Abstract
Pungarayacu field is believed to has the largest heavy oil concentration in the Ecuadorian Oriente Basin. This study re-evaluates the Original Oil in Place (OOIP) and the potential reserves to be obtained by applying SAGD and steam flooding. The static and dynamic models were constructed considering new stratigraphic and sedimentological findings.
The proposed static model includes non-reservoir coaly facies obtained from density logs in order to generate a new petrophysical interpretation. Considering that some wells were drilled 30 to 40 years ago and the density logs were either reported in counts per second or non-existent, it was necessary to create a synthetic density log by Neural Network (NNT) for most of the wells in the northern part of Pungarayacu. A structural model was developed that represented the geological structure of the Hollin formation. Field is compartmentalized due to the presence of faults that generate several blocks with different WOCs (Water Oil Contacts). For building stratigraphic and sedimentological model, it was used stratigraphic correlations and previous depositional environments analysis of Upper Hollin sandstone (influenced by tides) and Lower Hollín sandstone (fluvial). For the petrophysical model the petrophysical properties distribution were based on probability maps and variograms. Pungarayacu oilfield has 8°API and a viscosity from 66,000 cp to 11,000,000 cp at 40°C showing severe oil biodegradation. Considering previous EOR screening analysis, the injection pilot of Cyclic Steam Stimulation developed by the last operator in the field and the quality of the sand; SAGD technique was applied in areas where the Hollin formation presents a low presence of shale and sandstone continuity; this allowed to develop a steam chamber for efficient oil drainage. In areas with shale intercalations, steam flooding was applied, because it allows lateral sweeping of the oil zone and improve the recovery factor. The new OOIP reported is approximately 21 billion barrels, from which 12.7 billion barrels can be produced by these two EOR thermal methods and the other 8.3 billion barrels are considered to be at depths shallower than 95 meters. In addition, the simulation results show that in 15 years the recovery factor will be 1.52 percent, equivalent to approximately 194 MMSTB, and in 32 years the recovery factor will be 3.15 percent equivalent to approximately 400 MMSTB.
