bluuebunny/crossref_metadata_2025 huggingface dataset:
An Evaluation of Gas Injection in the Emery West Pool, West Coyote Field, California
Authors: Craddock Sheldon F.
Published: December 2007

The Emery West pool provides an 11-year case history of successful gas injection operations in a depletion type California reservoir producing 32° API oil. The original oil in place was 50 million bbl. Reservoir calculations indicate that only 23 per cent of this oil would have been recovered by normal depletion, but that 33 per cent will be recovered by gas injection operations. This is an increase if 5 million bbl of oil recovery by gas injection. In addition 3,250,000 bbl of natural gasoline and LPG, not recoverable by normal depletion, will be recovered as a result of gas injection. This is an increase of over 200 per cent in the expected natural gasoline and LPG recovery.

Introduction and History

After 11 years sufficient historical data is available on the Emery West pool to predict with some confidence the ultimate benefit from gas injection. The early history of the pool and the details of the injection operations have been adequately presented in a previous paper and are, therefore, only briefly summarized herein. The purpose of this paper is to review the performance of the pool to date, to present the results of reservoir calculations predicting the future production, and to summarize the benefits of gas injection.

The Emery West pool was discovered in 1930. Development proceeded gradually and the basic well spacing pattern was essentially completed in 1943. There has been no drilling activity subsequent to 1943 except in the year 1952. In that year seven small producers were completed at the west end of the pool.

Gas injection was started in July, 1944. Ten MMcf/D of gas was injected into the pool from 1944 to 1949 when injection was increased to 20 MMcf/D to provide virtually full pressure maintenance. Injection has continued at 20 MMcf/D since 1949.
A Strongly Coupled, Fully Implicit, Three-Dimensional, Three-Phase Well Coning Model
Authors: Trimble Russell H. , McDonald A. E.
Published: December 2007

WELCOS is a robust, three-dimensional, three-phase well coning simulator that couples the well rate equation to the reservoir flow equations. This strong coupling allows well rate to be determined simultaneously with reservoir pressures and saturations. The flexibility obtained permits the use of dynamic constraints on well rates, resulting in a highly stable model. The model may be used to obtain the maximum well productivity for a given set of physical limitations and regulatory constraints – e.g., minimum surface pressure, maximum allowed GOR, WOR, water rate, gas rate, etc. The model can function either as a production well or an injection well and, in general, may be used to study any single-well behavior.

This paper describes a strongly coupled formulation and discusses its utility in relation to other implicit models. The linearization of the nonlinear finite difference equations and solution of the resulting linear equations are discussed. Example field applications are included to show the utility of user-supplied production constraints in determining well performance.
Determination of Relative Permeability and Recovery for North Sea Gas-Condensate Reservoirs
Authors: Chen H. L. , Wilson S. D. , Monger-McClure T. G.
Published: December 2007

Coreflood experiments on gas condensate flow behavior were conducted for two North Sea gas condensate reservoirs. The objectives were to investigate the effects of rock and fluid characteristics on critical condensate saturation (CCS), gas and condensate relative permeabilities, hydrocarbon recovery and trapping by water injection, and incremental recovery by subsequent blowdown.

Both CCS and relative permeability were sensitive to flow rate and interfacial tension. The results on gas relative permeability rate sensitivity suggest that gas productivity curtailed by condensate dropout can be somewhat restored by increasing production rate. High interfacial tension ultimately caused condensate relative permeability to decrease with increasing condensate saturation. Condensate immobile under gas injection could be recovered by water injection, but more immediate and efficient condensate recovery was observed when the condensate saturation prior to water injection exceeded the CCS. Subsequent blowdown recovered additional gas, but incremental condensate recovery was insignificant.
When Do Drilling Alliances Add Value? The Alliance-Value Model
Authors: Brett J. F. , Craig V. B. , Brett K. V. , Wadsworth D. B. , Pile K. E.
Published: December 2007

A recent Gas Research Institute report details three previously unstudied aspects of alliances: specific measurable factors that improve alliance success, how a successful alliance should be structured, and when an alliance makes economic sense. For the purposes of this report, an alliance is defined by "technical process integration," which includes joint planning, execution and evaluation. Technical process integration shifts the definition of an alliance beyond a simple focus on the commercial terms. The most innovative tool to emerge from the report, the Alliance-Value model, addresses those aspects surrounding when an alliance makes economic sense.

The theory behind the Alliance-Value model is that the long-term viability of any drilling relationship hinges on its ability to create real value and achieve stability. Based upon the report's findings, the most effective way to form such an alliance is through a detailed description and integration of the technical processes involved. This new type of process-driven alliance is characterized by a value chain which links together a common set of technical processes, mutually defined bottom-line goals, and shared benefits.

Building a process-driven alliance requires time and people and therefore has an associated cost. The real value generated by an alliance must exceed this startup cost. The Alliance-Value model computes the net present value of the cash flows for four different operating arrangements: (1) business as usual (conventional competitive bidding process), (2) process-driven alliance (linking technical processes to accelerate production and reduce expenses), (3) incentivized process-driven alliance (linked technical processes with performance incentives to promote stability), and (4) no drill case (primarily used to gauge the market value of services).

These arrangements test different degrees of process integration between an operator and its suppliers. They can also help determine if the alliance can add enough value to exceed startup costs and if the relationship will be stable. Each partner can test the impact of the relational structure on its own profitability. When an alliance is warranted, all participants can benefit from real value generated in a stable relationship. However, relationships that focus on commercial terms, instead of on process linking, may be playing a zero-sum, no-win game.
The Effect of Bacteria on Sandstone Permeability
Authors: Kalish P.J. , Stewart J.A. , Rogers W.F. , Bennett E.O.
Published: December 2007

Detailed descriptions are given of materials, apparatus and the experimental procedure used to study the effect of bacteria on sandstone permeability. The factors affecting permeability during injection of bacterial suspensions which have been investigated are:

- concentration of bacteria;

- core permeability and median pore size;

- species of bacteria, mode of aggregation and relative size;

- injection rate or pressure differential;

- mean pressure; and

- depth of penetration of bacteria.

The investigation demonstrated that bacteria cannot reduce core permeability to zero and that their effect on permeability is subject to definite limitations. Remedial or permeability restoration studies also were made. Acidization in combination with reverse flow was found to be an effective method for restoring permeability in cores partially plugged with bacteria.

The relationship between the bacterial quantities in the laboratory tests and those found in field operations is discussed. The linear laboratory flow data have been translated into terms of field radial systems; these data indicate the most practical methods of maintaining injection rates in the presence of bacteria are to increase injection pressures or hydraulically fracture the formation.

Introduction

It has long been known that various bacteria flourish in the above-ground components of oil field water- injection systems. The presence of these bacteria has led to the suspicion that they might enter into the causes for reduction of injection well permeability, but only recently has an attempt been made to describe the effects quantitatively. Biocides are used in many cases without a firm knowledge as to whether the bacteria are killed, or if they are, whether the dead cells affect formation permeability. This project was undertaken as part of a study to determine the effect of bacteria, residual oil and precipitated solids such as iron sulfide or calcium carbonate on the permeability of sandstones and to learn whether any of these materials adversely affect brine injectivity in secondary recovery or disposal operations. This report deals with that portion relating to the effect of bacteria.
An Oil Man Looks at Atomic Energy
Authors: Duce James Terry , Chapman A.H.
Published: December 2007

Introduction

In Oct., 1954, the authors prepared a study of future energy requirements of the world. These requirements were balanced against reserves of conventional fuels. To fill the gap left by future deficiencies of oil and coal, it was shown that atomic energy could play a vital role.

We have now had the opportunity to examine the papers presented at the United Nations Conference on the Peaceful Uses of Atomic Energy. We now can present a better assessment of when and how atomic energy is likely to be used to help satisfy the world's seemingly insatiable thirst for power. In this paper we will point out some interesting highlights in nuclear development, some problems to be overcome in commercial utilization, and estimates of the future relationships between conventional and nuclear power.

Military Leadership

In the past, the first change in energy relationships has almost invariably appeared in military operations, and in that respect today is no different from the past. With the advent of atomic energy, the traditional pattern is repeating itself. Military impetus has sparked preliminary development and economic necessity for the development of new sources of energy. This is clearly visible to students of the energy producing industries. Scientists assure us that the world's crust will yield almost limitless reserves of atomic fuels and that they are well on the way to devising dependable means for commercial utilization of atomic energy.

In discussing atomic energy, oil men must not view the future with the trepidation of the buggy whip manufacturer who saw the automobile as the ruination of his business. At a time when the demand for energy in the world is following such a sharply ascending curve - with ample room for all known forms - we should welcome the contribution of the atom to the over-all energy supply and thus to the prosperity of the world.

We shall proceed, therefore, to discuss some recent developments in atomic technique and economics and also try to take a look into the future.
Waterflooding Performance of Communicating Stratified Reservoirs With Log-Normal Permeability Distribution
Authors: El-Khatib Noaman
Published: December 2007

An analytical solution is developed for waterflooding performance of layered reservoirs with a log-normal permeability distribution with complete crossflow between layers. The permeability distribution is characterized by the Dykstra-Parsons (DP) variation coefficient VDP or the standard deviation of the distribution σk. The performance is expressed in terms of vertical coverage as function of the producing water-oil ratio. Also an expression for the dimensionless time (pore volumes of injected water) at a given water-oil ratio is derived. Expressions are also derived for pseudorelative permeability functions and fractional flow curves that can be used in reservoir simulation. Correlation charts are also presented to enable graphical determination of the performance. The variables are combined in such a way that a single chart is constructed for the entire range of water-oil ratio, mobility ratio and permeability variation.

Analogy to the Buckley-Leverett (BL) multiple-valued saturation profile is found to occur at low mobility ratios (M<1) where a multiple-valued displacement front is formed. A procedure similar to the BL discontinuity is suggested to handle this situation. Successive layers with different permeabilities are allowed to move with the same velocity resulting in a single-valued profile with a discontinuity. No such behavior is observed for mobility ratios greater than unity. A criterion for the minimum mobility ratio at which this behavior occurs is presented as a function of the variation coefficient VDP.
Determination of Waterflood Residual Oil Saturation From Routine Core Analysis
Authors: Kazerni H.
Published: December 2007

Proposal Proposal Rathmell et al. proposed a method for estimating water-flood residual oil saturations from core saturations where the cores must he taken with water-base muds having a filtrate loss in excess of 5 cc at bottom-hole conditions. Their equation is

(So)res = (So)coreBoE .........................(1)

where

(So)res = average post-waterflood residual oil saturation in the flooded region of the reservoir

(So)core = average oil saturation from cores

BO = oil formation volume factor at the time of coring

E=bleeding factor- proposed to he 1.11.

In my opinion. Eq. 1 must be corrected for waterflood displacement efficiency through multiplication by the reciprocal of the conformance factor. The conformance factor may be obtained from a reservoir simulator that accounts for reservoir heterogeneity, capillary effects, and mobilities of oil and water. in the absence of a reliable reservoir simulator, the conformance factor is estimated by (1 − V2)/M, as reported by Craig. Using this empirical factor, I propose Eq. 2 as the most practical and the most convenient method to calculate waterflood residual oil saturation from the average of the oil saturations obtained from routine core analysis (provided the cores are taken with water-base mud):

(So)res = (So)core BoE M .........(2) 1 − V2

where

M= mobility ratio, the ratio of the mobility of water at the average water saturation in the reservoir at breakthrough to the mobility of oil in the oil bank ahead of the displacing front. V= permeability variation calculated from reservoir core samples as described in Ref. 2.

Example

This example applies to the 119-R Project of the Henry reservoir, which has been reported elsewhere. The data are obtained from Marathon Oil Co. files or from Ref. 3. The average core oil saturation was obtained from cores taken at the end of waterflooding and before the application of the Maraflood process. The pertinent data are

(So)core = 0.248 SWc = 0.25 M = 1.3 V = 0.325

Using Eq. 2 we get

(So)res = (0.248)(1.01)(1.11) 1.3 (So)res 1 − (0.325)−2

The post-waterflood residual oil of 0.404 compares favorably with the results of other methods reported in Ref. 3. In fact, the "best" estimate of post-waterflood residual oil for the 119-R Project, as reported in Refs. 4 and 5, is 0.40.
Mud Filtration at the Bottom of the Borehole
Authors: Havenaar I.
Published: December 2007

This Technical Note is one page in length.

Experimental Data

In an article by C. K. Ferguson and J. A. Klotz, experiments on the filtration of drilling muds under borehole conditions are discussed. Experimental data on mud filtration through the wall and the bottom of the hole are presented. From the data on bottom-hole filtration it was concluded that the filtrate does not flow freely into the formation, but that the pores of the formation are plugged by the mud.

A quantitative interpretation of the data can be given, by using a formula for bottom-hole filtration, derived below. This formula is based on the following assumptions,Each time a blade of a drag bit, or a cone of a roller bit, moves along the bottom of the hole, the mud cake is completely removed.A new mud cake is immediately formed on the freshly produced surface, and losses of "whole" mud into the formation are negligible (this is equivalent to an immediate plugging of the pores).The filtration of the mud on the bottom of the hole follows the classic law: (Equation 1), where t is the time required to yield a volume of filtrate V, A is the surface area of filter cake, and C is a constant. The application of this equation means that any eroding effect of the mud stream on the mud cake is neglected.
Estimated Effect of Horizontal Fractures in Thick Reservoirs on Pattern Conductivity
Authors: Landrum Bobby L. , Crawford Paul B.
Published: December 2007

An electrical model study has been made to estimate the effect of horizontal fractures in thick reservoirs on pattern conductivity. For the patterns studied, it is shown that fracturing all the wells in the pattern increases the conductivity considerably more than fracturing only single wells. For certain conditions one large fracture is more effective in increasing conductivity than several fractures of half the radius. Particularly in thick reservoirs and with large fractures, the center of the pay is found to be more responsive than other locations. For the seven-spot pattern fracturing the center well is more effective in increasing pattern conductivity than fracturing all outer wells with fractures of the same size.

Introduction

Although commercial fracturing has been used for some time very little quantitative information is known about the effects of fractures on reservoir behavior. The purpose of this work was to estimate the effect of horizontal fractures in thick reservoirs on the conductivity of various flooding and cycling patterns. Circular fractures originating at the wellbore and extending symmetrically into the pay were considered.

Analysis

Electrical models were used in making this study. Horizontal fractures were simulated by copper sheets shaped like the fractures and of a proportional size; the well bore was simulated by a copper wire. A dilute salt solution served as a conducting medium. A conductivity bridge was used to measure the conductivities of the various patterns studied.

Effect of Horizontal Fractures on Conductivity

Fig. 1 shows the effect on square and staggered line-drive patterns of horizontal fractures located in the center of the pay. The model is shown schematically in the insert. The upper and lower groups of lines show the effect on conductivity when all wells are fractured, and when only one well is fractured, respectively. In general, pattern conductivities are substantially improved by fracturing all wells.

Fig. 2 shows the effect of multiple horizontal fractures on the conductivity of a line-drive pattern.
Comparative Evaluation of Foam Stability to Oil
Authors: Mannhardt Karin , Novosad J. J. , Schramm L. L.
Published: December 2007

Foam performance was evaluated by several experimental methods (corefloods, bulk foam stability, micromodel observations, interfacial parameters) using three commercial surfactants, either by themselves or mixed with a fluorinated surfactant. The presence of oil reduced foam mobility reduction factors (Fmr) to different degrees; excellent Fmr were still attained with some surfactants in the presence of residual oil. Using the fluorinated surfactant as additive enhanced the oil tolerance of some, but not all, foams. The tested foams exhibited oil transporting properties. Each foam adjusted to its own residual oil saturation and corresponding level of mobility reduction. Foam performance in corefloods did not correlate in general with predictions based on the other experimental methods.
Development of the Downhole Dynamometer Database
Authors: Waggoner John R. , Mansure A. J.
Published: December 2007

The Downhole Dynamometer Database (DDDB) is a compilation of test data collected by Sandia National Laboratories (SNL) with a set of five downhole memory tools built by Albert Engineering (AE), and deployed in the sucker rod string with sensors to measure pressure, temperature, load, and acceleration. The purpose of the Database is to provide industry with high quality measurements of downhole sucker rod pumping dynamics. A Microsoft Windows-based interface allows users to browse and visualize the more than 40 MB of data, and to extract data from the database for use in their own programs. The database is available upon request from Sandia National Laboratories at http://www.sandia.gov/apt/.
Surfactant Criteria for Successful Carbon Dioxide Foam in Sandstone Reservoirs
Authors: Kuhlman M. I. , Lau H. C. , Falls A. H.
Published: December 2007

Laboratory results demonstrate that surfactant adsorption on sandstones is minimized and foam performance improved by reducing the ethoxylate chain length in alcohol ethoxy sulfonates and blending unethoxylated and ethoxylated sulfonates to optimize desirable properties. The results also show that laboratory adsorption measurements can only be extrapolated to reservoirs by (1) replicating the anaerobic conditions of reservoirs, and (2) differentiating authogenic minerals from drilling mud found in reservoir cores.
Control-Volume Method for Simulation in the Well Vicinity for Arbitrary Well Configurations
Authors: Ding Yu , Lemonnier P. A. , Estebenet Thierry , Magras J-F.
Published: December 2007

Advanced wells are getting more and more used in reservoir engineering to increase the oil recovery. However, accurate modeling of these kinds of wells is still a challenge due to the scaling problem related to the large gridblocks used in the simulation and the small wellbore diameter. In this paper, a control volume method is proposed, which is suitable for the well singularity flow modeling. Both the well performance and the flux calculation in the well vicinity can be accurately handled with this method. The use of this control volume approach for advanced well modeling with distorted gridblocks is particularly addressed. Some examples are presented to illustrate the efficiency of the approach.
Dynamic Behavior and Design of Offshore Caissons
Authors: Hong S.T. , Brooks J.C.
Published: December 2007

Free-standing caissons are used for supporting flare pipes and single-well production platforms. However, caissons tend to be flexible and dynamically sensitive, and the static design practice may not be adequate for this type of practice may not be adequate for this type of structure. To assess motion effect on the integrity of the structural system and to quantify the allowable motion for safe operation on board a caisson platform, analytical and experimental studies of platform, analytical and experimental studies of the dynamic behavior of a caisson structure were conducted and are described here. The analytical simulations agree well statistically with The motion measurements.

A caisson design procedure considering dynamic effects was developed Design considerations include ultimate strength failure, fatigue failure, excessive motion, and possible damage during installation. A key feature in an effective caisson design is that the upper part of the caisson should be made as small as possible so that wave loading and the caisson period can be minimized The fatigue design procedure was verified with past caisson operational experience. To illustrate past caisson operational experience. To illustrate the procedure, a flare-pipe support caisson in 185 ft of water was designed and analyzed.

Introduction

Free-standing caissons are used for supporting flare pipes or single-well production platforms. The attractiveness of a caisson structure lies in the potential economy and the short time required for potential economy and the short time required for fabrication and installation. However, a caisson tends to be flexible, and dynamic effects may increase the design requirements from both strength and functional standpoints. To assess the motion effect on the integrity of the structural system and to quantify the allowable motion level for effective operation on board a caisson platform, analytical and experimental studies of the dynamic behavior of a caisson structure were conducted, and a procedure was formulated for designing a caisson considering dynamic effects. Observations from the experimental data and computer simulations of the caisson behavior are described. Verification of the computer simulation and some useful information for developing and using such simulations as well as practical interpretation of the analytical results practical interpretation of the analytical results also are given. Differences between a static design and a dynamic design are illustrated in an example design of a flare-support caisson in 185 ft water.

MOTION MEASUREMENT

Motion data were taken from a caisson platform offshore Louisiana. General dimensions of the caisson are shown in Fig. 1.

SPEJ

P. 291
Optimum Fractures in High-Permeability Formations
Authors: Morales R. H. , Norman W. D. , Ali S. A. , Castille C. T.
Published: December 2007

This paper describes an analytical model that (1) designs the pumping schedule of tip-screen-out (TSO)(frac-pack) fractures for high- and low-permeability formations, (2) estimates the reservoir production, and (3) determines the optimum propped length using the net present value concept. Sensitivity studies show the influence of the proppant permeability to propped fracture width. Sensitivity runs also show the influence of drainage area (and formation permeability) to optimum fracture length. A field example demonstrates the benefits of an appropriate fracture design.
Tax Considerations in Various Oil Transactions
Authors: Bullion J. Waddy
Published: December 2007

Introduction

This paper considers tax aspects of transactions involving production payments. In addressing engineers, it is fitting and proper that the terms be first defined. What is a production payment? It is essential that a production payment be dischargeable only out of runs accruing to a property and the holder of the payment must look exclusively to the proceeds of the sale of production accruing to the payment for its satisfaction and liquidation. It is also essential that the payment be of limited duration - that it not last for the life of the property or properties. The payment in most instances is free and clear of all costs of operation and development and is dischargeable out of a specified fraction of the runs. The size of this fraction will vary, depending, in part, upon the nature of the transaction involved. A production payment is normally payable out of a stated percentage of the runs until from the sales proceeds of such runs there has been paid a specified sum of money. The amount of a payment may also be stated in terms of barrels of oil or cubic feet of gas. It is possible to create a true production payment which is based on neither a dollar amount nor units of production. Such a payment would have attributed to it a specified percentage of the net proceeds from the operation of the properties and would terminate when the remaining reserves under the properties reach an agreed percentage of total reserves.

Types of Production Payments

What are the kinds of production payments? Basically there are two types of production payments - the reserved payment and the carved out payment. A reserved payment is created where the owner of a property or properties assigns all of his leasehold or working interest to another and in such assignment reserved to himself a production payment.

A carved out payment is one which is assigned out of a larger depletable property; for example, if A, the owner of an oil and gas lease, assigns to B 75 per cent of the runs accruing to such lease unit B has received from the proceeds of the sale of such runs the sum of $100,000, A has carved a payment out of his leasehold estate. There are two types of carved out payments.
Quantifying Drilling Efficiency and Disruption: Field Data vs. Theoretical Model
Authors: Putot C. J. M. , Guesnon Jean , Perreau P. J. , Constantinescu Andrei
Published: December 2007

Mechanical and kinematics data at the bit have been collected during drilling operations and organized to identify optimal drilling efficiency. Transitional conditions towards abnormal behavior have been distinguished. Normal drilling is usually characterized by regular linear relationships between global control variables at the bit, which approximately correspond to an upscaling of a local Mohr-Coulomb-type failure mechanism of the rock. Most of our experimental data confirm this classical disposition. However, considerable departure from these relationships is noted, especially when there is bottomhole assembly (BHA) resonance or when there is partial balling at the bit. The field tests presented here allow us to verify classical theory and to draw up new guidelines for behavior in nonoptimal or dangerous, evolving operating conditions, such as those that occur under poor cleaning conditions. The main features of a mechanical structuring model involving transition towards low-efficiency conditions are presented, and it is shown how this model confirms our interpretation of field data. The model couples the drillability of rock and the general dynamics of the bit in an original and synthetic way. It makes it possible to understand and test the sensitivity of bit response to variables such as "weight on hook," torque on the drillstring, and flow rate of the fluid.
Unique PDC Bit Technologies Combine To Reduce Drilling Time in Interbedded Formations
Authors: Taylor Steven , Besson Alain , Minto Djoko , Mampuk I. S.
Published: December 2007

Interbedded formations cause difficulty when selecting a drill bit for optimum section performance. Hard stringers require bit features that conflict with those required for softer homogeneous formations. Limited by conventional technology, this culminates in the selection of a bit too heavy set to maximize penetration rates through the soft formation or too light set to drill the hard stringers. This paper describes a unique combination of PDC bit technologies that provide a solution to consistently drill interbedded formations without compromising bit selection. The unconventional design consists of features to maintain high-penetration rates in soft formations and the stability and life required to pierce through hard stringers.

The technologies are combined on a steel bit body. The nature of this material allows its fundamental engineering properties to be exploited to produce extreme features that cannot be achieved using matrix powder technology. This material is the cornerstone that expands the design and manufacture windows for conventional PDC bit technologies.

Soft formations imply high-penetration rates: the technologies developed are a novel hydraulic arrangement, bit face design, cutter size, and usable diamond volume. Hard stringers require high stability in order to maintain bit life by preventing premature component failure. Technologies developed are conventional antiwhirl theory, localized cutter placement to extend bit life, and an innovative low-friction gauge pad that spans two blades and encloses a junkslot.

The case history demonstrates the significant performance improvement that can be achieved through interbedded formations by combining innovative PDC bit technologies. The study examines the development of the 1214-in. section in the Tunu field, Indonesia. The continual development of the project is discussed including a lighter set variant to complete the same application and the successful translation of the design philosophy into a slimhole program.
Coiled-Tubing Drilling of Horizontal Sidetrack in House Mountain Field, Alberta
Authors: Milligan M. R. , Andreychuk M. T. , Lunan W. B.
Published: December 2007

In 1995, the first horizontal sidetrack successfully drilled using coiled tubing (CT) was carried out at Shell's House Mountain oilfield. The objective was to drill underbalanced a 378-in. diam by 300-m-long horizontal hole section from an existing vertical, cased oil well. The existing well was re-entered using a conventional drilling rig; a window milled in the casing, and the build section drilled to an inclination of 90°. 238-in. CT was then used to directionally drill the horizontal section underbalanced with nitrified water. The zone of interest was a Devonian-age reef-edge and limestone structure, at a depth of about 2200 m, called the Slave Point.

A case history of directionally drilling the horizontal sidetrack using 238-in. OD. CT is provided. Coiled-tubing drilling proved to be a cost-effective alternative to drilling the horizontal sidetrack without using a conventional drilling rig. Shorter trip times, underbalanced drilling, enhanced rates of penetration (ROP), and the ability to maintain weight on bit were all achieved. ROPs increased by up to three-fold while drilling underbalanced.
Shear Effects on Polyacrylamide/Chromium (III) Acetate Gelation
Authors: Broseta Daniel , Marquer Olivier , Zaitoun Alain , Baylocq Pascal , Fery Jean-Jacques
Published: December 2007

In practice, gel formulations used in water shutoff and conformance improvement treatments are subjected to hours of strong shearing in surface and well equipment (i.e., pumps, tubings, etc.) and in the near-wellbore part of the formation before being left under quiescent conditions (well shut-in). The purpose of rheological measurements presented in this paper is to assess the influence on polyacrylamide/chromium (III) gelation of shearing sequences representative of those occurring in the field. The gel properties investigated are the gelation time and final yield stress, which are related, respectively, to the pumping time and to the maximum differential pressure the gel can withstand in the reservoir (matrix or fracture).

Two different polyacrylamide/chromium (III) formulations were analyzed, one of which, involving a high-molecular-weight polyacrylamide, is adapted for plugging fractures, and the other one, involving a low-molecular-weight polyacrylamide, is usually employed for plugging porous matrices. These formulations had previously been used in some specific field applications. The experiments consisted of a series of viscosity, storage modulus and yield stress measurements on the gelling solutions, with the purpose of quantitatively characterizing the gelation kinetics and final strength of the gel formed.

The results demonstrate that the effect of shearing is to restrain gelation and, in particular, to limit the viscosity rise due to the formation of aggregates of crosslinked polymers (microgels). The gelation time, defined in relation to this viscosity rise, increases with shear rate for the high-molecular-weight (non-Newtonian) formulation, but is unaffected by shear for the low-molecular-weight (Newtonian) formulation. Experiments have also been conducted in which an extended initial period of strong shearing was followed by another extended period of rest. The final gel strength of both formulations, evaluated from yield stress measurements, turned out to be independent of the shear rate history.
Application of Lévy Random Fractal Simulation Techniques in Modeling Reservoir Mechanisms in the Kuparuk River Field, North Slope, Alaska
Authors: Gaynor G. C. , Chang E. Y. , Painter S. L. , Paterson Lincoln
Published: December 2007

Incorporating a suitable level of heterogeneity into reservoir simulations is necessary for accurate prediction of production rates and final recoveries. Spatial correlation of petrophysical properties, particularly permeability extrema, exerts a profound influence on flow underlying reservoir displacement and depletion processes. Common modeling techniques are founded on Gaussian assumptions for statistical distributions. Such Gaussian-based approaches can inadequately model the permeability extrema that can dominate reservoir performance. However, optimal reservoir management strategies at the Kuparuk River Field require that significant efforts be made to correctly model reservoir behavior.

This study utilizes a new method, Lévy fractal simulation, for interpolating permeability at a former gas injection area now being targeted for oil production. The main producing interval is a diagenetically and mineralogically complex clastic unit. The diagenetic complexity causes difficulties in the lateral modeling of large changes in petrophysical properties observed in near-vertical wells, particularly permeability. Prior efforts at modeling the movement of gas, at typical interwell scales, have met with limited success. In this study, the Lévy technique employs automatic calibration with log and core data for the interwell interpolation of the spatially complex reservoir properties. The Lévy fractal simulations preserve the sharp jumps in reservoir properties observed at stratigraphic boundaries and within reservoir subzones. The spatially correlated petrophysical properties are consistent with geologic experience.

A fine-scale permeability model incorporating well conditioning data was built using the Lévy fractal interpolation technique. This model encompassed not only the gas injection area but drillsite patterns immediately adjacent. The model preserves the geometry of the reservoir units so that truncation and onlap relationships are preserved. The permeability extrema in the model are characterized by lateral continuities extending over many grid-blocks away from control locations. Porosity was modeled using sequential Gaussian simulation in which well porosity logs were used as the primary conditioning data, and the modeled permeability used as secondary conditioning data. The fine-scale model was then used as input in an upscaled dynamic simulator built to test reservoir mechanisms. The model was also useful for prognosing porosity and permeability at proposed well locations. Early drilling results indicate that substantial quantities of producible oil remain in the former gas injection area.
Comprehensive Model for Predicting Corrosion Rates in Gas Wells Containing CO2
Authors: Farshad F. F. , Garber J. D. , Polaki Venugopal
Published: December 2007

A WINDOWS-based computer model has been developed which can help predict the location of corrosion and the life of a carbon steel tubular in a gas condensate well containing carbon dioxide. This model provides a physical description for the five different flow regimes that can occur in gas wells. This description has proven to be useful in the prediction of the corrosion rates of these wells. The model does not use the partial pressure of CO2 in the calculation of corrosion rate. It has been found that the hydrodynamics is the most important parameter in this type of corrosion. The model has an expert system associated with it which takes into account the volume fraction of condensate and water in the tubing. When the water level reaches and exceeds 50% of the total volume, the tubing is completely water-wet and the corrosion rate is a maximum. At the point where 30% or less of the volume of the fluid is water, the corrosion rate is believed to be zero. Caliper surveys have played a role in our ability to establish these points of transition within the model. Case histories have been presented which illustrate how the model can help in performing failure analysis and design of gas condensate wells.
Laboratory Modeling of Mudcake Application and Erosion for Gravel-Pack Design in Horizontal Wells
Authors: Becker T. E. , Gardiner N. H.
Published: December 2007

Successful gravel packing of long horizontal sections depends in part on preventing carrier fluid from leaking off to the surrounding permeable reservoir. This requires correctly designed drill-in fluids to apply a thin filter cake, rendering impermeable the sand formation at the wellbore wall. Filter cake must be embedded sufficiently within the formation interstitial space to resist scouring by flowing sand during the gravel-packing operation. This paper summarizes testing using a large-scale laboratory apparatus and procedure designed to test the effectiveness of drill-in fluids planned for use in horizontal wells recently drilled in the Gulf of Mexico.

This paper shows the benefits of modeling a horizontal gravel-pack interval before attempting to install the gravel pack. Gravel-packing techniques for long horizontal well sections were evaluated with a laboratory model of a casing/borehole annulus. In the horizontal section modeled, permeability is sufficient to interfere with the transportation and distribution of pack sand from total depth to dogleg when positive differential pressure is maintained. The goal of this modeling experiment was to predict whether the formation's permeability at the sandface could be reduced enough to allow successful gravel packing without damaging the formation far beyond the sandface.

Gravel-packing technology is well established for near-vertical wells, with off-the-shelf equipment and textbook procedures readily available. The exceptionally long producing intervals in horizontal wells present a greater challenge for gravel packing, however, interval permeability is, by design, continuous. This continuous permeability both enhances well productivity and allows increased wellbore fluid flow into reservoir rock. When the permeable formation absorbs the fluid energy necessary to evenly disperse pack sand throughout the section, sand bridging can result, restricting the flow before the pack sand is fully distributed across the entire interval.

The laboratory model simulates the axial flow of drilling and/or completion fluids through an annulus. The model has an impermeable confining wall (simulating the casing) and a permeable wall (simulating reservoir rock). Recently, it was used for testing the capacity of a drill-in fluid to reduce reservoir near-face permeability, and allow sand propagation throughout a long horizontal interval. Results obtained both in the laboratory and in subsequent field trials validate the use of a drill-in fluid in reducing near-sandface permeability. The procedure has been used successfully on multiple horizontal wells with typical horizontal section lengths of 1,000 to 2,500 ft. Plans are underway to continue the practice in additional wells.
Evaluation of Selective vs. Point-Source Perforating for Hydraulic Fracturing
Authors: Underwood P. J. , Kerley L. A.
Published: December 2007

"Select-fire" (SF) and "point-source" (PS) perforating completions were used to fracture the Reef Ridge diatomite formation in the Midway-Sunset field, Kern county, California. Fracturing treatment analysis and production history matching were used to evaluate the reservoir and fracturing parameters for both completion types. Single fractures were created with the PS completions, and multiple fractures resulted from many of the SF completions.

Descriptions of the reservoir, production history, and fracturing techniques used leading up to this study are presented. Fracturing treatment analysis and production history matching were used to evaluate the reservoir and fracturing parameters for both completion types.

The work showed that single fractures were created with the PS completions, and multiple fractures resulted from many of the SF completions. A good correlation was developed between productivity and the product of formation permeability, net fracture height, bottomhole pressure, and propped fracture length. Results supported the continued development of 10 wells using the PS concept with a more efficient treatment design, resulting in substantial cost savings.
New Treatment for Removal of Mud-Polymer Damage in Multilateral Wells Drilled Using Starch-Based Fluids
Authors: O'Driscoll K. P. , Amin N. M. , Tantawi I. Y.
Published: December 2007

Significant improvement in production from horizontal, multilateral wells has been realized through the application of specific enzyme breaker (SEB) technology for the removal of natural starch polymers used in drilling operations. This new treatment allows placement of a fluid to remove polymeric mud damage at the cessation of drilling operations for each multilateral section, which could not otherwise be re-entered for cleanup and effective stimulation during completion of the well.
Estimation of Gross Rock Volume of Filled Geological Structures With Uncertainty Measures
Authors: Abrahamsen Petter , Hauge Ragnar , Heggland Knut , Mostad Petter
Published: December 2007

The gross rock volume of a filled structure is uncertain because of uncertainty in the determination of caprock depth and the uncertainty in depth to the hydrocarbon contact determined by the spill point of the caprock. Ignoring this uncertainty might lead to biased volume estimates. This paper reports two procedures to assist with assessing this uncertainty to obtain better estimates. The first is to use conditional simulation techniques to generate realizations of the depth to the caprock. The second procedure is a new fast algorithm that determines the location of the spill point and trapped area of each caprock realization. Taken together, the two procedures determine the thickness and lateral extension of each reservoir realization. Finally, gross rock volume for each realization can be calculated and the volumetric uncertainty can be quantified in terms of expectation, histograms, percentiles, etc., for the whole set of realizations. A synthetic example and an example from the North Sea illustrate the use of these procedures. A method for including knowledge of the spill-point depth for improving depth maps is also presented.
A Simulation Approach To Validate Petrophysical Data From NMR Imaging
Authors: Zuluaga Elizabeth , Majors Paul D. , Peters Ekwere J.
Published: December 2007

Nuclear magnetic resonance (NMR) imaging was used to map the 3D porosity and permeability distributions in heterogeneous sandstone cores under controlled laboratory conditions. The porosity and permeability distributions so obtained were used to numerically simulate first-contact miscible displacements in the cores. The spatial and temporal solvent concentrations from the numerical simulations were compared to those from imaging experiments in the cores in an effort to validate the porosity and permeability data. The results show that with calibration, useful 3D porosity and permeability distributions of heterogeneous cores can be derived from NMR imaging (NMRI).