Exceptional Length of Coring Recovery in a Very Loose Sand or Unconsolidated Formation in South Natuna Sea Block B at 8-1/2" Hole Section with a Conventional Full Closure System

Abstract

Abstract The South Natuna Sea Block B field is located in the waters of the Riau Archipelago and is a large and fragmented PSC that covers a number of oil and gas fields in the Natuna Sea, of which a few are currently operated by Medco E&P Natuna Ltd. Coring Service is one of the processes that is required by Medco E&P Natuna Ltd. for unconsolidated formations as the target reservoir zone. Unconsolidated formation is very challenging to core, especially with the standard conventional system, as the core could slide and slip off from the inner barrel assembly of the Standard Conventional System while pulling out of the hole while the whole coring assembly is in progress. A Full-Closure System technology with a Double catcher assembly (Clam Shell Catcher and Spring Catcher as the main component) is necessary to address the problem. The full closure system technology, which was created specifically to catch any unconsolidated formations, has gained widespread acceptance for its effectiveness in a variety of fields, particularly in Indonesia. Even when the Full Closure system is assembled and run in the hole, anomalies like core jamming and milling the core are difficult to detect at the surface gage while coring is taking place at unconsolidated formations. The challenge is further increased by the 90-foot length of the core that must be retrieved in a single-run in order to save cost by reducing the number of trips. This plan goes against the best advice or rule of thumb given by the majority of coring services, which stated that when coring, especially in an unconsolidated formation, a shorter length of barrel is highly recommended, such as per joint or only 30 feet to be done in one run, for example, for a Total of 3 (three) × 30 feet to retrieve the entire target of 90 feet, in order to avoid any unforeseen anomalies. Since vibration always increases the likelihood of core jamming, a shorter core barrel could potentially cause less vibration while coring is taking place. If this happened, the core would then be milled. Therefore, a shorter barrel always presents a lower risk of losing precious data samples if core jamming and core milling anomalies ultimately occur undetected. This paper is made to inform, demonstrate, and discuss how Full-Closure System technology and certain key procedures that are strictly followed and monitored could mitigate the potential hazards or risks mentioned to Successfully Core the 90-foot core target in one run at an Unconsolidated formation and be the first to ever do it in that length, especially in Indonesia.