bluuebunny/crossref_metadata_2025 huggingface dataset:
Pressure Transient Analysis of CO2 and Enriched-Gas Injection and Production Wells
Authors: MacAllister D. J.
Published: December 2007

A theoretical basis for pressure transient analysis of gas wells with emphasis on the real gas pseudo pressure approach is outlined. An analysis procedure is developed to analyze wells either injecting or producing predominantly CO2 or enriched gas. This procedure is used to calculate flow capacities and skin factors from pressure transient tests in injection and production wells from two CO2 projects. A computer program is documented which aids in the analysis of gas wells with the real gas pseudo pressure. Finally, example calculations are shown for a CO2 well, an enriched gas well, and an enriched gas well contaminated with CO2 / H2S.
Automatic Pressure Buildup Data Acquisition and Interpretation Using a Microcomputer-Based Acoustic Liquid Level Instrument
Authors: Podio A. L. , McCoy J. N. , Huddleston K. L.
Published: December 2007

Production is lost when skin damage restricts fluid flow into the wellbore. The presence and degree of skin damage is most commonly determined through analysis of pressure buildup tests. This forms the basis for selecting wells as candidates for stimulation, workovers and recompletion. Traditionally these tests have been conducted using downhole pressure bombs or in the case of most pumping wells through the use of acoustic annular fluid level data which was processed off-site. The logistical complexities and high cost of these methods have limited the extent and frequency of well testing. Given the present need for production optimization and operating cost reduction, the development of a cost effective method for buildup testing represents a major advance in petroleum technology.

This paper describes the design, implementation and application of a microcomputer-based system for automatically performing pressure buildup tests in pumping wells, from surface measurements, and analyzing the data in realtime at the wellsite. The system is based on a portable PC which controls the operation. A solenoid-actuated acoustic source, powered with compressed gas, generates accurately repeatable acoustic pulses at variable programmable intervals. Acoustic echo travel time is interpreted in terms of position of the liquid level in the wellbore. Simultaneously the computer acquires wellhead pressure and temperature data, using high precision transducers, from which bottomhole pressure is calculated. Strip chart recordings of the acoustic signals are also made to periodically control the quality of the data. At any time during the test the operator can obtain standard graphical display of the buildup test ( Horner plot, dP vs. dT, MDH, etc. ) as well as conventional interpretation in terms of skin, afterflow rates and duration. Results from three field tests of the system are presented. They indicate that the system was used successfully in fairly harsh environmental conditions and was able to acquire buildup data of quality comparable to that obtainable with bottomhole pressure bombs. Interpretation of the results are in agreement to those obtained independently by DST.
Asphaltene Flocculation During Oil Production and Processing: A Thermodynamic Colloidal Model
Authors: Leontaritis K. J. , Mansoori G. A.
Published: December 2007

The need for understanding the nature of asphaltenes and asphalts and their role in the production and processing of crude oit is well recognized around the world as manifested by the current activities in the Petroleum Industry towards the exploration, drilling, production and processing of heavier oils (higher in asphaltene content). Asphaltene deposition during production and processing of oil ranks as one of the costliest technical problems the Petroleum Industry faces today. In the present report a thermodynamic-colloidal model has been developed capable of predicting the onset of flocculation of colloidal asphaltenes in oil mixtures due to either changes in composition (i.e.: solvent addition) or electrical phenomena (i.e.: streaming potential generation due to flow of asphaltenes containing oil in conduits or porous media). For oil mixtures from which flocculation is caused simply by flow, the model can make predictions as to the velocity ranges where colloidal asphaltene flocculation can be avoided. This could have a significant impact on allowed reservoir drawdown rates, well spacing, and tubing design.
Polymers for Mobility Control in CO2 Floods
Authors: Dandge D. K. , Heller J. P.
Published: December 2007

The very low viscosity of the displacing fluid is the probable cause of much of the early breakthrough and poor areal sweep efficiency that plagues most applications of CO2 flooding technology. A focussed and already partially successful research program is described, to develop polymers that are soluble in dense CO2 and raise its viscosity sufficiently so that they can be used as direct thickeners for mobility control. Such water-free additives will offer greatly improved displacement efficiencies on both microscopic and macroscopic scales.

Developed correlations between molecular structure and solubility in both simple hydrocarbon-CO2 and in polymer-CO2 systems are reviewed. Guided by these, we have synthesized amorphous poly-1-hexenes as a first step towards the preparation of more complex multicomponent polymer systems. Reported in this paper are results on the solubilities and viscosities of various α-olefin polymers in dense lower hydrocarbons such as n-butane and n-propane, which are close to dense CO2 in many solvent properties.

Also reported are other experimental details, including the development of gas chromatographic techniques to follow the course of higher α-olefin polymerization, and measurements of molecular weights and molecular weight distribution of the synthesized polymers. It is pointed out that polymers of narrow molecular weight distribution must be used for accurate determination of solubilities in dense CO2.
The Role of Adsorption in Polymer Propagation Through Reservoir Rocks
Authors: Zaitoun A. , Kohler N.
Published: December 2007

Low shear injection of different-nature polymers through various sand and sandstone cores has been performed to study the specific influence of adsorption on polymer propagation and flow behavior.

As predicted by the depletion layer theory, polymer propagates faster than brine through non adsorbing porous media giving a mobility ratio less than solution viscosity ratio. An increase in clay content both decreases permeability and increases polymer adsorption. Thus a polymer propagates through pores having a smaller cross-section at a lower rate. When pore sizes become close to macromolecule size, polymer adsorbs, forming bridges in pore throats, thus giving very poor and irregular propagation rates. A dynamic method for adsorption measurements on heterogeneous rocks is proposed. Our experimental results effectively fit a capillary flow model with a crossflow section reduced by an impenetrable adsorbed layer.
Oil Price Stability: An Impossible Dream?
Authors: Kelly M.
Published: December 2007

With the introduction of netback deals negotiated in August 1985, the Saudis abdicated their role as the swing supplier to world oil markets. Their action ended 25 years in which first the international majors and then OPEC had held the line (officially) on crude prices at the expense of downstream margins. In 1986, oil price instability hit new highs, as sellers fought for market share in the absence of a "gatekeeper" on production and a marker crude reference price. Tranquility is not likely to be restored soon.
Stratification of Bank Energy Loans
Authors: David A. , Carson G. P.
Published: December 2007

Due to an increased number of problem oil and gas bank loans, the office of the Comptroller of Currency (OCC) recently revised guidelines for troubled reserve-based loans. While credit classification of oil and/or gas reserve-based loans is predicated on an assessment of all relevant credit factors, an important part of the credit worthiness is the quality of engineering data that is used to prepare an engineering report. The engineering report is addressed by the OCC with regard to "realistic" pricing and discount factors, as well as its timeliness.

Because cash flow generated from the sale of oil and/or gas in the future is the primary basis for reserve-based loan values, the OCC calculates the ratio of loan balance (Loan) to the discounted Present Worth of the future net income (PW) of proved developed producing properties as a test in determining the safety of a loan. This ratio, (Loan/PW), is defined as the Loan Ratio. According to the OCC, whenever the loan balance exceeds 65% of the discounted Present Worth of the proved producing properties, the expected cash flow cannot meet the planned amortization schedule, and the total support of the debt is provided solely by the pledged collateral, the OCC has guidelines for banks to use in classifying their problem credits. Depending on the magnitude of the undercoverage, a loan may be classified as Other Assets Especially Mentioned (OAEM), Substandard, Doubtful, or Loss.(1) Banks, in turn, are required to reserve funds for possible loss or write-off as a loss, depending on the loan classification. The reciprocal of the Loan Ratio is used by many banks and is defined as Loan Coverage, (PW/Loan). For the sake of consistency, Loan Coverage will be used in the remainder of this analysis.

Any loan write-off or loan loss reserve directly affects the profit of a bank as the amount reserved is subtracted from earnings. Creath etal(2) describe the determination of loan loss reserve and its effect on a bank's profitability. Briefly, varying magnitudes of loan loss reserves are required by the OCC when Present Worth to loan coverage (PW/Loan) drops below guideline ratios that indicate the loan's principal and interest may not be recovered. Energy banks do not intentionally make risk-oriented loans. This "no-risk" approach is the primary reason the cost of bank loans should be among the lowest available.
Application of Exploration Statistics to Venture Assessment: Potential Merits and Problem Issues
Authors: Rapoport L. A. , Grender G. C.
Published: December 2007

Appropriate historical data on exploratory drilling and discoveries can provide valuable background information to assist in the projection of the economic outcomes of exploration ventures. This can be accomplished by using discovery statistics derived from historical data as a reference for, or supplement to, the specific assumptions made about the likelihood and size of potential discoveries in the venture under consideration.

This paper, based on an extensive body of data developed for each of the U.S. petroleum provinces, discusses the utilization of exploration statistics in the form of "discovery functions" (relations between cumulative discoveries and cumulative exploratory drilling) for the purpose of prospect or venture assessment. In particular, we illustrate the validity of these functions, and demonstrate their application to the estimation of the discovery probabilities for fields of different sizes.

However, we show that meaningful analysis requires that these probabilities be estimated separately for (suitably defined) individual depth zones. Another problem issue is that the measurement of exploratory drilling is not unequivocal: it may be defined in terms of the number of wells that are specifically targeted to, or terminating in, the zone under consideration, or in terms of both the terminating wells and those transversing the depth zone and going to deeper horizons. The effects of using these different measures of exploratory drilling in the derivation of discovery probabilities and subsequent venture assessment are outined.
Synergistic Approach for Siting and Design for Injection of Hazardous Liquid Wastes: Case Study in Western San Joaquin Valley, Kern County, California
Authors: Wilson M. J. , Kiser S. C.
Published: December 2007

Subsurface injection of wastes is a technology on which a great deal has been written in the last 25 years. Some of the key references are mentioned in Subsurface Wastewater Injection by Warner and Lehr (1977).

The earliest controlled waste water injection program outside of oilfield operations may have been in 1939 (Harlow, 1939 in Warner and Lehr, 1977). Its use has expanded in the last 30 years to the point that, nationally, 60% of the 15.6 billion gallons (59 million cubic meters) of hazardous waste legally disposed of in the U.S. is being injected through wells into deep aquifers (Gordon, 1984). In the past 30 years of hazardous waste injection, there has been a failure rate of only 2.4% (Morgan, 1986) where groundwater (either drinkable or non-drinkable) has been contaminated.

In California, commercial hazardous waste is transported to one of seven approved sites located around the state (Figure 1). None of the currently operating sites utilize deep well injection as a final disposition for Class I liquids. However, the geologic setting of the Great Valley in California was determined to be potentially suitable for deep-well waste injection by Repenning (1960) and Warner and Lehr (1977). The most common form of Class II liquid disposal in California is deep well injection.
Tapping the Bicameral Mind: A New Approach for Petroleum Engineering Management
Authors: Underwood E. A.
Published: December 2007

The petroleum industry has had to curtail incoming manpower in the last few years due to a changing economic landscape. This change has made optimal use of engineering resources imperative. The optimization need not cause major upheavals within the industry. A shift in managerial thinking and a strategic integration of engineers and engineering managers into functional syndicates will aid in tapping the engineering energy and expertise present in an organization.
A Versatile, Fully Implicit, Black Oil Simulator With Variable Bubble-Point Option
Authors: Farnstrom K. L. , Ertekin T.
Published: December 2007

A stable and efficient, general-purpose, variable bubble point black oil simulator is presented. The program utilizes the method of substitution of variables for modeling gas phase appearance and disappearance. Paralleling its application in conventional reservoir simulation, recent work has shown that the present model forms a solid basis for the development of more specialized simulators containing unique options.

The objective of this paper is to present a general description of the simulator and to describe in detail the numerical methods and specific programming techniques utilized. At the heart of the model is the variable bubble point formulation. This employs relatively complex Jacobian building routines and switching schemes. These are specially designed for efficiency and acceleration of convergence.

The automatic timestep selector for thermal simulation presented by Sammon and Rubin has been modified to accommodate the substitution of variables in black oil simulation. Techniques for implementation of this timestep selector are presented.

To solve the system of nonlinear flow equations, a modified Newton-Raphson procedure is presented. In comparison with the classical Newton-Raphson procedure, the present method requires a larger number of iterations per time step, but overall computation time is significantly reduced. A series of tests are presented to compare the classical and the modified Newton-Raphson procedures and to illustrate the efficiency and stability of the model.
A Regression Technique With Dynamic-Parameter Selection or Phase Behavior Matching
Authors: Agarwal R. , Li Y-K. , Nghiem L.
Published: December 2007

The major problem associated with phase-behavior matching with a cubic equation of state is the selection of regression parameters. There are many parameters that can be selected as the best set of parameters, and therefore a dynamic parameter-solution scheme is desired to avoid tedious and time-consuming trial-and-error regression runs.

This paper proposes a regression technique where the most significant parameters are selected from a large set of parameters during the regression process. This reduces the regression effort considerably and alleviates the problem associated with the apriori selection of regression parameters.

The success of the technique is demonstrated by matching the experimental data for a light oil and a gas condensate.
Unsteady State Flow In Pipeline Networks
Authors: Ruehr Otto G.
Published: December 2007

Publication Rights Reserved

This paper was prepared for the Society of Petroleum Engineers Gas Technology Symposium to be held in Omaha, Nebr. Sept. 15–16, 1966. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers Office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

This paper attacks the problem of computing transient flow in gas pipeline networks by means of finite differences and digital computation. Pressure (P) and flow (Q) are assumed to he dependent upon a single space variable (x) along the pipe and on the time (t). A greatly simplified but generally accepted mathematical model consistent, of a system of nonlinear partial differential equations is the point of departure:

Following simple changes of variable (w = p2, v = Q2), the problem is reduced to the solution of:

A stable predictor-corrector method of finite difference approximation due to Jim Douglas, Jr. and B.R. Jones, Jr. is employed to reduce the computation to the solution of a system of linear algebraic equations (matrix inversion). The incorporation of initial conditions, boundary conditions, and internal flow conservation equations, all of which in finite difference form become linear algebraic equations, results in a single matrix equation for the calculation of pressures and flows in the pipeline network.

DERIVATION OF FINITE DIFFERENCE EQUATIONS

The computation of transient flow in gas pipeline networks is complicated mathematically by the nonlinearity of the governing partial differential equations. This is in marked contrast, of course, to the situation in steady state flow, where the corresponding equations, at least in their simplest form, have exact mathematical solutions. The mathematical model we assume has resulted from a number of simplifications, including the neglect of altitude and temperature variation. Although it is beyond the scope of this note to discuss the validity and significance of these simplifications, it is generally believed that the equations we will discuss are an accurate first order description of the actual physical system.
Using Multiple Radioactive Tracers To Optimize Stimulation Designs
Authors: Williams R. L. , McCarthy J. T.
Published: December 2007

Multiple radioactive tracers have recently been used by Santa Fe Energy to assess the effectiveness of acid and fracture stimulations. Until recently, only one radioactive tracer1, usually Iridium–192, was used and its distribution was surveyed with a conventional gamma ray logging tool. However, there are instances, such as multistage frac jobs or long interval acid stimulations, where two or more tracers would be very beneficial in assessing the effectiveness of a stimulation effort. Recent multistage fracture stimulations in the Mid-Continent using two radioactive isotopes2 allowed the operator to assess frac sand placement and vertical height growth in a single logging pass. The tools used were modified open hgle natural gamma ray spectroscopy logging systems3-6, which were originally designed to measure Potassium (K), Uranium (U) and Thorium (Th) concentrations. The energy range was expanded on the cased hole version of these tools to allow the deconvolution of individual gamma rays emitted by specific radioactive tracers. Depending upon background levels and computer software limitations, three or more tracers could be logged in a single pass.

Santa Fe Energy has used up to four isotopes in a single wellbore, Antimony–124, Scandium–46, Iridium–192, Silver–110 and Gold–198 have been placed in several conventional sand fracs, while Scandium–46, Iridium–192, Iodine–131, Antimony–124 and Silver–110 were used in a number of acid fracs to assess the stimulation efforts, using two different logging companies' cased hole tools. The data generated by these logs have allowed Santa Fe Engineers to successfully modify and improve their completion and stimulation programs. Examples of logs reflecting initial and modified frac and acid designs are provided. Procedures concerning the on-site handling of radioactive material and subsequent preparations to ensure adequate logging conditions are also presented.
An Analytical Solution for Unsteady Liquid Flow in a Reservoir With a Uniformly Fractured Zone Around the Well
Authors: Prado L. R. , Da Prat G.
Published: December 2007

An analytical model is presented which describes the pressure behaviour of a well completed in a reservoir wherein natural fractures occur over a limited area around the wellbore. The flow in the reservoir is treated as a composite reservoir flow problem, the region adjacent to the wellbore being considered as a fractured medium and the outer region as an homogeneous one. Wellbore storage and skin effects are included in the solution, and the flow in the fractured region is mathematically described by Warren and Root's double porosity theory.

Dimensionless log-log plots of pressure vs time show the existence of several well-defined flow regimes, which can be used in the interpretation of pressure transient tests data to estimate the fractured region parameters as well as its radius around the well. This last parameter is of considerable importance for the purposes of reservoir development or infill drilling programs, for it would allow the reservoir engineer to estimate the areal extension of the fractures in the reservoir.

Based on the model results for different values of the parameters involved, guidelines are provided for conducting and interpreting a pressure test with the objective of determining the characteristics and areal extent of a natural fracture system.
Recovery Efficiency Aspects of Horizontal Well Drilling in Devonian Shale
Authors: Salamy S. P. , Saradji B. S. , Okoye C. O. , Mercer J. C. , Yost A. B.
Published: December 2007

This study is part of the Department of Energy's Eastern Gas Shales research whose primary objective is to increase the gas reserves for the Devonian shales in the Appalachian, Illinois, and Michigan Basins. The study simulated the effect of using horizontal wells to increase the recovery efficiency of shale gas from two specific sites: Wayne County, West Virginia, where vertical well gas production has been historically high and no permeability anisotropy is thought to exist, and Meigs County, Ohio, an area with a history of moderate gas production and a calculated permeability anisotropy of approximately 8:1.

In this study, a three-dimensional, dual-porosity reservoir simulator was used to characterize the study areas after sensitivity analyses were made to determine those parameters significant in determining gas production profiles. Once the study areas were characterized, the 20-year production profile for a 2,000- foot (610-meter) horizontal well was simulated for three well locations in Wayne County and one location in Meigs County. The performances for several vertical wells were also simulated and compared with those for their corresponding horizontal wells in Wayne County. Results of the simulation showed that a horizontal well could produce seven to ten times more gas than a vertical well placed at the same location for the Wayne County site. In the Meigs County area, the study showed that permeability anisotropy is an important factor in determining the orientation that a horizontal well should be drilled. Furthermore, the study concluded that horizontal wells are more efficient than vertical wells in producing Devonian shale gas from a fixed volume of rock.
Reservoir Properties Required for Profitable Stimulations
Authors: Dietzel H. J. , Ernst P. L.
Published: December 2007

Profitability of production from low permeability gas reservoirs is mainly determined by the increment of production obtainable by hydraulic fracturing as well as by the initial flow capacity of the untreated well.

In this paper a method is presented, which allows a judgement of profitability of low permeability gas production on the basis of log-analysis and well-testing data only.

Deduced from reservoir models production profiles for an untreated and a fractured well, respectively, are calculated. To these production profiles basic profitability analysis are applied, considering –drilling and completion costs–surface treatment installations–MHF-treatment charges

The limiting value of profitability is characterized by a dcf-rate of 15 %.

On the basis of economic considerations, limiting values for reservoir properties are determined as requirements for a profitable stimulated or non-stimulated production from low permeability gas reservoirs.
Polymer Emulsion: The Revival of a Fracturing Fluid
Authors: Roodhart L. P. , Davies D. R.
Published: December 2007

Polymer emulsion hydraulic fracturing fluids were widely employed some 10 to 15 years ago, but became less popular after the introduction of cross-linked, water-based gel systems. The latter were thought to have a higher viscosity and be easier to handle, as well as being cheaper. However, during the last few years, polymer emulsions have enjoyed an increasing popularity in Europe because of their flexible viscosity response and their non-damaging properties1. In addition, their cost per unit volume of proppant placed is now comparable to that of water-based fluids.

Addition of a well-dispersed internal phase will increase the viscosity of any fluid over that of the external phase alone. For polymer emulsion fracturing fluids the continuous phase is gelled water, the viscosity being enhanced by the addition of diesel, kerosene or crude oil at typical volume fractions between 0.5 and 0.7. During the proppant stage, the fluid rheology is further complicated by the addition of a second internal phase (sand) to the emulsion, which will not only increase the viscosity, but will also affect the stability of the emulsion if the total internal phase (sand + oil) exceeds a maximum value. However, the existence of two different internal phases offers the possibility of gearing the volume fractions of two alternate phases to each other in such a way that the slurry viscosity is constant and independent of the sand concentration. This is particularly important in situations where the tubing head pressure is limited and tubing friction becomes critical and cannot be allowed to increase as the sand concentration is increased during the job.

A last, but not the least, parameter affecting the emulsion rheology is the amount of shear applied to the emulsion while generating it. It was noticed that emulsions prepared in the field had a lower viscosity than emulsions prepared in the laboratory. This difference could be attributed to a different oil droplet size distribution in field- and laboratory-prepared samples. The efficiency of the equipment used in the field to generate an emulsion lags behind that of laboratory equipment, especially at high oil/water ratios and high gel loadings. This is an area where further improvements can be made by the service companies.

Polymer emulsion frac. fluids are thus attractive because of the wide span of control available to the operator.

Field data (THP and BHP data) proved that these rheological correlations effectively described the situation in the field, the predictive accuracy of the formulae being such that the fracture shape may be evaluated from THP data.

Some 25 fracturing treatments have been carried out in Europe using polymer emulsion fracturing fluid with a very high success ratio. Productivity improvement factors of nearly 30 were achieved with few operational problems using sand concentrations up to 14 lb/U.S. gal.
Hydraulic Fracture Treatment Design Simulation for the Rotliegendes Formation
Authors: Acharya A. , Kim C. M.
Published: December 2007

As an increasing number of gas fields are being developed or are planned to be developed in the permian red beds (Rotliegendes) of northwest Europe, hydraulic fracturing has become a major stimulation method to obtain economic production rates from this tight gas formation. Optimization of stimulation design and its implementation in the field become more crucial in the formation such as Rotliegendes, where a water bearing zone is underlain. The objective of this work was to simulate fracture growth under various conditions so that optimal treatments can be designed and implemented successfully to this tight gas reservoir. Formation rock properties of the payzone and adjoining barriers, fracturing fluid properties and their leakoff coefficients selected were experimentally determined in the laboratory using various Rotliegendes core samples. A 3-D model of Meyer and Associates was used to simulate the fracture length, width, height, proppant transport and settlement, fracture closure, and post-frac performance. The same treatment data were simulated using a 3-D model developed by Palmer and Carroll. Results obtained from the two models are compared on a rational basis.

Two field applications are presented to demonstrate the proper design and successful stimulation treatments in the Rotliegendes.
Source Rock Evaluation: A Method of Predicting Dominant Reservoir Mechanisms of Deeply Buried, Low-Permeability Coal Reservoirs
Authors: Decker A. D. , Horner D. M.
Published: December 2007

The ability to produce low cost, pipeline quality gas from low permeability deep coal reservoirs depends largely on thorough integration of exploration methods with appropriate drilling, completion and production strategies. In the extreme case, areas that are not economic with current completion technologies should be avoided with adherence to prudent exploration practices. Therefore, reliable predictive geologic methods to specify coal reservoir conditions need to precede drilling and completion decisions.

Dominant coal reservoir mechanisms include: permeability, saturation, reservoir pressure and gas-in-place. Production characteristics from low permeability coal reservoirs are most sensitive to the interaction between type of saturation and reservoir pressure. The geologic processes responsible for these reservoir conditions have been examined in the Piceance Basin. This basin, known for low permeability reservoirs, was selected for geologic evaluation due to the large coalbed methane resource and large data base. Also located in the basin is the Deep Coal Seam Project, a multiyear, multi-well, field laboratory joint venture by the Gas Research Institute and Resource Enterprises, Inc., providing fully integrated reservoir and geologic engineering data on deep coal reservoirs.

Reservoir diagnostics and modeling suggests that reservoir pressure and type of saturation demonstrate an interaction between catagenesis and permeability. Thick, thermally mature coal deposits actively generate more gas than can be adsorbed by the coal or be diffused through a low permeability system. In these regions over-pressuring occurs. Ultimately, pore pressure will exceed in-situ stresses resulting in tensional fractures through the coal bearing sequences. While the coal seams remain in the active gas generation phase, the fractures and pore spaces become gas saturated. Eventual temperature reduction through erosion will halt the gas generating phase, resulting in an under-pressured reservoir. Imbibition of water into these reservoirs is unlikely in areas of low permeability.

In summary, source rock evaluation techniques have been applied to characterize and predict coal reservoir mechanisms in low permeability basins.
The Use of Simulation and History Matching To Determine Critical Coalbed Methane Reservoir Properties
Authors: Zuber M. D. , Sawyer W. K. , Schraufnagel R. A. , Kuuskraa V. A.
Published: December 2007

Key coalbed methane reservoir properties can be determined using a logical history matching analysis procedure that incorporates laboratory, geologic and production data. Methane and water production data were history matched using a dual-porosity, two-phase finite difference reservoir simulator modified to account for the storage and flow mechanisms unique to coal. Two field examples demonstrate the results and show the applicability of reservoir modeling to assessing the effectiveness of stimulation and predicting well performance.
The Analysis of Complex Travis Peak Reservoirs in East Texas
Authors: Holditch S. A. , Robinson B. M. , Whitehead W. S.
Published: December 2007

In order to evaluate the effectiveness of a hydraulic fracture treatment, one must be able to correctly analyze post-fracture production and pressure buildup data. In many cases, conventional analysis techniques or simple single-phase, two-dimensional models are all that is required to obtain satisfactory results. However, in complex reservoir systems, such simplified techniques may provide incorrect solutions. As part of a research program sponsored by the Gas Research Institute (GRI) a substantial engineering effort is being exerted towards better understanding of complex reservoir systems. The thrust of this work has been in the Travis Peak formation of east Texas which is a multi-layered reservoir that normally produces both gas and water. To properly analyze this formation, a three-dimensional and/or two-phase reservoir simulator is needed.

This paper presents a thorough discussion of the problems associated with the analysis of complex reservoirs and illustrates these problems with numerous field examples. Examples are included in which short, high conductivity fractures are calculated when conventional analysis techniques are used. However, a longer, more realistic estimate of fracture length is computed when one uses a multi-phase, multi-dimensional reservoir model to accurately history match the gas and water flow rates as well as the wellbore pressures.
An Equivalent Cell Block Porosity and Permeability Concept for Modeling Multiphase Flow in Naturally Fractured, Lenticular Reservoirs
Authors: Evans R. D. , Ubani E. A.
Published: December 2007

A mathematical model is presented which forms the basis of a multiphase, three dimensional reservoir simulator for characterizing multiphase flow in naturally fractured, lenticular formations. The model is general in that it can treat the presence or absence of natural fractures and/or sand lenses in a statistical fashion based upon a known distribution for each. A double porosity medium is approximated by an equivalent single porosity medium for each cell block. Similarly an equivalent permeability for each cell block is approximated by calculating an effective principal permeability as a function of rock matrix and fracture permeabilities. In any given cell block the fractures can have any orientation. The model can be used to simulate the behavior of a double porosity medium composed of heterogeneous, anisotropic rock matrix, and a heterogeneous, anisotropic fracture system. In addition it possesses the capability of including sand lense lenticularity and hydraulically created fractures with finite or infinite conductivity. Simulation results are presented for an actual field case and for hypothetical wells producing under multiphase flow conditions.
Coupling of Production Forecasting, Fracture Geometry Requirements and Treatment Scheduling in the Optimum Hydraulic Fracture Design
Authors: Meng H. Z. , Brown K. E.
Published: December 2007

There are a number of considerations to be made in the process of designing a fracturing stimulation treatment. The reservoir deliverability, well producing systems, fracture mechanics, fracturing fluid characteristics, proppant transport mechanism, operational constraints and economics should be considered and integrated in order to obtain the most cost-effective design and to maximize the benefit of a well stimulation treatment.

The main purpose of this work is to develop an analytical scheme which mathematically couples each elements as described above. The criteria used to determine the optimum size of the treatment are: (1) optimize reservoir deliverability, (2) maximize propped fracture penetration, (3) optimize pumping parameters, (4) minimize treatment cost, and (5) maximize economic returns of the well.

Firstly, an analytical inverse algorithm has been derived based on 2-D PKNC (Perkins, Kern, Nordgren and Carter) and KZGD (Khristianovic, Zheltov, Geertsma and de Klerk) formulations. It allows us to calculate the fluid and proppant volume needed for a desired fracture geometry and conductivity. Secondly, a technique to search for optimal pumping parameters and to maximize the proppant coverage for a given hydraulic penetration is developed. This allows us to optimize the propped geometry taking into account the operational constraints. Thirdly, a coupling algorithm is developed to link the reservoir producibility, well producing systems and the optimized fracture geometry. This enables us to optimize the wellhead deliverability based on the balance between the reservoir and the fracture characteristics. Finally, the overall economic analysis is performed to calculate the net present value for various design options. The most cost-effective treatment design can then be determined based on the point of diminishing return on the well's net present value.
Realistic Fracture Conductivities of Proppants as a Function of Reservoir Temperature
Authors: McDaniel B. W.
Published: December 2007

The steady-state conductivity of a propped fracture is significantly lower than has been reported in most of the data presently being used in fracture design calculations. When laboratory testing incorporates realistic parameters for temperature, and the tests are held for extended time periods, measured conductivity may only be a fraction of the previously reported value. Several authors have addressed this concern, each citing a very limited quantity of data. In some cases, only a few proppants were tested, while other authors addressed only one or two specific temperatures.

This work is based on the results of more than one hundred tests where each stress level was held for extended times to create a complete family of data for a representative number of proppants. The data covers a formation temperature range of 70° to 325°F and a stress range of 2,000 to 13,000 psi for several of the most commonly used proppants. The data were then incorporated into various computerized frac design simulation programs and in reservoir production simulation models.
GASWAT-PC: A Microcomputer Program for Gas Material Balance With Water Influx
Authors: Wang B. , Teasdale T. S.
Published: December 2007

GASWAT-PC is a microcomputer material balance program that calculates original gas in place (OGIP) from production history for gas reservoirs with or without water influx. Several well-known analytical techniques, and some extensions and improvements, are applied to a single input data set. The output for each method is given in both tabular and graphical form.

GASWAT-PC also has the capability to predict reservoir pressure and recovery efficiency for a specified production rate if OGIP and aquifer properties are known. An option is included to account for the effect of a large pressure gradient in the water-invaded region.

Case studies illustrate the application of GASWAT-PC to an abnormally pressured reservoir and to two water drive reservoirs. Finally, we compare the pressure performance predicted by a numerical simulator and by GASWAT-PC for a water drive reservoir with a high dip.
Optimized PC-Based Expert Systems
Authors: Zamora M. , Merchant M. A.
Published: December 2007

Expert-system technology has emerged from beneath the umbrella of Artificial Intelligence and into the mainstream of engineering problem solving. There already are several notable examples of the application of this state-of-the-art technology in the petroleum industry.

Clearly, expert systems that run efficiently on standard personal computers are particularly of value. A new expert-system generator that overcomes the speed, memory and mass-storage limitations of XT/AT-class personal computers is presented in this paper. The shell is optimized for the specific characteristics of the target user, knowledge expert and computer. Expert systems developed using this shell currently are being used by our technical personnel for drilling fluid and related applications.
A New Two-Dimensional Single-Phase Waterflood Model for Microcomputers
Authors: Rezaei A. A. , Donaldson E. C.
Published: December 2007

In the performance evaluation of any reservoir, a knowledge of the pattern of fluid flow within the reservoir is essential. This is especially true in the case of reservoirs under waterflood, where an analysis of injected fluid migration within the porous medium is very important. Hence, reservoir simulation has become a valuable tool for reservoir engineers, allowing them to gain greater insight into fluid flow within the reservoir. If properly conducted, a simulation study can aid in optimizing depletion by answering many specific questions related to a given reservoir.

This paper describes a single phase, two-dimensional, compressible front tracking model for microcomputers, which can be used to simulate waterfloods. It can be used for any type of heterogeneous reservoir with variable thickness, permeability, porosity and flow boundaries.

A complete discussion of the mathematical model, operating logic of the program, and sensitivity to input data is provided. Also, a listing of the program in FORTRAN is included. Anyone with access to a microcomputer can use the program to analyze the anticipated pattern of injected fluid migration within the reservoir as a function of time.
Applications of a Microcomputer Facilities Network Modeling Program
Authors: Startzman R. A. , Barnes G. A. , Wong S. A.
Published: December 2007

This paper presents a system modeling program, designed for use on a microcomputer, which calculates steady-state pressures and flowrates for a single-phase gas or water system. The program can model flow through 1) well completions using IPR formulas; 2) flow lines (inclined, vertical, or horizontal); 3) fixed orifice chokes; 4) and single- or multi-stage reciprocating compressors. The program uses nodes to identify pressures and node connecting elements to identify flowrates and determine which type of element that is being modeled.

The program determines unknown pressures by either sequential or simultaneous methods. In the sequential method the program analyzes each node connecting element individually. The simultaneous solution creates a matrix containing flow balance equations from each node in the system. Next, the program solves this matrix simultaneously to determine values for the unknown pressures and flowrates. The purpose of this paper is to explain the logic of the modeling program and demonstrate its applicability in a microcomputer environment using examples.
Measurement-While-Drilling Tool Performance in the North Sea
Authors: Knox David J. W. , Milne John M.
Published: December 2007

The in-hole failure rate and survey accuracy are key areas when judging the performance of Measurement While Drilling (MWD) tools. Shell UK Exploration and Production (Shell Expro) extensive use of two major MWD companies has enabled the underlying trends to be identified.

The mean time between the failure rates of both directional-only and directional plus Gamma Ray tools, is presented by year from 1981 until April, 1987. Over this period, the mean time between failure (MTBF) of directional-only tools has risen from 225 hrs in 1981 to 360 hrs in 1986 with an average of 260 in-hole circulating hours between failures over the 6.3 year period. The average MTBF rate for Gamma Ray tools for 1983 until the end of 1986 is 160 hrs.

Survey accuracy has been established by comparing the horizontal difference between the 13 3/8 inch casing shoe position calculated from the MWD surveys and the positions measured by the Ferranti FINDS survey tool. 125 wells were analysed; 95% of these wells exhibit errors of less than 7, 9, 12, and 14 ft/1,000 ft of along hole depth surveyed for averaged inclinations of 0 – 15, 15 – 25, 25 – 35, 35 – 50 degrees respectively.

The data does not reveal any strong trend towards lower accuracy in East/West wells, but does indicate that magnetic disturbance is a major error source.
A History of Downhole Scale Inhibition by Squeeze Treatments on the Murchison Platform
Authors: Payne G E
Published: December 2007

The formation water of the Murchison reservoir has a natural scaling potential. As pressure reduces from reservoir conditions carbonate scaling can occur. Also the water has a barium and strontium content so that when injected seawater broke through to the producing wells sulphate scaling also became possible. Initial scale inhibitor squeeze treatments achieved what scale itself to that date had not. They plugged the wells. Since then scale inhibitor squeezes have been successfully carried out and regularly achieve squeeze lives of up to a year.

This paper outlines in historical form the philosophies and events of downhole scale inhibition for the Murchison wells. The initial difficulties and present successes are described. Details are also given of previous problem areas of downhole asphaltene deposition and present thoughts on squeeze treating different producing zones within the same wellbore.
Thermite Sparking in the Offshore Environment
Authors: Hay E. , Adermann R.
Published: December 2007

In flammable and explosive environments, sparks have to be eliminated for reliable operation and safety. Thermite sparking is a comparatively rare phenomenon which produces a relatively hotter spark than friction sparking. It involves aluminum alloys and rusted steel. This paper reviews and compares the mechanism of generating thermal and friction sparks and assesses the risks from thermite sparking. Various methods which can abolish this hazard are illustrated. The work reflects the findings of 200 publications.

The methods of thermite spark suppression in this paper will apply to all aluminum structures in drilling and production platforms. Such information will enhance safety in the use of aluminum alloys clarifying doubts about their use in the offshore environment. The paper will assess what precautions may be taken in the increasing use of aluminum on offshore structures.
Offshore Platform Removal and Abandonment 1987 – Review and Update
Authors: Boyd N. G.
Published: December 2007

The publishing of the UK Government's "Petroleum Bill" has generated much interest and controversy in the subject of Removal and Abandonment of offshore installations; it is therefore particularly timely to review all the influences that may affect the situation and update the position for 1987.

It has now become apparent that there are many bodies, governments and other factors that may generate an impact on Removal and Abandonment and this paper starts with a brief outline of the situation in 1986. New influencing factors are then introduced and reviewed and the likely impact of these influences assessed. The paper concentrates on the UK sector but all the various influencing factors are equally relevant to the whole of the North Sea.