Coupled static and dynamic modeling of a Jurassic Arab Formation reservoir: Parameter sensitivities and impact on the quality of history-matched simulation outputs, Dukhan Field, State of Qatar
Authors: Fenter David , Stanley Rowan 
Published: May 2016

A close coupling of geoscience and engineering disciplines has generated a history-matched model for the Dukhan Arab C reservoir serving as a platform for testing of forward development strategies. The Arab C reservoir is a heterogeneous organization of limestone and dolomite lithologies deposited on a shallow water Jurassic ramp system. Hydraulically, the 80ft thick interval represents a network of grainstone conductors compartmentalized by muddy carbonate baffles resulting in layer-constrained dynamic behavior. The reservoir has been under development for over sixty years, with an early period of natural depletion followed by peripheral water injection utilizing hundreds of vertical and horizontal producers and injectors.

As part of an effort to update the field development plan, a new geologic model was developed that formed the basis for reservoir simulation studies and depletion planning. Initially, a series of tests were conducted to determine the sensitivity of model responses to input variables, and these tests helped to guide subsequent static model adjustments. Horizontal permeability defines aquifer response, waterflood front advance and early pressure trend, while vertical permeability significantly controls subsequent dynamic behavior. Thin mudstone baffles are common at parasequence boundaries and their continuity and association with stylolites determines inter-zonal vertical communication. Variable salinity of injected water was shown to have a large impact on water encroachment patterns and derivation of appropriate relative permeability functions improved the calibration of the full-field dynamic reservoir simulation model. Knowledge of the controlling parameters ranked according to dynamic sensitivity facilitated an emphasis on regional variations constrained by geological trends and helped to minimize the requirement for localized adjustments.

Lessons learned as a result of this geoscience-engineering feedback can expedite future model building by focusing technical expertise on the most critical parameters controlling fluid flow.

Introduction

The Qatar Petroleum-operated Dukhan Field is located onshore Qatar, approximately 80km west of Doha (Figure1). The Arab C reservoir interval is a carbonate anticlinal structure lying 5500–7000ft below the surface and is approximately 70km long by 8km wide. The Arab C interval is about 80ft thick with moderate to high reservoir quality (typically 18% porosity, 100mD permeability). A high degree of vertical heterogeneity relates to a sedimentary origin in a near-shore shallow ramp environment featuring high-order depositional cyclicity. Lateral ranges of 1–4km for baffling thin-beds supports a localized layer-constrained dynamic behavior, though communication pathways are impacted by sporadic occurrences of cross-cutting conductive and resistive faults. Arab C production development began in 1949 with a period of natural depletion followed by conversion to water drive in the 1960s via peripheral water injection utilizing hundreds of vertical and horizontal producers and injectors.