Abstract

The volume of hydrocarbons contained in tight petroleum reservoirs is gigantic. Thus, their development is crucial to satisfy the worldwide energy demand. A critical aspect for the development of these formations is the stress-dependency of rock properties. As pore pressure changes, porosity, permeability and compressibility of both matrix and natural fractures in tight reservoirs also changes, affecting the wells production behavior.

A practical problem in the estimation of stress dependent properties is that the amount of core data available to perform the corresponding studies in tight formations is generally scarce. Under these circumstances drill cuttings can be used to obtain this information. These observations lead to the key objective of this paper: to develop a reliable approach for estimating stress-dependent properties through the introduction of an innovative methodology that quantifies changes in properties of tight reservoirs and how to apply this methodology in drill cuttings.

The model is developed based on the relationship between the cube root of a normalized permeability and the logarithm of net confining stress. An empirical exponent (α) is introduced to fit the experimental data from confining tests conducted on both vertical and horizontal core samples. This exponent allows developing an equation that works independently of the initial net confining stress, which is the main limitation of the models already available in the literature. A statistical analysis is performed to verify the appropriateness of the proposed model for the prediction of rock properties as a function of net confining stress.

It is shown that current formulations are particular cases of the proposed model based on the results obtained for the empirical exponent α. Semilog cross-plots of the cube root of normalized permeability versus the net confining stress using core laboratory data corroborate the robustness of the proposed method. The application of the method with drill cuttings is also demonstrated.

It is concluded that the proposed method provides a more accurate methodology for estimating stress-sensitive properties of rocks in tight formations which are usually naturally fractured. Porosity, permeability and compressibility of tight formations are estimated following the generalized methodology proposed in this study.

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