AbstractsEarth & Environmental Science

This thesis consists of multiple approaches to develop a new model to determine the porosity, permeability and the rate of desorption of 1.5-inch shale samples. The raw NMR signal of the sample in the coreholder is measured before methane injection and is used as base signal. During the injection of methane the raw NMR signal increases. The base signal is subtracted from the response during the methane injection. This difference is Laplace transformed to only obtain the T2 distributions and T1 − T2 correlations related to the injected methane in the shales. T2 distribution holds information on the pore size distribution. Using cut-off values to separate the signal, different zones can be extracted. During injection and production of fluids, the rate and the total fluid filled porosity are used to calculate the permeability related to the individual pore size distributions. To test this theory, a high porosity carbonate rock from the Khuff formation is first injected with water. Thereafter shale samples from the Posidonia and Qusaiba formation are put to the test with injection of methane. In the majority of shale gas formations, there are two types of pore systems are present; kerogen-hosted organic pores(OP) and inorganic pores (IP). By fully saturating 1.5-inch shale cores and by continuously mea- suring the NMR signal it is possible to determine the individual porosity and permeabilities of the pore sys- tem. T1 − T2 measurements are made to confirm the individual zones and the mobility of the fluid in the zones. A single exponential decay formula is defined to calculate the permeability. This formula is tested with an Eclipse simulation to validate the calculated value. Eventually a multi-exponential model is used to distinguish the high and low permeability components in shales. This high permeability component is interpreted to represent the inorganic pores and micro fractures, while low permeability component is interpreted to represent the organic pores and the desorption from pore surface. The Posidonia samples have an OP of 2.2-3.5% and an IP of 3.2-4.2%, while the Qusaiba have an OP of 0.2-0.3% and an IP of 0.45-0.9 %. Therefore the Posidonia core samples show better production potential than the Qusaiba samples. Understanding the shale porosities for different storage mechanisms as well as the corresponding permeabilities is essential for developing shale reservoirs and target zone selection.