High Efficiency Coring in Deviated, Interbedded and Unconsolidated Formation. A Case Study from Offshore Southeast Asia and Potential Technology Enabler for CCUS Wells
Authors: Says I. P. , Hashim S. , Khaw A. L , Krishanderan K. 
Published: February 2024

Core jamming is the primary factor that negatively impacts the efficiency of coring operations, especially in deviated wells in sandstone reservoirs which are highly interbedded with shale lamination. Additional coring trips are frequently needed to cut the remaining target reservoir which results in additional cost and reduced coring efficiency. An additional challenge is the acquisition and recovery of cores in a soft and young unconsolidated sediment with unconfined compressive strength (UCS) of less than 1000 psi within interbedded reservoir sections using conventional catchers.

This paper discusses the techniques and technology required for overcoming these challenges and provides supporting case studies from selected wells. The reservoir geology obtained from these offset wells’ core samples was studied and evaluated. Coring operating parameters and lessons learnt from the offset wells were reviewed in connection with the previous coring system deployed. The recovery from previous wells was low, based on the best available technology at that time. This insight led to the utilization of jam mitigation technology, commonly used in consolidated and fractured formation applications, to be integrated with a full closure catcher system typically used in soft formation. Combining both individual systems into a unified single coring system addresses the challenges of both jamming in highly interbedded formations and recovering soft and young unconsolidated sediment. Also, by the nature of the full closure system's IT shoe, there is less interaction with the core catcher which allows for reduction of early onset jamming as well.

This technology has been successfully developed and deployed in three wells in offshore Southeast Asia (SEA) based on the challenges of these applications, and the performance of this uniquely integrated coring system proved successful on all three wells in two different fields. The high recovery percentage of 98.6% of 171 cored meters proved that this technology addressed the challenges of coring recovery and efficiency in a sandstone reservoir which is highly interbedded with shale lamination and unconsolidated soft formation. The jam mitigation system activation in three out of the eight runs prevented an extra trip and the full closure catcher contributed to a high recovery rate.

This coring technology enhancement is a critical solution which enables improved coring efficiency, reduced coring runs, an increased core recovery percentage, and optimizes coring performance in similar challenging future reservoirs. In addition, the high quality of cores acquired using this technology will also be beneficial for coring and laboratory analysis in both caprock and reservoirs for all potential sustainable storage solutions. Integrating reservoir studies with high quality core-based results will help in project planning by reducing risks and improve the outcomes for both Conventional and Energy Transition domains.