For the development of the HPHT gas field Dvalin a completion scheme using standalone screens is planned. To secure maximum clean-up and productivity, even after long term suspension, comprehensive lab testing of specific properties from drilling and completion fluids at downhole conditions, e.g. optimum bridging, minimizing formation damage, thermal stability and mobility was carried out. Furthermore, compatibility with production screens and formation fluids were verified. Drill-in fluid systems were advertised by different vendors to be compatible under the given initial reservoir conditions. For the sake of efficiency, the systematic test program consisted of a sequence of four test phases, where only successful fluids went to the next phase. The most important parameters of the test program were long-term high temperature stability and related sand screen compatibility, a detailed rheology characterization as well as complementary formation damage and return permeability tests. Finally, the additive concentrations of the awarded fluid system were systematically optimized to yield the least completion- and formation damage and highest return permeability.
The Dvalin gas field is located in the Norwegian sea on NCS and is operated by Wintershall DEA Norge. It is supported by two independent reservoir structures, Dvalin East and Dvalin West. The field was explored through wells 14S and 15S in 2010 and 2012, respectively. The field is characterized by dry gas, high CO2, high temperature (160 °C) and high pressure (SIWHP 620 bar). The targeted Garn sandstone has good reservoir quality, but with a high permeability contrast. The field development was sanctioned in 2016 and calls for a 4 well solution through a centrally located subsea template, producing gas back to the host platform Heidrun TLP 15 km away. Water depth at location is 380 m and targeted reservoirs are at 4140 m MSL (East) and 4240 m MSL (West). Production plateau rates are estimated to be approximately 106 MMscf/D (3 million std m3/d) per well where thin high-permeability zones within the Garn formation are expected to dominate the inflow. The lateral facies development is thought to be relatively homogenous throughout the field, thus S-shape wells falling off to vertical through the reservoir will ensure effective drainage. Sand failure is expected after short time of production and would increase the risk of erosion causing severe damage to well jewelry and production facilities. It has been decided to integrate sand screens as a means of downhole sand control as part of the primary lower completion design. The sand screens will offer sand control, erosion resistance, hot spotting resistance as well as robustness towards a full hole collapse during reservoir pressure depletion. As the subsea completions are carried out from a mobile drilling unit in harsh environments, protection of the sand control filter media during installation is of utmost importance. This paper will describe the selection process of sand control and qualification steps carried out to use ceramic screens as the stand-alone screen solution for successful deployment and integrity for the Dvalin field development
Formation damage by the drill-in fluid has been identified as a major risk for the Dvalin HT gas field. To ensure the long-term stability and mobility of the mud even after an extended suspension time between drill-in and clean-up of the wells, a novel static aging test under downhole temperature and high pressure was conducted. Experiments have shown that the downhole stability is commonly underestimated when the surrounding pressure is lower than in the field. Thus, a high-pressure cylinder was used in vertical orientation in a heating oven with a pressure pump regulating the pressure up to 200 bar. The reservoir section was drilled with the optimized organo-clay-free oil-based drilling fluid (OCFOBDF) specified in the qualification phase. Tracers in the lower completion were used to identify clean-up from the upper high-permeability streak and the deeper (relatively lower) high-permeability streak. Due to extended wait on weather after drilling and completion of the first of the four wells, the lag time until clean-up was almost 11 weeks (74 days). It could be experimentally shown that the qualified OCFOBDF system weighted with micron sized barite remains mobile without phase separation even after static aging at 160 °C and 200 bar for the maximum estimated lag time between drilling and clean-up of 3 months. The absence of a gas cap in the set-up also better represents downhole conditions in the reservoir section and has shown that it improves the fluid´s stability. The clean-up of the well was successful with a maximum flowrate of 3.0 MM Sm3/d. Analysis of the tracers has proven that clean-up was successful for the entire reservoir section, including the deeper part. It could be concluded that in alignment with the lab tests that the mud fulfilled its requirement to be mobile even up to three months. Because of the superior properties, settling of solids (bridging and weighting material) could be avoided, resulting in no blockage of the (lower part of the) reservoir. The use HPHT aging has been the key to proving the long-term stability and mobility of the combined Drill-In and Completion Fluid. This technique falls outside of current API RP testing practices but is believed to be highly beneficial for qualification of fluids that will be left in the lower completion for long periods, especially in open hole completions under high temperature and pressure.
This paper describes how the information from inflow tracer technology was used to optimise the trajectory of a well during the development phase of Dvalin field. The Dvalin field is a high temperature (HT) gas field in the central part of the Norwegian Sea that consists of two separate structures. Each structure has two high perm streaks, the shallower of which was thought to have good reservoir properties whereas there was more uncertainty around the deeper one, the suspicion being that it was of a lower quality. During the exploration phase a DST was performed and it was uncertain if only the upper high permeability streak flowed on the assumption the mud was not optimised for the application. Additionally, the lower high permeability streak was not easily identifiable on the logs, although it was clear from the core. The initial field development concept consisted of drilling four production wells. Due to the uncertainties around the lower reservoir section, it was seen as highly beneficial to obtain information in the early development phase and, due to the challenging environment (HT and subsea), the choice of monitoring technologies was extremely limited. Inflow tracers were therefore chosen for the four planned producers, a technology whereby unique permanent chemical tracers are integrated into polymer rods which are then deployed as part of the lower completion. They remain dormant until encountering a specific target fluid – in this case oil-based mud (OBM). Once activated, they will release into the target fluid for a certain designed life period (in this case for a few months) and flow to surface upon opening the well where they will be sampled and analysed. The analysed data is then interpreted to confirm the zonal clean up and flow contribution. The initial drilling plan consisted of slanted wells penetrating both, the upper and lower high permeability streak. In the event, the inflow tracer from the first well confirmed that the lower reservoir section not only cleaned up effectively but, crucially, demonstrated good productivity the operator could prove they selected the optimal mud and also the presence and contribution of a lower high permeability streak. In addition, a decision was made to change the configuration of the final well from slanted to horizontal in the upper zone, resulting in a 4x increase in well productivity where the tracers played a key role in the decision process. Monitoring well performance at the zonal level is a challenge, especially in HT and subsea wells. In this case inflow tracer technology was successfully used to provide validation of clean-up and flow contribution and thereby helped to optimize the drilling plan and well productivity in the course of the field development thereby increasing the value of the project.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.