World Oil: Holistic optimization approach improves coring efficiency, sample quality


To acquire a high-quality core in as few runs as possible, and reduce operational costs, a provider must maximize ROP while ensuring efficient, safe surface handling of the rock sample and coring assembly. To satisfy these requirements, HT30 Max, a full-gauge core barrel system with jam mitigation technology, has been introduced.

To improve initial production and ultimate recovery, we must first fully understand the reservoir rock. Full-gauge coring is the first line-of-sight into a reservoir. The actual formation samples recovered at the surface are the “groundtruth” that provides the basis for accurate reservoir evaluation and modeling. Cores are almost always acquired—and in many countries are required—for exploratory wells. They also are taken in development wells, even in well-known areas, to help operators better understand or confirm that the reservoir rock in one well exhibits the same characteristics as in previous wells.

The larger the core size, the better for core analysis, because more information about the formation can be gathered in less time. Additionally, a core with larger dimensions means less, easier-to-mitigate invasion into the zone of interest, so better plots can be made.

It is often argued that cutting core is time-consuming and results in high costs per foot of core recovered. As tougher conditions are encountered more frequently, coring operations become more challenging and expensive. In deepwater applications, for example, temperature, pressure, depth, mud weight, and other parameters directly affect and diminish core barrel length and reliability, which results in increased cost for core acquisition. Interbedded and fractured formations on land, or offshore, can cause the core to become jammed, Fig. 1.

Fig. 1. Interbedded and fractured formations can cause the sample to become jammed in the core barrel.

When jamming occurs, several feet of core are usually damaged. The damage can be mitigated with an anti-jamming or jam mitigation system. Concentric inner core barrel sleeves automatically telescope if a rock sample becomes jammed in the core barrel, allowing operations to continue without interruption.

Depending on the barrel size, the system can accommodate three to four successive jams before requiring POOH, reducing coring trips necessary to recover the same amount of core. However, core diameter is often sacrificed.

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