Combining a Liquid Jet Compressor with Nitrogen Lifting Through Coiled Tubing for Logging a Low Pressure Horizontal Well

Abstract

Abstract A coiled tubing (CT) campaign was executed on the Skjold field in the Danish sector of the North Sea in 2014. One of the objectives of this campaign was to perform production logging in horizontal oil producer wells, located in a highly fractured chalk reservoir. Most of these wells are unable to flow without artificial lift due to the high water cut and low reservoir pressure. Stable flow for logging was achieved by combining CT operations with a surface Liquid Jet Compressor (LJC). The campaign was successful in acquiring both production (PLT) and spectral noise logging (SNL) data. The SNL tool complemented conventional PLT as it provided information on quality of zonal isolation, vital in planning of water shut off and/or re-stimulation activities. Well A was completed with a gas lift valve straddle which had to be retrieved to gain access to the wellbore for production logging. Retrieving the straddle disabled access to lift gas, which meant the well was unable to produce. Liquid jet compressor technology in combination with nitrogen lifting through CT was implemented to allow steady fluid flow for logging. The surface liquid jet compressor (LJC) lowered the production system backpressure seen by the well from 500 psig to 0. Together with the continuous nitrogen pumping through CT, stable well flow was achieved and the logging program was successfully executed. The results were used to identify fluid flow behind casing, water producing zones and to identify sub-optimally producing oil zones for re-stimulation. Using the LJC significantly reduced the total nitrogen volume required by 60%. This was crucial as limited crane capacity and deck space presented additional logistical and operational challenges. In order to overcome these, equipment had to be rigged up on a bridge connecting two platforms with the CT reel lifted in three spools and welded on location. This in turn required the fiber optic cable to be injected on-site offshore. The novel combination of a surface LJC with nitrogen lifting via CT reduced the number of crane lifts, load outs, nitrogen transfers and overall cost. Furthermore, it improved operational efficiency and job safety. Ultimately, this combined concept enabled successful acquisition of the required data.