Identifying and Evaluating Potential Well Integrity Risk Factors Based on Available Geological, Hydrogeological and Related Subsurface Data

Abstract

Public awareness of potential environmental impacts associated with upstream oil and gas operations increased dramatically in recent years. Environmental assessment of industry activities requires an understanding of potential risks and impacts associated with drilling and completing wells. Evaluating and characterizing well integrity, along with potential impacts associated with compromised wells, represents a new technical resource topic for environmental assessments. Comprehensive environmental assessment requires accurately delineating subsurface geological and hydrogeological conditions. Well bores represent primary potential vertical gas migration conduits. Numerous leaking wells are documented at oil and gas fields and at underground natural gas storage facilities, some with adverse consequences. Most leaks are associated with abandoned oil and gas wells or old dry holes, but may include newly constructed wells with defective annular seals. Safeguarding groundwater quality from oil and gas related exploration and production activity is a major public concern. Maintaining well integrity is the primary tool for protecting 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. Various factors contribute to leaks in operating or abandoned wells, including engineering design and construction challenges associated with downhole conditions. Several geologic factors that may cause or contribute to compromised well integrity are listed below. Geologic and other factors affecting annular seals and confinement: (a) “Shallow” gas bearing zones, (b) Aquifers, especially artesian aquifers, (c) “Mud cake” on borehole wall, (d) Fractured zones. Thoroughly evaluating downhole conditions for geological risk factors is fundamental to design well completions that address possible problematic subsurface geologic conditions, and thereby, minimize potential adverse consequences. This presentation covers geological, hydrogeological and related subsurface risk factors that may affect well integrity, along with techniques to identify potential adverse downhole conditions from typical borehole logs and other data collected during drilling.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016