Borehole Stability and Field Stress Analysis With Azimuthal Logging-while-Drilling Technology: A Case History in Multilayered Reservoirs

Abstract

North Kuwait Asset uses integrated Geomechanical modeling activity in multiple stacked reservoirs which pose severe drilling complications. The model is updated and refined with diverse data and used in planning for drilling horizontal and multilateral wells to accelerate production from mature pays and thin sands. Real-time azimuthal acoustic measurements introduced recently in the logging-while-drilling (LWD) industry was used as part of the bottomhole assembly (BHA) to acquire information related to principal stress orientations and geological information in the deltaic to marine Zubair clastic sequence of Raudhatain Field in North Kuwait. A deviated 8.5-in. hole section of the well was planned through sand-shale sublayers with a borehole inclination ranging from 46 to 88°. This section is characterized by time sensitive borehole deterioration and significant variations in pore pressure, which results in severe hole instability and ultimate stuck ups and require relatively high mud weights to maintain wellbore stability. LWD azimuthal acoustic technology, free from chemical sources, was used for the first time both in drilling and wipes modes to facilitate time-lapse field stress and wellbore stability analysis. Principal stress orientations were identified from three different sources; namely, borehole breakouts from azimuthal acoustic caliper, compressional and shear slowness images, and acoustic anisotropy evaluation. The results were then compared with the existing offset geomechanics data and existing 3D Geomechaninical model. Variation in observed stress orientation, seismic reflection pattern and pressure history in offset wells were used to map a fault which is responsible for bypassed oil and occurrence of tar and gas. The interpretation was extended to other low throw strike slip faults and more fault compartments were identified which could impact the pressure maintenance scheme of the field. This paper discusses the planning, design, and execution of LWD azimuthal acoustic technology and the viability, integrity, robustness of interpreted results and its use in detailed geological interpretation in terms of stress orientation, fault trapping and areal fluid variation. Optimization of real-time drilling operations and petrophysical data acquisition requirements were investigated to improve future field development and overall reservoir management strategies.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015