2D and 3D anisotropic depth migration case histories

Abstract

Anisotropic depth migration (ADM) has become more commonplace over the past four years. The data-processing examples detailed here illustrate the robustness of the method in a variety of structured settings in the Alberta Foothills. The public-domain structural line, the Husky/Talisman dataset, illustrates subtle improvements in imaging with a dramatic improvement in accuracy of horizon depths when ADM is applied to these data. A 3D survey in a difficult imaging area, Nordegg/Chungo, shows significant healing of broken basement reflectors when we correct for anisotropy in the complex-dipping clastic overburden. Finally, in the Blackstone area where we observe intense folding in the near surface, comparisons between poststack time migration, prestack time migration, prestack depth migration, and prestack anisotropic depth migration in the Blackstone area show the similar stepchange improvements as we imrove the technology of our algorithm.

The effects of anisotropy on Canadian foothills exploration: A case history

“…In dipping strata, the anisotropic symmetry axis is tilted causing reflection point smearing and lateral positioning errors due to sideslip effect (Vestrum, 2002). While the Thomsen parameters epsilon (ε) and delta (δ) may stay the same for the overlying geology, the dips of the strata may vary laterally which will affect the magnitude and direction of the reflector positioning and smearing (Vestrum, 2003) Thomsen's parameters of ε= .11 and δ of .03 were used for the overburden based on previous foothills studies (Vestrum, 2003).…”

Adequate velocity model as a basis for effective seismic imaging when mapping hydrocarbon traps associated with salt domes

“…çîíòîâ ìîãóò çàíèìàòü íåïðàâèëüíîå ïîëîaeåíèå ïî ãëóáèíå [Vestrum, 2002]. Îáû÷íî îíè èçîá-ðàaeàþòñÿ ãëóáaeå ñâîåãî èñòèííîãî ïîëîaeåíèÿ, ïîñêîëüêó ñêîðîñòü ñóììèðîâàíèÿ ÷àñòî ïðå-âûøàåò èñòèííóþ âåðòèêàëüíóþ ñêîðîñòü .…”

“…Âîçíèêíîâåíèå çíà÷èòåëüíûõ ëàòåðàëüíûõ è âåðòèêàëüíûõ ñìåùåíèé ñåéñìè÷åñêèõ èçîá-ðàaeåíèé îáúåêòîâ îòíîñèòåëüíî èõ èñòèííîãî ïîëîaeåíèÿ ïðè èãíîðèðîâàíèè àíèçîòðîïèè ñ íàêëîííîé îñüþ ñèììåòðèè äåìîíñòðèðóåòñÿ âî ìíîãèõ ðàáîòàõ (íàïðèìåð, [Vestrum et al, 1999;, 2002Isaac, Lines, 2002;Vestrum, Vermeulen, 2004 ìåòðû ïîëó÷åíû â ðåçóëüòàòå îáðàáîòêè ìàòå-ðèàëîâ àçèìóòàëüíîãî òðåõêîìïîíåíòíîãî ÂÑÏ â îäíîé èç ñêâàaeèí íà ïëîùàäè. Ïåðåêðûâàþ-ùèå ñîëü îñàäêè â ïðàâîé ÷àñòè ðàçðåçà õàðàê-òåðèçóþòñÿ íàêëîííîé îñüþ ñèììåòðèè àíèçî-òðîïèè (ϕ = 30°), à ñàìà ñîëü âåðòèêàëüíîé îñüþ (ϕ = 0°).…”

Reflection point sideslip and smear in imaging below dipping anisotropic media

“…The velocity model is simply a horizontal reflector at the base of a homogeneous dipping anisotropic layer, 2000 m in vertical thickness, with an axis of symmetry tilted at 15° from the vertical. The anisotropic parameters used for the overburden in these tests were chosen to be ɛ= 0.12 and δ= 0.03, which are commonly used values in thrust‐belt anisotropic depth migration (e.g., Vestrum 2002; Gittins, Vestrum and Gillcrist 2004). Figure 2 shows minimum‐traveltime raypaths for offsets ranging from 0–4000 metres for this model.…”