RIASSUNTO
Abstract
Concepts on well multiple zone completion systems applied in marginal wells in Los Perales Oil Field, located in the Gulf of San Jorge Basin, Santa Cruz province Argentina. The field is fully operated by Repsol-YPF.
The paper narrates the challenge and experience of completing three marginal production wells (LP-2384, LP-2354 and Hue.xp-10), using concepts on well zone isolation, flow control capability, production management and easy well access in future workovers. The field is characterized by a stratified reservoir which is created by changes in depositional condition therefore each layer has different rock properties and flow characteristics (fluvial type reservoir). Gas oil and water are being produced commingle from different layers. The traditional method used to avoid production of a specific layer was cementing the layer or leaving it below a drillable plug (type N-plug). Despite difficulties, three wells were completed based on these concepts:
LP-2354: Selective zone completions, allowing reservoir and production management of three different gas sand beds.
LP-2384: Selective isolation of gas and water sand layers. Oil zone was put into production, allowing for ultimate gas recovery using pulling rig and a wireline unit instead of a workover recompletion.
Hue.xp-10: Gas ultimate recovery increased with a rig less workover completion. Killing the well, thus damaging the formation, was avoided.
Each well completion and intervention was designed, based on a cost effective and fit for purpose, criteria. Different arrays of tools (straddle retrievable packers, side pockets mandrels, mandrel valves and tubing screens) were run into the wells. The main enhancements were the following:
Cost-effective rig less workover.
Higher artificial lift performance by avoiding commingled flow using multiple zone isolation (no gas pound on the pump, no unwanted producing fluids).
Cross flow and formation damage prevention due to commingled production.
Easy well access to increase gas ultimate recovery, using a pulling rig instead of a workover recompletion.
Recompletion of gas wells by means of wireline conveyed casing guns and wireline setting packers without killing the well in order to pull down tubing string and therefore preventing formation damage.
Introduction
This paper presents the experience of completing three marginal well in Los Perales Oil Field.
In 1936 the well was drilled. Los Perales is being operated at 100% by Repsol-YPF, and is located in the western section of the Gulf of San Jorge basin in Argentina (figure 1). Actual Los Perales oil production is 4100 m3/d and gas production is 1.9 Mm3/d. Los Perales is considered to be a marginal field, because average well oil production is 2.5 m3/d (14 STB/d), this fact makes cost effective solutions a paramount in Los Perales field. Geologically Los Perales is characterized as a multilayer fluvial type reservoir. Average sand beds thickness is 3 m, and they can produce water, oil, gas or all of them together. A typical well completion is perforating every layer that is considered, by logs interpretation and then swabbing each of them. Upon the results of the swabbing, engineers and geologists decide which layer will be put in production, cementing or isolating the ones that are out of interest. Finally a rod sucker pump is run in hole and the well starts producing with a commingle flow of oil gas and water.