bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling a Repressured Waterdrive Gas Reservoir
Authors: Moltz A.K.
Published: December 2007

Reservoir modeling confirmed reserve losses occurring in a waterdrive gas reservoir to justify blowdown project initiation. The material-balance models initially used could not match the water influx and repressuring observed in the reservoir. This paper shows that material-balance calculations need to be modified to account for trapped-gas compression that occurs with repressuring, and demonstrates the use of a "simple" numerical simulation model to predict performance. Numerical simulation enabled us to match reservoir behavior successfully, quantifying the effects of trapped-gas compression, and to identify the importance of critical blowdown rates and timing for optimizing reserve recovery from this repressuring waterdrive gas reservoir.

Introduction

The Tom O'Connor 5,100 Ft Sand is a gas reservoir located in Refugio County, TX. This fairly homogeneous Frio sandstone contains dry gas with a moderate directional waterdrive from the southwest. Fig. 1 gives a composite log and a structure map of the reservoir. At the start of this study, the reservoir was already in the later stages of depletion, having recovered 85% of the original gas in place.

During a period of low gas market demand, the reservoir experienced significant water advancement and gas-zone repressuring from a lengthy production curtailment by the purchaser. Gas-zone pressures increased from 800 to 1,100 psig during this period (see Fig. 2). The operator successfully demonstrated that substantial reserve losses were occurring and obtained a special gas allowable to blow down the reservoir .

Reservoir modeling was performed to confirm and quantify the gas reserve losses resulting from production curtailment and to predict the additional recovery that would result from blowdown initiation. Numerical simulation was used effectively to model the historical performance of the reservoir and to determine the optimum blowdown rate to maximize recovery.

Model Development

A simple tank-type model was developed with constant reservoir rock and fluid properties. The model incorporated radial flow from one central producer and contained a limited, directional aquifer as indicated by performance. Fig. 3 gives the reservoir input properties and model layout. Fig. 4 shows historical water encroachment and remaining free-gas volumes determined from known gas/water contact locations based on drill wells and gamma ray/neutron log surveys. Model accuracy was enhanced by the lengthy performance data available, which allowed excellent model calibration through history matching.
Genesis of a Three-Phase Subsea Metering System
Authors: Dowty E. L. , Hatton G. J. , Durrett M. G. , Dean T. L. , Jiskoot R. J. J.
Published: December 2007

This paper describes the development of a three-phase metering system for installation on seabed templates at or near subsea wellheads. It tracks the development of the system from its conception through continuing tests on a production platform in the North Sea. The paper also reviews modification of the original design as a result of 1989 offshore tests.
Continuous Improvement in Drilling Performance: A Challenge for the Industry
Authors: Buchan Robert
Published: December 2007

In 1990, extensive drilling activity was matched by significant improvements in drilling performance across a range of North Sea blocks. Major reductions in well costs were achieved as a result. The paper describes how a fresh approach to well planning and design led to these improvements and how continuous improvement is possible by creating an environment for innovation that includes teamwork, risk analysis, and a "value for money" approach to well planning.
New Water-Based Muds for Tertiary Shale Control
Authors: Reid P. I. , Minton R. C.
Published: December 2007

This paper describes laboratory and field assessments of a series of inhibitive water muds developed by BP. RCS 1 contains cationic starch to control fluid loss and to inhibit shale expansion further. RCS 2 is a highly inhibitive version of RCS 1 containing polyglycerol. RCS 3, the most inhibitive mud of the series, contains a phosphate salt and polyglycerol. Levels of inhibition appear close to those of oil-based mud.
Model Study of Foam as a Sealant for Leaks in Gas Storage Reservoirs
Authors: Bernard George G. , Holm L.W.
Published: December 2007

Previous studies have shown that foam, because of its unique structure, reduces gas flow in porous media. This blocking action of foam appears to be especially suitable for sealing leaks in underground gas storage reservoirs. Such reservoirs often have permeable areas in the overlying caprock that allow permeable areas in the overlying caprock that allow vertical migration of gas from the storage zone to the upper formations. The escaped gas represents both a safety hazard and an economic loss.

Our objectives in this study were to evaluate the effectiveness of foam in preventing the escape of gas from a leaky gas storage reservoir and to find the foaming agents that were most suitable for this purpose.

We simulated the behavior of a leaky gas reservoir with a sandstone model and found that foam was 99-percent effective in reducing leakage of gas through the model.

The amount of foaming agent required to seal a leak depends on the adsorption-desorption properties of the agent. After testing many foaming agents, we concluded that best results are obtained with certain modified anionic esters of relatively low molecular weight. Less than 0.3 lb of such agents is required per barrel of pore space in Berea sandstone.

This study indicates that foam generation should be an effective and economical method for reducing or stopping gas leakage from an underground storage reservoir.

Introduction

The practicality of underground gas storage is greatly dependent upon the confinement that the caprock provides for the formation to be used as a storage reservoir. In spite of numerous precautions, several gas storage projects are plagued by vertical migration of gas from the intended storage zone to upper formations. Such gas leaks pose a safety hazard and represent an economic loss. If leakage is very high, the storage operation may be uneconomical.

In at least one cases the leak problem is minimized by periodically collecting the escaped gas from the upper formation and reinjecting it into the storage reservoir. While such a solution is feasible, it is economically unattractive because the leak limits pressures and gas injection rates. Furthermore, energy must be expended in order to circulate the escaped gas.

Recent studies have shown that foam, because of its unique structure, reduces gas flow in porous media. This blocking action of foam appears to be uniquely suitable for sealing leaks in underground gas storage reservoirs. Our objectives in this study were to determine the effectiveness of foam in reducing gas flow in a model of a "leaky" gas storage reservoir and to find foaming agents most suitable for this purpose.
Foams as Blocking Agents in Porous Media
Authors: Albrecht Robert A. , Marsden Sullivan S.
Published: December 2007

Although foam usually will flow in porous media, under certain controllable conditions it can also be used to block the flow of gas, both in unconsolidated sand packs and in sandstones. After steady gas or foam flow has been established at a certain injection pressure pi, the pressure is decreased until flow pressure pi, the pressure is decreased until flow ceases at a certain blocking pressure pb. When flow is then reestablished at a second, higher pi, blocking can again occur at another pb that will usually be greater than the first pi. The relationship between pi and Pb depends on the type of porous medium and the foamer solution saturation in the porous medium. A process is suggested whereby porous medium. A process is suggested whereby this phenomenon might be used to impede or block leakage in natural gas storage projects.

Introduction

The practice of storing natural gas in underground porous rocks has developed rapidly, and it now is porous rocks has developed rapidly, and it now is the major way of meeting peak demands in urban areas of the U. S. Many of these storage projects have been plagued with gas leakage problems that have, in some cases, presented safety hazards and resulted in sizeable economic losses. Usually these leaks are due to such natural factors as faults and fractures, or to such engineering factors as poor cement jobs and wells that were improperly abandoned. For the latter, various remedies such as spot cementing have been tried but not always with great success.

In recent years several research groups have been studying the flow properties of aqueous foams and their application to various petroleum engineering problems. Most of this work has been done under problems. Most of this work has been done under experimental conditions such that the foam would flow in either tubes or porous media. However, under some extreme or unusual experimental conditions, flow in porous media becomes very difficult or even impossible. This factor also has suggested m us as well as to others that foam can be used as a gas flow impeder or as a sealant for leaks in gas storage reservoirs. In such a process, the natural ability of porous media to process, the natural ability of porous media to generate foam would be utilized by injecting a slug of foamer solution and following this with gas to form the foam in situ.

This paper presents preliminary results of a sandy on the blockage of gas flow by foam in porous media. It also describes how this approach might be applied to a field process for sealing leaks in natural gas storage reservoirs. Throughout this report, we use the term "foam" to describe any dispersed gas-liquid system in which the liquid is the continuous phase, and the gas is the discontinuous phase.
Automated Geological Evaluation of Continuous Slim-Hole Cores
Authors: Spain David R. , Morris Steven A. , Penn John T.
Published: December 2007

Slim-hole continuous coring and drilling techniques applied to oil exploration are receiving wide recognition. Slim-hole coring methods produce high-quality continuous cores that yield valuable exploration information. Amoco Production Co.'s geological evaluation modules furnish an on-site automated instrumentation system to extract a maximum of information from the core, thus providing the vital link in developing high-speed slim-hole coring into an integrated exploration tool.

"Inverse logging" (logging the core instead of the borehole) is the primary goal of on-site geological evaluation. Up-hole measurements on cores include gamma scan, magnetic susceptibility, infrared mineralogy, ultraviolet fluorescence, nuclear magnetic resonance porosity, and pyrolysis (source rock) data; macroscopic and microscopic video images for analysis and archiving; and sedimentological/lithological description.

Continuous rock samples through entire basin-filling sequences are used to calibrate seismic and well log data. This information provides insight into opportunities and risks associated with exploration and development in all types of basins.

Introduction

In recent years it has become apparent that the oil and gas industry needs major innovative changes to improve exploration effectiveness and decrease the costs of finding. The results of studies done to assess the technical risk associated with exploration and development indicate a need to better understand the actual geological and geophysical characteristics of reservoir, seal, and source packages. In both basin reconnaissance and subtle-trap exploration modes, the need has never been greater to pursue the acquisition of continuous cores actively to better analyze subsurface hydrocarbon systems and improve technical databases.

Continuous cores acquired through complete sedimentary sections enhance geological and geophysical data. Direct observation of lithology, sedimentary structures, fossils, reservoir pore geometry, source-rock characteristics, seal characteristics, and petrophysical rock properties permits fact (instead of interpreted, indirect information) to guide subsequent exploration and exploitation programs.

Traditional slim-hole continuous coring and drilling techniques are receiving wide recognition in their application to oil exploration; core analytical capabilities are considered deficient and present a challenge to the oil industry. Automated geological analysis of continuous slim-hole cores results in on-site, real-time evaluation. The geological evaluation modules provide the critical link for connecting high-speed slim-hole coring into an integrated exploration system, and, thus, have the potential to revolutionize exploration and development philosophies and create entirely new oil and gas paradigms. Slim-hole drilling and on-site evaluation can be applied to all phases of exploration and development, including rank wildcat well analysis, field development studies, and regional trend or basin analysis studies.
Accounting for Silica Precipitation in the Design of Sandstone Acidizing
Authors: da Motta E. P. , Plavnik Benjamin , Schecter R. S. , Hill A. D.
Published: December 2007

Mud-acid treatments normally are designed by approximating the complex mineralogy of a sandstone with a "lumping" procedure. Minerals are classified as either fast- or slow-reacting and the rates of their reaction with HF are determined by analysis of the acid effluent from acidized core plugs. For most treatments carried out at modest temperatures and reasonable rates, this approach is satisfactory. In this paper, we show that at higher reaction temperatures, the simple two-mineral dissolution model does not apply because an intermediate product of the HF reaction with quartz, feldspars, and clays (H2SiF6) begins to react further with both clays and feldspars. This new reaction must be included to model data. The additional reaction, not observed at lower temperatures, has important consequences. For example, the acid injection rate is no longer critical. The analysis presented here shows that retarded acids are unnecessary. Contrary to previous concepts, mud acid itself provides a deep-penetrating capability. This surprising result may account for the high percentage of successful treatments even when this treatment is carried out under a wide range of conditions.
What Difference Does Internal-Taper Length Make on Drillpipe Fatigue Life?
Authors: Wilson G. E. , Shepard J. S.
Published: December 2007

Premature drillpipe failure is a serious drilling problem. Such failures normally occur in internal-upset (IU) and internal, external-upset (IEU) drillpipe in the internal taper (Miu) or near where the IU blends into the drillpipe tube ID. This paper illustrates some of these types of failures and offers a new long-taper, thick-wall upset as a solution.
Prevention of Bit Balling in Shales—Preliminary Results
Authors: Roy Sanjit , Cooper G. A.
Published: December 2007

Bit balling is a major problem that occurs during drilling of a formation containing water-sensitive clays, such as shales. This paper discusses a new technique for eliminating this problem that establishes an electric potential between the formation and the bit with the bit as the cathode. Laboratory drilling experiments in Pierre shale showed that, under favorable conditions, bit balling was reduced. The rate of penetration (ROP) doubled when the bit was negatively charged with respect to the rock, compared with the case where no potential was applied. This method suggests a new approach to reducing bit balling without toxic chemicals or oil-based muds, which are subject to serious environmental restrictions.
Drillstring Imaging—An Interpretation of Surface Drilling Vibrations
Authors: Booer A. K. , Meehan R. J.
Published: December 2007

A brief review of drillstring vibration literature is followed by the development of a model-based approach to analyze drillstring vibrations. The resulting image calculated from vibration data allows identification of interaction points between the wellbore and the drillstring. Field data examples are given.
Foam in Porous Media: Characteristics and Potential Applications
Authors: Raza S. H.
Published: December 2007

A laboratory study was made of the variables which affect the generation, propagation, quality und nature of foam produced inside a porous medium. It is shown that foam can be generated and propagated in porous media representative of reservoir rocks at pressure levels ranging from atmospheric to 1,000 psig, and under pressure differentials ranging from 1.0 to 50 psi/ft. The quality of foam depends on the type of foaming agent, the concentration of foaming solution, the physical properties of the porous medium, the pressure level, and the composition and saturation of fluids present. The nature of foam depends upon the type of foaming agent and its concentration in the foaming solution.

The study shows that the flow behavior of foam in a porous medium is a complex one which cannot he correctly described in terms of the high apparent viscosity of foam. Also, the concept of relative permeability is not applicable to the flow of foam due to the associative nature of its components.

On the basis of the discussed characteristics of foam, several applications of foam are suggested in oil recovery processes.
Instant Well-Log Inversion With a Parallel Computer
Authors: Kimminau S. J. , Trivedi H.
Published: December 2007

Well-log analysis requires several vectors of input data to be inverted with a physical model that produces more vectors of output data. The problem is inherently suited to either vectorization or parallelization. PLATO (parallel log analysis, timely output) is a research prototype system that uses a parallel architecture computer with memory-mapped graphics to invert vector data and display the result rapidly.

By combining this high-performance computing and display system with a graphical user interface, the analyst can interact with the system in "real time" and can visualize the result of changing parameters on up to 1, 000 levels of computed volumes and reconstructed logs. It is expected that such "instant" inversion will remove the main disadvantages frequently cited for simultaneous analysis methods, namely difficulty in assessing sensitivity to different parameters and slow output response.

Although the prototype system uses highly specific features of a parallel processor, a subsequent version has been implemented on a conventional (serial) workstation with less performance but adequate functionality to preserve the apparently instant response. PLATO demonstrates the feasibility of petroleum computing applications combining an intuitive graphical interface, high-performance computing of physical models, and real-time output graphics.
From DOS to UNIX: An Independent's Experience
Authors: Hepguler Gokhan , Meehan D. Nathan
Published: December 2007

Union Pacific Resources Co. (UPRC) is a large independent operator with about 100 petroleum engineers. UPRC has a reasonably sophisticated PC network with many hundreds of PC's connected by several local area network (LAN) servers. Essentially all engineers have a 386-based PC on their desks with access to a host of software packages, peripheral devices, and mainframe computers. Many engineers have acquired 486-based PC's. UPRC's solution has involved migrating from a DOS-based platform on individual users' desks to UNIX workstations. Dozens of UNIX workstations are networked; some are "on the desk, " while others are located in central locations. Reservoir simulation, geostatistical modeling, image processing, and log analysis are now done exclusively on the UNIX workstations. Numerous DOS-based programs, however, have not yet been migrated into the UNIX environment.

This paper describes the topography of both PC DOS and UNIX workstation networks in UPRC and examines the flow of information in each network configuration to identify differences. The successes and failures of various techniques for providing access to both platforms are presented.
Field Installation of a Distributed Database Application—Concept vs. Reality
Authors: Evans E. L. , Berry M. R. , Goings M. C.
Published: December 2007

A PC-based equipment-failure reporting system was designed as a distributed database over a wide area network (WAN). Speed-related communication problems were encountered, necessitating program redesign. In the original design, data for local failures were to reside in several local field offices. Division-level reporting was to be accomplished by concatenating the field offices' databases over the network. Validation information was to reside in several small databases on the division fileserver. These data were to be accessed by the field offices as a remote link. The program executables were to reside on yet another fileserver belonging to the service organization that maintained the program code. Both the field and division offices were to access the program code as a remote link.

It soon became apparent that the communications link between the division and field offices was too slow for both division failure reporting and field failure validation. Although not encountered, a break anywhere in the chain of communications would disable the application in all locations. These problems were overcome by actually running from local copies of the files but continuing to treat the various files as if they were in remote locations. Maintenance routines were created to update the local copies.

This paper discusses the network and communications facilities in place, the original design, the performance encountered, the design changes, and current performance. A brief discussion of possible future modifications is included.
A Simple Low Cost Method for Determining the P.I. of High Gas-Oil Ratio Pumping Wells
Authors: Deax David W.
Published: December 2007

Determining productivity index (PI) is a problem that confronts operators in many areas problem that confronts operators in many areas where beam units are used. With sucker rod pumping, it is not uncommon for equipment to pumping, it is not uncommon for equipment to be over or under designed because of a lack of productivity information. This paper describes a simple, low-cost technique for determining the PI of a pumping well which will be referred to as the "shut-in annulus" test. The method is especially useful in areas where gas and foam limit the use of conventional fluid level techniques. A two-pen recorder is used to measure tubing and casing pressure, permitting an accurate estimate of working pressure at pump depth. Using this information along with data on static pressure, producing rate, and gas-oil ratio, the PI can be calculated.

A comparison of calculations by this method to measurements with bottom-hole pressure gauges was made, and the results pressure gauges was made, and the results showed that the "shut-in annulus" test gives a reliable estimate of PI. A group of deep, gaseous pumping wells was then tested using this technique. No productivity information was available at the time of testing, but all of the wells were suspected of having additional producing capacity. PI's were calculated and changes in production equipment were made to satisfy the requirements of individual wells. Based on the results of testing, it is concluded that the method gives a reliable estimate of PI, and it has consistently proven to be a good "yard-stick" for production purposes.

Introduction

Accurate productivity index (PI) information is needed to design artificial lift equipment and its importance is increased where there are no allowable restrictions. Many methods with varying accuracy are used to find the PI of beam pumped wells. A common method is to fix the working fluid level using a well sounder and calculate flowing bottom-hole pressure with an estimated gradient; however, gas, foam or paraffin frequently cause erroneous results. Another method is to run a gauge below the pump to record pressure while the well is produced. This procedure is not widely used because of time and expense.

This paper describes a simple, low-cost technique (called the "Shut-In Annulus Test") for determining the PI of a pumping well.
Development of an Antiwhirl Core Bit
Authors: Sinor L. A. , Warren T. M. , Armagost W. K.
Published: December 2007

The application of whirl-reducing technology to core bits has provided significantly improved coring performance. Laboratory and field tests show that the elimination of bit whirl reduces core jamming problems and produces cores that are smoother, closer to gauge diameter, and less fractured than those drilled with standard polycrystalline-diamond-compact (PDC) core bits. Eliminating bit whirl also results in a more efficient cutting process, which can lead to improved rates of penetration. Utilizing the antiwhirl core-bit technology can improve the economics of conventional coring operations significantly and also can make wireline-retrievable coring with conventional rigs and drillstrings a practical alternative.
A Liquid-Freon Permeameter
Authors: Hurd B.G.
Published: December 2007

HURD, B.G., SOCONY MOBIL OIL CO., INC., DALLAS, TEX.

A liquid-Freon permeameter suitable for making routine permeability determinations on small plug samples is described. The instrument is characterized by simplicity of design and ease of operation, and can be assembled inexpensively from stock items of laboratory equipment. It combines the unique advantages of both liquid and gas permeameters while eliminating many undesirable features of both general classes of instruments. Precision and accuracy of the specific Freon permeability measurements compare favorably with results of conventional liquid and gas permeameters.

Introduction

The liquid-Freon permeameter described in this paper was designed and built for special investigations of the properties of petroleum reservoir rocks. However, its unique advantages over conventional gas and liquid permeameters make it eminently suitable for routine use in the core analysis of small plug samples. In general, gas permeameters are very popular because of their simplicity of design and ease of operation. However, apparent gas permeabilities are normally higher than true specific permeabilities unless special corrections for gas-slippage are applied. Since these corrections require two or more measurements at different internal gas pressures, much of the time advantage of the specific gas permeability measurements is lost. Liquid permeability measurements, on the other hand, require no slip correction, but liquid saturation of the sample is time-consuming and difficult to insure. Often, too, the saturating liquid must be extracted or dried from the plug before it can be used for another experiment. The liquid Freon permeameter described herein retains the inherent accuracy of the liquid permeameter, while affording the speed and ease of operation of the gas permeameter. Freon-12 (dichlorodifluoromethane) is a halogenated hydrocarbon, immiscible in the liquid phase with water. It may be considered as an oil phase in laboratory fluid-flow studies. Like butane and propane, it is a gas at normal room temperatures and atmospheric pressure but can be liquefied at moderate pressures. Complete liquid saturation of a plug sample with any of these fluids can be easily achieved by condensing vapors in the sample and operating the permeameter at a pressure above the vapor pressure of the liquid. Freon-12 is superior to butane or propane for permeability measurements only in that it is relatively non toxic and completely incombustible, and thus presents no fire or explosion hazard. Freon-12 is believed to be completely nonreactive with most petroleum-reservoir rock samples. It volatilizes immediately from a plug on depressurizing to leave a clean, dry sample suitable for subsequent experiments. Thus, the inherent risk of changing physical properties of rock samples by cleaning and drying operations between permeability measurement and subsequent experiments is eliminated.

DESCRIPTION OF THE PERMEAMETER

The design of the liquid Freon permeameter is shown schematically in Fig. 1.

SPEJ

P. 18^
Solutions to Problems Drilling a High-Temperature, High-Pressure Well
Authors: Cassidy S. D.
Published: December 2007

This paper is a case history of a deep, high-temperature, high-pressure (HTHP) well, drilled in the U.K. sector of the North Sea. The topics covered include the use of a vertical seismic profile (VSP) ahead-of-the-bit prediction combined with measurement-while-drilling (MWD) information to assist in picking a critical casing point. This technique permits penetration of the high-pressure transition zone without reaching a previously identified kick zone. Also discussed is an assessment of the suitability of different casing elevators to run a heavy casing string. New laboratory data indicate that some elevators will initiate localized yielding of the casing material at tensile loads much lower than those predicted by theory. Field data are presented that demonstrate the limitation on oil-based mud (OBM) circulating rates caused by flowline temperatures approaching the base oil flashpoint.

Although this material relates to a HTHP well, much of the information may be applied to improve the safety and efficiency of drilling operations in other deep, overpressured, or close-to-balance drilling environments.
A New, Effective Matrix Stimulation Diversion Technique
Authors: Paccaloni Giovanni
Published: December 2007

This paper describes the theory and application of a new matrix stimulation diversion technique, maximized pressure differential and injection rates (MAPDIR), that uses injection rate as the key parameter to obtain sustained, planned bottomhole differential pressure, ∆p, levels. The technique, applicable wherever Darcy's law is valid (in sandstones and in unfractured or microfractured carbonatic reservoirs), favorably replaces diverting agents and extends to long intervals (> 100 ft) the main advantage provided by mechanical zone isolation for "selective stimulation," which is maximized ∆p. The use of slightly viscosified stimulation fluids can further extend the range of application and improve the economics by reducing both the amount of hydraulic power and the fluid volumes required for stimulation. A multilayered reservoir case illustrates the application of the MAPDIR technique. A new log-log plot of skin evolution vs. injected-acid volume shows significant damage removal trends and provides important information for matrix stimulation treatment optimization. Field experience includes the successful treatment of horizontal pay intervals of up to 460 ft.

Because the real objective of diversion techniques is the effective removal of damage from the whole exposed pay, the meaning of "diversion" in this paper is not narrow (i.e., applicable only to diverting agents and ball sealers) but includes "placement" and "coverage" techniques, such as mechanical isolation, viscosified acids, and MAPDIR.
The Rejuvenation of the 30-Year-Old McAllen Ranch Field: An Application of Cross-Functional Team Management
Authors: Durrani A.J. , Escovedo B.M. , Ordemann Bill , Bickley J.A. , Tepper B.J. , Simon J.M.
Published: December 2007

This case history overview describes the application of crossfunctional team management in redevelopment of a 30-year-old south Texas gas field. Multidisciplinary cooperation and synergism were emphasized, and efforts focused on a common team goal. The results have been extraordinary; all areas have shown significant improvement, including gas production, which is up by more than 250%.

Introduction

By the mid-1980's, McAllen Ranch field gas production had declined to a low of 24 MMcf/D owing to reservoir depletion and curtailment. The end of curtailment and subsequent development drilling activity increased the rate to 80 MMcf/D by early 1988. However, with reduced drilling and natural decline, the rate had fallen again to about 50 MMcf/D by early 1989.

At this time, a cross- functional team was established to evaluate additional investment opportunity and to develop a plan to increase production from the noncontributing reserves that were behind pipe. This team looked at all aspects of the field's production and developed a consensus plan that included acquisition, processing, and interpretation of a fine-grid 3D seismic survey; development drilling focused in the northern portion of the field (B-area); procedures to obtain regulatory approval to commingle noncontributing reserves in existing wellbores; and enhanced drilling and completion techniques.

This paper describes the interaction and synergism among the various specialties and functions involved in the producing operations at McAllen Ranch and how the concept of cross-functional team management has led to the rejuvenation of this 30-year-old field. It focuses on the process of cross-functional team management rather than just the results achieved.
Loads on Drillpipe During Jarring Operations
Authors: Aarrestad Thor V. , Kyllingstad Age
Published: December 2007

Jarring implies heavy loads on the drillstring. The highest load on the drillpipe before jarring is at the rig floor. This paper discusses loads on drillpipe before, under, and after jarring. We show that for most situations, the shock wave from the jar impact does not imply additional load on the drillpipe compared with static load. The theoretical results are confirmed by measurements of a jarring operation with stuck point at ≈ 1200 m measured depth. Loads on the drillpipe can be a limiting factor in jarring operations because fear of possible additional loads from jarring dynamics may restrict the trip force (overpull) on the jar. Our main conclusion is that dynamic jar forces do not give additional loads on drillpipe. This information can be used to set an optimal trip force on the jar.
Amplification of Pulse-Testing Theory
Authors: Culham W.E.
Published: December 2007

Pulse-testing theory as originally outlined is based Pulse-testing theory as originally outlined is based on the standard exponential integral solution to the radial form of the diffusivity equation. This paper presents a new solution to the subject diffusivity presents a new solution to the subject diffusivity equation and outlines how this type of solution can be used to clarify the "tangent construction method" of analyzing pulse data. The new solution is composed of a periodic part and a transient part. The splitting of the total solution into two parts facilitates the extension of pulse-testing to include steady-state conditions The differential equation and auxiliary conditions that define the periodic pulsing problem are

.......(1)

with the initial condition of

...........(2)

and boundary conditions of

.............(3)

.............(4)

where

............(5)

and H(t) is the unit step function. The solution to this boundary value problem is usually represented by the summation of appropriate exponential integral terms. A solution that splits the total solution into periodic and transient portions can be obtained as periodic and transient portions can be obtained as follows. Utilizing Laplace transform theory, the solution to Eqs. 1 through 4 is

................(6)

where, the real part of the complex integration limits, is taken large enough so that all singularities of the integrand lie to the left of the line ( - i, + i ). Complex variable theory was used to evaluate the integral in Eq. 6; and the final solution, in field units, can be shown to be

.........(7)

P. 1245
Oil Recovery From Bottomwater Reservoirs
Authors: Islam M.R.
Published: December 2007

Introduction

Billions of barrels of oil remain unrecovered in "bottomwater" reservoirs with a highwater-saturation zone in communication with the oil zone. Typically, the water cut in such reservoirs increases rapidly during primary production, leading to low primary oil recovery. If a water zone were not present, many of these reservoirs would be good candidates for waterflooding. Instead, the performance is poor under conventional waterflood and worse if the oil is highly viscous. Several techniques and production strategies have been proposed recently to improve waterflood performance of such reservoirs. These are the subject of this paper.

Problems In Producing Bottomwater Reservoirs

Water coning is the most common problem in producing oil from a bottomwater reservoir. Once the water reaches the perforations, it is produced in preference to the more viscous oil, and the producing WOR becomes prohibitively high.

In heavy-oil formations, a high water cut often causes excessive sand deposits in the wellbore. A specific minimum oil flow rate is required to mobilize sand in most heavy-oil reservoirs. In most cases, with an increase in the water cut, the sand-carrying capacity of the produced fluids drops considerably and the wellbore sands up.

The detrimental effect of the bottomwater zone sometimes is alleviated by shale breaks, which reduce vertical permeability. A number of heavy-oil reservoirs with water legs have not been affected significantly by an underlying high-saturation water zone because of the presence of frequent horizontal shale breaks. Similar horizontal shale breaks probably will increase productivity in light-oil reservoirs with bottomwater as well.

Field Experience

The Bonnie Glenn field of Alberta is a light-oil bottomwater reservoir that has produced successfully under primary production. This light-oil (35 to 40 deg API) reservoir has a water zone, yet the oil production rate has been steady with little water influx from the bottomwater zone. One interesting feature of this reservoir is the presence of a gas cap. Also, the reservoir has a very high vertical permeability, resulting in an efficient gas cap drive with maximum pressure gradient from the top of the reservoir. As a result, oil can be produced with relatively small drawdown and minimum influx from the bottomwater zone. However, the reservoir is maturing after producing (with gas reinjection) some 80% of the original oil in place (OOIP). Currently reported WOR values are high.
Correlations of Gas-Oil Ratio History in a Solution-Gas-Drive Reservoir
Authors: Roberts Thomas G. , Ellis H. Edison
Published: December 2007

Instantaneous producing gas-oil ratio histories are calculated for a large number of hypothetical solution-gas-drive reservoirs from the basic data used by Arps and Roberts, and the results are presented in graphical form. A correlation is thus established wherein a typical GOR history can be obtained for a given gravity oil, with a given solution GOR, produced from a given type of reservoir rock.

Introduction

In 1955, Arps and Roberts presented the results of 72 solution-gas-drive recovery computations made on hypothetical reservoirs. The study covered six different types of reservoir rocks representing maximum, average and minimum conditions for sandstones and limestones. These six types of reservoir rock were assumed to be saturated with 12 synthetic crude-oil and gas mixtures representing oil gravities of 15 degrees, 30 degrees and 50 degrees API, and solution gas-oil ratios of 60, 200, 600, 1,000 and 2,000 scf/STB. The calculations, made using a Muskat-type differential equation, resulted in the relationship of stock-tank oil recovery (as a fraction of total pore volume) vs reservoir pressure for each hypothetical reservoir. From these data a correlation was developed between oil recovery and original solution GOR, API oil gravity and type of reservoir rock. The purpose of the present paper is to extend the original work of Arps and Roberts by presenting calculations of the instantaneous producing GOR histories for these same hypothetical sandstone reservoirs. The solutions representing the limestone cases have been omitted.

Gas-Oil Ratio Equation

The instantaneous producing gas-oil ratio R can be calculated by the following equation.

. . (1)

JPT

P. 595^
Some Effects of Contaminants on Real Gas Flow
Authors: Zana E.T. , Thomas G.W.
Published: December 2007

In gas well testing and deliverability forecasting, failure to make corrections for contaminants can lead to intolerable errors. In general, where impurities exceed ten percent by volume, corrected values of the real gas pseudopressure function should be used.

Introduction

Isothermal gas flow through porous media has been the object of considerable study - the work, in general, deals with the flow of ideal gases and is therefore not generally applicable to gas reservoirs having low permeabilities or high reservoir pressures. This is because ideal gas flow treatment implicity assumes that pressure gradients in the system are small. Furthermore, the pressure dependence of gas viscosity and the gas law deviation factor are usually neglected. Recently, Al-Hussainy et al. presented a theory for real gas flow. Unlike previous work, theirs demonstrated that the pressure dependence of viscosity and the gas law deviation factor could be taken into account by expressing the gas flow equation in terms of a pseudopressure function. A nonlinear flow equation similar to the diffusivity equation was developed that did not require the assumption of small pressure gradients. In addition, a table of the real gas pseudopressure function was presented for gases containing pseudopressure function was presented for gases containing small amounts of contaminants. In a companion paper Al-Hussainy and Ramey showed how the real paper Al-Hussainy and Ramey showed how the real gas flow theory could be applied to standard gas well tests. Again, this study was limited to gases containing small amounts of contaminants. The purpose of our paper is to investigate some of the effects of gas contamination on real gas flow. Particular attention is devoted to constructing tables of Particular attention is devoted to constructing tables of the real gas pseudopressure function corrected for various amounts of nitrogen, carbon dioxide and hydrogen sulfide. Comparisons are made with the uncorrected results of Al-Hussainy et al. Finally, several example calculations are presented for some typical well tests, showing the errors that can occur in failing to make adequate corrections for gas contaminants.

Real Gas Flow Equations

For completeness, some of the development of Al-Hussainy and Ramey is included here. Principal assumptions are:Flow is isothermal and laminar.Gas composition is constant.The gas law is pV = znRT.The reservoir is homogeneous and isotropic.The formation has constant thickness and no dip. The equation for radial flow of a real gas is

(1)

Eq. 1 can be expressed in terms of the real gas pseudopressure function defined by pseudopressure function defined by

(2)

which yields

(3)

where cg(p)is the isothermal compressibility of gas given by

(4)

The pressure Pm is an arbitrary base pressure.

JPT

P. 1157
Optimizing the Distribution of Cathodic Protection Current
Authors: Roberson Glenn R. , Schremp F.W.
Published: December 2007

Relative currents applied for a given potential may vary because of variations in distance from well to ground bed, in resistivities between wells and ground bed, and in pipe-to-soil resistance. Here is a simple method of measurement - more economical than the potential profile - that is sensitive to the variables and that makes it possible to compensate for them.

Introduction

In most instances wells are given cathodic protection on an individual basis. However, when well density is great, the interactions between cathodic protection systems and the electrochemical differences between wells cannot be overlooked. We shall discuss here various factors that affect the cathodic protection of well casings, and a procedure that can be used to optimize the distribution of cathodic protection current.

Methods of Current Distribution

Fig. 1 shows a typical control arrangement for a multiwell system. A variable rectifier generates a given total current output that is distributed according to a plan with the aid of a variable resistance at each well. The conductors may be flowlines, or they may be special conductors installed to carry the current. Fig. 2 illustrates, for each well, individual variable rectifiers that can be adjusted according to plan. In some cases two- to four-well systems are adjusted only by a central rectifier, and the current is allowed to flow to each well in inverse proportion to the resistance in that leg of the circuit.

Measurement of Current Requirements A number of methods have been used for measuring current requirements for each well. Following are some examples.E-Log I on a sampling or on all wells.Some variation of E-Log I.Potential profile data.Current density.Estimated economic limit.Some combination of these.

Of these methods, only the potential profile has enough sensitivity to give a measure of current requirement under operating conditions.

Variations in Current Requirement

Fig. 2 shows an installation with equal spacing between the wells and their individual ground beds. In actual practice, because of topographic adaptation or selection of ideal ground-bed soil, there is usually considerable variation in wellhead to ground-bed distances. In Fig. 3 the best ground bed is located close to two wells and distant from the other three. Fig. 4 shows the location of the ground bed in an almost ideal position; but two wells are in a subsurface salt water aquifer with the ground bed, and the other wells are not. Fig. 5 shows two wells where the low resistant area of the mud pit includes the upper casing and two where it does not. According to potential theory, the change in voltage (E) with distance (x) from a spherical anode is given by:

(1)

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P. 812