Patent ID: 7774140

Claim:
A method of detecting a fracture with residual width from a previous well treatment during a well fracturing operation in a subterranean formation containing a reservoir fluid, comprising the steps of: (a) injecting an injection fluid into the formation at an injection pressure exceeding the formation fracture pressure; (b) gathering pressure measurement data from the formation during the injection and a subsequent shut-in period; (c) transforming the pressure measurement data into a constant rate equivalent pressure; and (d) detecting the presence of a dual unit-slope wellbore storage in the transformed pressure measurement data, said dual unit-slope being indicative of the presence of a fracture retaining residual width; wherein the reservoir fluid is compressible; the transformation of pressure measurement data is based on the properties of the compressible fluid contained in the reservoir; and the transforming step comprises the step of calculating: a shut-in time relative to the end of the injection: Δt=t−t ne ; an adjusted time: t a = ( μ ⁢ ⁢ c t _ ) ⁢ ∫ 0 Δ ⁢ ⁢ t ⁢ ⅆ Δ ⁢ ⁢ t ( μ ⁢ ⁢ c t ) w ; and an adjusted pseudo pressure difference: Δ ⁢ ⁢ p a ⁡ ( t ) = p aw ⁡ ( t ) - p ai ⁢ ⁢ where ⁢ ⁢ p a = μ _ g ⁢ z _ p _ ⁢ ∫ 0 p ⁢ p ⁢ ⁢ ⅆ p μ g ⁢ z ; wherein: t ne is the time at the end of injection; μ is the viscosity of the reservoir fluid at average reservoir pressure; (μc t ) w is the viscosity compressibility product of wellbore fluid at time t; (μc t ) 0 is the viscosity compressibility product of wellbore fluid at time t=t ne ; p is the pressure; p is the average reservoir pressure; p aw (t) is the adjusted pressure at time t; p al , is the adjusted pressure at time t=t ne ; c t is the total compressibility; c t is the total compressibility at average reservoir pressure; and z is the real gas deviator factor.