Poisson's ratio, Uniaxial Compressive Strength, and internal friction angles. Additionally, critical drilling event data, such as Leak-off Tests (LOT), Formation Integrity Tests (FIT), and documented instances of loss, kick, and ballooning, were incorporated to refine the model's estimation of minimum horizontal stress. This allowed for identification of high-risk zones and adjustments in the mud weight window and casing points.

Applying the 1D-MEM on platform SA-3 yielded substantial operational improvements, including a 70% reduction in NPT due to formation integrity issues across 15 reservoir intervals. This application reduced drilling risks, cut costs by approximately 60% compared with prior campaigns, and enabled a 5% reduction in drilling time per well. Employing a risk-based traffic light system (Red, Yellow, Green), the model allowed proactive management of subsurface challenges, enhancing operational efficiency.

Insights geomechanical information from SA-1 and SA-2, the SA-3 campaign demonstrates the critical role of geomechanics in HPHT fields, showing that calibrated 1D-MEM models can provide key stability assessments for high-stress environments. This success in the SA Gas Field highlights the value of leveraging technology to optimise drilling, mitigate risk, and support PTTEP's broader mission of energy sustainability. With this established framework, future applications of the model can extend across similar HPHT reservoirs. Plans to incorporate further data, such as sidewall core analysis and dipole sonic logs, will enhance the model's predictive accuracy and real-time alignment.

In conclusion, deploying the 1D-MEM and geomechanical models with near wellbore analysis has proven effective in addressing HPHT drilling challenges in the SA Gas Field, enhancing wellbore stability, reducing NPT, and improving cost efficiency. These advancements benefit the current SA platforms and set a benchmark for future HPHT projects. By proactively integrating geomechanical insights, PTTEP can optimise drilling operations, secure resources effectively, and drive sustainable production to meet energy demands while maintaining cost and operational excellence.