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Exploration & Production: The Oil & Gas Review - 2003, Volume 2
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With these global trends (the transition to a methane economy, an ever-increasing proportion of oil production coming from complex reservoirs, natural gas production coming from unconventional reservoirs and an ever-increasing proportion of production coming from known fields), the need for advanced reservoir characterisation to produce fossil energy resources efficiently and economically has never been greater.
The Previous Generation–1-D and 2-D
In the 1950s, ‘development geology’ was largely a onedimensional (1-D) wellbore process. Development geologists in the 1950s did not possess the glamour or prestige of exploration geologists and served largely to support the engineers and help identify ‘good sands’ from which to perforate spontaneous potential and resistivity logs. Fields were being discovered across the US, most on primary production, and well spacing was commonly uniform: 640 or 160-acre spacing for gas, and 40, 20 or 10-acre spacing for oil. The need for advanced reservoir characterisation as we know it today did not exist at that time.
Throughout the 1960s and 1970s, studies of modern depositional systems (1-3) and ancient outcrops, (4,5) led by some of the major oil company research laboratories and supported by several key universities, resulted in advanced understanding of ancient depositional systems in the subsurface. (6,7) Two-dimensional studies of oilfields consisted of linking well log cross-sections supported by qualitative core descriptions between wells and constructing isopach and structure maps to identify sand trends. (7,8) Maps were used to calculate volumetrics and to help design field management strategies. In these two decades, 2-D seismic data resolution was too poor to support development geology, and stratigraphic understanding was not sufficient to help construct adequate reservoir architecture frameworks.
The Current Generation–3-D
For those working in the industry in the 1980s, there was a growing need for secondary and tertiary recovery processes in many of the larger US fields. Development geology became known as reservoir geology, no longer simply a well-based process to identify key productive sands, but instead one of true volumetric reservoir understanding. Multi-disciplinary approaches were beginning to be discussed publicly and recognised for the value they added to the corporate bottom line. Seismic stratigraphy, introduced by several seminal papers in the American Association of Petroleum Geologists Memoir 26, (9) was becoming mainstream for exploration-scale studies but, for the most part, was not yet being applied at the field scale, and reservoir work was still carried out using paper logs, seismic sections and hand-drawn maps.
In the late 1980s and 1990s – with the explosion of computer technology, digital data, 3-D modelling software tools and the early promise of 3-D seismic technology – rock, log, seismic and production data began to be fully integrated into digital reservoir models, visualised in colour and animated in 3-D space. The term ‘flow units’ was introduced as a means to capture the understanding that reservoirs behaved as volumes. (10)
Advanced outcrop studies were being conducted to define the nuances of high-frequency sequence stratigraphy and to place reservoir parameters into a proper stratigraphic framework. (11,12) Lessons from the outcrop were being applied at the reservoir scale to open up new levels of reservoir architecture understanding' (13) and complex 3-D models were being scaled up and used in fluid flow simulation. Modern 3-D reservoir characterisation had arrived. (14-16)
Category:
Reservoir Engineering
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Dr Scott W Tinker is Director of
the Bureau of Economic Geology at
The University of Texas at Austin. He
is the State Geologist of Texas and
holds the Allday Chair in Subsurface
Geology in the university's Department
of Geological Sciences. Among the
achievements of his 19-year career
in the oil industry, he has received
best paper recognition in two major
scientific journals and has been a
distinguished lecturer for the American
Association of Petroleum Geologists
(AAPG) and the Society of Petroleum
Engineers (SPE). Dr Tinker is a
member of many professional
societies, boards and committees and
is a certified professional geologist
and certified petroleum geologist.
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