3D Geomechanics Research Articles

Structurally-controlled failure and damage around an opening in faulted Opalinus Clay shale at the Mont Terri Rock Laboratory: In-situ experimental observation and 3D numerical simulation

We present a combined experimental and numerical study of failure and damage in faulted Opalinus Clay shale around an opening at the Mont Terri Rock Laboratory, Switzerland. An experiment borehole with a diameter of 0.6 m and a length of 12.9 m intersecting a major fault zone at an acute angle of ∼40° was drilled, with subsequent overbreaks closely monitored. To investigate the underlying mechanisms that lead to the observed overbreaks, we developed a 3D geomechanics model to simulate the deformation and failure behaviour of faulted Opalinus Clay shale. To represent geological structures including the major fault zone and secondary fracture sets, a site-specific fracture network was constructed. Our model captured many important geomechanical properties and responses of the faulted Opalinus Clay shale, such as anisotropy of the shale matrix, deformation of the fault zone, dislocation of secondary fractures, and growth of new cracks as well as generation of overbreaks around the opening. We compared our simulation results with in-situ experimental observation of short-term overbreak patterns along the borehole and found that the overbreak occurrence is strongly controlled by both stress conditions and geological structures. Our results indicate that the damaged zone is characterised by an inner shell and an outer shell, where the former (dominated by extensive tensile/shear cracks) has a thickness of about one quarter of the borehole diameter and the latter (dominated by sparse shear cracks) extends by half to one borehole diameter into the surrounding rock. We further elucidated the impacts of the major fault zone and secondary fracture sets as well as the borehole–fault intersection angle on the deformation, damage, and failure characteristics. The findings and insights obtained in this study have important implications for the stability evaluation of waste emplacement drifts and long-term safety assessments of nuclear waste galleries in faulted argillaceous rocks.

3D Geomechanical Finite Element Analysis for a Deepwater Faulted Reservoir in the Eastern Mediterranean

AbstractHydrocarbon reservoir structures are subjected to tectonic forces along the geological time that cause rock deformation and break into faulted zones. Faulted reservoirs, enclose certain complexity in terms of the distributed effective stresses, rock plastic alteration, slipping and fault block displacement. In this study, we develop a three-dimensional (3D) geomechanical reservoir model with faulted and compartmentalized geometry, located in the offshore deepwater environment of the Levantine basin in the Eastern Mediterranean, based on non-linear finite element analysis (FEA). A regional structural and stress map was also constructed, integrating various data sources, to present the regional stress setting to enhance this work. The assessment of the geomechanical impacts on the reservoir provides important information in reservoir studies, that can analyze potential stability issues during the depletion to optimize the field production planning. Stress–strain evolution in the reservoir is primarily affected by the in situ stresses, the geometry of faults, and the degree of compartmentalization. The results demonstrate clearly the mechanism of stress transfer transmission and the impact between the fault block compartments in the reservoir. Fault contacts exhibit a higher tendency for rock displacements and deformations. Plastic yielding develops at a narrow extent along the faults. The risk of fault slipping depends on the depletion strategy, but it is low in all cases. No significant reduction in permeability was found at the end of reservoir depletion. Overall, geomechanics integration enriches and improves the dynamic reservoir models and applications.

Uncertainty of stress path in fault stability assessment during CO2 injection: Comparing smeaheia 3D geomechanics model with analytical approaches

This study investigates the limitation of simplified stress path assumptions, particularly uniaxial strain conditions, in fault stability assessments for CO2 injection sites. We conducted a 3D geomechanics simulation for the Smeaheia fault block in the Norwegian North Sea and compared the results with simplified stress path assumptions. Our results indicate that the uniaxial strain assumption underestimates the change in effective horizontal stress, particularly for bounding faults subjected to a significant change in pore pressure gradient with soft surroundings. Rotations of maximum horizontal stresses parallel to soft surroundings are also observed along the bounding faults due to the directional difference in stiffness contrast along faults. This underestimation results in overestimation of fault stability by up to 60% for an extreme case. Our study thus highlights that the uniaxial strain assumption, which limits to account for lateral deformation on the fault/reservoir boundary, overlooks critical changes in the effective horizontal stress and associated critical scenarios for fault stability assessments. When bounding faults are juxtaposed with low-stiffness shale formation under a normal stress regime, calibrating the fault stability assessment by 30% for a base case and 60% for a conservative assessment can provide a practical way to correct the uncertainties caused by using uniaxial strain assumption.

A Semianalytical Formulation for Estimating Induced Surface Subsidence of a Poroelastic Reservoir

Summary Monitoring and controlling surface subsidence are important to the safety of production operations as well as to the compliance of environmental regulations. Quantitively predicting surface subsidence caused by subsurface pressure change due to well production or injection would be very useful for operators. However, running a 3D geomechanics simulation for such a purpose is technically demanding and computationally expensive. Currently, a quick and easy alternative to get accurate results to fulfill such a task is lacking. In this work, we propose a semianalytical formulation to efficiently calculate the surface subsidence of a reservoir during the primary and enhanced recovery processes. Our method is based on the Green’s function solution of the Navier-Beltrami-Michell equation of poroelastic rocks. It takes the pressure field from a reservoir simulator or an analytical solution as the input and calculates the surface displacement along the vertical direction. We benchmarked the proposed formulation with numerical methods on a refined grid as well as with a semianalytical solution to ensure its accuracy. We applied the developed formulation to optimize the injection well position and vertical injection zone for pressure management. Compared to the previous analytical formulations that are based on the average pressure decline of the reservoir, our method explicitly considers the spatial distribution of the pressure field and is therefore more accurate. Compared with numerical methods, our method avoids the discretization of the caprock region and is thus faster by several orders of magnitude.

Microseismic Monitoring During Hydraulic Fracturing Treatments Complements 3D Geomechanics Modelling

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3D geomechanics modeling of Indonesia B oilfield and its application in wellbore stability

3D geomechanics modeling of Indonesia B oilfield and its application in wellbore stability

Uncertainty of Stress Path in Fault Stability Assessment During Co2 Injection: Comparing Smeaheia 3d Geomechanics Model with Analytical Approaches

Uncertainty of Stress Path in Fault Stability Assessment During Co2 Injection: Comparing Smeaheia 3d Geomechanics Model with Analytical Approaches

3D Geomechanics Characterization in V Field

Upstream oil & gas operators faced many challenges in drilling activities during a field development phase where the reservoir pressure depletion might disturb the stresses equilibrium in the formation and triggered stress redistribution in the reservoir and its surrounding rocks. These changes could lead into more problematic drilling experiences such as the narrowing of safe drilling mud weight windows and potential operating losses due to related wellbore instability issues. 3D Geomechanics analysis conducted to identify the stress redistribution and predict the field wellbore instabilities behaviour that honour the geological features in the area. The 1 D Geomechanics model is created for offset wells which consist of rock strength and elastic properties, pore pressure and stresses profiles. Seismic inversion volume is used to populate the properties in the 3D static model and field Geomechanics simulation conducted to obtain the field stresses profile. V field data is used as the data available in this field is complete to support this study (wire-line logs, petrophysical interpretations, VSP, core analysis, production log, drilling reports, and the seismic velocity cube). The results of the integrated reservoir Geomechanics characterization with seismic inversion managed to predict the wellbore instabilities model in the offset wells.

Coupling 3D geomechanics to classical sedimentary basin modeling: From gravitational compaction to tectonics

Classical sedimentary basin simulators account for simplified geomechanical models that describe material compaction by means of phenomenological laws relating porosity to vertical effective stress. In order to overcome this limitation and to deal with a comprehensive poromechanical framework, an iterative coupling scheme between a basin modeling code and a mechanical finite element code is adopted. This work focuses on the porous material constitutive law specifically devised to couple 3D geomechanics to basin modeling. The sediment material is considered as an isotropic fully saturated poro-elastoplastic medium undergoing large irreversible strains. Special attention is given to the development of a hardening law capable of reproducing the same porosity evolution as provided by the standard basin simulator when the sediment material is submitted to gravitational compaction under oedometric conditions. A synthetic case is used to illustrate the ability of the proposed workflow to integrate horizontal deformations in the basin model as such effects cannot be captured by the simplified geomechanics of the standard basin code. The results obtained by the coupled simulation demonstrate that horizontal compression may significantly contribute to overpressure development and brittle failure of the basin seal rocks, highlighting the importance of a coupled approach to simulate complex tectonic history.

Coupled 3D Simulator Models Wastewater-Injection-Induced Seismicity

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 191670, “Wastewater Injection and Slip Triggering: Results From a 3D Coupled Reservoir/Rate-and-State Model,” by Mohsen Babazadeh, SPE, and Jon•Olson, SPE, The University of Texas at Austin, prepared for the 2018 SPE Annual Technical Conference and Exhibition, Dallas, 24–26 September. The paper has not been peer•reviewed. This paper presents a coupled 3D fluid-flow and geomechanics simulator developed to model induced seismicity resulting from wastewater injection. The simulator modeled several cases of induced earthquakes with the hope of providing a better understanding of such earthquakes and their dominant causal factors, along with primary mitigation controls. Implementation of rate-and-state friction to model friction weakening and strengthening during fault slip to accurately model earthquake occurrence, and an embedded discrete fracture model to efficiently model fluid flow inside the fault, are among the essential features of the simulator. The complete paper presents results from a combined model that brings together injection physics, reservoir dynamics, and fault physics to explain better the primary controls on induced seismicity. Introduction Since 2009, a substantial increase in the number of earthquakes in the central and eastern United States has occurred. Oklahoma has been one of the most affected regions, with several earthquakes of M•5+, including the Prague earthquake in 2011 and the Pawnee earthquake in 2016. This has prompted efforts to find and understand any correlation between oil and gas activity—mainly wastewater disposal—and the occurrence of the earthquakes. Induced or triggered seismicity associated with wastewater injection, mining, oil and gas extraction, and geothermal operations has been identified since the earthquakes at the Rocky Mountain Arsenal in 1960s. Fluid injection into subsurface formations can increase pore pressure, reduce the effective stress, and induce slip on faults. Laboratory studies show that the sliding displacement may enhance fracture transmissivity and create a hydraulic pathway through the formation. In an unconventional reservoir, the enhancement could lead to improved hydrocarbon production by using the slipped natural fractures. But in some formations, such as water-disposal aquifers, seismicity might be induced when faults are activated within the igneous basement. Seismicity induced by fluid injection is controlled by several groups of parameters (injection, reservoir, and frictional). A fundamental understanding of which factors are the most important in triggering slip in areas of active wastewater injection and disposal has been hampered by interrelationships between the various parameters, leading to suggestions of injection volume, rate, or pressure being the most important. However, necessary reservoir characteristics, such as size and permeability, are not well characterized at the well or in the subsurface, and remain the main challenge for deterministic models. Additionally, rupture nucleation on faults near a region of injection depends on rate-and-state and related physics. The literature contains many relevant seismicity studies, which are identified in the reference section of the complete paper. A 2D simulation of fluid flow inside the fault zone suggested that post-shut-in earthquakes are likely to occur nucleating at the fault edges. Using a similar numerical scheme, other researchers investigated the 2011 Prague earthquake sequence to model the delayed triggering mechanism between the M 4.8 fore-shock and M 5.6 main shock. The result of the study contributed to defining constraints on values of fault transmissivity, fault compliance, and rate-and-state frictional properties. Although expensive, these types of full-physics models are capable of characterizing reservoir and fault properties. A 3D simulation in 2015 modeled fault activation under direct injection into the fault during shale-gas hydraulic fracturing. It found that for brittle faults, the moment magnitude can be higher.

Building a 3D Geomechanical Model for the Fitzroy Trough

Building a 3D Geomechanical Model for the Fitzroy Trough

Effects of Finite Strains in Fully Coupled 3D Geomechanical Simulations

Effects of Finite Strains in Fully Coupled 3D Geomechanical Simulations

Construction of a 3D Geomechanical Model for Development of a Shale Gas Reservoir in the Sichuan Basin

SummaryCurrently, there is large-scale shale gas exploration and development in the Sichuan Basin, western China. Caused by high tectonic stress and presence of fracture systems at various scales in the lower Silurian Longmaxi reservoir formation, hydraulic fracturing in shale gas reservoirs in the Sichuan Basin has encountered many difficulties, such as placing sufficient proppant, poor-production performance for some wells, and ambiguity as to the factors controlling the production of reservoirs. It has been recognized that lack of geomechanical understanding of the shale gas reservoirs is a major obstacle to effectively addressing these difficulties.A 3D full-field geomechanics model was constructed for the Changning shale gas reservoir in the Sichuan Basin through integrating seismic, geological structure, log, and core data by following a newly formulated work flow. The 3D geomechanical model includes 3D anisotropic mechanical properties, 3D pore pressure, and the 3D in-situ stress field. Through leveraging measurements from an advanced sonic tool and core data, the anisotropy of the formation was captured at wellbores and propagated to 3D space guided by prestack seismic inversion data. The 3D pore-pressure prediction was conducted with seismic data, and calibrated against pressure measurements, mud-logging data, and flowback data. A discrete-fracture-network (DFN) model, which represents multiscale natural-fracture systems, was integrated into the 3D geomechanical model during stress modeling to reflect the disturbance on the in-situ stress field by the presence of the natural-fracture systems.The 3D pore-pressure model was used to calculate more-reliable estimates of gas in place in the shale gas reservoir, and the geomechanical model was used to reveal the root cause of difficulties of proppant placement in this tectonically active and unevenly fractured shale gas reservoir.The paper presents the highlights and innovations in constructing the 3D geomechanical model for the shale gas reservoir, and explains how the 3D geomechanical model is used to address technical challenges encountered during drilling and completion. Also, it demonstrates that a reliable 3D geomechanical model, with proper characterization of anisotropy, pore pressure, and natural fractures, provides a critical opportunity to improve the development in this shale gas reservoir.

3D Full-Field and Pad Geomechanics Models Aid Shale Gas Field Development in China

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper IPTC 18984, “Three-Dimensional Full-Field and Pad Geomechanics Modeling Assists Effective Shale Gas Field Development, Sichuan Basin, China,” by Liang Xing, PetroChina; Xian Chenggang, SPE, Schlumberger; Shu Honglin, PetroChina; Chen Xin, Schlumberger; Zhang Jiehui, PetroChina; Wen Heng, Schlumberger; Wang Gaocheng, PetroChina; and Wang Lizhi, Guo Haixiao, Zhao Chunduan, Luo Fang, and Qiu Kaibin, SPE, Schlumberger, prepared for the 2016 International Petroleum Technology Conference, Bangkok, Thailand, 14–16 November. The paper has not been peer reviewed. Copyright 2016 International Petroleum Technology Conference. Reproduced by permission. The oilfield-development plan (ODP) for a shale gas field at the southern edge of the Sichuan Basin in China started in early 2014. The first wells drilled in the field and its adjacent blocks experienced significant challenges, such as severe mud losses, stuck tools, losses in the hole, high treating pressure, and unexpected screenout. Because an accurate understanding of geomechanics and its roles at various scales is vital, 3D full-field and pad geomechanics models were developed for achieving efficiency and effectiveness in implementing the ODP. Introduction The Ordovician-Silurian Wufeng-Longmaxi hot shale is an emerging shale gas play in China. Currently, the major exploration and development activities of the play are in the Sichuan Basin and its adjacent areas. For shale gas development in the Sichuan Basin and its adjacent areas, using the megascale, high-density, and continuous and regular pad drilling as is used in North America is difficult because surface and subsurface conditions are significantly different from those of the well-known North American shale plays. The strong environmental and social constraints that typify the Sichuan Basin and surrounding area are shown in Fig. 1. Drilling pads for shale gas developments are commonly located in narrow valleys that are often home to farmland and residential villages with dense populations. Differences of elevation among neighboring pads can be from several hundred meters to more than 1000 m. To speed up development of marine shale gas in the Sichuan Basin and its adjacent areas with a minimized learning curve, a geoscience-to-production integration of research, engineering, and operation with its associated research and development, methodologies, and work flows must be applied. This geoscience-to-production integration aims to optimize both efficiency and effectiveness dynamically at single-well, pad, and field scales with systematic and continuous optimization of technologies and solutions and the accumulation of knowledge and experience to enhance well productivity. One shale gas field, which is the study area of this paper, is in the mountainous area at the southern edge of the Sichuan Basin. The first wells drilled in this field and its adjacent blocks experienced significant geomechanics-associated challenges, such as severe mud losses, tools or drillingpipe sticking, losses in the hole, high treating pressure while hydraulic fracturing, and unexpected screen out of fracturing stages. Having reliable yet evolving understanding of geomechanics and its role at various scales during the progress of the ODP is vital. This paper describes the development of 3D full-field geomechanics models and high-resolution 3D pad geo-mechanics models and their engineering applications.

Optimization design of foundation excavation for Xiluodu super-high arch dam in China

With better understanding of the quality and physico-mechanical properties of rocks of dam foundation, and the physico-mechanical properties and structure design of arch dam in association with the foundation excavation of Xiluodu arch dam, the excavation optimization design was proposed for the foundation surface on the basis of feasibility study. Common analysis and numerical analysis results demonstrated the feasibility of using the weakly weathered rocks III1 and III2 as the foundation surface of super-high arch dam. In view of changes in the geological conditions at the dam foundation along the riverbed direction, the design of extending foundation surface excavation area and using consolidating grouting and optimizing structure of dam bottom was introduced, allowing for harmonization of the arch dam and foundation. Three-dimensional (3D) geomechanics model test and finite element analysis results indicated that the dam body and foundation have good overload stability and high bearing capacity. The monitoring data showed that the behaviors of dam and foundation correspond with the designed patterns in the construction period and the initial operation period.

Technology Focus: Seismic Applications (March 2015)

Technology Focus In recent years, the geophysical industry, fueled by high global activity levels, invested considerably in new equipment and technologies. The capital-intensive marine seismic-acquisition market segment especially experienced a small boom with the introduction of many new vessels and highly advanced sensor technologies. Marine broadband seismic acquisition and processing has quickly become the norm rather than an exception, and seismic-acquisition companies launched several new purpose-built seismic vessels suited for extended operations in remote and harsh environments. This trend was less pronounced in the land seismic-acquisition market segment, where entry levels for new crew startups are generally lower and where more providers, often with a more regional focus, are active. Nevertheless significant improvements were realized, notably for the high-production and high-channel-count onshore seismic crews operating in desert environments, a niche that is still dominated by the bigger global service companies. For more-challenging terrain, nodal acquisition has matured, enabling smaller crew footprints and increased efficiency. However, the changing business climate with reduced oil- and gas-production revenues is forcing oil and gas companies worldwide to focus more rigorously on cost efficiency and to reconsider exploration spending, being a stark reminder of the volatility of the oil and gas business and the seismic market in particular. The coming year will be challenging for the global geophysical industry and for seismic-acquisition companies in particular. Integrated geophysical service companies that made timely investments in technology upgrades as well as in operational safety and efficiency should be better positioned to weather the coming period and to offer their technologies at affordable rates. Seismic, though cost intensive, will remain a pivotal technology. With continued cost pressures, one has to expect, though, that the range of available geophysical tools and technologies will be applied more selectively. This can be achieved only through an early and deeper integration with geology and other relevant subsurface disciplines. Cost-efficient nonseismic technologies such as gravity and magnetics will provide important early information in a staircased exploration-derisking approach before more-costly technologies such as high-end seismic or controlled-source electromagnetic are applied. Solid geophysical expertise and knowledge will remain critical for selecting the appropriate tools for the relevant exploration or development phases and to meet requirements for ever shorter turnaround times. The articles chosen for this technology review provide examples of the accuracy, efficiency, and business impact of geophysical-technology applications for exploration and production. JPT Recommended additional reading at OnePetro: www.onepetro.org. SPE 165092 Continuous Land Seismic Reservoir Monitoring of Thermal EOR in the Netherlands by Julien Cotton, CGG, et al. SPE 170808 Time-Lapse (4D) Seismic for Reservoir Management: Case Studies From Offshore Niger Delta, Nigeria by Sunday Amoyedo, Total, et al. SPE 171832 3D Geomechanical Models Inverted From Prestack Seismic Data by Leonardo Azevedo, Center for Modeling Petroleum Reservoirs, et al.

Well-Integrity Evaluation for Methane-Hydrate Production in the Deepwater Nankai Trough

Summary Large accumulations of methane hydrates are known to exist in the deepwater Nankai Trough off the southern coast of Japan. Because of its enormous potential as an energy source, there is growing interest in the production of methane gas from these deposits. An offshore production test was scheduled to test the technological viability to produce the methane hydrate with a depressurization method. However, methane-hydrate production may cause large amounts of compaction and subsidence, which can damage well integrity and cause loss of zonal isolation in the overburden. This condition could provide potential leakage pathways for methane gas to the surface and endanger offshore operations. The paper presents a study in which well integrity was evaluated for a methane-hydrate-production test well in the Nankai Trough. In this study, a new work flow was proposed and applied to honor both fieldwide formation heterogeneity and near-wellbore geometry. The geomechanics properties were determined through integration of seismic inversion data, log data, and core data from the Nankai Trough. Interface elements were installed between the casing and cement and the cement and formation to evaluate the impact of cement-bond quality on the well integrity. The numerical simulation was conducted through coupling of the simulation results produced by a methane-hydrate production simulator from a third party with a 3D finite-element geomechanics simulator. The study predicted the occurrence of 2 cm of subsidence on the seafloor generated by approximately 1.5% of reservoir compaction for a production test of 20 days. Over this period, casing would yield with a plastic strain of approximately 1%. Most findings indicated a low risk in the loss of zonal isolation that is consistent with the results of the production test conducted in March 2013. This simulation evaluated potential risks related to well integrity, and provided critical information for the preparation and execution of the pioneering offshore methane-hydrate production test in the Nankai Trough.

Characterization of Pliocene and Miocene formations in the Wilmington Graben, Offshore Los Angeles, for Large Scale Geologic Storage of CO2

Abstract Geomechanics Technologies has completed a detailed characterization study of the Wilmington Graben offshore Southern California area for large-scale CO 2 storage. This effort has included: an evaluation of existing wells in both State and Federal waters, field acquisition of about 175 km of new seismic data, new well drilling, development of integrated 3D geologic, geomechanics, and fluid flow models for the area. The geologic analysis indicates that more than 100 million tons of storage capacity is available within the Pliocene and Miocene formations in the Graben. Combined fluid flow and geomechanical analyses indicates that injection and storage can be conducted without significant risk for caprock fracturing or fault activation, if injection pressures are limited to below 110% of hydrostatic pressure. Numerical analysis of fluid migration indicates that injection into the Pliocene Formation at depths of 5000 feet would lead to undesireable vertical migration of the CO 2 plume. Recent well drilling however, indicates that deeper sand is present at depths exceeding 7000 feet, which could be viable for large volume storage.

Model Test of Anchoring Effect on Zonal Disintegration in Deep Surrounding Rock Masses

The deep rock masses show a different mechanical behavior compared with the shallow rock masses. They are classified into alternating fractured and intact zones during the excavation, which is known as zonal disintegration. Such phenomenon is a great disaster and will induce the different excavation and anchoring methodology. In this study, a 3D geomechanics model test was conducted to research the anchoring effect of zonal disintegration. The model was constructed with anchoring in a half and nonanchoring in the other half, to compare with each other. The optical extensometer and optical sensor were adopted to measure the displacement and strain changing law in the model test. The displacement laws of the deep surrounding rocks were obtained and found to be nonmonotonic versus the distance to the periphery. Zonal disintegration occurs in the area without anchoring and did not occur in the model under anchoring condition. By contrasting the phenomenon, the anchor effect of restraining zonal disintegration was revealed. And the formation condition of zonal disintegration was decided. In the procedure of tunnel excavation, the anchor strain was found to be alternation in tension and compression. It indicates that anchor will show the nonmonotonic law during suppressing the zonal disintegration.

Research on 3D Geomechanics Model Test for a Large-Scale Offspur Tunnel Project

Geomechanics model test has some distinctive advantages in simulating changing laws of stress and strain of rockmass as well as failure mechanism of surrounding rockmass of tunnel. In order to systematically study mechanics deformation properties of a large-scale offspur tunnel under excavation state, we design and manufacture a large scale 3D model test rack installation with hydraulic equipment. The test rack is 3.7 meters long, 2.2 meters wide and 4 meters high, which is the largest 3D geomechanics model test rack in present Chinese communication trades. The new-type similar material of model is a kind of cementitious composite which is mixed with iron ore powder, blanc fix, quartz sand, rosin, industrial alcohol and gypsum powder. 3D geomechanics model test for a large-scale offspur tunnel is carried out by utilizing the test installation and the similar material. The original design and construction of the offspur tunnel has been effectively optimized by results from model test.