Murchie, Stuart (Altus Intervention) | Jørgensen, Erland (Altus Intervention) | Egeland, Alexander (Altus Intervention) | Saetrevik, Martin (Altus Intervention) | Boge, Erik (Altus Intervention) | Hals, Knut (A/S Norske Shell) | Sbordone, Andrea (TIOS AS)
A/S Norske Shell needed to carry out tubing hanger crown plug (THCP) removal from a riserless light well intervention (RLWI) vessel in the Norwegian sector of the North Sea. There were concerns that the conventional application of mechanical jarring with slickline tools could not be used due to the combination of deep water and high sea currents in the specific field. A safer, more controlled and assured method was needed to withstand this extreme environment and provide the certainty of task success.
Theoretical studies and practical testing were conducted at the supplier's test site to verify the impact sea current had on cables and toolstring assemblies. Different scenarios were analysed and the most effective and lowest cost solution was determined. An electric line deployed and powered electrohydraulic stroker device was selected, which did not require any cable actuation to generate the pull forces required to unseat the crown plug.
Toolstring space-out was critical to ensure the stroker anchor was above and clear of the well control package (WCP) and positioned to prevent any inadvertent damage to the lubricator. In addition, a release tool and a shearable stem provided back-up safety capability for well control. A modification to an existing stroker was designed and a prototype built and tested at the onshore facility.
The final stroker toolstring design was tested out successfully on a more benign shallow subsea well, where the highly accurate force and movement control of the stroker, coupled with real-time surface readout, enabled a safe and secure crown plug pulling and installation operation. The targeted operation in a deep-water, high-sea current environment was then carried out successfully, applying many lessons learned and process improvements from the trial well.
In conclusion, the use of electrohydraulic stroker technology was proved to be a viable alternative for crown plug retrieval and setting operations, whilst bringing heightened visibility and control to such an operation.
Chee, S. S. (Schlumberger) | Tan, H. (Schlumberger) | Ando, M. (Schlumberger) | Pai, S. (Schlumberger) | Yandon, E. (Schlumberger) | Yamamoto, K. (Japan Oil, Gas and Metals Corporation) | Suzuki, S. (Japan Oil, Gas and Metals Corporation)
Gas hydrate production commenced from two production wells drilled in 1,000 m of water in the Nankai Trough, Japan, in May 2016. Two adjacent monitoring wells were drilled to monitor the in-situ event change of the hydrate reservoir over a two-year monitoring period. To achieve this monitoring purpose, an innovative design of wellbore gauges was installed downhole to provide valuable temperature and pressure data to show the dynamic nature of the gas hydrate dissociation front.
Using two seabed located autonomous subsea monitoring systems, data were continually logged from the monitoring gauges since they were installed in May 2016. To gain access to the recorded wellbore data, early project thoughts revolved around either recovering the large subsea monitoring systems or deploying remotely operated vehicles (ROVs) to tieback umbilical cables from the two subsea monitoring systems to the drillship, once it arrived at the field site. These techniques proved to be expensive and of increased risk to both personnel and equipment.
With a view to future safe and more cost-effective data harvesting techniques, a project was instigated to investigate using autonomous, unmanned surface vehicle (USV) along with vessel-based "dunker" methods to upload data from each of the monitoring wells using integrated high telemetry acoustic modem technology. The main objectives of the study were to verify data could be harvested and delivered to the client using a USV along with safe and repeatable piloting of the USV from a remote location.
Two USV missions have since been conducted, one in June 2016 and the other in March 2017. Lessons learnt from the initial USV mission, such as higher than expected sea surface currents and thrust limitations of the USV, were incorporated into the second deployment. This resulted in roughly 200 days' worth of data being uploaded and delivered from each of the two monitoring wells.
In this paper, we will outline how the project objectives were met and how some of the challenges, both technical and environmental, were overcome.
The autonomous unmanned vehicles (AUV) are the important tools of the underwater investigations. The high accuracy of AUV navigation is one of the important conditions of the effective AUV work. The AUV navigation is based on the use of the several wide spread methods. One of the most useful of them is single beacon navigation also called the synthetic or dynamic long base method. To use this method one must measure the distance between maneuvering AUV and single beacon on different time intervals and use the obtained estimates together with the estimates of the AUV course and speed for the AUV positioning. The method was firstly announced in 1995 but by the now it is considered as one of the most useful method for AUV navigation. The purpose of the work is the synthesis of the maximum likelihood single beacon navigation algorithm and its accuracy investigation.
Autonomous underwater vehicles (AUV) are a promising tool for studying and development the World ocean [Kim, Eustice, 2015; Millar, Mackay, 2015; Newman, Leonard, Rikoski, 2003; Scherbatyuk, Dubrovin, 2012].
One of the main demands brought to AUVs to fulfill there tasks is precision navigation in three-dimensional underwater space.
To navigate AUV the following methods are used [Kinsey, Eustice, Whitcomb, 2006]:
– inertial navigation method (INM) which uses on-board navigational devices, including inertial navigation system (INS), hydroacoustic (absolute) lag (HL), which measures the speed of AUV in the longitudinal and transverse directions relative to the bottom, and a depth sensor (DS). This method must be referred as basic because all other methods are in addition to it. The advantage of inertial method is full autonomy, and the disadvantage is steady increasing position error with the time of underwater motion, due to gyro drift and low accuracy of AUV speed measurement in the deep sea;
– satellite navigation method (SNM), which consists in determining the coordinates of AUV using a GPS satellite navigation system (SNS). The advantage of this method is the high precision of coordinates determination, and the disadvantage is the need for the surfacing of AUV, which is associated with a high energy consumption and the loss of time of the mission;
– long base method (LBM) consisting in determining the AUV coordinates by simultaneous measuring its distance to several (at least three) beacons which coordinates are known with high accuracy, and resolving the relevant system of equations. Beacons can be fixed (usually on bottom) and moving (typically drifting). In last case their coordinates are determined using the SNS. For this purpose special buoys called GPS Intelligent Buoys (GIBs) are often used [Desset, Damus, Morash, Bechaz, 2003; Thomas, 1998]. The advantage of the long-base method is the high precision (up to tens of centimeters) of the AUV coordinates determination [Kebkal, Kebkal, Kebkal, 2014]. The disadvantages of this method are obvious: it requires an expensive equipment of AUV navigation area, and the size of this area, as a rule, does not exceed 10 km;
Subsea cooling in oil and gas production might seem to be opposite to the usual flow assurance challenge, maintaining a high enough flowing temperature of the produced stream in order to ensure problem free transport of the crude from well to the host. During FEED and detailed design, particular focus is aimed at maintaining a required temperature with insulation and even electrical heating are employed in order to achieve this. Hydrate formation, wax and asphaltene deposits are challenges that are connected with too low temperature, and considerable effort is spent in quantifying acceptable temperature, and cool down times of subsea equipment. So one might ask why and where is the need for subsea cooling? It turns out that there are situations where the well fluids are very warm and reduction in the temperature is required for profitable development of a field. For example, where an expensive flow line material would render the installation too costly, a reduction in temperature might make the investment evaluations look attractive, or where heat is generated subsea by for instance a subsea gas compressor. The temperature greatly affects the corrosion rate, and by changing the temperature, chemical dosage can be optimized, which further strengthens the financial analysis of a field development. This paper focuses on active subsea coolers, i.e. subsea cooling systems that are equipped with adjustable means, and attempts to analyze and benchmark four different subsea cooler types using a generic wet gas production case. A recent development involving a sea current controlled active cooler is introduced and compared with three other active cooler types and how they operate with a given set of operation and turndown conditions are presented. A comparison of weight, size, auxillary equipment and required topside scope is also included.
Oil and gas (O&G) operators are increasingly focusing their efforts on exploration and development of arctic regions as traditional fields are rapidly depleting. In this regard, one main concern with offshore O&G development in the arctic is seabed scouring due to iceberg impact with the soil (ice gouging). Offshore pipelines in the arctic are buried below the mud line so as to be protected from iceberg impact. However, due to difficulties in determining accurately the gouge depth, pipeline embedment depth designs are overly conservative resulting in greater installation costs or cancelling of projects at the preliminary stages altogether. Therefore, a sustained challenge in the O&G industry is the accurate prediction of the depth of the ice gouge, and consequent pipeline embedment design depth.
In the present paper, a simplified model of the motion of a grounding iceberg for determining the gouge depth into the seabed is proposed. Specifically, taking uncertainties into account and modeling the sea current velocity and the soil strength as a stochastic process and as a stochastic field, respectively, a nonlinear stochastic differential equation (SDE) governing the evolution of the gouge length in time is derived. Further, a recently developed Wiener path integral (WPI) based approach for solving approximately the nonlinear SDE is employed; thus, circumventing computationally demanding Monte Carlo simulations (MCS). Ultimately, under certain assumptions regarding the seabed topography, the probability density function (PDF) of the gouge depth at a given point is determined at a low computational cost, rendering the approach potentially useful for preliminary design applications. The accuracy/reliability of the approach is demonstrated via comparisons with pertinent MCS data.
Fujisaki, A. (Department of Environmental & Ocean Engineering, School of Engineering, University of Tokyo) | Yamaguchi, H. (Department of Environmental & Ocean Engineering, School of Engineering, University of Tokyo) | Duan, F. (Department of Environmental & Ocean Engineering, School of Engineering, University of Tokyo) | Sagawa, G. (Department of Environmental & Ocean Engineering, School of Engineering, University of Tokyo)