Advances In Measuring Porosity And Permeability From Drill Cuttings
- Roland Lenormand (Institute Francais du Petrol IFP) | Olivier Fonta (Geopetrol)
- Document ID
- Society of Petroleum Engineers
- SPE/EAGE Reservoir Characterization and Simulation Conference, 28-31 October, Abu Dhabi, UAE
- Publication Date
- Document Type
- Conference Paper
- 2007. Society of Petroleum Engineers
- 1.11 Drilling Fluids and Materials, 1.12.3 Mud logging / Surface Measurements, 5.6.2 Core Analysis, 4.1.2 Separation and Treating, 5.6.1 Open hole/cased hole log analysis, 5.5.8 History Matching, 4.3.4 Scale, 1.6 Drilling Operations, 5.6.4 Drillstem/Well Testing, 1.2.3 Rock properties, 4.1.5 Processing Equipment, 5.2 Reservoir Fluid Dynamics, 1.6.9 Coring, Fishing, 5.1 Reservoir Characterisation, 5.5.2 Core Analysis
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Drill cuttings can provide quick and useful information for reservoir characterization, especially when cores are not available. So far, several petrophysical properties can be determined from cuttings: porosity, permeability and T2 NMR distributions (directly related to the pore size distribution) Several laboratories are working to improve the techniques of measurements and also the drilling tools to minimize the damage to the rock. In this paper, we present new results for porosity and permeability measurements down to cuttings of diameters around 0.5 mm and the application to a field test.
The methods for measuring the porosity on cuttings are the same as for cores when the sizes are larger than 3mm. For smaller cuttings (most of cases), the best results are obtained using a centrifuge or a porous plate to remove the interstitial liquid with a controlled capillary pressure. With this method, porosities were measured within 1-2 PU (Porosity Units), even for the flat cuttings with diameter around 1mm and thickness around 0.5 mm collected during the field case.
For permeability, we used the technique developed by IFP based on the diffusion of a pressure wave in a viscous liquid saturating the cuttings. The results were improved by a better choice of the viscosity of the liquid used to saturate the cuttings. The suitable viscosity must satisfy two opposite constrains: high viscosity for a relaxation time large enough to be measured (larger than 0.2 second), and low viscosity to allow spontaneous imbibition in a short time. The results of the study are presented in a diagram, showing the viscosity to be used as a function of cuttings sizes and permeability.
Porosity and permeability methods have been tested on synthetic cuttings obtained by crushing cores of known parameters.
Finally, the methods were tested on real cuttings sampled especially for this study every 20 cm in a carbonate formation (125 samples). The results are discussed and compared to porosity logs obtained in the same well. The porosities measured on cuttings agree with the log value for values larger than 5 PU. The T2 NMR relaxation times (peaks) are also in good correlation with the amount of clay given by the gamma ray log. However, the porosities and the sizes of cuttings are two small for permeability determination. Both porosities and T2 relaxation times give a good depth matching prediction with log less than 1 meter.
The early determination of rock petrophysical properties is one of the main concerns during the reservoir characterization process because it impacts directly the reserves (porosity, saturation) and also the well deliverability (permeability). Logs generally provide a good estimate of porosity and saturations along the well, but permeability is more difficult to obtain because this parameter refers to conductance of the reservoir rock to flow.
Cuttings are routinely used by mud loggers to build the "master log", in which the geological description of the drilled formation is reported. Hydrocarbon indices are also determined from cuttings to identify the reservoir levels. Although cuttings rock material is coming directly from the reservoir, few applications of porosity and permeability characterization are reported in the literature.
In this paper, we will review the methods used for porosity and permeability determinations on cuttings and present our results on crushed cores. The main result is the accurate determination of porosities for 0.5 mm diameter cuttings for permeability equal or less than the millidarcy. We will also present the porosities and relaxation times T2 measured on real cuttings from a well in Paris Basin, and compare the results to the logs.
Porosity measurement on cuttings
Standard methods, similar to the methods used in routine core analysis, have been described by Meazza et al. and Marsala et al, 1997. More recently, Siddiqui et al, 2006 presented results obtained using a medical based CT-scan. The main conclusion of all these studies is a very poor accuracy for porosity on cuttings with diameter below 2.5 mm.
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