Development of an Embedded Discrete Fracture Model for Field-Scale Reservoir Simulation With Complex Corner-Point Grids

SPE Journal ◽  
2019 ◽  
Vol 24 (04) ◽  
pp. 1552-1575 ◽  
Author(s):  
Yifei Xu ◽  
Kamy Sepehrnoori
Keyword(s):  
Case Studies ◽  
Reservoir Simulation ◽  
Corner Point ◽  
Slight Modification ◽  
Fracture Model ◽  
Hydraulic Fractures ◽  
Field Scale ◽  
Discrete Fracture Model ◽  
Model Complex ◽  
Discrete Fracture

Summary Corner-point grids have the capability to model complex geological features, such as faults and irregular reservoir boundaries. As an industry standard, they are widely used to simulate different types of reservoirs, including conventional and unconventional reservoirs. It is necessary to effectively simulate natural or hydraulic fractures in such reservoirs. In this work, a discrete fracture model is developed to conveniently simulate fractures in geologically complex reservoirs represented by corner-point grids. The method is an extension of the embedded discrete fracture model (EDFM). We first present the difficulties in terms of geometrical calculations pertaining to corner-point grids, including the irregularity and degeneracy of block geometry and irregular connections between fracture segments. A general-purpose geometrical algorithm is developed to find the intersections between the matrix and fractures in corner-point grids. This algorithm properly handles the intersection between a general polyhedron and a general polygon, in which both the polyhedron and the polygon can be convex or concave. Transmissibility-factor formulations are also further developed for connections and intersections between fractures. The calculation of effective well indices in different situations is also discussed in detail. Several case studies are presented to illustrate the accuracy and applicability of the developed model in standard black-oil or compositional simulators. The accuracy of the developed model is demonstrated by comparing its simulation results with those of local-grid-refinement (LGR) models. It is also found that the accuracy of the EDFM is not sensitive to matrix gridding when the average size of gridblocks is similar. Field-scale studies using synthetic and realistic reservoir models are presented to illustrate the significance of fractures during secondary recovery. Existing simulators can directly be used in conjunction with the proposed approach with slight modification in simulation input, if the simulators have nonneighboring-connection (NNC) functionality. Through the case studies, the algorithms and methodology developed in this work are shown to be highly effective for the modeling of fractures in field-scale reservoir-simulation studies with complex corner-point grids.

Impact of Complex Fracture Networks on Rate Transient Behavior of Wells in Unconventional Reservoirs Based on Embedded Discrete Fracture Model

2021 ◽  
pp. 1-12
Author(s):  
Jiazheng Qin ◽  
Yingjie Xu ◽  
Yong Tang ◽  
Rui Liang ◽  
Qianhu Zhong ◽  
...  
Keyword(s):  
Flow Regimes ◽  
Natural Fracture ◽  
Fracture Model ◽  
Hydraulic Fractures ◽  
Natural Fractures ◽  
Fracture Networks ◽  
Discrete Fracture Model ◽  
Complex Fracture ◽  
Discrete Fracture ◽  
The Impact

Abstract It has recently been demonstrated that complex fracture networks (CFN) especially activated natural fractures (ANF) play an important role in unconventional reservoir development. However, traditional rate transient analysis (RTA) methods barely investigate the impact of CFN or ANF. Furthermore, the influence of CFN on flow regime is still ambiguous. Failure to consider these effects could lead to misdiagnosis of flow regimes and underestimation of original oil in place (OOIP). A novel numerical RTA method is therefore presented herein to improve the quality of reserves assessment. A new methodology is introduced. Propagating hydraulic fractures (HF) can generate different stress perturbations to allow natural fractures (NF) to fail, forming various ANF pattern. An embedded discrete fracture model (EDFM) of ANF is stochastically generated instead of local grid refinement (LGR) method to overcome the time-intensive computation time. These models are coupled with reservoir models using non-neighboring connections (NNCs). Results show that except for simplified models used in previous studies subjected to traditional concept of stimulated reservoir volume (SRV), in our study, the ANF region has been discussed to emphasis the impact of NF on simulation results. Henceforth, ANF could be only concentrated around the near-wellbore region, and it may also cover the whole simulation area. Obvious distinctions could be viewed for different kinds of ANF on diagnostic plots. Instead of SRV-dominated flow mentioned in previous studies, ANF-dominated flow developed in this work is shown to be more reasonable. Also, new flow regimes such as interference flow inside and outside activated natural fracture flow region (ANFR) are found. In summary, better evaluation of reservoir properties and reserves assessment such as OOIP are achieved based on our proposed model compared with conventional models. The novel RTA method considering CFN presented herein is an easy-to-apply numerical RTA technique that can be applied for reservoir and fracture characterization as well as OOIP assessment.

scholarly journals The Application of Integrated Assisted History Matching and Embedded Discrete Fracture Model Workflow for Well Spacing Optimization in Shale Gas Reservoirs with Complex Natural Fractures

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Qiwei Li ◽  
Jianfa Wu ◽  
Cheng Chang ◽  
Hongzhi Yang ◽  
Chuxi Liu ◽  
...  
Keyword(s):  
Shale Gas ◽  
Reservoir Simulation ◽  
History Matching ◽  
Fracture Model ◽  
Natural Fractures ◽  
Gas Reservoirs ◽  
Discrete Fracture Model ◽  
Shale Gas Reservoirs ◽  
Well Spacing ◽  
Discrete Fracture

An appropriate well spacing plan is critical for the economic development of shale gas reservoirs. The biggest challenge for well spacing optimization is interpreting the subsurface uncertainties associated with hydraulic and natural fractures. Another challenge is the existence of complex natural fractures. This work applied an integrated well spacing optimization workflow in shale gas reservoirs of the Sichuan Basin in China with both hydraulic and natural fractures. The workflow consists of five components: data preparation, reservoir simulation, estimated ultimate recovery (EUR) analysis, economic calculation, and well spacing optimization. Firstly, the multiple realizations of thirteen uncertain parameters of matrix and fractures, including matrix permeability and porosity, three relative permeability parameters, hydraulic fracture height, half-length, width, conductivity, water saturation, and natural fracture number, length, and conductivity, were captured by the assisted history matching (AHM). The fractures were modeled by the embedded discrete fracture model (EDFM) accurately and efficiently. Then, 84 AHM solutions combining with five well spacing scenarios from 517 ft to 1550 ft would generate 420 simulation cases. After reservoir simulation of these 420 cases, we forecasted the long-term gas production for each well spacing scenario. Gas EUR degradation and well interference would imply the critical well spacing. The net present value (NPV) for all scenarios would be calculated and trained by K -nearest neighbors (KNN) proxy to better understand the relationship between well spacing and NPV. In this study, the optimum well spacing was determined as 793 ft, corresponding with a maximum NPV of 18 million USD, with the contribution of hydraulic fractures and natural fractures.

Three-Dimensional Projection-Based Embedded Discrete-Fracture Model for Compositional Simulation of Fractured Reservoirs

SPE Journal ◽  
2020 ◽  
Vol 25 (04) ◽  
pp. 2143-2161 ◽  
Author(s):  
Olufemi Olorode ◽  
Bin Wang ◽  
Harun Ur Rashid
Keyword(s):  
Fractured Reservoirs ◽  
Unconventional Reservoirs ◽  
Fracture Model ◽  
Hydraulic Fractures ◽  
Natural Fractures ◽  
Compositional Simulation ◽  
Discrete Fracture Model ◽  
Fracture Surfaces ◽  
Discrete Fracture ◽  
Simulation Results

Summary Most unconventional oil and gas reservoirs are known to have several natural fractures in different orientations, which are consistent with the prevailing stresses when they were created. The accurate and efficient modeling of natural and hydraulic fractures presents a significant computational challenge. In this work, we show the limitations of the embedded discrete-fracture model (EDFM) and present the first 3D projection-based EDFM (pEDFM) algorithm and compositional simulation studies with realistic fracture networks in a fully 3D space. The simulation results from this work indicate that the pEDFM presented can model realistic fractured unconventional reservoirs accurately and efficiently. To validate the model, we present some simplistic fracture cases that can be meshed and modeled easily using explicit-fracture modeling in commercial-reservoir simulators. From the cases studied, we observe that using progressively finer grids near the hydraulic-fracture surfaces helps to improve model accuracy because this allows us to capture the sharp pressure drops expected near these fracture surfaces. The simulation results show that, unlike EDFM, the robust pEDFM algorithm presented here is accurate even at the low fracture-conductivity values expected in many of these ubiquitous natural fractures. In this paper, we present the first full 3D compositional modeling with pEDFM. We demonstrate that our model can accurately and efficiently model multiply fractured horizontal wells in unconventional reservoirs, which have complex networks of thousands of fractures at various orientations.

Efficient Modeling of Unconventional Well Performance with Millions of Natural and Hydraulic Fractures Using Embedded Discrete Fracture Model EDFM

2021 ◽  
Author(s):  
Wei Yu ◽  
Anuj Gupta ◽  
Ravimadhav N. Vaidya ◽  
Kamy Sepehrnoori
Keyword(s):  
Fractured Reservoirs ◽  
Horizontal Wells ◽  
Development Planning ◽  
Fracture Model ◽  
Computational Time ◽  
Hydraulic Fractures ◽  
Natural Fractures ◽  
Well Performance ◽  
Discrete Fracture Model ◽  
Discrete Fracture

Abstract The complexity of dynamic modeling for naturally fractured reservoirs has increased in recent years to incorporate more data and physics, as well as to handle advanced completion designs and development scenarios. While these complex models can provide more insight to difficult problems, they come with higher computational costs. Such a limitation prohibits an asset team from working with a large number of well/fracture scenarios that correctly represent geological uncertainty. This study presents a powerful non-intrusive Embedded Discrete Fracture Model (EDFM) method to efficiently handle millions of natural and hydraulic fractures with hundreds of horizontal wells, which has never been modeled in the literature. Specifically, we built a 3D geological model using a black oil reservoir simulator with 100 square miles in the horizontal area and 11 layers of 165 ft thickness. The total number of matrix cells without considering fractures is over 3 million. In total, 400 horizontal wells with well length of 6000 ft were modeled in two target layers. Each layer contains 200 wells. Each well has 112 hydraulic fractures with cluster spacing of 50 ft. The total number of hydraulic fractures is 44,800. In addition, we generated three cases with 10K, 100K and 1 million 3D natural fractures with dip angle from 70 to 90 degrees. For the case with 1 million natural fractures, the total number of cells is over 42 million. Well performance for the field example, with and without natural fractures, was investigated. This work adds significant value to the well and fracture spacing optimization process during field development planning. The non-intrusive EDFM method has been proven to be an efficient fracture modeling tool for simulating million-level complex hydraulic/natural fractures, which significantly improves accuracy and reduces computational time.

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