Changing the Status Quo: Cases of Production Restoration in Inactive Offshore Oil Wells

The United Arab Emirates oil and gas reservoirs are continuously intersected with a growing number of horizontal wells and longer drains at varying bottomhole static temperatures. This results in a variety of naturally flowing and more challenging wells where stimulation is required for sustainable flow. Hence it became important to not only rely on plain acid systems for production gain, but to also include more sophisticated acid stimulation systems that can provide improved results in more challenging environments where plain acid may be found lacking. These results were recently achieved via the introduction of single-phase retarded acid (SPRA) as well as viscoelastic diverting acid (VEDA) in inactive wells offshore. The application of SPRA and VEDA was subsequent to extensive laboratory testing including core flow tests, solubility tests, and emulsion tendency testing to the performance of these blends against existing acid recipes such as plain HCl and polymer-based diverting acid. These tests proved that a combination of SPRA and VEDA would allow maximizing lateral coverage in heterogenous reservoirs due to the chemical diversion capabilities from thief zones without imposing further damage that polymer-based diverted acids may cause. The combined SPRA and VEDA would also enhance acid wormhole penetration due to the reduced rate of reaction caused by acid retardation. Such tests were supported with software simulations that provided acid dosage, pumping rate, and pumping method sensitives. Proposing SPRA and VEDA at higher pumping rates enabled the delivery of previously unattainable production influx at sustainable wellhead pressures. In addition, 28% acid content typically used for dolomitic reservoirs was considered unnecessary as 20% retarded acid proved sufficient in such environments. This allowed bullheading treatments, which was previously not possible due to the restriction on pumping 28% acid content across wellheads to avoid causing corrosive damage. Other treatment parameters such as volumes, rates, and acid/diverter sequence and ratio were also adjusted for optimal wormhole penetration across all zones using a fit-for-purpose carbonate matrix acidizing modeling software. The success of SPRA and VEDA was clear in post-treatment evaluation for the cases of previously shut-in wells. These wells were able to produce sustainably at the required tubinghead pressure (production line pressure) after unsuccessful attempts to flow prior to stimulation. The novelty of this paper is the assessment between legacy carbonate stimulation results in UAE using plain HCl acid and polymer-based diverting acid (PDA) and using SPRA and VEDA in shut-in or inactive wells. It also highlights the game-changing solutions that suit the increasing challenges observed in offshore inactive wells including well placement, lithology, bottomhole static temperature, and permeability contrast.

Phenothiazines to Treat Alzheimer’s Disease

Current treatments of Alzheimer’s Disease (AD) are largely ineffective and do not address underlying pathophysiological processes. The model organism C. elegans has been successfully used to discover compounds to treat human diseases, some now in clinical trials. To develop novel drugs and explore pathways to treat AD, we took on a forward pharmacological approach with a C. elegans model for AD, completed with studies to expand results to lifespan as well as healthspan. We screened 2560 drugs from the Microsource Spectrum library for their ability to delay proteotoxicity (indicated by paralysis) in an Abeta transgenic C. elegans muscle model of AD (CL2006) in liquid medium. Among the most protective drugs were phenothiazines, which are orally active and cross the blood-brain barrier, desirable properties of drugs to treat AD. 80 phenothiazines congeners were further assessed; 60% were protective in CL2006 worms. 9/20 tested phenothiazines increased lifespan in N2 worms and 2/3 phenothiazines tested promoted significantly higher pharyngeal pumping rates compared with control till day 10 of adulthood in N2 worms. 2 of the drugs were protective in the C. elegans neuronal model of AD. This phenotypic screening approach led to the discovery of potential drugs to treat AD. These phenothiazines protect against Abeta toxicity, and assessment of efficacy to protect against other forms of proteotoxicity are ongoing. These studies suggest the utility of C. elegans to discover drugs to treat human diseases. Future studies will assess molecular mechanisms mediating the protective effects of these compounds.

Laboratory and Numerical Study of Saltwater Upconing in Fractured Coastal Aquifers

This study investigated the saltwater upconing mechanism in fractured coastal aquifers. Head-induced saline intrusion was initiated into three narrow sandbox aquifers containing individual horizontal discontinuities placed on different positions. Subsequently, using a peristaltic pump, freshwater was abstracted from the aquifers’ center, triggering saltwater upconing. Progressively larger pumping rates were applied until critical conditions, resulting in the wells’ salinization, were achieved. Advanced image analysis algorithms were utilized to recreate the saltwater concentration fields and quantify the extent of the saline wedges with a high accuracy. A numerical model was successfully employed to simulate the laboratory results and conduct a comprehensive sensitivity analysis, further expanding the findings of this investigation. The impact of the fractures’ length, permeability and position on the upconing mechanism was identified. It was established that the presence of high permeability discontinuities significantly affected aquifer hydrodynamics. The conclusions of this study could constitute a contribution towards the successful management of real-world fractured coastal aquifers.

Studying the effect of design parameters on riverbank filtration performance for drinking water supply in Egypt: a case study

Riverbank filtration (RBF) is an affordable technique to provide drinking water with adequate quality. The ultimate objective of this study is to facilitate the transferability and application of this sustainable technique in Egypt. In this work, a numerical model was constructed using Groundwater Modeling System (GMS) to study the effect of four design parameters on the RBF performance parameters (i.e., river filtrate portion and travel time) with the aid of MODPATH and ZONEBUDGET. The design parameters were; (1) the pumping rates of the RBF wells, (2) number of operating wells, (3) distance between wells and the river, and (4) the spacing between wells. This study was focused on the hydraulic aspects of the technique. The results demonstrated that; (1) the river filtrate portion exceeds 75% regardless the design conditions. (2) The hydraulic performance of RBF technique is highly controlled by the production capacity of the wells and their positions relative to the surface water systems; the spacing between wells has a minimum effect. Two equations were developed to estimate the river filtrate portion and minimum travel time as functions of pumping rate and distance between the pumping well and the river.

Decision Support for Local Water Authorities in Guantao

Policy selection and implementation rely on monitoring data and technical decision support tools. Monitoring data of Guantao County include groundwater levels at 55 observation wells, pumping rates of 7600 wells, surface water flows, precipitation, and land use in monthly time steps.

Pumping Well Layout Scheme Design and Sensitivity Analysis of Total Critical Pumping Rates in Coral Island Based on Numerical Model

Groundwater on small coral islands exists in the form of freshwater lenses that serve as an important water resource for local inhabitants and ecosystems. These lenses are vulnerable to salinization due to groundwater abstraction and precipitation variation. Determination of the sustainable yield from freshwater lenses is challenging because the uncertainties of recharge and hydrogeological characteristics make it difficult to predict the lens response to long-term pumping. In this study, nine pumping well layout schemes along a line are designed using the orthogonal experimental design method, and an optimal well layout scheme is determined by multi-index range analysis and comprehensive balance analysis method. The total critical pumping rates of the freshwater lens corresponding to different schemes are calculated by numerical simulation, and the sensitivity of the total critical pumping rates to hydrogeological parameters is analyzed. The results show that the calculation of the total critical pumping rates needs to be combined with the specific well layout scheme with consideration to the length of well screens, the number of wells and the distance between wells. The difference in total critical pumping rates between different schemes can be up to three times. The uncertainty of hydrogeological parameters has a great impact on the total critical pumping rates. Within the range of a 30% reduction in parameters, α and K are the key risk factors of pumping; within the range of a 30% increase in parameters, α, ne and K are the key risk factors; α-ne combined changes had the greatest impact. The management of freshwater lenses and the assessment of sustainable yield will continue to be important tasks for coral islands in the future, and this study can help with the sustainable exploitation of island freshwater lenses.

Collaborative Approach Overcomes Cementing Challenges in Narrow Pressure Window Environment

The collaborative approach used for cementing the production liner in an onshore development well in Russia is presented. The reservoir has a narrow window between pore and fracture pressures, which has previously caused formation instability and severe lost circulation issues during well construction, compromising zonal isolation objectives. Total loss of fluids experienced while cementing the 114.3 mm production liner in the first appraisal well in the field led to revising the cementing strategy. Collaboration among various parts of the drilling department and the opportunity to define a new approach resulted in a decision to introduce managed pressure drilling (MPD) to address the challenges associated with a narrow pressure window and uncertainty in pore pressure while drilling and cementing. This enabled implementing the optimal mud weight and adjusting equivalent circulating density (ECD) during cementing with minimum overbalance. Reducing the mud weight from 1.20 SG to 1.05 SG eliminated losses after running the liner and while cementing it. As a result, pre-job circulation rates and pumping rates during cementing could be increased, improving mud removal efficiency and achieving top of cement at the required depth. The constant-bottomhole-pressure mode of MPD was used to maintain the same ECD during displacement of the well to a lighter fluid and during cementing, avoiding well influx during pumpoff events by compensating for the annular friction pressure loss with surface backpressure. This first onshore managed pressure cementing operation executed within the same field in Russia (later named as field A) was completed flawlessly, with no safety or quality issues, zero nonproductive time, and achievement of the required zonal isolation across the challenging production section. The collaborative approach used was a novel strategy, with the mud weight program strategically adjusted before and during the cementing operation to achieve zonal isolation objectives.

Optimization of Groundwater Pumping and River-Aquifer Exchanges for Management of Water Resources

Groundwater pumping influences the rate of River-Aquifer (R-A) exchanges and alters the water budget of the aquifer. Therefore, fulfilling the total water demand of the area, with an optimal pumping rate of wells and optimal R-A exchanges rate, is important for the sustainable management of water resources and aquatic ecosystems. Meanwhile, comparison of the output of different simulation-optimization techniques, which is used for the solution of water resource management problems, is a very challenging task where different Pareto fronts are compared to identify the best results. In the present work, mathematical models were developed to simulate the R-A exchanges for the lower part of the River Ain, France. The developed models were coupled with optimization models in MATLAB environment and were executed to solve the multi-objective optimization problem based on the maximization of pumping rates of wells and maximization of groundwater input into the river Ain through R-A exchanges. The Pareto front developed by different simulation-optimization models was compared and analyzed. The Pareto fronts were juxtaposed based on the convergence, total diversity, and uniformity with the help of different performance metrics like hypervolume, generational distance, inverted generational distance, etc. The impact of different groundwater models based on domain size and boundary conditions was also examined. Results show the dominance of MOPSO over other optimization algorithms and concluded that the maximization of pumping rates significantly changes after considering the R-A exchanges-based objective function. It is observed that the model domain also alters the output of simulation-optimization, therefore the model domain and corresponding boundary conditions should be selected carefully for the field application of management models. ANN models were also developed to deal with the computationally expensive simulation model by reducing the processing time and were found efficient. Keywords: Simulation-Optimization, Multi-Objective optimization, Artificial Neural Network, River-Aquifer exchanges.

Diverting from the Status Quo: Leveraging Acid Retardation for Production Enhancement in Offshore Carbonates in UAE

With the expanding offshore rig activity in United Arab Emirates leading to an increased number of horizontal wells and longer drains, coupled with changing rock fabrics, it became imperative to diverge from the existing stimulation methods to deliver more consistent and reliable results. These results were achieved via the introduction of single-phase retarded acid (SPRA) and viscoelastic diverting acid (VEDA) to both active and shut-in wells offshore. The introduction of SPRA and VEDA was possible after extensive laboratory testing including core flow tests, solubility tests, emulsion tendency testing, and corrosion inhibition tests to evaluate and benchmark the performance of these blends in comparison to the existing acid recipes such as plain HCl and polymer-based diverted acid. These tests showed that a combination of SPRA and VEDA would allow maximizing lateral coverage and enhance acid penetration due to the reduced rate of reaction and chemical diversion capabilities from thief zones. Combining the introduction of SPRA and VEDA with a shift to bullheading and higher pumping rates enabled the delivery of previously unachievable production results at sustainable wellhead pressures or even well revival of shut-in wells. In addition, reduction of acid content for dolomite stimulation was possible due to the implementation of acid retardation, which also allowed protecting wellheads from exposure to higher acid concentrations while bullheading. Treatment parameters such as volumes, rates, and acid/diverter sequence and ratio were then adjusted for optimal wormhole penetration across all zones using a new carbonate matrix acidizing modeling software. Post-treatment evaluation for the cases of previously shut-in wells has proven the success of the SPRA and VEDA combination. Shut-in wells that were unable to produce sustainably at the required tubing-head pressure (production flowline pressure), were able to produce sustainably with a 100% increase in production compared to prestimulation testing. Similarly, for gas wells, the combination of SPRA and VEDA resulted in a 50% increase in production at a similar bottomhole pressure. In addition, water injectors have also exhibited sustainably increased levels of injectivity compared to prestimulation levels, leading to better sweepage. The novelty of this paper is the comparison between historical carbonate stimulation results in UAE using plain HCl acid with polymer-based diverted acid and using SPRA with VEDA. It also sheds light on the game-changing solutions that suit the ever-increasing challenges observed in offshore oil and gas wells including well placement, lithology, permeability contrast, and type of hydrocarbon within the various target sublayers.

Hydraulic performance of riverbank filtration: case study West Sohag, Egypt

Riverbank Filtration (RBF) Technology has been found to be a safe, renewable, sustainable, and cost-effective drinking water treatment or pretreatment technology. The Egyptian government has recently turned to riverbank filtration to conserve drinking and industrial water at a lower cost and higher efficiency. The study aims to assess the hydraulic performance of the riverbank filtration system in west Sohag, Egypt. MODFLOW and MODPATH 10.2.3 were used under the platform of Groundwater Modeling System (GMS) to construct a hydraulic groundwater flow model to simulate the flow of the riverbank filtration system. Six pumping rates with two scenarios were conducted to investigate the system's hydraulic performance. Water samples were collected from the Nile River, abstraction wells, and groundwater to characterize the water quality. The results indicated that the application of riverbank filtration is promising due to the significant hydraulic connection between the Nile and the aquifer. However, the system hydraulic aspects should be taken into consideration during the design phase as they may affect the RBF hydraulic performance and its efficiency. It became apparent how effective RBF is at eliminating pathogens and suspended solids. Infiltrated water, on the other hand, has higher iron and manganese amounts than the Nile water.