3-D seismic imaging and seismic attribute analysis of genetic sequences deposited in low‐accommodation conditions

Abstract

A multidisciplinary team, composed of stratigraphers, petrophysicists, reservoir engineers, and geophysicists, studied a portion of Boonsville gas field in the Fort Worth Basin of North‐Central Texas to determine how modern geophysical, geological, and engineering techniques could be combined to understand the mechanisms by which fluvio‐deltaic depositional processes create reservoir compartmentalization in a low‐ to moderate‐accommodation basin. An extensive database involving well logs, cores, production, and pressure data from 200‐plus wells, [Formula: see text] [Formula: see text] of 3-D seismic data, vertical seismic profiles (VSPs), and checkshots was assembled to support this investigation. The reservoir system we studied was the Bend Conglomerate, a productive series of gas reservoirs composed of Middle Pennsylvanian fluvio‐deltaic clastics 900 to 1300 ft (275 to 400 m) thick in our project area. We were particularly interested in this reservoir system because evidence suggested that many of the sequences in this stratigraphic interval were deposited in low‐accommodation conditions (that is, in an environment where there was limited vertical space available for sediment accumulation), and our objective was to investigate how fluvio‐deltaic reservoirs were compartmentalized by low‐accommodation depositional processes. Using an extensive well log database (200 plus wells) and a core‐calibrated calculation of rock facies derived from these logs, we divided the Bend Conglomerate interval into ten genetic sequences, with each sequence being approximately 100 ft (30 m) thick. We then used local VSP and checkshot control to transform log‐measured depths of each sequence boundary to seismic two‐way time coordinates and identified narrow seismic data windows encompassing each sequence across the [Formula: see text] [Formula: see text] 3-D seismic grid. A series of seismic attributes was calculated in these carefully defined data windows to determine which attributes were reliable indicators of the presence of productive reservoir facies and which attributes could, therefore, reveal distinct reservoir compartments and potentially show where infield wells should be drilled to reach previously uncontacted gas reservoirs. Our best success was the seismic attribute correlations we found in the Upper and Lower Caddo sequences, at the top of the Bend Conglomerate. These sequences were deposited in a low‐accommodation setting, relative to other Boonsville sequences, and we found that reflection amplitude and instantaneous frequency, respectively, were reliable indicators of the areal distribution of reservoir facies in these low‐accommodation sequences.

A Review of Coalesced, Collapsed-Paleocave Systems and Associated Suprastratal Deformation

“…The overlying strata were generally lithified, but the sag also affected concurrent sedimentation patterns (Hardage et al, 1996b). The deformation in the deformed suprastratal zone consists of normal, reverse, and cylindrical faults and fractures (Loucks, 1999;McDonnell et al, in press).…”

Sequence stratigraphy, sedimentary systems and petroleum plays in a low-accommodation basin: Middle to upper members of the Lower Jurassic Sangonghe Formation, Central Junggar Basin, Northwestern China

“…It is also unclear how tectonic movement and paleoclimate affected the architecture of sequences in the Central subbasin. Lowaccommodation settings are attractive targets for hydrocarbon exploration, but in such settings, reservoir development is notoriously unpredictable and reservoirs are internally complex and commonly strongly compartmentalized (Hardage et al, 1996). A better understanding of how strata formed in low-accommodation conditions could have considerable potential for predicting the presence of hydrocarbons (Allen and Fielding, 2007).…”

Calibration of Seismic Attributes for Reservoir Characterization

“…Chen et al (1997) suggested that more than 200 seismic attributes (not all of them are independent) would be useful in constructing reservoir depositional model. Other researchers (Horkowitz, et al, 1996;Hardage et al, 1996b;Cooke, et al, 1999) claimed that instantaneous frequency and/or instantaneous phase are effective at highlighting facies changes. Similarity analysis based on multiple point-based attributes, their means and deviations was used to map seismic facies (Michelena, et al, 1998).…”

“…However, these studies were mainly focused on the entire Fort Worth Basin. Hardage et al (1996b;1996c) and Carr et al (1997) analyzed the reservoir distribution and depositional subfacies using a few typical wells from this study area, but their model is not sufficiently detailed to be useful for facies analysis of this thin Caddo sequence. In addition, the tight non-reservoirs were generally not studied even though both the limestones and reservoir sandstones exist and appear seismically similar in the Boonsville Field.…”

“…The main delta system was recognized in the east and the possible second delta system was observed at the northwestern corner, but appears to be mostly outside of the study area ( Figure 35). Coleman et al, 1982;Thompson, 1982;Emery et al, 1996;Hardage et al, 1996b,;and Carr et al, 1997) The main delta system was divided into three delta subfacies: distal channel in the east margin, proximal delta front in the east, distal delta extending to south and northeast, and interdelta in the south and southeast. As depicted in a cross-section through the main delta system (Figure 36), the depositional subfacies and reservoir distribution in the eastern oil producing region are characterized by the distal channel and the proximal delta front are the depositional subfacies in which the thickest sandstone reservoir (up to 52 ft) was deposited; the distribution of limestones is limited, but the limestones can be correlated as the GR log trend is similar and correlative; the sandstone reservoirs are widely distributed in the delta front subfacies.…”