In situ Stress and Rock Strength in Rang Dong Field - Off shore Vietnam - Implications for Drilling in Basement Rocks

Abstract

An integrated geomechanical model which describes the rock strength, fluid pressures, and in situ stresses for the Rang Dong Field, offshore Vietnam has been developed using drilling data, geophysical log data, seismic data, and production/well testing data. The field-wide state of stress was constrained by direct observation of drilling induced wellbore failure, including both breakout (BO) and drilling induced tensile fracture (DITF). Some of the fine-scale variation of the orientations of drilling induced failure relate to local influences of faults and/or fracture zones. These fine-scale features enable the understanding of how faults and fracturing in the basement are influencing the stress field. Rang Dong Field is characterized by a strike-slip state of stress, where the intermediate principal stress is vertical (Sv=S2), and the maximum and minimum horizontal principal stresses (SHmax=S1 and Shmin=S3) are horizontal. SHmax is oriented approximately 152° N (NNW-SSE). Development at Rang Dong Field has involved drilling of highly deviated, and in some cases horizontal, trajectories. These have been completed with some difficulty, depending on local conditions. In some cases nearly total fluid loss was experienced, and drilling was completed at depths as great as 4000 metres TVD with seawater and lubricant additives.

Geostatistics application in spatial analysis of geomechanical properties

“…Unconfined compressive strength is defined as the maximum axial compressive strength that a right-cylindrical sample can withstand under unconfined conditions.There are many correlations to determine UCS based on seismic and well logging data. This study used MsNally's correlation which can be applied for sand reservoir [3].…”