Benoît Brouard

A Salt-Cavern Abandonment Test

Thousands of caverns have been leached out from deep salt formations. They are used for saturated brine production and/or hydrocarbons storage. They will be abandoned some day: the access well will be plugged with cement, isolating a large bubble of saturated brine. The later evolution of such a bubble raises serious concerns for environmental protection; salt creep and brine thermal expansion can lead to brine pressure build-up and rock-mass fracture, then brine seepage can lead to pollution of overlying water-bearing strata. Taking into account salt formation permeability leads to less pessimistic scenarios. An 18-month test has been performed on a deep brine-filled cavern. The objective was to measure the brine equilibrium pressure reached when the cavern is closed. Such an equilibrium is reached when salt mass creep, which leads to cavern shrinkage, balances brine permeation through the cavern wall. This objective was met by imposing different pressure levels and observing whether the pressure increased (or decreased) with respect to time. Data misinterpretation (i.e., a well leak instead of a cavern-proper leak) was precluded by a special monitoring system. The observed equilibrium pressure was significantly smaller than geostatic pressure, alleviating any fracture risk for a sealed and abandoned cavern in this salt formation.

Review of static and dynamic compressibility issues relating to deep underground salt caverns

Abstract Compressibility of deep fluids-filled cavern is discussed. Compressibility is measured both through statical and dynamical tests. Statical compressibility is influenced by cavern shape and the nature of cavern fluids. This parameter plays an important role for such applications as the determination of stored hydrocarbons volume, of volume lost during a blow-out and of pressure build-up rate in a closed cavern. Dynamical compressibility is measured through the periods of waves triggered by pressure changes. Both tube waves and longer period waves associated to the existence of an interface between a liquid and a gas can be observed. They allow checking of the results of the statical tests and can provide additional information, for instance the existence of trapped gas in the well-head.

Static and Dynamic Compressibility of Deep Underground Caverns

Compressibility of deep fluids-filled cavern is discussed. Compressibility is measured both through statical and dynamical tests. Statical compressibility is influenced by cavern shape and cavern fluids nature. This parameter plays an important role for such applications as the determination of stored hydrocarbons volume, of volume lost during a blow-out, and of pressure build-up rate in a closed cavern. Dynamical compressibility is measured through the periods of waves triggered by pressure changes. Both tube waves and longer period waves associated to the existence of an interface between a liquid and a gas can be observed. They can provide additional information, for instance the existence of trapped gas in the well-head.

Une mesure de la perméabilité et du fluage d'une caverne dans le sel

Abstract Rock mass properties differ significantly from those measured on samples in the laboratory. A test has been performed on a deep brine-filled cavern, with the objective of measuring the equilibrium pressure reached when the cavern was closed. Such an equilibrium is reached when salt mass creep, which leads to cavern shrinkage, balances brine permeation through the cavern wall. A K = 2·10 −19 m 2 value of the average in situ intrinsic permeability has been deduced from the test; it is significantly higher than the intrinsic permeability measured in a well or in the laboratory. This result supports cavern abandonment scenarios in which the risk of natural fracturation due to high brine pressures is alleviated.