| Popis: |
Abstract Gas-bearing reservoirs southeast of Trinidad are often difficult torepresent geometrically in spite of excellent quality 3-D seismic dataavailable in the area. Developmental challenges of this field include:multiple pay sands (about 20);fault-induced compartmentalization;broad low-relief hydrocarbon accumulations; andcomplex velocityvariations. Variations in facies and burial rates in addition to shallow and localized gas-bearing sands give rise to a complex subsurface velocity field. The localized gas-bearing sands manifest seismically as pronounced "gas sags". Accurate depth representation of proven and non-proven resources wasaccomplished using a minimum number of seismic surfaces (the five besthorizons), all mappable faults, a robust velocity model (for depth conversion), and well data to build a depth model of all of the sands and shales in thesubsurface. Below the shallow gas-bearing sands, initial efforts were notadequate to completely remove the gas sags, which impact over 25% of the studyarea. To accomplish final depth reconstruction, a number of seismic traverseswere interpreted through wells which pass through the shallow gas-bearingsands. These lines were depth converted and used to remove the gas sag wherethe velocity model was inadequate due to incorrect imaging of the seismic data. This was an iterative process which made use of geospatial data (isopachs, welldata, fault displacements, etc.) and was tested against all geophysical data(seismic interpretation, amplitudes, and velocity data). The result was a modelwhich not only added 0.5 TCF of proven resources, but also explained thetrapping mechanism responsible for gas accumulations in multiple reservoircompartments. Geologic Setting The Parang field, part of exploration and production license 120, lies 50miles southeast of the coast of Trinidad (Fig. 1). The field is located in the Columbus basin, which formed between the Caribbean and South American plates. The Miocene to Pleistocene reservoir sands and intercalated shales weredeposited in a variety of depositional environments along the ancestral Orinocodelta. Sedimentary rocks deposited on basin floor to slope fans comprise thelower part of the stratigraphic section. The sands and shales in the middle andupper part of the section were deposited in a paralic setting ranging fromprograding shore facies to a fluvial and transitional barrier complex. Thesource rock is assumed to be early Miocene and/or late Cretaceous in age. |
