Efficiency is a key factor on any operation. In this paper, we introduce the heterodyne Distributed Vibration Sensing (hDVS), which is an innovative technology based on fiber optic system to improve the duration of borehole seismic operations. We designed a survey aimed at comparing standard downhole geophone accelerometers measurements to i) optical fiber seismic installed inside the hybrid Wireline cable and ii) optical fiber clamped permanently to the well completion tubing. This comparison was conducted using a standard rig source VSP in association to advanced Offsets VSP. The purpose of the study was to evaluate this innovative technology and to assess the feasibility of drastic operation time reduction without compromising output data quality. To better evaluate the readiness of the technology, we decided to compare three distinct types of downhole measurements and designed a specific advanced acquisition which allowed us to compare various configurations. Consequently, the borehole seismic acquisition performed in the MR-SE1 well located in Makhrouga field (Tunisia) was split into two phases. Phase #1: during open-hole Wireline logging, using the standard downhole geophone accelerometers (VSI) and fiber optic seismic cable (single-mode cable) installed inside the Wireline logging cable (called hybrid Wireline cable). Phase #2: at the departure of the drilling rig, using a fiber optic seismic cable (single-mode cable) installed permanently along the intelligent completion. The results highlight the effectiveness of the hDVS technology with a proven decrease on operation timing, with reliable and good SNR recorded data. Nowadays, efficiency is a key requirement for any data acquisition process. The heterodyne Distributed Vibration Sensing (hDVS) is an innovative technology designed to achieve such effectiveness by making the Vertical Seismic Profile (VSP) a matter of minutes instead of hours, as using standard downhole equipment, without compromising output data reliability and allowing the measurements repeatability (no well interventions required). Finally, based on the quality of the dataset acquired, further analysis can be conducted for imaging purpose by analyzing the reflected waveforms, which could bring additional information and could change the way we are operating.
Scope of this paper is to describe the acid stimulation campaigns carried out in Ghana Offshore field between 2019 and 2020. The campaigns were carried out with a Light Well Intervention (LWI) vessel using different subsea equipment which allowed to safely perform the stimulation operation connecting the vessel to the X-tree production facility.
The purpose of this document is the definition of the operational areas for floating rig during well testing operations, depending on the depth of water and meteorological conditions. The main problem for a floating system is the station keeping. In order to operate, in fact, the rig must be located around the well. Considering the Rig-Riser-BOP system, the latter is fixed to the bottom, while the rig is subject to the forces of the wind, waves and currents that cause it to move from the vertical of the well. As the rig moves, the riser tilts and lowers relative to sea level. At the same time, the telescopic joint and the tensioners extend up to their maximum available. Once these limits have been exceeded, the riser-rig connection is no longer guaranteed because either the telescopic joint goes out of travel, or the tension cables break. In the Well Testing phase, this situation is aggravated by the presence of the string inside the riser. Its position is fixed; therefore, a lowering of the riser corresponds to a lowering of the string at the end of which is the flowhead. It must be ensured that the lowering of the riser is less than the maximum distance flowhead – rig floor. Therefore, while the operational limits of a rig are dictated by the telescopic joint and by the tensioners, the operational limits for the test phase are dictated by the flowhead-rig floor distance. In order to avoid reaching these limits and endangering the safety of the system, areas are defined in which it is possible to operate, carry out the test, or areas where it is necessary to disconnect the riser and make the system safe.
During the last years, the total number of subsea wells considerably increased thanks to growing investments in the development of deep and ultra-deep water fields. At the end of their producing life, all these wells will need to be decommissioned and permanently plugged and abandoned, so the demand for technologies that will allow to fulfil this task in the respect of the regulations and at the minimum cost gained a lot of momentum. This paper describes a permanent P&A strategy of subsea wells to be carried out with Well Intervention vessel. The study first goes through the operation sequence and available technologies, defining an abandonment approach which is in line with international standards. Identified strategy results into a significant time and cost reduction comparing with traditional subsea wells decommissioning works performed by a floater rig, even maintaining the same level of safety and effectiveness. The study shows that the overall time reduction estimated by using an intervention vessel ranges from 40 to 55%, compared to a conventional rig-based approach, leading the wells abandonment expenditure savings up to 70%. For all those wells where the implementation of an intervention vessel is not guaranteed, there is still room to get time and cost savings of about 5-15% by combining the same riserless technologies with a conventional floater rig.
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