Sand production has proved to be a severe and often costly problem in many wells in the Oriente basin of Ecuador. Sand production has a negative impact over the productivity and lifting cost when it accumulates as sand plugs in the tubing, the surface flowlines or the surface pipes or vessels, and also when eroding the stages of the electric submersible pumps, shortening their run lives. Traditional techniques used to control sand production, such as conventional screens or gravel packs have been tried by Alberta Energy Company (AEC) in Ecuador resulting in impaired productivities of up to 75%, and therefore, are considered inefficient. Other techniques are not effective because of the broad grain size distribution, and also because the production of AEC in Ecuador typically comes from moderately thin and clean reservoirs, with bottom aquifers in the well. AEC and the majority of operators in Ecuador have not yet been able to control sand production without substantially reducing the oil production.
This paper presents an efficient and economic alternative to control sand production. It consists of a filter that is run in front of the perforations and that once properly packed, can virtually stop the sand without affecting the production of fluids. The completion is simple and significantly less expensive than comparable techniques. The proposed methodology has been tested so far in six AEC producers in Ecuador at flow rates up to 3000 bfpd, controlling the sand without affecting the total flow rate or the flowing pressure. A significant part of the success is attributable to a new procedure, introduced here, to naturally pack the screen.
This work summarizes the experience of AEC Ecuador in techniques to effectively control the sand production and it is supported by an extensive amount of field data. The results obtained here have served to demonstrate that designs customized to fit specific reservoir conditions can help maximize the well's productivity and to optimize the completion costs.
Sand production is a problem common to many reservoirs. 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 reservoir.
There are three mechanisms responsible for sand production: compressive failures, tensile failures and erosion1. 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.1, 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.
Production free of sand can be obtained from most completions as long as a Critical Drawdown Pressure (CDP) is not exceeded. The CDP for a specific reservoir can be obtained by coupling a perforating tunnel stability model with a pore pressure model; this last can be obtained from Darcy's equation. The sand strength model can be obtained by investigating the state of stress for a perfect Mohr-Coulomb material. Further details on how to determine the CDP can be found in the literature1–2.