Sand production is a severe and proved costly problem in many wells in Block-16 of Ecuador. Repsol YPF has a number of horizontal wells in Ecuador that can not be exploited efficiently due to severe sand production, often causing sand plugs in the casing, the flowline and the surface equipment, and also causing the early erosion of the electrical submersible pump stages, shortening their run
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Repsol YPF Ecuador has historically attempted the traditional techniques used to control the production of sand, such as conventional screens and gravel packs, with less than optimum results. Other technologies have not been effective or not applicable, essentially because of the broad grain size distribution, or due to the fact that the production in Repsol YPF typically comes from moderately thin and clean reservoirs, with strong water drives.
This paper presents an efficient and economic alternative to control sand production. It essentially consists of a filter that is run in the horizontal section of the production liner, and that once properly packed, it can virtually stop the production of sand with minimal effect over the fluids production or the flowing pressure. The completion is simple and significantly less expensive than other sand control techniques. The technology discussed in this paper has been tested successfully so far in four horizontal wells in the Repsol YPF Block-16 in Ecuador.
This work summarizes the experience of Repsol YPF Ecuador in techniques to effectively control sand production, and it is supported by an extensive amount of field data. Field results have also helped prove that designs customized for specific reservoirs can maximize the wells' productivity and optimize the well completion costs.
Introduction
Sand production has a severe negative impact in the lifting and operational cost in the Repsol YPF operation in Ecuador. It has been found that the formation sand erodes and eventually plugs the wellbore, the downhole completion components, the artificial lift system, and the surface pipes and vessels. Clean up and repair treatments are costly and impractical.
Sand production is a common oil field problem. It usually occurs in rocks where the cementation structure does not offer enough resistance to hold the sand grains in place at a given flow rate. The onset of sand production from reservoirs is a complex phenomenon; variations in the reservoir pressure and fluids saturation, and those dictated by the well's operating conditions may initiate the production of sand at any time in the life of a reservoir1.
There are three mechanisms responsible for sand production: compressive failures, tensile failures and erosion. Compressive failures refer to tangential stresses exceeding the compressive stress of the rock and can be triggered by depletion and drawdown. Tensile failures refer to tensile radial stresses that occur when drawdown pressures exceed the tensile resistance of the rock. According to Veeken et al.2, compressive failures occur predominantly in consolidated sandstones while tensile failures are more related to unconsolidated sands. Erosion is a special form of a tensile failure.
