Reservoir Management Plan Research Articles

The Assessment of Sedimentation Problems in Kenyir Hydropower Reservoir, Malaysia

Lakes may take a while to respond to management interventions because of the management implications of incremental development and degradation issues. This includes the requirement for the ongoing participation of key lake basin management institutions and their operations. This study’s objective is to assess the impacts of land use activities along the Kenyir Lake Basin based on the sedimentation problem level. There are a few hydrological methods that are necessary indicators to measure the level of sediment production, such as Total Suspended Solid (TSS), area of sub-catchment, river discharge measurement, and annual sediment load production. The results showed that the sub-catchment of Besar River released the lowest annual average estimation at 3833.70 kg/km2/year, and the sub-catchment of Kenyir River produced the highest annual average estimation at 128,070.86 kg/km2/year for annual sediment load flow produced from tributary rivers into Kenyir Lake. Kenyir Lake Basin’s downstream and midstream regions had higher sediment load values than its upstream regions. This study highlighted the significance of the effects of anthropogenic factors, hydrological, geomorphological, growth, and developmental factors, and climate changes as the key variables attributing to the sedimentation phenomenon along the Kenyir Lake Basin. The construction of a long-term lake or reservoir catchment development and management plan, combined with the formation of a vision and comprehensive strategic plan, are vital components of sound management practice. The efficient implementation of the suggested watershed management programmes depends on the active involvement of all significant catchment stakeholders.

Integrated Data Analysis Illuminates Commingled Smart Water-Injection Well

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 206503, “Implementation and Intermediate Monitoring Outcomes of the First Commingled Updip Smart Water Injection Well in PA-B Platform Piltun-Astokhskoye Offshore Oil and Gas Field,” by Alexander V. Tsarenko, Valentin N. Tarsky, SPE, and Lisa Jane Robson, Sakhalin Energy Investment Company. The paper has not been peer reviewed. _ The objective of the complete paper is to share an evaluation of the background, drilling outcomes, and production and reservoir-pressure effects during 2 years of monitoring the first commingled updip smart water injector drilled in the Piltun area of the Piltun-Astokhskoye offshore oil and gas field in Sakhalin. The authors highlight details of the well-maturation decisions and expectations based on output of dynamic modeling studies. Setting The Piltun area consists of six main reservoir units (XXI-S, XXI-3, XXII-1, XXII-2, XXIII, and XXIV-2) being developed over two fault blocks (Block 1 and Block 2). All reservoirs have aquifers and gas caps, although the volumes, reservoir properties, and productivity of these reservoirs varies considerably, with the XXI-S and XXIV-2 reservoirs having the best rock properties and the highest recovery factors. Updip Water-Injection History In the original field development plan (FDP) created in 2008 and the reservoir management plan created in 2006, the Piltun area was to be developed by rows of commingled vertical downdip and updip water injectors (UDWIs), displacing oil to mid-rim vertical oil producers. However, the original UDWI concept was challenged early in development when the following geological surprises were encountered during drilling of the initial development wells: - The structure was significantly higher than expected at the crest of the field. - Thin, high-permeability (superfacies) layers were encountered in the producers and updip pilot holes. - The injectivity of the downdip injectors was much lower than expected and required an upgrade to the water-injection pumps. The FDP was reassessed in 2011. The design of the UDWIs was changed to long horizontal wells located at the gas/oil contact in the XXI-S, XXII-1, and XXIV-2 reservoirs only. The 2011 FDP assumed that early water breakthrough could be managed by smart-well technology in the oil producers. However, these producers experienced technical failures, and the plan to install smart completions in all mid-rim producers subsequently was aborted. In a 2015 FDP update, the design of the UDWIs was changed to vertical commingled wells equipped with a smart completion type, targeting only those reservoirs where clear incremental recovery and economic benefit was observed.

Improved fixed-point seismic inversion constrained by instantaneous phase

Some subtle reservoirs are hidden in the weak reflection areas and thin layers in seismic profiles, and they cannot be identified easily. Thus, the thin layer interpretation and the subtle reservoir prediction are the essential in reservoir management plan while field development and production stage. To improve the recognition capability in the weak reflection areas and resolution, the fixed-point (FP) algorithm is employed to obtain the inversion results since the conventional FP seismic inversion (CFPSI) is sensitive to the weak changes in seismic signals. However, the CFPSI suffers from low convergence. Therefore, the new iterative equations of pre- and post-stack FP seismic inversion are designed to improve the computational efficiency and convergence. Besides, a new constraint, which is derived from the instantaneous phase of the seismic trace, is also sensitive to the weak changes of the seismic signal. The instantaneous phase constraint is then involved in the objective function, contributing to a significant improvement of identification capability in weak reflection areas and the resolution of inversion. Additionally, the initial model constraint is introduced into the objective function to weaken the multi-solution and noise sensitivity. The synthetic examples demonstrate that the computational efficiency, recognition capability in the weak reflection areas and resolution of the proposed approach are higher than those of the CFPSI. The field examples suggest that the subtle reservoirs and thin layers, which are hidden in the weak reflection areas in the field data, are accurately identified using our method. Thus, the proposed method is useful for improving the recognition capability in weak reflection areas and resolution of the inversion results.

Microseismic and Focal Mechanism Analyses for Structural Interpretation – Muara Laboh Geothermal Field

Microseismic monitoring has been used for gathering subsurface information in Geothermal field as part of reservoir monitoring and management plan. New micro earthquake (MEQ) stations were installed in the Muara Laboh geothermal field in the end of 2019, coinciding with the first operation of Unit-1. They have been continuously used to monitor the MEQ events until now. This paper discusses MEQ data analyses to support the subsurface structural interpretation in the Muara Laboh geothermal field. Geothermal production and injection activities create micro seismicity which is triggered by stress failure in fractures / fault planes due to percolation of fluid within fractures network. Distribution of hypocenter locations and magnitude are analyzed, considering highly operational activities, rock mechanic and slip orientation. There are two micro seismicity clusters observed, namely South and North clusters. The South cluster represents 80% of the total recorded micro seismicity events, having NE – SW trend direction; while the North cluster consists of 10% of the total events, correlated with the NNW – SSE structural trend direction. Focal mechanism analysis explains that micro seismicity observed on extended fault zone in the south is thought to be correlated with the distributed fractured network on the hanging wall of normal fault. It is shown by some micro seismicity swarms identified in the south basin-sidewall fault area. These orientations support the current kinematic model of the Muara Laboh geothermal field derived from the structural geology mapping and borehole image logs.

A Novel Empirical and Deep Ensemble Super Learning Approach in Predicting Reservoir Wettability via Well Logs

Accurately measuring wettability is of the utmost importance because it influences several reservoir parameters while also impacting reservoir potential, recovery, development, and management plan. As such, this study proposes a new formulated mathematical model based on the correlation between the Amott-USBM wettability measurement and field NMR T2LM log. The exponential relationship based on the existence of immiscible fluids in the pore space had a correlation coefficient of 0.95. Earlier studies on laboratory core wettability measurements using T2 distribution as a function of increasing water saturation were modified to include T2LM field data. Based on the trends observed, water-wet and oil-wet conditions were qualitatively identified. Using the mean T2LM for the intervals of interest and the formulated mathematical formula, the various wetting conditions in existence were quantitatively measured. Results of this agreed with the various core wettability measurements used to develop the mathematical equation. The results expressed the validity of the mathematical equation to characterise wettability at the field scale. With the cost of running NMR logs not favourable, and hence not always run, a deep ensemble super learner was employed to establish a relationship between NMR T2LM and wireline logs. This model is based on the architecture of a deep learning model and the theoretical background of ensemble models due to their reported superiority. The super learner was developed using nine ensemble models as base learners. The performance of nine ensemble models was compared to the deep ensemble super learner. Based on the RMSE, R2, MAE, MAPD and MPD the deep ensemble super learner greatly outperformed the base learners. This indicates that the deep ensemble super learner can be used to predict NMR T2LM in the field. By applying the methodology and mathematical formula proposed in this study, the wettability of reservoirs can be accurately characterised as illustrated in the field deployment.

Characterization of carbonate reservoir using post-stack global geostatistical acoustic inversion approach: A case study from a mature gas field, onshore Pakistan

Seismic characterization of carbonate reservoir is a challenging undertaking for geo-scientists due to their complex depositional settings, internal structure, and pervasive diagenetic history. Results from post-stack deterministic inversion are band limited due to missing low and high frequencies in the wavelet, which generally poorly resolve thin beds which are of prime interest in reservoir characterization of a mature gas field and help locate prolific infill drilling locations. In this paper, we employed and compare performance of Post-stack Global Geostatistical Acoustic Inversion (PGGAI) with the Post-stack deterministic inversion to better characterize thin beds and maximize reservoir potential of Eocene (S1) carbonate reservoir from a mature gas field lying in the Middle Indus Basin, onshore Pakistan. We discovered that both the inversion methods derive a broad-band acoustic impedance from the band-limited post-stack seismic data. The results show that PGGAI produced high resolution (thin bedding) p-impedance attribute and mapped spatial distribution variations along with uncertainty quantification hitherto not possible from standard deterministic inversion approach and therefore result in possible increasing confidence in the interpretation. Furthermore, high resolution p-impedance attribute from PGGAI served as input for porosity prediction using probabilistic neural networking (PNN). Stepwise validation of PNN provided high precision porosity estimation which showed significant amount of correlation between the input attribute property. In addition, high resolution volumes offered optimistic scenarios of the distribution of impedance and porosity lateral extent and helpful in determining perspective zones and proved useful in designing the subsequent reservoir management plan and proposing future infill drilling locations.

End-Point Model for Optimization of Multilateral Well Placement in Hydrocarbon Field Developments

Drilling cost is one of the most critical aspects in the reservoir management plan. Costs may exceed a million dollars; thus, optimal designing of the well trajectory in the reservoir and completion are essential. The implementation of a multilateral well (MLW) in reservoir management has great potential to optimize oil production. The object of this study is to develop an integrated workflow of end-point multilateral well placement optimization integrated with the reservoir simulator supported by artificial intelligence (AI) methods. The paper covers various types of MLW construction, including: horizontal, bi-, tri-, and quad-lateral wells. For quad-lateral wells, the capital expenditure is highest; nevertheless, acceleration of oil production affects the project’s NPV (net present value), indicating the type of well that is most promising to implement in the reservoir. Tri- and quad-lateral wells can operate for 12.1 and 9.8 years with a constant production rate. The decreasing hydrocarbon production rate is affected by reservoir pressure and the reservoir water production rate. Other well design patterns can accelerate water production. The well’s optimal trajectory was evaluated by the genetic algorithm (GA) and particle swarm optimization (PSO). The major difference between the GA and PSO optimization runs is visible with respect to water production and is related to the modification of one well branch trajectory in a reservoir. The proposed methodology has the advantage of easy implementation in a closed-loop optimization system coupled with numerical reservoir simulation. The paper covers the solution background, an implementation example, and the model limitations.

Reservoir Management Analysis of Water Quality and Pollution Load in Jakarta

Jakarta as the Capital City of Indonesia has a high level of population growth. Hence, urban infrastructure movements have developed automatically. This implies some open spaces such as reservoirs are poorly managed. Reservoirs as one of blue open spaces (BOS) can function as a water catchment area to mitigate flooding during the rainy season, and drought during the dry season. Combating the reservoirs, the DKI Jakarta Government has taken action by revitalizing several untreated reservoirs. Therefore it is necessary to assess the water quality and pollution load on the reservoir. One of the supporting factors to maintain water quality and pollution load of the reservoir is to develop a robust reservoir management plan to revitalize their sustainable function. The reservoir management plan is based on the assessment of water quality and pollution load on three reservoirs in Jakarta. The formulation of reservoir management plan starts with evaluating the reservoir water quality using the Storet Method. The results of reservoir water quality based on physical parameters are in the range of class A (very good category) and B (Good Category), while based on chemical and biological parameters are in the range of class C (quite good category) and D (bad category). The results obtained from all parameters of reservoir water quality evaluation are in class D (bad category) for the three reservoirs. Further analysis was identifying the level of pollution by using the pollution index method. The result shows those three reservoirs are on heavily polluted level. Based on SWOT analysis for water quality and pollution load of the reservoir, the total score for both internal and external factors are 2.39 and 2.47, so it shows V quadrant that indicates hold and maintain strategy position and produce 8 alternatives as the result.

Predictive modeling of thermogenic methane hydrate formation and geobody distribution – Results from numerical simulations

Reservoir characterization of thermogenic gas hydrates have so far been limited to seismic mapping, well log interpretation, and lab scale experiments, with numerical modeling mostly focusing on gas production from hydrates. What is unknown however is the hydrate saturation at the sub-seismic and interwell scales. This study uses numerical simulations for predictive modeling of hydrate formation and geobody distribution using TOUGH + Hydrate. Results indicate that the flow of gas is buoyancy and advection dominated, and affects hydrate formation rate and saturation distribution. Geological controls such as fault angles, stratigraphic thickness, permeabilities and permeability anisotropies and contrasts with adjacent formations significantly impact distribution of hydrate saturation, and geobody shape. Hydrates form in both high and low porosity rocks. While full-scale reservoir modeling is contingent upon the availability of detailed reservoir and fluid data, this study underscores the importance of using numerical modeling tools for quantitative predictive modeling and reservoir characterization of hydrate reservoirs for better resource estimation, well-placement decisions, reservoir management and production planning.

Integrating Multi-Disciplinary Data for Building Fit-For-Purpose 3D Mechanical Earth Model

Understanding geomechanics influence early in the field development phase facilitates reservoir management planning. To capture complex geology and associated field development, a 3D Mechanical Ear...

The effect of forest rehabilitation on runoff and hydrological factors in the upstream area of the Ubolratana Reservoir in Thailand

Abstract Thailand's forests in reservoir watershed areas are declining at an alarming rate due to land use demand. Reforestation aiming at maintaining optimum forest areas becomes a top priority in reservoir management planning which needs hydrologic responses as inputs. This study aims at measurable assessment of the changes in hydrologic responses of the Ubolratana Reservoir in northeastern Thailand due to increasing forest areas. The assessment was done in two parts: (i) forest areas by CA Markov model and (ii) rainfall–runoff by Soil and Water Assessment Tool (SWAT) model. Assessment results indicate that increasing forest areas cause a decrease of runoff, peak flow, and hence, inflow volume into the reservoir. The optimum size of forest area was found to be much larger than the existing size, confirming the need for existing reforestation. Additional benefits of pursuing reforestation include less erosion and sedimentation which are required in reservoir management planning.

Management of Tropical River Basins and Reservoirs under Water Stress: Experiences from Northeast Brazil

Due to global warming, a reduction in available water will occur in many watersheds and conflicts concerning water use will take place. This situation is already typical in semi-arid areas, where many reservoirs have been constructed for water storage. Increased energy demands and climate change have led to severe and increasing pressure on aquatic systems. Today, the environmental policies of many countries, such as Brazil, give priority to constructing new reservoirs for hydropower use, and an adopted reservoir and river basin management plan must minimize environmental impacts. Moreover, the production of energy plants will promote more requirements for new dam projects. The Itaparica reservoir is 30 years old, located in the São Francisco river in Northeast Brazil, and is the focus of an environmental study. The article focus of investigations is on the environmental and social impacts after the construction of Itaparica reservoir, governance difficulties, and adopted actions to minimize those impacts. Significant environmental impacts are recognizable, such as increased sedimentation in the inflow area, damage to the lakeshore zone by operational water level variation, water losses by evaporation and infiltration, and degradation of inundated vegetation. Furthermore, a trophic upsurge has been registered with severe eutrophication processes, such as the occurrence of cyanobacteria, oxygen deficit in the hypolimnion, and mass development of macrophytes (Egeria densa). With the creation of the dam there was compulsory displacement of the population of the municipalities around Itaparica reservoir with consequent difficulties of adaptation in the new spaces. Furthermore, there was de-structuring of social relation networks, loss of arable land and improvements, and small and insufficient indemnities for land. In this context, concepts for an advanced reservoir management under consideration of water scarcity are presented and discussed. This study aims to contribute to sustainable reservoir management

Integrating multi-disciplinary data for building fit-for-purpose 3D mechanical earth model

Understanding the influence of geomechanics early in the field development phase facilitates reservoir management planning. To capture complex geology and associated field development, a 3D mechanical earth model (3D MEM) with finite element method (FEM) approach was selected to analyse the geomechanical-related risks associated with two fields in the North West Shelf, Australia. The 3D MEMs were constructed using geological static models, and seismic-derived horizons and faults. The 3D properties were propagated based on core-calibrated 1D properties and controlled by stratigraphy, 3D facies and seismic inversion volumes. The FEM was used to calculate the equilibrium of stresses and strains within the 3D MEMs. The 3D properties and pre-production stresses were validated in blind test wells before forward modelling. The 3D MEMs were linked to the dynamic reservoir models to capture the pressure evolution throughout the field lifecycle. The results were used to analyse the risks associated with compaction, subsidence, fault instability, completion integrity and drilling stability of infill wells through depleted reservoirs. The results provided insight in managing the risk early in field development stage. The study’s largest challenge was integrating a large volume of data to ensure that the structural complexity and rock heterogeneity were captured and consistent with the geological understanding of the field. A multi-disciplinary team of earth scientists and reservoir and geomechanics engineers worked together, and the value of data integration, good communication and teamwork were key success factors. Lessons learned and best practices were captured throughout the study and provided valuable feedback for future works.

Relative Effects of Mortality versus Emigration on a Reservoir Walleye Population

AbstractMechanisms influencing population fluctuations are an important component of fisheries ecology. Fishes can be lost from populations due to mortality or emigration, potentially resulting in population declines. Although emigration in large, open‐river systems is well recognized, emigration may also occur in reservoirs that are conventionally considered closed systems, potentially resulting in important population‐level effects. However, little is known regarding annual variation in reservoir emigration rates, the influence of reservoir discharge on emigration, or the influence of emigration compared to mortality in regulating populations. We used tagging data collected from 1990 to 2000 to evaluate the effects of various discharge patterns on reservoir Walleye Sander vitreus emigration and the importance of emigration versus mortality for regulating the population. Walleye annual mortality was variable, ranging from 0.05 to 0.46, but was similar between sexes. Walleye emigration ranged from 0.02 to 0.26 and was best explained by variation in mean April discharge and the number of days discharge exceeded 14 m3/s. Emigration rates were similar to mortality rates in 5 of 9 years but lower than mortality rates in the remaining 4 years, suggesting that both processes likely contribute to fluctuations in population abundance. Combined, our results indicate that wet years requiring prolonged reservoir discharge, even at relatively low rates, result in increased Walleye emigration, with up to 26% of the population emigrating. Larger, more severe precipitation events are predicted to occur in the future as a result of climate change, thus altering reservoir management plans and threatening the sustainability of reservoir fisheries.

Stress estimation in reservoirs using an integrated inverse method

Estimating the stress in reservoirs and their surroundings prior to the production is a key issue for reservoir management planning. In this study, we propose an integrated inverse method to estimate such initial stress state. The 3D stress state is constructed with the displacement-based finite element method assuming linear isotropic elasticity and small perturbations in the current geometry of the geological structures. The Neumann boundary conditions are defined as piecewise linear functions of depth. The discontinuous functions are determined with the CMA-ES (Covariance Matrix Adaptation Evolution Strategy) optimization algorithm to fit wellbore stress data deduced from leak-off tests and breakouts. The disregard of the geological history and the simplified rheological assumptions mean that only the stress field, statically admissible and matching the wellbore data should be exploited. The spatial domain of validity of this statement is assessed by comparing the stress estimations for a synthetic folded structure of finite amplitude with a history constructed assuming a viscous response.

A Simulation Approach for Screening of EOR Scenarios in Naturally Fractured Reservoirs

Undoubtedly, plenty of hydrocarbon sources are located in carbonate rocks, particularly those which are naturally fractured that is still needed to study their characterization, because of their complex and unconventional behavior. Therefore, applying any processes that cause Enhancing Oil Recovery (EOR) from Naturally Fractured Reservoirs (NFR) seems necessary and useful. However, selecting the best developed scenario is always challenging. Screening criteria would determine the possibility of implementing an EOR process. While, utilizing trade marketing simulators can solve this problem. Moreover, simulation can evaluate other parameters such as water cut and gas-oil ratio. In this research, an aquifer-supported Iranian NFR with two parts that are separated to each other with a shale layer is considered in order to select the best EOR scenario. The fluid model is created using PVTi software. Various production scenarios included natural depletion, water flooding, miscible carbon dioxide injection, water-alternating-gas (WAG) injection, simultaneous water- alternating-gas (SWAG) injection, hybrid injection, and gas recycling are simulated in ECLIPSE Compositional (E300) and their recovery factor recorded as the target parameter. The developed scenarios are designed in a way that gives the optimized results, i.e. higher recovery factor, less water cut as well as the less gas-oil ratio. As a result, SWAG shows better conditions and is recommended for the further studies of the reservoir management plan in the future. Also, the role of the aquifer in the SWAG scenario is positive by creating a natural WAG in addition to the SWAG. Additionally, the average reservoir pressure through fractures reduces less in the SWAG than the other Scenarios, the oil and gas production rate reduce less in the SWAG and SWAG/ miscible gas respectively than the other scenarios. The maximum and the minimum water cut are related to the water flooding and SWAG, respectively.Finally, the simulation approach of EOR screening in NFR is better than other approaches, from the perspective of economic issues as well as the simplicity of the methods.

Fluid flow characteristics of Bandanna Coal Formation: a case study from the Fairview Field, eastern Australia

ABSTRACTFluid flow characteristics of cleat systems in coalbed methane reservoirs are crucial in reservoir management and field development plans. This paper aims to evaluate the cleat system properties including cleat porosity, permeability, and aperture as well as the impact of permeability growth on production performance in the Bandanna Coal Formation of the Fairview Field, eastern Queensland. Owing to the presence of bad hole conditions and poor core recovery of the coal intervals, the petrophysical well logs and laboratory measurements cannot be used as a source of information for this purpose. Hence, a new approach is employed that utilises early water production data to measure water in place and absolute permeability of the coal. In addition, micro-computed tomography (CT) scan method is used to investigate the cleat system that is preserved in a core sample and results are compared with the ones obtained by analysis of production data. Cleat system evaluation by analysis of production data and micro-CT scan technique provides a comprehensive approach that brings confidence in measurements and helps to obtain cleat properties at the sufficient scale for reservoir engineering purposes. The necessary information including production data and core samples are collected from a dewatering well and the nearby observation well in the study area. Analysis of early water production data (single-phase flow) indicates that coal permeability is 189 mD and the average cleat porosity is approximately 5%. High cleat porosity describes the large volume of water produced over the life of the study well. The 3D model of the fossilised cleat system constructed by the micro-CT scan method reveals that coal is well-cleated and cleat spacing and mean cleat aperture are 4 and 0.136 mm, respectively. The average cleat porosity that is measured by the micro-CT scan method is 5.7%, which is fairly close to the cleat porosity measured by analysis of production data. Production data analysis indicates that effective permeability to gas starts to grow at the midlife of the well and it strongly controls the shape of the production profile. The results of this study help in future field development and infill drilling programs in the Fairview Field and provide important insights into cleat system of Bandanna Coal Formation.

Impact of temporary desiccation on the mobility of nutrients and metals from sediments of Loskop Reservoir, Olifants River

South Africa is prone to droughts and is heavily dependent on stored water resources. Few studies in South Africa have investigated the impact of drought on water quality when rainfall resumes and reservoir sediments are rewet. Other research has shown that several negative impacts may occur with rewetting, including eutrophication, and acidification with increased metal solubility. In this study, the impact of drying and rewetting sediments on the mobility of nutrients and metals is explored using sediments from Loskop Reservoir. Rarely exposed sediments were collected from three sites, dried at 35°C for 36 days, and then rewet under aerobic conditions. Filtered water samples were collected on Days 1, 2 ,4, 7, 11 and 16 following rewetting, and analysed for NH 4 + , NO 3 - , NO 2 - , total N, total P, PO 4 3- , dissolved Al, Fe, Mn, and SO 4 2- . Results were expressed as mass/m 2 , and were compared to reference (non-drought) treatments that were maintained under saturated conditions. Acute toxicity tests were performed using Daphnia magna to establish if toxic effects were associated with changes in water quality following sediment rewetting. Following rewetting, elevated SO 4 2- indicated the mobilisation of acid from sulfide oxidation, with an associated reduction in pH. Nitrification was evident as high quantities of organic N and NH 4 + were initially released, followed by increases in NO 2 - + NO 3 - . Total P increased, but PO 4 3- reduced. This was attributed to complexes formed between PO 4 3- and Fe (FePO 4 ) and Al (AlPO 4 ). Amounts of Fe and Al released were lower following rewetting due to the formation of relatively immobile (hydr)oxides. In contrast, Mn increased substantially reaching maximum values > 2 300 mg/m 2 (14 000 μg/L). There were no acute toxic effects observed to D. magna. This study highlights the potential for acidification, mobilisation of nutrients, SO 4 2- , and Mn following rewetting of reservoir sediments under aerobic conditions. This information may be incorporated into reservoir and catchment management plans in the form of revised water quality guidelines and a better ability to predict how drought impacts water quality in our stored water resources. Keywords : sediment, drought, drying, rewetting, nutrient and metal release, Loskop Reservoir

An efficient approach for optimizing full field development plan using Monte-Carlo simulation coupled with Genetic Algorithm and new variable setting method for well placement applied to gas condensate field in Vietnam

This paper presents an efficient technique to optimize a gas condensate field development plan under economic uncertainties. Many studies have been conducted to optimize development plan but mostly limited to oil field under fixed economic environments and required huge number of simulation runs. It is proved that black oil model can be a reasonable alternative of compositional model to complete field development optimization within acceptable period when reservoir pressure is higher enough than dew point pressure. This study implements Monte-Carlo simulation to Genetic Algorithm to assess economic uncertainties while optimization procedure is being performed and to avoid duplicating whole optimization procedure by changing economic assumptions. An idea for setting optimization variables for well placement is also introduced to reduce required number of simulation runs. A real field application confirms that the technique can be applied to optimize a gas condensate field with contractual gas sales obligation, and the idea plays a key role to find the optimized solution with limited resources by reducing the number of simulation runs required during the optimization procedure. The proposed technique can be applied to optimize not only full field development plan but also reservoir management plan and it will be helpful to improve economics of all kinds of E&P projects under lots of uncertainties.

Estimating hydrologic budgets for six Persian Gulf watersheds, Iran

Estimation of the major components of the hydrologic budget is important for determining the impacts on the water supply and quality of either planned or proposed land management projects, vegetative changes, groundwater withdrawals, and reservoir management practices and plans. As acquisition of field data is costly and time consuming, models have been created to test various land use practices and their concomitant effects on the hydrologic budget of watersheds. To simulate such management scenarios realistically, a model should be able to simulate the individual components of the hydrologic budget. The main objective of this study is to perform the SWAT2012 model for estimation of hydrological budget in six subbasin of Persian Gulf watershed; Golgol, Baghan, Marghab Shekastian, Tangebirim and Daragah, which are located in south and south west of Iran during 1991–2009. In order to evaluate the performance of the model, hydrological data, soil map, land use map and digital elevation model (DEM) are obtained and prepared for each catchment to run the model. SWAT-CUP with SUFI2 program was used for simulation, uncertainty and validation with 95 Percent Prediction Uncertainty. Coefficient of determination (R2) and Nash-Sutcliffe coefficient (NS) were used for evaluation of the model simulation results. Comparison of measured and predicted values demonstrated that each component of the model gave reasonable output and that the interaction among components was realistic. The study has produced a technique with reliable capability for annual and monthly water budget components in Persian Gulf watershed.