Effective Seismic Workflow to Improve Carbonate Drilling Efficiency

Abstract

Carbonate rocks are widely distributed in the world and contribute about of the world’s hydrocarbons production and reserves. However, carbonates typically present drilling challenges due to their heterogeneous nature. When large cavity has been encountered, the results can be potentially disastrous. Large cavities (caves and vugs) forming high-conductivity channels can quickly drain drilling fluid, leading to total or partial losses of circulation, which can precede loss of well control. This is especially important for expensive offshore drilling. For example, potential mud losses in gas-bearing carbonate structures have been the issue attracting most attention in planning and executing the drilling programs for gas development projects in offshore Sarawak, where hundreds of Miocene carbonate build-up host many gas fields with extensive large cavity features in them as drilling hazards, water-break conduits and excellent reservoir spaces.

There are many preventive and remedial solutions to counter recurring mud losses and other cavity-associated geo-hazards before, during and after drilling these carbonate wells. Among these solutions, the most efficient approach is the seismic approaches to reveal and capture the large cavities before drilling through carbonate. In seismic, the large cavities could be observed as strong “pair of beads” bright-spots, evident of subtle depending mainly on the size and fillings of the caves and the resolution limit and image quality of seismic data. The experiences in Miocene carbonate in Luconia Basin, offshore Malaysia and Ordovician carbonate in Tarim Basin, west China have provided valuable references. This knowledge provides guidance to reveal and delineate geohazard in carbonate with proper seismic approaches. High density seismic acquisition has significantly improved lateral resolution and S/N ratio and therefor reveal much more large cavity features than legacy data. Targeted seismic processing has revealed both geometry and geophysical detail to data limitation to maximize the information on large cavities (zone). Integrated seismic interpretation/modelling to effectively delineate the size, location and connectivity of the large cavities. Well-path optimization could improve drilling and production efficiency associated with sweet-spots (high production and recovery) and/or bitter-spots (drilling hazards, early water-break through, low recovery).

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018