bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of Fracture Cleanup Using Flowback Analysis
Authors: Willberg D. M. , Steinsberger N. , Hoover R. , Card R. J. , Queen J.
Published: December 2007

A field study in north-central Texas shows how flowback procedures can be optimized to improve fracture cleanup and well productivity in low-permeability formations. Load water and polymer returns from 15 Barnett shale hydraulic fractures were analyzed and quantified. These were massive hydraulic fracturing treatments (1.4 million lbm of sand and 10,000 to 15,000 bbl of fluid) in an ultra-low-permeability (0.001 md) formation. These wells were fractured using low gel loading borate-crosslinked fluid. Well productivity is correlated with fracture cleanup.

Aggressive flowback procedures improved fracture cleanup and well productivity. The maximum flowback rate was increased from 0.6 bbl/min at the beginning of the field test, to as high as 6 bbl/min. Polymer returns at conservative flowback rates, < 3 bbl/min, averaged 31 ± 6% of the total amount pumped on the job. Polymer returns from wells aggressively flowed back, >3 bbl/min, averaged 46 ± 9%. Aggressively flowed back wells produced on average 19% more gas over the first 180 days of production than conservatively flowed back offsets.

Recovery of polymer continued throughout the early stages of production in addition to the polymer returned during flowback. Significant polymer concentrations were recorded in produced water samples collected up to five months following the treatment. Recovery during production can yield 10 to 13 % of the polymer pumped during the job in addition to the amount recovered during flowback.

Similar patterns of polymer recovery are observed when the Barnett shale results are compared with those from the Codell formation (0.010 md) in Colorado. This is in spite of differences in treatment size, job design, and fluid selection. Therefore, it is plausible that the results from these two studies can be generalized, and applied to many other low-permeability formations. Significant differences are observed when the Barnett results are compared with those from the Cotton Valley formation in east Texas. These differences are primarily due to the production of water by the latter formation.
Case History: Formation Damage and completion Techniques in Water Sensitive Basal Colorado gas Reservoirs of Southeastern Albeta, Canada.
Authors: Claussner R.M. , Potocki D.J. , Stevens L.M.
Published: December 2007

Basal Colorado Channel sandstone reservoirs can be clay- bearing and highly water sensitive. This presents a technical challenge from reservoir performance and completion design standpoints. The sandstones are fine to medium grained mineralogically immature and chemically unstable litharenites with significant amounts of feldspar and volcanic rock fragments. Dissolution of these grains has contributed to the precipitation of variable but significant amounts of potentially damaging pore-filling kaolinite and pore-lining smectite, chlorite and chlorite/smectite clays. The combination of overall high clay and variable smectite content makes prediction of reservoir productivity from drill stem tests, conventional log response and routine core petrophysical measurements difficult. As these reservoirs contain gas-water contacts, hydraulic fracturing likely would result in high water production. Therefore, alternative completion and stimulation techniques were required.

This is a review of an integrated reservoir analysis approach which was successfully applied to several gas wells in these sandstones. This approach included: characterization of reservoir quality, laboratory core plug testing to define severity of formation damage, and application of test results to selection of completion fluids and completion/stimulation techniques. These included the use of an extended lance tool with a high salinity brine jetting fluid. Candidate selection criteria based on field experience are presented. Production results to date demonstrate that the procedures developed have resulted in successful completion and stimulation of these problematic clay-bearing gas reservoirs.

P. 209
Monte Carlo Techniques for Evaluating Producing Properties
Authors: Gilman J.R. , Brickey R.T. , Red M.M.
Published: December 2007

When purchasing property, selling property or estimating future cash flow from a project, forecasts of future production rates are required. Whether those forecasts are made with detailed reservoir simulation or decline curve techniques, there will be uncertainty in the forecasts. Even if the reservoir description was exact and an accurate reservoir simulation could be made, the field development plans would be uncertain because of uncertainty in future product prices and expenses. This paper demonstrates how Monte Carlo techniques were used to generate a range of production profile distributions to estimate the economic value of a producing property.

The basic methodology used decline curve equations for each well in the field to describe the future production rate of the wells. Hyperbolic decline equations were used for all wells. Gas-oil ratio was modeled by another empirical equation. The standard decline equations were modified to properly account for downtime while still honoring ultimate recovery. Downtime thus resulted in delayed production. However, a well did not always reach its expected ultimate recovery if it "failed" for mechanical reasons or if the field was abandoned for economic reasons. Well failure was modeled as a discrete distribution (i.e., the producing rate was multiplied by a value of zero or one).

Another unique aspect of the spreadsheet presented here was the incorporation of mechanical and workover failure probabilities. The decline equations were modified to allow for changes in reserves and rate as a result of workovers. The expected change in reserves could have some probability of being negative if there was risk of damaging a well as a result of an unsuccessful workover. Also, a workover could have some chance of failure resulting in no change to the expected reserves.

The parameters which were risked for each well were downtime, well life, well failure, workover reserves, workover incremental rate, workover failure, and workover expense. For the field, the "risked" variables were hydrocarbon prices and operating and abandonment expenses. All the uncertainty described here could not have been properly assessed without the use of Monte Carlo techniques.

P. 221
Production Analysis of Linear Flow Into Fractured Tight Gas Wells
Authors: Wattenbarger Robert A. , El-Banbi Ahmed H. , Villegas Mauricio E. , Maggard J. Bryan
Published: December 2007

Sometimes decline curves for tight gas wells indicate that linear flow may last for over 10 or 20 years. These decline curves may show outer boundary effects but no pseudo-radial flow. This paper presents decline curve analysis methods for such wells. Values for k xf and drainage area can be calculated. Stabilized (bounded) flow equations are also presented for forecasting. The solutions and type curves developed are for both infinite-acting and stabilized flow with either constant Pwf or constant rate. Several field cases are shown with example calculations.

P. 265
Multidisciplinary Risk Assessment for Tight Gas Development
Authors: Heslop D.O. , Schuler S. , Calvo J.J. , Copeland D.L.
Published: December 2007

Risk analysis can be a powerful tool for developing an overall strategy and evaluating drilling and completion alternatives for tight gas reservoirs. Instead of relying on intuitive judgment, quantitative models which incorporate the available experience can be developed to arrive at risk and economic indicators.

This paper illustrates the application of these techniques for the field development planning of the Sohlingen Dethlingen Rotliegendes tight gas reservoir in Germany, operated by Mobil Erdgas-Erdol GmbH (MEEG) in partnership with BEB Erdgas-Erdol GmbH, RWE-DEA AG and Wintershall AG. The Rotliegendes sandstone is a deep reservoir (4800 m TVD) with very low permeability (<0.02 md). These reserves could not be economically developed with conventional hydraulically fractured vertical wells. A process that combines various engineering, risk and economic modeling tools was utilized to arrive at the development plan recommendations. A multi-disciplinary approach was undertaken which included the development of risked costs for the drilling, completion, stimulation and associated surface facilities for each of the candidate well configurations. The first multi-frac horizontal well in this field was very successful and produced at a rate of 20,000 m /hr. A detailed engineering effort was then undertaken to optimize the development plan for a multi-well program to efficiently recover the remaining reserves.

P. 301
Stimulation Optimization for Horizontal Wells in Carbonate Formations
Authors: Miller M.J. , Geehan T.
Published: December 2007

Horizontal well productivity is highly dependent on the reservoir quality as well as many drilling and completion practices. This paper discusses a process for evaluating the impact of stimulation treatments on horizontal wellbores with openhole completions in low-permeability carbonate formations in North America.

Central to the process of optimizing stimulation practices is a method for evaluating the expected productivity improvement that the horizontal wellbore should have over existing vertical wells. The technique employed uses pseud Monte Carlo simulations to generate a distribution of expected productivity improvement factors (PIFs). Stimulation or completion practices that yield PIFs substantially worse than those estimated by numerical simulations are scrutinized, and new, improved stimulation practices are implemented.

This pseudo Monte Carlo technique has been employed for several reservoirs in North America. The reservoirs include an oil reservoir undergoing waterflood, an oil reservoir undergoing CO2 alternating waterflood, and a retrograde condensate gas reservoir. Each reservoir contained horizontal wellbores that underperformed expected PIFs to different degrees. Stimulation improvements included steps to improve acid coverage along the wellbore length and careful acid system and pump schedule design to optimize etched fracture half-length and fracture conductivity. The pseudo-Monte Carlo technique was very successful at identifying low-performance stimulation practices. Reservoirs with the largest gap between expected and actual PIFs showed the greatest PIF increase when improved stimulation practices were implemented.

P. 329
What Causes Bumps in Minifrac Pressure Declines?
Authors: Shaoul Josef R. , de Pater C.J. Hans , Roodhart Leo P. , Meijers Hans C.
Published: December 2007

Minifrac tests are performed to estimate the key design parameters prior to propped-fracture treatments: leak-off coefficient, closure stress and net fracture overpressure. It is very important, especially in the case of Tip-Screen-Out or Fracand-Pack designs, to determine these parameters as accurately as possible, since errors will enhance the chances of a premature screen-out of the propped fracture treatment.

The key parameters are determined by analyzing the pressure decline after a pump-in shut-in test. For this analysis, one assumes that the pressure falls smoothly after shut-in. However, in many cases a momentary increase is observed in the wellhead pressure after shutting in the pumps, which could compromise reliable interpretation of the pressure decline. In order to determine the cause of the pressure bump, we examined a group of mini-frac data sets which exhibited this anomalous behaviour and mini-fracs in comparable wells that showed a normal decline.

We found that the cause of the pressure bump was severe under displacement of crosslinked gel at the end of pumping the mini-frac. The crosslinked gel at the bottom of the well- bore may create a plug, which effectively makes the wellbore a closed vessel disconnected from the fracture. Heating of the relatively incompressible fluid in the isolated wellbore section then causes the pressure to increase until the yield strength of the crosslinked gel has been overcome and the plug starts to move downwards. This explains the observed bump in the pressure decline plot.

To avoid this bump it is recommended to displace the crosslinked gel to the perforations or even slightly overdisplace. In our experience, if a pressure bump is still observed, it is best to check the calculated and measured displacement volume and repeat the minifrac. If this is impossible, the simplest correction for the pressure bump is to use the initial pressure decline before the bump, and shift the final decline after the bump downwards by the magnitude of the bump. However, this procedure would be invalid if the point of fracture closure coincides with the bump.

P. 385
An Interpretation of M-Site Hydraulic Fracture Diagnostic Results
Authors: Warpinski N. R. , Branagan P. T. , Peterson R. E. , Wolhart S. L.
Published: December 2007

Experiments at the GRI/DOE M-Site have shown that hydraulic fractures have a considerable degree of complexity that is difficult to account for using current understanding. Several of the key features are reviewed and an attempt is made to examine them relative to fracture mechanics, elasticity, and fluid-flow mechanisms. Key features include unexpected fracture containment, multiple fracture strands, secondary and T-shaped fracturing, large pressure drops down the fracture, significant differences in microseismically imaged geometry as a result of fluid-system changes, unexpectedly large residual width/deformation measurements after unpropped fracturing, large discrepancies in fracture area (and, thus, volume) between imaging and modeling results, evidence of complexities in proppant transport, and measurement of a clearly defined fracture closure pressure using a pressure independent technique.
Evaluation of Fracturing Treatments in the Hassi Messaoud Field, Algeria
Authors: Bouazza L. , Ziada A. , Ramses W. , Boulatsel A. , Fragachan F.E.
Published: December 2007

The Hassi-Messaoud field is a low permeability (0.5 - 10 md) average thick sandstone (Cambro-Ordovicien) reservoir covering an area of approximately 2500 km2. It is a flattened anticline and it is located on the north of the El-Biod - HassiMessaoud elevation formed by a sequence of horsts and grabens contained by faults in a submeridiene direction. The faults are in general SSW to NNE oriented and cross all the producing reservoir.

The producing reservoir is at a depth of 11,000 ft and consists of four distinct formations : R3, R2, Ra, in addition to a "zone d'alternance" (transition zone). The Ra is the main producing formation and it is subdivided into five different drains (layers) characterized by distinct petrophysical properties. Overall the field consists of 25 separate zones under pressure maintenance by means of water and/or gas injection. Fig. 1 shows the field different zones and a cross section of the Cambro Ordovicien formation.

Fracturing activities started in the Hassi-Messaoud field in the early sixties as a mean of increasing production. Few massive fractures were performed during the seventies and early eighties. Results were less than satisfactory.

Fracturing activities stopped from 1983 until 1990. This was a period for evaluation and understanding of the results. Activity resumed in 1990 and since over 150 wells have been fractured in the field.

This paper addresses the fracturing activities since it resumed in 1990. It briefly reviews the evolution of fracturing practices. It discusses the existing field limitations and challenges and their effects on fracturing treatment outcome.

An effort is made to match actual job pressures against model. The after fracturing production is presented including efforts to validate post fracture well performance using available pest fractures well tests. Decline rates are grouped in accordance to their severity and the reservoir conformance behavior. Finally, overall conclusions are presented together with recommendations for future treatments.

P. 459
Three-Dimensional Transport in Acid Fracturing Treatments: Theoretical Development and Consequences for Hydrocarbon Production
Authors: Romero J. , Gu H. , Gulrajani S.N.
Published: December 2007

While the effect of two-dimensional (2D) proppant transport during hydraulic fracturing has been extensively studied and frequently debated, relatively little attention has been given to a similar consideration for acid fracturing treatments. In addition to fluid density differences and gravity-driven segregation, spatial variation of the acid temperature and of the rock chemical properties result in more complicated physical phenomena for acid fracturing. In addition, the acid diffusion in the fracture has been estimated empirically with no considerations being made to correctly model the acid flow across the fracture width. The etched width profile resulting from three-dimensional (3D) flow could be significantly different from that predicted by the one-dimensional (1 D), piston-like displacement normally included in acid fracture simulators. An important consequence of this variation in the etched pattern is a substantially different prediction of the fracture conductivity, and hence the post-stimulation hydrocarbon production. The acid flow in the fracture thus can affect the outcome of reservoir stimulation and must be considered when designing acid fracturing treatments.

The equations governing fluid flow are initially developed for a 2D pressure profile. These equations are coupled with the formulations for acid wall reaction, heat transfer and diffusion within the framework of a pseudo-3D hydraulic fracturing simulator. The theoretical formulation for acid transport across the fracture width is then presented and coupled with the equations for 2D acid flow. The equation of acid diffusion is then solved across the fracture width, hence solving the equations of fluid flow for three dimensions in the fracture. The resulting fracture geometry and conductivity are subsequently used with a reservoir simulator to illustrate the consequences of the 3D acid formulation on hydrocarbon production.

P. 475
Gel Dehydration During Extrusion Through Fractures
Authors: Seright R.S.
Published: December 2007

Some of the most successful water shutoff treatments in fractured reservoirs used relatively large volumes of gel that extruded through fractures during the gel placement process. Laboratory experiments show that gel extrusion through fractures occurs at an unexpectedly low rate if the fracture conductivity or width is sufficiently small. This paper demonstrates that this low rate of gel propagation occurs because the gel dehydrates as it extrudes through fractures. Our experiments used a Cr(III)-acetate-HPAM gel that is commonly injected during field applications. In fractures with conductivities between 1 and 242 darcy-ft (effective average widths between 0.006 and 0.04 in.), the gel was concentrated (or dehydrated) and gel propagation was delayed by factors typically between 20 and 40 during the extrusion process. The gel dehydration effect became less pronounced as the fracture width increased. However, a fracture width around 0.4 in. was required to completely eliminate the effect.

For a given fracture conductivity, a minimum pressure gradient (i.e., a yield stress) was necessary to extrude gel through the fracture. A correlation was developed that provides a good estimate of the required pressure gradient for gel extrusion for a wide range of fracture conductivity and width values. For example, to extrude the gel with a pressure gradient less than 1 psi/ft, the fracture width should be at least 0.1 in. During gel extrusion through fractures of a given width, the pressure gradient and degree of gel dehydration were nearly independent of position and velocity during both radial and linear flow. During brine injection after gel placement, no significant gel washout occurred for fracture widths up to 0.4 in.

P. 487
High Velocity Gas Flow Effects in Porous Gas-Water System
Authors: Grigg Reid B. , Hwang Myung K.
Published: December 2007

This paper deals with high-velocity gas flow behavior in gas-liquid systems. It reports results of non-Darcy flow experiments in single and two-phase flow in porous media. The effect of both mobile and immobile liquids is significant in both decreasing the effective permeability Keff and increasing the effective non-Darcy coefficient Beff. Mobile liquid seems to have greater effect on Keff and Beff than does immobile liquid, but the values are much more difficult to quantify. The Pe~ value for a serially connected composite core, as determined from a simple averaging equation, is experimentally validated. Finally, it is shown that resistivity measurement with material balance can be used to determine the brine saturation distribution along a composite core during an oil-going core flood test.

P. 203
An Abrasive Jetting Scale Removal System
Authors: Johnson Ashley , Eslinger David , Larsen Henrik
Published: December 2007

We describe a novel abrasive jet cleaning system for removing scale from production tubulars. By careful selection of abrasives we can remove the mineral growth without damage to the steel. We also describe a field test for the system where it ran back to back with mills, an impact hammer and water jetting tools.

The abrasive selection is a critical parameter in the performance of the system. Pure water jets will clean certain soft scales, although they tend to lift the growth off the tubular in large pieces which are not conducive to good hole cleaning. Some water jetting systems use acid to soften the scale, but this limits the applicability of the system. The use of sand as an abrasive is common for certain jetting applications, however this can damage the tubing of jewelery. We discuss the selection of the Sterling Beads to clean the scale without damaging the steel.

We also describe the first field test of the system, where it was run in a well to clean Aragonite scale from 2 3/8 in. tubing. Numerous milling and tools had been tried, but all had failed to clean the tubing, and most had been destroyed. As had other mechanical and water jetting systems. The new abrasive jetting system using Sterling Beads was run and cleaned the tubing at a high penetration rate with minimal damage to the plastic coating which had originally coated the production tubing and no damage to the steel itself.

P. 105
Effective Management of Coiled Tubing Workstrings
Authors: Conrad A. Bruce , Morrison Dan W. , Mullins Rufus
Published: December 2007

This paper discusses methods for prolonging the life of coiled tubing (CT) workstrings. The paper focuses on six consider?ations: fatigue management, string design choice, data acquisi?tion systems, corrosion prevention, mechanical damage preven?tion, and equipment choice.

This paper also presents case histories demonstrating that a focused tubing management program (TMP) can significantly reduce tubing failures. A TMP that was implemented in the Gulf of Mexico (GOM) area of operations reduced the tubing failure rate by 300%. The combined efforts of research, training, and field operations personnel helped prevent three predominant failure mechanisms: cycle fatigue, internal corrosion, and exter?nal corrosion. Computer programs based on derived fatigue algorithms were used to track the fatigue of all the strings in the theatre of operations.

This paper discusses the influence that high- and low-pressure applications can have on string design choice. The paper concludes by discussing ways in which the proper choice and maintenance of equipment can minimize cycle fatigue and prevent mechanical damage to coiled tubing.
High Strength Coiled Tubing
Authors: Badrak Robert P.
Published: December 2007

An overview of higher strength coiled tubing is presented with the advantages and disadvantages associated with the higher strength grades. The advantages include increased tensile load, torsion, burst and collapse limits. These increased limits permit coiled tubing to be used to higher pressures, longer lengths and increased applications. The disadvantages include decreased ductility and toughness with increased susceptibility to environmental cracking.

Knowledge of these advantages and limitations permit safe use of these higher strength grades of coiled tubing. Data is presented on a commercially available 90 ksi minimum yield strength grade with initial test results of a new generation 100 ksi and 110 ksi yield strength grades.

P. 209
Neural Network Knowledge-Based Modeling of Rock Properties Based on Well Log Databases
Authors: Nikravesh Masoud
Published: December 2007

Analyzing data from well logs is often a complex and laborious process because a physical relationship cannot be established to show how the data are correlated. In this paper, we will develop the next generation of "intelligent" software that will extract rock properties and relevant reservoir information from well log databases. Our objective is to develop the next generation of "intelligent" software tools that will extract information from well log databases. The software will use fuzzy logic techniques because the data and our requirements are imperfect. In addition, it will use neural network techniques, since the functional structure of the data is unknown. In particular, the software will be used to group data into important data sets; extract and classify dominant and interesting patterns that exist between these data sets; discover secondary, tertiary and higher-order data patterns; and discover expected and unexpected structural relationships between data sets.
Permeability Modification of Diatomite During Hot Fluid Injection
Authors: Bhat S.K. , Kovscek A.R.
Published: December 2007

One area of concern that has accompanied steam injection into diatomite for oil recovery is the evolution of permeability and porosity as silica dissolves in hot steam condensate and is redistributed on rock surfaces as condensate cools. Since grain size is quite fine and typical pore throat dimensions in diatomite range from roughly 1 to 6 m, dissolution of silica near pore throats should increase permeability drastically. Likewise, a small amount of deposition at pore throats will cause clogging.

Our goals are to improve understanding of the effects of mineral dissolution/reprecipitation in diatomite and to formulate permeability versus porosity relationships necessary for reservoir simulation. We employ a network model to gauge how evolving pore topology affects permeability and porosity. Hence, we calculate macroscopic trends by incorporating pore-level physics. The model is anchored to real rock through actual pore-throat and pore-body size distributions. Results indicate that plugging of the network and a corresponding decrease in permeability occur when moderate amounts of silica precipitate. Plugging is most severe for small values of network connectivity and large values of the pore-body to pore-throat aspect ratio.

When porosity change from 0 to 10 % is examined closely, it is found that permeability decrease correlates with porosity decrease according to a power-law expression with power-law exponents in the, range of 8 to 9. Such a power-law dependence has been measured previously by experiment. These values confirm the strong dependence of permeability on deposited silica. The dissolution process displays an equally strong dependence on porosity change and again permeability increases most dramatically for dissolution in networks with small values of connectivity and large values of the pore-throat to pore-body aspect ratio. Again, power-law expressions adequately describe permeability increase as a function of porosity for a moderate range of dissolution.
Improved Pump Run Time Using Snow Auto-Rotating Plunger (SARP) Pump
Authors: Houghton J.E. , Snow J.M. , Holland R.B. , Gibson H.L.
Published: December 2007

Snow Auto-Rotating Plunger (SARP) pumps improved sucker rod pump performance at Aera Energy LLC's North Midway- Sunset Field. A program to install the SARP (a patented adapter that hydraulically rotates the pump plunger on each down stroke) was instituted in order to reduce subsurface maintenance costs associated with pulling and repairing worn down-hole pumps. The SARP induces random rotation of the plunger on each stroke promoting uniform wear. The pump's ability to wipe sand from between the plunger and barrel is enhanced by the rotation of the plunger, reducing the odds of the plunger galling or becoming stuck because of solids. When the pilot test was initiated in April 1995, the well pulling frequency was 2.04 pulls/well/year. In two years, pull frequency was reduced by 51% and pump repair costs were reduced 37%.
Increasing Heavy Oil Production Utilizing Dual String New Technology
Authors: Evans B. L. , Muth G. M.
Published: December 2007

Increasing demand for heavy oil production worldwide has resulted in a strong effort by the petroleum industry to develop, through new technology, improved methods of pumping heavy (8–20 degrees API) oil producing wells. Recent technological changes in downhole pumping systems have shown that heavy oil production can be significantly increased through the use of modified conventional downhole pumps and dual tubing strings. In this system, one tubing string acts the "power string" and the second string serves as the "production string". This system utilizes modified conventional API insert pumps, tubing pumps and positive cavity pumps (PCP's). Reduced frictional forces can increase oil production, lower the loads on rods and surface equipment and decrease operating costs. High volumes of sand production are also possible with this new system. Rod corrosion can also be eliminated.

This paper describes the features of this new pumping system and presents the results of actual field installations in California and Venezuela.
Effects Of Grid Systems on Predicting Horizontal Well Productivity
Authors: Wan Jing , Penmatcha V.R. , Arbabi Sepehr , Aziza Khalid
Published: December 2007

This paper compares horizontal well performance simulated by a uniform coarse grid, a uniform fine grid, a nonuniform fine grid using the Peaceman's well model, and a non-uniform fine grid with explicit well modeling. An analytical solution is used to evaluate numerical solutions. We find that when a coarse grid is used to simulate a partially penetrating horizontal well, the fiow rate of the well is under-predicted, which means the well index calculated by Peaceman's method needs to be increased for the numerical simulator to predict the well productivity correctly. Peaceman's well model was developed for two-dimensional flow problems. Since these assumptions are violated for a partially penetrating horizontal well, Peaceman's formula does not accurately predict well performance. On the other hand, explicit modeling is a technique where the well blocks are of the same size as the well so that the well block pressure can be considered as the wellbore pressure. This eliminates the need for using a well index. However, our analysis shows that the non-uniform fine grid used for explicit modeling of wells, as reported in a recent paper, can lead to incorrect results. This is mainly because nonuniform grids can introduce large numerical errors into the computation of well block pressure which is made to be the same as the wellbore pressure, which is the explicit modeling technique. We demonstrate that the best way to obtain the correct well productivity is to use an appropriate analytical solution. When an analytical solution is not available, a uniform fine grid plus explicit well modeling can also yield correct results, but with large computational expense. We show that for such situations, use of non-uniform grids plus explicit modeling with uniform local grid refinement gives satisfactory results with reasonable computational costs. In this paper we also propose practical methods for calculating the correct well index.
A New Technology for the Metering of Low Quality Steam
Authors: Gagliano Thomas , Medizade Mason M.
Published: December 2007

The use of saturated mixtures of water for the purpose of steam flooding is common to heavy oil production operations. These multi-phase flows require the implementation of technology to simultaneously meter the saturated gas and saturated liquid fractions comprising the flow to obtain accurate thermal allocation information. A new technology has been developed to serve this purpose. We have designed a measurement system to measure two phase fluid flows whose total volume flow rate is 85 to 100% gas (85-100 gas volume fraction (GVF)).. By carefully designing a system that is non-intrusive and flow regime independent, we have produced a metering technology that can accurately meter wet steam flows over a wide range of flow rates.
Field Testing of Dielectric Steam Quality Sensor
Authors: Griston Suzanne , Hutchinson Dan
Published: December 2007

Proper management of steamflood projects requires accurate information about the amount of heat input into the petroleum reservoir. A logical step toward obtaining this information is to meter the steam flow rate and quality directly at the injector wellhead. Numerous devices and methods have been developed and marketed over the past few decades to measure two-phase steam rate and quality.

Steam quality metering devices include a two-phase separator, orifice-choke in series, densitometers, dielectric sensors, and radiation detectors. Over the past ten years, with the exception of separator vessels, no steam quality metering device has proven to be commercially viable. However, recent application of dielectric (or impedance) sensor technology to steam quality measurement has shown promising results.

This paper presents results of field testing to evaluate the performance of a commercially available dielectric steam quality sensing device over an extended range of conditions. Overall accuracy of the device compared to separator vessel measurements is discussed. Recommended guidelines for sensor sizing and installation at injectors, to ensure reliable performance, are also presented.
Two-Phase Flow Splitting at Side-Branching Tees
Authors: Griston Suzanne , Choi Jai H.
Published: December 2007

The primary function of a steam distribution system is to deliver uniform-quality steam at the desired rates to each injection well within a steamflood project area. Historically, the distribution system has included either side-branching or impacting tees to split the steam. However, both of these standard pipe junctions have been found to be inadequate for the distribution of two-phase steam.

Field tests were conducted to evaluate steam flow splitting through side-branching tees with and without a reduced diameter side-branch. The main objective was to obtain a better understanding of two-phase flow splitting at side-branching tees over a wide range of steam conditions. In addition, tests were conducted to evaluate the performance of modified side-branching tee designs.

This paper presents field test results for several different side-branching tee configurations, compares test results to other published studies, and discusses the relative merits and limitations of side-branching tees for steam flow splitting.
Disposal of NORM Waste in Salt Caverns
Authors: Veil J. A. , Smith K. P. , Tomasko D. , Elcock D. , Blunt D. , Williams G. P.
Published: December 2007

Some types of oil and gas production and processing wastes contain naturally occurring radioactive materials (NORM). If NORM is present at concentrations above regulatory levels in oil field waste, the waste requires special disposal practices. The existing disposal options for wastes containing NORM are limited and costly. This paper evaluates the legality, technical feasibility, economics, and human health risk of disposing of NORM-contaminated oil field wastes in salt caverns. Cavern disposal of NORM waste is technically feasible and poses a very low human health risk. From a legal perspective, there are no "fatal flaws" that would prevent a state regulatory agency from approving cavern disposal of NORM. On the basis of the costs charged by caverns currently used for disposal of nonhazardous oil field waste (NOW), NORM waste disposal caverns could be cost competitive with existing NORM waste disposal methods when regulatory agencies approve the practice.
Utilisation of "Waste" Gas and Water Streams: An Example of Environmental Impact Reduction Effort during Field Development Planning in the Niger Delta
Authors: Ashiedu Rufus I. , Olarewaju-Alo Bayo O.
Published: December 2007

Shell Petroluem Development Company of Nigeria Limited (SPDC) is taking major strides at incorporating environmental impact minimisation schemes at the forefront of its oil/gas business development. This move is driven by its commitment to continuous improvement and the philosophy of "doing it right" as a preference to the standard curative end-of-pipe approach. One of the schemes is in the area of disposal of by-streams or "waste" gas and water associated with oil production. This disposal issue has remained topical and a continuous point of focus given some peculiarities of the Nigerian situation, i.e. high GOR crude, absence of sufficient gas disposal routes, increasing produced water levels and a struggling economy with limited project funding capacity. Despite these circumstances, SPDC has evolved strategies for harnessing these streams thus reducing their potential environmental risks. The strategies include plans for flares-out by 2008, proposals for produced water re-injection and the concept of "oil - protection" for new developments. This paper presents an overview of the company's enabling policies/objectives/plans and the outcome of an integrated development proposal for Cawthorne Channel - a major oil field in the company's Eastern Division.
Totally Catalytic Processing of H2S Containing Gas Streams to Get the 99.9% Recovery Performance
Authors: Savin S. , Mouraille O. , Nougayrede J.
Published: December 2007

This paper relates to the development of a new totally catalytic process aimed at recovering sulphur from H2S containing gas streams with a performance as high as 99.9%. This process is based on the particular development of a catalytic step able to oxidise H2S directly into sulphur in the presence of air, at a temperature below sulphur dew point, even below sulphur freezing point. Consequently, it involves the implementation of at least two reactors operating alternatively according to the cyclic succession of the two following sequences:

⇒ an adsorption sequence where the sulphur is formed from the oxidation of H2S and trapped within the catalyst structure; ⇒ a regeneration sequence at a higher temperature (around 300°C) where the trapped sulphur is recovered from the catalyst.

This paper provides details concerning the reaction data acquired experimentally with the newly developed catalyst in view of the further modeling of the H2S oxidation process. The industrial performances of this catalyst under particularly low temperature conditions should shortly be confirmed through a pilot demonstration plant due to start up mid 1998 in the South of France.
Comprehensive Study of the Production Water Treatment, Phase I: Selection of the Production Water Treatment System for Mingo Station
Authors: Camacho Fernando , Alí José
Published: December 2007

The results of selecting the production water treatment system, for crude oil separation at Mingo station are reported. This unit is operated by PDVSA SUR, and is located in Barinas state, south-west of Venezuela. This unit runs a crude oil-water separation process, generating 70,000 bls of production waters per day (bpwd).

This study included the gathering and revision of effluent characterization for a period of four years. Additional studies were carried out to complete the technical information. Pilot-scale experimental studies were done for the evaluation of effluent treatment processes, including biological treatment for phenol removal and physico-chemical treatment for sulfur reduction.

As a result, treatment processes were identified and selected based on technical and economic aspects, as well as possible adaptation of the existing installations. The selected treatment consists in the application of polymers at the entrance of the API separator for removing the total crude oil content up to less than 20 ppm.

Effluent temperatures, could be reduced to 32°C using cooling towers with plastic material filling. Phenol and sulfur removal will be carried out through biological treatment at an aeration lagoon located downstream the cooling system. At present, treatment equipment are being installed and operation is being initiated.
Zinc-Iron Reactive Aeration Trench: Passive Treatment of Chlorinated Hydrocarbons
Authors: Miller John A. , Deuell Rick , Linse Steven J.
Published: December 2007

Chlorinated solvents have been used for a number of years for parts cleaning and maintenance work on trucks and heavy equipment in the oil field industry. If and when the chlorinated hydrocarbons are spilled or otherwise released to groundwater, they tend to gravitate to the bottom of the saturated zone and are difficult to remediate by traditional groundwater pump-and-treat systems that employ either groundwater extraction wells or interceptor trenches.

Reactive metals, such as zinc and iron, have been shown to provide reductive dechlorination of groundwater in laboratory studies. Innovative construction techniques were employed to provide a single pass interceptor trench with simultaneous excavation, backfilling with a zinc-iron-sand mixture, and installation of a flexible drainage pipe along the bottom of the trench. Results to date are reported.
Shooting Seismic Safely - A Case History From the Orinoco Delta
Authors: Laven A. J. , Pring D. , McGrail A.
Published: December 2007

The prospect of acquiring safe seismic under extremely difficult conditions is a significant challenge for any company. Over a period of two years and more than 3 million manhours, nearly 1000sq.km of 3D seismic have been acquired by one crew in the Orinoco delta.

By using a complete HSE management system, regular reporting and auditing, safety performance was demonstrably improved. The focus was shifted from lost time injuries to the more useful areas of reports and minor accidents. The HSE management system is described with regards to its use rather than content as only in this way does it deliver any value to the operation.

The overall performance has been extremely encouraging and demonstrates that, despite significant inherent risks it is still possible to produce an outstanding result. In addition, it also shows that continual improvement may be achieved, and provides for the possibility of safety performances far better than the current average. By sharing our experiences and views it is hoped that the industry can become a safer and more enjoyable place for people to work.
Environmental Assessment of Synthetic Based Drilling Mud Discharges to Bass Strait, Australia
Authors: Terrens G. W. , Gwyther D. , Keough M. J. , Tait R. D.
Published: December 2007

Esso Australia Ltd. (Esso) on behalf of the Esso/BHP joint venture undertakes exploration and development drilling activities to produce oil and gas from the Gippsland Basin in eastern Bass Strait. As part of the environmental management of the operation, a field monitoring program was undertaken to verify the predicted limited effect on the seabed of the discharge of residual synthetic based mud (SBM) adhered to drill cuttings.

Reservoir studies of the mature Fortescue oil field identified scope to more efficiently deplete existing reserves as well as develop undrained oil pools within the known reservoir system. As such, 18 additional wells were drilled from the Fortescue platform in 1994–1996 following the original development drilling program when 21 wells were drilled in 1983-1985.

Esso's standard drilling fluid in Bass Strait is an environmentally acceptable water based mud (WBM). However, due to the high frictional forces involved the greater lubricating properties of a non-water based drilling mud were required to drill the long reach, high angle sections of seven of the additional wells. The ester SBM was chosen on the basis of its lubricity and biodegradability, to reduce any potential environmental effects from the persistence of non-water based mud in seabed sediments.

A seabed monitoring program was undertaken around the Fortescue platform by taking seabed samples from August 1995 to August 1997 at sites along a transect following the predominant ocean current and at control sites, before, during and after the period in which SBM cuttings were discharged.

The seabed sediments were measured for esters, barium, biological changes and grain size. Results show clearly the increase in esters concentration in sediments during drilling, then the rapid decrease after completion of cuttings discharge. After a recovery period of 11 months from completion of SBM drilling, SBM esters were not detected in sediments. Sediment barium concentration was also found to be elevated, but only after SBM had been used, indicating greater dispersion of WBM than the more cohesive SBM. The barium concentrations found generally do not have measurable effects on biota. The impact on the sediment biology was found to be limited to the sampling site 100 m from the platform with recovery evident within four months of completion of drilling.

Mechanisms for recovery of the minimal zone of effect are thought to be a combination of the biodegradation of the ester SBM used and the physical seabed dispersion process evident in eastern Bass Strait generated by the continuous series of storms which pass through especially in winter.
Safety in Helicopter Transport of Personnel in Elf Exploration Production (EEP)
Authors: Serra Vincent De Rocca
Published: December 2007

ELF's technological risk management policy is directed at ensuring protection of personnel, respect for the environment and safeguarding of assets in the pursuit of petroleum activities.

As regards helicopter transport, prevention is stressed in priority, in view of the serious risks involved in the event of an accident. It is implemented by means of numerous specific rules applied throughout our subsidiaries.

The Company rules are based on international and national regulatory requirements and recommendations:

the air company chosen must operate its helicopters in observance of public air transport standards, the helicopters must, as a general rule, be twin-engine and piloted by a crew of two, minimum qualification and experience requirements must be met for both flight and ground personnel, follow-up of maintenance and operation programs must be regularly controlled, audits are conducted periodically by the EEP Chief Aviation Officer who checks on application of the rules and recommendations and assesses the level of air safety in each subsidiary, offshore, helicopters are inspected as part of such audits.

This paper details the main rules and provisions laid down in respect of prevention and control, and their scope of application. Any difficulties for implementing an identical strategy in each different geographical area are discussed and explained.
Designing for a Step Change in Benefit from Combustible Gas Detection Systems
Authors: Bonn R. J. C. , Moros A
Published: December 2007

Gas detection plays an important role in the safety of offshore sites, particularly for large, manned production facilities. It is common practice to install many hundreds of point type gas detectors to provide blanket coverage. This approach is not only costly, there is also increased risk for the people who have to inspect and test the instruments in the field.

This paper presents a way to determine where gas detection should be installed to obtain the optimum balance between efficient detection against increased risks and costs. Over one hundred platform years of experience using this method have shown that substantial improvements are possible over more conventional, opinion-based designs.

Included in the paper are the results of studies into the behaviour of gas releases in the complex geometry of offshore sites.

The paper also reveals how conventional designs will frequently miss significant gas hazards. Since adopting this new approach, our success rate for the detection of releases has improved dramatically.