Porosity and lithology prediction at Caballos Formation in the Puerto Colón Oil Field in Putumayo (Colombia)

Abstract

At a given pressure and temperature, differences in the velocities of propagation of P-and S-waves in rocks can indicate differences in various properties of the rocks, including porosity, lithological composition, and the fluids occupying the pore space. In the absence of direct S-wave observations, we study the response of interfaces between rock units to wavefronts with different angles of incidence to infer changes in S-wave velocities. We have used modern techniques of seismic inversion that involve P-and Simpedance estimation from various angle stacks to estimate the rock properties.This study presents the results of a seismic inversion analysis and interpretation of the Acae-3D seismic volume. The main target is the higher-quality areas of Caballos Formation at Puerto Colón oil field in the foreland of Columbia's Putumayo Basin ( Figure 1). The oil field is a faulted anticline or monocline with regional dip (Figure 2). The study was based on 3D angle-dependent seismic data and well-log information, which were used to obtain Pimpedance (PI) and S-impedance (SI) response. The log data available was of mixed quality due to poor borehole conditions. As a result, this study used existing rock physics models and extreme well-log editing to create suites of highly corrected logs, including modeled V S logs, for inversion and interpretation.Caballos Formation (Aptian-Albian) is mostly a sequence of sandstones, interbedded with dark gray shales with thin coal laminations. The mean thickness is 250 ft and average porosity in the sands is 12%. This sequence represents the initiation of the Cretaceous sedimentation in a transgressive deltaic environment over Jurassic volcano-sediments. Figure 3 shows more details of the stratigraphic sequence.Puerto Colón, discovered by Texaco in the late 1960s, is at a depth of 10 500 ft. The field has produced 31 million barrels of 30.5°API oil. A large difference between the reservoir pressure (4300 psi, almost constant since the discovery due to a strong water drive) and the bubble pressure of the oil (1600 psi) implies that a free gas phase is unlikely to ever be present in the field. This fact and the low GOR of 458 SCF/STB makes oil and water indistinguishable using seismic observations, thus limiting the study to the characterization of the solid fraction of the rocks (porosity and lithology).Seismic and well data. The Acae 3D seismic volume was recorded by Ecopetrol in 2000 in an effort to identify additional high-quality areas. The seismic data are 36 fold within 20 ǂ 40 m bins, with good offset distribution and narrow azimuthal range. Data from preprocessed CDP gathers in an area covering 31 km 2 (Figure 4) were separated into four overlapping angle-dependent gathers, (0-20°; 10-25°; 20-35°; and 25-40°). These gathers were independently stacked, migrated, and aligned, to produce four angle-stack seismic volumes (ASVs). The different ASVs show similar phase and frequency content, but the amplitude differences with offset can be seen in the angle-dependent gathers and in the...

Lithology and fluid seismic determination for the Acae area, Puerto Colón oil field, Colombia

“…The reservoir at the Caballos Fm is sub saturated with permanent water drive; initial reservoir pressure was 4750 psi @ -9625' and currently is 4350 psi; bubble pressure is 1600 psi. Due to the difference between the bubble pressure and the reservoir pressure, the GOR and volumetric factor have not changed after 30 years of production, and no free gas cap has been developed (Acevedo, 2002). Properties of the reservoir water are: specific gravity of 1,02, salinity between 10,000-20,000 ppm, and resistivity of 0,25 ohm-m.…”

Generating Pseudo-Synthetic Seismogram with Resistivity Logs Considering the Effect of Gas: Application to Bizzy Field, Onshore, Niger-Delta, Nigeria

“…Many researchers including Acvedo and Pennington [4], Faust [5] and Quadir et al [6] carried out transformation of different log types to pseudo-sonic logs. At first, their work was informed by the observed similarity in signature of the logs with sonic log.…”