ABSTRACT

In the past, measuring the NMR petrophysical properties of drill cuttings has been very difficult for two reasons: first, small rock samples yield only a small NMR signal which corresponds to a small signal-to-noise ratio and, second, the procedures for sample preparation and processing did not allow fast enough turn-around time. The combination of these two factors prevented NMR measurement of drill cuttings from becoming a mud logging routine. We have developed technology to obtain the NMR petrophysical parameters both at the well site and in the laboratory. The instrument uses modern electronics to overcome the signal-tonoise problem and weighs only 25 kg, making it easily portable. Using our procedures on drill cuttings during mud logging allows us to determine: ? Total and Effective porosity; ? Absolute permeability; ? Irreducible water saturation Swirr. Most other NMR petrophysical parameters (identifying pay zones, wettability condition etc.) can, in principle, also be derived. They will be the topic of a later paper, as deriving them with short turn around times depends primarily on the NMR measurement skills of the user. A new model was developed for NMR permeability estimates for multi-saturated cuttings and core plugs from clastic deposits. Cuttings larger than 1 mm, washed from mud with water, are suitable for permeability estimations. Unwashed cuttings (or drilling mud) can be used for preliminary rejection of the rocks with distinctive non-reservoir properties based on the NMR measurements, so long as the drilling mud does not contain oil. Cuttings fractions larger than 3 mm, washed from mud with water, are suitable for the evaluation of the reservoir rock and saturating fluids properties. Smaller cuttings (from 1mm to 3 mm) can only be used to evaluate the above parameters if the rock does not contain pores with the filtration radius of Rf >20 ?m. The technology has been successfully applied on a number of artificial models, outcrops and real cutting samples from oil and gas reservoirs in Canada, USA, China and FSU. It offers a lowcost option for log calibration and even an alternative solution when it is difficult to obtain NMR logs from a wireline. In the past, measuring the NMR petrophysical properties of drill cuttings has been very difficult for two reasons: first, small rock samples yield only a small NMR signal which corresponds to a small signal-to-noise ratio and, second, the procedures for sample preparation and processing did not allow fast enough turn-around time. The combination of these two factors prevented NMR measurement of drill cuttings from becoming a mud logging routine. We have developed technology to obtain the NMR petrophysical parameters both at the well site and in the laboratory. The instrument uses modern electronics to overcome the signal-tonoise problem and weighs only 25 kg, making it easily portable. Using our procedures on drill cuttings during mud logging allows us to determine: ? Total and Effective porosity; ? Absolute permeability; ? Irreducible water saturation Swirr. Most other NMR petrophysical parameters (identifying pay zones, wettability condition etc.) can, in principle, also be derived. They will be the topic of a later paper, as deriving them with short turn around times depends primarily on the NMR measurement skills of the user. A new model was developed for NMR permeability estimates for multi-saturated cuttings and core plugs from clastic deposits. Cuttings larger than 1 mm, washed from mud with water, are suitable for permeability estimations. Unwashed cuttings (or drilling mud) can be used for preliminary rejection of the rocks with distinctive non-reservoir properties based on the NMR measurements, so long as the drilling mud does not contain oil. Cuttings fractions larger than 3 mm, washed from mud with water, are suitable for the evaluation of the reservoir rock and saturating fluids prope

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