Application of After-Closure Analysis Techniques to Determine Permeability in Tight Formation Gas Reservoirs

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe primary objective of hydraulic fracturing is to create a propped fracture with sufficient conductivity and length to maximize or at least optimize well performance. In permeable reservoirs where transient flow is short lived, a fracture with a Dimensionless Fracture Capacity, F CD , of 2 is required to meet the design objective. In low permeability formations where transient flow can be extensive and where fracture fluid cleanup requires additional conductivity, an F CD in excess of 10 is desired. As a result, reservoir permeability becomes/is a key fracture design and analysis parameter. In higher permeability applications, permeability is determined simply, inexpensively, and routinely through conventional well testing techniques. Conventional well testing in tight formation gas reservoirs has not been proven as effective, can be expensive (cost of lengthy tests and production deferment), and is quite simply not routinely utilized. These reservoirs are often non productive without fracture stimulation and post fracture stimulation testing requires extensive shut-in time as the time to pseudo radial flow is proportional to the square of the fracture half-length. As a result, the development and routine use of any technique to determine permeability in these tight formation gas reservoirs has great value.In addition, without adequate well testing techniques and capabilities in tight gas reservoirs, the engineer is left with the use of log derived values of permeability which can often overstate in-situ permeability by factors of five to ten. Determination of in-situ permeability not only aids the well completion and stimulation but can be used to calibrate the log and core derived estimates of permeability improving performance predictions and field development. Prior papers have developed the use of After Closure Analysis techniques in permeable reservoirs, this paper will show the application of this technique to several tight gas formations in North America.This paper will demonstrate the following: 1) The effective application of this technique in tight gas formations in the U.S. and Canada, 2) Develop a cost effective and operationally simple means of collecting and analyzing the data, 3) Compare and contrast the technique to other methods of determining permeability in tight formation gas reservoirs, such as impulse, Perforation Inflow Diagnostic (PID), Closed Chamber Drill-Stem Tests (CCDST), post-frac build-up, production decline analysis, Modular Dynamic Formation Tester (MDT). 4) Show the application and value of calibrating log and core-derived permeability with in-situ measurements for improved well performance predictions.

Optimization of Stimulation Treatments in the Wamsutter (Almond) formation by Means of Pre-Fracture Impulse Diagnostic Tests

“…The idea of using pre-fracture impulse tests to estimate reservoir data has been explained by other authors [4][5][6] . In its simplest sense, attaining pseudo radial flow following a short injection test enables the estimation of pressure and permeability for the zone of interest.…”

Formation-Tester Pulse Testing in Tight Formations (Shales and Heavy Oil): Where Wellbore Storage Effects Favor the Determination of Reservoir Pressure

“…However, this assumption is unrealistic, especially in low mobility formations in which there could be no sealing mudcake to isolate the reservoir from hydrostatic pressure. In tight formations, the invasion rate is slowed by the formation, and mudcake may form slowly or it may not exist (Proett et al 2000;Schrooten et al 2007;Britt et al 2004). Therefore, the measured pressure in these cases is substantially greater than the formation pressure as a result of the lack of sealing mudcake.…”