Assessing the feasibility of sidewall coring in thinly laminated unconsolidated reservoirs: insights from field operations and core analysis

Reservoir characterization remains particularly challenging in unconsolidated reservoirs containing thinly laminated formations. Although sidewall coring is commonly employed due to its operational efficiency and lower cost compared to conventional coring, its applicability in unconsolidated reservoirs remains poorly documented. This study investigates the feasibility of sidewall coring in thinly laminated unconsolidated sandstone reservoirs using real field data from six wells and 294 targeted coring depths. The evaluation incorporated sidewall coring operational parameters, plug recovery, plug conditions and wellsite observations, supplemented by core analysis including geological descriptions, computed tomography (CT) imaging, and routine core analysis (RCA). Results showed that the average intact plug recovery was 51%, decreasing to 37% in one well, while total recovery increased to 63% when rubble was included. Only 25 sandy plugs were recovered, representing just 8.5% of all attempts, and successful recovery occurred predominantly in mechanically competent, clay-rich laminations rather than reservoir quality sands. Coring performance was adversely affected by cable stretch effects, limited gamma ray depth control, bit spinning caused by a high-quality filter-cake, inner barrel expansion, severe mud invasion, and plug fragmentation during retrieval. CT imaging revealed widespread internal fractures, many of which appeared externally intact. These findings demonstrate that current sidewall coring technologies cannot reliably recover representative reservoir-quality samples from thinly laminated unconsolidated formations for reservoir characterization. This study provides a comprehensive field-scale assessment integrating sidewall coring operational observations with advanced core characterization techniques and offers a practical guideline for future coring campaigns in similar reservoirs.