Core Jamming in Unconsolidated Formations

Abstract

In coring operations, core jamming is a permanent concern, taking place when the rock core sample becomes stuck within the inner core barrel, thus preventing further acquisition. This is undesirable in hard formations, for it stops the penetration of the drill bit and results in waste of time and money, especially if it occurs at the beginning of the core run. In unconsolidated formations, there are even more disadvantages, as the jammed sample may rotate along with the core bit, leading the formation to be flushed instead of acquired. This phenomenon is unnoticeable on the surface, and, as a result, the drillers are given no indication of it, thus hindering them from making the decision to pull out of the hole prematurely. Consequently, the characterization of the reservoir rock will be permanently incomplete due to the unrecovered material that was flushed. Despite its importance, the topic of core jamming has not been studied at length. This paper presents an analytical and experimental study in order to contribute for the understanding of jamming processes in unconsolidated or poorly consolidated formations. The study comprises the development of an analytical model, experiments and numerical analysis of the problem. Results are presented and implications for field applications are discussed.