Bore and well induced inter‐aquifer connectivity: a review of literature on failure mechanisms and conceptualisation of hydrocarbon reservoir‐aquifer failure pathways

[摘要] The project “Bore and well induced inter-aquifer groundwater connectivity: Consequencemodelling and experimental design” focuses on identifying the consequences associated withpreferential pathways generated by failed or open bore holes associated with coal seam gasdevelopment. The project aims to develop methodologies and techniques that will identifyand potentially quantify the potential risks associated with well and bore-induced inter-aquiferconnectivity. The project has two components: i) a critical literature review and localgroundwater modelling to identify the types of compromised bore integrity that may bemeasureable in CSG-bearing basins, and ii) regional groundwater modelling to assess theconsequences of well and bore hole connectivity and the number of required connectivepathways to create a range of noticeable impacts. This report represents the literature reviewthat provides the framework to guide local-scale simulations to establish i) the potential forlocal-scale impacts of well or bore failures, ii) the level of discharge or cross-formationalleakage that would be required to produce measurable changes in groundwater chemistry(major ions, stable isotopes or tracers), and iii) experimental designs that could be applied tomeasure local impacts of wells or bores that may have failed.This review addresses some aspects of well failure, such as failure mechanisms, failure ratesand knowledge gaps in the context of understanding the potential impacts of well failure onaquifer connectivity in CSG (coal seam gas) producing environments. Onshore oil and gaswells, water bores as well as coal seam gas wells are included in this review.Well failure or loss of well integrity may result from a well breach (or number of wellbreaches), and can take the form of a hydrological or environmental breach. The three typesof breaches are defined as: Well breach - failure in cement, casing, downhole and surface sealing components Hydrological breach - fluid movement between different geological units, or Environmental breach – fluid leaks at surface and causes contamination of watersources.Key well failure mechanisms are addressed for each phase of an entire well life cycle, i.e.,well design and/or construction, production and abandonment phases and have beensummarized below.Well design and/or construction phase: Well design and/or construction that is inadequate to prevent hydrological orenvironmental breach; includes lack of casing and/or annulus seal, and, in case of awater bore, screening across multiple aquifers; Well failure that may occur during or as a consequence of i) drilling fluid being lostinto overburden and reservoir formations due to naturally fractured formations or highdrilling fluid pressure that generates a hydraulic fracture unintentionally, or ii) fluidinflux into the well from the surrounding formations due to the drilling fluid pressurebeing lower than the formation pore pressure; Wellbore instability may occur due to a lower drilling fluid pressure than required.Wellbore instability not only produces washout that can lead to a poor cement job, butalso creates a disturbed zone with enhanced permeability surrounding the well;Page | x Failure in cement sheath and cement bond integrity may lead to well failure. Cementsheath and cement bonds play a critical role in protecting casing from corrosion andin preventing fluid migration behind the casing. The factors that can affect cementsheath and cement bond integrity include cement slurry losses into formations, poorwellbore condition, poor mud conditioning,pressure cycles imposed on casing andcement sheath during casing pressure test, and cement degradation. Tubing/casing corrosion resulting in well failure. Corrosion attacks every metalcomponent, including tubing and casing, if unprotected in all phases in the life of anoil and gas well.Production phase:In addition to the tubing/casing corrosion and cement rel

[发布日期] 2016-04-07 [发布机构] CSIRO

[学科分类] 地球科学(综合)