Joule-Thompson Cooling Effects Alter Pressure Transient Analysis Results. Western Canada Sedimentary Basin #welltests are often conducted in gas (#LNG) bearing formations. At the sandface, during production, Joule-Thompson (JT) cooling is the thermal effect most often observed. This phenomena is a result of gas expanding as it exits the perforations and is a function of insitu reservoir pressure and temperature conditions. When we perform a gas well drawdown or buildup pressure transient analysis (#PTA) our computer software uses pseudo-pressures vs. pseudo-times. This is supposed to help account for the fact that viscosity (µ) and compressibility (Z) are not constant due to changing pressures (the drawdown required to flow a well). This is according to the real gas law (pv = nZRT).