Identifying New Opportunities in a Mature Reservoir: Wara Formation, Wafra Field, Saudi Arabia/Kuwait Partitioned Zone

Abstract

The giant Wafra Field is the largest field in the Partition Zone (PZ) between Saudi Arabia and Kuwait. The Cretaceous Wara reservoir represents one of the most prolific producing zones in the PZ. The Wara is a Cretaceous sequence of channel sands (fluvial/tidal) that have locally complex vertical and a stacking patterns. These sands are interpreted to have been deposited in a tidally influenced lower delta plain depositional environment in a low angle ramp setting characterized by low accommodation space. Stratigraphic complexity is high and in general, sandstone bodies are below seismic resolution. The Wafra Wara reservoir is a structural accumulation formed by a low amplitude anticline with 4-way dip closure, with some structural complexity at the reservoir level, consisting of normal faults with small displacements. Although the Wafra Wara clastic reservoir is mature, new "sweet spots" with original formation pressure were drilled recently in the middle of the development area, and there is also still significant remaining oil on the current margins of the field where deeper OWCs have recently been encountered. Increasing water cut and an active aquifer present some challenges to maintaining good oil production in the reservoir, mitigated by production optimization efforts and a rigorous surveillance program. A comprehensive multidisciplinary study was performed to identify new infill well and workover opportunities within the most mature portion of the field to increase production and recovery. The team reviewed all existing data and performed detailed 3D-seismic interpretation to refine stratigraphy and structure, generate production attribute maps and to understand the production history and current state of the reservoir. Production, well-test data, cased-hole logs and analytical techniques were used to identify areas with by-passed oil and to predict initial rates and incremental recovery for infill wells. Deterministic and probabilistic forecasts were generated using field and offset well decline curve analysis. New opportunities were then ranked based on geological and engineering criteria. This paper highlights the challenges and lessons learned from this integrated reservoir management study to define remaining oil and to identify opportunities to increase ultimate recovery.

Petroleum Geology of Kuwait

“…In south Kuwait, based on log analysis and well correlation, Wara is divided into three stratigraphic units: Lower, Middle, and Upper (Masarik et al, 2012). The middle Wara represents the best quality reservoir unit which is comprised of interbedded fine to medium-grained sandstone, siltstone, and shale with average porosity of 26%, net permeabilities ranging from 500 to 3000 mD, and average water saturation (S w ) from 18 to 20%, while the Upper and Lower units compose of shales, coals, shaley sandstone, and glauconitic sandstones.…”

“…Fig.6.18 Depositional model for Wara reservoir in Wafra oil field, south of Kuwait (afterMasarik et al, 2012) …”