Amplified Geochemical Imaging
The 3 Km by 6 Km Pietu Siupariai field had until the end of 1999 produced a total of 0.2 MMBO from 3 wells. The Cambrian Daimena Formation reservoir was 70 meters thick in the field and had a porosity of 5 % to 15 % and a permeability 0.1 to 400 milliDarcy. The structure had a relief of only 30 meters above the 1,970 meter sub sea oil/water contact. Productivity of the old wells in the field varied considerably from no production in the G-14 well to 160 BOPD in the PS-1 well. The G- 12 well tested 750 BOPD on a DST but was not completed due to mechanical problems.
Although the G-18 and G-7 wells both produced 120 BOPD, the latter well only penetrated the uppermost 15 meters of the reservoir.
The survey was performed with the objective to identify reservoir sweet spots within the closing contour. Towards that end 99 field modules were placed in a 250 meter by 500 meter grid within a 20 Km2 area over the field. The passive surface modules were exposed for 17 days. For calibration purposes 30 calibration or model modules were installed at a producing well, a dry well and a well with shows.
Probability maps displaying similarity to the modeled geochemical fingerprints were statistically generated by correlating the field module fingerprints and the well model fingerprints. Since the survey microseepage mechanism was driven by a combination of reservoir pressure, porosity, and net pay thickness, the project results demonstrated a definite correlation between the geochemical probability maps and test/ production data.
The data also showed that production varied considerably between wells within the closing contour, namely in the range from 0 to 160 BOPD in past wells, potentially indicating nonhomogeneous reservoir characteristics. Total production was approximately 403 BOPD.
After the geochemical survey three wells were drilled on positive geochemical anomalies. Production from these three wells totaled 6,130 BOPD resulting in a production increase of approximately 15 times. The survey demonstrated that it was possible to use surface geochemical hydrocarbon mapping to determine reservoir sweet spots and predict subsurface reservoir quality variations within a producing oil field.
AAPG Search and Discovery Article #90185 © AAPG Geoscience Technology Workshop, Revisiting Reservoir Quality Issues in Unconventional and Conventional Resources, Austin, Texas, November 12-13, 2013