The Value of Integrating Existing 3D Seismic into Shallow Gas Studies

Abstract

wwuhl 1Q%m=~oRETEc~~oL~v coN==NcE Th#smWr msptavrti tilpr-n-atme&hore Tockno~y Conferenceheldln Ho.stcm Texas, 6.9 MaY 196S This Pawrwa8 salectnd for presentation by the OTC Prowam Commmea following revmw of mfomurton Cont8imd in m ab$tmd subnuttsd by the authm(s) Contents of ttw paver as F#eseoted hava motbnn lewmd by the Otfshore Technc.!qy Confe!exe and we subject to conectjmbytfwwlhof[s)~cmabrtal, -me8eni~, tisdnmmsaf!ly refl=t any position cflhe Offshcfe Technology Contwence orkoffmsrs Permissm to COPYIS restricted to an abstract C4 nti more tfmn SW words Illustratmns may not be coPwd The abstract should conb,nconspgcuws achtidoemenb oltiere and bytiom the paper was presented @ . q AbstractConventional 3D surveys, although designed and processed wilh clear exploration objectives in mind, of{cn contain much valuable information in the shallow section This information can add significantly to shallow gas studies based on conventional high resohrlion seismic [cchniqucs. Examples from the North Sea are used to illustrate how an integrated approach to interpretation can lead to a better understanding of [he shallow geology and to a more accurate and reliable assessment of drilling hazards, particularly shallow gas. A ncw apprrx~chto site investigations has been tried and tested and has been found to be both time and cost etTecti\'e.

Iceberg ploughmarks illuminated by shallow gas in the central North Sea

“…The use of conventional 3D seismic data has proven valuable for identifying shallow gas (Gallagher and Heggland, 1994;Sallisbury et al, 1996). Shallow gas has many expressions in seismic data and descriptions of these can be found in e.g.…”

Review of progress in evaluating gas hydrate drilling hazards

“…Gas hydrate-related drilling hazards are generally modest, but particularly acute where gas hydrate occurs at high saturations and in association with free gas (denoted by "C"). Cowlard, 1996;Williams and Andresen, 1996;des Vallieres et al, 1996;Orren et al, 1996;Salisbury et al, 1996;Trabant, 1996;Campbell, 1999;Wood et al, 2000;Austin, 2004). This practice is sound and fully appropriate with respect to shallow water flows and free gas hazards; however, given the number of wells currently being drilled in the deepwater and the apparent ubiquity of gas hydrate, simple avoidance of any and all indications of gas hydrate, if not truly necessary, adds unnecessary costs and complications to well plans (Smith et al, 2005).…”

“…Overpressured gas sands can lead to the uncontrolled flow of gas into the well that can lead to a blow-out situation with risks to people, drilling operations, and the environment (Bryant and Roemer, 1983;Lukkien, 1985;Sills and Wheeler, 1992;BOEMRE, 2006;Flores et al, 2007;Judd and Hovland, 2007;and Kortekaas and Peuchen, 2008). The typical approach in assessing shallow gas hazards is through the identification and avoidance of "bright spot", high amplitude anomalies in seismic data consistent with zones of low acoustic velocity that indicate the presence of free gas (Luheshi et al, 1996;Orren et al, 1996;Salisbury et al, 1996;Hilterman, 2001;García-García et al, 2004;Sharp and Samuel, 2004;Orange et al, 2005). Disperse accumulations of gas bubbles at low saturation are also common (MacKay et al, 1994;Lu and McMechan, 2004) and, while not usually perceived as a threat to drilling safety, can add costs to the drilling program.…”

Quaternary lithology and shallow gas from high resolution gravity and seismic data in the central North Sea

“…Heggland (1997) identified shallow gas above the Sleipner Field and established migration paths from the gas reservoir. It is further necessary to map shallow gas to prevent serious problems while drilling exploration or development wells (Salisbury et al 1996). If shallow gas is unexpectedly encountered, the incidents may vary from delays and lost wells to catastrophic blowouts like the West Vanguard blowout in October 1985.…”