bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability Analysis of Pipe With Connectors in Horizontal Wells
Authors: Gao Guohua , Di Qinfeng , Miska Stefan , Wang Wenchang
Published: November 2012

Except for coiled tubing, most tubular goods used for downhole operations (such as drillpipe and sucker rod) have connectors. Because a connector and the pipe body have different outer radii, the deformation and buckling behavior of a pipe with connectors constrained in a wellbore is much more complicated. However, most buckling models were established by neglecting the existence and effects of connectors.

In this paper, buckling equations of a pipe with connectors in horizontal wells were derived with application of elastic-beam theory. The axis of an unbuckled pipe is a 2D curve in the vertical plane and has three configurations—no contact, point contact, and wrap contact. We derived the two critical distances between connectors, Lc1 and Lc2, beyond which a pipe changes its configuration from one to another. The authors proposed an algorithm to determine the critical force (Fcrs) of buckling by numerically solving the buckling equations using the fourth-order Ronge-Kuta method.

Both the distance between two adjacent connectors (Lc) and the radius difference between a connector and the pipe body (∆rc) have significant impact on the critical force, in addition to net clearance between a pipe and wellbore (r0), bending stiffness (EI), and weight per unit length (w) of pipe. When Lc is small, radial deflection is negligible. Fcrs increases as ∆rc increases. However, when Lc is close to Lc1, effects of radial displacement become significant, and Fcrs decreases dramatically as ∆rc increases. Fcrs decreases as Lc increases when Lc Lc1, and it reaches its minimum at Lc=Lc1. When Lc > Lc1, Fcrs fluctuates as Lc increases. Some curves of Lc1, Lc2, and Fcrs, all in dimensionless forms, were calculated and presented in this paper for practical applications.

Our numerical results show that the critical force may reduce by 20 to 60% for commonly used drillpipes and sucker rods with centralizers, which indicates that a pipe string designed without considering the effects of connectors may be risky. The results presented in this paper may provide some practical guidance for optimal design of centralizers for sucker-rod strings, or may avoid some risks because of improper design of drillpipe strings.
Effect of Discontinuous Microfractures on Ultratight Matrix Permeability of a Dual-Porosity Medium
Authors: Apaydin O.G.. G. , Ozkan E.. , Raghavan R..
Published: November 2012

This paper examines the effects of matrix microfractures on the effective matrix permeability of a dual-porosity medium. An analytical model is presented, with composite matrix blocks consisting of a core in which unconnected microfractures do not contribute considerably to flow capacity and a surface layer where the microfractures connected to the matrix surface (resembling wormholes) cause a stimulation effect. The composite matrix flow is coupled with the flow in a network of macrofractures, as in the conventional dual-porosity idealizations of fractured media. This paper investigates the effect of matrix-surface stimulation and demonstrates improved fluid transfer from the matrix medium to the fracture network because of matrix microfractures. It is shown that matrix microfractures accelerate production by providing earlier and more-effective contribution of the matrix into flow rates. This contribution of the matrix because of microfractures cannot be simulated by enhanced matrix permeability because the microfractured surface layer of the matrix causes flow characteristics different from those of a homogeneous (unfractured) matrix. The effect of the microfractured surface layer of the matrix cannot be taken into account by a triple-porosity model used to incorporate two sets of connected natural fractures or connected fractures and vugs.
Theoretical and Experimental Modeling of Residual Gel Filter-Cake Displacement in Propped Fractures
Authors: Ouyang L.. , Yango T.. , Zhu D.. , Hill A. D.
Published: November 2012

Fracture fluid damage caused by residual polymer gel in propped fractures results in low fracture conductivity and short effective fracture length, sometimes severely reducing the productivity of a hydraulically fractured well. The residual gels are concentrated in the filter cakes built on the fracture walls and have much higher polymer concentration than the original gel. The residual gel exhibits a higher yield stress and is difficult to remove after fracture closure.

In this work we studied polymer gel behavior theoretically and experimentally in hydraulic fracturing. We developed a model to describe the flow behavior of residual polymer gel being displaced by gas in parallel plates. We developed analytical models for gas/ liquid two-phase stratified flow of Newtonian gas and non-Newtonian residual gel to investigate gel cleanup under different conditions. The concentrated gel in the filter cake was modeled as a Herschel-Bulkley fluid, a shear-thinning fluid following a power law relationship, but also having a yield stress.

The model developed shows that three flow regimes may exist in a slot, depending on the gas flow rate and the filter-cake yield stress. At low gas velocities, the filter cake will be completely immobile. At higher gas velocity, the shear at the fracture wall exceeds the yield stress of the filter cake, and the gel is mobile, but with a plug flow region of constant velocity near the gas/gel interface. Finally, at high enough gas velocity, a fully developed velocity field in the gel is created.

The parameters for the gel displacement model were evaluated by experiments. We examined the filter-cake formation by pumping the fracture fluid through a conductivity cell, allowing leakoff to build the filter cake, measuring the cake thickness, and flowing gas through the cell to simulate the cleanup process. The results show that the yield stress of the residual gel plays a critical role in gel cleanup.
Quantification of Drillstring-Integrity-Failure Risk Using Real-Time Vibration Measurements
Authors: Arevalo Yezid , Fernandes Ashley
Published: November 2012

Vibration measurements have traditionally targeted the improvement of downhole-tool reliability. This paper targets the effects of vibration on the complete drillstring. Failures associated with drillstring vibration continue to happen despite the sophistication of today's measurements. These failures represent a very significant amount of lost time, which we target to improve.

The industry has a very limited database for evaluating indices to manage or quantify risks of vibration to the complete drillstring. This fact makes the use of the methods in the field heavily depend on the past experience of the drillers and on the rig types. Operators are faced with an unknown quantification of the risk severity when attempting to mitigate vibration. By quantifying the risk, this work demonstrates how the prevention of incidents can be achieved. These incidents include but are not limited to, twistoffs, backoffs, and bottomhole-assembly (BHA) component failures.

The proposed solution is based on real-time measurements of drillstring vibration to estimate an ongoing drillstring-integrity risk, which is used as a guideline to improve decisions while drilling the well. This solution has been developed through use of advanced vibration sensors to discriminate between different types of vibration. This was critical to estimating realistic cumulative damage to the drillstring, which is highly dependent on the type of vibration suffered by the assembly and the onset of vibration-mode coupling.

This paper shows that approximately 80% of drillstring-integrity failures analyzed can be identified and prevented through use of the proposed risk-quantification solution. This result has been obtained despite unknown fatigue or wear of drillstring components before a run, and vibration sensors were located at a single position in the drillstring. This indicates that the primary contributor to drillstring failures is the drilling conditions for any given run.
Effect of Methane Co-Injection in SAGD--Analytical and Simulation Study
Authors: Sharma Jyotsna , Moore R. Gordon , Mehta Sudarshan A.
Published: November 2012

Steam-assisted gravity drainage (SAGD) is a commercially viable recovery method for oil sands of Athabasca used where other methods have been unsuccessful. In one variation of SAGD, a small amount of a noncondensable gas is added to the injected steam to maintain pressure in the chamber while using the energy in place, reducing steam consumption and providing thermal insulation from overburden heat losses. The role of gas during steam-gas co-injection processes, in terms of its effects on chamber development, bitumen flow rates, and heat losses, is not fully understood, and therefore is the main focus of this work.

A new analytical model for gas injection in SAGD is derived, taking into account the three-phase flow of gas, oil, and water in the reservoir. The analytical theory is used to predict the fluid flow rates as well as phase mobility, relative permeability, and saturation profiles in the mobile oil region. The theoretical results are replicated by fine-grid numerical simulations. Methane was used as the noncondensable gas for the purpose of this study because it is the main solution gas in most reservoirs. It is, however, believed that the findings of this study are equally applicable to other noncondensable gases such as nitrogen, air, helium, and others. Fine-grid numerical simulations were performed to gain a visual understanding of gas distribution in a SAGD chamber and its effect on in-situ steam quality, overburden heat losses, phase saturations, and fluid-flow rates. The simulation results support the predictions of the mathematical theory.

The results of the analytical and numerical study reveal that methane co-injection with steam is in general unfavorable in a SAGD operation. The injected methane tends to accumulate at the steam condensation front, which lowers the heat transfer rate of steam to the adjacent oil, resulting in lower oil production rates and slower growth of the chamber.
Accurate Modeling of Faults by Multipoint, Mimetic, and Mixed Methods
Authors: Nilsen Halvor M. , Lie K.-A.. -A. , Natvig Jostein R.
Published: November 2012

The predominant way of modeling faults in industry-standard flow simulators is to introduce so-called transmissibility multipliers in the underlying two-point discretization. Although this approach provides adequate accuracy in many practical cases, two-point discretizations are only consistent for K-orthogonal grids and may introduce significant discretization errors for grids that severely depart from being K-orthogonal. Such grid-distortion errors can be avoided by lateral or vertical stair-stepping of deviated faults at the expense of errors in the geometrical fault description. In other words, modelers have the choice of either making (geometrical) errors by adapting faults to a grid that is almost K-orthogonal, or introducing discretization errors because of the lack of K-orthogonality if the grid is adapted to deviated faults.

We propose a method for accurate description of faults in solvers based on a hybridized mixed or mimetic discretization, which also includes the MPFA-O method. The key idea is to represent faults as internal boundaries and calculate fault transmissibilities directly instead of using multipliers to modify grid-dependent transmissibilities. The resulting method is geology-driven and consistent for cells with planar surfaces and thereby avoids the grid errors inherent in the two-point method. We also propose a method to translate fault transmissibility multipliers into fault transmissibilities. This makes our method readily applicable to reservoir models that contain fault multipliers.
A Comprehensive Theoretical and Experimental Study on Fluid Displacement for Oilwell-Cementing Operations
Authors: Aranha Pedro Esteves , de Miranda Cristiane Richard , Cardoso Walter F. , Campos Gilson , Martins André Leibsohn , Gomes Frederico C. , de Araujo Simone Bochner , Carvalho Marcio S.
Published: November 2012

Displacing fluids in downhole conditions and for long distances is a complex task, affecting several steps of well construction. Cementing gains relevance the moment that fluid contamination compromises cement-sheath integrity and consequently zonal isolation.

Density and rheology design for all the fluids involved is essential to achieve operational success. Properties hierarchy and preferred flow regimes have been empirically defined and tend to provide reasonable generic results. Challenging operations, including ultradeep waters and their narrow operational-window scenario, require further knowledge of the physics involved to prevent undesirable events.

This paper presents the in-house development of software for annular miscible fluid displacement that analyzes fluid displacement in typical vertical and directional offshore wells, for Newtonian and non-Newtonian liquids and laminar- and turbulent-flow regimes. The formulation proposed provides accurate results for a wide range of input parameters, including the cases in which the ratio of the inner radious to the outer radius of the annulus is small.

The computational work is validated by unique results obtained from an experimental test rig where detailed displacement tests were conducted. Contamination degrees were measured after the displacement of a sequence of fluids through 1192 m of vertical well. Effect of fluid-density and rheology hierarchy, flow regimes, and displacement concepts was investigated. The results provide relevant information for the industry and fundamental understanding on displacement of Newtonian and non-Newtonian liquids through annular sections.
Ultralightweight Proppants: An Effective Approach To Address Problems in Long Horizontal Gravel Packs Offshore Brazil
Authors: Jardim Neto A.T. , Prata F.G.M. , Gomez J.R. , Pedroso C.A. , Martins M.O. , Silva D.N.
Published: November 2012

Operators developing reservoirs and producing them from deep and ultradeepwater wells are pushing the technical limits regarding horizontal extension. Deepwater wells completed in unconsolidated formations usually have low fracture gradients, severe leakoff zones, and/or significant washouts. Long horizontal open holes, therefore, may become technically difficult or economically unfeasible to gravel-pack with the use of conventional fluids and gravels.

Typical completions in offshore Brazil start from a 9⅝ - or 10¾-in.casing, in which a 5½-in. premium screen and tubular string is hung along an open hole drilled with an 8½- or 9½-in. bit. Horizontal extensions range from 980 to 4,000 ft. A variety of openhole gravel-pack techniques proved to be complex and costly, but ultralightweight (ULW) proppants have enabled simpler and more-cost-effective gravel packing in these longer horizontal open holes. The reduced gravel density allows a significant reduction in pumping rate that avoids fracturing the formation, minimizes fluid loss, and eliminates the risk of premature screenout caused by excessive gravel settling.

ULW-proppant technology was introduced to Brazil in 2005 and has been applied successfully to gravel pack wells under extreme conditions such as low fracture gradient, severe fluid loss, and washed-out zones. ProppantULW-1.25 has proved to be effective for packing wells with narrow sections through the openhole interval, frequently found in horizontal wells completed through shale zones that are isolated by reactive packers and/or mechanical external casing packers. ULW-1.75 was introduced in Brazil in 2007 and has largely replaced ULW-1.25 for gravel packing wells in which an improvement in the operational pumping window is required. A combined package comprising ULW-1.75 during the alpha-wave phase and ULW-1.25 during the beta-wave phase is also discussed. This paper summarizes the procedures and results of almost 60 wells that have been gravel packed with the use of ULW-proppant technology pumped for a local operator.
Advanced Drilling Simulation Environment for Testing New Drilling Automation Techniques and Practices
Authors: Cayeux Eric , Daireaux Benoît , Wolden Dvergsnes Erik , Leulseged Amare , Torstein Bruun Bjørn , Herbert Mike
Published: November 2012

Newly developed drilling automation systems locate a computer interface between commands issued by the driller and instructions transmitted to the drilling machinery. Such functions are capable of faster and more precise control than can be achieved by an unaided operator and thus can help drilling within narrow margins. To ensure that these systems work properly in all circumstances, an advanced drilling simulator has been developed to enable testing under a wide range of simulated conditions.

The environment described in this paper uses hardware in the loop (HIL) simulation to verify that the automation techniques being tested respond correctly in real time. Rigorously validated physical models of the drilling process simulate the response of the well to the commands given to the drilling machines. Abnormal drilling conditions (e.g., packoffs, kicks) and equipment or machine-related problems (e.g., plugged nozzles, power shortage) are convincingly recreated.

The drilling simulator models the behavior of surface equipment such as the activation of gate valves to line up different pits or the flow in the mud return. It simulates changes in the drilling fluid properties when mixing additives to the mud. It is therefore possible to focus training sessions on cooperation between different groups at the wellsite. This is particularly useful when planning the introduction of drilling automation that involves new work procedures as a result of automation and adaptation of the drilling team to a new operational environment.

Drilling operations are becoming more and more complex. Automation has the potential to provide large improvements in efficiency and safety, but automation technologies must be implemented correctly at the workplace. Just as the aviation industry has used simulated environments for decades, drilling simulation environments are the key to the safe and successful implementation of drilling automation and the development of crew skills to face future challenges.
The Design of BHA and the Placement of Magnetometer Sensors Influence How Magnetic Azimuth Is Distorted by the Magnetic Properties of Drilling Fluids
Authors: Waag Tor Inge , Torkildsen Torgeir , Amundsen Per Amund , Nyrnes Erik , Saasen Arild
Published: November 2012

The magnetic property of drilling fluid is one of the substantial error sources for the determination of magnetic azimuth for wellbores. Weight material, cuttings, clay, and other formation material in addition to metal filings from tubular wear may distort the magnetometer readings. This effect is obviously linked to the amount and kind of magnetic material that is in the drilling fluid, and the development of corrective means has therefore highlighted the drilling fluid. The problem has been studied by laboratory experiments and analyses of downhole-survey data. However, there are several inconsistencies in the results, and the phenomenon is not understood fully. We focus on the geometric properties of the bottomhole assembly (BHA) and the magnetic directional tool in this study.

The influence on directional measurement while drilling (MWD) from drilling fluids has been studied using finite-element modeling techniques. The simulations have been performed for several cases with realistic representations of MWD-tool geometries and varying location of BHA vs. the wellbore. One important result is that for situations with perfect axial symmetry, the magnetometer readings are attenuated proportionally to the square of the magnetic susceptibility. Because the magnetic susceptibility is a small number, the effect on magnetometer readings is generally negligible. However, if the symmetry is broken, the distortion on the magnetometer readings can be increased significantly. This means that segregation of cuttings, metal filings, or weight material can have a strong influence on the strength of the measured magnetic fields.

With a collar-based tool that is asymmetric by nature, the model shows a complex distortion picture. The influence varies with the tool-face angle and shows both attenuation and amplification. The distortion maxima and minima for the two crosssectional magnetometers do not coincide. These findings underline how difficult it will be to find a straightforward corrective action.

The results from the simulations give increased knowledge about the influence from the magnetic properties of the drilling fluid. This is essential for accuracy estimation and multistation analysis of magnetic-survey data. Furthermore, the results demonstrate the importance of considering the geometry of the BHA and the tool and of the sensor placement when performing the mechanical design.
Design Considerations of Waterflood Conformance Control With Temperature-Triggered, Low-Viscosity Submicron Polymer
Authors: Izgec O.. , Shook G.M.. M.
Published: November 2012

In waterfloods, the existence of highly conductive thief zones causes poor volumetric sweep efficiency, resulting in early breakthrough and excessive production of water. A conventional strategy of redirecting injection by closing off perforations yields short-term benefits because diversion occurs near the wellbore. As an alternative, temperature-triggered submicron polymers with low viscosity (popping agents), which give an opportunity for conformance control deep in the reservoir, have been introduced in recent years. This technology aids conformance control by plugging the high-permeability zones and diverting the fluid to the unswept portion of the reservoir.

Understanding the critical parameters that lead to a successful treatment and accurate determination of the slug size are two important criteria for a technically and economically successful treatment. In this study, we first investigate the effect of different parameters on the success of a conformance control treatment. A comprehensive design-of-experiments (DOE) study resolves the effects (and combined effects) of kv/kh, treatment fluid concentration, thief-zone to matrix-permeability ratio, mobility ratio, and location of the placement in the reservoir. Next, a methodology is developed for accurate determination of the conformance slug size. The method is built on the temporal moment and residence time distribution analysis (RTDA) of interwell tracers. Dynamic flow- and storage-capacity curves are used to identify the optimum slug size.

3D thermal computer simulations show that thief-zone to matrix-permeability ratio and placement location of the polymer are the most important parameters that affect the success of a treatment. The most desirable setting is placement of the polymer deep in the reservoir, closer to the producer within high kv/kh reservoirs. Furthermore, the computer simulations confirm the power of the new technique for optimal slug-size determination. This new technique can avoid underestimation of the volume that must be treated, which is critical for the success of a treatment.
A Pilot Carbon Dioxide Test, Hall-Gurney Field, Kansas
Authors: Willhite G.P.. P. , Byrnes A.P.. P. , Dubois M.K.. K. , Pancake R.E.. E. , Tsau J.-S.. -S. , Daniels J.R.. R. , Flanders W.A.. A.
Published: November 2012

A pilot carbon dioxide (CO2) -miscible flood was initiated in the Lansing-Kansas City C formation in the Hall-Gurney Field, Russell County, Kansas. The reservoir zone is an oomoldic limestone located at a depth of approximately 2,900 ft. The pilot consisted of one CO2 injection well and three production wells. Continuous CO2 injection began in December 2003 and continued through June 2005, at which point 16.19 million lbm of CO2 had been injected into the pilot area. Injection was converted to water in June 2005 to reduce operating costs to a break-even level with the expectation that sufficient CO2 was injected to displace the oil bank to the production wells by water injection. By March 2010, 8,736 bbl of oil had been produced from the pilot. Production from wells to the northwest of the pilot region indicated that oil displaced by CO2 injection was produced from five wells outside of the pilot area, to the northwest. Approximately 19,166 bbl of incremental oil was estimated to have been produced from these wells as of March 2010. There was evidence of a directional permeability trend toward the northwest through the pilot region. The majority of the injected CO2 remained in the pilot region, which was maintained at or above the minimum miscibility pressure (MMP). Although the four-well pilot was uneconomical, the estimated oil recovery attributed to the CO2 flood is 27,902 bbl, which is equivalent to a gross CO2 usage of 4.8 Mcf/bbl.
Establishing Key Reservoir Parameters with Diagnostic Fracture Injection Testing
Authors: Nojabaei B.. , Kabir C.S.. S.
Published: November 2012

Diagnostic fracture injection testing (DFIT) is an invaluable tool for evaluating reservoir properties in unconventional formations. The test comprises injection of water over a short time, starting a fracture at the end of a well's horizontal section, followed by a long shut-in period. Analysis of the falloff data with the G-function plot reveals the fracture-closure pressure, and the fracture pseudolinear-flow period.

In most tests, wellhead-pressure (WHP) measurements are used because of cost considerations. A wellbore-heat-transfer model is used to allow conversion of WHP to bottomhole pressure (BHP) by accounting for changing fluid density and compressibility along the wellbore. This model, in turn, allowed us to assess the quality of solutions generated with the WHP data. For DFIT analysis, we adapted the modified-Hall plot for the injection period, whereas both the pressure-derivative and G-function plots were used for the analysis of falloff data. The derivative signature of the modified-Hall plot allows unambiguous estimation of the fracture breakdown pressure (pf,) during the injection period. As expected, the pf, always turns out to be higher than the fracture-closure pressure (pfc), estimated with the two methods during pressure falloff, thereby instilling confidence in the solutions obtained.

A statistical design of experiments with coupled geomechanical/fluid-flow simulation capabilities showed that the formation permeability is by far the most important variable controlling the fracture-closure time. Mechanical rock properties, such as Young's modulus of elasticity and the Poisson's ratio, play minor roles. In microdarcy formations, a longitudinal fracture takes much longer to close than a transverse fracture.
Simulation of Drilling Fluid Filtrate Invasion Near an Observation Well
Authors: Chassagne Romain L. , Hammond Paul S.
Published: November 2012

We used a commercial reservoir simulator to study, first, the dissipation of aqueous drilling fluid filtrate invasion around a cased observation well in an oil-saturated formation under the action of capillary pressure and, second, the interaction of a waterflood front with the cased well and remaining invaded zone. Hysteretic behavior of the capillary pressure and relative permeabilities is critically important to these processes and is taken into account by the use of the Carlson model, with the various bounding drainage and imbibition curves computed from a pore network model.

Filtrate invasion into a hydrocarbon formation influences the readings of well-logging tools. Although this phenomenon has been known, and corrected for, for many years, uncertainty remains with regard to the long-time behavior of invasion around observation wells where no flow in or out of the formation occurs after completion, and with regard to the influence of formation wettability. We find that after sufficient time, the invaded zone dissipates completely in a water-wet formation, but some invasion always remains in the oil/mixed-wet case. Nonwetting-phase trapping, manifested through relative permeability hysteresis, is the cause. Because trapping affects the values and the endpoints of the relative permeability curves, a waterflood front passing across an observation well is more distorted in the oil/mixed-wet case. The simulation results allow us to understand how logging-tool measurements made in cased observation wells are influenced by drilling-fluid invasion and will therefore lead to improved interpretation. This study shows strong links between the wettability of the formation and the persistence of invaded zone saturation and between invaded zone saturation and the distortion of subsequent flood fronts.
Application of Multirate Well Tests to Scale Management: Part 2—Interpretation of MRTs With Known Produced-Water Origin
Authors: Tjomsland Tore , Sandøy Bernt , Fadnes Finn Hallstein , McCartney Ross
Published: November 2012

Several multirate separator tests (MRTs) have been undertaken on wells in the Veslefrikk field that are on commingled production from the Brent Group and Intra Dunlin Sand (IDS). During these tests, produced-water (PW) samples were also collected. Integrated analysis of the results of interpretion of the PW analyses and the MRT results has provided a range of information for each production zone, including the nature and composition of the PW, the seawater fraction of these produced waters, the fraction of total water flow being produced, pressure, productivity index, oil and water rates, and water cut. This information can reduce the need for running production-logging tools (PLTs), allows the scaling potential between the deeper and the shallower zones to be evaluated, aids squeeze-treatment design, is beneficial for predicting formation damage from crossflow, and aids water-shutoff decisions.

In an accompanying paper, McCartney et al. (2012) describe how PW analyses from the MRT are interpreted to determine— among other parameters—the amount of water produced from each zone (water allocation) at each of the test rates during an MRT. In this paper, the methods of analyzing these results in combination with separator-test data are described with the aid of a field example to demonstrate how they provide detailed information about the downhole conditions and zone properties of the well. On the basis of the analysis, a set of well interventions was recommended. Following confirmation of the principal MRT results by a PLT, some of the recommended interventions have been performed successfully. Experience from Veslefrikk suggests that MRTs can be considered as a possible replacement for running PLTs or as an additional source of data that can be acquired more frequently.
A Dynamic Model of Percolating Gas in a Wellbore
Authors: Hauge E.. , Stamnes Ø.N.. N. , Aamo O.M.. M. , Godhavn J.-M.. -M.
Published: November 2012

The two-phase dynamics of gas percolating up a vertical well filled with water is described by two ordinary-differential equations and algebraic relations. We model the gas as bubbles distributed with a distribution function along the well. The model is based on first principles and accommodates tracking of the front of the gas. An unscented Kalman filter (UKF) is used together with the model and wired-drillpipe (WDP) pressure measurements to estimate the liquid-holdup profile as the gas is circulated out of the well. The performance of the model and the method of estimation are compared with results from a state-of-the-art simulator.
A Novel Tool To Improve the Rate of Penetration–Hydraulic-Pulsed Cavitating-Jet Generator
Authors: Fu J.. , Li G.. , Shi H.. , Niu J.. , Huang Z..
Published: November 2012

On the basis of the analysis of the jet-modulating mechanism, a novel tool—a hydraulic-pulsed cavitating-jet generator (HPCJG)— is designed to further improve the rate of penetration (ROP). The HPCJG combines the advantages of a pulsed jet and a cavitating jet. When the drilling fluid flows through this tool, the fluid will be modulated to the pulsed and cavitating jet by application of the impellers and by entering into the self-resonant chamber. During this process, a pulsed cavitating jet is formed at the outlet of the bit nozzle. Because of jet pulsation, cavitating erosion, and the local negative-pressure effect, the cleaning efficiency of the well-bottom cuttings and the ROP will be improved. Laboratory and oilfield tests have indicated that the pulsed-pressure amplitude and the pressure drop of the generator increase with the increase of the flow rate. However, the frequency of the pressure pulsation is invariable in this process. This generator has been applied to more than 100 wells in eight oil fields throughout China. The results show that the maximum density of the test drilling fluid is 1.93 g/cm3, the maximum test-well depth is 6162 m, and the operation time of the generator is more than 230 hours (the maximum operation time recorded was more than 520 hours). Furthermore, the average ROP was increased by approximately 16.7% to 104.4%. In conclusion, the generator has the characteristics of a simple structure, has a long lifetime, is able to adapt well with existing drilling equipment, and can provide a safe and efficient drilling technique for deep wells.
Geostatistical Population-Mixture Approach to Unconventional-Resource Assessment With an Application to the Woodford Gas Shale, Arkoma Basin, Eastern Oklahoma
Authors: Olea Ricardo A. , Charpentier Ronald R. , Cook Troy A. , Houseknecht David W. , Garrity Christopher P.
Published: November 2012

Evaluation of resources such as tight sands and gas shales requires the formulation of assessment models that are different from those used for the inference of conventional resources. Formulations in present use are based in classical statistics that ignore the partly organized and partly random geographical variation of attributes related to the occurrence of hydrocarbons. This paper is the third in a series of methodological tests aimed at enhancing the assessment of unconventional resources through more-effective use of implicit and explicit information contained in the data, moreaccurate evaluation of resources, and more-informative display of results. Reprocessing of estimated-ultimate-recovery (EUR) data at the Woodford gas shale in Oklahoma shows that subdivision of the play into areas as homogeneous as possible can produce results comparable to those obtained using several variables correlated to local productivity.
Definitive Petrophysical Evaluation of Thin Hydrocarbon Reservoir Sequences
Authors: Majid Azlan A. , Worthington Paul F.
Published: November 2012

The petrophysical evaluation of thinly-bedded sand/shale sequences is strongly dependent on the way in which layered and dispersed shales are taken into account. There are two underpinning issues: the recognition of thin bed geometries and the estimation of shale content from lithology logs. The first of these is managed through a scenario approach, whereby different downhole scenarios are set out according to specified ranges of bed thickness. Each range has its own interpretation protocol. The second issue relates to the inherent overestimation of clay-mineral volume fraction by shale indicators and its impact on the petrophysical evaluation of thinly-bedded sand porosity. This shortcoming is managed by applying a validated scaling factor to log-derived estimates of shale volume fraction so that these become workable estimates of clay-mineral fraction for the porosity evaluation of sand layers. Both these problems become more acute for thinner beds. These two key issues are addressed conjunctively through interpretive workflows, each of which relates to a discrete range of bed thickness and uses fit-for-purpose petrophysical data sets. In particular, the multicomponent induction log is adopted as a pivotal technology for the evaluation of sand resistivity within thinly-bedded sand/shale sequences. The objective is to achieve a sound petrophysical interpretation for each downhole situation. Therefore, groundtruthing through core data is advocated where this allows the shale problem to be managed better. The outcome is a systematic approach to thin-bed evaluation, based on prescribed data inputs that optimize project effectiveness. The benefits are illustrated through case histories that demonstrate a securable upside in projected hydrocarbon volumes.
Increasing Hard Winter Wheat Yield Potential via Synthetic Hexaploid Wheat: II. Heritability and Combining Ability of Yield and its Components
Authors: Cooper Jessica K. , Ibrahim Amir M. H. , Rudd Jackie , Hays Dirk , Malla Subas , Baker Jason
Published: November 2012

Introgression of new genes through crosses to synthetic hexaploid wheat [Triticum turgidumL. subsp.durum(Desf.) Husn. (syn.Triticum durumDesf.) ×Aegilops tauschiiCoss.] could contribute to the improvement of winter wheat (Triticum aestivumL). The purpose of this research was to explore the heritability of traits and combining ability of synthetic wheat in Texas. Ten elite primary synthetics from the International Maize and Wheat Improvement Center (CIMMYT), screened for desirable traits, were backcrossed to two Texas cultivars, ‘TAM 111’ and ‘TAM 112’. Heritability of traits and combining ability of genotypes for traits related to yield were determined in the BCF4and BCF5populations across five Texas locations in 2009 and 2010, respectively. Heritability estimates differed across locations. Single‐seed weight was the most heritable trait whereas yield was the least heritable trait. Primary synthetics that produced progeny superior to TAM 111 or TAM 112 were identified. Synthetics with high combining ability for yield also had high combining ability for head number or seed per head. This study suggests improved yield could result from selecting for increased seed per head in lines derived from synthetic populations.
Genomewide Selection versus Marker‐assisted Recurrent Selection to Improve Grain Yield and Stover‐quality Traits for Cellulosic Ethanol in Maize
Authors: Massman Jon M. , Jung Hans‐Joachim G. , Bernardo Rex
Published: November 2012

Genomewide selection (GWS) is marker‐assisted selection without identifying markers with significant effects. Our previous work with the intermated B73 × Mo17 maize (Zea mays L.) population revealed significant variation for grain yield and stover‐quality traits important for cellulosic ethanol production. Our objectives were to determine (i) if realized gains from selection are larger with GWS than with marker‐assisted recurrent selection (MARS), which involves selection for markers with significant effects; and (ii) how multiple traits respond to multiple cycles of GWS and MARS. In 2007, testcrosses of 223 recombinant inbreds developed from B73 × Mo17 (Cycle 0) were evaluated at four Minnesota locations and genotyped with 287 single nucleotide polymorphism markers. Individuals with the best performance for a Stover Index and a Yield + Stover Index were intermated to form Cycle 1. Both GWS and MARS were then conducted until Cycle 3. Multilocation trials in 2010 indicated that gains for the Stover Index and Yield + Stover Index were 14 to 50% larger (significant at P = 0.05) with GWS than with MARS. Gains in individual traits were mostly nonsignificant. Inbreeding coefficients ranged from 0.28 to 0.38 by Cycle 3 of GWS and MARS. For stover‐quality traits, correlations between wet chemistry and near‐infrared reflectance spectroscopy predictions decreased after selection. We believe this is the first published report of a GWS experiment in crops, and our results indicate that using all available markers for predicting genotypic value leads to greater gain than using a subset of markers with significant effects.
Genetic Analysis of Visually Scored Orange Kernel Color in Maize
Authors: Chandler Kristin , Lipka Alexander E. , Owens Brenda F. , Li Huihui , Buckler Edward S. , Rocheford Torbert , Gore Michael A.
Published: November 2012

Increasing levels of provitamin A carotenoids in maize (Zea mays L.) grain through plant breeding has potential to help humans suffering from vitamin A deficiency. In parts of Africa where this deficiency is prevalent, there is a consumer preference for white maize grain and an avoidance of yellow maize grain. White grain has minimal levels of carotenoids whereas yellow grain can have appreciable levels of carotenoids. There is a new effort to introduce orange maize that contains high levels of provitamin A, which appears to be a more acceptable color than yellow to consumers in Africa. The implementation of this program requires backcross selection to convert African‐adapted germplasm with white grain to orange. We conducted a study to assess the heritability of visual scores for relative intensity of orange kernel color and identify genetic markers associated with orange color across and within 10 families of the maize nested association mapping population. We found visually scored kernel color to have a moderately high heritability and identified five common quantitative trait loci (QTL) and six rare QTL for intensity of orange color. Notably, half of them coincided with carotenoid biosynthetic genes. Our results indicate that breeders in Africa, Asia, and throughout the world would have flexibility to select for orange kernel color visually and/or with gene‐specific markers. Such selection can be combined with marker‐assisted selection efforts to increase provitamin A levels in maize grain.
Potential of Genomic Selection for Mass Selection Breeding in Annual Allogamous Crops
Authors: Yabe Shiori , Ohsawa Ryo , Iwata Hiroyoshi
Published: November 2012

Mass selection is an important method for genetic improvement of allogamous crops. It is nevertheless inefficient mainly because of the inaccuracy of single‐plant evaluation. Genomic selection (GS) based on whole‐genome markers might improve mass selection efficiency. Our objective was to assess the potential of mass selection with GS for the genetic improvement of an annual allogamous crop population under various conditions. Allogamous crops often have low levels of linkage disequilibrium. Therefore, we assumed linkage equilibrium in an initial breeding population and conducted simulations to compare GS with phenotypic selection (PS) and conventional marker‐assisted selection (MAS) and to evaluate the impact of changing various features of GS breeding. We also evaluated the genetic gain per unit cost for GS and PS breeding. Results show that GS resulted in higher genetic gain than either PS or MAS. The mode of inheritance of markers made only a small difference. Genomic selection with a larger population size and more cycles attained higher genetic gain except when the population size was as small as 50. The cost efficiency of GS was higher than that of PS with identical population size when the genotyping cost was lower than about one‐fourth of the phenotyping cost. Genotyping costs are decreasing rapidly. Therefore, GS is anticipated as an important breeding method to support mass selection of allogamous crops.
Preceding Crops Affected Soybean Iron‐Deficiency Chlorosis and Vesicular‐Arbuscular Mycorrhizal Fungi in Soybean Cyst Nematode‐Infested Fields
Authors: Chen Senyu , Kurle James E. , Sun Manhong , Naeve Seth , Wyse Donald L. , Stahl Lizabeth A.
Published: November 2012

Iron‐deficiency chlorosis (IDC) and soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) are important factors limiting soybean [Glycine max (L.) Merr.] yield. Vesicular‐arbuscular mycorrhizal fungi (MF) are generally beneficial to crops. The effect of preceding crops with known variation in MF colonization was tested in two SCN‐infested fields in Waseca and Lamberton in Minnesota to determine the effect of MF and other soil biotic and abiotic factors on IDC. No crop effect on soybean yield was detected. There was no difference in SCN population density following nonhost crops at Lamberton, but sunn hemp (Crotalaria juncea L.) resulted in lower SCN population density than corn (Zea mays L.) at Waseca. Chlorosis rating and colonization frequency of soybean roots by MF were lowest following canola (Brassica napus L.) and sugar beet (Beta vulgaris L.), the two nonmycorrhizal crops. Soybean had lowest number and weight of N‐fixing nodules following soybean, highest following corn, and intermediate following other crops. Iron‐deficiency chlorosis was positively correlated with MF and negatively correlated with nodulation and soil Fe at both sites. The correlations of SCN, other soil elements, and soil penetration resistance with IDC were either insignificant at both sites or inconsistent across the sites. No consistent correlation of soil factors with MF was detected. This study suggests that a causal relationship between MF and IDC might exist, but it requires further exploration.
Effects of Row Spacing, Seeding Rate, and Planting Date on Establishment of Switchgrass
Authors: Foster Jamie L. , Guretzky John A. , Huo Chengjun , Kering Maru K. , Butler Twain J.
Published: November 2012

Switchgrass (Panicum virgatum L.) has been identified as a potential biomass crop for marginal cropland, but establishment can be problematic. In Exp. 1, treatments (seeding rate and row spacing) were arranged as a randomized complete block in a split‐plot design with four replicates in which the main plot treatment was row spacing (17.8, 35.6, 71.1, or 88.9 cm) and the subplot treatment was seeding rate (1.12, 2.24, 3.36, or 4.48 kg pure live seed [PLS] ha−1). In Exp. 2, treatments (seeding rate and planting date) were arranged as a randomized complete block in a split‐split‐plot design with four replicates in which the main plot treatment was planting date (September, February, or May), the subplot treatment was switchgrass ecotype (upland ‘Cave‐in‐Rock’ or lowland ‘EG1101’), and the sub‐subplot was seeding rate (2.24, 4.48, 6.72, 8.96, or 11.20 kg PLS ha−1). In Exp. 1, row spacing did not affect seedling density, but switchgrass at the widest row spacing (88.9 cm) produced the least dry matter (DM) yield during the establishment year. However, row spacing had no effect on DM yield after the establishment year. In Exp. 2, increasing seeding rate increased seedling density but had no effect on DM yield. In addition, seedling density was greatest for both ecotypes planted in September; however, February‐ and May‐planted EG1101 produced the greatest DM yield. While upland switchgrass may be successfully planted in autumn in the southern Great Plains, lowland switchgrass should be planted only in the spring because of seedlings’ susceptibility to freezing.
Genetic Relationships in Zoysia Species and the Identification of Putative Interspecific Hybrids Using Simple Sequence Repeat Markers and Inflorescence Traits
Authors: Kimball Jennifer A. , Zuleta M. Carolina , Kenworthy Kevin E. , Lehman Virginia G. , Harris‐Shultz Karen R. , Milla‐Lewis Susana
Published: November 2012

Zoysia Willd. are warm‐season turfgrasses used throughout the southern United States and upward into the transition zone for their superior heat and drought tolerances and their relatively low input requirements. Understanding the population structure present within Zoysia germplasm can assist plant breeders in exploiting available variation. The objectives of this study were to assess simple sequence repeat (SSR) allelic diversity within and among Zoysia spp., evaluate the genetic constitution of putative interspecific hybrids, and determine if Zoysia spp. and hybrids can be differentiated by inflorescence traits. Sixty‐two Zoysia accessions selected as a subset of genotypically and phenotypically diverse genotypes were evaluated with 50 SSR markers and six inflorescence traits. Both an unweighted pair group method with arithmetic averaging (UPGMA) phylogram and principal coordinate analysis (PCO) analysis revealed a continuum of genetic variation present within and among the species. The model‐based program STRUCTURE revealed two distinct subpopulations within Z. japonica Steud. as well as a distinct Z. matrella (L.) Merr. subpopulation. Based on SSR analysis, 23 Zoysia accessions evaluated had evidence of admixture. Six inflorescence phenotypes also revealed a continuous range of variation. This study was able to verify the presence of hybrids between Z. japonica and Z. matrella and provided further evidence for the hypothesis that Zoysia spp. are subpopulations or ecotypes within one species and not separate species.