Royalty Lease Evaluation (RLE) distillation analysis was performed on six hundred (600) wells in Petrotrin's Soldado acreage. This data has been traditionally generated for use by Petrotrin's refinery to determine if the crude oil feedstock is compatible to the refinery configuration or if the crude oil could cause yield, quality and production problems. These made for refinery reports have become part of Petrotrin's legacy data. The authors decided to examine this dormant dataset to ascertain what hidden stories it may tell about the oilfields from which they came. In this investigation no data is generated, but an existing and dormant dataset will be analysed. Several components in a RLE distillation report on crude oil samples will be observed for trends, patterns and relationships. Ternary diagrams and cross-plots will be employed. Specific geochemical revelations from the RLE data will be validated by comparison to conventional gas chromatography data. This investigation will illustrate how evaporative fractionation, which is a later charge of light hydrocarbons mixing with an emplaced biodegraded oil is evidenced by a phenomenon called the" Gas Oil Anomaly", seen in the RLE data. Essentially this is the absence of any gas oil fraction combined with the presence of light hydrocarbons in the distillation data. It will also be demonstrated that presence of the later charge of light hydrocarbons has been the key factor in the prolific production from the Soldado reservoirs. Additional analysis of the light oil and gas oil fractions of a crude oil will reveal properties and characteristics that suggest there were different sources for both the originally emplaced oils and the later charge of light hydrocarbons. The data also shows that due to the evaporative fractionation phenomenon there is no correlation with API Gravity, oil viscosity, Sulphur content and depth of the reservoirs in Soldado. It will also be demonstrated that the data can be used as a qualitative tool leading to exploration plays in the Soldado acreage. Explorationists at Petrotrin will find the results of this investigation to be both useful and provocative as it directs their attention to specific Trinmar Soldado oilfields as deep exploration play areas in a manner that traditional geochemical analyses have not been able to. It also allows the practioners in the Petrotrin Soldado acreage to better understand the productivity and complex fluid distributions in the Soldado reservoirs.
Vertical Seismic Profiling (VSP) is a technique in geophysical exploration, which involves recording downgoing and upgoing wavefields propagating through the stratigraphic section. In a Zero Offset VSP the receivers are located in the wellbore, allowing the wavefront produced by the source to have a shorter path to reach them. As a primary consequence of that, there is less attenuation of of high frequencies, which means better resolution. A Time – Depth relationship and a corridor stack are generated in to correlate with surface seismic at 1D response (i.e. well seismic tie). However, a rig-source VSP survey acquired taken on deviated wells can also provide a 2D image below the wellbore trajectory. A rig-source VSP was conducted on a deviated well in a field located in the Gulf of Paria, Trinidad and Tobago. Three (3) component data was recorded and 3-C processing was used to obtain a corridor stack as well as a 2D image. This information is to assist in the reservoir delineation and characterization, as well as in the development of a velocity model for ongoing 3D seismic processing in this field. This 2D image has a frequency content of approximately about 90Hz, which showed higher frequencies in comparison to surface seismic acquired in 2005. The correlation of the image with the seismic section was excellent, illustrating deep structural features with better resolution than seen on surface seismic. In addition, Q absorption values using spectral and multi-spectral methods were calculated, resulting in values of 63.00 and 62.85 respectively. This was interpreted as medium values of absorption for these formations. The Q values are presently being used to balance amplitudes in an ongoing 3D seismic processing project. This example confirmed the importance of the VSP as an excellent tool for calibration, interpretation and processing of seismic data that will ensure more accurate planning and placement of new wells.
To date Trinidad has produced close to three billion barrels of oil from onshore and offshore fields. Formations penetrated range in age from the Lower Cretaceous to the Pleistocene. Ninety three wells have been drilled to the Cretaceous with varying degrees of success, these wells have identified whether source rock facies are present or absent across the island. Based on well and outcrop data, the Upper Cretaceous interval is shale dominated with occasional turbidite sandstone reservoirs and a siliceous mudstone locally known as "Argilline". Geochemical research by Kuarsingh (1986), Rodrigues (1987, 1988, 1993), Talukdar et al (1990), Requejo (1991), Persad et al (1993), Requejo et al (1994), Baseline/DGSI (2004) indicated that most of the hydrocarbons in Trinidad have been sourced from Type II kerogens contained in Cenomanian-Santonian and Aptian aged marine shales of the Naparima Hill and Gautier Formations respectively, Maastrichtian and Tertiary sediments are dominated by mainly woody and coaly kerogens. Total Organic Contents range from 0.1 to +\- 9%. Rodrigues (1989) mapped the distribution of geothermal gradients identifying hot and cold areas, this data has implications for petroleum systems modeling, especially for the timing and top of the oil generating window. Royalty Lease Evaluation (RLE) analysis of oils produced from Upper Cretaceous sandstone and naturally fractured intervals (Specific gravity / API, viscosity, % Sulphur, % of products by distillation) give clues to the origin and history of these oils. Integration of these results and data can result in identification of areas with potentials unconventional source rock plays.
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