Integrated 3-D reservoir modeling based on 3-D seismic: The tertiary Malampaya and Camago buildups, offshore Palawan, Philippines

Three-dimensional (3-D) seismic interpretation and drilling results indicat e complex sedimentary geometries of the Malampaya and Camago buildups (offs hore Palawan, Philippines) with localized progradation due to unidirectiona l offbank transport alternating with vertical aggradation. Successive reduc tion of size during buildup growth and backstepping of the protected landwa rd margin in response to transgression ultimately appear to have triggered the demise of carbonate production and platform drowning. The shallow-water platform top sediments repeatedly show signs of subaerial exposure before reflooding, A modeling functionality was developed to allow development of multiple-sce nario 3-D reservoir models in an exploration or appraisal stage. The model enables merging of seismic-scale observations based on 3-D volume and horiz on analyses with subseismic scale information from well data; however, inhe rent noise within the seismic data introduced by the complex buildup morpho logy has resulted in inconsistent attribute distribution and fault dimming, These difficulties are compounded by erratic velocity distribution within the limestone, nonhyperbolic move out, and a narrow relatively low-frequenc y spectrum, all of which prevent the use of the 3-D seismic volume as hard data but rather allow its use as a soft constraint for guiding the geologic al interpretation and ultimately the modeling process. Seismic data quality in such complex morphologic settings and scarcity of well data hamper grea tly the use of geostatistically driven modeling approaches; therefore, a ne w functionality was developed within Shell's proprietary integrated 3-D mod eling suite (GEOCAP), which allows deterministic model reservoirs using sei smic horizon and volume interpretation, sequence- and cyclo-stratigraphic a rchitecture, and the concept of reservoir rock type. Seismic velocity in clean carbonate formations is predominantly a function of porosity distribution. To assess time-to-depth conversion uncertainty, t he reservoir rock type based models were first produced in the time domain. Only after differential 3-D depth conversion of these models could the sce narios be reconstructed in the depth domain. The depth models subsequently were used to derive permeability and saturation 3-D distortions, and thus h ydrocarbon volumes for each deterministic scenario. The models were then us ed for simulation purposes.