SummaryUnconventional gas reservoirs are characterized by low porosity and low permeability. Due to the low permeability in these types of plays, hydraulic fracture stimulation is required to achieve gas production. An effective stimulation connects the existing natural fractures and effectively links as much reservoir rock as possible with the wellbore.
Previous studies have shown that, if used under the right perspective, Lambda-rho/Mu-rho cross plots can be used to quantitatively grade reservoir rocks in conventional as well as in unconventional plays. The validity of this statement is corroborated with actual field data. Specifically, production logs recorded in four neighboring horizontal wells in the Lower Barnett after hydraulic fracturing was carried out, strongly agree with the hypotheses that:
1. Low values of Lambda-rho and Mu-rho are indicative of high porosity and therefore high reserves in place, in this case gas.
2. For any given porosity or original gas in place (OGIP), the recovery factor and therefore the gas rate increases with decreasing Poisson's ratio.
This study shows that production logs such as the temperature log and the differential gas production log when plotted in the Lambda-rho/Mu-rho background are in agreement with the two hypotheses. High temperatures correspond to high gas rates; therefore, high temperatures and high gas rates are clustered together towards the lower left hand side of the Lambda-rho/Mu-rho cross plot, while lower temperature and lower gas rates cluster towards the upper right hand side of the cross plot.