Detailed reservoir characterization is the main objective of all petrophysical measurements. The information obtained from petrophysical logs and well testing measurements is integrated with core-based sedimentological studies and core analysis measurements. Core-based information is crucial in the exploration phase of a field because it enables an extensive understanding of the reservoir rock potential. To reduce the operational time and cost, conventional full-core acquisition programs are often curtailed and operators rely on sidewall coring. Rotary sidewall cores provide accurate depth-controlled core plugs in various lithologies in a quicker and cost-effective way.
A new rotary sidewall coring tool has been utilized in Saudi Arabia that enables recovery of high-quality core plugs even from small-sized boreholes. The acquired core plugs have sufficient size for use in conventional and special core analysis, and petrographic studies. The capability to recover up to 60 samples in a single trip enables good coverage of the different lithologies during one acquisition. The core acquisition time per sample is significantly improved over previous generation tools, thus enabling a significant reduction in coring operation time. In addition, the ability to obtain 60 samples in one run enables operators to modify their core-acquisition programs, as sidewall cores provide a good alternative if conventional core programs are not properly executed.
This paper reviews experience and examples where rotary sidewall cores were obtained from several clastic and carbonate formations from different fields in various locations within Saudi Arabia. The operational environments and borehole conditions in which sidewall cores were obtained were exceedingly heterogeneous. These cases include very hard sandstones, mixed sand and shale layers, and limestone to dolomitic carbonates.