New completion techniques using expandable casing with swelling elastomers to seal the annulus, or just swelling elastomers used as packers are becoming available. Diagnostic services are required for these new completions such as evaluation of the annular seal, analogous to cement evaluation. Both conventional and new generation Wireline ultrasonic measurements have been used to characterize and possibly evaluate zonal isolation using swellable elastomers. So far, the following 360 degs circumferential measurements were studied: Ultrasonic radii, acoustic impedance (AI), as well as attenuation and third interface Echo (TIE) reflections from flexural wave data. Radii measurements show a "springback" effect, indicating that expansion against the formation has been achieved. Flexural attenuation has a much better dynamic range over the elastomer sections compared to the acoustic impedance measurements. Both measurements do not consistently distinguish rubber-backed casing with ordinary casing in our examples. The TIE from the latest generation imaging tool tracking the external rubber interface, may provide the measurement the industry needs. First results look promising and further experiments to characterize the tool response are ongoing. The casing geometry of expanded liners was also studied. Introduction The introduction of expandable metal technology and new "smart" materials like swelling elastomers will provide more options for well construction and completion:New techniques in zonal isolation are now possible for over - underpressured, fractured zones and zones with fluid losses [1], [2],Allowing monobore well design [3],Production of selected zones will be made easier, like selective perforation, completion, and stimulation [4],Multilateral junction sealing will be made easier. The effectiveness of zonal isolation and long-term well integrity for this new technology needs to be evaluated and proven. " Smart Material" - Swelling Elastomers Swelling elastomers are now offered by several service companies and have been used by operators for a variety of applications: As a means to establish zonal isolation in liner completions where conventionally a cement column would be used [5], as a production separation packer (swelling packers are used to replace conventional hydraulically or mechanically set packers) [6], and as an integral part of an expandable open hole clad [1]. By incorporating filler materials into an elastomeric matrix the material reacts or swells with time if in contact with water, depending on the elastomer and the requirements [7]. A water swellable elastomer swells through the absorption of (saline) water (osmosis process). An oil swellable elastomer swells primarily through the absorption of hydrocarbons (diffusion process). The typical swelling ratio is about 1.75 to 2.5 and swelling pressures are up to 150 bar. Swelling time is from 5–100 days depending on produced water salinity, temperature and oil viscosity and composition. The longevity of swelling elastomers still has to be quantified.

This paper was prepared for presentation at the 1998 SPE International Symposium on Formation Damage Control held in Lafayette, Louisiana, 18–19 February 1998.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractPetroleum Development Oman (PDO) is planning a major brown-field re-development project. For that reason a waterflood appraisal drilling campaign has been executed. Drilling through fractured reservoir sections causes drilling losses that have to be cured prior to liner cementation. Liner cementation in wells with severe or heavy drilling losses has had limited success despite novel loss curing materials.Expandable tubulars with swelling elastomer seals have been applied in 8 wells as an alternative to cemented liners with the objective to • Provide zonal isolation, to • Attempt time savings by eliminating loss curing and liner cementation and to • Slim down the well design.The reservoir sections of 2 vertical water injector wells and 6 vertical oil producer wells were drilled with losses and lined with expandable casing. Elastomer seals isolate the multiple reservoirs from each other. Expandable casing enables a slim oil producer design still using a 2 7/8" gaslift string. 4 slim wells were drilled. Zonal isolation has been created without cement. This novel approach to drill fractured carbonate reservoirs has proven technically feasible in terms of installation operations, zonal isolation and slimming down well designs. The paper describes the experience with expandable tubular technology for waterflood well delivery.

Analysis of the performance of perforated, gravel-packed wells compared with openhole gravel-packed wells has indicated that the perforation could be responsible for the low productivity of internally gravel-packed wells. A series of laboratory experiments on weak rock (UCS = 1200 psi) was conducted to quantify this. Castlegate sandstone rock samples, 7 in. in diameter and 18 in. long, were perforated with shaped charges under downhole conditions. The perforations were gravel packed by circulating a gravel slurry past the tunnel entrance while applying a differential pressure. The preperforation, post-perforation and post-gravel-pack productivities of the core samples were monitored at different flow rates (5 to 20 b/d/perf). Sectional photographs of the core samples were taken at post-gravel-pack conditions for qualitative analysis. Performance evaluation of gravel-packed "realistic perforations" (debris and loose sand in the tunnel removed by drawdown-induced flow) versus "ideal perforations" (debris and loose sand removed by external means) showed the post-gravel-pack productivities of realistic perforations to be much lower than ideal perforations in oil-phase as well as water-phase experiments. Injection of fluid after gravel packing only temporarily unplugged the perforation tunnel. The study shows the importance of fines- and debris-free perforation tunnels in maintaining the productivities of gravel-packed completions. Introduction Gravel packs have been applied extensively over past decades for sand control. Although efficient for sand exclusion, gravel packs are often associated with relatively high values of skin and low completion efficiencies. In particular, internal (cased hole) gravel packs often represent a significant flow restriction in a well completion. The cause of impairment of gravel packs has been studied extensively in the past. The impact of poor completion operation practices such as dirty completion fluids and poorly selected fluid-loss control pills has been addressed in many studies. Although these factors are now generally recognised as contributing factors to impairment, field implementation of the results of these studies has not resulted in the anticipated improvement in gravel-pack productivity. Other studies have focused on the cause and consequences of low gravel permeability. Permeability reduction resulting from intermixing with formation material has long been suspected as a key factor in gravel-pack impairment. Work done by Saucier and Sparlin shows that gravel permeability reduces significantly when intermixing of gravel and formation sand occurs. A common observation in gravel-packed wells is a lower average completion efficiency of internally gravel-packed (IGP) wells compared to externally (openhole) gravel-packed (EGP) wells. This suggests that a significant part of IGP impairment may be directly related to the perforations. This is supported by a study carried out by Welling et al. on a large number of gravel-packed completion intervals. This study shows that besides well-known impairing factors, such as contaminated completion fluids and fluid-loss control pills, the perforation tunnel is the most critical area in an IOP completion. High pressure drops over the perforation tunnel were observed, indicating reduced gravel permeability inside the tunnels. P. 669

Since the IMPAIRMENT TESTS carried out inMay 1989 improvements have been made to asp's operating practices such as better shearing and filtering of the gravel carrier fluid and the introduction of new well bore cleaning procedures. A new carrier fluid viscosifier, SHELLFLO-S, was successfuHy tested. Ukewise, pre-packing the perforations prior to running the WWS was carried out either through the TCP string or the perforation washing tool. No significant productivity increase was observed. Further trials with acid pre-packing were carried out. Productivity data are, however, not yet aval7able.A Quality Improvement Project, which addressed the gravel packing process and identified some of the possible causes of impairment, was finalised. This resulted in further field trials in which the perforation area was increased by either double perforating (21-24 spf) or using larger guns (7'1. This was done in combination with perforation washing.A further move away from slurry packing towards conventional packing using an in..fine blender was made and a few wells were packed using low viscous brine as carrier fluid.