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CEMENTS FOR DURABLE ZONAL ISOLATION OF A CASED WELLBORE

Cel

The aim of the project is to demonstrate to the oil and gas industry that an approach developed in R&D to maintain the mechanical integrity of the cement sheath improves significantly the durability of zonal isolation. Durable zonal isolation is necessary to prevent the migration of hydrocarbon through the annulus which can cause severe damage to the environment. This improved durability will reduce the emission of hydrocarbons in the atmosphere, will avoid any fluid cross communication between various layers, will allow a better control of the oil production and ensure a better well mechanical integrity. Zonal isolation must be maintained not only during the life of the well, but also once the well has been abandoned. The proposed approach includes a procedure to establish requirements on cement mechanical and physical properties, the use of new cements with improved mechanical properties, and recently developed measurement/interpretation techniques to fully evaluate the cement sheath integrity. This demonstration will be first carried out on a laboratory mock-up of a well then on onshore wells.

The first step is the determination of the well environment. This includes a measurement of the mechanical properties of the formations and the expected loading the well will be submitted to during its entirely life. The well loading includes well pressure variation, well temperature variation, formation pressure variation and far-field stress variation. The geometry of the well has also to be taken into account such as the open hole diameter and the casing size. This step being achieved, the requirement in term of cement mechanical properties is determined using an internally developed software product, which uses as input the parameters measured above. This determines a set of possible properties the cement must have to provide isolation during the life of the well. In a database, one finds a set of cements with various properties. These properties include thermo-poro-elastic properties, tensile strength and compressive strength, physical properties (density, porosity, permeability and variation of volume during hydratation) and resistance to chemical attacks. Conventional slurries properties (which follows API standards) are also included. Some cements might have a high compressive strength and a high stiffness, others a low stiffness (high flexibility), and a low strength. Depending on the environment, the slurry which will give a cement with the most appropriate properties is selected.
This slurry is then pumped into the wellbore and placed into the annulus. The evaluation process can then take place by logging/measuring with currently used tools and new tools. We are aiming a getting information on the cement sheath, allowing to detect wether the cement has been properly placed and wether there is no gap between the casing and the cement and between the cement and the rock, and also to get some information about the elasticity of the cement, providing a quality check of the slurry design. The final evaluation is the measure of the annular pressure at the surface.

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Schlumberger
Wkład UE
Brak danych
Adres
26 rue de la Cavée
92140 Clamart
Francja

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