Heavy Oil in Ecuador: Pungarayacu Field,New Insights and Predictions forDevelopment Strategy

摘要

Pungarayacu field is believed to has the largest heavy oil concentration in the Ecuadorian Oriente Basin.Thisstudy re-evaluates the Original Oil in Place(OOIP)and the potential reserves to be obtained by applyingSAGD and steam flooding.The static and dynamic models were constructed considering new stratigraphicand sedimentological findings.The proposed static model includes non-reservoir coaly facies obtained from density logs in order togenerate a new petrophysical interpretation.Considering that some wells were drilled 30 to 40 years agoand the density logs were either reported in counts per second or non-existent,it was necessary to create asynthetic 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 iscompartmentalized due to the presence of faults that generate several blocks with different WOCs(WaterOil Contacts).For building stratigraphic and sedimentological model,it was used stratigraphic correlationsand previous depositional environments analysis of Upper Hollin sandstone(influenced by tides)and LowerHollin sandstone(fluvial).For the petrophysical model the petrophysical properties distribution were basedon probability maps and variograms.Pungarayacu oilfield has 8°API and a viscosity from 66,000 cp to11,000,000 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 qualityof the sand; SAGD technique was applied in areas where the Hollin formation presents a low presence ofshale and sandstone continuity; this allowed to develop a steam chamber for efficient oil drainage.In areaswith shale intercalations,steam flooding was applied,because it allows lateral sweeping of the oil zoneand improve the recovery factor.The new OOIP reported is approximately 21 billion barrels,from which12.7 billion barrels can be produced by these two EOR thermal methods and the other 8.3 billion barrelsare considered to be at depths shallower than 95 meters.In addition,the simulation results show that in 15years the recovery factor will be 1.52 percent,equivalent to approximately 194 MMSTB,and in 32 yearsthe recovery factor will be 3.15 percent equivalent to approximately 400 MMSTB.