Two gas wells in Germany showed a decline in production and wellhead pressures and were selected for acid treatments for skin removal. PLT measurements showed that certain reservoir intervals were not contributing to the gas production. To optimise treatment of individual zones a coiled tubing intervention with a resettable straddle packer assembly was chosen. Due to the depth-critical nature of straddle packer interventions, the use of an accurate depth correlation system was required. Straddle packer well interventions were performed with real-time data communication, using a mono-conductor cable inside the coiled tubing. The robust data communication system provides real-time information from a Casing Collar Locator (CCL), down-hole pressure and temperature gauges and is suitable for use during acid treatments due to a protective jacket around the cable. Information provided by the CCL tool ensures depth correlations, whereas differential pressure measurements from the down-hole pressure gauges provide positive information about the setting and sealing conditions of the inflatable packer system. The combination of the down-hole real-time temperature and pressure readings allow full control during the injection process to avoid re-fracturing during acidizing. Furthermore, down-hole temperature readings can be useful for optimizing the corrosion inhibitor loading in acid recipes. In this paper the real-time data communication system and the benefits in combination with straddle packers are discussed. Case histories in Germany illustrate the preparations, the execution and the lessons learned from selective treatment interventions with coiled tubing and real-time data communication in two gas wells. After the treatments the production of the wells was increased by more than 10% in each well. The real-time in situ pressures and temperatures were a valuable input to the reservoir engineering model and further action will be based on the results. With the use of the resettable straddle packer several zones were treated in one run resulting in reduced operating time and thus a minimum in lost production.

A North Sea gas well was drilled and completed in 2000. Soon after the well was put in production, sand was also produced and became a major problem. Since the process system on the satellite platform was not capable of handling the sand, sand screens were installed in the well to prevent any further sand production. During the following years the sand screens became completely blocked and production ceased. The well was shut in for the next 10 years until a thru-tubing recompletion program was executed: milling out the permanent packer, fishing and retrieving the existing sand-screens and installing 130 m of new screens in a live well, all with 2 3/8–in. intelligent coiled tubing (CT). Intelligent CT interventions are operations in which rea-time downhole data is used to improve operational efficiencies. The realtime downhole data that can be obtained during CT operations include accurate depth correlation, pressures, differential pressures and temperatures. In combination with a realtime downhole camera, the high quality of data proved to be very valuable during the decision-making process, since the actual downhole situation can be assessed while many uncertainties are being eliminated. The visuals obtained by the camera played an important role in the choice of fishing tools and in discovering the exact position of fish and packer elements. This paper describes the challenges, the operational execution and the lessons learned from the recompletion project. It also explains in detail the operational aspects of the intelligent CT and how it was beneficial to the successful execution of the intervention program. Following the successful operation, the well was produced through the well test package on board the support jack-up, and production figures exceeded expectations. After this initial well, interventions in several more wells followed, whereby thru-tubing sand screens were installed with use of intelligent CT.

fax 01-972-952-9435. AbstractFlow from gas wells is often hindered due to water loading problems as fields mature, which often require remedial completions for maintenance of well flow. Velocity and insert string completions, using coiled tubing, jointed tubular and continuous foam injection via micro strings are techniques used to prolong production from these depleted gas wells.The number of engineered and deployed insert/velocity strings represent a vast array of lessons learned, optimizations, and successful operations. The comparison between the different techniques offers a base for preparation and optimization of liquid unloading techniques. A decision tree has been prepared to assist in choosing the suitable installation type.

In the Southern North Sea, many fields are suffering from declining gas production due to depletion of the reservoir and associated liquid loading. At some time during the operating life of offshore production facilities, the ability for these facilities to keep operating economically at a further decline in gas production, will need to be evaluated. To avoid early abandonment of these offshore assets, well deliquification or liquid unloading techniques, like Velocity String (VS) installations, are considered for extending the operating life of these mature fields.Large diameter (2 3/8 and 2 7/8-in.) chrome coiled tubing (CT) strings are being installed in deep gas wells in the Southern North Sea, as part of a large-scale installation project, including some 20 wells over a period of two years. A self-propelled jackup work vessel is used to house all the coiled tubing, well test and associated equipment needed to enable well interventions on the small production platforms and NUI's (Normally Unmanned Installations). Critical to the success of the project was the cross-discipline approach to preparing, selecting and testing appropriate coiled tubing hardware and tools, hazard analyses and logistical coordination.In this paper the preparation of the project, the operational details and lessons learned are presented. Candidate well-selection criteria and the choice for the selected coiled tubing material and size are discussed as well. Due to the size of the project, which is a worldwide first of this magnitude and set-up, both in terms of investment and quantity of offshore installations, good case histories for large diameter offshore chrome velocity string installations are provided.At time of writing not all the velocity strings have been installed. The velocity strings installed thus far have yielded incremental gas production of the order of 50,000-150,000 sm 3 /d (1.7 -5.3 Mscf/day) per well, which is in line with expectations. Based on the initial production results and production expectations for the remainder of the wells, the production life of these assets is expected to extend with many years.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA well at an Underground Gas Storage location of NAM was identified to be impaired, this resulted in a significant reduction of well performance and jeopardized the integrity of the well, and as such, it classified as a stimulation candidate. However, an acid stimulation treatment in a business-critical environment such as the Grijpskerk Underground Gas Storage in the Netherlands (total peak capacity 2000 MM Scf/D), can only be executed when well and facility integrity are fully ensured.Corrosion in wells and at production facilities due to acid stimulation treatments are being reduced by the use of appropriate corrosion inhibitors. However, due to the introduction of oxygen in the treatment fluids, for example during loading, transportation, mixing and pumping down a well, fear for corrosion still remains. In order to minimize the risk of corrosion by oxygen, a process was developed, in which all treatment fluids were prepared such that oxygen levels were considered essentially oxygen-free. The process involved the use of purging tanks, mixing the treatment fluids with nitrogen, the addition of oxygen scavengers and dilution of back-produced fluids.The efficiency of acid treatments in pre-packed screens completions can be enhanced by the use of coiled tubing and the right choice of jetting method. Pre-packed screens generally do not resist high differential pressures, and therefore, the impact pressure of the jetting fluid on the screen needs to be kept low. At the same time, thorough treatment coverage onto the screen and into the pores of the pre-packed sand is desirable in order to achieve optimal stimulation results. A novel rotating/pulsating coiled tubing jetting tool was used that produces, apart from the non-damaging low impact pressure, hydraulic vibrations created by the pulsating effects of the jets. This pulsating effect dislodges insoluble fines in the pre-packed screen, and opens pore space normally unaffected by chemical action of the treatment fluid. The rotating nozzles ensure complete wellbore coverage.This paper presents a case study of an oxygen-free acid stimulation treatment, performed in a well, completed with pre-packed screens, at the Grijpskerk Underground Storage facility in the Netherlands. Contributing to the success of the operation was the cross-discipline preparation, the selection of the optimum coiled tubing jetting tool, the investigation of impairment mechanism, selection of treatment recipe in combination with screen integrity tests, development of a process to create an essentially oxygen-free environment and spent-acid back production strategy. A dedicated production and test program was designed, for which chloride ions, oxygen and pH levels were monitored at the production facility against pre-set criteria.