Gas Well Test Analysis: Use of Normalized Pseudovariables
- 1 December 1987
- journal article
- Published by Society of Petroleum Engineers (SPE) in SPE Formation Evaluation
- Vol. 2 (04), 629-636
- https://doi.org/10.2118/13082-pa
Abstract
Summary: Pressure data from gas wells are normally analyzed by use of pseudopressure, which is a transformation of measured pressure. When tests are associated with large pressure changes accompanied by a severe wellbore storage effect, such as in tight reservoirs, use is made of pseudopressure and pseudotime transforms. The purpose of the pseudovariables is to linearize "effectively" the governing diffusivity equation so that proper test interpretation can be made. In this study, normalized pseudovariables or transforms are introduced. Use of these new pseudovariables produces results identical to those obtained with the conventional pseudovariables. However, the proposed pseudovariables offer some distinct practical advantages. For example, units of pressure and time are retained, thus giving a physical "feel" for the pseudovariable definitions. Other features include use of liquid equations for solving the gas flow problems—i.e., constants of the working equations remain unchanged. This study also proposes two methods for estimating the rate-dependent skin, together with permeability, mechanical skin, and well deliverability. The first method involves logarithmic convolution of pressure with flow rate, both measured downhole, by use of a radial model. A trial-and-error approach is used to obtain the rate-dependent skin on a convolution plot. The second method requires a transient flow-after-flow test of short duration; a standard graphic technique allows the estimation of the desired reservoir parameters. Once the reservoir parameters are estimated with either method, the absolute open-flow potential (AOFP) of a well can be established by assuming a reservoir radius because the AOFP is relatively insensitive to this assumption.Keywords
This publication has 13 references indexed in Scilit:
- Semilog Analysis of Gas Well Drawdown and Buildup DataSPE Formation Evaluation, 1987
- The Use of Pseudotime: Wellbore Storage and the Middle Time RegionPublished by Society of Petroleum Engineers (SPE) ,1986
- Prefracture Testing in Tight Gas ReservoirsSPE Formation Evaluation, 1986
- Well Test Interpretation in Faulted ReservoirsPublished by Society of Petroleum Engineers (SPE) ,1986
- Interpretation of Pressure Buildup Test Using In-Situ Measurement of AfterflowJournal of Petroleum Technology, 1985
- Application of Pseudotime to Buildup Test Analysis of Low-Permeability Gas Wells With Long-Duration Wellbore Storage DistortionJournal of Petroleum Technology, 1982
- Analysis of Modified Isochronal Tests To Predict The Stabilized Deliverability Potential of Gas Wells Without Using Stabilized Flow Data (includes associated papers 12933, 16320 and 16391 )Journal of Petroleum Technology, 1978
- A Simplified Method of Pressure Buildup Analysis for a Stabilized WellJournal of Petroleum Technology, 1971
- Gas Well Testing With Turbulence, Damage and Wellbore StorageJournal of Petroleum Technology, 1968
- The Flow of Real Gases Through Porous MediaJournal of Petroleum Technology, 1966