bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple Characterization of Communication Between Reservoir Regions
Authors: Fox M. J. , Chedburn A. C. S. , Stewart G.
Published: December 2007

Many North Sea fields exhibit significant barriers to fluid flow between different regions in the reservoir. These may be in the form of vertical barriers due to faulting or stratigraphic changes, or horizontal barriers in layered systems.

A simple method has been developed to quantify such "interblock" communication using material balance and. steady-state pressure drop concepts. For single well blocks extended buildup or drawdown surveys can characterise communication and effective block volumes. For multiple communicating blocks steady- state pressure measurements can quantify interblock communication directly. Where steady-state information is unavailable, all available data can be integrated into a multiple cell analysis to characterise interblock communication and effective block volumes.

This method allows characterisation of partially communicating regions as a preliminary stage to aid 3D reservoir simulation.

Examples are presented from mature North Sea fields of an extended buildup test, steady state pressure measurements and an application to a complex inter-linked cell system. These examples detail how this simple analysis procedure can aid understanding of production behaviour in complex geology and deter-mine reservoir properties between wells.
Maintaining Balmoral Field Productivity While Controlling Sand Production with Gravel Packs
Authors: Scrimgeour J. A. , Shepherd C. E.
Published: December 2007

The Balmoral Field is situated 140 miles northeast of Aberdeen in 470' of water. Early well tests indicated the possibility of sand production. To eliminate potential problems with the subsea hardware, it was decided to control sand production with internal gravel packs if target post-pack productivity levels could be met. Trial wells indicated that the target of a Skin less than +25 was achievable by innovatively adapting available technology. Operational results have borne this conclusion out.
Use of Graded Salt Pills in the Montrose Field
Authors: Bennett N.
Published: December 2007

This paper reviews the development of an effective workover fluid system for the Montrose Field, comprising seawater and a graded salt pill bridging agent. The system was developed in response to substantial production impairment associated with earlier workover fluids.

On the Montrose Field, 13 wells are currently being lifted using Electrical Submersible Pumps, with workovers necessary to changeout ESP assemblies when they fail. The reservoir pressures established during field development will not suppport a seawater column. The first workover fluid systems employed seawater and a variety of blocking/ bridging agents such as Hydroxyethyl Cellulose (HEC)/Calcium Carbonate and temperature degradable polymer plugs. These were all unsuccessful, either permanently damaging the wells or being ineffective and allowing excessive seawater losses.

An invert diesel emulsion mud system was utilised for its ability to reduce overbalance and control losses to the formation. However, during the first six months of 1985, workovers on the Montrose resulted in up to a 65% reduction in well productivity. It was believed that mud lost to the formation during the workovers was causing an emulsion block, which was not being removed on return to production.

Since mid-1985, the use of graded salt pills spotted across the perforations with inhibited seawater has resulted in wells being returned to oil production rates greater or equal to the pre-workover rates. Underbalanced reperforating operations have been performed using tubing conveyed guns with the well being re-killed using the same workover fluid system prior to running the ESP completion. With thé seawater/salt pill system no adverse effects to well productivity were experienced.

The number and volume of salt pills required during well killing procedures has been assessed on a well-to-well basis with a view to optimising the pill requirements and reducing rig time. Such optimization should also reduce the clean-up period resulting from a workover. Cost savings of up to $24 per barrel have been realised through use of the graded salt pill system.
Generation of Oil-Wet Model Sandstone Surfaces
Authors: Takach N. E. , Bennett L. B. , Douglas C. B. , Andersen M. A. , Thomas D. C.
Published: December 2007

A technique for modifying the natural water-wetting behavior of clean, dry, Berea sandstone is discussed. The method involves chemically incorporating the vapor of an organosilane onto the surface of the rocks at elevated temperature and reduced pressure. This paper focuses on the first stage of the project, in which the technique was evaluated by silylating quartz plates as sandstone analogs. When the reaction was carried out with quartz at 275 C, strongly oil-wetting surfaces were generated and the wettability was maintained for extended periods of time upon soaking the plates in various liquids. Plates soaked in brine remained oil-wetting for 22 weeks. Altered wettability of plates soaked in toluene or dodecane persisted for 24 weeks. Application of the newly-developed dynamic Wilhelmy plate technique for rapidly and conveniently evaluating the wetting properties of silylated plates is discussed. Using a modification of the procedure described for silylating the quartz plates, we were recently able to prepare samples of strongly oil-wetting Berea sandstone.
The Development of Potassium Cellulosic Polymers and Their Contribution to the Inhibition of Hydratable Clays
Authors: Palumbo S. , Giacca D. , Ferrari M. , Pirovano P.
Published: December 2007

Water-base fluids with inhibitive properties require, as primary components, proper exchangeable ions and effective water soluble polymers; Potassium based drilling fluids formulated with optimized levels of KCl, KOH and water soluble polymers such as sodium carboxymethylcelluloses (CMC), polyanionic celluloses (PAC), partially hydrolized polyacrylamides (PHPA) and modified starches have been investigated by many authors. The field preparation of potassium based drilling fluids generally requires a high level of potassium to counteract the negative effect of sodium on hydratable clays. As a matter of fact nowadays the oilfield industry shows a growing interest in the use of sodium free, potassium based chemicals, examples of which are potassium lignite, potassium asphalt sulphonates and KOH.

This paper introduces a new class of polymers, potassium carboxymethylcellulose and potassium polyanionic cellulose, and demonstrates their contribution to the formulation of inhibitive fluids.
Drilling Fluid Polymer Degradation Studies Using High-Pressure Differential Scanning Calorimetry
Authors: Teeters D. , Kemp N. P.
Published: December 2007

Differential scanning calorimetry (DSC) performed under elevated pressures has been used to study the degradation of starch in aqueous solutions of varying pH. Kinetic parameters associated with starch degradation are presented. This study demonstrates the potential of DSC to easily and inexpensively determine the maximum use temperatures of drilling fluid components under high temperatures and elevated pressures.
New Inorganic Attapulgite Extender Provides Stable Rheology and Supports Heavy Cuttings Even Under Severe Conditions
Authors: Crabb C. R. , Burba J. L. , Holman W. E.
Published: December 2007

An insoluble crystalline inorganic compound has been developed which effectively extends attapulgite in fresh or salt water systems, imparting heretofore unobtainable stability against sedimentation. This novel compound provides a low solids drilling fluid with a variety of desirable properties such as low n value, high temperature stability and a more effective gel structure for carrying or suspending large cuttings. Both laboratory and field test results are given, the latter being in a saturated salt well. The compound shows low toxicity and is easy to apply with conventional equipment.
Miscible Displacements in Heterogeneous Core Systems: Tomographic Confirmation of Flow Mechanisms
Authors: Sorbie K. S. , Wat R. M. S. , Hove A. O. , Nilsen V. , Leknes J.
Published: December 2007

A series of stable and unstable floods has been carried out in a well-characterized, heterogeneous concentric core assembly in order to study predicted recovery mechanisms in such systems. A combination of effluent analysis from the separate layers in the core and computer simulation was used to establish the detailed flows which were subsequently confirmed using computer x-ray tomographic (CT) scanning. Good agreement has been obtained between experiment and theory for unit mobility, and viscous floods in which the respective roles of transverse dispersion and viscous crossflow have been clarified. Some of the main qualitative features found in the unstable displacement (viscous fingering) experiments have also been reproduced using fine grid simulations. CT scanning has been shown to be extremely useful for studying flow mechanisms in systems of this type.
An Experimental Study of the Interactions of Aluminum Citrate Solutions and Silica Sand
Authors: Rocha C. A. , Green D. W. , Willhite G. P. , Michnick M. J.
Published: December 2007

Aluminum retention and the distribution of the retained aluminum on a porous medium significantly affect the location and strength of polyacrylamide/aluminum citrate gels used to selectively reduce the permeability. This study was undertaken to investigate aluminum retention on silica sand when the solid is contacted by aluminum citrate solutions.

Batch experiments were used to investigate the effect of aluminum-to-citrate ratio on aluminum retention and the rate of release of retained aluminum. Displacement experiments with silica sand were conducted in order to investigate the effects of aluminum-to-citrate ratio and displacement rate on aluminum retention, and the effect of pH on aluminum release.

The major findings of this study are that 1) as the aluminum-to-citrate ratio increases, the aluminum retention increases, 2) the amount of aluminum retained by silica sand increases as the displacing rate decreases, 3) the process is reversible, but the rate of aluminum release is considerably slower than the rate of retention, 4) the amount of aluminum released is influenced by the type and pH of the flowing solution, and 5) citrate ions are retained by silica sand primarily as a part of the aluminum citrate complex.
Reserve and Price Security: An Analysis of New Insurance Plans
Authors: David A. , Carson G. P.
Published: December 2007

The energy industry, as any other industry or individual, uses insurance programs to protect itself from general liabilities. The common types of policies for field operations are almost as old as the industry itself, and include, among others, blow-out policies, environmental policies, and plugging and abandonment policies. In addition to general liabilities, the energy industry has always been concerned with minimizing the risk associated with its investments (exploration for oil and gas reserves). In the last several years, the insurance industry has responded to this challenge by offering a variety of risk minimization programs. These are policies that insure financial conditions. However, many were ill conceived and proved a disappointment to policy holders, and in some cases, a disaster to the policy issuers. Not all insurance programs have to be offered by insurance companies. For example, turnkey drilling may be considered insurance against cost overruns. Mesa Petroleum's famous presale of production insured a locked-in level of gross revenue.

Based on the success of the crude futures market and the volatility of oil prices, several groups are now offering programs that insure reservoir production, reserve volume, and/or product price. This paper reviews some of the types of reserve and price insurance programs from the point of view of producers and financial institutions. The interest in these policies is growing among producers as a means of obtaining higher loan value from financial institutions. Do the owners of the policies get more than piece of mind?
Political Risk and Overseas Oil Investment
Authors: Stauffer T. R.
Published: December 2007

Risk of expropriation reduces investors’ expected profit from overseas oil ventures, but possible compensation has little effect. In the event of expropriation, however, the quantum of compensation is intensely contested.

The wide disparity between valuations claimed by governments (net book value) and companies (DCF valuation) can be significantly reconciled. Book value requires certain adjustments, and the "Cinderella effect", the systematic overstatement of value, must be offset.

Indeed, except for windfall profits, net book value and DCF value in general will not differ greatly.
Exploitation of Abu Gharadig (AG) Field, Western Desert, Egypt
Authors: Kenawy F. A.
Published: December 2007

This paper presents the depletion performance during a time span of more than 10 years for the BAHARIYA Reservoir - the major producing horizon of the giant Egyptian gas field: ABU GHARADIG (AG). The paper emphasizes the results of a recent comprehensive geological/engineering study where a detailed volumetric and mass balance analyses were carried out to pinpoint the recoverable reserves under the existing operating conditions.

The results available todate demonstrate that the existing wells will adequately drain the proved gas reserves, and consequently inlet gas compression has to be installed in order to meet the contractual demand-rate and to increase the ultimate gas recovery as well. In addition, the paper offers a brief summary about the gas plant components, the piping system, and the operating methodology.
Application of Impermeable Cement Cement Additive in High Pressure and Easy Lost Circulation Wells and its Operation Technology
Authors: Shuren Tan , Gaodong Shi
Published: December 2007

The primary cementing of a high pressure well occurs a gas - flow quite often in the annulus due to the loss of hydrostatic pressure during the hydration and setting of cement, thus causes the hydrostatic pressure in the annulus to be unable to balance the formation pressure. The result can hardly be estimated of its severity.

This paper presents a study on the mechanism of hydrostatic pressure loss of cement slurry after placement. The experimental study shows that the loss of pressure could be divided into four steps. Furthermore, it is also found that hydrostatic pressure loss will continue even after the cement loses its own weight completely. This phenomenon was evidenced by the fact that the hydrostatic pressure decreases rapidly in the simulated test cylinder and it is named the "negative effect". Study on the process of gas migration into the cement is also presented in this paper. It is obvious that when the formation pressure is higher than the hydrostatic pressure in the annulus, gas will not migrate into the cement and gas flow does not happen either. Because the cement slurry has a certain resistance to the migration or percolation of gas into it, but when the resistance is lower than the gas pressure, the gas will percolate into the cement and result in a gas flow consequently. In order to prevent the gas percolation, it is necessary to increase the internal resistance of the cement until it is equal to or in excess of the formation pressure. Based upon the foregoing understanding, an impermeable cement additive G60 has been developed.

JZ 20-2-10 is a high pressure exploratory well in an oil field in Liaodong Bay of Bohai, China. During drilling, 840 cubic meters mud was lost into the payzone and from it gas kick came several times. When the well was circulated with 1.66 kg/1 mud, the pay zone took mud, but soon after the pump was shut down, the well started to flow. This paper describes the application of a cement additive G60 in cementing the 7″ liner, and the cement bond log and variable density log analyses are given. The cement job was indeed a great success.
Gorilla: A Launch Platform for Space Age From Oil Fields of Harsh Environment
Authors: Shetti B.
Published: December 2007

The object of this paper is to put features of the Gorilla jackup in perspective and see how it can provide following objectives. To provide an improved method for offshore launching of rockets.To provide improved equipment and facilities for space vehicle launch with greater stability and lower cost.To provide an environmentally objection-free launch option.
Case History: Installation of Two Self-Contained Platform Rigs on One Platform-The Planning, Coordination, and Execution
Authors: Parks W. A. , Mooney S. P. , Farag K. F.
Published: December 2007

This report will review the case history installation of two DUAL self-contained drilling rigs on STANDARD OIL's Ewing Bank 826 "A" platform. The early identi-fication of platform - rig interface requirements and limitations has been proven effective in avoiding costly field modifications. Industry wide homogeneity, in the application of API design specifications, is paramount to insured efficient utilization of labor and material resources.
Risk Allocation in a Turnkey Drilling Contract
Authors: Erickson C. R.
Published: December 2007

Turnkey drilling, the drilling of a well for a fixed lump sum price, is steadily gaining acceptance as a viable alternative to having wells drilled on a daywork or footage basis. However, there is considerable lack of understanding on the part of many operators and even some drilling contractors as to the concept of turnkey drilling. As a result there exists a variety of turnkey drilling contracts which are either incomplete in addressing turnkey obligations and risks or overbearing and require the turnkey contractor to assume extraordinary risks.

This paper will delineate and compare the expectations of operators and turnkey drilling contractors relative to the allocation of risk associated with turnkey drilling — what risks the turnkey drilling contractor will and cannot assume and what risks the operators want the drilling contractor to assume. In order to assist the industry in delineating turnkey risks and obligations, the International Association of Drilling Contractors (IADC) has adopted a turnkey contract for land drilling operations and is presently preparing a turnkey contract for offshore drilling operations. The IADC turnkey contracts and principles developed in the IADC daywork1 and footage2 basis contracts will serve as points of reference in examining allocation of risks associated with the turnkey concept.
First Real Time Measurements of Downhole Vibrations, Forces, and Pressures Used To Monitor Directional Drilling Operations
Authors: Cook R. L. , Nicholson J. W. , Sheppard M. C. , Westlake W.
Published: December 2007

A drilling mechanics sub has been developed to measure the dynamic collar forces, accelerations, and fluid pressures just above the bit. These quantities can be transmitted to surface using mud pulse telemetry to provide the driller with real time information about downhole conditions. The measurements have been obtained for the first time on two directional wells in the Gulf of Mexico. On the first well the sub was run in a rotary drilling assembly in the inclined section. On the second well the sub was run behind a steerable system on the build and tangent section of the well. The bending moment measurements gave a detailed description of the well trajectory each time a course correction was made; during jetting operations for the first well, and during oriented and rotary drilling using the steerable motor for the second well. Relatively high transverse acceleration levels were found to be associated with the doglegs of the wells, while relatively low axial acceleration levels were associated with drilling the soft shale formations. The transverse vibrations were shown, for the particular assemblies used, to vary almost linearly with rotary speed for the range studied. However, the transverse vibrations, as well as the bending moment were shown to be sensitive to downhole boundary conditions, especially in open hole sections. On each well measurements were made, at various flow rates, of the differential pressure across the components below the measurement sub; the bit for the first well, and a positive displacement motor plus the bit for the second well. From this data inferences could be drawn concerning pump efficiency and calibration of the downhole weight on bit measurement. In addition, measurement of the differential pressure can be seen as a potential aid in the identification of drillstring washouts, erosion or blocking of nozzles, and bearing wear in downhole motors.
A Rig Adapts to Today's Environment: Improvements in Efficiency and Changes in Cost Structure
Authors: Gensmer R. P.
Published: December 2007

Contractors are in the business of providing the Operator with a product which is a mix of equipment - capacity and willingness to use that capacity, risk-safety of operations and equipment maintenance, and personnel-experience and ability to do what is needed. To continue to provide the most efficient product mix at today's low rates, a Contractor must make adjustments to cost structure. In some cases, these costs can be changed without compromising the product. In fact, a superior product may be the result.

This paper will evaluate a single rig, from 1980 to 1988 with regard to improvements in rig performance, Operator's effective drilling costs, safety, and crew experience level. This evaluation will be presented along with a review of accompanying reductions in cost and changes in daily cost allocation between the categories of maintenance, labor, overhead, depreciation and other contract costs.
Underreamer Improvements for Drilling Moving Salt Formations
Authors: Greener J. M. , Webb D. D.
Published: December 2007

There exists a need in today's industry for a durable, yet versatile, underreamer which will withstand the tortures of hard rock drilling. This paper describes the design, field testing, and subsequent modifications of one such prototype underreamer. The underreamer was utilized, in conjunction with a bi-center polycrystalline diamond bit, to simultaneously drill and underream a fast moving salt formation. Due to the limited success of previously run underreamers, a new tool was designed and built to perform under the severe downhole conditions developed in a drilling/underreaming operation.

Comparisons are made between the prototype underreamer and a similar tool based on body/arm strength and the cutter usage, placement, and durability. Modifications and improvements are documented in a summary of the field tests performed. Recommendations are given to further enhance the performance of the prototype underreamer and expand its applications.
Use of Surface Seismic Data To Predict Formation Pore Pressures (Sand Shale Depositional Environments)
Authors: Weakley R. R.
Published: December 2007

All surface seismic data has velocity information built into it in the way of stacking velocities. From these stacking velocities, estimates of interval velocities can be determined. We have developed a quantitative technique for determining formation pore pressures from the relative changes in these velocities.

From the stacking velocity data, we develop curves which we refer to as ITT (Interval Transit Time) curves. The ITT curves are generated at the proposed location and are correlated to offset location curves to calibrate velocities. Offset location pore pressures are determined and are combined with structural geology to predict anticipated pore pressures of the proposed wellbore. With these curves, in conjunction with geological information to determine structural changes, and offset logs to determine pore pressures in offsets, we can predict pore pressures to be encountered in a proposed wellbore.

To date, we have made such predictions of pore pressure in approximately 20 exploratory wells on the gulf coast prior to their drilling, with excellent results. We will graphically show results on a number of these wells comparing both the mud weights required, as dictated by hole conditions, and the actual pore pressures encountered. Our statistics within Chevron, on the Gulf Coast, indicate that proposed casing programs are adequate for the needs of an exploratory well:

29% of the time if offset casing programs are used,

65% of the time if detailed geological information is used,

>95% of the time if ITT data is also incorporated.

Significant dollars can be saved and increased success in reaching objectives can be realized when pore pressures can be anticipated prior to drilling a well. This technique offers the opportunity to do so.
Simulation of Immiscible CO2 Injection in a Fractured Carbonate Reservoir, Bati Raman Field, Turkey
Authors: Spivak A. , Karaoguz D. , Issever K. , Nolen J. S.
Published: December 2007

This paper describes the use of a dualporosity, fractured reservoir simulator to investigate the application of the immiscible CO2 injection process in Turkey's largest Oil Field. Injection of CO2 into the Bati Raman field for the purpose of enhanced recovery commenced in 1986. The source of the CO2 is the nearby Dodan gas field, approximately 89 km from Bati Raman. This project is currently the world's largest application of the immiscible CO2 injection process.

Theoretical studies of both cyclic stimulation of wells and the gas drive process (continuous gas injection) are described along with field results for the first two years of gas injection.
Flexible Sand Barrier (FSB): A Novel Sand Control System
Authors: Dickinson W. , Knoll R. G. , Nordlund R. , Dickinson W.
Published: December 2007

A series of experiments were conducted to determine the utility of a Flexible Sand Barrier (FSB) (helically wound flexible metal tubing) as a permeable casing within horizontal boreholes. These experiments focused on its production capacity and filtering capability. A test cell was developed which allowed testing over a range of pressure drops with or without a gravel pack. Laboratory in flow tests indicated 0.10 to 0.21 m3/d per meter (0.2 to 0.4 bbl/d per foot) of FSB in a 30 psi (0.21 MPa) reservoir with 1.0 Pa s (1000 cp) oil. Several configurations of the product from various manufacturers were compared and a suitable candidate was chosen for field testing which is underway.
Directional Well Planning with Multiple Targets in Three Dimensions
Authors: Goldman W. A.
Published: December 2007

The purpose of this paper is to extend the radius of curvature method to 3 dimensional design problems. The technique utilizes transformation of coordinates involving simultaneous translation and rotation. A reference coordinate system is anchored at the surface conductor location while a traveling coordinate system progresses from target to target with the bit.

Current directional planning techniques involve approximations in the calculation of tool face angle and require an estimate of the direction change. The technique presented in this paper provides a direct solution for both tool face angle and azimuth. The method is applicable in planning a build-and-hold or "slant" directional well, or a build-hold-and-drop or "S-shape" directional well with multiple targets in 3 dimensions. This paper also applies the radius of curvature method to designing the lead angle of a directional well to compensate for expected bit walking tendency. Also presented is a method of determining whether it is possible to reach a given target based on the minimum rate of angle change required. The technique is well suited to programmable hand calculators for use in the field.
The Evolution of Fracture Stimulation Design for the Red Oak Formation in the Arkoma Basin: A Case Study
Authors: Sizemore J. C.
Published: December 2007

The evolution of fracture stimulation design for the Red Oak formation in the Arkoma Basin of Eastern Oklahoma has led to significant economic improvements manifested not only in greater production but in less expensive treatments. Over the past 32 months, over 48 stimulations have been performed ranging from 15,000 gallons to 290,000 gallons of fluid and from 10,000 pounds to 500,000 pounds of proppant. During this period, improvements in fracture fluid, fracture design and treatment implementation have all led to greater success.
A Tool to Eliminate Common Sucker Rod Pump Problems
Authors: Spears H. L.
Published: December 2007

This paper describes a tool which employs simple mechanical technology to solve common sucker rod problems of gas locking and sticking without undesirable impact and wear on the pumping equipment.
An Analysis of Oil/Water Flow Phenomena in Horizontal Pipes
Authors: Arirachakaran S. , Oglesby K. D. , Malinowsky M. S. , Shoham O. , Brill J. P.
Published: December 2007

Extensive experimental data were acquired for oil-water flow in horizontal pipes for a very wide range of oil viscosity. Pressure drop, flow rate, input water fraction, in-situ holdup, mixture temperature, and flow pattern data were obtained for 612 oil-water tests in 1.5-in. pipe, and 587 tests in 1-in. pipe. Oils with viscosities of 4.7, 58, 84, and 115 cp were used in the 1.5-in. runs, while the 1-in. tests used 237-cp and 2116-cp oils, all measured at 70 °F. Mixture velocities varied from 1.5 to 12 ft/s, while input water fractions ranged from 0.05 to 0.90, and mixture temperatures were between 50 and 98 °F.

A new correlation is proposed for the prediction of the inversion point of an oil-water dispersion. It was found that the input water fraction required to invert the dispersion decreases with increasing oil viscosity. Pressure drop due to friction was also found to increase abruptly when the flowing oil-water mixture reached the inversion point where the external phase inverted from water to oil.

Two pressure-gradient prediction models are presented; one for stratified, and the other for homogeneously dispersed oil-water flows. Comparison between model predictions and experimental data shows satisfactory agreement.

Experimental oil-water flow pattern maps were developed. The existing flow pattern in an oil-water mixture depends primarily on mixture velocity, input water fraction, and oil viscosity (only when oil is the external phase).
Use of an Automatic History-Matching Technique to Analyze Pressure Buildup Data Affected by Wellbore Phase Segregation: Case Histories
Authors: Rushing J. A. , Lee W. J.
Published: December 2007

An automatic history-matching technique has been developed for analyzing pressure buildup data affected by wellbore phase segregation. This automated type-curve analysis method uses a Gauss-Newton least-squares procedure to match observed field pressures and pressures simulated with Fair's1 phase segregation model. From this analysis we determine not only estimates of wellbore skin factor and formation permeability but also indications of the magnitude of the phase segregation effects.

The basis of conventional semilog analysis techniques for buildup tests is the presence and correct identification of a middle-time line whose slope is related to formation permeability. However, wellbore phase segregation may delay or completely suppress the development of this line, so semilog analysis methods often cannot be used. Fair1 has developed type curves for analyzing buildup data distorted by wellbore phase segregation, but unique solutions are difficult to obtain from manual type-curve matching. Since our automatic history-matching technique does not rely upon the presence of a middle-time line, this new method becomes especially useful when conventional semilog analysis techniques cannot be applied. In addition, comparisons of results from our automatic history-matching and Fair's1 manual type-curve fitting suggest that more reliable solutions can be achieved with this new automated procedure.

We present analyses of pressure buildup data taken from the petroleum literature and a previously unpublished field test. Comparisons of the results from our automatic history-matching, Fair's1 manual type-curve fitting, and the Horner2 semilog plotting method illustrate the applicability of this new method for analyzing field buildup tests distorted by wellbore phase segregation.
Field Calibration of Wedge Meter for Natural Gas Flow Measurement
Authors: Shen J. J. S.
Published: December 2007

This paper presents the methodology and results of calibrating a commercial 4" (102 mm) segmental wedge meter in a field environment using a high-gravity natural gas. By comparing the segmental wedge meter flow rates with the sonic nozzles and orifice meters installed in the system, it was determined that use of the factory-supplied flow coefficients would cause the segmental wedge meter to undermeasure the gas flow rate. Based on the sonic nozzle reference, new sets of flow coefficients were derived for the wafer-style wedge meter tested with an uncertainty of ±0.38%. It was concluded that the the nozzle-calibrated flow coefficients obtained in this field test should improve the measurement accuracy of the 4" (102 mm) segmental wedge meter for natural gas flow measurement.
Case Histories: Plunger Lift Boosts Production in Deep Appalachian Gas Wells
Authors: Schwall G. H.
Published: December 2007

Production increases of 50 to 100% and more have been obtained with plunger lift installations on gas wells in the South Burns Chapel Field in northern West Virginia. At the present time, 14 wells out of 35 are being produced with plunger lift. Pre-installation analysis showed that gas/liquid ratios (GLR) were high indicating potential success, but significant downtime was recorded during the initial phases of production. An operations guideline for plunger lift installation and startup has been developed to reduce downtime on future installations.
Asphaltene Deposition: A Comprehensive Description of Problem Manifestations and Modeling Approaches
Authors: Leontaritis K. J.
Published: December 2007

The so-called "asphaltene problem" manifests itself in almost all the facets of production, processing, and transportation of petroleum. Due to the multiplicity of the engineering disciplines involved in the above processes an interdisciplinary approach is best suited for seeking fundamental understanding of and solutions to the problem.

This paper gives a detailed description of how the asphaltene problem manifests itself in the field. It discusses in-situ formation damage deep in the reservoir matrix and near the wellbore, subsurface and surface production facilities problems, and refining, blending, and transportation problems due to asphaltene flocculation and deposition. The molecular and colloidal asphaltene models are described and recommendations are made as to the preferred physical model. Existing, published analytical asphaltene models based on either molecular or colloidal nature of asphaltenes are presented and analyzed. A preferred modeling approach based on the colloidal physical model is recommended. The colloidal model permits and supports calculations based on both reversible equilibrium thermodynamics and irreversible colloidal flocculation as well.
Water Blasting for Scale Removal in the Rangely Weber Sand Unit
Authors: Buell R. S.
Published: December 2007

Barium sulfate scale deposition is a serious operational problem in the Rangely Weber Sand Unit (RWSU), often resulting in lost oil production. The historical method in the RWSU to restore production was to mechanically scrape the scale from the wellbore and then hydraulically break through any scale remaining in and around perforations. An alternative mechanical method of scale removal was recently used on a trial basis in the RWSU. Water blasting was used which directs high pressure jets of water with polymer additive at the perforations and casing wall. Water blasting was used on four wells and the results indicate that while water blasting does remove some scale, it is not an attractive option for stimulating production where barium sulfate scale has caused reduced production.
Design and Evaluation of Acid Fracturing Treatments
Authors: Ben-Naceur Kamel , Economides Michael J.
Published: December 2007

During acid fracturing, different fluids, including a reactive one, are injected. As a result certain complex phenomena are evident. The determination of the performance of the treating fluids from injectivity tests departs from techniques that are applicable in propped fracturing because of the drastic change in rheological and leak-off properties between the viscous pad and the acid. Also, the simulation of the treatments includes the mechanism of diffusion of the reactive fluid to the fracture walls, and the injection of fluids with a large contrast in viscosities. Mechanical instabilities such as wormhole growth and viscous fingering have been shown to develop during the injection.

A design model coupling the fracture geometry to the diffusion mechanisms, such as heat and mass transfer, is presented. The model allows the simulation of both multi-stage injection treatments, with alternating stages of pad and acid, and gelled acid treatments.

A comparison between the two types of stimulation is performed. The implications on fracture conductivity after closure are analyzed based on different models of closure on etched channels in elastic and elastoplastic media. Guidelines for designing treatments in those formations are given, as well as a comparison with proppant injection.

An important aspect of the design is the estimation of fluid leakoff. Current pressure decline analysis techniques typically assume that a single fluid is injected. A method is offered to interpret injectivity tests with fluids having large contrasts in rheological and leakoff properties. Predicted pressures are finally compared with observed treatment pressures in the case of large viscosity contrasts.
Multi-Mechanistic Approach to the Reservoir Analysis of Tight Blanket Sands
Authors: Bezilla M. , Ertekin T. , Adewumi M. A. , Frohne K-H.
Published: December 2007

Tight sand formations, because of their peculiar characteristics, do not conform to the well established behavioral patterns normally associated with conventional natural gas reservoirs. These attributes of tight sands render the conventional reservoir models inadequate when applied to tight sands. It is widely projected that gas resources available in these tight formations, which in the Western United States alone stands at about 5,703 Trillion Cubic Feet, may be the cornerstone of the future energy sufficiency of this country. It is also believed that the major bottleneck in the development of these resources is the lack of understanding of the fluid dynamics in these formations. It is therefore imperative to evolve a good model based on a fundamental understanding of the rather unique physics of flow in this media. A very important unconventional characteristic of tight formations is its dual-porosity nature in the form of micro/macropore structure and the pressure-field, concentration-field driven flow potentials imposed on the system. This physics calls for the use of dual-porosity, multi-mechanistic approach for the description of the transport of natural gas in these formations. Such a model is presented here. Both synthetic and actual field examples are used to illustrate the predictive capability of the model. Results show that the conventional single-mechanistic approach tends to under-predict recovery. They also demonstrate that the dual-mechanistic approach is of the essence.
Direct Type-Curve Synthesis of Pressure Transient Tests
Authors: Tiab D.
Published: December 2007

"Direct Type Curve Synthesis" is a novel, direct, quick and accurate approach for interpreting pressure transient tests. This approach uses loglog plots of the pressure derivative versus time to calculate reservoir parameters such as permeability, porosity, skin, wellbore storage, half-fracture length, and distance to boundaries, without type curve matching. The method consists of obtaining characteristic points of intersection of straight line portions of the curves and their slope from a loglog plot of the pressure derivative as a function of time. These points and slopes are then used with special equations obtained from type-curve plots (i.e. loglog plots) of the dimensionless pressure derivative as a function of the dimensionless time for the appropriate reservoir system.

The new technique is illustrated in this paper for the case of pressure drawdown of vertically fractured wells. For the infinite-conductivity fracture case, pressure derivative plots reveal a dominant flow regime, called here the "bi-radial" flow. This flow regime, which corresponds to the transient period between the infinite acting radial flow and linear flow regimes, is described by a straight line of slope −2/π. Several simple equations, using the time of intersection of the three straight lines of slope −0.5 (linear flow), −2/π (bi-radial flow), and −1 (finite acting radial flow), and the pressure derivative values at test time of one hour have been derived. These equations can be used to calculate the half-fracture length independently of the permeability. The straight line portion of the bi-radial flow regime can be used to calculate k and xf even if the early-time pressure points, which describe the linear flow regime, were not recorded or discarded because of mechanical problems or too few to draw with confidence the half-slope straight line.
Prefracture Analysis of Red Mountain Sands: An Integrated Analysis of Openhole and Cased Hole Logs
Authors: Streeter R. W. , Hunt E. R.
Published: December 2007

Both gas permeability and in situ closure stresses computed from log analysis are confirmed by pre-fracture well tests and analysis of fracture stimulation operations on the No. 3 Deep Seam 30-4 in Mesa County, Colorado, one of three wells in a Red Mountain tight gas sands project funded by the Gas Research Institute. The log analysis provides porosity, water saturation, permeability, moduli, and in situ closure stress from an integration of open hole and cased hole geophysical well logs. Log analysis in the completed interval indicates an average gas permeability of 44 microdarcies as compared to 31 microdarcies from subsequent well test analysis. The in situ stress profile from log analysis indicates only moderately weak barriers above and below the completed zone, and this was later confirmed by the fracture modeling performed using the pressure versus time results of the well stimulation, which indicated no apparent constraints on vertical growth.

Permeabilities and in situ stresses needed for reservoir characterization and for hydraulic fracture design can be determined from the analysis of a combination of available open hole and appropriate cased hole logs. The available open hole data included resistivity, gamma ray, density, and compensated neutron logs. Acoustic velocities (Vp and Vs) are also needed for moduli and stress calculations, and cased hole full wave acoustic logs were recommended to provide these data. Prior to the full wave acoustic logs, cement bond logs were run on all three wells in the Red Mountain project to determine if good cement bond existed across the zones of interest. Presence of a microannulus, which was found in one well, causes strong casing acoustic signals that mask the compressional signals. In this well, good full wave acoustic log data were obtained by logging with the casing pressured up to 1500 psi. To obtain the necessary accuracy for pre-fracture analysis, quality control is a must.
Image Analysis of Pore Geometry: Relationship to Reservoir Engineering and Modeling
Authors: Ehrlich R. , Davies D. K.
Published: December 2007

Image analysis of thin section and SEM samples from core plugs, sidewall cores and cuttings samples provides rapid, quantitative data concerning the size and geometric complexity of reservoir pore systems. Several distinct classes of porosity (Pore Types) co-exist in many reservoirs. This is particularly true in reservoirs which are shaly or have under-gone diagenesis (sandstones with less than 25% porosity, and all carbonates). Each pore type has 1) a unique size distribution that is independent of other pore types in the same reservoir, and 2) a unique relationship between pore body and pore throat size. Reservoirs with similar values for porosity and permeability can have different production efficiencies due to variations in pore geometry.

Regression procedures provide a first order model between measured capillary pressure and image-derived pore types. This relates pore types to measured pore throat size and allows for the direct calculation of permeability and capillary pressure from small samples (sidewall cores). Three dimensionless variables (Tau, Epsilon and Sigma) are calculated from image analysis of pore geometry. These provide quantitative information regarding the relative efficiencies of individual sands within a reservoir and between various reservoirs. Comparisons of efficiency based on Tau and Epsilon, allow for a numerical ranking of reservoir quality based on a uniform, quantitative system of analysis.
The Study of Alternate and Unstable Gas/Water Displacements Using a Small-Scale Model
Authors: Amiell P. , Billiotte J. , Meunier G. , Arnould M.
Published: December 2007

The operation of an aquifer gas storage can be distinguished from the production of a classical gas field by two fondamental points:–the flow rates in an aquifer storage are much more important, with gas/water displacement sometimes becoming instable–the alternating movement of fluids brings about variations in petrophysical properties despite apparently identical conditions

These two principal problems need to be carefully treated to correctly forecast and strictly monitor the development and operation of an aquifer storage.

This paper presents the results of a study which was conducted on a small scale model of metric size, allowing the visualization and quantification of the different phenomena observed. The effect of different parameters (inclination angle, gas flow-rate, number of cycles, etc.) on stability, geometric characteristics of the gas bubble, the allowable quantity of gas injected, and the Trapped Gas Ratio were investigated. Results were enhanced by the use of video-taping as interpreted by image processing.
Measurement of Relative Permeability and Flow Properties of a Gas Condensate System During Pressure Depletion and Pressure Maintenance
Authors: Munkerud P. K.
Published: December 2007

The objectives of the work presented in this paper, were development and testing of techniques for measurement of relative permeability of gas condensate fluid systems by pressure depletion and dynamic displacement of retrograde liquid at different interfacial tensions. The experiments employed a six component model system and were based on measurements of basic core and fluid properties, preliminary compositional simulation of fluid behaviour, slim tube tests and displacement in long Berea core1-4.

The measurements showed that the relative permeability curves to the gas condensate model system in a depletion process, are similar to curves of ordinary gas/oil systems, and that gravitational segregation of condensate is pronounced even at liquid saturations below the critical saturation for flow. During dynamic displacement of retrograde liquid by gas in equilibrium with the liquid, the relative permeability to gas and liquid showed strong dependence on interfacial tension between the two phases.
NGL Treating With Zinc Oxide
Authors: Auld R. G. , Latimer T. R. , Ciancio D. J.
Published: December 2007

Minor quantities of certain sulphur compounds can cause natural gas liquids (NGL) to fail the copper strip corrosivity test. At Esso Resources Canada Limited's Quirk Creek Gas Plant, it was found that there were periods, during high plant throughput, when NGL quality excursions were experienced. To gain control of the NGL quality and to ensure that the product could be shipped by pipeline, a program was undertaken to test various ways of treating the NGL product. In this paper, the experimental work involving slip stream testing and analysis of sulphur compound removal capacity at ambient temperatures is discussed. The resulting design of a full stream catalized zinc oxide treating unit installed to assure the NGL product meets the copper strip corrosivity test specification is described.