bluuebunny/crossref_metadata_2025 huggingface dataset:
Drilling and Completing Deep Gas Wells in Sabalo Field, Bolivia - Lessons Learned
Authors: Cunha J. C. , Passarelli R. , Venancio J.
Published: December 2007

Sabalo Field is located in the south of Bolivia in the Sub-Andean Region. It is a giant gas field that just recently started its development. The wells in Sabalo field demanded careful planning not only due to the high depth of the wells, but also due to the fact that its completion should be done in order to handle massive gas production (more than 2.5 MM cubic meters per day) from multiple zones. Another factor that lead to special care during the planning phase was the experience from previous wells in the area that indicated complex drilling operations with frequent reports of stuck pipe, fishing jobs, sidetracks and gas kicks due to abnormally pressurized zones.

This paper shows details of well program, operation follow-up procedure and new technologies introduced in the area in order to improve the efficiency of the operations and reduce costs of field development.
3D Analysis and Prediction of Microseismicity in Fracturing by Coupled Geomechanical Modeling
Authors: Settari A. , Sullivan R. B. , Walters D. A. , Wawrzynek P. A.
Published: December 2007

Microseismic monitoring is widely used for mapping fractures but the fracture dimensions are only inferred from it. This paper presents a 3-D analysis to relate the seismic events and fracture geometry. The method is based on continuum geomechanical modeling and shows that the poroelastic as well as thermal stresses are the key to explaining the characteristic pattern of events recorded in the Cotton Valley waterfracs. The method provides a tool for relating the geometry of the fracture to the microseismic image. The analysis shows that events can occur ahead of fluid and also suggests possibility of recorded events far from the fracture.
Flow Test Validation of Direct Measurement Methods Used to Determine Surface Roughness in Pipes (OCTG)
Authors: Farshad Fred F. , Rieke H. H. , Mauldin Charlie
Published: December 2007

The impact of applying advance metrics technology in quantifying circular pipe surface roughness insures precise and cost effective piping designs for the chemical and petroleum industries. Flow test validation of the results from the Dektak3 ST Surface Profiler® and the Hommel Tester T 1000® was performed in order to warranty that such metrics technology could quickly and effectively substantiate the effects of surface pipe roughness on friction pressure losses, and energy characteristics.

The metrics test set consisted of nine joints of 2-7/8-inch OD, chrome 13 tubular pipe sections having varying internal diameters that consists of: (1) plastic coated (IPC 800) tube; (2) electropolished Cr13 with heavy metal removal; (3) electropolished Cr13 with moderate metal removal; (4) four electropolished Cr13 samples with low metal removal; (5) mill finished Cr13 descaled by garnet blasting; and (6) mill finished Cr13 chemically descaled tube, no electropolish. The Mechanical and Fluids Engineering Department of Southwest Research Institute (SwRI) tested the pipes for the purpose of measuring pressure drop, and thereby evaluating the friction factor created by wall surface roughness in each pipe. Each section were prepared and tested for surface roughness according to the DIN 4768 (Deutsches Institut für Normung C.V.) specification using Dektak3 ST Surface Profiler® and the Hommel Tester T 1000® at the University of Louisiana. Friction-factor test results using profiling instruments with those derived from the measured flow results using the Southwest Research Institute's flow facility validated test results as predicted by the Moody and Colebrook-White equations.
Effect of Mobility Ratio on the Pressure and Pressure Derivative of Wells in Closed Composite Reservoirs
Authors: Boussalem Rachid , Tiab Djebbar , Escobar Freddy H.
Published: December 2007

The presence of anomalies in a reservoir, such as faults or change in rock and fluid properties significantly affects the wellbore pressure behavior. An accurate reservoir description of heterogeneous reservoirs, such as a closed composite reservoir, is critical for optimizing the hydrocarbon recovery. Well test analysis provides the best technique for determining the permeability of different zones of the composite system, the skin factor, the pore volume of the inner region and the drainage area1.

The first type curves generated for a composite reservoir model appared in the literature in the early 1970s. Although these type curves were widely used for a period of time, some difficulties were found in using them. For example, the same match can be obtained on different dimensionless wellbore storage values. However, type curves were used as the basic mathematical model for several developments. Other investigations regarding the composite resevroir model with different types of applications were conducted, such as the effect of phase segragation, mobility contrast and conductivity ratio. Some researchers have mentioned the potential applications of reservoirs with a fluid bank and a burning front2-5.

In this paper an analytical model has been developed for a closed composite system. This model was validated by the numerical model already exist in the literature. An extension of conventional method and the Tiab’s Direct Synthesis technique6 are presented for a closed composite reservoir on the basis of the proposed analytical model. The effect of the mobility ratio, and radius ratio, on the pressure response has been thoroughly investigated.

A dual porosity behavior confirming the sugar-cube model is observed during the transition period for a high mobility contrast. Three important equations are derived and presented in this study: (1) An equation describing the pseudo-steady-state flow regime observed at the fingerprint of dual porosity behavior, (2) An equation describing the starting time of the pseudo-steady-state flow regime observed at the fingerprint of the dual porosity behavior, (3) An equation for the pseudo-steady-state flow regime governing the boundary effect. The formulated interpretation techniques have been tested on field cases and reasonable results have been obtained
Downhole Deployment Valve Addresses Problems Associated with Tripping Drill Pipe During Underbalanced Drilling Operations
Authors: Herbal Steve , Grant Rod , Grayson Brian , Hosie Dave , Cuthbertson Bob
Published: December 2007

Underbalanced Drilling (UBD) is becoming more widely used and accepted because of the many benefits it provides such as: Limitations to the formation damage common in regular overbalanced drilling.Increased rates of penetration.Increased production rates and in some cases production while drilling which can provide early cash flow and enhance economics.

However with these advantages come some drawbacks, the chief among which is the safety of the operation while tripping the drill pipe into and out of the well.

Since the well is allowed to flow in traditional UBD operations a flowing or shut in pressure results in the well. Any significant pressure at surface requires that special precautions be taken during tripping operations to control formation pressure. Several techniques can be used among which are: Killing the well, this provides for safe tripping but can obviate the very reason for using UBD - formation damage can result.Flowing the well, this can lead to a dangerous situation if a sloughing formation forms a temporary bridge in the annulus.A Snubbing unit can be employed, this enhances safety but can add considerably to the operational cost.

It is clear that a better and safer method is needed, since all the above carry disadvantages, and to this end a new method involving a downhole valve was conceived. In this approach a full opening valve which can be closed below the drill string while tripping, is deployed downhole below the "pipe light" depth and operated from surface by way of a hydraulic control bundle.

This paper will review the concept of the Downhole Deployment Valve (DDV), its design and operation. The authors will go on to provide details of the first field trial of the a 7" 26lbs/ft full opening valve in a multilateral well which was drilled underbalanced in the James Lime play in East Texas/Northwest Louisiana. They will conclude that this device can provide major enhancement to a UBD operation without in any way compromising its advantages.
A New Method of Calibrating Wireline Logs with Carbonate Core Measurements to Recognize Pay Zones
Authors: Weiss W. W. , Gottumukkala V. , Balch R. A.
Published: December 2007

Defining the initial water saturation in a dolomite reservoir in SE New Mexico was problematic and resulted in questions about possible oil left behind pipe after development. The application of Archie's equation was particularly suspect because of the variation in the resistivity of connate water samples.

Cores and logs were available from six wells in the Dagger Draw field and showed intersititial, fractured and vuggy porosity. A global prioritizing technique called fuzzy ranking was used to select log tracts to correlate with core measurements.

Selected log tracts then served as inputs to a neural network to develop multivariate correlations with the core measurements. The cores defined bulk volume oil, bulk volume gas, bulk volume water and aspect ratio. The focus of this paper is the estimates of bulk volume oil.

Optimal neural network architectures were developed for each of the six available well datasets. All architectures were designed to maintain a ratio of neural network weights to samples ratio less than 0.5.

Each network was blind tested against the remaining five datasets. One of the datasets with 200 whole core measurements was found to be particularly robust and was used to generate BVO logs in fourteen partially cored and uncored wells in the field.

The statistical properties sum, average, and standard deviation calculated with the BVO logs correlated with the initial oil-producing rate. Thus a new method to recognize behind pipe pay zones in a dolomite/carbonate reservoir and estimate the first years oil-producing rate was developed. The method has particular utility in finding bypassed pay for recompletion projects.
Advances in the Prediction and Management of Elemental Sulfur Deposition Associated with Sour Gas Production from Fractured Carbonate Reservoirs
Authors: Hands Nicholas , Oz Bora , Roberts Bruce , Davis Paul , Minchau Mike
Published: December 2007

Shell Canada has experienced significant deposition of solid sulfur during the production of dry sour gas from several of its deep carbonate pools located in Southern Alberta. In several cases, wells have become completely plugged with sulfur in the reservoir within several months. Accurate prediction and effective management of the sulfur deposition are crucial to the economic viability of these fields.

A new analytical model has been developed for predicting sulfur deposition associated with sour gas production in naturally fractured reservoirs. Key features of the model include incorporation of reservoir temperature profiles and the concept of critical velocity, which accounts for dynamic effects, resulting in a zone of reduced deposition close to the wellbore.

The model has been used to successfully match and predict sulfur deposition in several sour gas producers. The modeling results have been used as a design basis for downhole sulfur treatments and clean-out operations, the optimization of well completions and off-take rates to minimize the impact of sulfur deposition, and the development of new well designs and operating strategies for sulfur producers.
In-Situ Permeability Anisotropy vs. Depth in a Fluvial Sandstone Reservoir Using a Multiprobe Formation Tester
Authors: Domzalski S. , Boydell W. G. , Pop J. J. , Hadbi A.
Published: December 2007

This paper presents a case history from an Algerian fluvial sandstone oil reservoir where near to 60 in-situ measurements of permeability anisotropy, Kv / Kh, were obtained by running vertical interference tests (VITs) with a multiprobe formation tester during openhole (OH) logging operations. The formation tester, configured with four probes and a recyclable constant rate flow module performed VITs on an average 10 stations per well for several key wells in the field. The spatial displacement of the probes along the wellbore at each test station enabled simultaneous overlapping measurements of permeability anisotropy on 0.70 meter and 3 meter length scales (similar to vertical grid block sizes used in field reservoir simulators). These measurements provided Kv / Kh ratios in homogeneous "clean" sections of sedimentary units and information on sealing properties through the determination of the effective Kv / Kh of tight streaks, shales, laminations and "dirty" sections straddled by the probes.

The various steps in the data acquisition chain are discussed, including the prejob VIT feasibility simulation runs and the choice of modules for the formation tester tool. Also described is the onsite decision-making process for choosing VIT stations based on the petrophysical and geological imaging wireline logs and classic formation tester pretest data. On-site quick-look data interpretation and subsequent interpretation results of several VIT stations along with core-derived values averaged over the VIT measurement scale are presented.

With careful job planning and execution the case history shows that it is possible to obtain multiple in-situ permeability anisotropy measurements in a geologically consistent manner during OH logging operations.
CO2 Enhanced Gas Recovery Studied for an Example Gas Reservoir
Authors: Clemens Torsten , Wit Krijn
Published: December 2007

In the wake of the Kyoto protocol, CO2 emission reduction to control the level of CO2 in the atmosphere has become an important goal. One possibility of reducing greenhouse gas emission is to separate and inject CO2 from gas fired power plants into gas fields.

To investigate the effects of CO2 injection on methane recovery, five different CO2 injection strategies were investigated for an example gas reservoir. The injection scenarios included installation of a Zero Emission Power Plant (ZEPP) at surface, supplying the reservoir with a constant CO2 rate over 25 years.

Installation of a ZEPP enabled using a lower tubing head pressure than for gas delivery to the gas distribution grid resulting in accelerated methane production. For most of the cases investigated, the cumulative methane production was increased as well. CO2 breakthrough occurred between 3 and 15 years. The CO2 which was produced in the production wells was fed into the ZEPP and re-injected with the newly generated CO2.

The highest incremental gas recovery was obtained for the case of conventional depletion of the gas reservoir until abandonment and subsequently injection of CO2, leading to enhanced gas recovery. The maximum incremental gas recovery was about 10 % of Gas Initially In Place (GIIP). For the case of injection of CO2 early in the life of the gas field, the methane recovery was decreased compared with conventional gas production by depletion.
Drilling Parameter Selection for Well Quality Enhancement in Deepwater Environments
Authors: Kravis S. , Irrgang R. , Phatak A. , Martins A. , Nakagawa E.
Published: December 2007

The study of overall well quality is a neglected area of the industry. Aspects such as formation damage, drilling interactions, and hole rugosity tend to be treated separately in the literature. This paper describes a software tool that uses stored well data and drilling experiences to produce an overall set of well quality metrics that facilitate the assessment of drilling and completion performance in a given field. The tool is particularly useful for risk assessment when drilling complex trajectories and for improving the design of new deepwater wells.
Modeling, Simulation and Comparison of Models for Wormhole Formation During Matrix Stimulation of Carbonates
Authors: Panga Mohan K. R. , Balakotaiah Vemuri , Ziauddin Murtaza
Published: December 2007

A new averaged/continuum model is presented for simulation of wormhole formation during matrix stimulation of carbonates. The model presented here differs from existing literature models in three fundamental aspects. First, we show that the dissolution process creates a Darcy velocity field with non-zero divergence. Second, we use two concentration variables to account for the local gradients at the pore level caused by the coupling between the flow, species diffusion and chemical reaction. Third, we account for both the asymptotic/diffusive and convective contributions to the local mass transfer coefficient between the fluid and solid. We argue that models that do not account for these effects do not retain the qualitative features of the reactive dissolution process and hence cannot be predictive. The averaged model developed here accounts for pore level physics by coupling the local pore scale phenomena to the macroscopic variables (Darcy velocity, pressure and reactant cup-mixing concentration) through the structure-property relationships (permeability-porosity, average pore size-porosity and interfacial area-porosity), and the dependence of the fluid-solid mass transfer coefficient and fluid phase dispersion coefficient on the evolving pore scale variables (average pore size and local Reynolds and Schmidt numbers).

A preliminary analysis of the model is presented and the influence of various factors on flow channeling is examined using the new model. The model predictions are compared with the available laboratory data.
Produced Water Regulations in the United States: Then, Now and in the Future
Authors: Caudle Dan D.
Published: December 2007

The discharge of produced water into surface waters has been regulated since the late 1960's. The regulations prohibit discharge of any water that would cause permanent harm to the environment and sets limits on waters that are discharged based on best available technology for removing regulated contaminants. The United States is subdivided into categories under United States Environmental Protection Agency (EPA) regulations. Discharge limits in the subcategories range from no discharge to surface waters to discharges limited by toxicity and oil content. Discharge limits are determined by available technology for controlling toxicity and oil and grease.

This paper reviews the development of the guidelines and limits on produced water discharges and the technology to meet the regulatory limits for each category. It also discusses the problem of new exploration areas that might not fit into a one of the existing categories. As the exploration production industry advances, it is moving into areas such as very deep water that may have different technology constraints than those addressed by past regulations. Currently each subcategory has limits determined by technology appropriate to that subcategory. If future exploration areas do not fit into a recognized category, what should be done? For example, in very deep water, is a new subcategory needed with limits appropriate to water treating technology that can be economically applied in that environment?
Numerical Simulations of NMR Responses for Improved Interpretations of NMR Measurements in Reservoir Rocks
Authors: Øren P. E. , Antonsen F. , Rueslåtten H. G. , Bakke S.
Published: December 2007

We reconstruct the three-dimensional (3D) microstructure of Fontainebleau sandstone samples of different porosities by a process-based reconstruction method. Permeabilities of the reconstructed media are computed by solving the Stokes equations, while the formation factors are computed by solving a Laplacian equation. Nuclear Magnetic Resonance (NMR) responses are determined by a random walk simulation, and the results are compared with experimental data. Permeabilities estimated from commonly used NMR correlations are compared with the computed permeabilities. The comparison shows that the accuracy of the NMR-derived permeabilities can be improved significantly by accounting for tortuosity effects and variations in surface relaxivity.
Knowledge Discovery in Databases and Multiphase Flow Metering: The Integration of Statistics, Data Mining, Neural Networks, Fuzzy Logic, and Ad Hoc Flow Measurements Towards Well Monitoring and Diagnosis
Authors: Alimonti C. , Falcone G.
Published: December 2007

The usual approach to the interpretation of producing wells is based on mechanistic models for the simulation of steady state and transient flow regimes. However, there are significant reservations about convergence problems, computational limits, the need for extensive tuning on field data, the instability of boundary conditions, the limited applicability of existing multiphase flow models, and the uncertainties associated with choke valve models. The current industry standards are critically reviewed within this framework.

The real-time monitoring of producing wells is recognised as the best way of optimising field performance. Monitoring a producing well implies the ability to track, in real-time, any changes in fluid composition, flow rates, or pressure and temperature profiles. Multiphase Flow Metering (MFM) plays a key role in this scenario. Such information, combined with the critical analysis of historical data from the well itself or from analogue wells, allows diagnosis of the system and prediction of future trends. However, field data per se ’ do not necessarily generate knowledge. This is particularly true for large databases, which are difficult to manipulate to provide suitable inputs for wellbore simulators.

This paper suggests how MFM, Knowledge Discovery in Databases (KDD) and Fuzzy Logic (FL) can offer an alternative approach to the analysis of producing wells. KDD is the automated extraction of patterns representing knowledge implicitly stored in large information repositories. Distributed, ad-hoc field measurements (including MFM and downhole measurements) can be processed via data cleaning, data integration, data mining, artificial intelligence, and pattern evaluation. FL can then manage the resulting information in terms of flow assurance and production optimisation.

The same techniques can also be extended to the reservoir and the production network, for an integrated approach to production system analysis.
Relative Permeability Modifier and Scale Inhibitor Combination in Fracturing Process at San Francisco Field in Colombia, South America
Authors: Castano R. , Villamizar J. , Diaz O. , Avila M. , Gonzalez S. , Dalrymple E. D. , Milson S. , Everett D.
Published: December 2007

Water production in the San Francisco field in Colombia is characterized by a severe carbonate scaling tendency, particularly in the lower Caballos zone. Following several fracture stimulation treatments which incorporated RPM (Relative Permeability Modifier) in San Francisco field, it was observed that, although the RPM decreased the anticipated water production, there was an undesirable effect in regard to scaling problems. Some wells ended up losing a portion of the increased production which had been gained by using the RPM fracturing process. This decrease in production was attributed to carbonate scaling after the wells were back on production for several months.

A well candidate was chosen (San Francisco 60) and laboratory flow tests were performed in representative cores to determine if a detrimental impact would occur in regard to the ability of the RPM to function properly when the scale inhibitor was part of a combined treatment. Based on these results, a combined fracturing treatment which incorporated a water reduction agent (RPM) in combination with a scale inhibitor was performed in the SF 60 well. To our knowledge, this was the worlds first combined application of an RPM and scale inhibitor in a hydraulic fracture treatment. Further, this new systematic approach to two very difficult problems yielded excellent results: Following the treatment, the well increased production by almost 10 fold while at the same time, water cut was reduced by 30%. This procedure reduced the cost of water management and associated scaling problems, which had been common in this field. This new system has created many more fracture stimulation opportunities which in the past had not been considered economically attractive.

The work described in this paper is the result of a true team effort (operator/Service company) and describes the focus in solving several production problems (as experienced in San Francisco field) which resulted in a multi-purpose treatment. The net result of the method developed is fewer required stimulation/workover jobs while maintaining the same or increased hydrocarbon production, and less water (which also translates into lower lifting costs).

This paper will present the following:

Data illustrating the type of production problems being experienced in the San Francisco field The results of approaching the water production issues and scaling tendencies individually The laboratory evaluation techniques and data obtained when combining the individual treatments into a "system" The resulting "job design," treatment, and production response when the combination stimulation/water control/scaling treatment was actually put into practice.
Chemical and Physical Characterization of Aphron-Based Drilling Fluids
Authors: Ivan Catalin D. , Growcock Frederick B. , Friedheim James E.
Published: December 2007

The depleted reservoirs in many of the world's mature fields contain hidden problems that can make further development unprofitable. Some zones are typified by water-wet sands that frequently trigger costly seepage losses and differential sticking. Others are characterized by laminated sand and shale sequences, which create the conditions for slow, dangerous and unduly expensive drilling when conventional rig equipment is used. If operators turn to underbalanced drilling as an alternative, the extra time and equipment required for safe operation can seriously degrade project economics in some applications.

Aphron-based systems are engineered drilling-fluids that aid in well construction by controlling losses in depleted, high-permeability sands while stabilizing pressured shales. One of the more attractive features of an aphron-based system is that it does not require any of the extra equipment used in air or foam drilling. There are no compressors, high-pressure hoses or connections to add costs and safety concerns. The system uses conventional fluid-mixing equipment to form tough, flexible micro-bubbles.

Once formed, these micro-bubbles, or "aphrons," differ from the bubbles produced in air or foam drilling in two significant ways. First, aphrons resist coalescence into larger bubbles. The aphrons are attracted to lower-pressure regions in the formation but remain discreet from each other, forming a strong network of individual micro-bubbles. Second, aphrons are tough and stable. They are comprised of a core of air surrounded by layers of a proprietary polymer and a tensoactive additive.

The authors will detail the chemical and physical characteristics of aphron-based drilling fluids that make them uniquely qualified to solve some operational problems.
Pollut-Eval: An Innovative Tool for Direct Hydrocarbon Characterization in Oil Base Mud & Cuttings
Authors: Benoit Yves , Dalmazzone Christine , Audibert-Hayet Annie
Published: December 2007

Throughout the world, the drilling process generates a huge variety of contaminated solid waste. The environmental impact of these side products depends on their composition and concentration but also on the employed drilling technologies, based on water base mud (WBM) or oil base mud (OBM).

The various local and international Guidelines will gradually ban the discharge into the sea of these contaminated drilling waste.

The OSPAR 2000/3 decisions will soon prohibit their disposal into the sea and will recommend a "zero %" discharge of organic based drilling fluids.

With the emphasis placed on environmental safety, the oil companies are developing economical methodologies to clean oil contaminated field waste, such as cuttings or used drilling muds. One of the major challenge is to develop sensitive analytical tool to measure in a short time low oil content in a great variety of mineral matrix without major interference.

In this framework, this paper provides answers concerning the problem of quantification of low oil content in complex solid waste. A study has been performed to demonstrate the ability of the Pollut-Eval method to characterize and quantify hydrocarbon contamination without any pretreatment. In a first step, analytical results of pure hydrocarbon cuts commonly used in drilling muds (iso and n-paraffin, α olefin, ester and diesel cuts) will be presented to demonstrate the qualitative and quantitative efficiency of the method.

In a second step, evaluation of the total organic content of various drilling muds will be compared to their hydrocarbon concentration to demonstrate that no major interference occurred in the characterization or quantification of these petroleum cuts despite the various and complex mud formulations. In a last step, Pollut-Eval residual oil content (ROC) and total organic carbon (TOC) of undersea discharged cuttings sampled at 200 m depth (more or less distant from an offshore rig) will be presented and compared to capillary gas phase chromatography results.

As a conclusion, Pollut-eval performance will be discussed and compared to other methods commonly used in oil industry: global carbon organic determination by catalytic oxidation and retort kit distillation.
Standoff Compensation and Hole Size Correction of a New LWD Density/Neutron Logging System
Authors: Mickael M. , Jones D. , Phelps D.
Published: December 2007

A new LWD porosity logging system has been developed that addresses specific issues related to the repeatability and accuracy of porosity measurements while drilling. This system provides density and neutron porosity measurements at penetration rates up to 400 ft/hr with the precision and accuracy of an equivalent wireline tool. Designed to operate in the offshore deepwater and ultra-deepwater environment, system specifications include operating pressures up to 30,000 psi. The system is designed to reduce standoff effects on the density measurement and correct the neutron and density measurements for the effects of standoff and borehole size while drilling.

Standoff compensation of the density measurement is achieved using a new technique called "Self Binning". This technique relies on measurements made by the density tool itself to correct for tool standoff. The count rate of the near detector is sampled at a very high rate and combined in such a way as to divide the borehole into segments of fairly constant standoff. A standoff correction is applied to each segment and an average corrected density is calculated after removing data with excessive standoff.

A similar technique is used to segment the borehole according to formation density. The corrected densities sampled at a high rate are sorted according to formation density to provide a continuous profile of the azimuthal formation density around the borehole circumference.

Additionally, estimates of tool standoff and borehole diameter are determined while the tool is rotating. This information is applied to the neutron measurement to obtain a neutron porosity measurement corrected for borehole and standoff effects.

Details of these new algorithms as well as modeling and experimental data used to optimize and test these algorithms are presented. Examples are presented that show the accuracy and repeatability of the new toolstring.
LWD Sonic Logging in Large Diameter Surface Holes
Authors: Market J. , Hauser M. R. , Althoff G. , Deady R. J. , Varsamis G. L.
Published: December 2007

Sonic logging in large diameter surface holes in offshore environments such as the Gulf of Mexico has traditionally been problematic from both operational and economic perspectives. Acquisition of high-quality wireline sonic log data in large diameter, shallow holes is often compromised by borehole enlargement or washout that may occur before wireline tools are run, and by the typically high signal attenuation encountered in shallow formations and large boreholes. Even if adequate quality wireline sonic data can be obtained, the rig time and cost required for the wireline run may be as great as that required for the actual drilling of the surface hole. However, sonic velocity data in these shallower intervals can be particularly important to geophysicists for use in seismic velocity modeling or time-depth correlation. Sonic log data can also be used for formation evaluation and for drilling applications such as pore pressure determination.

To improve sonic data acquisition while eliminating rig time and costs associated with wireline logging, a 9 ½" diameter LWD sonic tool has been developed particularly for these logging environments. The tool is designed with two opposed transmitters capable of firing strong signals at multiple frequencies, and dual, seven-element receiver arrays for a high signal/noise ratio in the soft, highly-attenuating formations. The tool is mechanically compatible with larger BHA's used to drill large-diameter surface holes, while providing high-quality compressional slowness (Δtc) logs in boreholes ranging from 14 ¾" to 26" in diameter. Centralization is not required, and the tool is compatible with bi-centered bits; thus, it can also be used to provide porosity and pore pressure information in applications where bi-centered bits preclude the acquisition of high-quality LWD neutron porosity and density data. The sensor is combinable with 9½" directional, gamma ray, resistivity, and annular pressure sensors to facilitate both drilling and formation evaluation applications in real time in large boreholes. Along with the design and modeling of the 9-1/2" sonic tool, example data are presented from large surface holes (17 ½" to 26") in the Gulf of Mexico.
Engineering Calculations of Gas Condensate Well Productivity
Authors: Mott Robert
Published: December 2007

The productivity of many gas condensate wells is reduced by the formation of a condensate bank in the near-well region. Forecasting of gas condensate well productivity usually requires fine-grid numerical simulation to model the formation of the condensate bank, and to account for high-velocity phenomena such as non-Darcy flow and changes in relative permeability at large capillary numbers.

This paper presents a new technique for forecasting performance of gas condensate wells, using simpler techniques, which can be used in a spreadsheet. The calculation uses a material balance model for reservoir depletion and a two-phase pseudopressure integral for well inflow performance. The pseudopressure integral technique has been extended to include high-velocity effects and also to allow for the change in produced fluid composition due to the formation of the condensate bank.

The new technique has been tested by comparison with the results of fine-grid compositional simulation, and the results are in good agreement for a wide range of cases covering vertical, horizontal and hydraulically fractured wells.

The spreadsheet model provides a useful tool for rapid forecasts of condensate well performance, for examining the effects of condensate blockage in different well types or for studying sensitivities. It is also valuable where simple models of condensate reservoir performance are required for use in integrated studies involving issues such as surface facilities, drilling schedules and gas sales contracts.
Case Studies Using Reservoir Characterization To Improve Remediation System Design and Operation
Authors: Bust Vivian K.
Published: December 2007

Improved remediation design and operation resulted from effectively using reservoir-aquifer characterization tools to identify hydraulic flow units and connectivity of sediments in contaminant-affected shallow aquifer-aquitard systems. The objective of this approach was to utilize an improved understanding of subsurface conditions to develop more effective remediation designs and operating plans. This was accomplished by developing an increased understanding of aquifer storage and flow properties, preparing geologic models, and identifying contaminant migration pathways and permeability barriers. Characterization methods practiced in petroleum exploration and production were applied to near-surface sedimentary sequences to describe the subsurface hydrogeologic setting. Stratigraphic analysis using continuous core, detailed core descriptions and analogous sedimentary environments of deposition was employed to develop deterministic geologic models of the subsurface. Predictive mapping was used to delineate contaminant-affected soil and groundwater, and interpretations were adjusted in an iterative manner with the acquisition of data.

This paper will discuss case histories of overall project characterization and remediation of two sites located in Southern California, USA. These case studies demonstrate the effect of subsurface soil heterogeneities and variation in contaminant distribution on remediation.
The Value of Flexibility in Managing Uncertainty in Oil and Gas Investments
Authors: Begg Steve , Bratvold Reidar , Campbell John
Published: December 2007

This paper deals with improving the oil and gas industry's ability to manage the impacts of uncertainty on investment evaluations. We first review the economic performance of the industry and conclude that it is not good. Under-performance is attributed largely to poor investment decision-making, which is in turn due to inaccurate evaluation of the economic impacts of uncertainty. We describe how undue focus on Value of Information (VoI) and classical DCF techniques can prevent full value creation from an investment opportunity, by not encouraging exploration of the use of flexibility to manage, or even exploit, uncertainty. A Real Options (RO) approach has considerable appeal in overcoming this problem. However, its widespread application has yet to occur due to unfamiliarity, issues around its robust implementation and a focus on valuation rather than value creation.

Here, the VoI concept is extended to assessing the Value of Flexibility (VoF). Building on a previously published framework (SPE 71414), we show how VoI and VoF analyses can be performed using a Stochastic Integrated Asset Model and thus offer a practical means to capture some of the benefits of a real options approach. The VoI concept is reviewed and illustrated by the example of executing a seismic study to reduce OOIP uncertainty. VoF is illustrated by planning extra slots on a platform to manage residual OOIP uncertainty and by estimating the value of incremental water injection facilities to manage uncertainty in aquifer strength. Value creation from flexibility is illustrated by considering the potential to change production rate as oil price changes.
Quantification of Petrophysical Uncertainty and Its Effect on In-Place Volume Estimates: Numerous Challenges and Some Solutions
Authors: Fylling Arne
Published: December 2007

The subject of this paper is the quantification of uncertainty in the petrophysical variables porosity, water saturation and net to gross ratio as estimated in wells, and the significance of such uncertainty for in-place volume estimates. If the nature of petrophysical uncertainty is not properly accounted for in this process, directly misleading uncertainty estimates may be derived. This can be the case if one or more of the following issues are disregarded:

Firstly, the petrophysical variables are not independent. This can be taken into account by replacing the individual petrophysical variables with the variable Hydrocarbon Pore Fraction, HCPF, in the uncertainty estimation. This variable is the hydrocarbon fraction of the gross rock volume, and uncertainty in this variable can conveniently be combined with uncertainty in gross rock volume to derive the uncertainty in hydrocarbon pore volume (HCPV)

Secondly, randomly distributed errors in petrophysical variables are usually insignificant for in-place volume uncertainty, due to averaging of large data volumes. Systematic errors are not removed by averaging, and a key issue is the estimation of such errors, which cannot be done by applying statistical procedures to the data. The effect of such errors on HCPV uncertainty is critically dependent on the degree of correlation between errors in different wells and zones.

Thirdly, the errors caused by the combined effect of reservoir properties, differences and limitations in logging tool response functions and the choice of evaluation model and parameters are a major source of uncertainty in any reservoir with some degree of heterogeneity. Therefore, estimating the uncertainty at the log depth increment level by more or less rigorous and comprehensive error propagation or Monte Carlo methods based on log, core measurement, evaluation model and parameter uncertainty only, is insufficient.

The systematic nature of the petrophysical uncertainty in wells will cause general HCPV level uncertainty. The uncertainty relating to mapping of properties between wells is an issue by itself. However, in many cases uncertainty related to water saturation mapping functions can be conveniently linked with uncertainty in HCPF in the wells, and quantified by simple spreadsheet methods as part of the petrophysical uncertainty estimation. The methods and algorithms for doing so are also given in this paper.
Implementing Intelligent Well Completion in Brown Field Development
Authors: Johnstone Stuart , Duncan Gavin , Giuliani Corrado , Denholm Allan
Published: December 2007

Intelligent Well Completions (IWC) is an emerging technology, which allows operators to optimise reservoir management and field facilities performance. The implementation of this technology has generally been restricted to new field development due to the perceived complexity of integrating high-end IWC (combined monitoring and flow control) into current Subsea Production System (SPS) designs. However, intelligent completions can be applied to mature fields where reservoir performance and value added by IWC are well understood. The BP Machar well application is a typical example.

One of the challenges facing the project team was the integration of the IWC control system within the constraints of the existing SPS. Minimum modification to the existing hardware and control system equipment was a requirement.

A system approach, similar to the forthcoming ISO standard for integration of IWC into Subsea Production Systems, was used to ensure robustness of the design and testing concepts.
Prudhoe Bay Oil Production Optimization: Using Virtual intelligence Techniques, Stage One: Neural Model Building
Authors: Mohaghegh Shahab D. , Hutchins Lynda A. , Sisk Carl D.
Published: December 2007

Field data from the Prudhoe Bay oil field in Alaska was used to develop a neural network model of the cross-country gas transit pipeline network between the production separation facilities and central gas compression plant. The trained model was extensively tested and verified using 30% of the data that was not used during the training process. The results show good accuracy in reproducing the actual rates and pressures at the separation facilities and at the gas compression plant. The correlation coefficient for rate and pressure were 0.997 and 0.998 respectively.

This is the first phase in the development of a tool to maximize total field oil production by optimizing the gas discharge rates and pressures at the separation facilities. The second phase, development of a state-of-the-art genetic algorithm to perform the optimization, is currently being tested and will be the subject of a future paper.
The Potential for State-of-the-Art Decision and Risk Analysis to Contribute to Strategies for Portfolio Management
Authors: Simpson G. S.
Published: December 2007

The titles of papers given at industry conferences over the last couple of years suggest a significant rise in the level of awareness of the potential for decision and risk analysis (D&RA) techniques to impact portfolio-related decisions, from exploration acreage acquisition through drilling and development decisions to transportation and downstream issues.

This may well be a function of the increase in the number and complexity of upstream partnerships and alliances and that, combined with a tightening of money markets, leads to greater difficulties in reaching agreement on portfolio-related decisions.

These portfolio management decisions include those that relate to: –which assets should be in, or out of, the portfolio?–what are the appropriate equity levels in each asset?–when is the best time to start, or continue, investing in each asset?

The increase in interest might also be a result of competitive pressures: if some companies are seen to be using techniques which appear or promise to give them a competitive advantage – smarter decisions leading to more efficient portfolios – then other companies will quickly feel the need to do the same.

This paper presents a model for portfolio management strategy formulation which starts with the application of the latest D&RA tool developments to individual asset value assessments, continues through the generation and analysis of potential portfolios, and ends with the incorporation of the insights thus generated into a strategy formulation and implementation stage.

The paper argues that the ultimate objective of D&RA is to optimize a company's portfolio of assets, that the use of sophisticated D&RA tools is a critical foundation necessary for achieving that objective, and that the industry still has some work to do before some potentially very important techniques, such as real options valuation, are practical working tools which everyone can and should use.