Wireline Logging in High Overbalance High-Temperature High-Pressure Deepwater Gulf of Mexico Well with Water-Based Reservoir Drilling Fluid

Abstract

Open hole wireline logging, due to its lower overpull capacity relative to logging-while-drilling, is subject to increased stuck tool risk and can lead to costly fishing operations, lost-in-hole charges, and the need to sidetrack the borehole. The risk increases in higher overbalance environments typical for depleted reservoirs but there are other controls on sticking risk that can be managed. This paper describes the measures taken in an open hole wireline logging operation in a Deepwater Gulf of Mexico well under close to 7000 psi overbalance in a high temperature-high pressure (HTHP) slim-hole environment using water-based reservoir drilling fluid (RDF) to achieve a successfully efficient logging operation without incurring lost time attributed to conveyance related issues. A wireline program was designed that paid close attention to the RDF properties to ensure excellent fluid loss performance and a thin filter cake, a recipe to keep differential sticking in check. The target reservoir was an aeolian sandstone with a porosity of 19% and permeability in the tens of millidarcy range. Additional steps taken to mitigate sticking risks included good borehole cleaning practices, sticking assessment during drilling, use of high-pull capacity cable, minimization of tool contact area with the borehole through reduced tool string length and use of rollers and standoffs, minimization of stationary time within depleted reservoir, tension monitoring during wireline operation, and inclusion of a jar in the tool string to increase the chance of pulling free when stuck. A high temperature and pressure rated sampling tool was run in a 7″ borehole with a 25° open-hole deviation to acquire the pressure profile in the reservoir. Correlation was performed inside the casing such that the only stationary time the tool string experienced was during the pressure sampling operation. The sampling itself was limited to no more than ten minutes. As a result of the mitigation measures implemented, a total of five good pressure points were obtained in approximately 150 ft of reservoir interval. Negligible tension drop-off was observed when moving down from one pressure station to another and no overpull was observed when picking up the tools. The tool string was successfully retrieved at the surface. From the authors’ knowledge, this is the first time logging under such high overbalance has been performed with a water-based RDF. The fluid mentioned in this paper has been engineered to overcome the typical shortcomings of water-based RDF when it comes to differential sticking. Learnings from stuck tool experiences during previous wireline logging attempts in the same field will be described, providing the rationale for some of the mitigation steps pursued in this paper. The success of differential sticking mitigation during this logging program opens the door to possibilities for performing future open hole wireline logging under extreme conditions.