Proper Reservoir Management Research Articles

Diagenetic imprints in the reservoirs of Agbada Formation, Niger Delta Basin: Implication for reservoir quality and appraisal of calcite cement

The main exploration targets for hydrocarbons in the Niger Delta Basin are within the Agbada sandstone reservoirs. The current study utilizes a multitechnical approach (SEM-MLA, SEM-EDS, XRD and LA-ICP-MS) to evaluate the roles of framework composition and diagenetic processes, particularly calcite cementation on reservoir quality in Miocene intervals of the Agbada Formation sandstone, Niger Delta Basin. Petrographic analysis reveals that the sandstones are feldspatho-quartzose to quartzose sandstones, with a preponderance of quartzose sandstones. The overall diagenetic imprints suggest minimal compaction and lack of pervasive cement, which have contributed significantly to the high porosity. Although the degree of mechanical compaction is generally low, it has comparatively exercised a better control on porosity than the growth of cement, excluding some intervals with considerable cementation (siderite and ferroan calcite) where compactional porosity-loss was minimal. The occurrence of ferroan calcite cement (CaCO3 = 95.9 ± 0.4, MgCO3 = 0.8 ± 0.1, FeCO3 = 2.9 ± 0.2 mol%) is generally small, probably discontinuous and unlikely to represent significant barriers to fluid flow with their localized influence, but understanding their locally significant influence may still contribute to building good reservoir models. Petrographic observations suggest that the precipitation of “poikilitic” calcite was early, but the shale normalized REY patterns do not mimic seawater patterns (Y/Ho ratios; 36.3 ± 1.6) due to possible contributions from clastic or detrital grains and/or incorporation of particulate matter that can preferentially scavenge LREEs from the overlying water column. A possible concern during reservoir production is the occurrence of clay mineral matrix (mostly kaolinitic) anticipated to cause the production of fines and formation damage, but this can be mitigated with proper reservoir management.

Analyzing the dynamical relationships between meteorological and hydrological drought of Wadi Mina basin, Algeria using a novel multiscale framework

Understanding the relationship between hydrological and meteorological drought in drought-prone regions is critical for proper reservoir management. This study presents a novel multiscale framework for investigating the associations between hydrological and meteorological drought based on the Time-Dependent Intrinsic Correlation (TDIC) method. Firstly, the characteristics of short, medium and long term standardized precipitation index (SPI) and the standardized runoff index (SRI) of the Wadi Mina basin (Algeria) have been analyzed based on data from 6 rainfall and hydrometric stations. Then an Improved Complete Ensemble Empirical Mode Decomposition with adaptive noise (ICEEMDAN) method is used to decompose the most correlated SPI and SRI series to different scales. A stronger association between the two types of droughts is evident in the low-frequency trend component regardless of the station, but their evolution pattern does not remain the same. Subsequently, a TDIC based running correlation analysis is performed between the modes to examine the SPI–SRI associations over the time domain and across the time scales. TDIC analysis has proven the dynamic behavior in the SPI–SRI associations bearing frequent alterations in nature and strength across the process scales and along the time domain. In general, at the intra-annual scales the SPI–SRI correlations are mostly weak positive with localized alterations to negative along the time domain, whereas the relationship is dominantly strong positive and long range at inter-annual scales up to 4 years. This dynamic behavior in the SPI–SRI association and the evolution pattern of trend decipher that the rainfall processes are not directly transferred to streamflow drought, but it also gets controlled by many other local meteorological processes.

Understanding Oil Production: Investigating Factors Affecting the Oil Production Decline in Blocks 3 & 7 of South Sudan (2017-2022)

The study has comprehensively examined factors that have led to oil production decline in block 3 & 7 in Paloch of South Sudan from 2017-2022 as well as appraising solutions to the oil production decline. The study objectives were subjected through rigorous empirical literature review and the gaps in the literature were filled through field research. During fieldwork, mixed research methodology was deployed. This includes qualitative and quantitative research design. Research instruments such as questionnaires and interview guides were used to collect the data with a target population of 100 people that was later determined via Yamane’s formula to end up with a sample of 80 respondents. The study found systematic and drastic oil production decline of block 3 & 7. From 2017, the average daily production was 131,000 barrels per day (bpd). However, in 2022 the average daily production was 97,267 barrels per day (bpd). The study findings indicate that the causes of oil production are high water cut (produced water), too much sand produced, floods, poor & obsolete technologies and wars & conflicts in block 3 & 7 of Paloch. The study found the solutions to this oil production decline as re-injection of the water to the reservoir, proper reservoir management, laboratory testing for the sand before it accumulates, use of dykes and river Nile dredging for floods prevention, use of modern and relevant technologies and finally maintenance of genuine peace and security across the country. The study concludes with immediate implementation of the solutions to the oil production decline and carrying out more explorations as most of the oilfields are still green fields for new discoveries.

Pressure transient analysis for stress-sensitive fractured wells with fracture face damage

Fracture networks improve wells’ deliverability of fluids from underground reservoirs. However, conductive fractures may lose efficiency because of fracture closure or formation damage that needs to be monitored and detected for proper reservoir management and intervention. Fracture hydraulic conductivity is a function of fracture geometry and its hydraulic aperture, which tends to degrade during operations because of fracture compaction and closure. Furthermore, pore-clogging of fracture walls (faces) results in a damaging skin zone that may reduce fracture-matrix transmissibility. Current Pressure Transient Analysis (PTA) models in the literature do not consider the interconnected combined effect of stress-dependent conductivity of fractures and fracture face skin. Modeling fracture closure without accounting for the skin effect may mislead the PTA interpretations of well performance. This work proposes a rigorous PTA model to account for fracture closure combined with fracture face skin for single and multistage hydraulic fractures with uniform and complex geometries. The solution approach is based on subdividing the domain into three flow regions, matrix, damage zone, and hydraulic fracture (HF). The proposed model is verified extensively using a commercial simulator and other less comprehensive models from the literature. The pressure response in fractured wells with stress-sensitive fractures is analyzed at early, middle, and late times. In each flow regime, we identify pressure signals to detect fracture closure by incorporating fracture closure and skin effects. Results show that the fracture face skin has a significant effect on fracture performance as it introduces an additional pressure drop that triggers an earlier and more pronounced occurrence of fracture closure. We proposed a semi-log approach to identify fracture closure for low compressible fractures and a pseudo-radial simplification to generate late-time response curves. The proposed method serves as a PTA diagnostic tool to detect fracture conductivity degradation due to fracture closure and formation damage.

Impact of emergency drawdown in off-stream brackish reservoirs – The case of La Loteta dam in Spain

• Off-stream reservoirs produce changes in water regime to diversion catchments. • Off-stream reservoirs in saline soils enrich the ion concentration in dammed waters. • Emergency drawdown at off-stream brackish reservoirs can have meaningful impacts. • Extension and duration of the flood and physicochemical changes are meaning impacts. • Conductivity exceedance probability curves allow comparison and impact assessment. Reservoirs are the main component of regulation of water resources in basins. Off-stream reservoirs are a particular solution where water is stored in a secondary catchment other than the basin that produces the water resource. This under certain conditions can modify the water regime of the downstream secondary catchment. Although uncommon, one of the reservoir management operations is emergency emptying in the event of possible incidents that could put proper reservoir management at risk. One of the environmental requirements of the drawdown operation of reservoirs is the study of environmental impacts in the event of a complete discharging event from a full reservoir state, given the huge amount of water to be emptied and the duration of the operation, which can last for days. Logically, the impact will be greater when it comes to diversion basins. It is imperative to evaluate the physical impact of prolonged flooding in downstream areas, especially in areas of special ecosystem sensitivity. Additionally, on certain occasions, a physicochemical impact can be produced on flooded areas when the chemical composition of the discharged water differs from the usual concentrations. Exceedance probability curves for conductivity allow identification and assessment of potential impacts of off-stream reservoirs. This article presents a practical case assessment of the impact of an off-stream reservoir located in evaporitic soils with a high content of salts increasing the chemical concentration of stored water that is distributed in different compositional strata. The emptying is carried out on a wetland with important ecological value, and the impact of extension and duration of the flood on the wetland are studied, as well as exposure to the presence of water with different chemical concentrations over the time the incident lasts.

Multiphase Flow Meters Targeting Oil & Gas Industries

In oil fields, multiphase flow meters (MPFMs) yield important data for proper reservoir management to maximize the oil-gas production throughput. MPFMs are also required in downstream industries such as refineries to monitor the quality of the end product and in power generation to estimate the amount of wet steam, which if its flow rate is high may damage the blade’s turbines. For decades, radioactive γ-ray-based MPFM remains the most widely used and reliable device, especially for a high gas void fraction (GVF), which is however not safe and hazardous. This has prompted researchers to suggest other alternative technologies, among which some were successfully assessed either in multiphase flow loops or even in oil-gas fields. Most of these technologies still can’t operate for all flow conditions and are relatively expensive hindering their wide industrial deployment. This review paper presents the most recent findings in multiphase flow metering and the main research challenges encountered in each of them. Important and significant research works are cited in an attempt to provide a reasonable cross-section of various techniques. The paper can be useful for either a fresh researcher in the area or for a skilled R&D engineer involved in the design of a MPFM.

Practical Reservoir-Management Strategy To Optimize Waterflooded Pools With Minimum Capital Used

SummaryIn this consistently low–oil–price environment, where infill drilling and new field developments struggle to meet economic metrics, production optimization continues to be a focus and driver for the industry. Currently, waterflooding contributes significantly to global oil production and is one of the main nonthermal techniques that can be applied to increase pool recovery. Although proper reservoir management of assets under waterflood (WF) is critical to reaching the highest recovery factor (RF) possible, it is difficult to achieve and maintain given the inherently dynamic nature of the production mechanism. Further, to achieve optimal reservoir management while providing the opportunity to leverage alternative enhanced–oil–recovery (EOR) technology, the existing subsurface and surface infrastructure should be fully optimized. Optimizing the subsurface and surface infrastructure in parallel with achieving optimal reservoir management will result in higher capital efficiency while improving key economic metrics such as operating costs (Opcost); reserves–replacement ratio; depreciation, depletion, and amortization; and overall earnings. Given the existing challenges that include reservoir–conformance problems, lack of reservoir energy, excess fluid production, wellbore/pipeline–integrity issues, and infrastructure constraints, how to fully optimize the current infrastructure while achieving optimal reservoir management in parallel is the main question and challenge.Husky Energy's medium–oil–reservoir–management strategy has been highly successful in reinforcing WF as a sustainable long–term recovery method. In this paper we will present a practical workflow to tackle the challenges highlighted by using a systematic reservoir/production–engineering approach with minimum additional capital expenditure (Capex). First, a robust framework was developed to answer three main questions: What is happening?, Why is it happening?, and How can it be improved? Then, a comprehensive dynamic surveillance methodology, consisting of both numerical and analytical techniques and a 10–step workflow for optimizing a WF project, is discussed. This is followed by the results achieved by using this strategy in three WF fields: the Wainwright Sparky, Wildmere Lloydminster, and Marsden–Manitou Sparky pools in the Lloydminster oil block. The positive effect that this reservoir–management process has had on all key financial metrics will be discussed. As an example, since the beginning of the optimization initiative, the Wainwright and Wildmere pool production has increased 21 and 23%, respectively, and the Opcost has decreased by 33 and 42%, respectively. Further, since implementing a similar strategy in 2016 at the Marsden–Manitou WF, its production has increased by 30% and its Opcost has decreased by more than 18%. Finally, we will present a WF–protocol checklist that has been developed as a guideline for engineers who need to optimize pool performance even in a capital–constrained environment.

Semi-analytical transient pressure solution for power-law polymer injection in a vertical well

Enhanced Oil Recovery (EOR) is a process that extends reservoir life through field operations that aim to increase reservoir displacement efficiency. Injection of polymeric solutions, which is a chemical EOR process, improves sweep efficiency by decreasing the mobility of the injected fluids. One challenge in polymer flooding is to model the non-Newtonian rheological behavior of the injected solutions due to the complex interdependence between fluid flow velocity, fluid viscosity and shear rate. Proper reservoir management requires a thorough understanding of non-Newtonian fluid flow behavior through porous media, thus the need for new and improved mathematical models that describe the transient pressure behavior in wells. In this work we consider the flow of non-Newtonian pseudoplastic fluids in homogeneous isotropic porous media. To describe the rheological polymer behavior, we used the well-known power-law model, which leads to a nonlinear problem. In this paper, a novel semi-analytical solution is obtained by combining spatial domain discretization with pseudotime, so the flow problem is rewritten as a system of linear equations in Laplace domain. We also presented a variation of the proposed solution by assuming a pseudostationary behavior of the non-Newtonian velocity. Both approaches are compared to previously published approximated analytical solutions. One interesting aspect of our work is that it can be extended to more realistic polymer rheological models.

Inference of near-borehole permeability and water saturation from time-lapse oil-water production logs

The conventional interpretation of production logs (PL) acquired in time-lapse mode helps petrophysicists to detect the advancement of fluid contacts in the near-borehole region. Without inclusion of a dynamic reservoir model, conventional time-lapse interpretation remains limited to describing time variations of fluid inflow rates produced from or injected into fluid-producing rock formations. However, proper reservoir management requires quantifying depth variations of near-borehole properties (e.g., formation damage and fluid saturation) over time to construct reliable field-scale reservoir models.This paper develops a new borehole-formation fluid flow model capable of simulating oil-water production measurements acquired from vertical and deviated boreholes. We implement an iteratively coupling flow algorithm to explicitly interface a borehole fluid flow model to a reservoir multiphase flow simulator. The specific application considered in this study invokes the coupled borehole-formation fluid flow model to estimate near-borehole permeability and water saturation from time-lapse oil-water production measurements.Borehole fluid flow simulation is based on an isothermal two-fluid formulation that applies separate mass and momentum conservation equations to the oil and water phases. When solving momentum conservation equations, we compute interfacial drag and buoyant forces based on the assumption of spherical oil or water droplets with negligible interfacial mass transfer. Subsequently, the spatial distribution of droplet diameter associated with the discontinuous fluid phase is dynamically modified to accurately account for variations of slip velocity across fluid-producing layers. Linkage of the borehole and formation fluid flow models is next carried out by introducing additional source terms into the borehole mass conservation equations.In a synthetic reservoir model supported by an infinite-acting aquifer, the coupled flow algorithm integrates production logs acquired in time-lapse mode to construct a near-borehole reservoir model that describes depth variations of skin factor over the elapsed time. Feasibility studies show that the estimated petrophysical properties can be adversely influenced by the large volume of investigation associated with PL measurements. Moreover, undetectable fluid production across low-permeability layers decreases the sensitivity of production logs to layer incremental flow rate, thus increasing estimation uncertainty. Despite these limitations, estimated fluid saturation and permeability across high-permeability layers are within 15% and 20% of the corresponding actual values, respectively. The developed interpretation algorithm additionally integrates well logs and production logs acquired in an oil-water field example to construct a PL-calibrated near-borehole reservoir model. Results enable (a) the differentiation of low-permeability layers from highly-damaged formations, (b) the identification of layers accountable for high water production, and (c) the quantification of the added value of remedial workover operations to isolate water-producing layers. In addition, the coupled model is used to study sensitivity of production logs to near-borehole petrophysical properties. We show that production logs are mainly sensitive to formations’ absolute and relative permeabilities, water saturation, and pressure.

Production Data Analysis in a Gas-Condensate Field: Methodology, Challenges and Uncertainties

Production data analysis techniques have been widely used for estimating reservoir properties such as gas in place and average pressure. Knowledge of this information is crucial for proper reservoir management. The present study discusses the roadmap, challenges and uncertainties for analyzing production data in an Iranian gas-condensate offshore field. This work is an integrated study involving the quality check of production data, platform process simulation, orifice simulation, modeling choke performance, well modeling, and Rate Transient Analysis (RTA). The study is an inverse analysis which starts from production platform and continues down to the reservoir. To perform data analysis, we propose five general steps which are: Data gathering/extraction/quality check, well rate determination, well bottom hole pressure estimation, layer rate allocation, and reservoir property estimation. In this study, these steps are discussed elaborately. Furthermore, challenges of each step are presented and discussed. In addition, the required input and also missing data for each step is mentioned. Also, to cope with lack and/or uncertainties of data, feasible solutions are proposed for the current field situation as well as future developments. This paper can help petroleum engineers to know where to start and how to proceed to get to the final step of the analysis, i.e. estimating field gas in place. It also provides insights to challenges and uncertainties of the production analysis in gas-condensate fields.

Technical Note: Initial assessment of a multi-method approach to spring-flood forecasting in Sweden

Abstract. Hydropower is a major energy source in Sweden, and proper reservoir management prior to the spring-flood onset is crucial for optimal production. This requires accurate forecasts of the accumulated discharge in the spring-flood period (i.e. the spring-flood volume, SFV). Today's SFV forecasts are generated using a model-based climatological ensemble approach, where time series of precipitation and temperature from historical years are used to force a calibrated and initialized set-up of the HBV model. In this study, a number of new approaches to spring-flood forecasting that reflect the latest developments with respect to analysis and modelling on seasonal timescales are presented and evaluated. Three main approaches, represented by specific methods, are evaluated in SFV hindcasts for the Swedish river Vindelälven over a 10-year period with lead times between 0 and 4 months. In the first approach, historically analogue years with respect to the climate in the period preceding the spring flood are identified and used to compose a reduced ensemble. In the second, seasonal meteorological ensemble forecasts are used to drive the HBV model over the spring-flood period. In the third approach, statistical relationships between SFV and the large-sale atmospheric circulation are used to build forecast models. None of the new approaches consistently outperform the climatological ensemble approach, but for early forecasts improvements of up to 25 % are found. This potential is reasonably well realized in a multi-method system, which over all forecast dates reduced the error in SFV by ∼ 4 %. This improvement is limited but potentially significant for e.g. energy trading.

Dilema ético y epidemiológico sobre el tratamiento de perros para la leishmaniasis visceral en América Latina

In the Americas there are between 4,500 and 6,800 annual cases of severe visceral leishmaniasis, and mortality is estimated to range between 7 and 10%. However, underreporting and subclinical infections mask the real epidemiological importance of visceral leishmaniasis. Control efforts, which have typically focused on insecticide spraying of sand fly vectors and dog culling, have yielded disparate results. Nevertheless, thousands of dogs are sacrificed each year in countries endemic for visceral leishmaniasis. Additionally, current guidelines of leishmaniasis control programs have banned dog treatment with drugs of human use while therapy with other drugs resulted in high rates of relapses. Society requires that control programs take a more humanitarian approach aimed at limiting dog culling. There is an urgent need to promote responsible dog-ownership and support research on: a) novel veterinary therapies, b) low-cost molecular diagnosis of canine visceral leishmaniasis, and c) determination of dog infectivity threshold for proper reservoir management.

Ethical and epidemiological dilemmas in the treatment of dogs for visceral leishmaniasis in Latin America.

In the Americas there are between 4,500 and 6,800 annual cases of severe visceral leishmaniasis, and mortality is estimated to range between 7 and 10%. However, underreporting and subclinical infections mask the real epidemiological importance of visceral leishmaniasis. Control efforts, which have typically focused on insecticide spraying of sand fly vectors and dog culling, have yielded disparate results. Nevertheless, thousands of dogs are sacrificed each year in countries endemic for visceral leishmaniasis. Additionally, current guidelines of leishmaniasis control programs have banned dog treatment with drugs of human use while therapy with other drugs resulted in high rates of relapses. Society requires that control programs take a more humanitarian approach aimed at limiting dog culling. There is an urgent need to promote responsible dog-ownership and support research on: a) novel veterinary therapies, b) low-cost molecular diagnosis of canine visceral leishmaniasis, and c) determination of dog infectivity threshold for proper reservoir management.

Application of Integrated Reservoir Studies and Techniques To Estimate Oil Volumes and Recovery—Tengiz Field, Republic of Kazakhstan

Summary Recent technical studies and probabilistic techniques have been integrated to build reservoir models for Tengiz field. Tengiz is one of the deepest supergiant oil fields in the world and is on the shore of the Caspian Sea within the Republic of Kazakhstan. Knowledge of the uncertainties inherent in oil recovery is a key to proper reservoir management of this important oil field. Probabilistic techniques gave insights into the importance and ranking of key reservoir uncertainties. This ranking is used to reduce reservoir uncertainties and to guide reservoir management activities. A structured Monte Carlo Technique has been used to construct several thousand static models of Tengiz field. Construction of Monte-Carlo models is fast and allows the impact of key uncertainties to be explored. Static reservoir uncertainties investigated include wireline log calibration, structural elevation, geostatistical parameters (such as variogram length), water saturation, and location of the boundary between facies intervals. Investigating the uncertainty in the dynamic performance of the model is computationally intensive. Experimental design techniques were used to minimize the number of computationally expensive simulation runs. Key dynamic variables investigated include: oil in place (OIP), gas/oil relative permeability, permeability enhancements, vertical-to-horizontal permeability ratio, well productivity, the water/oil contact (WOC) depth, and production capacity. The methodology for generating the range of possible outcomes for some development scenarios in Tengiz is discussed here. The application of Monte Carlo and experimental design techniques to identify the high impact static and dynamic parameters is reviewed. The construction of a probabilistic distribution of OIP and recoveries is demonstrated for one development alternative for Tengiz field. This study found that for this development alternative, the OIP, gas/oil relative permeability, and ratio of vertical to horizontal permeability have the greatest impact on the estimated oil recoveries.

Poisson dampening factor

Reservoir discrimination and characterization for proper lithology and fluid-content distribution is a must for proper reservoir management. Seismic inversion methods using variation of amplitude with offset (AVO) are regularly used in differentiating lithology along with its fluid content. Acoustic impedance (AI), shear impedance (SI), and density (ρ) are the fundamental rock properties often derived using AVO equations. The AI and SI estimates are more stable as compared to the density estimate that remains unstable because of its dependence on far-angle amplitude information. Various attributes, e.g., lambda-rho, mu-rho, elastic impedance, Poisson's ratio etc., derived from these inversion results are routinely used to discriminate lithology along with its fluid content. A new approach using Poisson dampening factor (PDF) attribute, derived using AI and SI values and making density estimate intrinsic within it, is applied and found to improve reservoir delineation and description.

Multi-attribute seismic volume facies classification for predicting fractures in carbonate reservoirs

Poststack seismic attributes are beginning to be routinely utilized in the analysis of 3D seismic data for both reservoir development and exploration targets. In addition to conventional geologic and engineering data, seismic attributes can provide valuable insight into how carbonate reservoirs are fractured. Optimized oil production in one prolific Jurassic carbonate reservoir in Saudi Arabia can be affected by fracturing (Pham and Ali, 2003). Proper reservoir management considers that reservoir fluids move differentially along these natural migration pathways. The detailed and accurate mapping of the distribution and extent of these fractures is important for reservoir management. New types of seismic volumetric attributes and better integration of geophysical, geologic, borehole, and engineering data are being adopted to meet this challenge. Volumetric seismic attributes computed from 3D seismic data are being used to map and interpret small faults and fractures that may affect fluid flow. These fractu...

The Clogging Capacity of Reclaimed Wastewater: A New Quality Criterion for Drip Irrigation

The paper proposes a new water quality criterion for the evaluation of the water potential to clog screen filters which protect drip irrigation systems. This additional parameter is required by the increasing use of reclaimed wastewater for drip irrigation. A filtrability test which simulates actual clogging processes is used to analyze reservoirs receiving different portions of reclaimed wastewater (0 to 100 %) and the use of fish to reduce the particle content of water. The study demonstrates the suitability of the filtrability test to measure and analyze the clogging capacity of irrigation water, and the possibility to reduce clogging problems by proper reservoir management.

Development and Implementation of a Reservoir Management Plan

Proper reservoir management is a key to success when operating mature oil fields in Kansas and the mid-continent region. Many oil fields are at their economic limit and risk being plugged and abandoned if proper reservoir management techniques are not used. This paper describes the development and implementation of a reservoir management plan in the Zenith field. The Zenith field in central Kansas produces from a complex composite set of reservoirs and has had poor secondary oil recovery efficiency. The developed plan consists of five basic steps which involve (1) database development, (2) volumetric and data analysis, (3) field testing, (4) field work to improve operations and economics, and (5) reservoir simulation to better characterize the reservoir and predict the optimum recovery process. These steps are placed in the general order in which they were implemented; however, most of the steps were ongoing throughout the study. This paper emphasizes the importance of reservoir description in reservoir management. The methodology of field testing, personal computer mapping, and reservoir simulation is described along with a prediction of the optimum recovery process.

Design, Fabrication, Hookup, and Commissioning of North Cormorant Topside Facilities

Summary The North Cormorant platform in the North Sea was built and commissioned within budget and ahead of schedule to a high standard of quality. Some of the factors relating to the topside facilities that helped achieve this successful result are described for each of the design, procurement, fabrication, hookup, and commissioning phases. Of key importance was careful attention to the project objective and to planning, control, organization, people, and contracting methods. Some recommended improvements for a future project also are addressed. Introduction The Shell/Esso North Cormorant platform went into production in Feb. 1982, less than 3 years after fabrication production in Feb. 1982, less than 3 years after fabrication started and 9 months after the platform jacket was launched (see Table 1). During this process, several new records and "firsts" for the North Sea oil industry were set, but most important perhaps were the records of cost containment and schedule achievement without any sacrifice in quality of the finished product. It is believed that new standards of efficiency and economy have been attained. The piled steel platform accommodates a combined drilling and production operation. Provision is made for 40 well slots and a number of J-tubes to permit subsea production/injection development should it be required production/injection development should it be required later. The facilities are designed to process a crude throughput of 180,000 B/D [28 600 m3/d] and a water treatment and injection rate of 220,000 B/D [35 000 m 3 /d]. Crude oil is exported at 90 psi [621 kPa] through a 20-in. [5 1 -cm] pipeline to Cormorant A and thence into the Brent System pipeline; a 10-in. [25-cm] pipeline ties the platform to the western leg of the Far Liquids and Associated Gas System (FLAGS) for export of sales gas. Accommodation is provided in a living quarters block with 124 cabins to give maximum bed occupancy of 240 men, and the quarters are surmounted by a landing pad designed for Chinook helicopters. The operating weight of all topside facilities is 17,000 U.K. tons [864 Mg] which includes 5,500 U.K. tons [279 Mg] for the single drilling rig with maximum derrick pull and a full complement of consumables. This operating weight is substantially lower than achieved to date elsewhere in the North Sea for comparable platform capabilities. This paper describes methods adopted to contain costs and meet schedules in the interests of the project objective, which was to maximize the economic return from the development with due consideration for proper reservoir management, safety, and quality standards. The paper specifically addresses the topside facilities, and it complements two other papers one reviewing the project as a whole and the other addressing the platform substructure. The work phases are covered from development of the design concept through offshore hookup and commissioning. Several new approaches were adopted in the course of executing the project, and these are explained where there is potential application for future projects. Inevitably, improvements could have been made to achieve even better results, and some of these also are explained. Design Concept The chosen method of development of the North Cormorant field was installation of a single fixed platform located centrally in the field and supported at a later date, if necessary, by subsea wells to tap the extremities of the reservoir beyond the reach of platform wells. The first phase was to establish the design concept for the topside phase was to establish the design concept for the topside facilities on which to carry out the detailed design and engineering. The dominant considerations in establishing the design concept were, as for all phases of project execution, cost, schedule, and quality. Therefore, particular emphasis was given to separating the true needs for an operable and safe facility from the desirables, which are not strictly necessary. Appraisals were based on economic return and denied if there would be no positive contribution. Operational flexibility and facility maintenance were key considerations, for the former can affect production uptime and the latter maintenance costs and, at worst, production uptime, too. Efficiency and speed of offshore hookup production uptime, too. Efficiency and speed of offshore hookup and commissioning were addressed carefully, since these greatly influence both project costs and the schedule to first production, and were recognized as an area where the greatest gains might be made. In addition, for each tonne of facilities installed there is a requirement for roughly the same weight of structural steel in modules, and both weight and space have a profound effect on the substructure. For operational flexibility, two process trains of three-phase separation (each with two stages) and of gas compression to export pipeline pressure were selected. JPT P. 124

Reservoir Management in South Louisiana With the Pulsed Neutron Log

Summary This paper illustrates through case histories how the pulsed neutron log aids proper reservoir management in strong water drive reservoirs in south Louisiana. An economic analysis performed on the results of remedial operations using pulsed neutron logs clearly shows the benefits of risk reduction when compared with those remedial operations without pulsed neutron logs. Introduction The studied area, southwest of New Orleans (Fig. 1), provides an excellent illustration of reservoir management using the pulsed neutron log. The geologic structures in the area studied consist of deep-seated salt domes, which were delineated by reflection seismograph. The productive sands are of the Miocene and Pliocene ages. As wells go off production, remedial work must be performed either to initiate production in a new interval or to restore production to the same interval. The pulsed neutron log has become an integral part of the remedial work program in the studied area to ensure proper reservoir depletion. The first pulsed neutron log in the area was run in 1964, and since that time the yearly average number of pulsed neutron logs has risen to 35 to 40% of the total number of remedial operations. The log is being used to a large extent in the studied area due to the characteristics of the reservoir drive, which as a whole is a strong water drive. However, several sands exhibit a "bottom water" drive, which results in the coning of water to the perforations. This premature water break through limits the radius of depletion that can be achieved. Since the oil/water contact varies throughout the reservoir according to the extent of coning and amount of production, pulsed neutron logs are the most efficient means of monitoring the depletion of the reservoir and the movement of the oil/water contact. Other applications of the pulsed neutron log have been to ensure the proper depletion of membered sands to aid in the evaluation of low-resistivity sands, to identify the sealing nature of small faults, and to evaluate the effects of permeability barriers on recovery. Theory Neutron bursts with energy levels of 14 MeV are emitted every 1,000 microseconds. These high-energy neutrons are captured primarily by chlorine but also by the rock matrix, hydrogen, and materials in the wellbore. After capture of the neutrons, fixed-energy-level gamma rays are emitted from the capturing nucleus. It is these gamma rays that are counted during the 1,000-microsecond cycle. The number of capture events is proportional to the number of uncaptured neutrons at any time. Therefore, what is measured is the intensity and the rate of decay of the capture gamma ray flux. Many papers and articles have been written on the subject of evaluating pulsed neutron logs. The water saturation is calculated using this equation: (1) To calculate a quantitative SW, values for porosity, water salinity, shale content, and hydrocarbon type must be assigned or derived from the pulsed neutron log using nearby clean (nonshaly) water sands. After a water saturation has been calculated, a check for possible errors can be made by comparing the water saturation calculated from the pulsed neutron log with the original water saturation of the open hole electric log. A significant difference in these water saturations would indicate an error in calculation or the possibility of a depleted zone. JPT P. 419^