Patent ID: 8204724

Claim:
A method of predicting a delayed actuation of a downhole tool, comprising: providing a first pressure chamber; providing a second pressure chamber; connecting the first pressure chamber with the second pressure chamber by way of an orifice; metering fluid initially contained in the first pressure chamber through the orifice into the second pressure chamber; providing a model of at least one rheological characteristic of the fluid; according to the model, predicting, using a computer, a behavior of the tool for at least one expected condition in a well, wherein the tool includes an actuator that uses the fluid; and according to the provided model, predicting, using a computer, a behavior of a tool for at least one expected condition in a well, wherein the tool includes an actuator that uses the fluid, wherein the modeling comprises using a viscosity equation, η mod ( T, P, t 0 , γ 0 )=η exp ( T 0 , P 0 , t 0 , γ 0 )*exp {−δ[(1/ T 0 )−(1/ T )]}*exp{( P−P 0 )/β}, where t 0 represents an initial time, γ 0 represents at least one shear rate of interest, η mod (T, P, t 0 , γ 0 ) is measured fluid viscosity at a reference temperature (T 0 ) and pressure (P 0 ) prior to being subjected to aging, δ is a rate of change of viscosity of the fluid with temperature (T), and) β is a rate of change of viscosity of the hydraulic fluid with pressure (P); and subjecting the fluid to aging, where the aged fluid viscosity is represented as η mod (T, P, t, γ 0 )=η mod (T, P, t 0 , γ 0 )*[1−α(T)*t], where η mod (T, P, t 0 , γ 0 ) is estimated fluid viscosity at given temperature (T) and pressure (P) prior to being subjected to aging, and α(T) is a rate of viscosity degradation at temperature T per unit of time (t), wherein providing the model comprises providing a viscosity model, η mod (T, P, t 0 , γ 0 )=η exp (T 0 , P 0 , t 0 , γ 0 )*exp {−δ[(1/T 0 )−(1/T)]}*exp{(P−P 0 )/β}, where t 0 represents an initial time, γ 0 represents at least one shear rate of interest, η exp (T 0 , P 0 , t 0 , γ 0 ) is measured fluid viscosity at a reference temperature (T 0 ) and pressure (P 0 ) prior to being subjected to aging, δ is a rate of change of viscosity of the fluid with temperature (T), and) β is a rate of change of viscosity of the hydraulic fluid with pressure (P).