The first production log ever run in a heavy oil, long horizontal well completed with premium screens in open hole and through a Y-tool was successfully executed by Petroregional del Lago S. A. (a joint venture between PDVSA and Shell) in the Urdaneta West Field (Lake Maracaibo, Western Venezuela). The purpose of the job was to identify the origin of water in a well that experienced water break-through from the first day of production. A specialized set of logging tools was run to detect both water and oil flow, as well as to determine any flow behaviors like cross-flow that would help understand the source of water in the formation, obtain sufficient data to prepare a water shut-off program, and establish basic productivity information from the well, being this also the first production log run in the heavy oil wells in the field, which require artificial lift to flow. The results of the production log indicate that a sand package is producing water from an unexpected zone, which will require a water shut-off workover. This paper describes the planning, operational and interpretation processes of the logging activity, and presents a number of lessons learnt and useful recommendations for similar activities in heavy oil wells.
Petroregional del Lago S. A. (abbreviated PERLA) is a joint venture between Petroleos de Venezuela S.A. (PDVSA) and Shell International Exploration and Production (60% and 40% share, respectively). The company operates the Urdaneta West Field, located in Lake Maracaibo in west Venezuela. The field has three producing reservoirs, with very different geological characteristics and well types. One of these reservoirs is the Misoa formation, which is a Miocene formation consisting of unconsolidated sands and containing very significant reserves of heavy oil. The main characteristics of the Misoa Reservoir are summarized in Table 1.
The well UD-785 (MIB-10) was drilled as a heavy oil producer in the Misoa formation and completed with an Electric Submersible Pump (ESP) completion with a Y-tool. The Premium screens (mesh type construction) were installed in the reservoir section, in open hole. The well was not gravel packed. The final completion diagram is shown in Figure 1.
The well was started to production with the ESP, and in the first day of production the water cut stabilized quickly to 98%. The salinity of the produced water was measured and was found to be equal to the known formation water. The well initially produced at a rate of 2000 bbl/day for 5 days, and it was shut in to avoid operational problems associating with handling the produced water at the tank terminal. The initial well test evaluation indicated a big productivity index of 13 bbl/day/psi, one order of magnitude above the expected productivity based on the logs. A down-hole multi-sensor was installed with the ESP assembly, so data was available of the different pump parameters. The pump intake pressure measurements indicated a higher than anticipated reservoir pressure, with a fast build up period after the well shut-in.
The geological and petrophysical analysis of the open hole logs obtained with LWD tools indicated that a stratigraphic marker that had never been drilled before in the area had been penetrated. The normal porosity, resistivity and shale content cut-offs used in the reservoir were applied to the logs in this section, indicating the presence of oil, but also of higher that typical water saturation. This sand package became the main suspect for water production. See Figure 2.