bluuebunny/crossref_metadata_2025 huggingface dataset:
Compaction in Soft Weak Rocks Due to Water Flooding
Authors: Papamichos E. , Brignoli M. , Schei G.
Published: December 2007

The mechanical behavior of some Adriatic soft weak reservoir rocks obtained from cores is characterized taking into account water saturation effects. The characterization includes triaxial compression, and uniaxial strain (oedometric) tests, as well as water injection tests under reservoir conditions. From the experimental results, a uniaxial strain compaction model for weak rocks is calibrated for use in reservoir compaction studies in the Adriatic Sea area. A porosity-dependent elastoplastic model is used to capture the variation of compaction in the materials in the reservoir zone.

P. 411
A Comparison of Deterministic and Reliability-Based Design Methodologies for Production Tubing
Authors: Raney James B. , (Suri) Suryanarayana P. V. R. , Maes Marc A.
Published: December 2007

In this paper, we compare reliability-based procedures for design of production tubing with the traditional working-stress design method. The basic approach of Working Stress Design (WSD), Load and Resistance Factor Design (LRFD) and Quantitative Risk Assessment (QRA) are discussed. Load and resistance methodologies for the three approaches, and their impact on the tubing design are contrasted. The relationship between the Safety Factor (SF) used in WSD, the Load Factors (Lf) and Resistance Factors (Rf) used in LRFD, and uncertainity propragation used in QRA is illustrated. These relationships are then compared and contrasted with the determined reliability for a given design. A few illustrative examples are provided for the three different design methods. Graphs illustrating the relationship between SF and estimated design reliability allow a reliability-based interpretation of WSD, and give insight into the design reliabilities implicit in WSD. By means of such a comparison to a familiar design format, this paper aims to give the reader an understanding of, and confidence in LRFD/QRA format for the design of production tubing. The tendency of WSD to overdesign tubing from a reliability stand-point is illustrated. It is concluded that while QRA is the best approach to designing production tubing to a desired reliability, LRFD allows reliability-based design in a format that is relatively easy to apply.
Analytical Burst Strength Prediction of OCTG with and without Defects
Authors: Klever F. J. , Stewart G.
Published: December 2007

Casing and tubing are generally designed against burst by requiring a safety margin between the calculated stresses and the yield strength of the material. This same formula is then often used to determine the remaining burst strength of casing that suffered from drillstring wear or wireline wear, in the latter case sometimes including an additional penalty to account for stress concentrations. This approach is very conservative and, moreover, leads to actual safety margins against burst that vary widely over different grades.

Improved and novel approaches towards tubular design and fitness-for-purpose call for models that can accurately predict failure as opposed to conservative assessment procedures. Much progress has been made in developing verified burst strength models for ‘regular’ pipe, accounting for the acceptable wall thickness variability. In this paper attention is paid to pipes with cracks, but the main focus is on the accurate quantification of the degradation of the burst strength due to longitudinal wear.

Burst tests have been carried out on a number of pipe specimens with a wear groove machined at the inside; some of these with axial cracks at the outside. Also finite-element analyses have been performed, simulating the burst of these pipes and also others from different grades and sizes, with defects of different depths and shapes ranging from drillstring wear and wireline wear to sharp cracks.

By combining the results of the tests and the analyses, a simple analytical burst model has been developed that shows an excellent performance for regular pipe and worn pipe. The equations developed here are also applicable to describe the limit behaviour of pipes with crack-like defects, provided ductile tearing is taken into consideration and fracture instability does not occur. More details on the approach to account for flaws in the burst strength of OCTG is presented in a companion paper by Stewart and Klever [1].

This work is directly applicable in the design and fitness-for-purpose analysis of casing and tubing.
Improved Production Log Interpretation in Horizontal Wells Using a Combination of Pulsed Neutron Logs, Quantitative Temperature Log Analysis, Time Lapse LWD Resistivity Logs and Borehole Gravity
Authors: Brady J. L. , Watson B. A. , Warner D. W. , North R. J. , Sommer D. M. , Colson J. L. , Kleinberg R. L. , Wolcott D. S. , Sezginer A.
Published: December 2007

A novel combination of logs and their unique interpretations are used to improve the understanding of production in horizontal wells on the North Slope of Alaska. Two techniques using Pulse Neutron Capture (PNC) logs to identify and quantify liquid productive intervals were previously presented in a paper by Brady et. al1. These techniques are compared and combined with two additional techniques: 1) the use of time lapse LWD resistivity to determine productive intervals and liquid flow profiles while drilling, and 2) a non trial-and-error method to determine quantitative gas production using temperature logs in a two-phase flow. Finally, modeling shows borehole gravity logs can be used to track the vertical movement of gas or water tens of feet above or below horizontal wells.

Integrating the time lapse differences between shallow LWD resistivity logs run while drilling and logs run several hours after drilling show a strong correlation with PNC liquid flow profiles for wells producing at solution GOR. Additionally, combining a quantitative gas flow rate analysis from the temperature log with the liquid profile provides a complete analysis of the production profile for two-phase flow in horizontal wells. Finally by combining the production profile analysis from a horizontal well with the modeled timelapse borehole gravity data, a complete understanding of the fluid movements in the well borehole and up to two hundred feet into the formation can be obtained.

These techniques can be applied to both horizontal and vertical wells with both slotted liner and cemented perforated completions to obtain a quantitative production profile. The LWD resistivity data, collected while drilling, provides an indication of the productive reservoir rock before the well is completed. Time lapse borehole gravity provides an understanding of the reservoir fluid movements affecting the wellbore flow profiles after the well has been put on production.
Heavy Oil Production from Unconsolidated Sandstones using Sand Production and SAGD
Authors: Dusseault Maurice B. , Geilikman Mikhail B. , Dusseault T. J. T. (Tim)
Published: December 2007

Three major new technologies developed in the past decade in the heavy oil regions of Alberta and Saskatchewan are long, shallow horizontal wells, Steam-Assisted Gravity Drainage (SAGD), and Cold Production (CP). These three technologies are briefly reviewed. They can be combined in a general approach to heavy oil reservoir development that will give the advantages of reasonable early oil production rates, continued long-term production, and excellent long-term recovery.

A combination of vertical wells and horizontal wells are used to achieve early CP, which is then gradually replaced by long-term SAGD production. As the processes progress, vertical CP wells will decline in production rate; when they are no longer economical to produce, these wells are converted to other purposes. They can be used as inert gas injectors, control wells, low-rate thermal injection or production wells, or even sand disposal wells, as long as they help maintain the reservoir at the appropriate pressure for SAGD. The proper balance of pressures through injection or production to maintain the long-term stability of processes in the gravity-dominated flow regime is critical to SAGD success.

Given price fluctuations and long-term projections, economic factors related to heavy oil must be addressed. It is appropriate to point out that within 10-15 years, the current conditions of low prices and over-supply of conventional crude oil will be replaced by a world-wide shortfall in oil supply, which should bring a permanent increase in oil prices.

This suggests that corporations should be making substantial investments in heavy oil at the present time.
Effects of Single and / or Combined Application of Water and Oil Based Drill Cuttings in a Tropical Agricultural Soil Located in JusepíN Oil Field (Monagas State, Venezuela)
Authors: Caraballo Luis , Urich Juan , Vásquez Pedro , Marcano Pedro , Muzziotti Reinaldo , Rodríquez Alberto , López Carlina , Marcano José , Rodríquez Pedro , Colombo Pedro , Quiñones Rubén , Asuaje Ramón
Published: December 2007

At eastern Venezuela, the oil developments are established mainly in areas with agricultural and cattle rising activities. This compel to an effective and environmentally safe treatment for water (WB) and oil based (OB) drill cuttings (DC), according to the Venezuelan regulations. In order to determine the effects of individual and combined applications of WB and OB in an acid soil (Ultisol), it was designed and installed on January 1997 a field test in the Jusepín Oil Field (Monagas State). In 9 plots of 0.7 ha. each one, were applied the following treatments (equivalent doses in m3/ha.): WB: 0, 125, 250, 500; WB/OB: 90/72; 180/140, 360/280; and OB: 100, 200, 400. Then were applied an adjusted fertilization (N, P, S), complementary amendments and periodical tillage, to stimulate the hydrocarbons biodegradation (TPH). After a 87 days period, the TPH percentage in OB treatments (45.9 %) was smaller than WB/OB (53.3%). Due to the use of CaO at the output of solids control equipment as dryer for DC, some soils plots showed high Ca++ and pH, mainly at high DC doses (an over liming effect). Other soil and leacheates parameters (electric conductivity, Cl-, TPH and heavy metals), were found under the established limits by ad hoc environmental regulation (actually being reviewed). The 500 WB treatment shown both, high soil fertility and grasses growth. The results shown that is feasible the WB/OB application, being reduced the treatment area for the safe disposal of more than 2000 m3 DC by well
A Simple Correlation to Predict Wellbore Pressure Drop Effects on Horizontal Well Productivity
Authors: Yildiz Turhan , Ozkan Erdal
Published: December 2007

This study presents a simple correlation to predict horizontal well productivity influenced by wellbore hydraulics. The correlation is developed from a rigorous finite-conductivity analytical solution. An inflow factor concept is introduced as the ratio of the pressure loss inside a solid horizontal pipe to that along a horizontal well. It is shown that the inflow factor may be correlated in terms of the Reynolds number and friction factor based on total well flow rate, wellbore size, and hydraulic well conductivity. The inflow factor is used in a simple empirical equation to estimate the productivity of a horizontal well under the influence of wellbore hydraulics. The results estimated from the empirical equation are within 2% of the results from the rigorous prediction method for most practical applications.
Improved Sliding Through Chemistry
Authors: Bland R.G. , Halliday W.S.
Published: December 2007

New mud chemistry is shown to improve the efficiency of directional drilling with steerable motor systems in the slide drilling mode through improved cuttings management. Both laboratory drilling simulator results and field case-histories are presented documenting the effectiveness of this technology.

P. 69
Chemicals and the North Sea Environment: A Challenge for the New Millennium
Authors: Craddock Henry A. , Moorfield John L.
Published: December 2007

This paper will discuss the changing regulation surrounding chemical use and discharge in the North Sea. It will discuss the pros and cons of such regulation and look at some options and scenarios for the 21st Century.

This paper will cover some background on the use of chemicals and the progress made to develop more cost effective and efficient chemicals and chemical management leading to environmental impact of the potential discharge of chemicals in the North Sea from the oil exploration and production industry.

This paper will examine the current situation of increasing controls and regulations, problems with appropriateness of certain test protocols, reliance on hazard assessment and the potential dangers this could pose to the oil and exploration and production industry in the North Sea.

This paper will also look forward to the ‘zero’ discharge scenario which will become the norm in the not too distant future as set out in the Oslo Paris Convention ( 2020) and the interim requirements of harmonisation of controls. It will propose that the way forward is through risk assessment of chemical hazard and overall environmental impact, leading to a mature and sensibly regulated market place that will encourage the development of better products, both in terms of technical efficacy and environmental profile
Effectiveness of a Dry Gas Injection WAG Process in a Previously Waterflooded Chalk Reservoir
Authors: Wegener D. C. , Thomas L. K. , Sylte J. E.
Published: December 2007

Little has been published about the effectiveness of dry gas injection, as part of an immiscible WAG process, at recovering hydrocarbons from a previously waterflooded, light oil reservoir. In a PVT cell where the gas and liquid phases are placed in intimate contact, hydrocarbon vaporization can readily be demonstrated to be an effective mechanism for extracting hydrocarbons from light oils. Less easily demonstrated is the effectiveness of gas injection at recovering hydrocarbons from a low permeability porous matrix with a high water saturation.

This laboratory study investigates the potential effectiveness of gas injection, as part of an immiscible WAG process, at recovering hydrocarbons from the Ekofisk reservoir as it would exist in a post-waterflood condition. Reservoir simulation was used to design the laboratory portion of this study which in turn generated results that improved reservoir simulation. Portland outcrop chalk, similar in porosity and permeability to Ekofisk, was used along with live Ekofisk oil. The experiment was conducted at 125°F and 4000 psig which represents a cooled and partially re-pressured region of the Ekofisk reservoir.

The results of the experimental work indicated that approximately 25 weight percent of the C5+ hydrocarbons, inplace in the residual oil at the start of the gas injection phase of the experiment, were recovered after 1.0 pore volume of gas injection. Estimates of the hydrocarbon recovery attributable to swelling/viscous displacement versus that attributable to vaporization were quantified versus pore volumes of gas injected.
Adverse Effects of Poor Mud Cake Quality: A Supercharging and Fluid Sampling Study
Authors: Sarkar Amit K. , Lee Jaedong , Kasap Ekrem
Published: December 2007

Wireline Formation Testers (WFT) are routinely used at discrete depths of a well to collect reservoir fluid samples and to estimate undisturbed reservoir pressures, near-wellbore formation permeabilities, fluid compressibilities, and saturation pressures. A pressure profile in the vertical direction yields fluid densities and fluid-contacts (GOC and WOC) in the reservoir. Reliable results are obtained when the mud cake isolates the wellbore from the formation. When mud cake cannot provide isolation, mud filtrate invasion continues and supercharging occurs. The issue of sample quality becomes critical when using oil-based muds because the filtrate is also oil and is difficult to separate from the formation oil, a pure sample of which is needed for fluid characterization studies. This study investigated the effects of poor mud cake seal on sample quality and formation test data and its analysis when oil-based muds are used. Modeling studies were conducted using a finite element simulator.

The results of the study indicate that mud cake permeabilities need to be less than one microdarcy and mud cake to formation permeability ratios need to be less than 10−4 to achieve sample qualities higher than 90%. Conditions such as high pumpout rates, low overbalance pressures, and shallow filtrate invasion depths improve sample quality. The presence of a permeability-damaged zone around the mud cake improves sample quality but reduces the sampling pressure. The Formation Rate Analysis (FRASM) technique estimates formation permeability accurately in the presence or absence of supercharging. The formation pressure estimated using the buildup data is the pressure at the mud cake-formation interface. The supercharged pressure must be subtracted from the apparent formation pressure to obtain the true formation pressure. A simple procedure is developed for estimating the mud cake permeability and the supercharged pressure. Supercharged pressure is shown to be a product of the apparent overbalance pressure, mud cake to formation permeability ratio, and an invasion factor representing the distance up to which supercharging extends.
Stability and Flowing Properties of Aqueous Foams for Underbalanced Drilling
Authors: Argillier J-F. , Saintpere S. , Herzhaft B. , Toure A.
Published: December 2007

Foam stability and rheology are important parameters for foam used as a drilling fluid in underbalanced drilling. A low density fluid is one way to avoid formation damage or borehole fracturing when the reservoir has a low pore pressure, or is depleted. However foamed drilling fluids are not well understood, their stability and rheology are more complex than a conventional drilling fluid. Rheological data have to be applied to model flowing properties within the drill string and the annulus to predict and control the down hole pressure.

In this work we have studied the physico-chemical properties and the flowing properties of aqueous foams formed with a commercial system. Foam stability has been studied as a function of different parameters, including the presence of electrolytes (mono and divalent salts) and contamination by hydrocarbons. Addition of water soluble polymers to increase the stability of the foam has been studied as well as the influence of the hydrodynamic conditions on foam stability.

Flowing properties have been studied by circulation tests in a laboratory transparent flow loop (4 m long and 1 inch internal diameter). Foam circulation experimental data have been used to calculate pressure losses during foam circulation using software based on a published model (Economides 1995). The effect of the quality of the foam on the accuracy of the model has been shown, thus allowing the estimation of the domain of validity of this model. Different methodologies for rheology measuring have been compared. The influence of other parameters such as polymers concentration or foaming agent concentration have been studied also.

P. 185
History Matching Finite Difference Models With 3d Streamlines
Authors: Emanuel Alan S. , Milliken William J.
Published: December 2007

In the past several years, 3D streamline simulation (3DSL) software has become available to the industry through commercial vendors, university coop projects, and DOE sponsored research. This paper describes the use of 3D streamlines to assist in history matching conventional finite difference reservoir simulation models.

One of the most difficult tasks in history matching individual well performance in a finite difference model is the identification of the grid blocks that affect the performance of a well. The task is exacerbated by the progression to large, complex, geostatistical models. This paper describes a technique that integrates, in a simple computer program, streamline and finite difference simulation to identify the grid blocks that affect each well and to effect changes to the model for history matching. Two case studies are presented: case 1 is a thick, stratified 60 well eolian sandstone producing under pattern waterflood and case 2 is a 70 well carbonate anticline producing under partial aquifer drive. The two cases illustrate the efficiency of the streamline-based code and the potential of the process to greatly simplify history matching.
Estimation of Hydrocarbon Viscosity with Multiple TE Dual Wait-Time MRIL Logs
Authors: Chen Songhua , Olima Oscar , Gamin Héctor , Georgi Daniel T. , Minetto J. Carlos
Published: December 2007

In this paper, we report a successful example of using multiple TE dual wait-time (TW) log acquisitions for quantitative characterization of San Jorge Basin reservoir oil viscosity. Previously, dual TW logs have been used to separate gas and oil, while dual TE logs have been used as a qualitative light oil indicator. Although theoretically simple, quantitative determination of viscosity from dual TE logs is complicated by several factors, including poor signal-to-noise ratio, difficulties in separating oil from water, and the uncertainty of internal gradient strength.

We used multiple TE acquisitions of dual TW logs to isolate the oil from the water signal. The values of viscosity of the reservoir fluids can be estimated from three NMR properties: intrinsic T2, apparent T2, and T1. All three approaches have advantages and disadvantages. Since T1estimates are not affected by diffusion, the uncertainty in the internal field gradient has no effect on T1-based viscosity. However, T1 is difficult to estimate because it relies on small differences in the dual TW echo data. In estimation of the apparent T2, we used a model that does not explicitly require knowledge of the internal gradient, thereby minimizing the effects arising from the uncertainty of the internal and tool gradient strengths. Since T1 and intrinsic T2 are estimated independently, the degree of agreement between the two values provides an indication of the reliability of the two estimates.

The method has been used successfully in San Jorge Basin, Argentina. Three values of TE, 1.2, 2.4, and 3.6 ms were used and a dual TW log was acquired for each TE. The data were analyzed without need for other geological information or log data from other logging tools. To complicate the matter, previous NMR core analysis of the core plugs cut from another well in San Jorge Basin showed great porosity and permeability variations. Furthermore, no reliable reservoir fluid measurements were available. Thus, interpretation was based only on the NMR log data. The four zones selected for this study were thought to contain heavy, viscous oil. However, our analysis indicated that the viscosity values of the oil are less than 5 cP. Our predictions have been substantiated by production of light hydrocarbons from the three zones that have been perforated. Further, viscosity measurements on the reservoir fluid from one of the three zones is 2.6 cP, which is in good agreement with the NMR-derived estimate of 3.3 cP.
A New Algorithm for Analysis of NMR Logging Data
Authors: Menger Stefan , Prammer Manfred
Published: December 2007

Nuclear magnetic resonance (NMR) logging has become an important input to formation evaluation. T2 spectra calculated from pulse-echo trains are the basic building blocks for further analysis. This paper discusses the influence of acquisition parameters such as inter-echo spacing, echo train length, and noise on T2 resolution.

The latest generation of pulse-echo logging tools allows to simultaneously record different NMR data for optimized wellsite efficiency. A new method is presented to merge these different raw echo trains into a single combined echo train. The result is a data set that is optimized with respect to T2 resolution. This echo train can be processed in an efficient way.

This paper presents laboratory and field-test data, recorded with a new generation, multi-volume NMR logging tool, demonstrating that the new algorithm is fast, stable, and yields accurate results.
More Oil with Less Water Using Downhole Water Sink Technology: A Feasibility Study
Authors: Shirman Ephim I. , Wojtanowicz Andrew K.
Published: December 2007

The paper reports on recent R&D progress in the Downhole Water Sink (DWS) technology resulting in an establishment of a joint industry/LSU project - DWS Initiative. Presented are recent case histories of DWS design and successful field trials. The results are then analyzed comparatively in view of the superiority of DWS over the single conventional completions. The analysis shows that, although DWS increases production of oil, its potential for reducing production of water is unknown and remains a controversial issue among operators.

The case history analysis is followed by results from the authors' theoretical and experimental study on water cut suppression with DWS. The study was performed by comparing WC development in the single (conventional) and dual (DWS) well completions for a broad range of oil reservoirs with bottom water columns. These theoretical results are supported with experiments conducted using a laboratory physical model of a dual/single completed well - reservoir system. The results, included in this paper, demonstrate the persistence and irreversible nature of WC in conventional wells compared to its flexibility and easy control in DWS completions. Defined is the range of production rates where DWS may give a sizable, up to 40%, reduction of WC. It is also shown, with calculations, how to determine the expected WC reduction for a given reservoir and well- completion design.

P. 215
Quasi K-Orthogonal Streamline Grids: Gridding and Discretization
Authors: Edwards Michael G. , Elf Regis Agut , Aziz Khalid
Published: December 2007

A new grid generation technique based on streamlines and equi-potentials is developed for reservoir simulation. The natural property of streamlines provides a grid that has a concentration of grid lines in high velocity regions of the flow field thereby optimizing nodal placement. Results computed with the new streamline-potential grids demonstrate a significant improvement in accuracy when compared with conventional Cartesian grids of similar resolution. Streamlines and equi-potentials are shown to be K-Orthogonal. This fundamental observation has major implications for reservoir simulation. A comparison between a two point flux approximation and a full tensor flux approximation is presented for the K-Orthogonal streamline-potential grid systems. P. 373
Problem Identification and Improved Treatment Method of a Thief Zone in a West Texas CO2 WAG for Profile Modification
Authors: Dalrymple E. D. , Creel P. , Hirth J. B.
Published: December 2007

During a field's pilot evaluation of a CO2 water-alternating-gas (WAG) injection into the San Andres formation in a central west Texas unit, a problem was identified: Profile information and no offset response showed the CO2 and water injections were being lost into an upper high permeability layer. This problem was allowing one of the pilot injectors to communicate into a temporary abandoned injection well 2¼ miles away.

To remedy the situation, a chemical treatment was needed that would account for such factors as continual injection of CO2, degradation of the material caused by bacterial growth, deep penetration into the thief interval, development of sufficient strength to withstand pressure extrusions, intermixing, and possible removal.

A diagnostic analysis of selected injection wells was accomplished through multirate injectivities combined with profiled entry analysis; this technique established other criteria for the solution. The solution was governed by two conditions: (1) injection had to occur at a precise rate without significant pressure resistance so that entry would occur only in the problem interval, and (2) the treatment had to be placed deep enough to prevent the CO2 WAG from re-entering the thief interval.

One of the pilot injectors selected for treatment indicated 100% of the inj ection was being lost through a 10-ft interval in the upper portion of the payzone at a determined rate. After the application, the thief zone had been shut off, and the injection was reaching the remaining reservoir. Because this action required fluid entry into more restrictive permeabilities, an increase in pressure was necessary to flood the payzone effectively.

This paper discusses the optimal treatment selection and the laboratory investigations regarding the chemical resistance to CO2. It also discusses the placement techniques chosen and provides field results, which indicate a modified injection profile.
A Computationally Efficient, Transient-Pressure Solution for Inclined Wells
Authors: Ozkan E. , Raghavan R.
Published: December 2007

This work provides an efficient algorithm to compute transient pressure responses of inclined wells. The solution is derived in the Laplace domain and cast into computationally efficient forms for all inclination angles. The algorithm allows the computation of pressures and derivatives at the wellbore as well as at observation points. Short- and long-time approximations for the evaluation of pressure responses are also provided. The long-time approximation is used to derive a general pseudoskin expression that is applicable for all inclination angles. Example computations are presented in the forms of tables and figures to display the efficacy, accuracy, and the practical use of the algorithm.

P. 343
Pressure-Transient Behavior of Multibranched Wells in Layered Reservoirs
Authors: Larsen Leif
Published: December 2007

Analytical methods are presented to determine the pressure-transient behavior of multibranched wells in layered reservoirs. The computational methods are based on Laplace transforms and numerical inversion to generate type curves for use in direct analyses of pressure-transient data. Any number of branches with arbitrary direction and deviation can in principle be handled, although the computational cost will increase considerable with increasing number of branches. However, due to practical considerations, a large number of branches is also unlikely in most cases.
Productivity Correlation for Horizontal Sinks Completed in Fractured Reservoirs
Authors: Sato Kozo
Published: December 2007

When completed in fractured reservoirs, horizontal sinks (hydraulically fractured wells or horizontal wells) are believed to intersect several fractures and outperform their vertical counterparts. Based on the numerical experiment outcomes, productivity correlations are developed with horizontal-sink length and fracture parameters as the correlating parameters. The correlations are of use in predicting the expected value and the most-likely minimum value of productivity for a horizontal sink parallel or perpendicular to fractures.

Analyzing the developed correlations enables us to quantify the individual contributions of a sink itself; distributed fractures, and sink-intersecting fractures to the horizontal-sink productivity. Fractures tend to yield a significantly magnified contribution to the productivity when they intersect the horizontal sink. The advantage of completing a horizontal sink perpendicular rather than parallel to fractures is attributed largely to such fractures.

P. 357
Estimation of Production Forecast Uncertainty for a Mature Production License
Authors: Jensen Trond B.
Published: December 2007

A comprehensive effort to estimate the range of uncertainty in the long term forecast for the mature Ekofisk and surrounding fields (Eldfisk, Embla and Tor) located in the Norwegian sector of the North Sea is presented. Even for this mature production license (PL018) which has been on production for more than 25 years we experience significant discrepancies between actual and forecasted production. This prompts the need for estimating the range of uncertainty in the reservoir production prognosis. Decision tree analysis formed the basis for our methodology in which each branch on the decision tree is coupled with a full field 3D numerical reservoir model. A large number of full field, numerical simulations were run to forecast the different realizations. Reservoir, operational and facility uncertainties were considered. These results were coupled with straightforward statistical techniques to allow estimation of probabilistic forecasts. Individual fields production forecasts were aggregated into a single license production forecast using Monte Carlo simulation.

P. 331
Acidizing in the Teak Field: A Comprehensive Approach
Authors: Gdanski R. , Jurai V. , Mohan R. , Chung R.
Published: December 2007

Even though reasonably successful acidizing treatments have been performed in the Teak Field for a number of years, many of the treated wells returned to the pretreatment production rate within 4 to 5 months.

A comprehensive approach was therefore undertaken in 1997 to improve production from damaged wells in the Teak Field. Using new techology and relying on historical perspectives and experience, a stimulation team set out to identify the causes of damage, recommend damage removal treatments, verify treatment effectiveness, and determine methods to prevent damage.

To accomplish these goals, team members had to establish the formation mineralogy, the damage mechanisms, the type of HF blends to use, the acid volumes to use, the amount of diverter to use, and which wells to acidize. After the acidizing jobs were performed based on these specific recommendations, the treating charts and flowback returns from these treatments were analyzed.

When these results were combined with available mineralogical and production data, the damage mechanism for each particular sand body could be determined, and these bodies were categorized into four groups. Stimulation designs could then be tailored to treat the specific type of damage that appeared in a given category.

Damage prevention strategies were also developed, which reduced the number of stimulation treatments required. The outcome of this approach has been a 37% increase in incremental production over the previous year, and an increase in estimated reserves of about 1 million barrels of oil, even though fewer acidizing jobs were done, and the jobs were begun later in the year. This paper describes how this improvement was achieved in just 1 year.

P. 451
Fluid Placement Model for Stimulation of Horizontal or Variable Inclination Wells
Authors: Eckerfield L.D. , Zhu D. , Hill A.D. , Thomas R.L. , Robert J.A. , Bartko K.
Published: December 2007

Acidizing is a common method of stimulating horizontal wells. The acidizing process is fundamentally different when applied in a horizontal well compared with application in a vertical well. The fluid distribution in a horizontal well is affected by a longer welibore length. a broader variation in the reservoir properties along the wellbore, and possibly different mechanical means to place the fluids in the wellbore. A comprehensive fluid placement model linked with a reservoir acidizing simulator is essential to precisely design acidizing treatments for horizontal wells.

This paper presents a model of fluid placement in a horizontal well. The model predicts the placement of injected fluids by tracking the interfaces between different fluids in the wellbore. It is capable of tracking multiple interfaces for multiple injection stages in horizontal wells. For injection with coiled tubing, the model allows tubing tail movement during injection. It also handles simultaneous injection from the annulus and from a tubing string. A unique feature of the model is that it considers gravity under-riding of the denser injected acid when the wellbore is not perfectly horizontal. Both analytical and discretized solutions of the model are presented in the paper. Examples in the paper illustrate the effects of such factors as velocity of tubing movement, annular injection, non-uniform distribution of flow into the reservoir, and gravity segregation under-riding in inclined wellbore sections on fluid placement in an acidizing treatment.

The wellbore placement model has been linked with a matrix acidizing model calculating damage dissolution and skin reduction near the wellbore. An example is provided comparing different placement techniques such as bullheading and injection through coiled tubing with and without simultaneous injection through the annulus.

The simulator can help to determine optimum tubing tail locations and optimal injection volumes of acids, to select the most appropriate diverting methods, and, hence, to maximize the benefits of an acidizing treatment.

P. 473
Dehydration of Heavy Crude Oil Using Disc Stack Centrifuges
Authors: Dhuldhoya Nimish , Mileo Mike , Faucher Mark , Sellman Erik
Published: December 2007

Heavy (low API gravity) crude oils are more difficult to dehydrate than light crude oils. Traditional treatment systems for dehydration of heavy crude oil use large separators and large amounts of heat, in combination with the dosing of large quantities of demulsifier chemicals. The traditional treatment systems are bulky and require large structures / deck area for support.

This paper demonstrates that heavy crude oils can effectively be dehydrated (achieve pipeline BS&W specification) using disc stack centrifuges. Due to the compactness of the disc stack centrifuges and the relatively small hold up volumes, the treatment facility can be made more compact and reduce both the required deck space and structural support load on the structure. P. 371
Quantitative Formation Permeability Evaluation from Stoneley Waves
Authors: Brie A. , Endo T. , Johnson D.L. , Pampuri F.
Published: December 2007

Reservoir engineers need a continuous measurement of permeability to optimize well completion and produce the formation effectively. The borehole Stoneley wave has been shown to be sensitive to fluid mobility, the ratio of permeability and viscosity. The phenomenon is well described using the Biot theory, and models to account for the effect of the mudcake have been proposed. Existing techniques use either the Stoneley slowness or its attenuation at low frequency to estimate the fluid mobility with simplified Biot models. However, the results of these techniques usually show unexplained differences from core measured permeabilities, or with well test results. The objective of the methodology presented in this paper is to improve the reliability of the estimation and to take into account important factors that have been neglected.

The evaluation technique described in this paper uses the Stoneley waveforms over a wide frequency range and inverts for fluid mobility applying the full Biot theory. The mudcake is modeled as an elastic membrane. The most important parameters in this evaluation are the mud slowness, mud attenuation, membrane stiffness and pore fluid compressibility. Practical techniques are proposed to obtain these parameters with sufficient accuracy from the recorded data. Stoneley waveform inversion provides a direct and continuous fluid mobility estimate near the wellbore (i.e., in the invaded zone). The intrinsic permeability of the rock can then be derived, provided that the various fluid components, their relative permeabilities and their viscosities are known. Finally the presence of irreducible water in the rock is also discussed as it can affect the estimation of mobility through the reduction of the effective porosity. The application of this methodology to actual data sets is the subject of an accompanying paper.

The Stoneley wave provides a continuous estimation of the formation permeability along the well. Core measurements are not required although they can be used for verification. This technique will find applications in reservoir engineering optimization of well production through better placement of the perforated intervals.

P. 389
A New Method for Remote Sensing of Critical Stratigraphic Bed Boundaries and Reservoir Positioning of Horizontal Wells
Authors: Leggett J.V. , Dubinsky V.S. , Nakken E.I. , Viken R. , Sandvik S.E. , Molz E.B. , Lotsberg O. , Bolshakov A.
Published: December 2007

Stratigraphic features such as fluid contacts, geological markers and reservoir target boundaries are key drilling markers for placing a well. Determining the position of a wellbore relative to these stratigraphic features, at a range to 20 meters, above and below a deviated wellbore, has been a major goal for "Tieing-in" to a reservoir model while drilling. Acquiring, processing raw data, and identifying these features at this range in a measurement while drilling (MWD) tool in real time has not been possible with existing MWD Formation Evaluation and geo-steering systems.

An experimental field prototype tool was run to identify these stratigraphic features. It was run as a pipe conveyed logging operation with wireline and wet-connector inside the pipe for two-way communication. Sonic measurements were also made to provide real time measurement of acoustic velocity/slowness which was used to insure accurate formation velocity. This combined measurement was essential in determining the correct distance to the feature.

This paper presents the proposed configuration of a Sonic While Drilling measurement method of reservoir navigation and lithological boundary identification. The method and benefits of this new type of Acoustic MWD measurement are detailed in this paper.

Stratigraphic positioning and reservoir navigation, formation dip estimation, coring point selection, seismic correlation and high resolution near wellbore reservoir imaging are key applications for this new acoustic measurement method. The field test results demonstrated by this new method indicate that these key applications can be implemented as a new Sonic While Drilling measurement.

P. 413
Advanced Processing Methods for a New Generation Propagation Resistivity Tool Improves Interpretation Methodology
Authors: Hearn F.P. , Meyer W.H. , Wisler M.M.
Published: December 2007

Much more accurate formation evaluation is now made possible by new generation propagation resistivity tools that make more measurements than previous systems. The additional measurements provide new information from the borehole and the near borehole environment as well as the formation itself. They also provide the capability to identify and differentiate between environmental effects.

An new, advanced processing method combines many of the measurements collected by the tool then identifies and corrects for environmental effects. This includes a new method for dielectric constant correction. The method also calculates horizontal (Rh) and vertical resistivity (Rv) for high angle wells where anisotropic effects are present. A global solution for Rh and Rv is derived using a minimum of four measurements. This eliminates uncertainty where multiple solutions of Rh and Rv are possible.

After corrections are made for environmental effects the method then generates four resolution-matched resistivity curves with fixed depths of investigation (radii) at 10", 20", 35", and 60". This format facilitates invasion interpretation, particularly where both resistive and conductive invasion are occurring proximal to one another.

Field comparisons to wireline array resistivity measurements demonstrate the robustness of the method under a variety of formation resistivity environments and clearly shows where interpretation methodology is improved.

P. 431
Pressure Buildup Analysis With Acoustic Data in Beam-Pumped Wells
Authors: Fair Walter B.
Published: December 2007

Pressure buildup analysis in beam-pumped wells has suffered from the difficulty in directly measuring pressures at the bottom of the well. Often the only reasonable method for acquiring pressure data in such wells is to combine casing pressure and acoustic liquid level measurements with estimated fluid densities to indirectly estimate the bottomhole pressure, which is then analyzed. This procedure introduces errors in the bottomhole pressures, thereby degrading the quality of the analysis. It is also difficult to judge the accuracy of the analyses, since the pressures being evaluated are not directly measured.

This paper presents a simple wellbore model that is applicable to pressure buildup tests in beam-pumped wells. When coupled with the normal wellbore and reservoir fluid flow equations, it is possible to directly model the casing pressures and fluid levels that are measured in acoustic surveys. By adjusting the model parameters to directly match the measured data, an improved evaluation is obtained.

Statistical considerations indicate that, since twice as much data is being used, the results should also be more reliable. In addition, however, it has been found that the casing pressure is extremely sensitive to the wellbore effects, particularly phase redistribution. Since an improved description of the wellbore effects are obtained by matching the casing pressure, improved estimates of the skin and reservoir parameters are also obtained.

This paper presents the theoretical and statistical basis for the improved analysis method as well as the mathematical model. In addition, several examples of actual field analyses are shown. Based on the mathematical model, the effect of errors in the data are also estimated and described.

P. 453
In Search of Thickness-Independent Permeability From Transient Pressure-Rate Data
Authors: Kabir C.S. , Joseph J.A.
Published: December 2007

This paper describes a method for estimating formation diffusivity (k/ ct) from the early-time pressure-rate linear relationship. Both radial and spherical flows, often associated with thick formations, are considered in this formulation. Our formulation assumes that the constant-storage wellbore model applies and the rate-time behavior, during both flow and shut- in tests, is well represented by the exponential model.

The proposed method is general in that the type of fluid (oil or gas or oil-water) or mode of flow (production or injection) does not pose any problem. Initially, we verified the method with synthetic examples and then validated it with four field examples.

Validation is shown two ways. In two examples, k values computed by the proposed and conventional methods are compared directly in absence of downhole flow profile. In two other cases, contributing reservoir thickness h was discerned by first estimating the kh product from conventional analyses and then evaluating k using the proposed method. Thereafter, h so obtained by taking the ratio of the two results was compared with the measured flow profiles. Overall, good agreement was achieved in all cases. P. 491
From Seismic to Reservoir Properties Using Geostatistical Inversion
Authors: Lamy P. , Swaby P. A. , Rowbotham P. S. , Dubrule O. , Haas A.
Published: December 2007

Our confidence in a reservoir model is greater if this model is based not only on well logs and geological knowledge, but also on seismic information. The methodology presented in this paper incorporates these disparate data types to produce models of reservoir parameters and uncertainties associated with them. A 3D seismic dataset is inverted within a geological and stratigraphic model using the geostatistical inversion technique. Several reservoir-scale acoustic impedance blocks are obtained. On the one hand, quantification of uncertainty is determined by computing statistics on these 3D blocks. On the other hand, Collocated Cokriging allows the transformation of impedances into reservoir parameters (Vshale in our case) through a petrophysical relationship while respecting information at wells. Finally, these results are transferred from the time to the depth domain for flow simulation.