Resource Volume Estimation; Dynamically Guided Volumetric Evaluation Using Streamlines

Abstract

Resource estimation is a basic statutory requirement and expectation in reservoir management. Proper resource estimation allows for robust field development planning in addition to the fact that the field resources should be correctly captured at all times in the books for audit purposes. The methods for resource estimation include the following: Volumetrics, Simulation, Material Balance modelling and Decline Curve Analysis. The method applied usually depends on several factors including the reservoir complexity and production history (brown or green reservoir). The DAZ field under review has structurally complex reservoirs with closely spaced producing wells and advanced production history. Several projects with different levels of maturation are planned for this field. These projects include work overs, implementation of field-wide gaslift and recompletions. For the completions with matured performance data, the use of Decline Curve Analysis and Material Balance fractional flow techniques for resource estimation were adequate. However, volumetrics and simulation model are the preferred techniques for the new completions and conduits with immature production performance history. The low case simulation model methodology proved inadequate as it was difficult to obtain a good well-level history match of the production data due to the structural complexity of the reservoirs, whilst still fulfilling the requirements of hydrocarbon limits both vertically and laterally. The conventional volumetrics method also was inadequate due to the proximal well spacing, dense faulting and the resultant complex flow patterns. The implication of this is that the drainage pattern becomes difficult to delineate and a conserved drainage area is purely theoretical. A hybrid method which integrates the results from a well history-matched base case simulation model with the ideals of a volumetrics evaluation (drainage area and RF from analogue reservoirs) for low case resource determination is hereby presented. Essentially, the streamlines which is indicative of flow path at the end of history match from the simulation model provides guidance on the drainage pattern and area. This guide is thereafter applied in a volumetric sense to estimate the resource that can be produced by the conduit. This alternate method incorporates all the static properties and elements of the dynamic simulation model in a qualitative sense, via the use of streamlines to guide the drainage pattern and area. It also provides for consistency in the estimation of low case and base case volumes. The result of this hybrid evaluation method realistically estimate both the in-place and recoverable volume. This volume estimation met statutory requirement of realistically reporting recoverable volume. The estimated volume was also used for reservoir management purposes.