A Complete Petrophysical-Evaluation Method for Tight Formations From Drill Cuttings Only in the Absence of Well Logs

Abstract

The amount of tight-formation petrophysical work conducted at present in horizontal wells and the examples available in the literature are limited to only those wells that have complete data sets. This is very important. But the reality is that in the vast majority of horizontal wells, the data required for detailed analyses are quite scarce. Petrophysical evaluation in the absence of well logs and cores can now be considered owing to the possibility of measuring both the permeability and porosity of drill cuttings. This is essential because the application of the successive correlations used throughout the paper is based on porosity and permeability data. To try to alleviate the data-scarcity problem, a new method is presented for complete petrophysical evaluation derived from information that can be extracted from drill cuttings in the absence of well logs. The cuttings data include porosity and permeability. The gamma ray and any other logs, if available, can help support the interpretation. However, the methodology is built strictly on data extracted from cuttings and can be used for horizontal, slanted, and vertical wells. The method is illustrated with the use of a tight gas formation in the Deep basin of the western Canada sedimentary basin (WCSB). However, it also has direct application in the case of liquids. The method is shown to be a powerful petrophysical tool because it allows quantitative evaluation of water saturation, porethroat aperture, capillary pressure, flow units, porosity (or cementation) exponent m, true-formation resistivity, and distance to a water table (if present). Also, the method allows one to distinguish the contributions from viscous and diffusion-like flow in tight gas formations. The method further allows the construction of Pickett plots without previous availability of well logs, and it assumes the existence of intervals at irreducible water saturation, which is the case of many tight formations currently under exploitation. It is concluded that drill cuttings are a powerful direct source of information that allows complete and practical evaluation of tight reservoirs in which well logs are scarce. The uniqueness and practicality of this quantitative procedure originate from the fact that it starts only from the laboratory analysis of drill cuttingssomething that has not been performed in the past. Laboratory Work The laboratory procedure starting with data collection has been summarized by Ortega and Aguilera (2012b) and is presented here for completeness. For a deeper treatment on the subject, refer to Ortega (2012) and Ortega and Aguilera (2012a). Chronologically, the steps are as follows: Sample collection Microscopic analysis Measureable-sample selection Cleaning and drying of samples Porosity measurement Permeability measurement Sample Collection. Drill cuttings are available in many instances and provide a valuable direct source of information. They are collected generally every 5 m (16.4 ft) and sometimes every 2.5 m (8.2 ft). If drill cuttings are used, care should b...

A Case Study on Formation Evaluation of Horizontal Wells in the Tight Gas Nikanassin Group of the Western Canada Sedimentary Basin Using Drill Cuttings

“…A similar equation (Eq.1) that relates porosity and permeability to pore throat aperture was developed by Aguilera (2002): This equation is rigorously valid between 30 to 90% water saturation, but in practice we have been able to extend it beyond those limits with reasonable results for the tight formations we are studying in the GFREE research group (Aguilera 2002 andOrtega et al 2013). The porosity and permeability obtained from drill cuttings were used to estimate the pore throat radii (r p35 ) shown in Column 5 of Table 1.…”

“…In a recent work, Ortega et al (2012) concluded that in the absence of well logs and cores; complete petrophysical evaluation can now be considered a possibility owing to the fact that permeability and porosity can now be measured directly from drill cuttings. Ortega and Aguilera (2013) study was on vertical wells drilled in the tight gas Nikanassin group of the western Canada sedimentary basin (WCSB). The present study extends the work to that of a horizontal well where drill cuttings are available in the same geological area.…”

Quantitative Properties From Drill Cuttings To Improve the Design of Hydraulic-Fracturing Jobs in Horizontal Wells

“…Twenty-five samples from 3095 to 3205 m were analyzed for determining porosity and permeability. Most of the samples were collected every 5 m. More details about the reservoir under consideration and the use of drill cuttings for formation evaluation have been published by Ortega and Aguilera (2013).…”

“…The methodology has been further extended so as to use data extracted from drill cuttings for quantitative formation evaluation including the estimation of irreducible water saturation (S wi ), true formation resistivity, porosity (or cementation) exponent m, the possibility of distinguishing between viscous and diffusion-like flow, and the construction of Pickett plots (Ortega 2012;Ortega and Aguilera 2013). In the Nikanassin Group of the WCSB considered in this study, there is no water leg.…”

“…In the Nikanassin Group of the WCSB considered in this study, there is no water leg. Nevertheless, in those reservoirs where a gas/water contact (or a water/oil contact) is present, it is possible to make an estimate of the location of the contact and the capillary pressure at the depth where the drill cuttings were obtained, and to distinguish viscous from diffusiondominated flow (Ortega and Aguilera 2013).…”