Lesson Learned Coring Job at “P” Field using Conventional Coring Full Closure System

Abstract

To ensure high recovery of core from the first coring job, a conventional coring full closure system was used. A full closure coring tool is an ideal solution, not only for soft, sandy, unconsolidated formations, but for problematic applications such as gravely, fractured, or under-gauge core that conventional spring catchers cannot handle. Full closure coring tools ensure capture and a high recovery rate with hydraulically activated which minimizes mechanical parts and increases reliability for a broad range of applications.

“P” field itself has a gravely characteristic formation that gives challenges to hole cleaning, but the main target of coring is at “B” formation below gravel depths. B formation characteristic is shally-sand/sandstone and already depleted showing from surrounding wells that give another challenge to loss circulation.

Prior to penetrating this sand formation, selected producers well within a radius of 200 m which produces from the corresponding layer of formation are shut in to overcome the loss circulation risk. Coring fluid also contained additional preventive LCM as a bridge agent across the depletion zone.

Another lesson learned is the coring BHA cannot be used as “reamer” prior the 2 coring. Major concern was it may cause shear pin to prematurely sheared. Therefore, after directional BHA continue to the 2nd top coring depth, a hole opener was used to smoothen the wellbore and to ensure its hole cleaning. This practice proves successful to overcome the risk of shear pin  rematurely sheared inside coring BHA at the top of coring depth.

The original plan coring job is to be done in 2 runs which target 30 ft in each run, but in the second run, after 14 ft of coring, there is no ROP, therefore the third run is required to finish the rest of 16 ft formation. The first run was successfully done with 99.3% recovery, the second run with 65.7% recovery but the third coring is only 13.7% recovery. During the coring job, there is no loss circulation occurs.