Full waveform inversion (FWI) is a waveform matching procedure which can potentially provide subsurface models with a wavelength-scale resolution. However, sophisticated regularization techniques are required to decrease the sensitivity of FWI to the initial model and noise and reduce the ill-posedness of the problem resulting from uneven illumination. The subsurface may be considered as a combination of a blocky part and a smoothly-varying part. Due to the difference in statistical properties of each part, different techniques are needed to regularize them. To tackle this issue, we propose a new hybrid regularization method, which combines Tikhonov and total-variation (TV) regularizers. The Tikhonov regularization is used to stabilize the reconstruction of the smoothly-varying background part of the subsurface, while the TV regularization is used for recovering the large contrasts associated with salt bodies for example. The new Tikhonov-TV (TT) regularization is implemented in frequency-domain FWI based on wavefield reconstruction, an efficient penalty method to extend the parameter-search space, using an iterative refinement strategy and the split Bregman technique. The relevance of the TT-regularized FWI is illustrated with two synthetic examples, a toy example and a target of the large-contrast 2004 BP salt model. The results show that the TT method outperforms the TV method in recovering both the smooth and blocky parts of the subsurface.
Presentation Date: Thursday, October 18, 2018
Start Time: 8:30:00 AM
Location: 207C (Anaheim Convention Center)
Presentation Type: Oral
Fractures are crucial to characterize fluid flow and solute transport in the geological environments, and estimate the hydraulic properties of fractured-rock formations. Seismic radial anisotropy can be used as a strong attribute for forecasting fractures. The seismic radial anisotropy refers to the differences in the estimated S-wave velocities obtained from the Rayleigh and Love waves. We obtain the seismic radial anisotropy models of the subsurface for a fractured bedrock acquirer using the Multichannel Analysis of the Surface Waves (MASW) method. We show that the seismic radial anisotropy strongly correlates with subsurface fractures.
Presentation Date: Tuesday, October 16, 2018
Start Time: 1:50:00 PM
Location: Poster Station 18
Presentation Type: Poster
Injection and production historical data are easily accessible and using them does not incur the costs of running field tests. The capacitance model (CM), an analytical model based on injection and production data, has recently been applied successfully in several field cases. The CM has two outcomes, rate prediction and well to well connectivity evaluation and primarily derived for waterflood period. This paper modified this model for primary production period.
The CM has been developed from linear productivity model and material balance equation and predicts the total production rate of each producer as a function of the injection rates of all injectors in the system and the bottomhole pressures (BHPs) of all producers. In this paper the CM is modified based on two methods, Pseudo Injectors and BHP methods. Pseudo Injectors method is used for well to well connectivity assessment and BHP method is used for production prediction.
The modified CM was applied for several synthetic field examples and one Iranian oil reservoir. The results of synthetic fields showed that the modified CM can assess the interwell connectivity, reservoir heterogeneity, strength of aquifer, and wellbore productivity in primary production period. In addition, the modified CM can predict production rate and determine suitable areas of future IOR application. The results of modified CM on Iranian field assessed the effect of aquifer in the area and evaluated the degree of heterogeneity of the sands around the producers.
Unlike simulation-based methods, the CM does not require geological and geophysical data to generate the initial model. Developed modified CM can be applied before IOR implementation to assess reservoir continuity and manage future IOR strategies such as well pattern and amount of injected fluid.
One of the necessities in drilling operations is the ability to predict the performance of rock drills. To explain the effects of various parameters on the drilling rate (drilling velocity) and the drilling tool wear, the term drillability is being used. In this research, drillability is defined as a penetration rate. The correlation between drilling rate index (DRI) and some rock properties is inspected in this survey in order to examine the influences of properties of strength indexes and brittleness of rocks on drillability. To achieve this, uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) values of different rock samples were used as geomechanical properties data. Then, the brittleness of rocks which use the uniaxial compressive strength and tensile strength of rocks were determined from calculations. Afterwards, artificial neural networks (ANN) as an artificial intelligence technique was employed in order to relate datasets of UCS, BTS and brittleness as input data to the DRI as the target. The suggested correlation between DRI and both mechanical rock properties and brittleness concepts were analyzed, and acceptable correlations between drillability of rocks and the input parameters was achieved. It is concluded that by the use of data of uniaxial compressive strength, Brazilian tensile strength and rock brittleness, ANNs can evaluate drilling rate index accurately.
Nowadays, Tunnel excavation utilizing mechanical excavation techniques such as tunnel boring machines (TBM’s) and roadheaders is growingly becoming common. Choosing the machinery and hardware must be under consideration of physical, mechanical and petrographic properties of rock, otherwise it can result in considerable detriments. Hence, earlier than tunnelling operations, it is vital to investigate rock properties (Yarali and Soyer, 2011).
Undoubtedly, Roadheaders are one of the most versatile excavation machine types operated in soft and medium strength rock formations’ tunneling and mining. An essential aspect of a successful roadheader application is definitely the performance prediction which is basically concerned with machine selection, production rate and also bit consumption. Evolving a new roadheaders’ performance prediction model in various operational conditions and also different material is the primary intention of this research. Investigation on previous works revealed that three main features have great influences on the bit wear of a roadheader. Brittleness which can be utilized as a cuttability factor in mechanical excavation perspective is actually one of some parameters which is absolutely in relation with breakage properties. In addition to the rock brittleness, rock quality designation (RQD) and instantaneous cutting rate are employed as input parameters for the prediction of pick (bit) consumption rate (PCR). For the purpose of this paper, using previously published field datasets, a new prediction model using the application of artificial neural networks as an artificial intelligence technique is developed, trained and tested to estimate PCR based on data of brittleness, RQD and instantaneous cutter rate. Results demonstrated that PCR is highly correlated to the input parameters, and the ANN model could produce acceptable predictions.
In recent years, mining business has been under the influences of global trends, environmental limitations, and variant market requirements to be more and more productive and profitable. Utilizing mechanical miners like roadheaders, continuous miners, impact hammers and tunnel boring machines for ore extraction and excavation of development drivages, increases profitability. The mentioned miners result in continuous operations and consequently, the mechanization of mines with mechanical miners is presumed to make mining projects more productive, more competitive, and less costly. As a result, ordinary drill and blast technique could be avoided. Roadheaders which are applicable in tunnelling, mine development, and mine production of rock types of soft to medium strength, are very adaptable excavation facilities. The efficiency of roadheader application is rudimentary related to machine selection, production rate and bit consumption (Ebrahimabadi et al., 2011).
Summery In the multichannel analysis of surface wave (MASW) method, the conventional procedure obtains an S-wave velocity model based on the inversion of the phase velocity. However, the group velocity inversion has some advantages over the phase velocity; in particular, the group velocity does not require an estimation of the initial phase, nor to have a dense array of geophones. However, the estimation of the group velocity is not very straightforward due to the uncertainties associated with the transformation by which the group velocity is calculated. In this study, we introduce a new approach for the estimation the group velocity of the surface waves using the sparse S transform and sparse slant stacking. Compare to the conventional methods for the estimation of the group velocity using the generalized S transform, our approach does not require any adjustment to the Gaussian window in the transformation while yields a more accurate estimation of the group velocity.
Behzad Hosseinzadeh, University of Tehran; Mohammad Bazargan, Sharif University of Technology; Behzad Rostami, University of Tehran; and Shahab Ayatollahi, Sharif University of Technology Summary Diversion in heterogeneous carbonate reservoirs plays the most important role to the success of acidizing. Without the use of diversion, more acid preferentially flows into the high-permeability region and leaves the low-permeability region underreacted. But a clear understanding of diverting agents, such as polymer-based in-situ-gelled acids, can help uniformly stimulate the near-wellbore region. In this paper, we correct the rheological model that was developed by Ratnakar et al. (2013) according to experimental data from Gomaa and Nasr-El-Din (2010b) by considering shear-rate effect in a two-scale continuum model. It is found that the rheology parameters and shear rate are influential parameters in diversion. In addition, the amount of acid required for the breakthrough is found to be strongly dependent on rheology parameters and permeability in single-coreflood simulation. In our study, the viscosity of the spent acid is found to be the key parameter for diversion efficiency. We have constructed a mechanistic model similar to that in Panga et al. (2005) that simulates the acid injection in two dimensions. Then, we extended our simulation to dual-core systems with different permeability contrasts. The results show that there exists an intermediate injection rate that develops a wormhole in low-permeability core. The results suggest that the dissolution pattern in the high-permeability core is dependent on the permeability contrast. It changes from wormhole to uniform shape when the permeability contrast increases. Introduction Carbonate-matrix acidizing is widely used in oil fields to increase well productivity.
ABSTRACT: Geomechanical modeling of a reservoir has a very important role in all parts of a field lifecycle. In this paper, we demonstrate a new method for modeling the distribution of elastic properties in the whole reservoir using the concept of geomechanical units (GMUs). In this study, a GMU is a cluster of Young’s, Bulk and shear modulus, Poisson’s Ratio and unconfined uniaxial strength. To establish these GMUs we used eight wells and the Post-stack seismic data in the field of interest. Dynamic elastic parameters were computed from logging data of mentioned wells. To convert these dynamic parameters to static values, empirical equations were determined in a neighboring field of Salman, in the interval of Kangan and Dalan formations. In the next step, Multi-resolution graph-based clustering was applied to these static elastic parameters to construct five distinct GMUs. For three-dimensional modeling of GMUs, the 3D acoustic impedance model of the field was made by genetic inversion and used as a secondary parameter of Co-kriging. The amounts of elastic parameters of each GMU at the location of well number six in the final 3D model are found to be in good agreement with the known values of this well.
Geomechanics is a petroleum engineering sub-discipline developed to address the mechanical behavior of the reservoir and bounding rocks during exploration and production activities (Zoback, 2010; Aadnoy and Looyeh, 2011). In this regard, Three-dimensional modeling of geomechanical parameters plays a significant role in whole life of a reservoir. These models are used for seismic modeling, interpretation, hydraulic fracture design, assessing borehole stability and stress calculations in geological studies. Therefore, any improvement in one of these momentous applications could lead to better and more sufficient field development plans, at the same time save the considerable amount of money and operation time.
This study employs an efficient approach to construct a 3D reservoir geomechanical model based on the concept of Geomechanical Units (GMUs). A GMU is a single unit for design and modeling purposes. A GMU can be selected from logs, cores, or judgment (Dusseault, 2011). The advantages of GMU use in engineering studies have been discussed by a number of authors including Uwiera et al. (2011) and Nygaard (2010). In this work, a GMU is a set of rock mechanical properties, such as: Young’s modulus, bulk modulus, shear modulus, Poisson’s ratio, and uniaxial compressive strength. These elastic parameters are clustered by using different clustering methods to establish the best GMU. The purpose of using this method is to determine the distribution of elastic parameters in whole parts of the field of study. The Kangan and Dalan formations are the reservoir layers in the field of study. These formations are consisted of carbonate and dolomite (Figure 1).
ABSTRACT: This paper describes an evaluation of the optimum number of reinforced concrete segments per ring that can best fulfil the tunnel lining function to support the design loads. Hence, the effects of number of segments in the ring were investigated among which the worst case has been selected for further investigation. Subsequently, the influence of Key-segment location has been considered in-depth. To construct the required models, the beam-spring concept has been employed. The required input data was obtained from Line-4, Tehran subway tunnels. Abaqus, a finite element program, was used to analyze the problem. This program has the capability of analyzing tunnel structures by considering the effect of two-dimensional rotational behavior of intersegmental joint condition. The results demonstrate that as the number of segments per ring increases, the corresponding maximum bending moment within the lining system decreases. Consequently, the related displacement due to the lining flexibility increases. Finally, it has been concluded that due to increase of the number of segments per ring, the importance of position dependency of the Key-segment within the lining system is significantly reduced.
Shield tunneling has become a widely-used method, in particular, for urban and suburban tunnel construction due to its superior performance compared to conventional methods. The method attributes negligible effect on surrounding environment, fast and safe construction, and outstanding performance in earthquake resistance. (Nadimi et al. 2010 and 2011, Zhang et al. 2004). The arrangement and number of segments in Shield tunneling may differ based on the existing situation; however, the entire assembling process is generally the same (Chen and Mo 2006). The design of the precast segmental lining is based upon the proposed tunnel alignment and the expected geological and hydrogeological conditions at the tunnel level. The existence of joints in a tunnel ring will influence the behavior of the support system and the induced stress pattern in the linin. Actually, inter-segmental joints can be used for the force and lining behavior evaluation. The segmental joint will have a behavioral mode somewhere between a total fixation and a hinge (Majdi et al., 2010, Nadimi and Shahriar, 2013). The orientation of joints within each segmental ring may vary along the tunnel route depending on the tunnel boring machine steering alignment. Furthermore, the possible mode of the joint orientation is governed by the joint numbers. The combination of these two factors might influence the stresses induced in the tunnel lining. Accordingly, both cost and planning purpose might be affected (Hefny and Chua, 2006). Therefore, the main purpose of this research is to investigate the influence of joint numbers and their orientations on the tunnel lining behavior. However, the tunnel lining design is almost based on empirical and analytical methods like the “beam spring model” which was proposed to analyze the tunnel lining under the ground loads (Murakami and Koizumi 1978). This method has become the standard technique to design shield tunnel lining in Japan (JSCE 1996). In this study, the model was used for representing the segmental joints and surrounding ground as rotational springs and non-tension ground springs, respectively.
Mehrgini, B. (University of Tehran and NPC Co.) | Memarian, H. (University of Tehran) | Dusseault, M. B. (University of Waterloo) | Sheikhmali, R. (University of Tehran) | Eshraghi, H. (POGC) | Ghavidel, A. (MAPSA Co. and NPC Co.) | Hassanzade, M. (MAPSA Co. and NPC Co.) | Badsar, A. (MAPSA Co. and NPC Co.)
ABSTRACT: Hydraulic fracturing (HF) to enhance ultimate hydrocarbon recovery factor – RF – is becoming a more common reservoir stimulation method in higher permeability reservoirs, extending its perceived use beyond merely accelerating production. HF is a complex engineering process with large capital costs; a rational and effective design process is the key step to mitigate the potential economic risks and increase the efficiency of the HF treatment. There are several numerical and analytical methods to simulate HF treatments and estimate the geometry of the induced fracture. In this study, the target reservoir formation, a conventional carbonate gas field, was divided into 5 geomechanical units (GMUs). Each GMU has different permeability values, which range from 3.5 to 300 mD. Geomechanical characteristics of each GMU were defined by laboratory tests to obtain fracture toughness (KIC), hydraulic tensile strength (THF), unconfined compression strength (UCS), Young’s modulus (E), Poisson’s ratio (v), cohesion (c′) and internal friction angle (Φ′). Then, using the finite element method (FEM), HF treatment was simulated in each GMU as continuous fluid (water) injection for 20 minutes at a rate of 20 bbl/min. A cohesive zone model (CZM) was assumed for all units as a behavioral rock failure model. The fracture aperture was compared with geomechanical characteristics of each GMU, showing that aperture is strongly related to E, KIC, and THF rather than v, c′, Φ′. Incidentally, as each of these five parameters (except v) increases, aperture decreases. Because slip and shear dilatancy of induced shear fractures was not addressed in this study, no meaningful relation between fracture aperture and c′ or Φ′ exists. For a given volume of injection, fracture length is necessarily in an inverse relationship with the five parameters (except v).
Improving hydrocarbon production, considering the global growing demand for hydrocarbon, is essential. Reservoir stimulation, particularly hydraulic fracturing (HF), is one of the main methods which seek to enhance hydrocarbon recovery by the faster delivery of the petroleum fluid. Basically, HF treatment works by improving the connections of the wellbore with the reservoir, aiding wells to produce fluids more quickly (Economides and Nolte, 2000, Daneshy, 2010).