TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractCrucial issues in formation evaluation are the determination of porosity, permeability, hydrocarbon volumes and net-to-gross ratio. NMR logging provides measurements that are directly related to these parameters. The NMR response of fluids contained in pores is governed by their T 2 and T 1 -relaxation times, diffusion coefficient and whether or not they wet the rock. In the case where fluids possess a sufficiently large contrast in these properties and NMR data has been acquired with suitably chosen acquisition parameters (i.e. wait times and/or interecho times) a separation of water, oil and gas NMR responses can be made. From these separate NMR responses the hydrocarbon volumes, porosity and permeability estimates are subsequently calculated. Key in these applications is the ability to include all the acquired log NMR data into the processing towards the desired end result. Methods exists to derive hydrocarbon volumes from T 2distribution or from echo decay data. However, these are all methods in which the difference between just two acquisitions that only differ in either wait time or interecho time are considered. Over the past years we have developed, tested and employed an alternative processing technique named MacNMR (Multi-acquisition NMR). MacNMR takes any number of log acquisitions (wait time and/or interecho time variations) and simultaneously inverts them using an rigorous forward model to the desired water and hydrocarbon T 2 spectra. In this paper we discuss the concepts of MacNMR and demonstrate its versatility in NMR log processing. An example will illustrate its benefits. MacNMR is implemented across Shell operating units worldwide and has been in use for over two years now.
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