Seismic expression of the Upper Morrow sands, western Anadarko basin, USA

Abstract

In the western Anadarko basin (Fig. 1), the lower Pennsylvanian Upper Morrow sands are both a prolific, and an elusive exploration target. Initial production from some of these sands can reach over 1000 BOPD and yet an offset well just 1000 feet away from a prolific producer can miss the sand entirely. This presentation explores the use of high resolution seismic data along with advanced geophysical modelling, seismic inversion processing, and seismic facies mapping, in detecting the sands before the drill bit. Two Upper Morrow fields in the Texas Panhandle have been studied: the Lear and Darden Fields. The Morrow sands reach an isopach thickness of ten to fifteen metres at a depth below surface of 2500 to 3000 metres. The sands are within the 'thin bed' regime. They are also below the 'tuning point where there is a linear relationship between the amplitude of the seismic reflection and the thickness of the sands. The sands have an interval velocity around 1000 metres per second faster than the encasing shales and are detectable on good signal to noise ratio seismic data. The comparison of geologic isopach mapping and geophysical seismic facies mapping shows a good correlation in the delineation of the Upper Morrow sands. The use of these seismic stratigraphy methods should substantially increase exploration and development success when high resolution seismic data and advanced interpretation techniques are employed.