Systematic survey on model predictive control schemes applied to offshore deep water wells in oil and gas industry

Geosteering in deep water wells presents unique challenges and opportunities within the oil and gas industry. This paper comprehensively reviews these challenges, including geological uncertainties, technological limitations, operational constraints, and economic and safety risks. Advanced geosteering tools and techniques, such as : Real time borehole image, resistivity inversion, anisotropy measurements, are discussed alongside the integration and the application of machine learning (ML) and artificial intelligence (AI) to enhance decision-making processes. Predictive modeling and uncertainty quantification are explored as essential components for optimizing wellbore placement and managing risks. Furthermore, the paper highlights emerging trends in geosteering technology, including augmented reality (AR), virtual reality (VR), and high-resolution sensors, which promise to improve the accuracy and efficiency of drilling operations. Sustainability considerations are also addressed, emphasizing the need for environmentally friendly drilling practices and reducing the industry's environmental footprint. This theoretical review underscores the importance of continuous technological advancements and the adoption of best practices to overcome the complexities of deepwater drilling. By leveraging innovative solutions and prioritizing sustainability, the oil and gas industry can enhance the success and safety of drilling operations, ensuring long-term viability and environmental stewardship.

Coupled modeling circulating temperature and pressure of gas–liquid two phase flow in deep water wells

Petrobrás started drilling deep water wells offshore Brazil in the mid-eighties. Nowadays, after ten years of experience, 180 wells have been drilled in water depths ranging from 400 m to 1800 m. Several records have been broken since the Marlim Field Pilot System came on stream. Recent activities and new prospects are pushing on limits into even deeper waters, where Petrobrás is committed to drill and produce wells in the near future. This paper addresses main problems faced in the Campos Basin area, southeast Brazil, during the deep water exploratory program and the solutions achieved to solve them. A a brief description of the current field developments is also given. Finally, a point about the future challenges to be overcome is made.

Deep water well design and drilling is challenging due to the narrow separation between pore pressures and fracture pressure. Comparing the fundamentals of deep water well design to shallow water / onshore well design is dramatic. Once the pore pressures and fracture pressures have been modeled, the shallow water / onshore well design begin with choosing the desired casing size at total depth. Establishing the desired casing size at total depth for shallow water / onshore wells for the most part determines the casing points from total depth to surface. This is often referred to as the "Bottom-Up" well design. On the contrary, deep water well design begins with the selection of the 20″ conductor depth. Once this depth has been selected, it determines subsequent casing points. This is commonly referred at the "Top-Down" well design. The deeper this string is set, the deeper the subsequent casing strings can be set. Extending this depth can eliminate entire casing strings. The challenge becomes to safely set the 20″ conductor as deep as possible. A major deepwater drilling program has successfully drilled more than 19 wells in deep water in the Krishna-Godavari Basin. The setting depth of the 20″ casing has been extended using 3-D seismic, seal capacity analysis, shallow pore pressure prediction, shallow fracture pressure prediction and "pump and dump". Once the 20″ conductor has been set, which is predominately in the very plastic Godavari clay, determining the maximum mud weight is also a challenge. The proper analysis will allow the next casing string to set deeper. Although deep water well design in the Krishna-Godavari Basin should not be considered routine, the appropriate pre-drill analysis has significantly reduced the risks and costs of deep water drilling.

A site investigation was conducted on corrosion damage to stainless steel alloy 316 Ti (UNS S31635) motor pump casings installed in deep fresh water wells. The damage consists of full-wall perforation, localized pitting and crack like attack. The corrosion attack was observed in the weld area and the heat affected zone (HAZ) of the motor casing longitudinal seam weld. The investigation revealed that small anodic sites were formed on the motor casing surfaces close to the seam weld as a result of poor welding and lack of post treatment. This is confirmed through a comparison of the same material welded using a good welding practice and adequate post treatment and installed in a similar environment. This paper presents the corrosion failure investigation and outlines measures to avoid such failures including precautions to be taken during welding of stainless steel alloys.

The challenges found in deepwater and ultra-deepwater drilling have, in a remarkable short period, forced the oil industry to develop new significant technologies and techniques. The characteristics of the deepwater environments have pushed design criteria, normally used in onshore and shallow water wells, to values beyond their traditional limits. All drilling phases of deepwater and ultra deepwater wells face challenges. The initial phases, generally composed of soft soil or just mud, have required a lot of experience in terms of jetting the conductor pipe to avoid sinking of the wellhead. In the intermediate phases, engineers must be very careful to avoid lost circulation due to the narrow window between pore pressure and low fracture pressure gradients. Besides, well bore instability, always an issue for directional drilling, often limits the length of the deepwater well departures to values considered small if compared to those obtained in shallow waters or onshore. In addition, the drilling of permeable rocks, many times just loose and unconsolidated sands, increases the chance of differential sticking. To complete the picture, watching closely well operation and drilling parameters to keep risks under control generally is not enough. Creativity is very often necessary to overcome the ultra-deepwater challenges. This paper describes Petrobras drilling experience in deepwater and ultra-deepwater. A number of historical cases are shown to illustrate the main obstacles an Operator normally faces when drilling in deepwater. The evolution of well design and drilling practices as the result of the increase of the water depth and its related problems, are also presented. Several experiences with new tools, rig performances and drilling fluid products specific for deepwater are described. Finally, deepwater projects that include extended reach drilling and other special studies are also discussed. Introduction The discovery of important deepwater oil fields such as Marlim and Albacora has inspired Petrobras to look for new frontiers located in deeper waters. However, initially thought as simple adaptation of the work done in shallow water, a number of new challenges also followed this move. According to the oil industry, deepwater wells are those wells drilled in water depths ranging from 300 meters to 1,500 meters. Wells located in water depths higher than 1,500 meters are classified as ultra deepwater wells. Deepwater drilling with dynamic positioned (DP) rigs has been a reality in Brazil since 1984. Up to 1991, Petrobras used only these types of rigs to drill exploratory wells in the Brazilian Basins, including Campos Basin. After having drilled a number of wells in water depths higher than 1000 meters, Petrobras has started in 1990 an extensive program to drill development wells in deepwater oilfields using both, DP and anchored rigs. Fig. 1 shows a schematic map of the Brazilian Coast and the distribution of deep and ultra deepwater wells along it. Campus Basin, where the main oilfields are located, has the majority of the drilled wells. Though, Espirito Santos Basin, where a number of new discovery have been announced by Petrobras, is expected to have a considerable increase of drilling activities in the future years. Fig. 2 displays the number of wells drilled in deep and ultra deepwater versus time in years.

SummaryIn the past decade, managed pressure drilling, a technology aiming at precise well pressure control, has been gaining increasing popularity and been a key enabler for some of the most challenging well drilling cases such as the offshore deep water well drilling. This paper attempts to solve two of the main challenges involved in the managed pressure drilling systems: first, the bottom‐hole states measurements are updated at a low rate, which can be practically viewed as unmeasured and thus need to be estimated in real time for both monitoring and control purposes and second, the drilling process is subject to uncertainties including unknown system parameters (e.g., frictions and densities), unmodeled actuator dynamics, and noise, which require a robust adaptive controller for control of the bottom‐hole pressure. Towards this objective, an integrated estimator andadaptive control scheme is proposed. The estimator provides estimation of the bottom‐hole pressure and flow rate, based on the available measurements from the topside. Theadaptive controller drives the bottom‐hole pressure to the desired value following a reference model, which also handles the time delays in the input signal. The design is based on a recently developed nonlinear drilling model. The results demonstrate that theadaptive controller has guaranteed performance bounds for both the input and the output signals of the system while using the estimation of the regulated outputs. Simulation results covering different operational conditions verify the theoretical findings. Copyright © 2016 John Wiley & Sons, Ltd.

Measurement and modeling of methane dissolution in synthetic liquids applied to drilling fluid formulation for deep and ultradeep water wells

ABSTRACT: Compared with the conventional surface conductor, the diameter of the suction bucket foundation is generally greater than 6 meters and the length is about 10 meters, which could bring less disturbance of shallow soil during installation and improve the load-bearing characteristics of the subsea wellhead. Theoretical model of the process of suction bucket foundation and bearing capacity calculation method is established, and the influence of diameter and length of the suction bucket on wellhead stability is studied by using the method of combination of simulation experiment and numerical analysis to compared with the surface conductor foundation. The results show that large diameter is mainly helpful to reduce the lateral displacement of subsea wellhead and improve the bending moment performance and vertical bearing capacity of the foundation can be significantly increased by increasing the length of the suction bucket. The large diameter will significantly increase the manufacturing cost and installation cost, with the increase of bucket length, it is difficult for the bucket to install due to the increase of soil resistance. Therefore, it is necessary to design the size of the bucket reasonably in combination with the load-bearing characteristics of subsea wellhead and the properties of shallow soil. 1. INTRODUCTION Oil and gas well construction in deep water with suction bucket foundation is the first practice in Norway (Trond Sivertsen et al., 2011). In 2020, the suction bucket foundation is successfully used in the ‘Shen-hu’ area of the South China Sea for the second trial production of hydrates, which combined shallow deflection and dynamic guidance technology, and achieved a breakthrough of 28700 m3/d and lasts for 30 days, (Ye et al., 2020). The application of suction bucket foundation ensures the stability of the upper formation of hydrate siltstone reservoir. The first suction pile-based jacket platform was launched in 1989 and successfully installed in Norway in 1994 (Morten Baerheim et al., 1995). In 1994, China applied a suction anchor to locate oil tankers in the Bohai Sea for the first time, and installed the double-tube suction anti-slide pile for the "Self-improvement" platform successfully in 1995 (Xu et al., 1995). In 2012, the suction pile underwater foundation plate was successfully installed in the South China Sea, which became the practical basis for the establishment of suction bucket foundation for deep water subsea wellhead (Gu et al., 2014). At present, the design of a suction bucket foundation for offshore deep water well construction is in its infancy, lacking theoretical guidance. To ensure the successful practice of the second round of hydrate production test in China, the diameter of the suction pile is 6.5 m, the penetration depth is 12 m, and the foundation weight of the suction pile is 96 tons. This design is considered by experts to be relatively conservative. It is necessary to continuously carry out theoretical and practical analysis to master the optimization design method of the suction bucket foundation. Reasonable design of the structural size according to the characteristics of formation parameters and wellhead load requirements is the key to the safe and efficient application of suction bucket foundation.

Low temperature and high pressure conditions in deep water wells and sub-sea pipelines favour the formation of gas clathrate hydrates which is very undesirable during oil and gas industries operation. The management of hydrate formation and plugging risk is essential for the flow assurance in the oil and gas production. This study aims to show how the hydrate management in the deepwater gas well testing operations in the South China Sea can be optimized. As a result of the low temperature and the high pressure in the vertical 3860 meter-tubing, hydrate would form in the tubing during well testing operations. To prevent the formation or plugging of hydrate, three hydrate management strategies are investigated including thermodynamic inhibitor injection, hydrate slurry flow technology and thermodynamic inhibitor integrated with kinetic hydrate inhibitor. The first method, injecting considerable amount of thermodynamic inhibitor (Mono Ethylene Glycol, MEG) is also the most commonly used method to prevent hydrate formation. Thermodynamic hydrate inhibitor tracking is utilized to obtain the distribution of MEG along the pipeline. Optimal dosage of MEG is calculated through further analysis. The second method, hydrate slurry flow technology is applied to the gas well. Low dosage hydrate inhibitor of antiagglomerate is added into the flow system to prevent the aggregation of hydrate particles after hydrate formation. Pressure Drop Ratio (PDR) is defined to denote the hydrate blockage risk margin. The third method is a recently proposed hydrate risk management strategy which prevents the hydrate formation by addition of Poly-N-VinylCaprolactam (PVCap) as a kinetic hydrate inhibitor (KHI). The delayed effect of PVCap on the hydrate formation induction time ensures that hydrates do not form in the pipe. This method is effective in reducing the injection amount of inhibitor. The problems of the three hydrate management strategies which should be paid attention to in industrial application are analyzed. This work promotes the understanding of hydrate management strategy and provides guidance for hydrate management optimization in oil and gas industry.

Testing and gathering data from a well to evaluate the potential of a new field is a common practice in the oil and gas industry. However, performing this task in ultra deep water presents significantly greater challenges to the operator and service providers, since testing in the depths required for the subject well had not previously been attempted, there were concerns of problems that might occur in maintaining response times and control of the test equipment. This paper will present the innovative solution that was devised to perform the testing in the deep water well. The equipment, the well, location condition, and procedures were used to safely and efficiently perform the evaluation testing will be discussed.

Frequent break-downs occuring at neighbouring water intake sites caused by an accelerated corrosion of deep water well casings, and the high cost of construction of deep water wells and collecting water pipelines, made it necessary to apply the cathodic protection of these structures at the site of a new water intake. In the paper the joint cathodic protection of 24 water wells, 40 m deeps, and the pipeline of 219-1016 mm in diameter is presented.

This paper discusses the most important drilling hazards related to borehole instability and pore pressure in deep water wells. A case study from a deep water well, which has experienced wellbore stability and loss of circulation problems, especially over intervals with higher angles of hole deviation, is presented. The answers provided by the study included properties, such as, recommended mud-weights (minimum & maximum) as a function of angle of deviation, rock strength and computed pore pressure. The determination of rock strength along with the optimum mud-weight windows improved overall the drilling performance in the next deep water well by minimizing washouts, loss of circulation and optimizing casing design by elimination of unnecessary casing strings. Moreover, improvement of bit performance was achieved by using the predicted rock-strength values. As a result, drilling time and well construction costs were significantly reduced. Introduction Wellbore stability and pore pressure related issues, especially in deep water blocks, cause frequently serious problems during drilling, logging and production operations. The narrow pore pressure and fracture gradient (PPFG) windows necessitate multiple casing strings to reach the target reservoir formations. Errors in predicting PPFG windows could result in significant loss of rig time and even failure of wells. The removal of rock during the drilling operation disturbs the natural rock formation that is being subjected to a state of compressive in-situ stresses at depth. The redistribution of the stresses around the hole thus produces stress concentrations at or near the borehole wall. Such a high stress buildup around the wellbore may lead to a number of hole problems that include stuck pipe, borehole collapse, sloughing shale and excessive fill. Several billions of dollars are lost each year worldwide directly or indirectly caused by wellbore stability and pore pressure related problems. Therefore, in order to fully obtain the benefits of the directional drilling technology, wellbore stability analysis and pore pressure prediction has been of increasing demand in the planning stage of the wells, especially in deep water where exploration and field development costs are very high.

Smith, Glynn D., Member SPE-AIME, and Parlas, Solon C., The Offshore Company Parlas, Solon C., The Offshore Company Copyright 1979, American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Petroleum Engineers, Inc. This paper was presented at the 54th Annual Fall Technical Conference and Exhibition of the Society of Petroleum Engineers of AIME, held in Las Vegas, Nevada, September 23–26, 1979. The material is subject to correction by the author. Permission to copy is restricted to an abstract of not more than 300 words. Write 6200 N. Central Expwy., Dallas, Texas 75206. Abstract Deep water exploration drilling has associated with it many unique problems including effects of weather, special equipment, logistics and specially trained personnel. However, deep water wells have personnel. However, deep water wells have been successfully drilled by moored and dynamically positioned drillships. Comparisons are made between two sister self propelled drillships; the Discoverer 534, propelled drillships; the Discoverer 534, which has drilled in 1,055 m (3,461 ft.) of water moored by anchors, and the Discoverer Seven Seas currently completing a well in 1,487 m (4,876 ft.) of water utilizing dynamic positioning and various aspects of the ever increasing technology and required expertise of deep water drilling. These drillships are owned by subsidiaries of The Offshore Company and each holds the current respective world water depth record; for a moored drilling unit in the case of the Discoverer 534 and a dynamically positioned unit for the Discoverer Seven Seas. Although the predominate number of deep water drilling units are dynamically positioned, exploration wells can be drilled in excess of 900m (3,000 ft.) if special equipment is available such as large mooring capacity anchor handling vessels and particular attention to detail is paid for the design of the mooring system. Both drilling units have operated in geographic areas around the world for various operators thus accumulating an interesting and successful history. Introduction The frontier for deep water drilling depths has progressed steadily from the 200 m (600 ft.) barrier in 1965 off the Southern California Coast to 1,487 m (4,876 ft.) in 1979. The 600 m (2,000 ft.) mark was exceeded in 1974 by the Sedco 445 dynamically positioned drillship and in late 1976 the 900 m (3,000 ft.) depth was surpassed by the Discoverer 534 in 1,055 m (3,461 ft.) of water offshore Thailand. The 1,200 m (4,000 ft.) barrier was surpassed in early 1978 by the Discoverer Seven Seas drilling in 1,325 m (4,346 ft.) of water off the Congo in West Africa with subsequent records of 1,354 m (4,441 ft.) off Spain and then 1,487 m (4,876 ft.) off Newfoundland, Canada in 1979. Figure 1 demonstrates how deep water exploration has progressed rapidly during the 1970's with floating drilling units now equipped to drill in excess of 1,500 m (5,000 ft.) of water. The capability of extending this to possibly 2,400 m (8,000 ft.) exists and dependent upon the results of deep water drilling, the frontier could be pushed that far during the 1980's. pushed that far during the 1980's. BACKGROUND Exploration drilling can be accomplished in deep water from either a moored drilling vessel or one that is dynamically positioned; however, in water depths of 900 to 1,200 m (3,000 to 4,000 ft.) or beyond, the practicality of drilling from a moored unit is doubtful since such a large array of mooring wire, chain and pendent wire is involved deployment is complex, costly, and time consuming. Special large capacity, anchor handling supply boats are required to adequately store thousands of feet of chain, mooring wire rope extensions and pendent wire rope. Table 1 shows the specifications of the workboats utilized for deep water anchor handling with the Discoverer 534. Additional rig time is also involved to anchor up and pick up anchors on each well. With a dynamically positioned drilling unit, it is possible to drill in deeper water depths with smaller workboats but with greater fuel costs to provide the power requirements for maintaining station. The Discoverer Seven Seas is not equipped with a mooring system or a mooring turret, but relies completely on dynamic positioning for station keeping.

Multilateral and intelligent well construction and completion technologies has proven themselves to be effective means of increasing recovery rates and improving operational efficiencies in subsea wells, yet, there are no known applications where both technologies have been applied in deep water in the same well. This paper discusses the evolution of the use of both of these technologies in subsea well environments and then the challenges and technology gaps that have to be overcome to develop a fit for purpose solution for deep water wells. This paper discusses the origins and benefits that the two technologies have brought to subsea wells while presenting examples of the integrations of both in installations in various areas of the world. The unique environment and challenges posed by deep water subsea wells introduce risks such as, limited number of wellhead penetrations, longer stroke lengths to position components in the wellbore, lack of rotational ability due to the control lines and safety concerns. This paper also discusses the successful track record of each technology, developing customized solutions for deep water subsea wells and mitigating risks involved. Finally, the challenges posed by the integration of both technologies in these deep water wells are presented. In these challenging economic times, the desires for solutions that reduce capital expenditures/operating expenditures (CAPEX / OPEX) are at the forefront of completion design discussion. Integrating various technologies to that effect is the next logical step. Efficient drainage of complex reservoirs can be achieved by effectively combining multilateral and intelligent completions technologies while actively managing CAPEX / OPEX. Monitoring and active control inside the lateral would be the ultimate solution for maximizing reservoir drainage and performance. For that to happen, it would require technology advancement that is currently non-existent or in its infancy stage at best. However the first logical step would be to monitor and control laterals from the mainbore which is achievable with some enhancements to existing technology. The second step would be to incorporate monitoring in the laterals as inductive coupler and disconnect technology begin to prove themselves. Finally as wireless technology, downhole power generation, and battery technology start to evolve, we will be able to monitor and actively control the reservoir within the laterals. This paper conveys some of the numerous challenges that exist for an integrated completions approach. It will require both operators and service companies to work together to overcome the numerous obstacles; and it requires thinking outside the box and challenging the traditional approach without which we as an industry will be limited in what we can achieve, which in the end is maximizing our return on investment.