bluuebunny/crossref_metadata_2025 huggingface dataset:
Sealing Casing Leaks through the Remote Deployment of Discrete Particles
Authors: Loveland M. J. , Klein P. , Ryan N. J. , Bowie C.
Published: July 2010

An outer casing leak can be a significant well integrity issue, primarily due to the inability to easily access the leak site for intervention. Recent outer casing failures caused by external corrosion on some wells in the Kuparuk Field of Alaska prompted research for a non-invasive repair method to delay or negate the need for a rig workover. Limited options for downhole access on outer concentric casing strings have an impact on the ability to define the leak in terms of location, size and shape, and consequently the ability to effect a seal of the casing.

The Platelet® technology discussed in this paper is an innovative means of sealing leaks which involves the remote injection of discrete particles into a well which are then carried to the leak site in the fluid flow. When the platelets reach the vicinity of the leak, fluid forces entrain them into the leak and hold them against the casing wall thus facilitating a seal allowing the well to be returned to service.

Previously proven for applications in subsea pipelines, platelet technology over the last 12 months has successfully been developed for downhole use. In January 2009, specifically engineered platelets were deployed into well annuli for the first time.

Two case studies will be presented where the technology has been used in the Kuparuk field in Alaska. In the first instance a ¼” corrosion induced hole in the surface casing at a depth of 126 ft was sealed with a single platelet by a deployment from surface into the outer annulus. The well was initially leaking at a rate of 0.5 bpm and subsequently passed an 1800 psi mechanical integrity test. The second study will review a seal of a 0.26 bpm leak at 30 ft depth which eventually gave out.

The paper will review the front end engineering development, the well site deployment, and lessons learned. The paper concludes by demonstrating the successful use of the platelet technology for sealing annulus leaks and how the technology has successfully postponed or negated the need for a rig workover to repair a surface casing leak. The results from this study have provided valuable insight into the behavior of the platelets in the fluid flow before entrainment and the behavior in the leak after entrainment.
Biot Critical Frequency Applied as Common Friction Factor for Pore Collapse and Failure of Chalk with Different Pore Fluids and Temperatures
Authors: Andreassen Katrine Alling , Fabricius Ida Lykke , Foged Niels Nielsen
Published: July 2010

A fluid effect towards higher strengths for oil saturated chalk compared to water saturated chalk has previously been identified and labeled the water weakening phenomenon, but has not been further characterized physically until now. The hypothesis of this paper is that the Biot critical frequency can be used to explain this behavior on the pore scale and be extrapolated to the macroscale failure and pore collapse properties. A large set of previously published laboratory test results on chalk was collected. The data spans three different chalk types which were tested at temperatures from 20°C to 130°C with the following pore fluids besides dry chalk: fresh water, synthetic seawater of different chemical compositions, methanol, glycol, formamide, decane and crude oil of varying viscosity.

The Biot critical frequency determines the transition from where an applied sound velocity is dominated by viscous forces to where it is dominated by inertial forces, i.e. when the pore fluid motion lags behind the applied frequency. It is therefore a measure of the internal surface friction between solid and fluid and is interpreted as a friction factor. The Biot critical frequency incorporates the porosity, permeability, fluid density and fluid viscosity, where the latter is highly temperature dependent. All these parameters are usually determined during laboratory tests and the fluid viscosity and density may be found in tabulated references. Besides the fluid effect there is an effect from the applied strain or stress rate on both the strength and yield properties. This phenomenon couples with the critical frequency through the use of a previously published study on the rate dependence.

The data show that the Biot critical frequency can be used as a common friction factor and is useful in combining laboratory results. It is also inferred that the observed water weakening phenomenon may be attributed to the friction between solid and fluid. The scope for the applicability of the Biot critical frequency as a friction factor is in analysis of the compaction of chalk fields where the effect of different fluids and temperatures is relevant.
Uncertainty Analysis of an Integrating Two Structural 3D Sthochastic Geological Models of a Siliciclastic Reservoir: Potiguar Basin, Northeast of Brazil
Authors: Fanha Ana Beatriz , Cavalcante Jose Sérgio , Reyes-Pérez Yoe Alain
Published: July 2010

The studied field is located in the Brazilian Continental Shelf, the Potiguar Basin. These reservoirs are Eo–Cretaceous sandstones, which correspond to the gradual passage from the continental to marine depositional environments.

The workflow used was chosen in order to reflect the concern in trying a more effective representativeness of the structural complexities of the studied field. It consists in building several three-dimensional stochastic reservoir models and in recalculate the STOOIP (Stock Tank Originally Oil In Place), based on the integration and the interpretation of available data. Two structural geological models were built with distinctive geophysical interpretations based on a seismic reference surface. These tectonic differences can modify the stratigraphic distribution of the reservoirs and change drastically the fluid flow on the petrophysical system of hydrocarbons distributions on the reservoirs.

The uncertainty analysis was built and the parameters that impacted the most the STOOIP were varied under each considered structural model. These parameters were: the range of the porosity values and the cut-off of oil. A risk curve of 520 simulations was developed, that identifies which models corresponds to the respective percentiles and obtain the respective realization to simulate on the flow the many probabilistic sets.

We create the Hydrocarbon Pore Volume maps – HPhiSo, for each percentile of each structural model. The percentiles P50 of these maps of the two models were superimposed, and it was defined a set of planned wells to the reservoir drainage. This permits to relate the biggest hydrocarbon column with the highest structural map, reducing the risk. The geological uncertainties analysis results from numeric numbers varying the STOOIP until 37%, while oil was considered in all blocks. Eight realizations of each 3D geological model will be submitted to flow simulation and the planned wells will be ranked according to their productions curves.
An Appraisal of Soil Pollution in Oil and Gas Production Environment: A Case Study of Heavy Metals Concentration in Ebocha and Akri Oil Fields
Authors: Ossai C. I. , Duru U. I. , Ossai I. A. , Arubi I. M.
Published: July 2010

The concentrations of heavy metals in the soil at oil and gas production areas were appraised at Ebocha and Akri communities in Niger Delta region of Nigeria. The pollution/contamination loading indexes of Zinc (Zn), Nickel (Ni), Copper (Cu), and Lead (Pb) in the two communities were determined from soil samples collected in eight locations (in triplicate) in each community using Atomic Absorption Spectrophotometer (AAS).

It was observed that Ebocha was slightly polluted with lead (contamination/pollution index, c/p = 1.3), severely contaminated with zinc (c/p = 0.642) and slightly contaminated with copper(c/p = 0.123). Omoku was also slightly contaminated with zinc (c/p = 0.225) while all other sampling locations at Ebocha were very slightly contaminated with zinc, copper nickel and lead (c/p <0.1). Akri was very slightly contaminated in all the sampling locations except for Afia-afor where lead slightly contaminated the soil (c/p = 0.113).

A significant correlation (p <0.01) was obtained for zinc (r = 0.65) while there was no significant correlation (0.05 <p <0.01) obtained for Ni (r = −0.14), Cu (r = 0.22), Pb (r = −0.08), Mn (r = 0.38) and Fe (r = 0.54). This correlation showed that the sources of the heavy metals in both communities are different. It was also observed that the increased concentration of heavy metals in oil and gas production areas is more due to other associated human activities in the areas than oil and gas core production activities.
Successful Perforating Campaign in Extended-Reach Wells Offshore Malaysia
Authors: Noya J. V. , Wibsono R. , Parta I. P. , Connell C. , Oettli M. , Erkol Z.
Published: July 2010

In offshore Malaysia, the use of coiled tubing (CT) e-line has become a viable alternative to perforate new wells as it eliminates the use of an expensive offshore drilling rig for the completion process. The CT can convey long gun strings in horizontal completions in a single run, while creating the necessary underbalanced conditions.

As the field development evolved, it required drilling complex extended reach wells (ERW) to access reservoirs farther from existing platforms, imposing more difficulties for the operation. The CT is predicted to lock up before reaching the target depth in some of the new wells. In addition, operational inefficiencies in past campaigns were common, primarily due to the design of CT e-line equipment used. Occasionally, the disconnect tool was actuated accidently due to sensitivity to pumping flow rates.

A solution based on the combination of a hydraulically actuated CT wired tractor and a new CT e-line head design with unique features was proposed and implemented during a recent perforating campaign. In this solution, the tractor provided the force necessary to overcome the CT lockup and conveyed the guns to total depth (TD). Unlike most CT e-line head designs, the one used had the ability to circulate fluids through the assembly down to the CT tractor, enabling its actuation. The technical solution, field experience and results are presented.

The perforating campaign included six highly deviated wells and two highly ERW [TD to true vertical depth (TVD) ratio of 3:1] for which the CT wired tractor was needed. All wells were successfully perforated under balance, with no observed sand production. The longest gun string conveyed to TD was 597 ft in length. Zero incidents were recorded in a total of 16 runs, in spite of the limited field test status of the CT e-line head design.

This is the first recorded use of a CT e-line application with CT wired tractor for perforating purposes in ERW. Thus, the operational envelope of CT e-line applications is expanded, addressing the intervention needs of the future field development plans based on the ERW design in the area.
Novel Methodology to Understand Wear Mechanism in High Gas Rate Production Tubing
Authors: Maschio Leonardo , Hochenfellner Federico
Published: July 2010

The San Martin field is east from Lima, in the heart of the Peruvian tropical forest (see Fig 1). It is home to one of the most important non-associated natural gas reserves in Latin America, a vital resource for the energy needs of the country.

Tubing integrity in San Martin area has been a concern and a subject of continuous control due to the wells high gas rate, difficult logistic and economic importance. Multi-finger caliper logs were run in all the wells in San Martin field to control and assess tubing condition and integrity. Although the wells produced with low carbon dioxide (CO2) and water content, and no solids, preliminary reviews of the logs showed that only the wells with the highest production rate have wear signs of material loss.

This paper recap an extensive investigation performed in all the wells in the San Martin area. In this document logs reports, calculation as well as the ASCII files revision and quality controls are shown. Subsequently, a synopsis of the wear mechanism, its trends, the variables that control it and the extent of the problem using a novel internal processing of the raw caliper data are discussed. Finally, a set of recommendations to reduce the wear effect is presented.

Understanding the wear mechanism and documenting the lesson learnt are paramount not only to improve the operations in the San Martin field, but also to use this knowledge to improve the decision-making and management of the upcoming field completions in the same area.
Dynamic and Static Thermal Well Flow Control Simulation
Authors: Stone T. , Naccache Paul , Neylon Kieran , Edwards David , Damas Carlos Emilio , Rowan David , Raffn Anne Gerd
Published: July 2010

A preliminary investigation is presented on the use of Inflow/Injection Control Devices (ICDs) to control steam placement in the early stages of a Steam Assisted Gravity Drainage (SAGD) process. The two parts of this process that are examined are the steam circulation period and the early stages of injection/production in which the steam chamber is beginning to form. A SAGD case study has been designed that accurately models the initial circulation period in which both wells circulate steam in order to conductively and, to a lesser extent, convectively heat the region around the well pair in order to establish communication after which both wells switch to injection and production. Flow control is examined in a variety of configurations in the steam injection well, the devices being placed to control steam/water flow along the tubing, along the annulus and from the tubing to the annulus.
Estimation of Future Production Performance Based on Multi-objective History Matching in a Waterflooding Project
Authors: Han Y. M. , Park C. , Kang J. M.
Published: July 2010

The paper presents a MOEA(Multi-objective Evolutionary Algorithm) applied to history matching of waterflooding projects, that is to search a feasible set of geological properties showing the reliable future performance. Typical history matching has concentrated on single objective function with linearly weighted terms, even as a realistic field includes many wells and well measurements in time and type. The optimal solution is sensitive to weight factor and competing match criteria of individual term in the objective function often reduces the likelihood of finding an acceptable match. The unacceptable error at a specified well can be observed in a heterogeneous reservoir where shows various well performances.

To overcome the matter, a new history matching approach is developed that allows the performance characteristics of the whole wells. Individual well performance is optimized separately using genetic algorithm coupled with non-dominated sorting and diversity preservation. The fitness is sorted along to the proximity and then the diversity is added by examining the crowding distance as the approach to arrive at the global optimum. Waterflooding is demonstrated in a heterogeneous oil reservoir with multiple production wells. The predictability of unknown future production performance is compared with that of single objective function, the conventional history matching method.

The model represents irregular performance tendency more accurately than the conventional history matching. It improves the predictability of the conventional model. The averaged error converges about 5%, that is much less than that of single objective function. The selection of adequate set of reservoir properties is possible among the feasible solutions unlike the conventional model. The developed method can be applied as a useful tool for uncertainty analyses in waterflooding projects.
Lithofacies Analysis and Modelling of the Kookfontein Deltaic Successions, Tanqua Depocenter, Southwest Karoo Basin, South Africa
Authors: Sonibare W. A. , Mikeš D.
Published: July 2010

Deltaic successions are an important habitat for some of the major world's fossil fuel reserves (i.e. oil, gas and coal). An outcrop analogue study of the excellently exposed Permian siliciclastic Kookfontein deltaic sequence will therefore improve prediction of sandbody geometries and complex internal heterogeneities of subsurface examples.

Preliminary findings from field outcrop log data show the nature of complexity that could be encountered in a deltaic system that fills a basin. The complexity of the Kookfontein deltaic system is reflected in the succession of sedimentary structures (i.e. cross laminations, ripple laminations, Hummocky, massive and homogenous slump layers and horizontal laminations) both in time and space in a more or less an unpredictable manner.

In order to establish a 3D model of the rock record that includes stratigraphic elements and boundaries of all scales, we propose an approach that combines outcrop log, gamma ray log and photo-panel analysis. This approach will allow critical examination of the lateral and vertical variations of facies and their properties regarding fluid flow i.e. geometry and internal heterogeneity. The photo-panel analysis allows 3D high-resolution interpretations of the lithological boundaries both laterally and vertically which cannot be obtained from seismic resolution.

Based on the nature and complexity of the facies association, this study will propose a standard facies model for the deltaic sequence that will test the applicability of Walter's law of facies associations in facies analysis. A 3D reservoir-scale model will then be constructed based on the 3D geological model. The emphasis here will be to depict possible errors that could arise if all the stratigraphic elements and their boundaries (both on small and large scales) are not fully incorporated into reservoir scale modelling.
Advanced Drillable Aluminum Plug Technology Solves Operational Concerns: Pinedale Wyoming
Authors: Lewis Ryan , Hodges David , Crawford Robert , Desai Ankur , Winn Alex
Published: July 2010

Efficiently fracture treating a large number of zones has created a unique downhole tool challenge. In many applications, the operator requires a drillable cased-hole bridge/frac plug to effectively isolate multiple zones for stimulation in a single borehole. The main objective of the drillable plug is to isolate the lower zones so effective stimulation can be performed in the upper zones. This minimizes wellbore interventions while maximizing the number of zones stimulated. During drill-up, the plug must breakdown into small cuttings that can be easily transported utilizing conventional flow-rates to ensure a clean wellbore and unobstructed perforations. The plug must be composed of materials that allow for rapid drill-out using standard downhole motors and milling equipment.

Drillable plugs have evolved due to multiple challenges associated with the escalating number of zones that must be treated. Most recently, the service industry has produced a variety of composite bridge/frac plugs that have advanced performance compared to standard cast iron versions. However operators have experienced multiple problems with composite plugs.

To addresses the issues, a plug was designed and manufactured from precision aluminum alloy. The aluminum plug technology (APT) has significantly increased plug life-span having successfully addressed degradation issues in the application's pressure/temperature range. The new plug stays locked downhole under extreme temperatures/pressures without degradation and a unique anchoring system eliminates spinning of multiple plugs during drill-out. Advanced materials and a compact design have reduced drill-out time to an average of 20 minutes, saving the operator expensive rig time.

Using the APT, the operator has the option to flow back the well for an extended period before plug drill-out. APT has also drastically reduced the incidents of fishing due to partially set plugs. APT has demonstrated reliable performance during stimulation, effectively eliminating the adverse effects of plug movement during treatment.
Proppant Hydraulic Fracturing in Low Permeability and Low Acid-Soluble Carbonate Reservoir: A Case History
Authors: Pujiastuti Silvie , Wijayanti Elisa , Nugroho Hestu Sapto , Istono Noviadi , Wijaya Rio , Komalasari Novi
Published: July 2010

Proppant hydraulic fracturing has been a successful stimulation method used to enhance production in sandstone reservoirs. But for fracturing carbonate formations, the possibility of the existence of natural fractures and the hardness of the rock can be challenging. This paper will elaborate on a carbonate-fracturing pilot project in Soka field, which is the leading carbonate proppant hydraulic fracturing project in Indonesia.

Platform carbonate limestone from the Baturaja formation is the major component of Soka field reservoir. The platform consists of limestone with infiltrate mudstone/packstone and chalky limestone with poor porosity. The limestone mudstone/packstone lithology is dominated by mud, clay, and fine silt carbonates which results in the limestone becoming dirty and causes the low acid-solubility value of limestone in the field.

Stimulation jobs were performed in two wells in Soka field. From log analysis, the carbonate formation in both wells shows a high shale content (20%) and low permeability (6 md). Acid-solubility tests performed on both well cores showed low acid solubility. Matrix acidizing was performed in both wells, but they still showed low influx. Well A, after being perforated and matrix-acidized, only produced 40 BFPD, with a 30% water cut and a high GLR 19,061 scf/STB. Well B, after being perforated and matrix-acidized twice, had very low influx from reservoir to wellbore.

Proppant hydraulic-fracturing stimulation was performed in both wells using hydocarbon-based frac fluid and 12/18-mesh ceramic proppant. After being hydraulically fractured, Well A produced 165 BFPD at 18/64 inch choke, with 60% water cut and a GLR of 700 scf/STB, while Well B produced 173 BFPD at 25/64 inch choke, with a 0% water cut and a low gas rate. Production from both of these wells is maintained at the reservoir critical rate for each well.
Unique Straddle Design for Placement Inside Damaged Down Hole Safety Valve Nipple Seal Area
Authors: Liland Tor Henning , Lund Are , Johanson Therese , Hiorth Espen , Bill Bjørn
Published: July 2010

Up until today operators have been facing a challenge on how to avoid recompletion of wells where the nipple seal area inside the TRSCSSV (Tubing Retrievable Surface Controlled Subsurface Safety Valve) is damaged due to large amount of well interventions or damaged due to corrosion.

Various methods have been used for repairing a TRSCSSV with a damaged seal area. This includes standard insert WRSCSSV (Wireline Retrievable Surface Controlled Subsurface Safety Valve), with normal and oversize swell packing elements. Honing of the upper and lower seal area prior to installing an insert valve has also been performed but with variable success.

To have the DHSV working properly it is vital to maintain barrier control of the well. If the DHSV nipple profile is damaged the alternatives are to repair it using one of the above mentioned methods or to secure the well for later recompletion

Since all the above mentioned methods of repairing a damaged seal area for insert valve have failed, Statoil initiated a development project for a straddle design using well know element technology based on an HPHT Bridge Plug design. The straddle has solid elements, which shape according to the damage inside the seal areas. In addition each element is equipped with expanding anti-extrusion back-up rings on both sides, trapping the element so it has nowhere to go when differential pressure is applied. The straddle uses the existing nipple profile above the no-go for anchoring and is equipped with dogs to fit this profile. A standard insert safety valve is made up to the bottom of the straddle and is then operated by existing surface control line.

This paper will compare the different methods used for repairing a damaged Down Hole Safety Valve nipple seal area and discuss the development process and qualification testing done for the new unique straddle system and setting tool. Case histories will also be presented from several prolific North Sea Wells.
The Diagnosis of Decline and Successful Recovery of PI in a ‘DRY’ HPHT Gas Well That has been Affected by In-situ CaCO3 Scale and Salt Deposition
Authors: Wat Rex , Iversen Anne Marie , Belsvik Yngve Heggheim
Published: July 2010

Over a period of 4 to 6 months one of the Kristin wells had experienced a rapid decline in production. The drop was unexpected and at the time there was no detectable formation water breakthrough in the well. The decline in productivity was interrupted by a number of erratic, but temporary, surges in production that fell off again soon after. By comparing the well performance with other wells having the same downhole completion type, attention was soon focused on the likelihood of in-situ CaCO3 scale deposition. The subsequent discovery of CaCO3 deposition in the near wellbore area was partly anticipated. However, the discovery of halide scale (by precipitation) and salt (by evaporation) deposition came as a major surprise given that the Kristin formation water contains less than 10% of Total Dissolved Solids (TDS). This paper will describe the early diagnostic approach to screen and finally identify the most likely cause of the productivity loss. It will present the multiple well treatments that followed, the logics, the results and their interpretations. In addition to the results from these multiple treatments the paper will provide a mechanistic explanation of such deposition processes. Most interestingly, a novel observation will be put forward in this paper to underline the erratic and temporary surges of production during the decline period and that can be attributed to a ‘self-healing’ mechanism.
Intervention System for the Perdido SPAR Wet Tree Wells
Authors: Larsen H. A.
Published: July 2010

A system has been developed to safely intervene into sub-sea, direct vertical access well from a SPAR with a non- compensated platform rig. The system ensures well integrity and compensation of movement due to heave and tide of all intervention well control equipment. The system will work for wireline, slickline, braided line, and coiled tubing as well as bullhead pumping operations.

The system consists of: Hydraulic latching tool (tree to landing string)High pressure marine riserHigh torque and/or high pressure landing stringRiser tensioner systemSurface BOP'sLanding string hang off toolAnnular slick joint3-Line FlatPack control linesClamps for the FlatPackInline compensator to be suspended from the derrick

Platform movement is compensated with two systems concurrently: the Riser Tensioner System and the Inline Compensator. These systems ensure that no part of the rig-up can be loaded beyond its operational capabilities. Operations are safer and efficient because the systems are passive and minimum real-time human interaction is required once the systems have been rigged up and the operational parameters are set.

Drawings have been prepared to ensure the fit and feasibility of using standard oil field equipment in this environment. Bottlenecks and potential solutions have been identified.
An Innovative Back-up System for a 9-7/8-in. HP/HT Permanent Packer Provides a Solution for Damaged or Worn Casing in the North Sea
Authors: Robb Thomas , Valentine Ernie
Published: July 2010

Permanent packers are qualified by ISO 14310 V0 in a test fixture to meet the API 5CT internal casing dimensions; however, they do not account for any wear or damage in the casing. A test program was developed to test the packer at HP/HT well conditions and in worn casing. A major operator in the North Sea had been experiencing a problem with worn casing at the packer setting depth of an existing HP/HT well, causing a leak into the production annulus. A workover was required, and a calliper survey conducted after retrieving the tubing revealed two sizeable grooves along the longitudinal axis of the casing at 120° to each other.

This paper discusses the qualification and installation of an HP/HT permanent packer for worn casing. The test program consisted of the following:

Install the packer in 9-7/8-in casing and flow test to 3 bpm at 180°F to verify that the circulation around the packer did not damage the Aflas® element. Perform an application test using synthetic oil to mimic packer loading until failure, including setting, production, and hot/cold shut in.; apply 9,000 psi annulus pressure to support the casing during testing. In this case, the maximum temperature was 343°F or above for over 200 hours. Perform a modified ISO 14310 V0 test at 450°F with 15,000 psi differential pressure and 400,000 lbf tension and compression.

The packer passed all tests with no extrusion of the three-piece multi-durometer Aflas® element, and no leaks were detected at any of the load points in the application (liquid) test or modified ISO V0 gas test.

The discussion will include information on the packer design, HP/HT test in worn casing, and casing acceptance criteria. This test was the first packer test performed in worn casing that demonstrated the capability of the compliant back-up system to support a packer in worn casing and at HP/HT conditions.
Analysis on Scaling Substance of the E252 Heat Exchanger of Cracking Unit
Authors: Wei-wei Duan , Hong-fen Wen , Li-shu Wang
Published: July 2010

The paper analyzed the composition of the scaling substance of the E252 heat exchanger of 20 million tons cracking unit of Liaoyang petrochemical company with thermogravimetric analysis and ultraviolet fluorescence and atomic absorption spectrometry. We did the qualitative and quantitative determination on the scaling substance. We confirmed that the scaling substance was composed of the petroleum coke and sulfur element and iron element. There were 10.1% sulfur elements and 4.4% iron elements in the scaling substance. We found out the major reason that resulted in the scaling substance was the corrosion of the container by the sulfur compounds in the chemical material of the cracking unit.
3D Finite Element Modeling of Laboratory Hydraulic Fracture Experiments
Authors: Alqahtani Naif B. , Miskimins Jennifer L.
Published: July 2010

Laboratory experiments are an excellent way to visualize and improve our understanding of the hydraulic fracturing process. However, in order to truly apply the results of laboratory work to the field, an understanding of what artificial conditions are being created during the laboratory process must also be developed. This paper describes 3D finite element modeling and associated results using actual laboratory block tests as a basis. These models consisted of seven basic block systems, including a single layer system, with and without a wellbore, as a control case; a three-layer model with and without a wellbore; and a seven layer system, with a wellbore, without a wellbore, and with a cased wellbore. These seven systems were based on actual triaxial hydraulic fracturing experiments that were performed on mid-sized blocks (11 × 11 × 15 in) consisting of the same single, three, and seven-layers.

The fracture growth patterns in the actual laboratory tests were extremely complex, not at all like the planar fractures dictated by hydraulic fracturing theory. The intent of the modeling was to 1) determine the spatial stress contrasts being created by the material property contrasts of the layered systems in the triaxial system and 2) determine if the complex fracture growth could be accounted for by these modeled contrasts. Results were also used to determine the potential for shearing across the layered systems. A commercial, modeling software, capable of numerically determining the 3D stress distributions in the various porous media, was used. Numerical results were validated with analytical calculations.

The results of the modeling provide insight into the time-dependent application of stresses in a laboratory setting. It helped to explain the complex fracture growth in the actual experiments and gave some insight into the conditions that would cause vertical or horizontal fracture growth in a layered system of different material properties. The modeling also documented the creation of shear stresses which accounted for some fracture path deviation. The results of this paper aid in understanding the mechanisms of complex hydraulic fracture growth in reservoirs settings. Additionally, insight into the shear and tensile fracture mechanisms that generate acoustic events was gained.
Re-development of the Frøy Field: Selection of the Injection Water
Authors: Østvold T. , Mackay E. J. , McCartney R. A. , Davis I. , Aune E.
Published: July 2010

The Frøy Field, Norwegian North Sea, was closed down in March 2001 but there are plans to re-develop it. Previously, seawater (SW) injection caused persistent BaSO4 scaling problems in the production wells, so this study was undertaken to determine whether there would be any benefit in using Utsira formation water (UW; low SO4) as opposed to seawater as the injection water.

Thermodynamic calculations indicated that whether SW or UW is injected, the principle scaling risks are from BaSO4 and CaCO3 deposition. Being more difficult to treat, the study focused on the BaSO4 risk. ECLIPSE modelling was used to estimate FW:SW:UW ratios over time for each new well assuming (a) SW injection and (b) UW injection. The results indicated that in each case, initial peaks in BaSO4 Saturation Ratio (SRBaSO4) would occur after ~1.5–2.5 years before declining. The peaks reflect co-production of seawater already present in the reservoir and formation water. The subsequent decline in SRBaSO4 reflects (a) decrease in the FW:SW ratio (SW injection case) and (b) dilution of produced Ba and SO4 as the produced UW fraction increases (UW injection case).

An evaluation of produced water analyses from Frøy and from analogue fields indicated that reservoir reactions will occur at Frøy whether SW or UW are injected but significant BaSO4 would only occur in the presence of seawater. Two methods were used to quantify SRBaSO4 in the new production wells over time after accounting for BaSO4 precipitation in the reservoir. In the first, the amount of BaSO4 deposition in the reservoir was predicted from past produced water analyses and applied to the ECLIPSE results. The second involved the use of STARS to model the effect of reservoir reactions on the scaling potential. There were some differences in the results related to the amount of mixing predicted to be occurring in the reservoir, but contrary to initial expectations, both methods indicated that UW injection would not be beneficial.

Based on these results, seawater has been selected as the injection water resulting in significant OPEX and CAPEX cost savings.
Modelling Multiple-Contact Condensation of Heat-Transporting Fluids in Thermal Floods
Authors: Lawal Kazeem A. , Vesovic Velisa
Published: July 2010

Multiple-contact condensation (MCC) is proposed as an additional mechanism in the conventional heat-transport treatment based on conduction and convection. The conceptual model assumes that condensation occurs by multiple contacts between injected fluid and heavy oil, with the injectant condensing progressively as it traverses the reservoir, delivering latent heat along its path. The mathematical model entails coupling the energy conservation equation and temperature-dependent fluid-property functions. The resulting partial differential equation has been solved using finite difference Crank-Nicolson method. Simulation results are qualitatively consistent with available published experimental data.

Parametric studies have been performed, examining relative effects of some operational and petrophysical variables on the heating rates for viscous-oil formations. The results indicate that effect of formation permeability is highly non-linear, its impact being highest for highly permeable reservoirs. It has been shown that the initial reservoir temperature and the steam temperature both enhance the heating rate, while the drainage of oil and condensate has a detrimental effect.

The temperature profiles obtained in this work indicate that incorporating MCC mechanism into current conduction-convection models would eliminate the need for such models to use relatively high effective permeabilities to fit experimental data.
Laminar and Turbulent Friction Factors for Annular Flow of Drag-Reducing Polymer Solutions in Coiled-Tubing Operations
Authors: Ogugbue C. C. , Shah S. N.
Published: July 2010

The challenge of theoretical and numerical studies of annular fluid flow with varying eccentricity is mainly due to the required coordinate systems. Computational fluid dynamics (CFD) modeling provides the state-of-the-art approach of investigating fluid flow in such complex geometries. In this study, results from a series of numerical simulations for the fully developed laminar flow of non-Newtonian power law fluids in concentric and eccentric annular geometries are used to investigate the effect of eccentricity, flow behavior index, and diameter ratio (ratio of the outer diameter of the inner tubing to the inner diameter of the outer tubing) on axial friction pressure losses.

The friction pressure gradients predicted by the CFD simulations were verified by comparing with the published studies and flow data from a field scale experimental set-up. At a constant flow rate, it is confirmed that frictional pressure losses are decreased with increasing eccentricity. A good agreement was obtained with the Haciislamoglu et al. correlation, and the results of this study, especially at low values of eccentricity. At very high eccentricities, data from the CFD model yields lower friction pressure compared to Haciislamoglu et al. correlation. Haciislamoglu et al. type expression is obtained, incorporating the improved data of this study.

Next, this paper presents the results of an experimental study carried out to investigate friction pressure behavior of drag reducing polymer solutions, flowing turbulently through an eccentric annulus. The experimental set-up includes 30 ft of 3½-in. x 2 3/8-in., 200 ft of 3½-in. x 1¾-in., 69 ft of 5½-in. x 4-in., and 79 ft of 5-in. x 3½-in. fully eccentric annuli. Data analysis enabled the development of a new correlation using fluids apparent viscosity at 511 sec-1, generalized Reynolds number, and diameter ratio, all of which can be easily determined in the field, as independent variables. These new correlations for laminar and turbulent flow of drag reducing polymer solutions present an improvement to existing correlations, and also permit undemanding hydraulic program calculations for varying annular configurations.
The Use of Diutan Biopolymer in Coiled Tubing Drilling Mud Systems on the North Slope of Alaska
Authors: Sarber J. G. , Reynolds C. , Michel C. M. , Haag K. , Morris R. A.
Published: July 2010

Diutan biopolymer has recently been introduced for drilling with coiled tubing on the North Slope of Alaska.

Diutan biopolymer has replaced a xanthan biopolymer based mud system when drilling new sidetrack laterals from existing wells and also in well servicing with non-rig coiled tubing operations. This change in fluid systems was made by replacing the existing xanthan biopolymer used in the solids free mud system with a diutan biopolymer. The new diutan based solids free mud has shown improvements in several areas thus providing a significant performance advantage.

Coiled tubing drilling (CTD) has been conducted in Alaska since 1994 with over 600 sidetrack laterals drilled to date. For the majority of these wells a solids-free mud system was used to drill in either an overbalanced or managed- pressure drilling mode. The solids-free mud used was based on a xanthan biopolymer. In 2009 planning for more difficult well candidates suggested that the existing xanthan drilling fluid systems would be inadequate for drilling certain wells without exceeding acceptable working pressures in the coiled tubing or surface equipment. The higher pump pressures expected, along with acceptable coiled tubing design parameters associated with this higher pressure demonstrated the need to modify the drilling fluid. The standard solids-free mud was modified by replacing the xanthan biopolymer with diutan biopolymer. This new system demonstrated a 20% reduction in pump pressure, better hole cleaning, a higher tolerance to the pH changes related to cementing operations and longer fluid system life.

This paper will document the development of the diutan reservoir drilling fluid (RDF) system, including laboratory testing, field testing, a comparison to the xanthan based RDF, and the results of drilling actual wells. This new drilling fluid system has been in use now since July of 2009 and is the preferred drilling fluid used for coiled tubing drilling and well servicing in Alaska.
Improved Production Strategy for Enhancing the Immiscibile and Miscible CO2-Assisted Gravity Drainage Oil Recovery
Authors: Jadhawar P. S. , Sarma H. K.
Published: July 2010

Fundamental understanding and application of process parameters in numerical simulation that leads to optimized gravity drainage oil recovery at field scale is still a major challenge. Reservoir simulations studying the effects of well patterns and type of gas injection wells have not been reported so far. In first ever attempt, the mechanistic benefits of production strategy on gravity drainage oil recovery are identified in this paper. Effects of irregular and regular well patterns and vertical and horizontal gas injection wells are investigated using a fully compositional 3D reservoir model in both the secondary immiscible and miscible modes under the conditions of voidage balance, constant injection and production pressure and injection rates below the critical rate.

Regular well pattern provided longer oil production time at a constant rate until CO2 breakthrough compared to irregular well pattern. It then dropped almost vertically at the same cumulative oil recovery even at higher production rates. However, gravity drainage oil recovery was higher at higher rate combination after CO2 breakthrough. Results also suggested that the regular pattern could result in horizontal CO2 floodfront parallel to the horizontal producers, maintaining reservoir pressure, thus optimizing the oil recovery by additional 2.5% OOIP. Vertical injection and horizontal production wells in both the immiscible and miscible modes provided nearly identical cumulative gravity drainage oil recovery compared to the combination of horizontal injection and production wells in the regular well pattern. This suggests that the type of injection wells may not be a significant factor to impact the CO2-assisted gravity drainage mechanism. Results obtained herein would help in the optimization of CO2-assisted gravity drainage EOR process.
New Field in East Siberia: Challenges of Performing CT Operation on Vankor Field
Authors: Bochkarev V. , Vorostov A. , Smetanin S. , Sitdikov S. , von Hertzberg B. , Zagranichniy S.
Published: July 2010

The search for commercially viable oil reservoirs has led to expanding the frontiers of oilfield development. A new field in Russia known as Vankorskoe, which is 100 km north of the Arctic Circle in Siberia has been placed on production. This field is extremely isolated with winter access only by ice road and summer access by barge. The primary means of transportation is by helicopter.

Production from this field comes from producing zones at TVDs of 1680 m and 2780 m. Most of the wells are horizontal with a screen completion in the producing section.

Coiled tubing has been used in the Vankorskoe field since July 2008 to perform clean outs, kick offs, stiff wireline logging and hydrate removal operations. To date (Sept 23, 2009), 68 coiled tubing well interventions have been performed on 40 different wells.

The well profiles are designed with a reverse bend in it allowing the horizontal section of the wellbore to be directly beneath the wellhead. This profile has led to some challenges in reaching TD inside the 114 mm completion screen assemblies. Horizontal sections of up to 1000 m exist in these wells, which required the introduction of vibrator technology to this field. There is an 800 m thick layer of perma-frost which is coupled with extremely low reservoir temperatures.

This paper reviews the engineering, operational and logistical issues related to utilizing coiled tubing in a frontier field and the innovative solutions required to overcome these issues. It also discusses the expanded role that coil tubing will have as the field matures and production enhancements are required.
Cleaning Horizontal Wellbores Efficiently with Reverse Circulation Combining with Wiper Trip for Coiled-Tubing Annulus Fracturing Application
Authors: Li J. , Aitken B. , Jumawid F. , Alingig G.
Published: July 2010

Annular fracturing of multiple zones with coiled tubing (CT) has been practiced for more than a decade. A typical treatment involves sand jetting perforating, cleaning the well, fracturing and isolation. It is economically desirable to perforate, fracture and isolate each interval quickly, allowing all intervals to be treated in the shortest time possible. However, CT lying on the bottom of horizontal wells creates a solids bed during the perforation and fracturing stage, this introduces additional complexities into the reliable execution of the fracturing process. For tight formations, proppant beds have to be completely or partially removed, otherwise the pad can entrain the proppant which creates a high potential for premature screen out.

In this paper, a new approach to cleaning the hole between multiple annular fractures is proposed. This hole cleaning process involves circulating the clean fluid through the annulus to the bottom of the wellbore and bringing the sands back to the surface through the CT; at the same time the CT pulls out of the hole (POOH). The sand particles at the top section of the wellbore are swept toward to the end of CT, while the solids near the end of the bottom hole assembly (BHA) are sucked into the CT as it is pulled out of hole. Eventually, all solids are removed with the CT partially pulled through the initial bed section. As a wiper trip to surface is not required, the efficiency of this new process is higher than other cleaning processes. A full scale flow loop was used to simulate the process. Maximum POOH speed and the hole cleaning time were determined under various conditions. Empirical correlations were developed to allow for optimization of the process under the down hole conditions.