There is growing awareness that sustainable urban drainage systems can offer a more sustainable option for the management of stormwater runoff than conventional drainage systems. This paper presents in‐situ performance data from a permeable pavement system which was installed to collect and treat stormwater runoff from a motorway servicestation car park. Data on rainfall at the site and outflow from the permeable pavement were collected over a thirteen‐month period, and twenty rain events were studied in detail. The system provided a large degree of attenuation in terms of (a) reduction in peak flows, and (b) extended duration of outflows compared with rain events. Infiltration tests provided information on the processes of water entry into the pavement system and impacts of clogging on hydraulic performance.
Sustainable urban drainage systems offer a sustainable option for the disposal of stormwater runoff ‐ reducing the risks of flooding and pollution of receiving watercourses. However, the adoption of such systems has been slow, with a lack of performance data identified as being one barrier. This paper presents in situ performance data from a perforated concrete ring soakaway which was installed to collect stormwater runoff from a school roof and paved area. Data on rainfall at the site and water depth in the soakaway were collected for a period of twenty months, and a number of rain events were studied in detail. Data from the soakaway were used to test the most recent design procedures for infiltration drainage systems, and it was found that the design equations gave reasonable predictions of system response to rainfall ‐ especially when the observed runoff coefficients were taken into account.
It is usual for initial development wells on marginal fields to follow a conservative drilling programme using conventional technology with known drilling performance. In the case of the Janice Field situated in block 30/17a of the UK North Sea it became apparent, following field appraisal, that to effectively exploit the reservoir it was necessary to drill complex 3D well trajectories. Such wells would require significant directional work with large associated costs. Specific challenges included high torque and drag profiles, slow rates of penetration, limitations of conventional directional drilling techniques, tight target tolerances and the requirement for effective reservoir navigation. After careful consideration, the operator, Kerr-McGee North Sea U.K. Limited determined that the application of Rotary Closed Loop Steerable (RCLS) technology was part of the appropriate technical and economic solution for the drilling of these wells. This paper describes how the combination of RCLS and conventional drilling technology was used to achieve the field development objectives. This provided a unique opportunity to make a direct comparison between RCLS and conventional steerable technology on similar 3D complex well trajectories. Specifically, key performance factors were measured enabling quantitative and qualitative statements to be made of drilling performance with the two technologies. The experience gained provides an insight to where it is appropriate to use this new technology and demonstrates the applications for which this technology can provide significant technical and economic advantages. Introduction The Janice Field was originally discovered in 1990 and appraised by three nominally vertical wells in 1995/96 (Figure 1). The field is currently being produced by subsea wells coupled with a floating processing facility. This paper focuses on the planning and execution of the first three horizontal wells drilled in the period 1998/99. The initial field development plan featured drilling slant wells from a central wellhead cluster. However, analysis of the appraisal wells showed the existence of three sand layers with some degree of vertical permeability separation. This suggested that it would be better to pursue a horizontal well development. The revised plan required the drilling of four horizontal producers and four horizontal injectors. Two of the appraisal wells were to be incorporated as producers. This not only placed limitations on the surface location, but necessitated the planning of more complex 3-dimensional well trajectories. Conventional Versus Rotary Steerable? Early in the well planning process, it was apparent that the horizontal well trajectories would be challenging for conventional directional drilling technology. This was substantiated by an analysis of drilling operations in an adjacent block1 in which the operator had found directional drilling in the Upper Cretaceous Chalk to be "troublesome and time consuming" in 12¼" hole size. A study into the value and availability of Rotary Steerable drilling technology was initiated for the project. The study suggested that the market at that time (1997) could not deliver a reliable Rotary Steerable system. Further, the systems readily available were limited to drilling hole sizes in the range 8 ½" - 9 7/8". Final selection of a Rotary Closed Loop Steerable System2,3,4,5,6,7 (RCLS), shown in Figure 2, was based on meeting the key performance criteria, namely system operation up to a temperature of 150°C and dogleg capability in the range 0 - 5 °/100ft.
Summary A combination of rotary closed-loop steerable (RCLS) and conventional drilling technology was used to drill 3D complex development wells in the Janice field in the North Sea. Direct comparison of RCLS and conventional tools showed that RCLS gave smoother holes, higher rate of penetration (ROP), and lower cost per foot. The experience gained provides insights into where it is appropriate to use this new technology and demonstrates the applications for which RCLS technology can provide significant technical and economic advantages. Introduction Initial development wells on marginal fields usually follow a conservative drilling program with conventional technology that has known drilling performance. In the case of the Janice field, situated in Block 30/17a of the North Sea, it became apparent, following the field appraisal, that to effectively exploit the reservoir, it was necessary to drill complex 3D well trajectories. Such wells would require significant directional work with large associated costs. Specific challenges included high torque and drag profiles, slow ROPs, limitations of conventional directional drilling techniques, tight target tolerances, and effective reservoir-navigation requirements. After careful consideration, the operator, Kerr-McGee North Sea U.K. Ltd., determined that applying RCLS technology was the appropriate technical and economic solution for drilling these wells. The Janice field was originally discovered in 1990 and appraised by three nominally vertical wells during 1995-96. The field is currently being produced by subsea wells coupled with a floating processing facility. This paper focuses on the planning and execution of the first three horizontal wells drilled between 1998 and 1999. The initial field-development plan featured drilling slant wells from a central wellhead cluster. However, analysis of the appraisal wells showed the existence of three sand layers with some degree of vertical permeability separation, which suggested that it would be better to pursue a horizontal well development. The revised plan required drilling four horizontal producers and four horizontal injectors. Two of the appraisal wells were to be incorporated as producers. This not only placed limitations on the surface location but also necessitated the planning of more complex 3D well trajectories. Conventional vs. Rotary Steerable? It was apparent early in the well planning process that the horizontal well trajectories would be challenging for conventional directional drilling technology. This was substantiated by analyzing drilling operations in an adjacent block1 in which the operator had found directional drilling in the Upper Cretaceous chalk to be "troublesome and time-consuming" in a 12 1/4-in. hole size. A study into the value and availability of RCLS drilling technology was initiated for the project. The study suggested that the market at that time (1997) could not deliver a reliable rotary-steerable system. Further, the systems readily available were limited to drilling hole sizes in the range of 8 1/2 to 9 7/8 in. Final selection of an RCLS system,2–7 shown in Fig. 1, was based on meeting the key performance criteria, namely system operation up to a temperature of 150°C and dogleg capability in the range of 0 to 5°/100 ft. The basic strategy was to use steerable motor assemblies to perform directional work in the 17 1/2- and 12 1/4-in. hole sections. Directional work was also required in the 8 1/2-in. hole section to line the well up with the final target. The plan was to use the 6 3/4-in. RCLS in this hole section, primarily to eliminate slide drilling problems and to reduce the risk of differential sticking. The trajectory for the first horizontal well, J2Z, is shown in Fig. 2. First Horizontal Well Casing and Well Design for Conventional Directional Drilling. The ideal casing scheme for the Janice wells placed the 9 5/8-in. casing at the top of the reservoir (see Fig. 3a). However, the consequence of adopting this scheme is the necessity of performing directional work in a 12 1/4-in. hole in a chalk formation. To avoid this, the casing scheme was modified to raise the 9 5/8-in. casing shoe to midchalk (see Fig. 3b). This facilitated drilling the planned wellpath with conventional technology but resulted in higher risks and inefficiencies in drilling, completion, and cementing operations. Specific areas of concern were mud overbalance, slide drilling, reservoir navigation capability, ROP, differential sticking, and running a longer production liner. Operations Overview-30/17a-J2Z The first horizontal development, Well 30/17a-J2Z, was successfully drilled to the revised casing design (see Fig. 3b). The 17 1/2-in. hole section was predrilled as part of a batch-setting program; initial directional work in the 12 1/4-in. hole section was carried out with a stabilized steerable motor assembly. Drilling performance was satisfactory to the first azimuth turn on the well trajectory. Thereafter, with increased difficulty in slide drilling, it was necessary to remove the stabilization from the assembly to complete the hole section.
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