Heavily Compartmentalized Reservoir: From Structural Synthesis to Optimum Development Plan

Abstract

Reservoir compartmentalization, either structural, stratigraphic, or combination, is one of key parameters for accurately characterizing the hydrocarbons distribution in the subsurface and it is an important component for optimizing hydrocarbon recovery. In order to accurately characterize its compartmentalization, structural synthesis has been applied for generating a representative structural configuration of the complex and highly faulted reservoirs of the studied field. This paper demonstrates detail structural synthesis of a Cretaceous Middle-Eastern carbonate reservoir. The studied field exhibits multiple fault blocks with different fluid composition and contacts variation. Log analysis and test results from a number of wells suggested oil rim with significant gas cap and water leg. Exploiting the oil and gas in highly faulted reservoir possesses a major challenge hence the optimum strategy of development plan was created. Multi-tectonics history of the Arabia in the region is demonstrated by both folding and brittle deformation represented by fault system comprising en echelon faults and joint sets. The most dominant faults are N75W and N45W trending strike slip fault systems. Kinematic analysis, outcrop analogue, and nearby field analogue revealed that the two fault systems have been developed by different tectonic events. The N75W trending faults have been developed as tensile fracture shortly prior to folding when SHmax azimuth was approximately oriented 120o azimuth. The N45W trending faults have been developed at a later stage possible as splay faults by branching from the pre-existing N75W when the SHmax trend was oriented approximately 90°. The N45W fault arrays show partitioning of displacement between the various splays, with relatively abrupt changes in the displacement at branchlines. Long ‘single faults’ are frequently shown to be segmented into en-echelon arrays. This expression defines a model of fault growth by radial propagation and linkage from a single seed fault as indicated from geometrical and kinematic evidence. Antithetic N45W fault exhibit a downward decrease in displacement towards a tip line near the N75W master fault. This suggests that the N45W faults were initially developed as Riedel shears which then propagated and linked to the pre-existing N75W system as splay faults. This has occurred by a continuous counterclockwise rotation of the causative SHmax stress from Cretaceous to present. Quantification of the orientations, segmentation, and offset magnitudes provided a foundation for defining their implications for fluid charging, fluid flow, and pressure development within the reservoir. Thus several development scenarios were constructed in order to maintain the pressure and production rate, considering various combinations of horizontal producers and injectors, number of wells, well orientation, horizontal length, and depletion schemes.