bluuebunny/crossref_metadata_2025 huggingface dataset:
Discrete Fracture Network Modelling of Faulted and Fractured Apulian Platform Carbonates (Altamura Formation, Southern Italy)
Authors: Giorgioni M. , Panza E. , Agosta F. , Zambrano M. , Tondi E.
Published: December 2015

In order to better understand the relative contribution of background and localized deformation on the petrophysical properties of fractured tight carbonates, Discrete Fracture Network (DFN) models of representative outcrops were build up by using a stochastic approach. The study carbonates, which crop out along the vertical walls and pavements of an abandoned quarry of southern Italy, represent a surface analogue of the hydrocarbon reservoirs currently developed in nearby areas of Italy. The outcrops expose a well-layered, tight, Cretaceous limestone crosscut by both background (diffuse) and fault-related (localized) deformation.

Fractures show a high variability of their spatial and dimensional properties (length, intensity, aspect ratio and aperture), according to the different structural domains (fractured host rock, fault damage zone and fault core) in which they were surveyed. Such variability highlights the different scales at which the structural domains affect the tight carbonates, and can be considered a key challenge to construct a realistic reservoir model. DFN modelling of representative rock volumes of the fractured host rock showed that both volumetric (P32 and porosity) and hydraulic properties (correspondent permeability) are mainly affected by the two main sets of Non-StrataBound fractures (NSB). Equivalent porous media modelling, which include both fractured host rock and fault zones, showed that the overall permeability of the Fault Damage Zones (FDZ) is 2-to-4 orders of magnitude higher than the fractured host rock permeability. The FDZ can be therefore interpreted as fluid conduits that enhance fluid flow, which is controlled by both the dimensional properties of the fractures and by their aperture values.
Vertical Heterogeneity of Kerogen and Fluid Compositions in the Vaca Muerta Unconventional Shale Play and Assessment of Producible Fluid Composition and Quality
Authors: Elias R. , Gelin F.
Published: December 2015

To better understand potential vertical variability of the original kerogen quality in an unconventional reservoir we have carried out organic geochemical analyses on hundreds of rock and fluid samples coming from the Upper Jurassic / Lower Cretaceous Vaca Muerta Formation (Neuquén Basin, Argentina). The studied samples are derived from six wells located in different parts of the Neuquén "embayment" where the Vaca Muerta Formation reached distinct maximum thermal maturities. This natural maturity sequence ranges from the peak oil to dry gas window (VReq ~ 0.7 % to 1.8 %). Applied geochemical analyses comprise high-frequency TOC measurements on a centimeter scale, conventional Rock-Eval analyses on a decimeter scale, and meter by meter molecular and isotopic mud gas analyses. In addition we have performed molecular and isotopic analyses on several hydrocarbon liquid extracts and produced oils. Our data clearly indicate highly heterogeneous vertical distributions of organic matter contents on centimeter scales reflecting the fine shale laminations in the Vaca Muerta Formation. Despite the regional control of thermal maturity on liquid and gaseous hydrocarbon compositions we also observe at well scale some remarkable vertical compositional kerogen and fluid variability. Molecular and isotopic analyses on liquid hydrocarbon extracts document vertical differences in the source organofacies. These vertical organofacies variances are responsible for the distinct compositions/properties of the produced fluids at well scale.
Feasibility of Produced Water Treatment and Reuse – Case Study of a GTL Plant
Authors: Onwusogh U.
Published: December 2015

In a GTL plant located in Qatar, produced water (PW) is considered for treatment and reuse in the existing onsite Effluent Treatment Plant (ETP).

The onsite ETP deploys both conventional and advanced water treatment technologies including flocculation flotation unit, biotreatment, membrane filtration (submerged Ultrafiltration (sUF) and Reverse Osmosis (RO) units), evaporation and crystallization processes, to produce water for reuse within the plant mainly for cooling and power generation among many other uses.

Current PW disposal is in deep wells. PW reuse was considered an economically viable option for the plant due to its quality (TDS < 4000 mg/L).

A test work was conducted to determine the feasibility to route the PW to existing onsite ETP. Firstly, the PW was chemically analysed for key contaminants including hydrocarbons (condensate), heavy metals and naturally occurring elements, Total Dissolved Solids (TDS) etc.

Hydrate inhibitor is normally dosed to the PW during the winter season while Corrosion Inhibitor (CI) is dosed continuously throughout the year. This results in two distinct streams, i.e. a "Winter PW stream" (Stream A) and a "Summer PW stream" (Stream B).

The potential impact of Stream A and Stream B must be evaluated before routing to onsite ETP is considered feasible.

Based on sample analysis (pH, conductivity, COD, TOC, ion chromatography, metals scan, toxicity tests and 28 days COD die-away test), it is known that both Streams A and B have the potential to adversely affect the daily performance of the onsite biotreater, with additional risk of sUF/RO membrane fouling (scaling).

The following have been considered in the study:

Hydraulic load of PW to the onsite ETP Quality of Streams A and B, in terms of Chemical Oxygen Demand TDS which is <4000 mg/L (0.4% wt) Presence of scaling components (Ca, Mg and Ba) Heavy metals in PW

Stream A is considered first for pre-treatment in an onsite Wet Air Oxidation (WAO) unit to destroy hydrate inhibitor, while Stream B will be stored temporarily in a holding tank to ensure complete condensate separation, prior to routing of both pre-treated effluent to the onsite ETP.

Experimental test work conducted over a period of 9 months using two bench bioreactors operated at similar hydraulic and solids residence times as the onsite ETP showed COD levels are reduced to levels that meet the specification for further polishing in downstream UF and RO units. Test work suggests PW (Streams A and B) to be compatible with onsite ETP.
Uncertainties in Fracture Apertures Calculated from Electrical Borehole Images
Authors: Maeso Carlos , Dubourg Isabelle , Quesada Daniel , ElNour Walid Abou
Published: December 2015

Parameters for fracture aperture calculations were calculated for a high-resolution logging-while-drilling (LWD) imaging tool, and the aperture calculation that has been applied to wireline tools was extended to the LWD tool. The causes of uncertainty in calculated apertures were determined and, where possible, their impact was quantified. The uncertainties were investigated for LWD electrical borehole images, but the principles can be applied to their wireline counterparts.

Electrical images of the borehole have been used to quantify fractures since the introduction of imaging tools in the late 1980s. Processing includes the calculation of fracture apertures based on the measured excess current as the tool crosses the fracture. The aperture calculation follows an equation published for wireline tools. In extending the aperture calculation to LWD tools, the tool response was modeled using a 3D finite-element code that accurately represents the tool, borehole, and formation configurations. The modeling covered a series of conditions, including variable standoff between the tool and the formation, different fracture widths and radial extent, multiple background formation resistivities, and different mud properties. In addition, the minimum and maximum apertures that can be calculated using the equation were determined. Field examples are shown from Qatar to illustrate the sources of uncertainty in the calculation. These examples are from data acquired with a high-resolution LWD imaging tool.

Results of this work provide an understanding of the conditions where fracture aperture calculations can be used in confidence and where they should be treated with care. The minimum and maximum extremes vary with the environmental conditions, but it is shown that for more conductive muds, the measurement is sensitive to fractures of a few µm in width. Major factors affecting the confidence of the aperture calculations are the properties of the fluid filling the fractures and the radial extent of the fractures. Uncertainty in the calculated apertures for these factors can be greater than a multiple of two in certain conditions. It is usually possible to recognize where these factors have high uncertainty (e.g., high losses). Other factors generally introduce much smaller uncertainties to the aperture calculation. These include the tool standoff, relative dip of the fracture, image scaling, and fracture spacing. Potential errors for the latter conditions are at a maximum of 30% of the calculated aperture in particular circumstances, but in most conditions the uncertainties are much smaller.

Fracture aperture calculations are widely used within the industry. They are a standard part of processing of many electrical borehole images. The addition of uncertainty guidelines will allow the users to understand where to use the aperture calculations with confidence and where to treat the results with caution.
A Quantum Leap in Borehole Imaging for Formation Evaluation: Deciphering the Photo-Realistic Geology of Abu Dhabi Carbonates in Oil-Based Mud
Authors: AlMutwali O. , Khemissa H. , Alfelasi A. , Dama S. , AlNeaimi A. K. , Ahmed S. N. , Shrivastva C. , Abdulrahim J. , Girinathan S.
Published: December 2015

Application of the legacy oilbased mud (OBM) borehole images in carbonates has posed challenges due to the limitation of resolution and borehole coverage; often providing too little for textural and sedimentological interpretation, and leaving a lot to be desired for optimal subsurface characterization. A new technology was required in UAE to acquire photorealistic images to decipher the carbonate heterogeneity for optimal characterization.

The Cretaceous carbonates of Abu Dhabi are very complex with varying heterogeneity through different reservoir intervals. To address various drilling challenges and coring requirements, OBM is being used by various operators in different acreages. Formation imaging becomes critical in such wells, where reservoir rocktyping and different enhanced oil recovery feasibility studies are planned. The study well shows the results of a new technology images in comparison with legacy OBM images and core. And, the image data is inverted for advanced processing to prepare standoff images and quantitative resistivity images for high resolution heterogeneity indicator.

The study well penetrates through a shallow marine carbonate setting ranging from shoal grainstone to the shelf setting wackestone and packstone exhibiting a lot of heterogeneity in facies distribution. In fact, a lot of variability was observed in the image logs against the interval of constant porosity observed in petrophysical logs. Stylolites and conductive seams seem to introduce a lot of barriers and baffles; however, stylofractures seem to be breaching the barrier in many intervals as well. The image log data was inverted to prepare the standoff images and quantitative resistivity images to understand the response of open vs. closed fractures; and vuggy/ mouldic porosity. The results were compared with the core photographs for validation of the interpretation. The high resolution heterogeneity indicators derived from the inverted images provided a means of highresolution facies typing; thereby providing electrofacies to be tied to petrophysical response for further reservoir rocktyping. The textural interpretation also helps in understanding the flow behavior. A detailed faciestyping with advanced interpretation is prepared to understand not only the geological characteristics, but also the variations in reservoir properties within seemingly similar facies.

This work presents the first account of interpretation based on a new technology for OBM formation imaging, with innovative inversion techniques. This also serves as a roadmap for carbonate reservoir characterization in Middle East in the wells drilled with OBM. Also, the encouraging results provide a trendsetting example of applications of this new technology.
Relative Permitivity Based Water-Cut Measurment Techniques for Permanent Downhole Applications in Multilateral Horizontal Wells
Authors: Arsalan Muhammad , Ahmad Talha J. , Black Micheal J. , Noui-Mehidi Mohamed N
Published: December 2015

The challanges associated with efficient and reliable permanent downhole water cut measurement in multiphase flow and in multilateral horizontal well environment are described in this paper. The principles of relative permittivity based water-cut meters are explained in detail. A comprehensive analysis of the state-of-the-art relative permittivity based water cut measurement techniques are presented in this paper to evaluate their suitability for permanent downhole deployment. The techniques are compared against a set of requirements suitable for permanent downhole water cut measurement.
Impact of Acid Jetting on Carbonate Stimulation
Authors: Beckham R. E. , Shuchart C. E. , Buechler S. R.
Published: December 2015

Many wells are drilled with long horizontal completions to maximize their contact with reservoirs. In carbonate reservoirs, such long completions present challenges to the even distribution of acid during matrix stimulation. One approach to addressing these challenges involves bullheading acid through a static limited entry liner engineered to choke back acid flow to the higher permeability and/or lower pressure zones through the sparse placement of small nozzles. While the pressure drop across the nozzles is straightforward to calculate, the interactions between the acid jets created by the nozzles and the carbonate formation are not well understood. Specifically, it is unknown how a high velocity acid jet impinging on a carbonate surface might alter the wormholing efficiency.

To explore the effects of jetting on carbonate dissolution, laboratory experiments jetted hydrochloric acid onto limestone cores at velocities between 100 and 200 feet per second. Consistently, the acid jet formed a substantial bulb-shaped cavity in the face of the rock. Wormholes formed into the rock from this cavity, even at overall flux rates normally too low to generate wormholes. In the absence of acid flux through the core, bulb-shaped cavities formed without wormholes. Low velocity acid jetting did not form cavities. No cavities or wormholes were observed when jetting with only water.

A turbulent jet impinging on a rock will create a localized surface pressure spike near the center of impingement. This pressure spike increases the local flux of acid into the porous rock, and is suspected of initiating the cavity. Once the cavity forms, two mechanisms of carbonate dissolution are active. The first is traditional matrix dissolution, which appears to be enhanced by the increased pressure inside the cavity produced by the kinetic energy of the jet. The second mechanism is surface dissolution, which is accelerated inside the cavity due to turbulent flow along the walls, and results in the enlargement of the cavity throughout the jetting process. Enhancement of the matrix stimulation by the jet is often a benefit. On the other hand, enlargement of the cavity is a disadvantage because it consumes acid that would be better used for wormhole growth into the rock.

Research using both experiments and computational fluid dynamics is ongoing to better quantify the influence of the jet on the two dissolution mechanisms. With such knowledge, it should be possible to better design lower completion liners that exploit the jetting effect for both acid distribution and enhanced stimulation.
An Evolved Approach to Performing Underbalanced Perforating Interventions in Mexico: A Step-Change Improvement in Efficiency, Reliability, and Safety
Authors: Narcizo O. Melo , Aguilar A. Martinez , Mendo A. Rosas , Gordillo J. C. , Ramondenc P. , Burgos R. , Basurto J. R. Cervantes , Rodriguez F. L.
Published: December 2015

An innovative approach to underbalanced perforating in horizontal and highly deviated wells uses a new perforating head specifically developed to leverage the conveyance and real-time telemetry capabilities of coiled tubing (CT) equipped with fiber optics. The results and advantages of this approach have been demonstrated in wells in mature Mexican fields featuring significant reach and pressure limitations.

In recent years, CT equipped with real-time fiber-optic telemetry has been a method of choice to perform interventions in deviated or horizontal wells, as it provides a cost-efficient and flexible alternative to heavier wired CT. In the Mexican fields, this real-time telemetry capability is used to accurately place the guns thanks to downhole casing collar locater and gamma ray tools. The need for pumping fluids to enable detonation, often performed during typical CT perforating operations, is eliminated through the use of a downhole microprocessor-controlled firing head, which is directed by commands sent from surface through the optical fiber.

The result is a nearly instantaneous detonation downhole and positive confirmation provided in real time through an array of sensors in the bottomhole assembly (e.g., accelerometers, pressure, and temperature). The absence of working fluid eliminates any concern of hydraulically loading the well or the need for shut-in, thus significantly reducing the extent of deferred production. It also mitigates uncertainties linked to the influence of downhole conditions on the behavior of working fluids or the potential malfunctions of drop balls. This system is capable of multizone, selective detonation, therefore improving operational flexibility through reduced gun runs. It is also compatible with any other traditional CT service and can easily be combined with a bridge plug setting, a nitrogen lift, or a cleanout within the same run. The approach and its associated workflow enabled a significant reduction in intervention turnaround time by cutting as much as 75% of the time necessary to detonate the guns once the depth has been correlated, while providing fast and clear confirmation of downhole detonation.

This evolved approach not only addresses the conveyance limitations of highly deviated and horizontal wells, it also greatly improves the safety, reliability, and efficiency of underbalanced perforating interventions by leveraging the real-time downhole monitoring and control capabilities of CT with fiber optic telemetry.
Parametric Analysis and Uncertainty Quantification for Flow Assurance
Authors: Twerda Aris , Omrani Pejman Shoeibi
Published: December 2015

Currently, decisions involving a huge amount of money and resources are based on the outcome of simulations. Consequently, an increase in the computational resources has attracted engineers and scientists to increase the complexity of the mathematical models and their numerical algorithms to design or analyze various systems. On the other hand, the transparency of these models has decreased and the sensitivity of the outcome of these simulations on, for instant, certain assumptions or input parameters is often not known a priori.

Furthermore, validation of the models for complex systems in which full scale measurements are limited or even impossible, gives more challenges to the decisions made based on these numerical simulations. Additionally, robust design to consider off-design conditions in a systematic manner is of great importance in oil and gas industry.

Therefore, it would be essential to develop a systematic procedure to quantify the sensitivities and errors associated with each set of simulations in an objective manner. Uncertainty quantification (UQ) could be used as a tool to provide the validity of a performed simulation.

This study describes the current research and opportunities for parametric analysis and uncertainty quantification in the flow assurance such as in performance prediction and validation, risk assessment, decision making and robust design. Additionally, we describe the importance and benefits of probabilistic analysis instead of deterministic analysis. Uncertainty quantification increases the computational expenses and effort of performing deterministic simulations. Therefore, an efficient method to quantify the uncertainties such as probabilistic collocation or surrogate models are required to reduce the computational costs without losing the accuracy of the analysis.

Parametric analysis and uncertainty quantification will give more insights in the validity of simulation data than traditional methods. For instance, using the newly proposed methods will expose the sensitivity of the simulation results to off-design conditions and consequently leads to a systematic decision making based on the probability of an event occurrence. These methods could be used to quantify the most sensitive parameters in the system and the effect of their propagation to the outcome of the model. It is shown that performing non-deterministic analysis in some cases is a necessity.
Mitigating Shale Drilling Problems through Comprehensive Understanding of Shale Formations
Authors: Al-Arfaj Mohammed K. , Abdulraheem Abdulazeez , Sultan Abdullah , Amanullah Md. , Hussein Ibnelwaleed
Published: December 2015

In order to develop an inhibitive water-based mud capable of mitigating the adverse effects of shale-mud interactions, it is important to characterize the shale sample in terms of its geological structure, mineralogical composition, reactivity potential, etc. Further, the shale-mud interactions should be studied through a series of experimental tests such as swelling, dispersion and inhibition durability.

This paper presents the results of characterization and testing of one of the studied shale samples with X-ray diffraction, micro-CT, ultrasonic rock mechanics testing, capillary suction time and cation exchange capacity. The paper also shows how petrophysics data of shale formations can be utilized to improve and optimize drilling practices in order to achieve the ultimate goal of enhanced wellbore stability. Depending on clay content, different shale formations have different responses when exposed to drilling fluids. It is therefore very important to characterize the shale formation to develop the appropriate drilling fluid.

The tested shale sample was found to be a silica-rich shale with a small percentage of clay minerals, mainly kaolinite. Characterization scheme included also Micro-CT where the images revealed the heterogeniety and fractures in the internal matrix. Dynamic elastic moduli were determined using ultrasonic rock mechanics testing. A cation exchange capacity (CEC) value of 2.5 meq and capillary suction time (CST) value of 42.6 seconds indicated low tendency of the shale rock to both swelling and dispersion.
An Experimental Study of Water Production Mitigation and Improved Acid Diversion during Acid Injection in Heterogeneous Carbonates
Authors: Ali Nour El Cheikh , Al-Sammaraie Mohammed , Goedeke Stefan , Benquet Jean-Claude , Aubry Eric , Julien Philippe , Gharbi Oussama
Published: December 2015

A well-designed acid stimulation treatment is a rapid well intervention operation that can lead to long-trim economical benefits. In carbonates, the main challenge is to better design acid stimulation treatments in order to meet the two main characteristics of carbonate reservoirs which are high water production and a wide range of heterogeneities. Acid diversion is one of the key factors for a proper distribution of acid which determines the success of these treatments, especially in heterogeneous carbonate formations.

In this study, we aim at producing novel solutions in order to reduce water production and enhance zonal coverage through effective diversion. The ultimate goal is to validate a single pumping sequence that combines water mitigation, diversion and acid injection. In order to achieve this, we rely on an integrated R&D approach combining single core and dual core experimental setups. The advantage of the dual core setup is to investigate different permeability contrasts, different saturations configurations and to experimentally validate wormholing in heterogeneous carbonates. In fact, in carbonate effective diversion happens when acid is flowing in the low permeability area at sufficient velocity. An easy way to validate this is through parallel core flooding.

We performed a series of high pressure and temperature single and dual core flooding experiments over a range of different carbonate samples having different permeability and porosities. The injection took place at 90 °C and 250 bars. We assessed the efficiency of polymer adsorption by measuring permeability during, before and after polymer injection. Computed Tomography scans were used in order to validate our conclusions. We showed that, adsorption of polymer in carbonates is possible but needs careful design.

We experimentally investigated acid diversion in high permeability contrasts (matrix-fissures) through core flooding. This is another novelty in this study. Finally, the combined pumping sequences were experimentally assessed. We validated diversion in carbonates and identified the optimum injection rates required for such applications. An optimum configuration of permeability contrasts and saturations exists for a combined pumping sequence.

The experimental results and observations are translated into a series of guidelines and procedures which are directly applicable to acid stimulation field operations. The areas of future required research in applied fluid-rock interactions will be highlighted.
General Parallel Reservoir Simulation
Authors: Beckner B. L. , Haugen K. B. , Maliassov S. , Dyadechko V , Wiegand K. D.
Published: December 2015

Faster reservoir simulation turnaround time continues to be a major industry priority. Simultaneously, model sizes are reaching a billion cells and the recovery mechanisms and reservoir management processes to be modeled are rapidly changing and are becoming computationally more expensive. A new reservoir modeling solution has been developed to quickly solve these largest and most complex modeling studies within ExxonMobil.
Stratigraphic Expression of Upper Cretaceous Tectonics in the Balambo- Garau Sub-Basin of the Zagros Foldbelt: Implications for Reservoir Presence
Authors: Mosola Amanda B. , Braaksma Kelley S. , Tai Po C. , Volkmer John E. , Grabowski George J. , Kendall Jerry , Liu Chengjie
Published: December 2015

Evaluation of the depositional environments of Upper Cretaceous strata in the Balambo-Garau sub-basin of the Zagros Foldbelt in western Iran into eastern Iraq provides insight into the distribution of reservoir and seal units, as well as potential trapping configurations. Such mapping within the upper sequences of the Cretaceous suggests a larger impact of Proto-Zagros flexure and localized re-activation of deeper seated structural trends in Iraq and Iran. Environment of deposition and unit thicknesses have been mapped and evaluated across western Iran into eastern Iraq using well logs and biostratigraphic data. From the middle Turonian to Santonian, outer-shelf argillaceous limestones overlie proximal to middle- shelf limestones. The deepening of the sub-basin, part of a broader trend of platform carbonates and associated deeper shelf and basinal facies, is concurrent with eustatic sea-level rise, but may also be affected by large-scale Cenomanian-Turonian adjustment. Environmental belts narrow and deposits lap onto highs exposed by localized uplifts as a result of the reactivation of deep-seated structural trends originating in the Permian (or possibly basement?). Outer- to middle-neritic sediments of the Ilam Formation, which onlap local structural highs, are higher quality reservoir facies of Coniacian–Santonian age and, where sealed, may be potential traps.

Deposits of the latest Campanian to Maastrichtian also show deepening of lower-shelf and basinal environments within the study area. Non-deposition and onlap of deeper water carbonate wackestone to marls onto highs in the Dezful embayment may further reflect the localized reactivation of deeper seated structural trends. Siliciclastic sediments of the Tanjero Formation shed from highs to the northeast are associated with paleogeographic reversal of the Proto-Zagros, depositing turbidites within the proximal thrust-front basin. Despite time-equivalent prolific oil-producing reservoir intervals in Iraq, ongoing deepening due to the Proto-Zagros Foreland Thrust results in largely non-reservoir marl facies of the Gurpi Formation acting as a seal to the underlying units. The Tarbur Formation, present in the Fars region, consisting of shallow-water rudist grainstone and packstone suggests a lack of accommodation created in association with the Proto-Zagros subsidence event.

Tectonostratigraphic trends of the Upper Cretaceous of the Zagros region of western Iran and eastern Iraq show the transition of a relatively quiescent ramp increasingly affected by localized effects of the Cenomanian-Turonian adjustment along with the Maastrichtian inception of Proto-Zagros thrusting and elucidates their impact on reservoir, seal and potential trap distribution within proven and unproven hydrocarbon systems in Iraq and Iran.
Modeling the Impact of Corrosion on Well Integrity for Offshore Wells
Authors: Narhi Ward , Kibey Sandeep , Kent David , Aylor Adam , Abdulhai Walid M. , Lam Gan Chee , Khemakhem A. S. David
Published: December 2015

Structural integrity of casings is critical for safe and economic operation of offshore wells and it can be compromised by external corrosion due to exposure to environment such as seawater. Assessing the impact of severe casing corrosion on the structural integrity of the well can be challenging due to complexities arising from local wall loss, non-uniform wall thickness, presence of holes due to severe corrosion, and non-bonded cement. Such complexities are not adequately addressed by existing codes/standards and available analytical equations.

This paper presents a study that utilized a combination of a thermo-mechanical well simulator and threedimensional (3D) finite element analysis (FEA) to model severely corroded offshore well casing strings towards assessing structural integrity of the wells. The goal of the study was to determine the extent of allowable corrosion in conductor and surface casing beyond which the wells would be at risk for failure, and if topping off the cement in the annulus would be beneficial for structural integrity.

A thermo-mechanical well simulator was utilized to model how corrosion wall loss evolved over time for both the conductor and surface casing, and the corresponding impact on their load capacity. In conjunction with the well simulator, full 3D FEA was conducted to model various complexities, such as the effect of corrosion holes and non-uniform corrosion. The 3D FEA helped assess the impact of remedial cementing on casing integrity and refine the critical wall thickness limit needed to withstand loads predicted by the well simulator. Compression and buckling were identified as governing failure modes and FEA results were compared with a buckled conductor in the field. The systematic, mechanics-based approach used in this study provided a basis for risk assessment where at-risk wells can be prioritized for remediation and/or abandonment.
A Collective Clay Stabilizers Review
Authors: AlMubarak Tariq , AlDajani Omar , AlMubarak Majed
Published: December 2015

Oil and gas fields encounter issues associated with clay minerals through drilling and production. Depending on the types of clay minerals, they pose the danger of swelling and migration upon exposure to incompatible water. Drilling introduces water through drilling mud, and production introduces water through different treatments such as acid stimulation and hydraulic fracturing.

The recovery of oil and gas from subterranean formations has been troublesome in formations that contain water-sensitive minerals, e.g., water-swellable clays, such as clays in the smectite group, and fines capable of migrating when disturbed, such as silica, iron minerals, and alkaline earth metal carbonates.

It has been common practice to add salts to the treatment fluids. The salts adsorb to the clay surfaces in an ion exchange process that can temporarily reduce the swelling and/or migration of the clays. Another method used is to coat the area with a polymer in order to physically block the surface of the clays.

This paper will mention the types of clays related to the oil industry, describe the structure of clays, mention the mechanisms behind swelling and migrating, and compare the different developments in the field of clay inhibition.
PreSDM Reprocessing of Dense WAZ Data - A Processing Team Delivers
Authors: Warzocha Stanislaw , Hermant Olivier , van de Rijzen Maurice
Published: December 2015

We present an example of how pre-stack depth migration (PreSDM) reprocessing of dense wide-azimuth (WAZ) data can improve imaging quality in areas with complex geology. The main challenges were the multiples hampering picking of proper primary signals, combined with a complex salt geometry. We will show that the experience gained over the years in using dense WAZ data for velocity model building and applying the latest technologies can significantly improve the imaging quality when compared to legacy processing.

Since 2010, the experience of working with dense WAZ data has built up especially on key processing steps like data preconditioning and velocity model updating.

In our case, there were two processing steps that were key to successful data preconditioning and residual moveout (RMO) picking: –Multiple removal by 3D dip filtering using local linear event extraction based on dip discrimination.–Using narrow-azimuth (NAZ) sectors instead of full WAZ data as input for picking.

For the velocity model building workflow, the most important aspects were: –The use of multi-layer non-linear slope tomography.–Salt scenario testing in areas with poor top salt visibility.–Intra-salt tomography.

RMO pick quality is critical for successful tomography for PreSDM. Most of the high amplitude train of multiples in the post-salt sediments could be removed using a dip-based demultiple algorithm. This allowed us to pick more stable and reliable RMO and dip information, which is a big improvement over the legacy PreSDM. Going back to azimuth sectors instead of using full WAZ data was mainly driven by experience. It was found that thorough and effective QC of RMO picks was easier and more accurate using MAZ data as opposed to WAZ data. As a consequence, more reliable and consistent pick information was used for tomography.

Using multi-layer tomography as an alternative to a layer stripping approach for velocity model building reduced the number of tomographic updates from five in the legacy PreSDM to three in the current project and produced more geologically consistent and accurate velocity models for PreSDM. Salt scenario testing improved the position of top salt and imaging below in areas with poor top salt visibility. Intra-salt tomography updated the smooth velocity within the salt and provided detailed velocity for intra-salt layers. Altogether this led to significant improvements in terms of velocity model building and imaging.

In this case study we present the results of the first PreSDM reprocessing of the first dense WAZ data acquired in the Sultanate of Oman. We explain in detail the methods used for data preconditioning and velocity model building and we show examples of the improvements achieved compared to legacy processing in terms of velocity model and imaging.
Gas Reservoir Management: How to Improve Gas Production Allocation Per Reservoir in Commingled Wells Using Geochemistry Technology?
Authors: Sabatier Lionel , Haidar-Qatargas Faesal , Mahdaoui Fatima , Dessort Daniel , Julien Philippe
Published: December 2015

In a commingled gas reservoir, it is crucial to determine the respective contribution of each produced reservoir for an efficient and reliable Reservoir Management, and to match the reservoir models. The Production Logging Tool (PLT) is commonly used to allocate the production to the individual layers. The limit of this process is that PLT results and therefore the layer-based equation change with time due to the evolution of reservoir characteristics such as reservoir pressure, mechanical skin, non-Darcy coefficient and sometimes PVT properties. PLT acquisition must be repeated to quantify this evolution and to determine time-dependent layer allocated equations. The repetition of PLT acquisition must be optimized taking into account the needs and the impact of time on results, but is as well highly constrained by cost and logistics, which prevent is some cases to get the desired frequency.

Geochemistry technology can provide additional and reliable data on the hydrocarbon fluid provenance in order to improve accuracy of the layer-allocated gas rate equations. Indeed sampling and geochemical analysis can be done at a higher frequency and much lower cost between each PLT. Fingerprinting is one of well-known techniques, which was tested recently in Qatargas in cooperation with Total and results appeared to be encouraging. All the analyses and data processing of the condensate samples were achieved in Qatar and a specific methodology was developed to get the best layer-based allocation process.

This geochemical approach is based on a statistical interpretation of High Resolution Gas Chromatography (HRGC) data of the condensate fraction from the produced fluids. There are several prerequisites for such a method to be applicable: identical separator conditions, excellent sample storage and handling, highest GC standards, appropriate statistical tools and availability of representative reservoir fluids. The individual reservoir fluids are considered as end-members which must be known to determine quantitatively the contribution of each reservoir in the produced well fluid.

This paper describes the details of the fingerprinting technique used, including how the samples are analyzed and how data are processed in an innovative way to get the most reliable results. In our case, the compositions of the different condensates show very subtil differences. As a result, we had sometimes to consider more than 1000 chromatograms peak ratios to differentiate the fluids coming from different layers. We concluded that geochemical production allocation was possible in some (but not all) areas of the field and that results were consistent with other types of dynamic and geological data.

These positive conclusions allowed us to envisage an operational application of this research feasibility study.
Insights on Potential Formation Damage Mechanisms Associated with Hydraulic Fracturing
Authors: AlMubarak Tariq A. , AlKhaldi Mohammed H. , Panda Saroj K. , AlMubarak Majed A.
Published: December 2015

Hydraulic fracturing technique, using water-soluble polymers, has been extensively used to improve the productivity of oil and gas wells, especially in low-permeability formations. However, the production enhancement by hydraulic fracturing can be hindered by the fracture conductivity damage and/or fracture face skin. This paper describes an approach to establish a suitable fracturing fluid cleanup process by analyzing the performance of different gel breaker types, especially in sours environments. In addition, the interaction of clay stabilizers with different gel breakers is investigated.

Several experiments were conducted to assess the effect of different gel breakers on high temperature fracturing fluid as a function of time. Most commonly used breakers- inorganic oxidizers (bromate and persulfate salts), specific enzymes and acids- were used in this evaluation. The effectiveness of each breaker was evaluated using various techniques, such as Zeta Potential, Gel Permeation Chromatography (GPC), High-Pressure/High-Temperature (HP/HT) aging cells, H2S compatibility tests and Environmental Scanning Electron Microscope (ESEM). All experiments were performed on borate and zirconate crosslinked carboxymethyl-hydroxypropyl guar (CMHPG) guar gum system with loading up to 45 lb/1,000 gals in addition to clay control agents potassium chloride and polymer-based clay stabilizers.

The results obtained from this study have shown that amount and size of the residual gel polymer chains, after its breakage, were mainly dependent on the type and loading of used gel breaker. Furthermore, it was found that both KCl and polymer-based clay stabilizers were effective in preventing clay-induced formation damage. However, laboratory tests have revealed that some gel breaker types may negatively affect the performance of polymer-based clay stabilizers. Additionally, this paper will highlight other negative interactions of common gel breakers, especially in sour environments.
Hyperspectral Remote Sensing for the Characterization of Dolomite Bodies: A Case Study in the Central Oman Mountains - Lower Khuff Analogue
Authors: Beckert Julia , Vandeginste Veerle , John Cédric M. , Guérillot Dominique , Foeken Jurgen
Published: December 2015

Recent ground-based studies of quarry cliff faces suggest hyperspectral imaging to be a convenient tool to distinguish highly similar carbonate phases in vertical cliff faces within short distances (Kurz et al., 2012). We take the technique further and use ground-based hyperspectral imaging to identify the presence of dolomite bodies along weathered and irregular shaped cliff faces. Dolomite bodies hosted in limestone successions, common in for example Khuff and Arab Formations in the Middle East, represent a challenging feature with respect to the characterisation and exploration of hydrocarbon reservoirs. For example, dolostones interfingered with limestones are present in the Ghawar and South Pars fields (Dasgupta et al., 2002; Ehrenberg, 2006; Ehrenberg et al., 2007). Detailed descriptions of fracture related dolomite bodies in the Ghawar field have been published by Cantrell et al. (2001), whereas Jones et al. (2011) recognized dolomite bodies in the North Field in Qatar. Other studies showed lithofacies controlled dolomitization in the Arab Formation (Clark et al., 2004; Honda et al., 1989). The exceptional importance of dolomite bodies is based on a potential increase of porosity of 13% or more (Weyl, 1960) compared to the non-dolomitized host rock. However, due to their commonly sub-seismic size these potentially highly porous zones often stay undetected on seismic profiles and thus require careful investigation. In this study, the distribution and shape problem has been approached by delineating dolomite bodies hosted in Lower Khuff outcrop analogues in the Central Oman Mountains by applying hyperspectral remote sensing. We examine the degree of precision of the remote sensing detection and characterisation of dolomite bodies at varying distances to the cliff face and assess its impact on a 3D geocellular model.
The Geverik Member of the Carboniferous Epen Formation, Shale Gas Potential in Western Europe
Authors: Zijp M. H. A. A. , Nelskamp S. , Verreussel R. , ter Heege J.
Published: December 2015

Since 2010 activity in shale gas exploration moved to the European continent. One of the potential targets identified in Western Europe is the Carboniferous Epen Formation (Lower Namurian A) and especially it's basal Geverik Member in the Netherlands, Belgium and Germany. In this study an updated investigation of the shale gas potential is presented using domestic geological information from the Netherlands and well data from the surrounding countries (Belgium and Germany), as well as a new basin modeling study.

Of the studied eighteen wells the bituminouos Geverik Member is found in eleven, where it is either deposited as a gradual transition from the underlying Dinantian strata or unconformably sitting on Dinantian carbonates. In seven of the wells the Geverik Member is locally absent either related to erosion or caused by a heterogeneous depositional pattern. Nevertheless it was attempted to correlate the Geverik Member over the whole study area using well log correlation which could be done succesfully. The overlying Main Epen Member is found to be greatly variying in thickness (250-1800 m) highlighting the drastic differences in accommodation space in the Basin during the deposition of the Epen Formation as well as erosion patterns.

The study shows that the area with highest shale hydrocarbon potential of the Epen Formation and the Geverik Member onshore can be found in the Northwestern provinces of Friesland and Groningen, the Eastern Netherlands bordering Germany, and the Southeastern province of Limburg. In the offshore region the northwestern corner has the highest potential, although exploration for these layers can be more demanding due to higher cost of drilling offshore. We conclude that especially the Namurian Geverik Member of the Carboniferous Epen Formation is a locally promising interval and should be farther investigated in smaller-scale studies, using seismic, core, well and outcrop analysis.
Regional Synthesis of Thermal-Burial Regimes in the Paleozoic-Proterozoic Series of the Taoudenni Basin, Adrar, Mauritania: Fluid Inclusion and Thermochronology Data
Authors: Girard J -P. , Eichenseer H. , Kabbej A. , Idris K. M.
Published: December 2015

Exploration for oil and gas in the ancient Paleozoic–Proterozoic Taoudenni cratonic basin has been revived in the recent years following the documentation of a viable and efficient petroleum system in the Adrar region of Mauritania. In order to gain better knowledge of the thermal history prevailing in the prospective area (Ta7-Ta8 blocks), extensive fluid inclusion and thermochronology studies have been conducted on outcrop samples as well as cores from recent and older wells in the Paleozoic and Proterozoic sections. The results indicate that the Adrar region was affected by complex and variable burial-thermal regimes. A major cooling-uplift event is documented at ~100–150 Ma, possibly resulting in as much as ~3 km sediment removal. Maximum burial temperature in the Proterozoic formations reached ~140–180°C depending on location. Higher temperatures (>200°C) are recorded which are attributed to short-lived heating events related to diabase emplacement, but no evidence supports a uniform thermal event of regional extension. Cooler burial-thermal regimes may have prevailed in the North-Eastern part of the prospective area. Record of petroleum migration is limited to the Meso-Protrozoic and lowermost Neo-Proterozoic formations, below the Lower Assabet (I14) regional seal. This work provides valuable information for future exploration of the Proterozoic section in this part of the Taoudenni basin.