bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic Study of Crude-Oil Combustion in the Presence of Carbonate Rock
Authors: Saraji S. , Kharrat R. , Razzaghi S. , Taghikhani V.
Published: December 2007

Based upon the reviewed literature, few works have been conducted in regard to the kinetic study of crude oil in the presence of carbonate rocks. However, this study was undertaken in order to obtain modeling parameters such as the Arrhenius activation energy (E) and pre-exponential factor (F) for oil in the presence of carbonate rock. Such values are needed for numerical modeling studies. Also, in this study the effect of different parameters, like oil API gravity, rock type (carbonate/sand) and oxygen enrichment on reaction kinetics were investigated.

A thermogeravimetric analyzer (TGA) was used to conduct non-isothermal thermogravimetric experiments on different crudes ranging from 8-25 °API. Oils were investigated in its original form or mixed with either sand, montmorillonite as clay or crushed carbonate, montmorillonite as clay. Experiments, also, were conducted in atmospheres containing different percentages of oxygen (21-80%) in nitrogen at atmospheric pressure.

It was observed that increasing oxygen partial pressure results in lower front temperatures, more rapid HTC reactions, and more complete reactions. Moreover, Presence of carbonate rock resulted in lower activation energy and frequency factor in HTC region in comparison with sandstone. It, also, was shown that front temperatures for three crude oils used in this study are lower than 600°C and Sarvak limestone rock decomposes at temperatures above 600°C.
Fifty Years of Wettability Measurements in the Arab-D Carbonate Reservoir
Authors: Okasha T. M. , Funk J. J. , Al-Rashidi H. N.
Published: December 2007

The Ghawar field in Eastern Saudi Arabia contains the largest accumulation of carbonate reservoirs in the world. The majority of wells in the field produce from the Arab-D reservoir, an Upper Jurassic limestone sealed by anhydrite. Oil production from the field started approximately 55 years ago. Water injection started in the 1970's. Long before water injection was considered for the reservoir, the evaluation of wettability was considered essential.

Our present day evaluation of Arab-D wettability takes into account a long historical record of wettability measurements and production history. The procedures, results and caveats of the original measurements have changed slightly but they also show a strong consistency fifty years later. Wettability indices obtained from initial tests, Amott, and USBM methods generally indicate neutral to slightly oil-wet character for cores processed and tested in a preserved state. Comparisons with restored state cores did not indicate major differences. Over the years fluids used in coring operations and core preservation have shown little impact on the observed results.

Local variations in wettability indicating mixed wettability and oil-wet tendencies can be observed when tar is present in a significant amount and in areas high on structure. The combination of methods from advanced SEM observations, to qualitative contact angle measurements, to relative permeability results all point to a common wettability value.
Enhanced Coalbed Methane Recovery Using Microorganisms
Authors: Jadhav Madhavi Vitthal
Published: December 2007

Energy consumption in the world is increasing every year with the energy requirement of 5.6% per annum hence forced to find alternative resources like CBM, Gas hydrates, Tar sand. CBM is a natural gas containing 100% methane produced from coal seam reservoirs. CBM is often produced at shallow depths and is often produced with large volumes of water. The methane inside the coal seams can be recovered by two methods i.e., Primary recovery and ECBM recovery. The CBM can be recovered up to 20-60% by primary methods but by ECBM the recovery can be enhanced by 60-80%. To improve the secondary recovery it would be suggested to use methane-eliminating bacteria along with the injection of nitrogen and carbon dioxide. It would assist nitrogen injection by partial pressure mechanism with nitrogen fixing techniques also it fixes carbon dioxide by eliminating methane.
A New Analytical Model of Geomechanics During Nonisothermal Injection
Authors: Kocabas I.
Published: December 2007

A new transient analytical model is presented to study the poro-thermal and poro-elastic stress transients during cold water injection into a hot reservoir. Earlier models have shown that pore pressure and temperature variations during a non-isothermal injection such as waterflooding or even drilling fluid invasion can influence the stress distribution in the field profoundly. Such effects are relatively easier to account for single phase flow or piston-like displacement cases.

In this work, a new solution is developed to further improve the coupling in the case of a non-isothermal Buckley Leveret type displacement. Thus we are able to account for the very important viscosity and relative permeability effects on the stress transients. In the model, first the transient saturation and temperature distributions are solved simultaneously and then transient pressure and stress fields are computed consecutively.

In order to decouple the equations for saturation and temperature from the equation for pressure incompressible fluid flow is assumed. Then, the pressure distribution in the system is obtained by superimposing pressure transient effects on a saturation profile known a priori with its mobilities and diffusivities. Then a plain strain model is developed to compute the poro-elastic and thermo-elastic stress transients for a non-isothermal Buckley-Leveret type displacement.

The results implied that the thermoelastic changes in the cooled zone could affect the surrounding stress fields in a profound manner. For instance for a porous medium with stiff material such as carbonate reservoirs owing to cooling by the injected cold water large scale tensile stresses arise and a major tangential stress concentration develops in front of the cooled zone. The thermally induced viscosity effects can dominate the near wellbore stresses at early times. The relative permeability also affects the stresses significantly in the invaded zone albeit to a lesser extent than viscosity.
Innovation in Drilling Using Replaceable Drilling Bit
Authors: Banerjee S. N. , Gupta Yash
Published: December 2007

In conventional drilling a majority of drilling problems occur during tripping such as key seating and wall sticking. This leads to increase in rig time hence cost is unnecessarily high, especially in deep sea drilling.

Conventional drilling techniques use rotary drill bits which need to be replaced depending on the formations encountered. If the formation is very hard, the bit has to be replaced by a diamond bit. These bit changes unnecessary increase trip time and eventually rig cost. This trip time which can take upto a day, especially for deep wells can be eliminated by using a novel "Replaceable Drill Bit" system.

The concept of replaceable drilling bits is attractive for deep drilling because of the high rig costs and the lengthy round trips needed to replace worn bits. These bits are sturdy, capable of withstanding the high dynamic loads imparted by the vibrating drillstring and are capable of operating with highly abrasive drilling mud containing large amounts of sand and drill cuttings.

Thus an entire hole can be drilled conveniently without frequent tripping operation to change the bit. Maximum efficiency can be achieved by this mechanism during drilling.
The Effect of Hydraulic Vibrations on Initiation of Buckling and Axial Force Transfer for Helically Buckled Pipes at Simulated Horizontal Wellbore Conditions
Authors: Barakat Elie R. , Miska Stefan , Yu Mengjiao , Takach Nicholas
Published: December 2007

An experimental study of the effect of hydraulic vibrations on initiation of buckling and axial force transfer for helically buckled pipes at simulated horizontal wellbore conditions has been conducted. Hydraulic vibrations have been induced inside the drillpipe by interrupting the fluid flow at controllable frequencies.

The results show that the hydraulic vibrations induced inside the drillpipe can reduce the buckling force by 11% to 45%. These results were collected by buckling the pipe with and without vibrations and comparing the loads at which buckling is initiated. It is also noticed that the friction force between the pipe and the wellbore and the stick-slip motion are reduced when compressing the pipe while inducing the vibrations. Regarding the effect of hydraulic vibrations on the axial force transfer, an increase in the axial force transmitted from the top end of the facility to the bottom end of the facility by 30% to 100% was found. This increase depends on the fluid flow rate, frequency of the vibrations, fluid type (i.e. viscosity) and magnitude of the applied top load. It was found that this technique highly depends on the viscosity of the drilling fluid used. Polymers showed a different behavior compared to water.

They were found to have a damping effect on the pressure pulses, therefore are less efficient compared to water.

The results of this study are important for extended reach drilling; i.e., reducing the friction due to buckling of coiled tubing and reducing torque and drag in the case of drillpipes and casing in horizontal wellbores.
Challenges Encountered During a Comprehensive Test Analysis for a Horizontal Well in a Thin, Carbonate Reservoir of the Greater Burgan Field, Kuwait
Authors: Ambastha A. K. , Anderson M. , Gandhi H. , Maizeret P. -D.
Published: December 2007

Mauddud reservoir in the Greater Burgan field is a thin, carbonate reservoir containing light oil in a 10-20 ft target zone with "good" porosity. Matrix permeability is low and natural fracture density can be variable in this reservoir. Thus, this reservoir must be exploited using horizontal wells. Recently, a 2,270 ft long horizontal well has been drilled in an area interpreted to have high fracture density. A comprehensive test program, including flowing and static pressure surveys, modified isochronal test, two buildup tests, and FloScan Imager (FSI) log, has been carried out to evaluate this well.

The material discussed in this paper provides a good basis for evaluating long-term production potential of horizontal wells exploiting tight and thin reservoirs with reservoir pressures close to the bubble-point pressure.

Test data interpretation highlights successful development of inflow and tubing performance relationships, bubble-point pressure estimation as well as quantification of reservoir parameters. This paper describes unique challenges encountered in interpreting transient pressure data from this horizontal well due to multi-phase flow and short production time. Impact of derivative shape on model selection is also discussed. The effects of analysis methodologies based on specific flow regimes vs. total model fitting, single- vs. multiphase production treatment, and assumptions regarding effective well length on the computed values of reservoir parameters emphasize the attention required to obtain meaningful interpretation from horizontal well tests. FSI data was instrumental in interpreting effective length of the well.

Overall, this test program yielded information that was critical in managing sustained production from this well, characterizing the effects of the natural fractures on production behavior, as well as quantifying reserves for this tight reservoir.
Field Trial of an Acoustic Downhole Monitoring System Retrofitted in an Existing Completion
Authors: Fyfe D. , Jarvis L. , Ing Tiang Ting , Farooqui Mohammad A.
Published: December 2007

This paper will discuss the findings from a field trial to evaluate the reliability of a retrofitted acoustic data acquisition system in an onshore well in Qatar for a three month period. The technology allows downhole data to be transferred from multiple locations in the well tubing to the wellhead utilizing acoustic waves. From the wellhead, the data is transmitted to engineers PC through a satellite communication system. This technology eliminates the need for expensive hardware or fiber optic cable used in the conventional downhole monitoring systems.

The field trial was successfully completed after 111 days of continuous data gathering and monitoring. All P/T gauges and the acoustic data transmission devices installed in the well performed excellently. The objectives of the trial were achieved. We not only were able to collect the downhole pressure and temperature data for well performance analysis but were also able to define the flow patterns (such as the slugging effects) occurring in the well due to changes in bottomhole pressure.

This system can be deployed as a temporary installation retrofit in the existing wells utilizing conventional wireline units, or permanently as part of the well completions for monitoring well performance for reservoir management or well performance monitoring purposes. The trial did not cover evaluation of the system under permanent installation mode as part of the well completion. Permanent installations can be considered once more long term experience has been gained from retrofit applications. IT involvement to provide support and the data transmission link is very essential.

The paper will describe the overall system, illustrate the quality and accuracy of real time data obtained during the trial and its utilization for well and reservoir performance evaluation purposes.
MRC Wells Performance Update: Shaybah Field, Saudi Arabia
Authors: Salamy S. P. , Al-Mubarak H. K. , Ghamdi M. S. , Hembling D.
Published: December 2007

This paper is an update of previous SPE technical papers1,2 highlighting the results of 25 Maximum Reservoir Contact (MRC) wells drilled in the Shaybah Field either as new wells or part of a workover strategy to convert existing weak 1-km single lateral wells to MRC wells with reservoir contacts ranging from 5 to 9 km.

Shaybah field, a low permeability reservoir overlain by a huge gas cap was initially developed in 1996 with 1-km single lateral horizontal wells to effectively drain the hydrocarbon while reducing gas coning. A step development approach by increasing the reservoir contact to improve well productivity and performance was the basis for the MRC concept. Results to date from 25 MRC wells have indicated a four-fold increase in well productivities and a three-fold decrease in unit development cost when compared to the one-km single lateral wells. A useful by-product of MRC drilling is the enhancement achieved in reservoir characterization.

In addition to MRC wells, smart technologies such as downhole flow control systems (smart completions), expandable liners, and production equalizers were deployed in Shaybah Field. These technologies have shown major improvements to well performance and recovery. Smart controls assisted in optimizing production from each lateral in a multi-lateral well in the event of premature gas or water coning. In addition, downhole smart completions improved well productivity in multi-lateral wells through an improved well cleanup process. Production equalizers when deployed in high GOR wells reduced gas coning and improved well productivity. To date over 21 expandable liners have been deployed as enablers to a workover strategy to convert single lateral wells to Multi-lateral/MRC wells thereby providing the platform for installation of downhole flow control systems.
Wellbore Stability analysis in UBD Wells of Iranian fields
Authors: Salehi S. , Hareland G. , Dehkordi K. Khademi
Published: December 2007

Drilling underbalanced is often used to prevent formation damage, avoid lost circulation, and increase rate of penetration. However, it is also risky and may lead to wellbore collapse due to lack of positive support provided by the hydrostratic wellbore fluid column. Hence, the application of underbalanced drilling (UBD) should be evaluated thoroughly through the use of in-situ stresses and rock mechanical properties to estimate under what hydraulic drilling conditions the wellbore is stable.

This paper presents a mechanical wellbore stability analysis for two depleted Iranian fields, named herein as field A and B. Depleted Iranian fractured carbonate fields are suffering from severe wellbore stability problems and lost circulation during overbalanced drilling conditions. The application of UBD in these fields with a pressure less than formation pore pressure brought on new wellbore stability problems like risk of shear failure and collapse of borehole wall. Using good geomechanical model description matching field characteristics in conjunction with rock failure criteria in some cases may lead to a good prediction for avoiding wellbore stability problems and choosing the optimum mud weight window. By analyzing cores, log and triaxial rock mechanical data, an elastoplastic model combined with a finite-explicit code was used in the wellbore stability analysis to estimatimate an optimum Equivalent Circulating Density (ECD) for these fields. Compared to some actual field data it was observed that using an elastoplastic constitutive model would be sufficient to analyze mechanical wellbore stability in these fields.
Pore Network Modeling: Analysis of Pore Size Distribution of Arabian Core Samples
Authors: Dong Hu , Touati Mustafa , Blunt Martin J.
Published: December 2007

We use X-ray microtomography (micro-CT) to image rock cuttings of poorly consolidated sandstone and vuggy carbonate from Saudi Arabian oil and gas fields. The cuttings are a few mm across and are imaged to a resolution between 3 and 12 microns. The details of the three-dimensional pore space can be clearly seen. A maximal ball algorithm is used to extract a topologically equivalent pore network: the largest inscribed spheres in the pore space represent pores, with throats representing the connections between them. The results are validated through comparison with networks derived by a different method from idealized sphere packings and Fontainebleau sandstone.

The aim of this work is to input the models into pore-scale network models to predict macroscopic properties such as relative permeability and capillary pressure. This acts as a valuable complement to special core analysis, enabling predictions of properties – such as three-phase relative permeabilities and the impact of wettability trends – outside the range of parameters probed experimentally. Furthermore, using microtomography, rock cuttings can be analyzed that are too small for conventional core flood experiments.
Accelerating Technical Competency Development to Meet Future Challenges: The Saudi Aramco Approach
Authors: Solares J. Ricardo
Published: December 2007

Saudi Aramco, as most other major oil companies around the world, will face a looming crisis when a large number of experienced and highly qualified engineer and earth sciences professionals are expected to retire and exit the oil industry within the next five years. In anticipation of this occurrence, the company has embarked on a number of initiatives all aimed at accelerating the development of technical competencies in young professionals to ensure a smooth "change of the guard" transition, and meet the ever-growing challenges of the future when implementation of highly complex technology will require well developed skills.

To confront these significant challenges, Saudi Aramco has developed and implemented a multi-strategy approach combining fit for purpose technical courses designed to reduce specific technical competency gaps, practical work experiences, formalized mentoring programs, special cross-training assignments, specialist skills development programs, knowledge sharing systems and others. Detailed individual long-term technical development plans are prepared for all technical personnel with clearly defined targets and expectations, which are then implemented and continually monitored to ascertain progress and make adjustments whenever required.

This paper elaborates on the Saudi Aramco approach, discusses results achieved to date, and shares ongoing way forward plans to strengthen the program and achieve its objectives.

The successful implementation of this effort will help the company mitigate the impact of losing experienced technical personnel to retirement, and will ensure that new generations are fully prepared to face a bright and challenging future.
Improving Formation Strength Tests and Their Interpretation
Authors: van Oort Eric , Vargo Richard
Published: December 2007

Verifying pressure integrity of a casing string and the adjacent formation is an important requirement during drilling of a well. Crucial decisions on mud weight, kick tolerance, and the setting depth of the next casing string are based on the outcome of formation strength tests (FST) such as leak-off tests (LOT) or formation integrity tests (FIT). Moreover, government regulations usually require that a minimum integrity is guaranteed before a well may be deepened.

Yet the majority of FSTs and their interpretation currently carried out in the field can only be characterized as inadequate. Commonly, FSTs lack quality and accuracy due to (in)sensitivity in the hydraulic system to subtle pressure effects in the wellbore, use of highly compressible synthetic or oil muds, non-linear thermal profiles, poorly-understood formation stress and strength behavior, or simply by poor data capturing (e.g. by hand-generated plots). This may have a significant negative impact on the drilling operation. For instance, when mud weight windows are incorrectly assessed after testing, lost circulation or well control problems may ensue on wells with tight drilling margins.

Here, we highlight several of the problems underlying current FSTs and their interpretation, illustrating them with actual field examples (such as the discrepancy often observed between surface readings and downhole pressure-while drilling (PWD) readings obtained while testing), and show how test artifacts can be either avoided or accounted for. A case is made for the use of downhole recorded pressure data to correctly determine casing shoe strength.
Real-Time Digital Interpretation of Subsea Blowout Preventer Tests
Authors: Winters Warren J. , Burns Tim A. , Livesay Ronald B.
Published: December 2007

A computer based method expedites interpretation of pressure data during subsea blowout preventer (BOP) tests. This can reduce the time and cost of current subsea BOP testing practices in a safe and objective manner.

Presently, individual tests can require more than 1 hr. of shut-in time and a complete series of subsea BOP tests may comprise at least 12 individual tests.

The digital method employs computer software to produce an accurate model of the pressure decline behavior relatively early in each test. The model can thus predict if future pressures will stabilize at an acceptable level. With regulatory approval and a reliable method to forecast pressure, the duration of subsea BOP tests can be significantly reduced.

Comparison of the digital method to conventional subsea BOP testing on numerous field trials shows excellent agreement. If implemented the digital method could save hours of valuable critical-path rig time during every series of subsea BOP tests.

Working in concert with regulatory authorities to gain endorsement of this method is integral to the project. Functionality of the software, example results and implementation status are reported.
Application of Global Optimization Methods for History Matching and Probabilistic Forecasting—Case Studies
Authors: Choudhary M. K. , Yoon S. , Ludvigsen B. E.
Published: December 2007

Subsurface uncertainties have a major influence on investment decisions in major capital projects. By understanding and quantifying subsurface uncertainties better, investment risks can be reduced and decision quality can be improved. Quantifying subsurface uncertainties for a mature field involves history matching or solving the inverse problem, which is not only difficult but also non-unique in nature. A suite of acceptable history matched models, which have multiple combinations of model parameters, is required to obtain a probabilistic view of the reservoir performance. Once a suite of models that all match history has been obtained, they are calibrated for predicting the future performance and assessment of uncertainty and risk associated with a particular development plan. In this paper, we demonstrate a structured approach to history matching, uncertainty assessment, and probabilistic forecasting for mature assets through application of global optimization methods.

This work involves application of global optimization methods (Evolutionary Strategy and Genetic Algorithm) for history matching, uncertainty assessment, and infill well optimization. Specifically, the process involves re-evaluation of manually history matched models, investigation of the possibility of achieving multiple history matches, and quantification of the impact these results had on the decision process. Furthermore, the study used a workflow to determine P10-P50-P90 outcomes without using response surface (or proxy) methodology.

Results from application of our approach to two mature West African reservoirs are presented here. Both these studies explore various subsurface uncertainties to achieve a probabilistic view of multiple history-matched models and optimization of various development scenarios. The case studies also show how a computer assisted approach coupled with a structured workflow can speed up the forecasting and uncertainty assessment process.
Innovation in Coiled–Tubing Tractor Technology Extends the Accessibility of Coiled Tubing in Horizontal Wells, Allowing Better Possibilities for Well Intervention
Authors: Al Omari Mazen , Plessing Hans
Published: December 2007

Recent advances in horizontal drilling technology have allowed drilling longer horizontal sections in the reservoir more efficiently and economically. While operators benefit from the well-known advantages of horizontal drains, such benefits cannot be maximized during the lifetime of the well without a viable well intervention means for well service and monitoring operations. Coiled tubing has been recognized as an effective technique for such interventions but with limitation on the total length that can be accessed especially in extended reach wells. This paper summarizes the utilization of innovative coiled tubing Tractor technology to improve coiled tubing accessibility in long horizontal wells.
Enhanced Cementing Practices Address Unique Issues Found With Solid Expandable Tubular Applications
Authors: Heathman James , Arredondo Eduardo , Olufowoshe Akin
Published: December 2007

New and innovative technology has a way of significantly influencing peripheral products and processes. A case-in-point is the relationship between solid expandable tubulars and cementing practices. The early years of cementing expandable casing were filled with researchers working to develop novel chemistries and resourceful techniques for annular sealants that varied from modified conventional cements to highly-specialized non-Portland systems such as resins. Experience and time relegated many of these chemistries and systems to specific situations.

Instead of needing atypical techniques and unique products, the more effective and applicable approach with solid expandables consisted of modified placement practices, training, logistics, and refined engineering of conventional cementing methods. But, as solid expandable tubulars are installed in deeper and higher-angled wells, annular sealant methods and products will be required to function in more extreme conditions.

This paper will examine the evolution of cementing processes and products for solid expandable tubulars. Emphasis is placed on best practices and lessons learned, with the intent of giving the reader a practical field guide. Checklists for key slurry design issues and how they correlate with the job logistics of the expansion operation will be included. This paper will also discuss foreseeable application trends in expandable use and logical modifications and enhancements in cementing procedures, technology and chemistries.
Formation Evaluation While Drilling Of a Complex Khuff–C Carbonate Reservoir in Ghawar Field, Saudi Arabia
Authors: Al-Fawwaz Abdullah , Al-Musharfi Nedhal , Butt Parvez , Fareed Abdul
Published: December 2007

Within the Saudi Aramco organization, complex reservoir formation evaluation is regarded as a key discipline - fulfilling a critical role in maximizing production and facilitating accurate estimation of reserves. The timely acquisition of high quality and detailed petrophysical properties of the various reservoirs in Saudi Arabia is central to this role. Towards this end, Saudi Aramco Reservoir Description Division (RDD) introduced a new-generation multi-functional LWD (Logging-While-Drilling) technology into Saudi Arabia, has been directed to evaluation of on-shore complex carbonate reservoirs.

The traditional LWD measurements of propagation resistivity, gamma ray, density and neutron porosity along with advanced gamma ray capture spectroscopy measurements into a single compact collar. The electronic pulsed neutron source required for the spectroscopy measurements also provides a much improved neutron porosity measurement1.

This technology has been used in a number of Saudi Aramco horizontal wells in carbonate and clastic reservoirs. The data from these wells has been comprehensively evaluated. The results of the evaluation of the data acquired by the new tool and conclusions about the tool's introduction into Saudi Arabia are summarized in this paper.
Reservoir Modeling With Global Scaleup
Authors: Wu X. H. , Stone M. T , Parashkevov R. R. , Stern D. , Lyons S. L.
Published: December 2007

We present a new global scale-up technology for calculating effective permeability and/or transmissibility. Using this innovative technology, we apply global flow solutions to improve scale-up accuracy. Global scale-up was proposed in the 1980s, and its benefits are well-described in the literature. However, global scale-up has not been adopted by the industry due to significant technical challenges in its application to real reservoir models. These models are often characterized by complex features like faults, pinch-outs, and isolated geobodies. Here, we overview several novel technologies that we have developed to overcome these difficulties.

Numerical examples applying global scale-up to several reservoir models are presented. Comparisons with local scale-up methods currently used in the industry are made.

The examples demonstrate that our new global scale-up technology leads to significant improvements in scale-up accuracy. In particular, when applied to challenging models with complicated fine-scale connectivity, the global scale-up method preserves the fine-scale connectivity more accurately than local scale-up methods. Sometimes, dramatic differences are seen. Moreover, we note that global scale-up can be especially effective when used in conjunction with unstructured grids.

Accurate scale-up is a critical link between fine-scale geologic descriptions and coarse-scale reservoir simulation models used for development planning and reservoir management. Predictive reservoir models that are consistent with geologic and production data gathered at different scales are critical for these tasks. Global scale-up is a promising technique for building more accurate reservoir models.
Success Story of a Waterflood Project in a Geologically Complex, High Viscosity Oil Reservoir in a Major Brownfield in South Oman
Authors: Choudhuri Biswajit , Al-Rawahi Mahir
Published: December 2007

A major reservoir in a large brown field in South Oman has been on production for more than 25 years. The reservoir comprises glacial sandstones of Palaeozoic age and is highly heterogeneous with wide variation in reservoir characteristics at scales smaller than well spacing. These variations include impermeable diamictite and shale beds and multi-Darcy gravel or conglomerate beds. The reservoir geology is further complicated due to the presence of faults and fractures that often provide highly conductive vertical pathways to the aquifer. The reservoir crude has high viscosity (90 cp) and moderate to low API gravity (22 deg API oil).

The field has been developed using vertical and horizontal wells in different phases of development. Water-flooding is in operation in the reservoir for more than 6 years. Injectors comprise vertical injectors in five spot pattern, horizontal injectors and inclined aquifer injectors in the flanks. Different water injection philosophy for different areas of the field has been adopted considering factors like primary drive mechanism operative in the reservoir, presence or absence of vertical barriers to flow, pre-existing field development pattern and more importantly future development for maximizing recovery from the reservoir over the entire life cycle.

Despite the geological complexity of the field and adverse mobility ratio conditions under which water-flooding is being carried out, the reservoir has responded very favourably to water flooding. The production decline trend from the reservoir has been arrested and reservoir pressure has increased in most areas of the field after initiation of water injection.

The paper presents the success story of water-flooding in a geologically complex reservoir containing high viscosity oil. The paper clearly illustrates that the success of a water-flood in a complex reservoir rests on implementation of a tailor-made development plan with flexibility to make changes to the same based on data from reservoir surveillance. The importance of well and reservoir management to maximize the value of waterflood is clearly brought out.
An Integrated 3D Volume Interpretation Approach is Successfully Used to Characterize Barriers to Flow within a Carbonate Reservoir
Authors: Al Khowaildi Shakir , Soroka William L. , Al Mehairi Yousuf
Published: December 2007

A method to quantify reservoir heterogeneities that should be included in a reservoir model to more accurately characterize a subsurface reservoir was successfully developed. Using a 3D volume interpretation approach it was possible to build a model of dense low porosity bodies within a reservoir layer that act as barriers to fluid flow. Pressure data confirmed cases where water injection wells were having negligible effect on up-dip production wells. The barriers to fluid flow were identified as a system of tidal channels and tidal pools, which were filled with dense, low porosity material, located within the porous reservoir layer.

A number of detailed studies were conducted to further identify and explain the occurrences of these dense bodies. The results of four independent studies were successful at characterizing the tidal channel-pool complex. The methods included seismic interpretation; well log analysis, seismic attribute analysis, deterministic and stochastic inversion and acoustic impedance to porosity volumes. When the fine details of the different studies were compared it was recognized that the different approaches used to identify the dense bodies showed subtle differences in size, location and geometries of the dense bodies.

A 3D volume interpretation approach was successfully used to integrate the different results and produce a most likely dense body model. The 3D volume interpretation included 3D visualization, co-rendering of multi attribute volumes, seed detection and use of available well control. Several wells had been drilled through the dense tidal channels and ponds and where used as calibration points to validate the analysis.

The final 3D geo-body model was provided to the reservoir modelers for incorporation into the geologic model. The addition of these subtle geologic features in the reservoir model is important for improved well planning, simulation and oil recovery.
Permeability and Microscopic Displacement Efficiency of M_1 Bimodal Pore Systems in Arab D Limestone
Authors: Clerke Edward A.
Published: December 2007

Extensive and detailed studies of the pore systems of the Ghawar Arab D limestone have been captured in very large mercury injection capillary pressure data sets1–3 in which all data have been analyzed using Thomeer functions4–6. These data give new insight into the pore geometry dependence of the reservoir dynamical properties: permeability and imbibition oil relative permeability7 and yield ultimate recovery rock types with algorithms for rock type based reservoir simulation studies of ultimate recovery. New carbonate petrophysical concepts are established.

The dominant subgroup of the examined carbonate limestone pore systems comprise the major Arab D reservoir section are denoted as an M_1 bimodal pore system3. The M_1 bimodal pore system consists of a macropore system (M), with a well defined and wide distribution of pore throat diameters and geometries, in conjunction with Type 1 microporosity with equally well defined and narrow distribution of pore throat diameters and geometries. This bimodal M_1 pore system results in a mixed wet reservoir condition in the bulk of the reservoir.

The role played by the macro and micro pores of the M_1 pore system has been related to the reservoir dynamical properties: permeability and relative permeability7. This work demonstrates fundamentally new pore geometry based formulations for calculating permeability and imbibition oil relative permeability and therefore delineates the pore geometry based variation in microscopic displacement efficiency for variations within these systems. For these reservoir rocks, the appropriate pore geometrical parameters to perform ultimate recovery rock typing have been identified.

This paper presents data and formulations for improved pore system based models of permeability and imbibition oil relative permeability in the M_1 bimodal pore system that reproduce measured laboratory data over a range of oil relative permeability from 1 to 0.0001 for seven waterflood composites. The relative permeability formulation uses two attributes of the pore system: permeability (already shown to be a function of pore geometrical parameters) and the volume of Type 1 microporosity alone. Both of these can be extracted from appropriate processing of appropriate well log data. These results show that shifts of the oil relative permeability curve to increasing water saturation (the right) commonly ascribed to wettability changes, result in this case from increasing the amount of Type 1 microporosity in the M_1 bimodal system which add an "ineffective" water saturation to the relative permeability water saturation axis.
Property Modeling: An Aid To Exploration Of Deep Jurassic Reservoirs In North Kuwait
Authors: Dey Arun Kanti , Singh Sunil Kumar , Al-Awadi Mishari Ameen , Rao N. Srinivasa
Published: December 2007

The emergence of multiple Jurassic carbonate play has opened up a new vista of exploration in the state of Kuwait. A strong need is felt to focus the exploratory efforts on the deep reservoirs below the oil producing Tertiary – Cretaceous strata across Kuwait. In absence of good quality seismic data below the Late Jurassic salt – anhydrite sequence the methods derived from the analyses of subsurface information obtained from exploratory drilling are utilized to complement to seismic study. The present paper describes one such method used as an aid to exploration of deep Jurassic reservoirs in North Kuwait.

Three exploratory wells have penetrated Jurassic Middle Marrat reservoir facies in the Raudhatain field. The wells are drilled 5 to 9 km apart in an area of about 160 sq. km. The initial test results show that this carbonate reservoir has a potential of producing light oil @ 3800 to 5300 BOPD and gas @ 8.5 to 15.5 MMscf / D. The production has been obtained from both limestone matrix as well as from secondary fracture and dolomite porosity.

Middle Marrat section was divided into eight zones on the basis of lithological heterogeneity. The log data was processed and was subsequently populated in the structure grids of different layers to develop a fine scale geocellular model. Porosity and water saturation are the properties used in this study. They were interpolated to decipher the distribution in vertical as well as in horizontal direction. The study was integrated with other geoscientific information to delineate the porous and oil saturated locations.

The model is useful in formulation of future exploration strategy in the area. In addition, it will also be used as an effective working model as the exploration and appraisal efforts mature.
Improved Understanding of Reservoir Fluid Dynamics in the North Sea Snorre Field by Combining Tracers, 4D Seismic, and Production Data
Authors: Huseby O. , Andersen M. , Svorstøl I. , Dugstad Ø.
Published: December 2007

To obtain improved oil recovery (IOR) it is crucial to have a best possible description of the reservoir and the reservoir dynamics. In addition to production data, information can be obtained from 4D seismic as well as tracer monitoring. Interwell tracer testing (IWTT) has been established as a proven and efficient technology to obtain information on well-to-well communication, heterogeneities and fluid dynamics. During such tests, chemical or radioactive tracers are used to label water or gas from specific wells. The tracers are then subsequently used to trace the fluids as they move through the reservoir together with the injection phase.

One of the appealing features of IWTT is that at first tracer breakthrough in a producer, immediate and unambiguous information on injector - producer communication is given. However, gas and water re-injection might complicate this simple evaluation, and later in the production history, this effect should be evaluated. Despite the appealing features of IWTT, they are still underutilised in the petroleum industry, and few of the tracer studies that are actually performed utilise the data to their full capacity - most tracer data are used in a qualitative manner [1].

To improve this situation, we combine tracer data evaluation, 4D seismic and available production data in an integrated process. The integration is demonstrated using data from the Snorre field in the North Sea. In addition to production data, extensive tracer data back to 1993 and results from three seismic surveys acquired in 1983, 1997 and 2001 were considered.
Evaluation of Steam Injection in a Fractured Heavy-Oil Carbonate Reservoir in Iran
Authors: Bahonar M. , Ataei A. , Masoudi R. , Mousavi Mirkalei S. M.
Published: December 2007

Steam injection in naturally fractured heavy oil reservoirs provides an extremely challenging problem as well as a potentially effective and efficient improved oil recovery method. Coupling of the two distinct and contrasting matrix and fracture systems results in a highly non-linear problem, and it gets even more complicated as a result of steep changes in fluid properties due to the thermal effects of steam injection. Modeling and designing an optimum steam injection operation in such systems requires an accurate characterization and representation of a naturally fractured heavy oil reservoir and steam injection operation parameters and dynamics1.

In this communication, the results of a feasibility study of steam injection in a highly fractured carbonate reservoir are discussed. The field is a giant structure located in south west of Iran at the coast of Persian Gulf. It is a symmetrical anticline with 56 mile length and 10 mile width in the surface with about 3.6 billion barrels of initial oil in place. The initial pressure is 927 psi at 1700 ft depth. The gravity of the oil is 7.24 °API with viscosity of about 2700 cp.

The Geological model was constructed based on the available 2D and 3D seismic investigation and conventional core data from different samples. Extensive fracture characterization has been conducted using core data as well as the petrophysical interpretation using imaging logs. Dynamic reservoir simulation model with thermal option has been developed and used for optimization of different parameters for steam injection and their effect on reservoir performance and recovery factor.

Reservoir simulation of the field showed that steam injection could improve oil recovery from zero up to nearly 12 %. Furthermore, the results illustrated that the important parameters for designing the steam injection are different strategies for perforating, well spacing, well type, pattern type and size. Additionally, the effect of other parameters such as injected steam quality, oil-water capillary pressure in matrix blocks, steam injection and oil production rate have been studied.
A Comprehensive Approach to Well-Integrity Management in Adma-Opco
Authors: Tarmoom Ihaab , Thabet Hussein Bin , Samad Saleh , Chishti Khalid , Hussain Ashiq , Arafat Mohamed
Published: December 2007

The last few years have seen a renewed emphasis on Well Integrity (WI) worldwide, and ADMA-OPCO in particular.

ADMA operates, more than 600 wells, in two offshore fields, which include oil producers, water injectors, gas producers/injectors and observation wells. A dedicated team was setup to focus entirely on WI and related issues. The team was given the objective to achieve the following. –Determine the Well Integrity Status of the entire well stock through risk review and ranking.–Recommend appropriate action plan for each well with unacceptable level of risk.

The team used a comprehensive and novel approach for handling this project. This paper is a case study of the methodology adopted by the team to achieve this task.

Since the main objective was to risk review and rank the entire well stock, a dedicated risk-ranking process was designed, which served as an automatic guide to risk review and ranking of wells. The industry Risk Ranking matrix was modified to make it more objective and easy to use.

It soon became obvious that risk evaluation of wells was only possible based on availability of good data organized in a user-friendly format. A dedicated database was setup in parallel with other activities. The web-based database was designed to contain all the data required for WI review of any well and is capable of tracking well integrity related tasks automatically.

Well Integrity data included well construction, annuli pressures, production, well intervention, etc. The data existed in the office files were promptly transferred into the database.

The team made a strong effort towards building the capabilities to acquire missing WI data such as Annulus Leak Rates, Integrity Test Results, Wellhead and Xmas Tree status. Annulus leak rate measurement skid was designed and built, in-house. One-off contracts were established to hot tap blind-flanged annuli and to perform Xmas tree and wellhead inventory survey and cavity checking/testing.

A completely new system of WI certification has also been established. So far, the team has successfully reviewed and risk ranked majority of the wells in the two assets of ADMA-OPCO.