Abstract
Seepage control is a prerequisite for hydrocarbon storage in unlined rock caverns (URCs) where the seepage of stored products to the surrounding host rock and groundwater can cause serious environmental and financial problems. Practically seepage control is performed by permeability and hydrodynamic control methods. This paper employs numerical modelling and genetic programming (GP) for the purpose of seepage prediction and control method determination for the crude oil storage URCs based on the effective parameters including hydrogeologic characteristic of the rock and physicochemical properties of the hydrocarbons. Several levels for each parameter were considered and all the possible scenarios were modelled numerically for the two-phase mixture model formulation. The corresponding seepage values were evaluated to be used as genetic programming data base to generate representative equations for the hydrocarbon seepage value. The coefficients of determination (R2) and relative percent errors of the proposed equations show their ability in the seepage prediction and permeability or hydrodynamic control method determination and design. The results can be used for crude oil storage URCs worldwide.
Highlights
Underground storage of hydrocarbons in unlined rock caverns (URCs) is more secure, safe, and economical than aboveground storage and has several environmental and operational advantages
The purpose of this study is to employ numerical modelling and genetic programming to predict the hydrocarbon seepage from the URCs (Iranian URCs in the limestone rocks) based on the allowable seepage value (m3/24 hr) to be able to decide on the seepage control technique selection
The results showed that, in order to control the oil seepage by permeability control technique such as grouting, the permeability of the rock must be less than 100 mD (10−13 m2) with proper water level above the cavern; otherwise the seepage of the stored products would be much more than allowable seepage value
Summary
Underground storage of hydrocarbons in unlined rock caverns (URCs) is more secure, safe, and economical than aboveground storage and has several environmental and operational advantages. Permeability control means applying techniques such as grouting or freezing to control and decrease hydrocarbon seepage by maintaining a specified low permeability and sealing of the rock mass. These techniques are very time-consuming and expensive [1]. It is meant that there is groundwater in the rock mass with the static head that exceeds the internal storage pressure resulting in positive groundwater gradient towards the cavern to prevent the escape of the stored products [2]. There is no standard for acceptable seepage value and how much sealing work is required It depends on the environmental and economic (operational) aspects. 75% and 25% of a cavern space are considered for liquid oils and gases, respectively [2]
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