Wellbore Compressibility (cwb)

Wellbore fluid compressibility is used to calculate the wellbore storage constant (C) for an afterflow (wellbore storage) analysis. It applies only in the case of a liquid-filled wellbore.

When the wellbore fluid is highly compressible (e.g., gas), the wellbore can store more fluid with increasing pressure. Subsequently, wellbore storage is higher, and the effects are seen for a longer period of time.

Theoretical development of the wellbore storage equations assumes a single-phase fluid in the wellbore with a constant compressibility. The value of the compressibility used corresponds to that of the primary, or dominant fluid type in the wellbore. In reality, this is not the case, since the wellbore often contains a mixture of oil, gas, and water. Thus, the fluid compressibility is not constant, but is a function of pressure. As a consequence, any value used for wellbore fluid compressibility is only an estimate.