Technique of Reservoir Modeling in a Heterogeneous Carbonate Reservoir: Mauddud Formation in Raudhatain
Field, North Kuwait
Al-Ajmi, Hussain Zayed,
Saikh Abdul Azim, Shehab A.M. Abdullah, Abdul Aziz
Al-Duwaihi, Kuwait Oil Company, Ahmadi, Kuwait
The Mauddud Formation is a giant hydrocarbon reservoir in North Kuwait over two domal
faulted anticlines. Reservoir description and distribution of rock properties
are challenging due to inherent reservoir heterogeneity resulting from diagenetic imprints on original depositional fabric. A
robust depositional model driven by sequence stratigraphy,
petrophysics tuned to dynamic data and innovative
static modeling techniques were used to characterize this complex reservoir.
In an overall low angle ramp setting, the carbonates were deposited in a transgressive systems tract followed by a highstand systems tract. Primary rock fabric controls the
best flow characteristics in high-energy inner ramp grainstone.
Reservoir quality deteriorates in mid ramp to inner ramp wackestones
and mudstones due to diagenetic carbonate
concretions. Main thief zones in the reservoir are in floatstones,
radially fractured concretions and small-scale
fractures in low-porosity brittle rocks. A deterministic permeability model
was developed integrating core data with openhole
logs, production logs, and pressure transient analysis. Logs have been
reprocessed to identify zones of secondary porosity and fracture–prone zones.
Separate Porosity-Permeability transforms for matrix properties and
fracture-prone intervals results in log-derived permeability profiles that
match production log profiles and well test Kh
estimates. A finescale Geological model using major
flooding surfaces captures the primary depositional units. The lithofacies associations have been modeled as composite
objects restricted to facies belts. As porosity was
observed to be decreasing towards the flank, trend modeling was used to model
the effective porosity. The small-scale heterogeneity caused by vuggy zones and fractures were captured in thin layers. Vugs and fractures have been modeled as objects restricted
within an area demarcated by poorer seismic coherence. The Matrix permeability
was enhanced by vuggy permeability and fracture
permeability. The paper describes the challenges in reservoir description and
static modeling of this complex reservoir in detail.