Application of 4D Seismic for Reservoir Management in Carbonates. Does it Work?
- Mohamed Saleh Efnik (Mubadala Oil & Gas) | Samsudin Haj Taib (University of Malaysia)
- Document ID
- Society of Petroleum Engineers
- SPE Enhanced Oil Recovery Conference, 19-21 July, Kuala Lumpur, Malaysia
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 5.2 Reservoir Fluid Dynamics, 5.4.2 Gas Injection Methods, 5.3.4 Integration of geomechanics in models, 4.3.4 Scale, 5.7.2 Recovery Factors, 5.4 Enhanced Recovery, 3.3 Well & Reservoir Surveillance and Monitoring, 5.1.9 Four-Dimensional and Four-Component Seismic, 5.5 Reservoir Simulation, 5.8.7 Carbonate Reservoir, 2.4.3 Sand/Solids Control, 1.2.3 Rock properties, 5.1.5 Geologic Modeling
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In the past ten years, time-lapse (4D) seismic has evolved from an academic research topic to a standard way of monitoring reservoir performance. The method is now being used as good reservoir management practice to provide evidence of saturation changes within the reservoir at field scale. 4D provides a new piece of data describing the dynamic behavior of the reservoir fluids between the wells, often limited to small scale monitoring at the borehole scale. Thus, it provides sophisticated techniques of reservoir monitoring and management relying on the integration of geological models, static and dynamic properties of the reservoir rock, and detailed production and pressure field data.
While 4D seismic data has been very successful in monitoring hydrocarbon production in clastic reservoirs, there is still no consensus on its applicability to carbonate fields. The main difficulty is the well-known fact that the acoustic velocities of carbonates are insensitive to saturation and pressure changes, relative to the clastics. Beside the geological processes such as production induced compaction which has large impact on porosity, density and permeability variation during the life of a 4D surveys, the complexity and heterogeneity of carbonate pore geometry and network further aggravate the difficulty of 4D applications. Although the geological characteristics may not change at small time scales but they are linked to fluid flow and distribution in the reservoir.
An Integrated approach of 4D seismic analysis using all historical production data along with open/cased hole logs and simulation models has demonstrated its viability to understand saturation changes in heterogeneous reservoirs. Thus using this approach as reservoir management tool to improve sweep efficiency and enhance field development plans.
The first repeated 3D seismic surveys (known as 4D seismic now) were acquired in North Texas in 1982/1983 to monitor a combustion process around an injection well. The feasibility of 4D time-lapse has evolved in recent years when studies has shown that certain rock properties such acoustic and pressure are affected by changes in production of hydrocarbons during the life of the field (Mathfoud, 2006). The use of time-lapse seismic data in conjunction with reservoir simulation models and production data allow the creation of internally consistent subsurface model. Herwanger (2009) has shown that the Acoustic Impedance (AI) and Poisson?s ratio are closely related to porosity and water saturation changes in Arne chalks. An increase in porosity causes a decrease in AI, increasing in water saturation (at constant porosity) causes strong increase in Poisson?s ratio.
An extensive seismic program has been carried out over CO2 injection area over 5 years span to monitor the CO2 storage that was injected in saline aquifer in Utsira sand in North Sea ((Arts, 2008). 4D seismic was among other geophysical techniques that were used to obtain additional information which could help the determination of reservoir quality characteristics and the prediction of fluid contacts (Dierendonck, 1997). Forward modeling of time-lapse seismic has been shown to be quite useful tool for reservoir management (Sung, 2000). In this approach the simulation model was combined with streamline method for modeling flow and ray-Born method for synthetic seismograms to compensate for the numerically expensive model due to large volumes in subsurface.
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