Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Static and Dynamic Heterogeneity Modeling of a Deepwater Clastic Reservoir
(1) Chevron Africa and Latin America Exploration and Production Company, Houston, TX.
Lucapa field is located in the Block 14 Concession of Angola; composed of multiple Miocene (biozone CN4) sandstone oil reservoirs of deepwater turbidite channel deposition. Core and petrophysical study illustrates channel complexes with highly heterogeneous reservoir quality, including high permeability (up to 7 Darcy) pebbly sandstone at channel bases and sand injectites. Field analogue studies demonstrate rapid production decline and early water breakthrough due to high reservoir heterogeneity. Early screening of static reservoir models was used to capture the uncertainty range of production forecast compared to producing analogue fields. Previous simplified Sequential-Gaussian-Simulation (SGS) models consistently underestimate reservoir heterogeneity and do not accurately predict reservoir dynamic performance of producing analogues. An integrated workflow is used to model and quantify static and dynamic heterogeneity for quality assurance purposes of the simulation model. This feedback is used to perform modifications to the static reservoir model, allowing for more reasonable dynamic uncertainty ranges which honor analogue production data.
A multipoint statistical method is used to capture petrophysical variation within and between three depositional facies which represent channel axis, channel margin, and overbank deposition. High permeability thief zones identified from core and well log are stochastically modelled and placed within this framework. Probabilistic models are built to integrate 3D seismic attributes, geologically interpreted depositional-maps, and rock properties from wireline logs and core. As a quick proxy of sweep efficiency, Dynamic Lorenz coefficient (DLc) is computed using ideal single-phase, steady-state streamline simulation. The DLc calculation takes less than one hour for a 16 million fine scale model and provides quick feedback to static modelers. DLc is used to 1) screen and rank fine static models; 2) benchmark with analogue fields and 3) identify thief zone flow regions. In this study, reservoir permeability continuity, stratigraphic barriers/baffles, and fault transmissibility were modified to capture dynamic uncertainty. Final reservoir models honor analogue production decline rate and water breakthrough time.