The Red Fork formation consists of incised valley fills which are formed during changes of sea level. While many of the producing wells can be correlated to stratigraphic features seen in the seismic, many of them do not, giving rise to the term “invisible” channels. The main objective of this work is to identify the different lithologies present in the valley system and model their response using a modern full waveform elastic equation algorithm. Given this response we will be able to predict whether to reprocess the data for AVO analysis, acquire higher frequency and more densely sampled P-wave data, or even to acquire SH-SH data.
Incised valley fills are distinctive features formed in a low-stand system tract. They are filled in a transgresive system tract. Most of the time they represent a reservoir characterization puzzle, since there are multiple sediments mixed in due to the changes of sea level. The seismic reservoir characterization of different lithologies is very challenging to image with seismic data. In this particular area the productive Red Fork sands cannot be seismically mapped, and are therefore called them invisible or “ghost” packages.
The main objective of this study is to create a base seismic model in which different characteristics (geophysical and geological) will be varied in order to understand the lithological variations within the valley system, to ultimately conclude what is the best approach to resolve those invisible valley fills that the conventional 3D seismic interpretation workflow cannot achieve. Since this survey contains over 600 wells, it serves as a natural laboratory to justify more expensive acquisition and processing in neighboring less-developed acreage.
The seismic surveys used in this study were acquired by Amoco during three different stages from 1993 until 1996 to be finally merged into a 136 mi2 survey, which is located in the eastern part of the Anadarko basin (Figure 1). The dominant frequency of the seismic data ranges from 50 Hz up to 80 Hz.
Seismic attribute assisted interpretation and well data were used to correlate the valley fills events. Correlation between seismic and well data has been partially achieved by using different seismic attributes, and with this we were able to recognize the study target zone.
The Red Fork zone is characterized by three coarsening upward marine parasequences (Lower, Middle, and Upper Red Fork, divided according to the oil and gas content in each one
Red Fork sands are characterized by their sorting which enhances their reservoir quality. The entire interval has some “breaks” or shale layers; all of which are produced by varying changes of sea level during the time of the Cherokee deposition (Desmoinesian) in the large Enid embayment from the Pennsylvanian age. The lower Red Fork is mainly deep-marine shale and siltstone. The middle is marine dominated and was deposited into a relatively deep basin on a steep, unstable delta-front slope and finally the upper Red Fork deposited in shallower water (in which we are going to focus to realize this study) is a deltaic sequence more fluvial dominated (Tolson, 1993).
