Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
An Integrated Fracture Characterization of a Heavy Oil Naturally Fractured Carbonate Reservoir
Baker, R.O. (Epic Consulting Services Ltd.) | Telesford, A. (Epic Consulting Services Ltd.) | Wong, S. (Epic Consulting Services Ltd.) | Li, V. (Sherritt International Corporation) | Smith, G. (Sherritt International Corporation) | Schoendorfer, H. (Sherritt International Corporation)
Abstract This paper presents an integrated approach to fracture characterization in a massive, naturally fractured carbonate, heavy oil reservoir. Such information is critical in understanding the reservoir drive mechanism and predicting recovery from this field. The characterization combines various techniques from geophysics, geology, petrophysics and engineering, including core data, Formation Micro Scanning (FMS) data, analogous field data, pressure buildup tests and inflow performance results. The description of the fracture system includes the number of fractures and their distribution, spacing, orientation, aperture and porosity. This information provides the basis for building a full field, three-dimensional reservoir model, which is then calibrated with production performance data. Introduction Developing a massive, naturally fractured carbonate, heavy oil reservoir in folded thrust belts presents extreme reservoir engineering and geological challenges and opportunities. These types of reservoirs are the extreme setting for large-scale high contrast and discontinuous reservoir properties. Horizontal wells in such a reservoir with bottom water drive allow economic development because of lower production drawdown pressures and reduced water coning. Yet, targeting optimum horizontal well location, length, spacing and recovery prediction represent a great challenge because it is sometimes unclear where flow is coming from. To accomplish optimal horizontal well placement, a fracture model needs to be developed first because the fracture spacing, geometry and permeability affect reservoir drive mechanisms as well as fracture-matrix cross flow. Fracture spacing, porosity and aperture as well as fracture distribution will be critical factors in determining the production and recovery factor for water drive in naturally fractured reservoirs. This paper ties the geological and engineering models together to determine a representative set of fracture parameters. It discusses the integrated forward (geological) and inverse (engineering) techniques used to improve the characterization of fractures. The results were used in reservoir model simulation and subsequent application in reservoir management of the Cuban Puerto Escondido heavy oil field. CUBAN PUERTO ESCONDIDO FIELD The geology of the Cuban Puerto Escondido North Coast oilfield is complex both stratigraphically and structurally (Figure 1). The hydrocarbon trap exists as a structural stack of thrust sheets in the Jurassic/Cretaceous carbonates of the Cifuentes and Ronda formations of the Veloz Group. Various porosity types are present; however, the dominant factor in oil migration and production is fracturing. The fields have multiple stacked thrust sheets. Each of these thrust sheets was faulted up and over undisturbed sections from south to north. Each subsequent thrust carries with it "piggy-back" all the preceding thrusts, creating an ever-higher stack of thrust sheets. The Cuban North Coast Veloz fields are also typically bounded on the east and west by SW to NE trending strike slip faults that probably were activated at the time of thrust faulting and occasionally continued to be active until recent time. To date, twelve wells have been drilled in this field including ten horizontal wells to produce oil from several thrust sheets. Many wells have produced the 9 - 12 °API oil at rates of 300 to 500 m/d.
- Geology > Petroleum Play Type > Unconventional Play > Heavy Oil Play (1.00)
- Geology > Geological Subdiscipline (1.00)
- Geology > Structural Geology > Tectonics > Compressional Tectonics > Fold and Thrust Belt (0.49)
- North America > United States > Texas > Permian Basin > Central Basin > Escondido Field (0.99)
- Asia > Middle East > Iran > Kohgiluyeh and Boyer-Ahmad > Zagros Basin > Gachsaran Field (0.99)
- North America > United States > Kansas > Beaver Field > Simpson Formation (0.98)
- (2 more...)
Abstract Dual-permeability models were developed to simulate the permeability of fractured reservoirs, including connected fracture networks, fracture corridors, unconnected fractures, and nonconductive fractures. The opening of nonconductive fractures was simulated based on either fracture dilation caused by shearing or fracture opening caused by tensile failure. In this way, the permeability change of all fractures (both conductive and nonconductive) can be simulated responding to the change in the effective stresses caused by reservoir depletion and/or injection. It is assumed that the conductive fractures possess a base-level permeability before production and injection, which corresponds to the residual permeability of the fractures. This implies that the apertures of fractures have closed to their irreducible limit at the reservoir depth and initial conditions, but minimum hydraulic apertures still exist. The newly developed dual-permeability modeling technique was applied to an areal model of a fractured/faulted reservoir containing 49 wells, which simulated 36 months of production with waterflooding in the presence of fracture sets and faults. This study was to understand the geomechanical influences on flow rates at individual wells, which were assessed with the spatial and temporal correlations in flow rates at pairs of wells. This example revealed the ongoing interaction between pressure, production/injection rate, permeability, and deformation in the fractured reservoir. The stress direction has an important effect on the evolution of fracture permeability. The sliding of faults induced significant permeability enhancement of the fractures around the faults. Long-range rate correlations were predominantly related to geomechanical links; short-range rate correlations were mainly related to high permeable channels.
Abstract The multimechanistic flow mechanism was proposed by Ertekin et al. in 1986. The principal hypothesis behind this mechanism was the transport of fluids under simultaneous influence of pressure and concentration gradients. In this study, we applied the multimechanistic flow concept to fractured reservoirs. We believe this application is relevant because multimechanistic flow may exist in naturally fractured gas reservoirs as well as coal seams. The development of the multimechanistic flow model, as applied to fractured reservoirs, is presented in detail in Chawathe et al. (1996), and the underlying physics of multimechanistic flow is explained in Chawathe et al. (1996). In this paper, we discuss identification of fractured systems undergoing multi-mechanistic flow. Preliminary studies indicate that multimechanistic flow results in significant increase in cumulative gas production. One of the primary observations of this study is that it is not the fracture permeability by itself, but the ratio of the fracture to matrix permeabilities that influences cumulative gas production characteristics. In conclusion, we present a multimechanistic flow map which may assist the engineer in identifying fractured systems undergoing multimechanistic flow behavior. Introduction Fluid production through naturally fractured systems has been conventionally modeled using the dual-porosity, single-permeability (DPSP) concept. This concept is based on the sugarcube approximation of a fractured reservoir (Warren and Root, 1963). However, it does not capture the physics involved in intra-matrix flow transport. This happens because the DPSP concept involves solving the transport equation in the fractures only. The matrix blocks contribute to the flow in the form of passive sources/sinks (Gilman et al., 1983). In case of the proposed multimechanistic flow, it becomes necessary to include the matrix blocks in the flow modeling because of the intrinsic gas-water interactions in the matrix associated with this type of flow behavior. Keeping this in mind, we chose to model such systems using the dual-porosity, dual-permeability (DPDP) flow concept. The DPDP formulation expresses the physical aspects of the fractured reservoir. The flow modeling, on the other hand, is generally done by substituting the momentum equation by Darcy's law to describe the superficial velocity vector in the diffusivity equation. This substitution addresses the convective (advective) aspects of the flow. This modeling practice has prevailed since most of the conventional models were designed to express liquid transport, such as oil, through porous systems. But is this adequate to express flow of gas through porous media? Probably not. We believe a better modeling approach should also involve the diffusion term especially when considering gas dynamics through tight, porous systems. The diffusion term is incorporated in the model by computing the vectorial sum of the corresponding Darcian and Fickian velocities. This sum is then substituted in the superficial velocity vector term in the diffusivity equation. The Dual-Porosity, Dual-Permeability Multimechanistic Model Although the details of the multimechanistic model development have been discussed in detail in Chawathe et al. (1996), we present some of the underlying equations here for completeness. The equations describing the flow of gas and water through the fractures as well as the matrix are derived based on the principle of mass conservation shown in Equation (1). (Mass In) - (Mass Out) = (Mass Accumulated) (1) P. 565
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- North America > United States > Texas > Permian Basin > Wolfcamp Formation (0.99)
- (21 more...)
Abstract The presence of fractures and faults play a significant role in recovery and performance of tight reservoirs exploited with hydraulically fractured wells. Faulting may result in asymmetric reservoirs, i.e. different quality reservoirs across the fault plane, due to the displacement of reservoir blocks along the fault plane. Typically, numerical well-test packages are used to match the pressure responses of such complex geology and well geometry. The limitations of such approaches in terms of ease of use and wide range of possible solutions plead for more attractive approach. Hence, here a semi-analytical approach has been followed to develop a new practically efficient flow solution for a well intersecting a finite conductivity vertical fracture in an asymmetric reservoir. The solution is characterised mainly by the bilinear flow resulting from formation and fracture linear flows. The pressure derivative curve exhibits a distinctive feature of an early fracture linear flow regime at a very early time reflecting the first fluid flow into the well from the fracture only. The shape of the derivative plot also suggests the characteristics of a bilinear flow, quarter slope, uttering the fracture characteristics, followed by a radial flow, zero slope, articulating the quality of the two reservoirs. Type curves of dimensionless time and pressure are presented along with field cases for vertical wells intersecting natural fractures or exploited by hydraulically fractures. The results of this paper enable reservoir engineers to carry out modelling of such complex reservoir/well scenarios with increasing certainty and long-term benefits and greater additional and favourable business impacts. Introduction Ramey (1976) and Raghavan (1977) have previously presented a review of the work done on flow along and toward fractures. They highlighted that intersecting fractures will strongly affect transient flow behavior of the well. Houze et al. (1984) described a well intersecting an infinite conductivity fracture in a naturally fractured reservoir simulated using a double-porosity model. Cinco-Ley and Samaniego (1978) presented a semi-analytical solution for the analysis of the transient pressure data of analysis for fractured wells in symmetric reservoirs, which is most likely to occur in the case of small fractures or strike-slip faults. Yet, in the case of reverse or normal faulting with large throw (Juxtaposing), different quality reservoirs could adjoin the fault plan. That is, faulting may result in a sudden displacement of rock along the fault plane that possibly yields, a large-scale slippage resulting in different quality fault blocks on both sides of the fault. Many production logs have shown two different fault-blocks resulting from a reverse fault that offset two zones sequence. Figure 1 illustrates a good example of faulting that juxtaposes different geology across the fault plane, whereby; two different quality zones are aligned through the fault plane. Here a semi-analytical solution for such a scenario is presented.
- North America > United States > California (0.28)
- North America > United States > Texas (0.28)
- Asia > Middle East > Saudi Arabia (0.28)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Lower Fadhili Formation (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff D Formation (0.99)
- Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff C Formation (0.99)
- (4 more...)
Abstract Unconventional gas reservoirs have become the focus of considerable attention as primary energy resource over the past decades worldwide. Numerical modelling technique plays a critical role in providing the essential tools for evaluating, optimizing and managing the development of such complex systems. In this work, we develop a generic simulation platform which allows investigators to rapidly implement and experiment with a wide array of alternate physical and constitutive models. The simulation platform is designed to incorporate the spectrum of known physics inherent in unconventional gas reservoirs, such as the non-Darcy effect covering various flow regimes, multi-phase behavior, adsorption/desorption, high-velocity turbulent flow, as well as the rock un-consolidation of natural fractures network. In addition, the platform provides maximum flexibility of representation for the complex fractured network with irregular and non-ideal fracture geometries in unconventional formations. Two types of hybrid fractures models which integrate discrete fracture models (DFMs) with continuum-type approaches were developed for describing the multi-scaled multi-continuum nature of the stimulated fractured system. The hybrid modelling techniques could be utilized for applications with different requirements for efficiency and accuracy considerations, such as long-term gas recovery evaluation, multi-well interaction, completion optimization and transient behavior characterization, etc. The simulation platform is designed and applied using a general abstraction that is built on top of the Automatically Differentiable Expression Templates Library (ADETL). In this paper, we conduct preliminary sensitivity studies to determine the key factors of reservoir and fractures that affect the production performance of unconventional gas wells. We present preliminary simulation results to demonstrate the model applications, and show the results of our model validation effort.
- Europe (1.00)
- North America > United States > Texas > Harris County > Houston (0.28)
- Well Completion > Hydraulic Fracturing (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Tight gas (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Shale gas (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)