Jack-up Rig Research Articles

Estimation of breakout force of spudcan footing in structured clay

For a jack-up rig installed in cohesive soil, assessing the extraction force is critical to ensure the safe and successful retrieval of each spudcan footing. The extraction force depends on the preceding stages, including installation and operation of the rig, due to soil strength changes around the spudcan. To investigate the entire ‘penetration - operation - extraction’ process of spudcan, an effective stress large deformation finite element analysis is conducted, with a Structured Cam-Clay model being incorporated to describe the behaviour of structured soil. The large deformation approach is validated against existing centrifuge tests. Parametric studies are then carried out to explore the influential factors on breakout force, including operation period, vertical load ratio, penetration depth, destructuring rate and soil sensitivity. A unique curve is formulated to predict the evolution of the recovery degree of breakout force over the operation period in structured cohesive soil. The soil sensitivity is identified as the dominant factor that affects the ultimate net resistance ratio, which is the key parameter required in applying the prediction curve. A simple method is proposed to estimate the ultimate net resistance ratio and a procedure to predict the breakout force is suggested.

Study Reviews Multilateral Installation Improvements on the North West Shelf

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 32910,“A Decade of Multilateral Technology Installation Improvements Down Under,” by Stefano Cappiello and Adam Pasicznyk, SPE, Halliburton. The paper has not been peer reviewed. Copyright 2023 Offshore Technology Conference. _ Multilaterals wells on the North West Shelf of Australia have been installed for over a decade. An overview of the well architecture, technology evolution, reliability, and efficiency of these operations is presented in the complete paper. The study is focused on subsea multilateral campaigns, where multiple global and regional first installations took place in mature fields. Introduction Multilateral developments in Australia mainly have been completed off subsea installations, with fewer performed from jack-up rigs. These multilateral completions mostly have been installed with the junction located in the producing reservoir sands. Technology Advancement of Multilaterals (TAML) Level 5 completions have successfully been deployed. The authors classify related systems as follows, with the most attention paid in the synopsis to the final two classes: - Generation One (Field A) - Generation Two (Field B) - Generation Three (Field C) - Generation Four (Field A) General Multilateral Well Design Because of sand production within the reservoir, these applications typically require a TAML Level 5 completion system. These systems deliver hydraulic and mechanical isolation at the junction through the completion. The junction is isolated above and below by production packers and by swell packers in the lateral. The junctions typically are installed horizontally within the reservoir. The original general requirements to construct Level 5 multilateral junctions included the following: - Ability to construct a Level 5 Junction in the 9⅝-in. casing or liner - Ability to run a landing profile or coupling as part of the 9⅝-in. production casing or liner - Ability to run and orient a premilled window at depth - Drill-out 8½-in. openhole section into the mainbore and into the lateral - Junction installed within the reservoir at high angle - Window milling to be performed in one trip - Lateral completion to be installed in one trip - Compressive strength rating capable of running screen sections over 2 km As the operators began to adopt multilateral technology in Australia, the following requirements were incrementally added: - Ability to deliver a Level 5 multilateral system in an existing well - Ability to deliver a trilateral well - Improve efficiency and reduce installation time

Large deformation analysis of spudcan settlement during operation

Jack-up rigs have been utilized to support booster stations in wind farms or to provide accommodation in oil and gas developments. In these scenarios, the dissipation of excess pore pressures and subsequent spudcan settlement during operation phase are of concern. However, predicting the spudcan settlement in naturally structured soil remains challenging. A large deformation finite element method, within the framework of effective stress analysis, has been developed to investigate the penetration and subsequent settlement of the spudcan footing. The inherent structure of cohesive soil and its degradation caused by spudcan penetration are described using the Structured Cam-Clay model. The large deformation approach is validated by comparisons with existing centrifuge tests. Parametric studies are then conducted with various operational loads and installation depths of spudcans. A backbone curve is provided, to estimate the history of spudcan settlement in kaolin with inherent structure. The distribution of excess pore pressures around the spudcan under different operation period is explored as well. A normalised dissipation curve at the largest cross-section of the spudcan during the operation phase is presented.

Effects of Prior Footprints on the Bearing Capacity of Spudcan Foundations: A Case Study

A jack-up rig is a self-elevating offshore drilling platform designed for mobile operations in the marine environment. The rig is supported by 3 or 4 legs, with spudcan foundations at the end. These spudcan provide the necessary stability and load-bearing capacity for rig foundation during drilling operations. The mobile rig sometimes revisits sites where prior installation, operation, and extraction activities have resulted in identifiable footprints on the seabed. The penetration of spudcan close to, or partially overlapping, footprints shall be carefully considered because the spudcan-footprint interaction may cause a change in the ultimate vertical bearing capacity (Fv). ISO 19905-1:2016 states that the interaction between a spudcan and a footprint is expected to be minimal when the edge-to-edge distance exceeds one spudcan diameter. This paper presents the effect of existing footprints on the vertical bearing capacity of a spudcan with various spacing variations from 0.5B to 1.75B, where B is the diameter of the spudcan. A 3D finite element method (3D FEM) is employed as the primary analysis tool in analyzing the effects of footprints on layered clay soil. The 3D FEM analysis is conducted because the analytical approach outlined in ISO 19905-1:2016 does not consider the influence of the footprint on the spudcan capacity. The analysis results show that bearing capacity may reduce by more than 50% when the center-to-center distance is less than 1B. Whereas, for distances greater than 1.5B, the influence of the footprint is relatively insignificant, only reducing less than 10% of the ultimate capacity of the spudcan.

Investigation of the peak punch-through capacity of spudcan on sand overlying spatially variable clay

Accurately estimating peak penetration resistance in punch-through sensitive deposits is crucial for managing risks during jack-up rig installations. While offshore clays exhibit significant spatial variability, necessitating consideration of spatial variability in predicting peak penetration resistance. This study investigates the effects of spatial variability of underlying clay on the failure mechanism and magnitude of peak penetration resistance during punch-through incidents. The Modified Linear Estimation Method was used to generate three-dimensional random fields, incorporated into coupled Eulerian Lagrangian finite element analyses to simulate spudcan penetration from the ground surface. Results show that while spatial variability has an insignificant effect on the failure mechanism in the upper sand layer, it significantly alters soil flow in the underlying clay, leading to variations in peak penetration resistance. The peak penetration resistance follows a log-normal distribution, and a relationship was established between the probability of failure and the factor of safety. This study highlights the importance of considering soil spatial variability and demonstrates the significant impact of underlying clay on the failure mechanism and magnitude of peak penetration resistance during punch-through incidents, which might be helpful for the safety management of industry.

Estimation of spudcan penetration in variable sand deposits with the Arbitrary Lagrangian Eulerian Finite Element Method

Offshore jack-up rigs are most commonly founded on large-diameter conical “spudcan” foundations, which are frequently designed using traditional analytical methods for shallow footings. This paper presents the design of a spudcan installed off the coast of Tunisia. The maximum penetration depth of the footing under the available preload is predicted by a combination of analytical techniques, 2-dimensional axisymmetric modelling and 3-dimensional Finite Element Methods (FEM) using large strain arbitrary Lagrangian-Eulerian (ALE) techniques. Spudcan penetration based on FEM simulation of CPT soil profiles forms the basis of a comparison with results from the Society of Naval Architects and Marine Engineers (SNAME) guidelines. Particular attention is given to model calibration using the limited site investigation data available. Results are presented for the effect of penetrating footings on the behaviour of neighbouring footings, showing good agreement with conventional prediction methods.

IDENTIFICATION ACTIVE POCKMARKS USING THE COMBINATION OF SIDE SCAN SONAR AND SUB-BOTTOM PROFILER

It should be suitable for direct inclusion in abstracting services and should not normally be more than 300 words. Geohazards assessments are important before any engineering activity as they could block facilities and cause millions of dollars in losses. Pockmark as geohazards is often observed on the seabed with various amounts, especially on the clayey seabed sediments. Pockmarks indicate that the gas escapes from below the seabed. Pockmark may cause the jack-up rig to be slipped, pipeline free-span, and even blow out while drilling if it has a gas trap below. Side scan sonar and sub-bottom profiler as the geophysical method using acoustic wave can be used to investigate the active pockmarks. By using these two datasets, the distribution of active and inactive pockmarks can be achieved properly. So that hazards that may occur in engineering activities in the future can be prevented.

Global Structural Behavior and Leg Strength for Jack-Up Rigs with Varying Environmental Parameters

In the mobile jack-up unit, the leg supporting the hull is a very important structure, and it is important to closely examine the changes in accident load, environmental load, and seabed ground during jack-up operation. Generally, jack-up rigs are three-legged structures with a triangular hull that comprises several movable legs used to raise the hull above the sea surface. They can be operated in shallow water at less than 120 m, while large jack-up rigs, which have a structure that can withstand severe environmental loads, can be employed at depths ranging from 150 m to 200 m. However, a complex process is required to finalize the structural design of a jack-up rig, and the influence of various parameters must be comprehensively considered. In other words, the rig will encounter variable environmental conditions with variations in parameters such as wave height, wave period, wind speed, air gap, and so on. A unified procedure is proposed to review the structural strength of legs, hulls, and cantilevers, and different models and analyses can be configured so that it can be solved within a unit flow-chart. Through this process, we can expect that engineering time and cost can be reduced. From survey results, it was possible to determine the inputs to examine the effects of variables, and a large jack-up rig operating under extreme environmental conditions was modeled. In the present study, the jack-up rig was operating in the North Sea, and leg length and water depth were 160 m and 100 m, respectively. The basic environmental characteristics included wave height (20 m), wave period (10 s), wind speed (30 m/s), and air gap (22 m). A parametric sensitivity analysis was performed with varying environmental parameters. Through sensitivity analysis of environmental characteristics, the significance and sensitivity of the effect of each environmental parameter on leg strength was clarified. It is expected that this will be very useful guidance about the effect of parameters during the conceptual design stage of jack-up rigs.

Оценка условий района и технологические особенности добычи углеводородов на участке Восточно-Сибирский 1

This article is devoted to the study of the conditions of the hydrocarbon production area on the East Arctic shelf: hydrometeorological, natural-climatic and mining-geological conditions. The paper provides an analysisof the characteristics of the mining area, and more specifically, the East Siberian 1 site, which is located north of the territory of the Republic of Sakha and the Chukotka Autonomous Okrug. Technological features are options for using existing domestic technologies, creating analogues based on them and using the reengineering method for the development of the East Arctic shelf. In the article, a concept was chosen for the development of the study area,taking into account its features. The article also discusses a jack-up rig for drilling wells in a selected production area. The use of an ice-resistant platform with a caisson and an underwater production complex, from where natural gas will be supplied to a floating LNG plant for liquefaction, is justified. A scheme for the transportation of oil and liquefied natural gas to consumers from the countries of the Asia-Pacific region is proposed.

Опыт выполнения морских операций в ходе подготовки и постановки самоподъемных плавучих буровых установок на ремонт в условиях ограниченной доступности сухого дока

Опыт выполнения морских операций в ходе подготовки и постановки самоподъемных плавучих буровых установок на ремонт в условиях ограниченной доступности сухого дока

Spudcan Deep Penetration in Multi-Layered Soils Incorporating Sand Relative Density

Installing a spudcan jack-up rig in sediments with an interbedded sand-over-clay soil profile is still challenging in the offshore industry due to possible punch-through failure. The current methods for predicting the punch-through of spudcan usually ignore sand relative density, which is one of the most important parameters for sand soil. For multi-layered soils with interbedded sand commonly met in the field, this paper aims to determine the effects of sand relative density on predicting the punch-through failure of spudcan. Modified Mohr-Coulomb (MMC) and extended Tresca models characterized by incorporating a variation of mobilized strength parameters were used to describe the mechanical behaviors of sand and clay. Besides four groups of centrifuge tests, one field case in the South China Sea was also numerically simulated to validate the large deformation finite element (LDFE) analyses conducted in this paper. The results showed that neglect of sand relative density may lead to underestimation of the potential for punch-through failure of spudcan.

Capacity of spudcan foundation on dense sand overlying clay under combined loading

The evaluation of spudcan foundation capacity under combined vertical, horizontal and moment loading is critical for the site-specific assessment of jack-up rigs. However, the investigation on the behavior of a spudcan on the surface of a sand layer overlying clay under combined loading is limited. This paper reports the results from a series of finite element analyses conducted to explore the failure envelope of spudcan on dense sand overlying clay before punch-through, considering the effects of the preload level on spudcan, the thickness ratio and the relative density of sand, and the underlying clay strength through parametric study. The numerical results provide insights that when the sand layer is sufficiently thick, the failure envelope expands with the increase of vertical load level, leading to higher horizontal and moment capacities; however, for the spudcan on a relatively thin sand layer, the horizontal and moment capacity may decline with rising vertical load level, resulting in eccentricity and shrinkage of the failure envelope. New design formulas for the failure envelope are proposed covering a comprehensive range of soil parameters and layer geometries of practical interest, which facilitates their general application in the site-specific assessment of the jack-up platforms.

On Cubic Spudcan Deep Penetration in Dense Sand Overlying Non-Uniform Clay

Installing spudcans for jack-up rigs in a layered seabed with an interbedded strong-over-soft layer is challenging in the offshore industry due to possible punch-through failure. The methods currently used to predict punch-through failure mainly focus on generic spudcans, usually ignoring the geometric features of the spudcan. The aim of this study is to determine whether the punch-through potential of a generic spudcan is applicable to a cubic spudcan of a BH12# jack-up rig installed in dense sand overlying non-uniform clay. We conducted a series of large deformation finite element (LDFE) analyses on dense sand overlying non-uniform clay using a generic spudcan and a cubic spudcan. The thickness of the sand layer was also varied to cover a range of practical interest. The special cubic spudcan was found to be less likely to induce punch-through failure on sand-over-clay sediments compared with the corresponding generic spudcan. Herein, we propose a method to predict the degree of post-peak bearing reduction, which is a key measure of the severity of punch-through failure.

Jacking and Energy Consumption Control Over Network for Jack-Up Rig: Simulation and Experiment

Abstract Oil and gas projects differ from regular investment projects in that they are frequently large-scale, categorised as vital national projects, highly technological, and associated with significant risks. Drilling rigs are a crucial component of the oil and gas sector and the majority of the systems and equipment aboard drilling rigs are operated automatically. Consequently, it is crucial to address the topic of an advanced control theory for off-shore systems. Network technology connected to control is progressively being used to replace outdated technologies, together with other contemporary technologies. In this study, we examine how to adapt a networked control jacking system to the effects of internal and external disturbances with a time delay, using a Fuzzy controller (FC)-based particle swarm optimisation. To demonstrate the benefit of the proposed approach, the developed Fuzzy Particle Swarm Optimisation (FPSO) controller is compared with the fuzzy controller. Finally, the results from simulations and experiments utilising Matlab software and embedded systems demonstrate the suitability of the proposed approach.

Experimental and numerical studies on the adjacent pile response to bucket spudcan penetration and extraction

ABSTRACT Jack-up rigs typically operate close to long-running jacket platforms. Unfortunately, penetration and extraction of the spudcan under jack-up rigs may impose an adverse influence on adjacent platform piles. In this study, the influence of bucket spudcan and inverted cone spudcan penetration and extraction on the lateral behaviour of adjacent pile were studied comparatively by conducting a series of model tests and numerical simulation in sand. The influence of spudcan-pile distance, pile diameter and pile head conditions on the spudcan-pile interaction were studied. Additionally, the soil flow patterns during penetration and extraction of two types of spudcans were analysed using the CEL. The results show that the pile bending moment and pile head displacement induced by bucket spudcan penetration and extraction are smaller than that of an inverted cone spudcan. It provides an engineering option for dealing with the adverse influence on adjacent piles induced by spudcan penetration and extraction.

Spudcan slip prediction of jack-up rig near the footprint: a coupled RPD-moment based solution

ABSTRACT When the jack-up rig is reinstalled near the old footprints, the spudcan will slide laterally and generate a bending moment at the bottom of the jack-up rig's leg due to the existence of the old footprints, endangering the jack-up rig's operation safety. The maximum bending moment is chosen as the input condition for spudcan slipping in the truss three-legged jack-up rig's model based on the results of square spudcan stepping on the footprints. At the maximum bending moment, the critical slip distance and its corresponding critical rack phase difference (RPD) of the verified model in different slip directions are obtained. Simultaneously, the effects of different bending moments on the critical transverse slip distance and critical RPD are analysed in different directions. As a result, the RPD real-time monitoring value on the top platform can be used to predict the spudcan's lateral slip distance. It is useful for platform designers and operators when jack-up rigs reinstall near existing footprints.

E&P Notes (March 2022)

E&P Notes (March 2022)

Research on Optimal Design of Spudcan Structures to Ease Spudcan-Footprint Interactions in Clay and Comparative Analyses with Different Measures

Abstract In order to ease consequences of spudcan-footprint interactions during jack-up rigs reinstalling in the vicinity of an existing seabed footprint, three new types of spudcan shapes, that is, a lotus-shaped spudcan with six circular holes, a flat-bottomed spudcan, and a concave-shaped spudcan, were proposed to perform an optimizing study of the spudcan structures, and the effectiveness of them were analyzed comparatively with other different measures. Firstly, 3D Large Deformation Finite Element (LDFE) analyses were carried out using the Coupled Eulerian-Lagrangian (CEL) method in the commercial finite element package ABAQUS. After calibrating the validity of the numerical calculation model against existing centrifuge test data and LDFE results, the differences in interaction mechanism between the novel spudcans and the generic spindle-shaped spudcan were studied when penetrating near an existing footprint with an eccentric distance of 0.5D, and the horizontal range of plastic deformation of the disturbed soils, the inclination angle of the spudcan and the offset distance of the pile legs were analyzed comparatively as well. The results show that the proposed novel spudcans can mitigate the maximum horizontal sliding force and the maximum bending moment at the top of the pile leg obviously, compared with those of the generic one, which were reduced by 32.59%, 22.47%, 28.18%, and 26.32%, 12.88%, 18.02%, respectively. It also can be seen that all novel structures can ease the adverse consequences of spudcan-footprint interactions effectively, and can improve the in -place stability of the spudcan as well. Finally, three possible measures in mitigating interactions of the spudcan-footprint were contrasted, that is, the novel spudcan (represented by the lotus-shaped spudcan with six holes), stomping method, and perforation drilling method. The results show that all of them can reduce adverse impacts induced by interactions of the spudcan-footprint, and also can improve the in-place stability of the spudcan during reinstallation. In addition, among them, according to the effect of reducing the additional stress of the spudcan, the effectiveness of them can be listed as follows: perforation drilling near an existing footprint > the lotus-shaped spudcan with six holes > stomping method. In terms of the vertical bearing capacity of the spudcan, the lotus-shaped spudcan with six holes can improve it as much as 16.33% compared with the spindle-shaped structure due to the particularity of the structure. While reducing the continuity and strength of soil foundations, the perforation drilling measure leads to the decrease of the vertical bearing capacity of the spudcan by 13.07%. It can be concluded that all the three measures have merits and demerits, so the relevant construction environment conditions and engineering practice should be fully considered when selecting measures to deal with interactions of the spudcan-footprint.

Estimation of Overall Fatigue Life of Jack-up Leg Structure

Jack-up platforms are designed to work in three conditions: Transit, Preloading and Operating. The fatigue life of the jack-up platforms in operating condition will be determined to be similar to that of offshore fixed steel structures. In preloading conditions, fatigue damage is usually ignored. Up to now, the fatigue damage of the jack-up leg structure in transit conditions has been calculated at approximately 20% of the total fatigue damage of the jack-up leg structure in two conditions (transit and operating). The approximate calculation method is usually accepted by consultants and register agencies. If the approximation is used, the fatigue life of the jack-up leg structure will be calculated only as for the jacket structure of the fixed offshore structure, with 80% of the allowable fatigue life based on standards. The approximation proved to have many disadvantages: the different travel times of each jack-up rig cannot be mentioned; hot spots that need to be maintained during the transit condition have not been pointed out; it is difficult to guarantee the safety of the jack-up leg structures in the transit condition. In order to overcome the limitations of the approximation method, this paper will propose a method to predict the overall fatigue life of the jack-up leg structure in three main problems. Firstly, we use the analysis method of fatigue of fixed steel offshore structures for jack-up leg structures in operating conditions. Secondly, we suggest a method to analyze the fatigue of the structures in transit conditions. Herein, motion analysis and determination of inertia forces on the leg structure are performed by the Boundary Element Model (BEM) in SACS software. Then the inertia forces are assigned to a Finite Element Model (FEM) in SACS to decide the internal forces of the structures. Hotspot stresses are determined by combining nominal stress from FE analysis results with a concentrated stress factor from the analysis of joint local models in the ANSYS program. Then, fatigue damage and fatigue life of hotspots of the structure are determined in the transit condition. Finally, a formula is suggested to determine total fatigue damage in operating conditions and transit conditions with different cases in relation to different fraction factors. These results are used to predict fatigue life corresponding to the most dangerous cases of structural joints. These new suggestions are applied to fatigue analysis for jack-up Tam Dao 05. Currently, the Tam Dao 05 platform has been operating in the Vietnam East Sea. Doi: 10.28991/CEJ-2022-08-03-06 Full Text: PDF

Enabling Formal Safety Assessment Method in Jack-Up Rig Operations

Since the inception of jack-up rig operations in the early 1950s, series of hazardous accidents has been witnessed, and losses recorded. These events are approximated to occur at least twice in a year. With this statistics, the harsh offshore environment demands jack-ups of premium quality. Designing a premium self-elevating (jack-up) offshore structure is one that must be founded on well-proven principles, industry-accepted reliability techniques and criteria. Construction must also follow a suitable classification society’s guidelines for the different aspects and phases of the jack-up.Before designing and constructing a jack-up which can optimally operate within the harsh offshore environment, identifying the hazards associated with the structure in this environment and how to mitigate or manage them is essential. The Formal Safety Assessment (FSA) is the methodology employed in the maritime industry to identify and check these marine hazards, and to design ways to bring them under control in a cost effective manner. The five steps in FSA are hazard identification, risk assessment, risk control option, cost benefit analysis/assessment, and decision making steps. In this paper, the jack-up rig was introduced and its operation principle explained from the transit mode to the operation mode offshore. The hazards associated with self-elevating units were identified using the Preliminary Hazard Analysis (PHA). The Capsizing Hazard which was identified as critical was considered and analyzed using the Fault Tree Analysis (FTA). Consequently, the Fishbone Diagram was used to analyze, state the root cause of capsizing of jack-up structures through the risk factors of sampled incident cases, and recommend measures to curb the special problem. Some recommended measures are a bolster of existing guidance. Recommendations and improvements on how to eliminate or reduce capsizing of jack-ups through early design and construction, and before in-service operation were made.