Integrated Reservoir Management Approach to Improve Injection Efficiency in a Low Transmissibility Sector of a Giant Carbonate Reservoir

Abstract

This paper provides a critical review of the integrated reservoir management process implemented to maximize ultimate recovery by maintaining an optimum reservoir pressure distribution in a low transmissibility sector of a giant carbonate reservoir. The peripheral water injection is the main driving mechanism in this reservoir due to the excellent areal transmissibility from the flanks towards the center of the reservoir. However, the study area is limited and characterized by a various degree of low transmissibility due to the degradation in reservoir quality and the presence of a tar mat at the flanks. The main challenge is to provide an adequate pressure support far away from the peripheral injection line and to sustain the required production capacity from the study area. Conventional peripheral water-flooding is insufficient to meet the ever increasing production capacity without an optimized injection set-up consisting of up-dip and down-dip peripheral injectors.The study demonstrates that cohesive understanding of the flow mechanism, which entails integration of various sources of information, is crucial to achieve successful pressure maintenance and voidage replacement schemes. Consequently, detailed characterization of the tar region was constructed through multiple realizations covering the entire spectrum of uncertainties and impacts on reservoir performance. The injection efficiency over various production scenarios was also carried out using finite-difference and streamline tracing to capture the interaction between producers and injectors. In addition, a coupled subsurface-surface integrated modeling was utilized to identify bottle-necks and evaluate development options.Production performance and acquired reservoir surveillance data vindicated the implemented practices. Optimum reservoir pressure distribution was observed over the entire study area. Conventional and advanced open-hole log results from strategically placed evaluation wells and time lapses of saturation logs from key monitoring wells over a 5 years period indicated favorable areal and vertical sweep efficiency.

Representative Sector Modeling and Waterflooding Performance in Rumaila Oilfield

“…Depending on the well logs response and final well report (FWR), FZI values were distributed among the reservoir major units, where the unit with good properties has taken a higher FZI value and so on. Based on these subdivisions, the permeability value was obtained using equation (2)(3)(4)(5) and FZI values were specified for each subunit. Figure-3 shows the plot of core and predicted permeability versus depth, which gives an acceptable agreement between core permeability and K-calculated from FZI approach.…”

“…These activities are utilized to develop and exploit a reservoir to realize a maximum hydrocarbon recovery with low economic cost. The beneficial outcome of reservoir simulation is to ensure the validity of the current strategy of reservoirs and promote a convenient future schema for any field [2,3]. Developing a full simulation study of large oil fields requires upscaling of the geological models that might minimize the level of detalization and inevitably.…”

Sector modeling using iterative boundary pressure estimation

“…Then we replicate the flow rates of the virtual producer to the virtual injector, also injecting oil, water, and gas. Lastly, the flow rate is adjusted by a correction factor ( Π ) to balance (5)…”

“…Each test with sectorized models ( S ) must be checked to estimate the similarity with the ref. Sectors are evaluated by combining their results to calculate the flow in 5,36,37,38,39,40,41,42,43,44,45,46,47,48] the entire reservoir. The normalized quadratic deviation with sign (NQDS) [4] is used as the main indicator to verify rates over time.…”

“…Several techniques are used to create a proper approximation of the shared boundary conditions. A widespread procedure is to select the sectors with an irrelevant or even no flux contour and implement a Dirichlet Boundary condition with fixed flux equal to 0 or another constant [1,5,14,16,20,23]. This type of solution is applied to reservoirs with low interaction among wells, when operational changes do not significantly impact the track of streamlines or when the objective is only to simulate a short period of time [2,15].…”