bluuebunny/crossref_metadata_2025_split huggingface dataset:
Managing Uncertainties in Hydrocarbon-in-place Volumes in a Northern Depobelt Field, Niger Delta, Nigeria
Authors: Akinwumi Femi V , Arochukwu Elias C. , Abdul-Kareem Abiola S. 
Published: December 2007

Abstract
Petroleum resources represent a significant part of a company's upstream assets and are the foundation of its current and future upstream activities. Often times, at the discovery of a new field or extension of an existing field, there are uncertainties associated with quantifying the amount of hydrocarbons in place. These uncertainties may be related to the structure, aerial extent of the accumulation, unseen fluid contacts to delineate the vertical extent, internal architecture of the reservoir and the characteristics of the resident fluid(s). In some cases, companies may complete and produce discovery wells before they can fully appraise the structure or may be forced by other considerations such as community disturbances to abandon appraisal drilling and continue to produce from existing well(s). All these and much more, have an impact on the evaluation of in-place hydrocarbon resources and consequently recoverable hydrocarbons. In Field Development Planning, it is routine to identify and quantify the impact of major subsurface uncertainties such as the in-place volumes and their distribution.
This paper presents the methodology and results of an integrated disciplinary effort at translating uncertainties into a range of static (in-place) volumes for the purpose of field development. Erratic sand development, paucity of biostratigraphic control coupled with a complex structure make the G1.0 complex of the EGBM field one of the least understood hydrocarbon reservoirs of the Northern depobelt - Onshore, Niger Delta, Nigeria. Lack of PVT samples and analyses also add to the uncertainty in fluid properties. The erratic distribution of the petrophysical parameters especially from the G sand core also contributes to the petrophysical uncertainties.
The construction of 3-D static reservoir models based on the understanding of facies and their relationships, through the integration of all available data have been used to enhance the understanding and quantification of the uncertainties. Standard evaluation of uncertainties in the spread of petrophysical parameters like porosity, hydrocarbon saturation and Net-to-Gross ratio was carried out and compared with the multiscenario concepts incorporated in the geological models. PVT parameters were derived for the reservoir based on analogy and correlations constrained with production and test data. Efforts were also made to comply with definitions of proved reserves by Securities and Exchange Commission (SEC) while still evaluating expectation volumes for internal purposes. An attempt has also been made in comparing results from the probabilistic volumetric evaluation of this reservoir and the deterministic (best estimate) method.
Quantifying Uncertainties in a New Field Development: A Swamp Field Case
Authors: Aigbe Christopher O. , Randle Jim , Fitzmorris Robert 
Published: December 2007

Abstract
The Chevron Nigeria Limited (CNL) swamp field, which has oil-in-place in excess of 139.0 MMSTBO, is currently one of the major undeveloped assets in CNL's portfolio. A reservoir simulation study was commissioned in January 2003 to devise strategies for the optimal development of this reservoir. Some study objectives include the determination of the number and location of new wells (producers and injectors), requirements for water injection and gas lift and the optimization of various operating and decision variables, all of which is geared towards maximizing the value of this major CNL asset.
It was recognized that an accurate validation of the 3D geologic model will not be possible because of the absence of historical pressure and production data in the new field, which had two producers and one water injector already drilled. The older techniques of evaluating risks and uncertainties by running sensitivities on various input parameters on the un-validated model on a one-at-a-time basis was considered inadequate since interactions between parameters, which could have significant impact on the forecast ultimate recovery, cannot be captured.
A more robust methodology, which systematically quantifies the impact of the uncertainties in model input variables on the ultimate recovery, using Experimental Design (ED) techniques was adopted for the reservoir study. A two-prong approach was employed in which uncertainties in the sub-surface variables (e.g. Kv/Kh, Kh_Multiplier, Internal Fault Integrity, Sorw, Oil Viscosity and Krw) were quantified using ED to screen for the most significant parameters that could impact ultimate recovery. A multiple regression of the most significant parameters from ED yielded a response surface on which Monte Carlo simulations were performed to generate the p-10, p-50 and p-90 models. The resulting Chears replicated p-50 model formed the basis for the sensitivity runs on the various operating and decision variables (e.g. number and location of wells, well type, offtake rates, gas lift rates and timing, WI rates, voidage replacement ratios, well timing etc.) on the project ultimate recovery.
The study results indicate that the optimized development case will recover 68.5 MMSTBO (representing 49.3% of OOIP of the 21.7 deg. API gravity crude). This represents incremental reserves of 29.8 MMSTBO (over the base case) from the drilling of additional 5 producers and 2 water injection wells.
The paper will present details of how ED approach can be used to quantify uncertainties inherent in model input variables using the CNL Swamp field reservoir as a case study. The development options and detailed results obtained from the study, which now commands a greater degree of confidence, will also be highlighted.
Challenges of Gas Development: Soku Field Oil Rim Reservoirs
Authors: Cosmo Claudio , Fatoke Oluwaseyi 
Published: December 2007

Abstract
The Nigerian LNG Project at Bonny is undergoing significant expansion from it's current 3 trains to 5 trains by the end of 2005. Shell's share of the additional gas demand is met by gas offtake from the Soku oil rim reservoirs. The challenge in Soku is to manage gas offtake between reservoirs to secure optimal hydrocarbon recovery from the oil rims under concurrent production of both gas caps and oil rims
This paper addresses the methods used to establish the sensitivity of oil rim recovery to reservoir uncertainties and development strategy. It shows how an idealised box model, preconditioned to match historic production in reservoirs, is used to guide development plans which are later validated in full 3D reservoir simulation models. The box models and full field simulation have been used to confirm that concurrent production of oil rims and gas caps from Soku oil rim reservoirs can be achieved while optimising oil recovery from the rims.
Targeting Thin-Oil Rims in Bottom- and Edge-Water-Drive Reservoirs
Authors: Kabir C. S. , Agamini M. O. 
Published: December 2007

Abstract
This paper proposes completion strategies to target the remaining oil, left behind when water invades the producing interval(s) in bottom- and edge-water-drive reservoirs. In the first option, a conventional horizontal well is completed below the gas/oil contact (GOC). Once the completion waters out, recompletion occurs in the gas zone.
For either drive mechanism, recompletion of the vertical segment of the same wellbore at the crest is prudent, provided economic gas disposition is not an issue. In the second option, one can initially complete at the same location where the recompletion occurs, thereby skipping the initial completion. In all cases, gravity-stable flooding or disciplined withdrawal rate is required to maximize reserves.
Extensive flow simulations in multiple, history-matched models show that the proposed strategy improves oil recovery significantly. We show that the proposed completion strategies do not involve production of total cumulative gas/oil ratio any higher than those done with conventional completion involving much less oil recovery. In fact, the two-stage depletion scheme doubles the recovery factor in a saturated reservoir with a 34-ft oil column, which is underlain by a moderate size aquifer.
Beyond the computational results, several field examples demonstrate the usefulness of the proposed completion methods. We show that the normalized GOR or the cumulative gas production is less than those experienced under conventional depletion schemes because of gravity-stable flooding.
Abandonment of Wells in Shell Nigeria Operations
Authors: Odita Charles , Adenipekun Adedokun , Wakama Miebaka , Ahire Dondo , Ojo James 
Published: December 2007

Abstract
Shell Petroleum Development Company of Nigeria Limited (SPDC) recently embarked on a campaign to abandon some wells in line with a corporate drive to enhance the safety of the wells in her portfolio. It is also to ensure that SPDC as a responsible operator aims to safeguard people and environment as required by law. The campaign is part of a larger campaign that had the objective of enhancing safety integrity in SPDC. It will also afford the opportunity to carry out relatively inexpensive repair and recompletions.
A total of six wells were abandoned in the land and swamp terrain within a year period utilising the Hydraulic Workover Units (HWU) for Land anda combination of the HWU and Self Elevating Workover Platform (SEWOP) in the Swamp. The 6 wells were amongst the most critical wells for abandonment based on SPDC defined criteria (e.g wells in Navigable water ways or in built up neighborhoods). In one of the wells on land, human habitation had since grown close to its proximity and the well experienced high annular pressures, hence the need for the abandonment. The others are in the waterways in the swamp with other technical problems. Most of the wells were drilled over 30 years ago and they have either outlived their useful life or there is plan to recover the remaining reserves in other offset wells.
The abandonment involved full subsurface and surface abandonment with the entire wellhead and casing structures removed from below the mudline or cellar (for land). The use of the HWU / SEWOP arrangement brought significant cost savings (25 – 50 %) when compared to the cost of using conventional workover rig. This paper reviews the work that was carried out in the abandonment and highlights the challenges as well as strategies that were applied towards the successful abandonment operations.
Water Shut-off using Rigid Polymer: The Etelebou Experience
Authors: Augustine Ekeigwe , Abiodun Laoye , John Madu , Chiji Onwuzurike , Olatunji Williams , Hugues Poitrenaud 
Published: December 2007

Abstract
Aging fields, dwindling production and increasing water cut are major challenges to all operators in the Niger Delta. Thus, finding efficient means to shut-off or control undesirable water production has become paramount. Ironically, the industry does not lack the suite of tools and products to address these problems but, a survey conducted in early 90's estimated that the world wide success percentage of water shut-off was a mere 35%. Identified as key to the poor performance are the deficient problem diagnosis and inappropriate remedial interventions. This low success ratio ultimately led to the loss of confidence in the use of rigid polymers for water shut-off. Although the chemistry of these rigid polymers are robust and well-proven1,2,3,4, the poor result recorded with them heightened most operator's reluctance to use them for water shut-off operations.
This paper addresses a Through Tubing (TT) water shut-off successfully carried out, using a rigid polymer. Identified early was the need for additional data to properly define the problem. Following data acquisition, water encroachment in some of the perforations was established. The diagnosis also identified an undrained interval located beneath the flooded zone. A multidisciplinary team was set up to review all data and advance the most economic and cost effective intervention option. The main challenges including maintaining through bore accessibility, easy wash-out etc. were listed. This led to the choice of a rigid polymer (MaraSEAL), which resulted in the desired solution5,6. The advancing water was checked and in addition access to reperforate on a deeper horizon was achieved. The well is back on production.
Regional Correlation on Saturation Height Function for Niger Delta Oil Province
Authors: Anijekwu C. , Odegbesan C. O. , Ogagarue E. E. E. 
Published: December 2007

Abstract
Saturation height function, a key parameter in reservoir models, is often derived from log data due to limited core data in the Niger delta. This approach culminates in lower or higher values of hydrocarbon saturation depending on nature of formation. Algorithms have been developed to predict saturation height functions required in simulation models.
The study presented in this paper was based on available rock and fluid properties from one hundred and thirty one core measurements from seventeen fields in the Niger delta oil province. Results from the derived relationships showed a good match between the derived height function and log derived saturation where there was no core measurement. They are particularly useful in partially appraised fields and exploration wells where little or no information is known about the formation type and are good for quality check of core measurements as well as Log derived saturation. Result obtained compared well with other methods. Saturation obtained from the correlation has also been used to calculate Stock tank oil initially in place (STOIIP) and free gas initially in place (FGIIP). Difference obtained in calculated volumes was 5% relative to those estimated using log derived saturations for most of the reservoirs.
A Case Study of Permeability Modeling and Reservoir Performance in the Absence of Core Data.
Authors: Ekpoudom Ofonmbuk , Obe Akin , Chike Ikechukwu , Onyekonwu Michael 
Published: December 2007

Abstract
Unavailability of core data in most Niger delta wells makes pertinent the need for a reliable permeability distribution.
This paper accounts for how permeability was modelled in a reservoir without core data in the Niger Delta by using five empirical approaches namely, Timur, Coates, Tixier, Udegbunam and also a correlation generated from core data of a nearby field. The five permeability results from the five approaches were used in building five different 3 D geological models.
Flow simulation was carried out for all the models to analyse their flow peformance. The permeability distribution from the correlation generated from the nearby field core data yielded a higher oil recovery.
Analyzing the Impact of Petroleum Fiscal Arrangements and Contract Terms on Petroleum E&P Economics and the Host Government Take
Authors: Iledare Omowumi O. 
Published: December 2007

Abstract1
The effects of fiscal terms and system parameters on the performance profile of exploration and production (E&P) ventures and the corresponding government take under different fiscal arrangements are examined in this paper. The fiscal regimes and terms governing E&P activities and operations are incorporated into a discounted cash flow model to address questions regarding how the choices of the parameters of fiscal regime affect the economics of E&P ventures. More generally, we investigated how fiscal systems should be structured and designed to maximize government take from E&P ventures keeping in perspective the underlying economic objectives of the contractors/operators.
Using a hypothetical field as a case study, the paper concludes that government participation in E&P ventures through joint venture arrangements does not optimize economic gains for the E&P firms. Neither does government participation necessarily maximize the fair market value of petroleum resources received by the government. We also found strong evidence to suggest that the petroleum sharing contract (PSC) arrangement can be more favorable to E&P firms in terms of economic returns than the joint venture arrangement (JVA) under the general and analogous fiscal parameters and terms specified in this study. The empirical results further suggest an asymmetric response of E&P economic performance indicators to product prices, discount rate, installed capacity, and EOR. Meaning that the response of the selected indicators of economic performance in this study to positive changes in each of these inputs does not equal the response of performance indicators to negative changes in the input parameters.
An Integrated System Approach to Wellbore Cleanouts With Coiled Tubing
Authors: Rolovic Radovan , Weng Xiaowei , Hill Stephen , Robinson Geoff , Zemlak Kean , Najafov Jeyhun 
Published: December 2007

Abstract
Wellbore cleanouts represent the main application of coiled-tubing (CT) services. Despite a long history of utilizing CT to remove sand and other fill material from oil and gas wells, advancement in the technology, and a growing body of experience, many wells are still not cleaned adequately, some wells cannot be cleaned at all, and a downhole stuck CT or other serious problems are encountered too often. Based on gathered experience and extensive research and development of new tools and techniques, a new, highly engineered and integrated system for wellbore cleanouts was developed. This paper presents the new integrated system approach, which can eliminate wellbore fill-removal problems and provide effective wellbore cleanouts under virtually any wellbore conditions. Case studies are included that show the performance of the new system in difficult field environments.
Analysis of the Effects of Major Drilling Parameters on Cuttings Transport Efficiency for High-Angle Wells in Coiled Tubing Drilling Operations
Authors: Ozbayoglu M. Evren , Miska Stefan Z. , Reed Troy , Takach Nicholas 
Published: December 2007

Abstract
Coiled Tubing (CT) Drilling is becoming more popular as the drilling technology is advancing. Most of the CT applications are associated with highly inclined or horizontal well drilling. In such wells, cuttings transport is still remaining as a major challenge. In this study, a layered cuttings transport model is introduced for high-angle and horizontal wells, which can be used for incompressible non-Newtonian fluids as well as compressible non-Newtonian fluids, i.e., foams. A computer program is developed based on the proposed model. The effects of major drilling parameters, such as flow rate, rate of penetration, fluid density, viscosity, gas ratio, cuttings size, cuttings density, wellbore inclination and eccentricity of the CT on cuttings transport efficiency are analyzed. The results are verified with the experimental data obtained at The University of Tulsa – Low Pressure – Ambient Temperature flow loop. The major findings from this study are, the dominating parameter on wellbore cleaning is the flow rate, and, as the viscosity of the fluid is increased, the thickness of the cuttings bed developed in the wellbore is significantly increasing. Also, cuttings properties, fluid density, wellbore inclination and eccentricity have some influence on cuttings transport.
Tapered OD Coiled Tubing System
Authors: Kalman Mark , Domann Bob , Rosine Randy , Stephens Rodney , Chambers Michael , Martin John , McWhorter David 
Published: December 2007

Abstract
A Tapered OD Coiled Tubing System (TODCTS) enabling the deployment of multiple outer diameter (OD) coiled tubing sections in a single string is being developed.1 By employing larger OD tubing sections near the top of the string and smaller OD sections near the bottom of the string, the tension along the string length is reduced while maintaining sufficient flow capacity for well intervention operations. The TODCTS can enable intervention service in deeper wells or installation of multiple OD velocity strings with the diameters optimized based on well production requirements.
This paper describes the development plan, system and component design, and the results of analyses and tests conducted to verify that the the tapered connector and surface equipment meets the requirements necessary to deploy the connector and adjoining strings of different ODs.
Implications of Coupling Fractional Flow and Geochemistry for CO2 Injection in Aquifers
Authors: Noh M. , Lake L. W. , Bryant S. L. , Araque-Martinez A. 
Published: December 2007

Abstract
The geochemical changes caused by CO2 injection into aquifers include acidification and carbonation of the native brine and potential mineral dissolution and precipitation reactions driven by the aqueous composition changes. The latter are important for evaluating the potential CO2 storage capacity in the form of minerals and can also influence the performance of the injection well.
The theories of geochemical flows and of fractional flow provide useful insight into several aspects of CO2 sequestration. This paper gives the mathematical formalism of combined geochemical and multi-phase flow. If local equilibrium applies, the theory leads to graphical solution, from which it is easy to see when and under what conditions mineralization will occur during the injection. The theory also illustrates the influence of post-injection flow on mode of CO2 trapping (hydrodynamic, solubility, mineral, residual saturation). We also show that co-injection of water significantly alters the mode of trapping.
Coiled Tubing and Vessel Motions for Riserless Coiled Tubing Systems
Authors: Hoen Christopher , Håheim Svein A. 
Published: December 2007

Abstract
Special care must be taken tomaintain the integrity of the coiled tubing when performing subsea well intervention from a lightvessel without the use of a riser. In these cases the coiled tubingwill act as a riser with respect to withstanding the external loads from waves, current andvessel motions. To avoid local buckling of the coiled tubing as it enters the subsea lubricator it is important to keep the vessel positioned such that the bending of the coiled tubingis kept as small as possible.
This paper will outline a method for estimating the optimal set pointfor the vessel positionduring riser less coiled tubing operations. The method is based on a combination of measurements and analytical methods for description of the structural behaviour of coiled tubing and the subsea stack. The analytical method developed is compared to simulations using commercial riser analyses software.