Geological, Hydrogeological And Related Subsurface Conditions Affecting Well Integrity & How Do We Identify And Evaluate Potential Risk Factors Based On Available Data?

Abstract

Groundwater protection is a primary concern for oil and gas related exploration and production activities in America. Maintaining well integrity is the primary tool for protecting our nation's groundwater resources from accidental well releases. Thorough evaluation of geologic and related technical considerations is critical to ensure well integrity and groundwater protection. Substantial risk is directly associated with inaccurate technical evaluations that lead to compromised annular seals, resulting in subsequent gas or fluid migration to the surface or groundwater aquifers. Well bores represent primary potential vertical gas migration conduits. Numerous leaking wells are documented at American oil and gas fields, some with catastrophic results. Most leaks are associated with abandoned oil and gas wells and old dry holes, but could include newly constructed wells with defective annular seals. Many factors contribute to leaks in operating or abandoned wells, including engineering design and construction challenges. Several geologic factors that may cause or contribute to well integrity are listed below and discussed in the presentation. Geologic and other factors affecting annular seals and confinement include: 1. “Shallow” gas bearing zones, 2. Aquifers, especially artesian aquifers, 3. “Mud cake” on borehole wall, 4. Fractured zones. Thoroughly evaluating downhole conditions for geological risk factors is fundamental to design well completions that address potentially problematic subsurface geologic conditions, and thereby, minimize potential adverse consequences. This presentation covers geological, hydrogeological and related subsurface risk factors that adverse effect well integrity, and techniques to identify potential adverse downhole conditions from typical borehole logs.

AAPG Datapages/Search and Discovery Article #90215 © 2015 Pacific Section AAPG Convention, Oxnard, California, May 3-6, 2015