Experimental and Numerical Modeling of Double Displacement Oil Recovery Process in Tight Fractured Carbonate Reservoirs
- Ali M. Al-sumaiti (The Petroleum Institute) | Hossein Kazemi (Colorado School of Mines)
- Document ID
- Society of Petroleum Engineers
- Abu Dhabi International Petroleum Conference and Exhibition, 11-14 November , Abu Dhabi, UAE
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 3 Production and Well Operations, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.3.2 Multiphase Flow, 5.8.7 Carbonate Reservoir, 5.2.1 Phase Behavior and PVT Measurements, 5.5.8 History Matching, 5.4 Enhanced Recovery, 5.5.2 Core Analysis, 5.8.6 Naturally Fractured Reservoir, 1.2.3 Rock properties, 5.3.4 Reduction of Residual Oil Saturation, 1.6.9 Coring, Fishing, 5.4.1 Waterflooding, 5.2 Reservoir Fluid Dynamics, 4.3.4 Scale, 5.4.2 Gas Injection Methods, 5.1.1 Exploration, Development, Structural Geology
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Waterflooding has been the most popular post-primary production approach for improving oil recovery. In fractured reservoirs with large structural relief, gas injection can produce much of the post-waterflood remaining oil by gravity drainage. Oil recovery by gas-invoked gravity drainage in waterflooded reservoirs is known as the double displacement process (DDP). One major reason, among many, is that the three-phase relative permeability residual oil saturation endpoint is generally smaller than the residual oil saturation endpoint for the water-oil displacement.
Field data indicate that the DDP has been successful in single-porosity sandstone formations. Intuitively, one can expect that DDP should produce similar results in reservoirs with ample intercommoned vertical fractures, which is the objective of this work. With the aid of tests on tight reservoir cores from a major Middle East carbonate reservoir, this study focuses on evaluating the DDP in fractured carbonate reservoirs where the wettability ranges from neutral to oil-wet conditions. The scope of the study includes: (1) assessment of the DDP experimentally in fractured cores using a high-speed centrifuge, (2) simulating the experiments numerically, and (3) upscaling laboratory results to field applications.
Results from water-oil gravity drainage tests followed by gas-oil gravity drainage in fractured and unfractured cores are presented. We also show numerical simulation results of matching the experiments using both transfer function and 2-D numerical simulation, and how results from our study can be used in field applications.
Typical waterflood oil recovery from 0.1-md to 2-md fractured carbonate cores has been noted to be around 38% of the initial oil in place while incremental additional oil recovery for gas-oil gravity drainage is nearly as much as the recovery from water.
Carbonate reservoirs contribute significantly to the world's crude supply, but much of oil in these reservoirs is left behind. Thus, significant technical work is required both from geologic and engineering standpoint for improving oil recovery. Specifically carbonate reservoir pore structure and connectivity are complex and require careful analysis. In addition, the presence of fractures adds additional complexity to the reservoir prediction.
Over the last three decades, the world has been experiencing a rapid rise in demand for crude oil while the number of giant fields remains unchaged. Given this situation, it is crucial to increase the ultimate oil recovery from the giant fields. One of the most effective oil recovery methods for such fields is often the gravity drainage process using gas injection in the crest of the reservoir structure. Research and field observations have indicated that this method has been very effective to increase oil recovery in many large carbonate fields such as Yates in the U.S., Cantarell in Mexico, Fahud Field in Oman (Alkandari, 2002), and several carbonate fields in western Iran.
Waterflooding could invoke gravity drainage, but the smaller density difference between water and oil as compared with oil and gas makes water-oil gravity drainage less effective. Nonetheless, waterflooding is often the cheapest and most convenient way to improve oil recovery which explains why it is used extensively worldwide, and why it is the first step in improved oil recovery. Natural water drive also plays a similar role as waterflooding. Waterflooding and water drive in oil-wet carbonate reservoirs often leaves a large amount of oil behind. The next step in oil recovery is to instigate gas injection, a process that is related to the concept of double-displacement process (DDP) in the reservoir regions where water has already invaded. This will be potentially very appropriate in the Middle East carbonate field where the reservoir is undergoing massive waterflooding.
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