bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermally Induced Wettability Alteration To Improve Oil Recovery in Fractured Reservoirs
Authors: Al-Hadhrami Hamed S. , Blunt Martin J. 
Published: December 2007

SummaryMany naturally fractured reservoirs are oil-wet; during water injection, water will not imbibe into the matrix but will flow preferentially through the fractures, resulting in very low oil recoveries. For instance, the Ghaba North field in Oman is an extensively fractured, oil-wet carbonate that has achieved only 2% recovery after more than 20 years of production.Experiments on core from fields in Oman and elsewhere have indicated that the rock will undergo a transition from oil-wet to water-wet as the temperature increases. The temperature could be increased in a reservoir setting through steam or hot-water injection. It is proposed to inject steam or hot water to heat the matrix sufficiently, inducing a wettability change and rendering the matrix water-wet. Hot water in the fractures can spontaneously imbibe into the matrix, displacing oil and resulting in favorable oil recoveries.A 1D model of the saturation and temperature profiles during imbibition into a matrix block is developed and solved analytically. Using Ghaba North properties, it is shown that the imbibition rate is limited by the diffusion of heat through the oil. The advancing water front is located where the rock temperature equals the transition temperature for wettability change. It is estimated that approximately 30% oil recovery could be achieved in a single matrix block after approximately 700 days. In less permeable media, the imbibition rate is limited by capillary forces, and the temperature front moves ahead of the water, resulting in slower recovery.
Gas-Cap Monitoring in High-Flow-Rate, Low-Porosity Clastic Reservoirs in Colombia Gives Big Economic Returns
Authors: Bullion David , Gonzalez Fabio , Markley Marvin E. 
Published: December 2007

Summary
Cased-hole neutron logging has been in use for many years and is often used to monitor gas movement in reservoirs behind pipe. This works well in high-porosity reservoirs but is rarely successful in low-porosity reservoirs. In Colombia, there are high-flow-rate reservoirs with significant permeability but low porosity [5 to 6 porosity units (p.u.)].
The challenge was to monitor gas-cap expansion, fluid movement owing to re-injection, and voidage. At the same time, the objective was to identify low gas/oil ratio (GOR) intervals behind pipe for possible recompletion.
A number of different examples illustrate both the technique and the economic benefit of the monitoring program. Many of these wells contributed significant additional oil from bypassed zones that were initially thought to be dry gas. In some wells, the instantaneous incremental production was over 10,000 BOPD from a single recompletion.
Gas-cap monitoring in very-low-porosity reservoirs in Colombia proved to be not only feasible, but also extremely profitable by differentiating dry-gas zones from low-GOR zones.
Asphaltene Stability in Crude Oils
Authors: Rogel E. , León O. , Espidel Y. , González Y. 
Published: December 2007

Summary
The influence of different factors on the asphaltene stability in crude oils was evaluated. Compositional studies and structural characterization of resins and asphaltenes were carried out to study a possible relationship between these properties and asphaltene deposition behavior. Asphaltenes were obtained by precipitation with n-heptane and characterized by elemental analysis and spectroscopic techniques. Low hydrogen to carbon ratios, high aromaticities, and high condensation of aromatic rings were the main characteristics of the asphaltenes from unstable crude oils. According to these results, the stability behavior of the asphaltenes was influenced strongly by their structural characteristics. However, it was also found that stabilization by means of a commercial inhibitor was affected by the composition of the crude oil. In particular, a high content of basic functionalities in the crude oil can be related to the decrease of the inhibitor's effectiveness (dodecylbenzene sulphonic acid). Based on these findings, some useful suggestions applicable to the oilfield operations are made.
Water Shutoff Using an Inflatable Composite Sleeve Polymerized In-Situ: A Case History on Forties Delta
Authors: Leighton J. , Saltel J. L. , Morrison J. , Welch R. , Pilla J. 
Published: December 2007

Summary
A new technology based on using in-situ polymerization of composites has been developed and has been used to shut off waterproducing perforations for the first time on Forties Delta. By exploiting the deformability of an unpolymerized flexible composite and the excellent mechanical characteristics of a polymerized composite, it was possible to run an expandable patch-through tubing and set in the liner below. The principles of running the composite patch on electric wireline and the specialized surface and downhole tools are described, along with the setting procedures and events offshore.
Results of this operation have shown an inflatable composite sleeve can be used as an efficient and cost-effective solution for reducing unwanted water production.
3D Transport in Acid-Fracturing Treatments: Theoretical Development and Consequences for Hydrocarbon Production
Authors: Romero J. , Gu H. , Gulrajani S. N. 
Published: December 2007

SummaryWhile the effect of 2D proppant transport during hydraulic fracturing has been studied extensively and debated frequently, relatively little attention has been given to 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 results in more complicated physical phenomena for acid fracturing. Acid diffusion in the fracture has been estimated empirically with no considerations made to model correctly the acid flow across the fracture width. The etched-width profile resulting from 3D flow could differ significantly from that predicted by the 1D, 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. Acid flow in the fracture can affect the outcome of reservoir stimulation and must be considered when designing acid-fracturing treatments.The equations governing fluid flow are developed initially 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 P3D hydraulic fracturing simulator. The theoretical formulation for acid transport across the fracture width is presented then and coupled with the equations for 2D acid flow. The equation of acid diffusion is 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 used subsequently with a reservoir simulator to illustrate the consequences of the 3D acid formulation on hydro-carbon production. Simulated and field examples are presented to illustrate the effects of 3D acid flow on the etched-width distribution and post-stimulation production.
Casing Shear: Causes, Cases, Cures
Authors: Dusseault Maurice B. , Bruno Michael S. , Barrera John 
Published: December 2007

Summary
Casing impairment leads to loss of pressure integrity, pinching of production tubing, or an inability to lower workover tools. Usually, impairment arises through shear owing to displacement of the rock strata along bedding planes or along more steeply inclined fault planes. These displacements are shear failures. They are triggered by stress concentrations generated by volume changes resulting from production or injection activity. Volume changes may arise from pressure changes, temperature changes, or solids movement (solids injection or production).
Dominant casing-deformation mechanisms are localized horizontal shear at weak lithology interfaces within the overburden; localized horizontal shear at the top of production and injection intervals; and casing buckling within the producing interval, primarily located near perforations.
Mitigating casing damage usually means reducing the amount of shear slip or finding a method of allowing slip or distortion to occur without immediately affecting the casing. Strengthening the casing-cement system seldom will eliminate shear, although in some circumstances it may retard it. Proper well location or inclination, underreaming, special completions approaches, reservoir management, and other methods exist to reduce the frequency or rate of casing shear.
Application of a New Model To Analyze Leak-Off Tests
Authors: Altun G. , Langlinais J. , Bourgoyne A. T. 
Published: December 2007

SummaryA leak-off test (LOT), commonly known as a formation-pressure-integrity test, is a verification method to estimate the fracture pressure of exposed formations. After cementing each casing string, a LOT is run to verify that the casing seat can withstand the wellbore pressure required to drill safely to the next casing setting depth. Fracture pressure determined from this test is used as the maximum pressure that may be imposed on that formation. Critical drilling decisions for subsequent casing setting depths are based on LOT results.Although a LOT is a simple and inexpensive test, its interpretation is sometimes difficult, particularly in formations that give nonlinear relationships between the pumped volume and the observed pump pressure. Ideally, a straight line is obtained that reflects the total system compressibility (i.e., the drilling fluid, the casing expansion, and the wellbore expansion.) Nonlinear LOT behavior is thought to be caused by gas in the system, by borehole failure, or by leakage of drilling fluid into the cemented casing/borehole annulus. There is, however, no mathematical model explaining nonlinear LOT behavior.In this study, a mathematical model is derived to assist in analyzing nonlinear LOT behavior. The model has been used to predict the observed nonlinear behavior of field examples. In some cases of a nonlinear LOT, the model can be used to predict the maximum fracture pressure of the formation.
Research and Development of Advanced Coiled-Tubing Construction and Performance
Authors: Urayama T. , Yonezawa T. , Hamada M. , Sugino M. , Takabe H. , Ikeda A. 
Published: December 2007

Summary
This paper describes joint industry project DEA107, in which BP plc, Amoco, Eni SpA. Div. Agip, Scottish Enterprise Operations, and Japan Natl. Oil Corp. (JNOC) participated. Objectives of this project were to investigate and to report on the low-cycle fatigue phenomena of coiled tubing (CT), to present a rational fatiguelife prediction model for CT, and to develop an advanced CT which could be applied to CT drilling of deep wells. In this paper, the effect of various factors on the cyclic bending performance of parent CT materials is predicted in relation to ballooning and low-cycle fatigue phenomena; corrosion and low-cycle fatigue phenomena of CT after long-term exposure in a mud environment are discussed, followed by fatigue performance and improvement of circumferential joining techniques.
A trial section of advanced CT of 2⅜-in. outer diameter (OD) and 0.190-in. wall thickness (WT) with a total length of 3,000 ft was manufactured by means of joining short lengths of seamless tubing using the amorphous diffusion bonding (ADB) technique. A CT drilling test at the JNOC Kashiwazaki test field in Japan was completed successfully using this advanced CT.
Exact Analytic Solutions for Pipe Buckling in Vertical and Horizontal Wells
Authors: Mitchell R. F. 
Published: December 2007

SummaryThe first buckling solution was developed by Lubinski and Woods. When the differential equation describing buckling was derived, this solution was found to be an exact solution for vertical wells. Since these results were published, no other exact analytic solution has been discovered. Many numerical results have been obtained, however, suggesting that other solutions did exist. Because the buckling differential equation is nonlinear, it is not surprising that no other analytic solutions have been discovered. This paper presents three new analytic solutions for the vertical well problem and two new analytic solutions for the horizontal well problem. These analytic solutions are valuable both for predicting previously unanticipated buckling behavior and for providing guidance in further numerical evaluations of this problem.In this paper, these five solutions are described, including techniques for evaluating the analytic functions. Buckling length change calculations are determined analytically, and pipe curvature, bending moment, and bending stresses are evaluated. The contact loads between tubing and wellbore are determined, then used to limit the range of validity of the solutions. The critical force for helical buckling is determined for horizontal wells.Possible applications for these solutions include the analysis of bottomhole assemblies, drillpipe, casing, and tubing. The solutions are simple formulas, but require computer evaluation of the analytic functions.
Experimental and Simulation Analysis of Jet-Perforated Rock Damage
Authors: Mahmoud Asadi , Shirazi Mogdeh K. , Ghalambor Ali , Pratt Dan W. 
Published: December 2007

SummaryThe finite-element method (FEM) is employed to evaluate stress distribution around a perforation tunnel with a sandstone formation. Experimental data are used to confirm the results of theoretical study. In the model, the effect of jet pressure, jet temperature, and the combination of both on formation are studied separately. The results indicated that a 3.5-g RDX charge is capable of disturbing rock formation up to 5 in. longitudinally and 2 in. radially. The extent of this damage zone for a 10.5-g RDX charge is 8 in. longitudinally and 4 in. radially. The linear effect is within the first few inches of the perforation tunnel entrance. In this region, rock grains are under an intensive sudden shock-pressure wave of 2 to 4 million psi for a fraction of a microsecond. As a result, the rock's physical structure will change to metamorphous with a lower bulk density than that of unshocked rock, causing a sudden decrease in formation porosity and, hence, formation permeability.
Well-Test Characterization of Wedge-Shaped, Faulted Reservoirs
Authors: Charles D. D. , Rieke H. H. , Purushothaman R. 
Published: December 2007

Summary
Two offshore, wedge-shaped reservoirs in south Louisiana were interpreted with pressure-buildup responses by comparing the results from simulated finite-element model studies. The importance of knowing the correct reservoir shape, and how it is used to interpret the generated boundary-pressure responses, is briefly discussed. Two different 3D computer models incorporating different wedge-shaped geometries simulated the test pressure-buildup response patterns.
Variations in the two configurations are topologically expressed as a constant thickness and a nonconstant thickness, with smooth-surface, wedged-shaped reservoir models. The variable-thickness models are pinched-out updip at one end and faulted at the other end. Numerical well-test results demonstrated changes in the relationships between the pressure-derivative profile, the wellbore location, and the extent of partial penetration in the reservoir models. The wells were placed along the perpendicular bisector (top view) at distances starting from the apex at 5, 10, 20, 40, 50, 60, 80, and 90% of the reservoir length. Results demonstrate that boundary distance identification (such as distance, number, and type) based solely on the log-log derivative profile in rectangular and triangular wedge-shaped reservoirs should be strongly discouraged. Partial-penetration effects (PPE's) in wedge-shaped reservoirs are highly dependent on the wellbore location relative to the wedge, and the well-test-data analysis becomes more complex.
Sonic-Magnetic Resonance Method: A Sourceless Porosity Evaluation in Gas-Bearing Reservoirs
Authors: Minh Chanh Cao , Gubelin Greg , Ramamoorthy Raghu , McGeoch Stuart 
Published: December 2007

Summary
For environmental reasons, there are times when the use of radioactive chemical sources for density and neutron logging is not possible. The inability to use these logging tools seriously affects porosity determination in gas-bearing reservoirs. Several tools, such as the nuclear magnetic resonance (NMR) tool, the sonic tool, or a minitron-based tool, determine porosity without using a radioactive source. These tools, however, are influenced by many effects and, when used alone, cannot deliver an accurate gas-independent porosity.
A new methodology that combines sonic and NMR logs for improved porosity evaluation in gas-bearing reservoirs is proposed. The first variant of the method uses the sonic compressional transit time and the total NMR porosity (ϕt,NMR) to determine the total porosity, corrected for the gas effect, and the flushed-zone gas saturation. In this approach, a linear time-averaged equation corrected for compaction is applied to the sonic compressional log. The simplicity of the solution, much like the previously published DMR1 Density-Magnetic Resonance Interpretation Method, allows fast, easy computation and a complete error analysis to assess the quality of the results.
In the second variant of the method, we show that the rigorous Gassman equation has a very similar response to the Raymer-Hunt-Gardner (RHG) equation for a water/gas mixture. This allows substitution of the complex Gassman equation by the much simpler RHG equation in the combined sonic-NMR (SMR) technique to estimate total porosity and flushed-zone gas saturation in gas-bearing formations.
Both techniques are successfully applied to an offshore gas well in Australia. In this well, the porosity in the well-compacted sands is in the 20 to 25 p.u. range and the compaction factor is approximately 0.77. The sonic-magnetic resonance results compared favorably to the established density-magnetic resonance results and also to core data. In another offshore gas well from the North Sea, the porosity in the highly uncompacted sands is in the 35 to 40 p.u. range, and the compaction factor is around 1.85. Both SMR techniques were able to produce a very good porosity estimate comparable to that estimated from the density-neutron logs.
Analysis of Horizontal-Well Responses: Contemporary vs. Conventional
Authors: Ozkan Erdal 
Published: December 2007

SummaryMost of the conventional horizontal-well transient-response models were developed during the 1980's. These models visualized horizontal wells as vertical wells rotated 90°. In the beginning of the 1990's, it was realized that horizontal wells deserve genuine models and concepts. Wellbore conductivity, nonuniform skin effect, selective completion, and multiple laterals are a few of the new concepts. Although well-established analysis procedures are yet to be developed, some contemporary horizontal-well models are now available. The contemporary models, however, are generally sophisticated. The basic objective of this paper is to answer two important questions: 1) When should we use the contemporary models? and 2) How much error do we make by using the conventional models? This objective is accomplished by considering examples and comparing the results of the contemporary and conventional approaches.
Reservoir Engineering Aspects of Light-Oil Recovery by Air Injection
Authors: Turta A. T. , Singhal A. K. 
Published: December 2007

Summary
This paper addresses the reservoir engineering aspects of air injection as an enhanced oil recovery technique for light-oil reservoirs. In its most successful form, the process has been applied in deep, carbonate reservoirs. The development of this process in conjunction with an application of the in-situ combustion (ISC) process to light-oil reservoirs, as well as the main mechanisms pertaining to ISC and to gas miscible flooding, are analyzed. It is seen that various air-injection processes (AlP's) can be classified, depending on their spontaneous ignition potential and gas miscibility at reservoir conditions, into four different processes. Based on an in-depth literature review, the best reservoir conditions for application of each of these four processes are derived. The main differences in operational aspects (pollution, corrosion, safety) for these processes are also discussed. Design considerations for pilot testing of the technique are presented. The crucial point is location of the pilot on the structure, which is also a key element in its proper evaluation, and its subsequent development to a commercial-size operation. Finally, recommendations on laboratory work in support of design and evaluation of a field pilot are also presented.
Characterization of a Carbonate Reservoir With Pressure-Transient Tests and Production Logs: Tengiz Field, Kazakhstan
Authors: Chambers K. T. , Hallager W. S. , Kabir C. S. , Garber R. A. 
Published: December 2007

Summary
The combination of pressure-transient and production-log (PL) analyses has proved valuable in characterizing reservoir flow behavior in the giant Tengiz field. Among the important findings is the absence of clear dual-porosity flow. This observation contradicts an earlier interpretation that the reservoir contains a well-connected, natural fracture network. Fracturing and other secondary porosity mechanisms play a role in enhancing matrix permeability, but their impact is insufficient to cause dual-porosity flow behavior to develop.
Flow profiles measured with production logs consistently show several thin (10 to 30 ft) zones dominating well deliverability over the thick (up to 1,040 ft) perforation intervals at Tengiz. A comparison of PL results and core descriptions reveals a good correlation between high deliverability zones and probable exposure surfaces in the carbonate reservoir.
Contrary to earlier postulations, results obtained from pressure-transient and PL data at Tengiz do not support rate-sensitive productivity indices (PI's). Inclusion of rate variations in reconciling buildup and drawdown test results addressed this issue.
We developed wellbore hydraulic models and calibrated them with PL data for extending PI results to wells that do not have measured values. A simplified equation-of-state (EOS) fluid description was an important component of the models because the available black-oil fluid correlations do not provide reliable results for the 47°API volatile Tengiz oil. Clear trends in reservoir quality emerge from the PI results.