Research and Application of Ultra-Short Radius Flexible Sealed Coring Technology in Re-Development of Matured Fields

Abstract After long-term water-flooding, many of the matured fields in China have experienced changes in the physical properties of reservoirs. Moreover, the inefficient cycle of water flooding in the reservoirs is serious, and the heterogeneity of reservoirs causes difficulty to determine the distribution of remaining oil. It is impossible to reflect the real situation of the stratum only by simulation analysis with the numerical simulation software. To core in a specific location through coring technology and analyze the core can not only re-conduct a more accurate evaluation of the stratum, but also can modify relevant data of existing models to improve the simulation accuracy. But the current technology can’t conduct coring operations near wellbore and in deep parts. Therefore, based on the ultra-short radius sidetracking technology, this paper aims to develop ultra-short radius flexible sealed coring technology to achieve coring outside the casing. Compared with the ultra-short radius sidetracking technology, the ultra-short radius flexible sealed coring technology has, in addition to the windowing, deflecting, and horizontal drilling tools, the core tools of this technology, that is, the flexible sealed coring tool. The tool is mainly composed of a flexible outer cylinder and a highly elastic titanium alloy inner cylinder. The flexible outer cylinder is connected by a multi-section of flexible units that can be bent up to 5°. And a special coring bit is connected to the front of the tool. The maximum length of the core taken in a single coring process is 1.1 meters; the core diameter is up to 40mm. By using this technology, the minimum horizontal distance of the core position and the borehole wall is 0.8 meter, and the maximum horizontal distance can be up to 100 meters. At present, the technology has been successfully applied to more than 10 wells, and the average core recovery rate has reached 90%, which provides valuable data for the geological departments and is of great significance for re-developing matured fields. This technology can obtain the core from outside of the casing and near wellbore, and offers a more accurate evaluation on changes of physical properties of the reservoirs, providing the basis for adjusting the subsequent water flooding development plans.