J. Matthew Herrin¹, Lawrence Teufel²

(1) New Mexico Institute of Mining and Technology, Socorro, NM
(2) New Mexico Institute of Mining and Technology

ABSTRACT: Simulating Natural Gas Flow in Stress-Sensitive Fractured Reservoirs

Successful management of naturally fractured hydrocarbon reservoirs requires a good understanding not only of fracture distribution, orientation, and connectivity, but also of the relationship between fracture permeability, in-situ stress, and geomechanics. Characteristics of the in-situ stress state (e.g., orientation of principal stress directions, stress magnitudes, stress differential) can play an important role in determining which fractures remain open and conductive, and which fractures provide little permeability enhancement. Thus, effective reservoir engineering requires an awareness of the current regional in-situ stress state as well as a knowledge of local stress field perturbations induced by production or injection operations. Numerical codes which model the behavior of stress-sensitive fractures have been developed to supplement a tight gas reservoir flow simulator. User-defined parameters such as principal stress orientations and magnitudes, initial fracture stiffness coefficients, and maximum fracture closure are coupled with gas pressure, fracture orientation, and fracture aperture data from the simulator. During flow simulation, changes in the effective normal stress resolved across each fracture are calculated as a function of fracture orientation and local reservoir pressure. This modified normal stress is translated into a change in fracture aperture (and concomitant fracture transmissivity) via fracture stiffness characteristics. The result is a reservoir simulator capable of modeling natural gas flow through networks of discrete, deformable fractures. This reservoir simulator has been used to characterize fluid flow in a tight, naturally fractured gas reservoir in western Colorado.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado