OMV-AUT is running the Schönkirchen-Reyersdorf and the Tallesbrunn gas storage facilities with capacities of 1.77 respectively 0.3 billion m3 in the Vienna basin. These facilities at depths between 1000 and 1300 meters are former sandstone gas reservoirs operated with traditional external gravel packed (GP) vertical wells. Increasing gas demand and the urge to increase efficiency prompted an effort to adapt the whole system to a state of the art operation by making full use of available technology. This included:Application of a novel low damage drill-in fluid systemRecompleting former inside as outside casing gravel packsDrilling high performance horizontal wellsCompleting these horizontals with an expandable sand screen (ESS) respectively with a horizontal open hole gravel pack (HOHGP) During the project, new field quality control procedures were established and laboratory tests run to demonstrate the potential of the mud system. The mud system used had been designed for oil wells, but never before proved for gas storage. Despite many simultaneous changes in parameters, well tests confirm the assumption of substantial gains due to meticulous QC, intense cooperation and modern technology. Introduction Basically the goal was to achieve a higher performance with less wells and concurrent reduction of the injection and withdrawal times. In the beginning existing wells were converted from inside casing GP (ICGP) to open-hole GP (OHGP) in order to gain experience with the new drilling/ workover fluid before establishing horizontal wells with big bore state of the art completions and subsequently a significant reduction of the number of wells by replacing existing wells by new horizontal wells drilled from cluster locations. All this was done using a novel drilling mud system developed for the use in oil bearing formations but never used for gas storage applications before. Exploratory Meetings In advance of the jobs multiple meetings within the company as well as with specialists from service companies were held in order to get an overview of new technologies available. The outcome was that the mud system for recompleting, workover as well as for drilling purposes had to be evaluated in detail. After intensive discussions with the mud system provider a novel drilling fluid (Tab.1 & Tab.2) was chosen, assuming that it complies with most of the requirements. During the planning phase of the completion design of the two horizontals with ESS respectively with OHGP, controversy arose about the suitability of the mud system especially regarding the well cleaning after the installation of the completion. The first production phase for both completion designs is critical, especially in case of the ESS completion. Expandable Sand Screens in general have a low permissible pressure differential. In case of an outside plugging of the screen they could collapse. The maximum allowed ?p is 20 bar in case of 5 ½" Screens in a ~8 ½" openhole. It is contended that the combination of classic fluid loss control material like carbonate and starch with their hydrophobic derivates act as selective barriers for water into the formation, while providing very low adhesion forces for the filter cake when flow is reversed during production. The vendor had examples showing that oil was easily able to penetrate the oleophilic channels in the cake, thereby lifting the cake off. However, it was not clear whether this would also hold for dry gas coming out of a storage well and whether the gravel and screen might not restrict the clean up process.
TX 75083-3836, U. S, A., fax 01-972.952.9435. AbstractEver rising water volumes and processing costs in the oil field have spurred OMV to look for alternatives to traditional water processing. Despite an elaborate central multistep water treating system, increasing injection pressures, water fouling in the pipelines and reservoir souring were noticed.A comprehensive water analysis program was instrumental to understanding that available oxygen, nutrients and the reeycling of water promoted the growth of bacteria in the large distribution system. Since, on the long run, no biocide proved effective, a soft strategy was adopted: by removing key components (sulfate, biodegradable carbon) essential for bacterial growth, the population could be starved and the injection water quality stabilized.The feasibility of this concept was tested in a laboratory clarification apparatus that helped establish critical parameters, optimise additives and define performance limits. After due accommodation time, bacteria recovered from a refinery waste treatment plant could eliminate >90Y0of BOD and the effluent water was biologically inert. At the same time, a field pilot plant was installed that now has been injecting biologically processed water since fall of 1996. Onsite core experiments demonstrate superior infectivity compared to normal brine. Other parameters (COD, TOC, turbidity, membrane filterability) support these findings.A revamp of the whole water conditioning system is now undenvay. So far, benefits of the new strategy have been considerable savings in biocide expenditures, reduced injection pressures, and a lower H2S production.
Rising water volumes and processing costs in the oil field have spurred OMV to look for alternatives to traditional water processing. Despite an elaborate central multistep water-treating system, increasing injection pressures, water fouling in the pipelines, and reservoir souring were noticed. In a five-year program involving field measurements, laboratory experiments, the construction of a pilot facility, and test injections, a new strategy was adopted. The central water-conditioning plant (WCP) has been revamped. Instead of biocide addition, removal of organic nutrients by a biological clarification step now produces a clear, well injectable, and stable injection water.
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