INTEGRATED STRESS AND ANISOTROPY ANALYSIS USING MULTI-WELL BOREHOLE SONIC AND IMAGE DATA IN THE KINABALU FIELD, MALAYSIA

摘要

The Kinabalu field, located offshore East Malaysia and operated by Talisman, is presently in a phase of rejuvenation with multiple deviated infill wells drilled from the same platform. Inclinations range from about 30° to 60° and trajectories are along main fault. Some of the reservoirs in the field show signs of depletion due to previous production. These reservoir sands were found prone to sanding. This is evidenced from the early producing wells that have been producing sands at surface.With the current well completions, the operator is constrained to produce the field at economic rates. Uncertainties associated with sand failure are constraining them from implementing a more efficient completion design capable of delivering the required production. To make a decision for an alternative completion, geomechanical risks associated to formation stresses and rock strength need to be addressed as the reservoir conditions have changed from initial pre-production conditions. An alternative completion strategy such as perforated cemented liner was considered as it would deliver higher production rates with significantly reduced cost, however there were risks associated. Due to lack of data and confidence, uncertainties in rock strength and stress characterization with regard to faulting and historical production were to be reduced; emphasis on measurements was needed. Objectives were to quantify rock strength and stress anisotropy to improve the reservoir characterization while minimizing assumptions and analogue field experience.To meet both geomechanical characterization and near-wellbore integrity evaluation objectives, the operator decided to acquire advanced wireline sonic and image tools. The advanced sonic processing providesazimuthal dipole measurements, shear anisotropy, slowness radial profiling and horizontal stress magnitudes. As technical difficulty arises in single-well data interpretation of borehole failure and acoustics, principally because of high inclination of the considered wells, a multi-well approach with advanced acoustics and image interpretations was proposed to overcome these limitations. The maximum stress direction was found more oblique to the fault than initially anticipated and the horizontal stress anisotropy was found to be higher that initially assumed. Most of the reservoir sands exhibit stress-sensitivity and near wellbore alteration. These together constrain the perforation and coring strategies in the final well of the rejuvenation drilling campaign. The sensitivity of sand failure and critical drawdown pressure to stresses and perforation design could then be better assessed.Given a development strategy with high angle wells and a pressing need to pin parameters down to improve sand failure prediction, acquiring monopole and dipole sonic in stress sensitive formations together with borehole image prove to be an important piece of information. The integrated stress analysis provides valuable information regarding the field stress state. It also provides information on location, extension and orientation of near wellbore alteration. Both play critical roles in sanding management and completion design. The operator integrated this information in their geomechanical model to mitigate sanding risk and optimized their completion strategy. The near wellbore alteration assessment complements the change of perforation design to lower density and deeper penetration. As a result, the operator increased production with faster clean up in the final well of the campaign.