Reservoir management is difficult for several gas fields in the flanks of the fold-thrust belt of the Eastern Cordillera of the Middle Magdalena Valley, Colombia. Technical complicating factors include (i) complex geology (faulting, naturally fractured), (ii) high tectonic stresses (> 1.0 psi/ft), (iii) high-angle formation dip (> 60°), (iv) overpressure (> 1.0 psi/ft), and (v) gas condensation. Due to the unusual stress/tectonic environment, a potential impact to reservoir performance is the stress-sensitive permeability (permeability reduction-rebound induced by fluid withdrawal-injection). Interpretation of well testing thus is challenging because of the combined effects from the above factors.

This paper presents an analysis of a field isochronal test. The effect of stress-sensitive permeability on well test response is emphasized through numerical simulations. Other factors complicating the well-test interpretation are also discussed. Pressure derivative analysis is shown to be very useful in identifying the permeability variation. The logarithmic slopes basically reflect the combined variations of permeability, producing thickness, flow rate, and fluid properties. Natural fracturing, gas-condensation, high gas rates, and stress-sensitivity permeability will contribute to the changing slopes of pressure response. The impacts are essentially reflected by the magnitudes of near-wellbore skin and reservoir permeability. Guidelines useful in identifying stress-sensitive permeability from well testing are proposed.

You can access this article if you purchase or spend a download.