Publications

The potential of nuclear magnetic resonance (NMR) logging for evaluating low resistivity reservoirs has been recognized for several years. The most commonly involved method was to acquire the data in multiple runs where the NMR measurements were acquired, with , either the wait time or the echo spacing only was varied. Interpretation methodologies are available for identifying the presence of hydrocarbons based on the NMR analysis using the diffusion and relaxation analysis on a 2-dimensional plot. This interpretation method is limited to a single depth of investigation.New developments in NMR logging have made it possible to record the NMR response at two different depth of investigations. This profiling technique helps in separating out the invading borehole fluid from the native bore hole fluid. Techniques are available to characterize and quantify the fluid at different depth of investigations. This method also allows us to estimate the saturations at two different depths of investigations.Different field examples are discussed which have identified the presence of hydrocarbons in low resistivity hydrocarbon bearing reservoirs using the magnetic resonance log. In one instance reasonable value of gas hydrogen index was computed from the NMR measurements. Saturations derived from NMR measurements match well with the resistivity derived water saturations. The NMR saturations are independent of the formation resistivity and other resistivity related parameters e.g formation water resistivity, cementation and saturation exponents. This non dependence on resistivity is likely to open up a new technique for estimating the water saturation in low resistivity sands.